Study of the chemical composition of polymers. Methods for identification of polymers Characteristics of modern methods for the study of polymers

Historically, the problem of establishing the structure of HMS was closely connected with the elucidation of the nature of dilute solutions of these substances. As a result of the work of G. Staudinger, V. A. Kargin, S. M. Lipatov and others, it was proved that these systems, contrary to the previously prevailing point of view about their colloidal nature, are true solutions. Consequently, macromolecules are in dilute solutions in the form of kinetically independent particles, and the determination of their size gives not the dimensions of the micelles, but the dimensions of the macromolecule itself, the molecular weight. Measurement of molecular weight using a number of independent methods has shown that all IUDs are indeed composed of very large molecules - macromolecules containing tens and even hundreds of thousands of atoms.

Although the properties typical of HMS are also observed in compounds with significantly lower molecular weights, it is now customary to refer to HMS all substances whose molecular weight exceeds 5000, and to low molecular weight - substances with a molecular weight less than 500. Although compounds with intermediate values molecular weight, the so-called oligomers, as a rule, and have the properties of low molecular weight, they at the same time differ from low molecular weight.

To determine the chemical composition of HMS, the usual methods of elemental analysis are used. One of the methods most often used in the study of IUDs is the destruction, or splitting of macromolecules into low molecular weight substances, the structure of which is proved by conventional methods - the complex problem of establishing the structure of high molecular weight substances is divided into a number of simpler tasks, each of which is solved separately. Knowing the structure and properties of the resulting "fragments" of the macromolecule, we can draw conclusions about the structure of the original substance.

Depending on the nature of the IUD and its resistance to various influences, hydrolytic, thermal, oxidative and other methods of destruction are used.

The destruction method, which reduces the study of IUDs mainly to the study of their decomposition products and often gives very valuable information, nevertheless reflects only one aspect of the behavior of a macromolecule and cannot lead to unambiguous conclusions about its structure even in cases where the cleavage mechanism is well known. Not to mention the fact that the essence of this mechanism is far from always clear; often, during the destruction of the IUD, side reactions occur, an incorrect assessment of which can lead to erroneous conclusions.

In the case of rubber and cellulose, the problem is greatly simplified by the fact that, as a result of degradation, a small number of relatively easily separable compounds were obtained. The position of the bonds connecting the elementary links was established relatively simply. When studying the structure of such complex IUDs as proteins, the degradation products of which contain more than two dozen different amino acids, which are also difficult to separate, the value of conventional degradation methods is much less. Therefore, along with the study of degradation products, it is necessary to study the properties and behavior of the macromolecules themselves. In this case, mainly not chemical, but physical and physico-chemical methods are used. The problem is so complex that sufficiently reliable information about the structure of the IUD can only be obtained as a result of the joint application of all these methods.

The most widely used methods are molecular spectroscopy (infrared spectroscopy and the method of Raman spectra), electron paramagnetic resonance and nuclear magnetic resonance, which are currently playing leading role when studying the structure of polymers; electron diffraction, radiography, and electron microscopy are also of great importance.

The above methods provide information not only about the structure of a macromolecule (the mutual arrangement and conformation of chains, the orderliness of their stacking, crystallinity), but also about the nature of the thermal motion of particles (the mobility of macromolecules and their fragments, diffusion processes), the mechanism of polymer synthesis and their chemical transformations, about processes occurring near phase boundaries, about the nature of the interaction of macromolecules with solvents, etc.

Convincing evidence was obtained by comparing the physical properties of high molecular weight members of the homologous series and lower molecular weight representatives of the same series, which have a known chain structure. At the same time, as the molecular weights of the former decrease and the length of the molecule of the latter increases, their properties converge without sharp transitions; with significant changes in the shape of the molecule, the smoothness of the transition must certainly be violated. In other words, high-, medium- and low-molecular representatives make up a single homologous series, the members of which have the same chain structure.

The chain structure of a macromolecule follows directly from the very methods of obtaining them using polymerization and polycondensation reactions. Only the chain structure can explain such an important physicochemical feature of macromolecular substances as a sharp difference in their properties in the longitudinal (along the chain) and transverse directions after orientation (the molecules are located along the stretch line).

Therefore, a characteristic feature of the IUD is the presence of long chain molecules; the loss of the chain structure entails the disappearance of the entire complex of properties specific to these substances.

Elucidation of the structure of the main chain is far from exhausting the question of determining the structure of a macromolecule. It is also necessary to establish the nature and number of functional groups, their mutual arrangement in space, the presence of "anomalous" links and some other details of the structure that have a significant effect on the properties of macromolecular substances.

Functional groups are determined by classical methods of organic chemistry. An important issue is the establishment of the mutual arrangement of functional groups, on which the flexibility of macromolecules and their ability to crystallize depend. In some cases, such information can be obtained in the study of degradation products, but most often this problem is solved by studying the ratio of the macromolecule itself to special reagents or using spectral methods.

Spectroscopic methods are also widely used in elucidating other problems of the structure of macromolecular compounds; For this, spectral absorptions are usually used:

Raman spectra,

ultraviolet,

infrared spectra.

These methods make it possible to distinguish between 1,2- and 1,4-additions, elucidate the structure of copolymers, and also establish, on the basis of characteristic frequencies, the presence of certain chemical groups and bonds, which is very important when chemical methods do not provide an unambiguous answer. or not sensitive enough. Comparing the spectra of IUDs and their low molecular weight analogues of a known structure, one can judge the nature of the distribution of elementary units in a macromolecule, the regularity of its structure, and also identify IUDs.

Of particular interest is the NMR method for establishing the mutual arrangement of substituents. The 13C NMR method, which is used to study compounds by the natural content of the heavy 13C isotope, is of great help in establishing the structure of branched IUDs.

Using X-ray diagrams, one can find periods of identity, that is, the distance between two equally spaced groups and atoms, which allows one to draw conclusions about the regularity of the structure of the macromolecule and the presence of isomers. For example, the period of identity in the x-ray pattern of natural rubber (stretched) is in the direction of stretching 0.816 nm; gutta-percha - an isomer of rubber - the corresponding period is only 0.48 nm. These data gave grounds to attribute to natural rubber cis-structure, and gutta-percha - trance-structure (according to the location of the CH 2 group).

Structure study macromolecules can be done by the following methods:

Chemical methods provide for the division of a macromolecule into low molecular weight compounds and their subsequent identification by analytical methods. Most often, ozone is used for splitting.

Spectral methods are based on the ability of a polymer to interact with an electromagnetic radiation field, selectively absorbing energy in a certain area of it. In this case, the energy state of such a macromolecule changes as a result of such intramolecular processes as electron transitions, vibrations of atomic nuclei, translational and rotational motion of the macromolecule as a whole. Absorption, UV, VI, IR and NMR spectroscopy, internal reflection spectroscopy are used.

6) Viscometry.

7) Gel permeation chromatography.

Research supramolecular structures can be done in the following ways:

1) Light spectroscopy.

2) Electron microscopy.

3) X-ray diffraction analysis

4) Electronography.

FLEXIBILITY OF POLYMERS

Chain flexibility is a property unique to polymers.

Flexibility- this is the ability of a macromolecule to change its conformation as a result of internal thermal movement or due to the action of external forces.

Distinguish between thermodynamic and kinetic flexibility.

Thermodynamic flexibility characterizes the ability of the chain to change its conformation under the action of thermal motion and depends on the difference in the energies of rotational isomers ΔU. The smaller ΔU, the higher the probability of a macromolecule transition from one conformation to another.

Thermodynamic flexibility is determined by the chemical structure of the repeating unit and the conformation of the macromolecule, which also depends on the chemical structure.

Diene series polymers:

CH 2 -C (R) \u003d CH-CH 2 - (R \u003d H, CH 3, Cl)

are characterized by great flexibility compared to vinyl series polymers:

CH 2 -CH- (R = H, CH 3, Cl, CN, C 6 H 5)

This is due to the fact that the difference in the energies of the rotational isomers in diene polymers is about 100 times less. This difference is associated with a decrease in exchange interactions (attraction-repulsion) between CH2 groups when a group with a double bond, which has a lower potential barrier, is introduced between them. The same picture is observed for macromolecules containing Si-O or C-O bonds in the chain.

The nature of the substituents has little effect on thermodynamic flexibility.

However, if the polar substituents are close to each other, their interaction reduces the flexibility. The most rigid are biopolymers, their stable helical conformations are formed due to hydrogen bonds.

Kinetic Flexibility reflects the rate of transition of a macromolecule in a force field from one conformation with energy U 1 to another with energy U 2 , and it is necessary to overcome the activation barrier U 0 .

Kinetic flexibility is estimated by the size of the kinetic segment.

Kinetic segment- this is that part of the macromolecule that responds to external influences as a whole. Its value varies depending on the temperature and speed of external influence.

Polymers consisting of units characterized by low values of U 0 exhibit high kinetic flexibility. These include:

1) carbon-chain unsaturated polymers and polymers of the vinyl series that do not contain functional groups - polybutadiene, polyisoprene, polyethylene, polypropylene, polyisobutylene, etc.;

2) carbon chain polymers and copolymers with a rare arrangement of polar groups - polychloroprene, copolymers of butadiene with styrene or acrylic acid nitrile (the content of the latter is up to 30-40%), etc.;

3) heterochain polymers, the polar groups of which are separated by non-polar ones - aliphatic polyesters;

4) heterochain polymers containing C-O, Si-O, Si-Si, S-S, etc. groups.

An increase in the number of substituents, their volume, polarity, and asymmetry of the arrangement reduces the kinetic flexibility.

CH 2 -CH 2 - ; -CH 2 -CH-; -CH 2 -CH-

If there is a double bond next to a single bond, then the kinetic flexibility increases. Polybutadiene and polyisoprene are flexible polymers that exhibit flexibility at room temperature and below. Polyethylene and PVC exhibit kinetic flexibility only at elevated temperatures.

In all cases, an increase in temperature, increasing the kinetic energy of macromolecules, increases the probability of overcoming the activation barrier and increases the kinetic flexibility.

The kinetic flexibility is greatly influenced by the speed of the external action. Due to the large length of the macromolecule and intermolecular interaction, a certain time is required for the transition from one conformation to another. The transition time depends on the structure of the macromolecule: the higher the level of interaction, the longer it takes to change the conformation.

If the duration of the force is longer than the transition time from one conformation to another, the kinetic flexibility is high. Under very rapid deformation, even a thermodynamically flexible macromolecule behaves like a rigid one.

Kinetic flexibility can be assessed by glass transition temperatures T c and flow temperatures T t.

Glass transition temperature is the lower temperature limit for the manifestation of flexibility. At T<ТWith the polymer is under no circumstances able to change its conformation, even being potentially flexible with high thermodynamic flexibility. Therefore, the glass transition temperature T c can serve as a qualitative characteristic of the flexibility of the polymer in the condensed state.

Pour point- this is the upper temperature limit of the change in conformations as a result of hindered rotation around single bonds without changing the center of gravity of the macromolecule. At T>T t, the movement of individual segments is already observed, which causes the movement of the center of gravity of the entire macromolecule, i.e. her course. The higher ΔT = T t -T s, the higher the kinetic flexibility of the polymer in the condensed state.

The flow and glass transition temperatures depend on the deformation mode, in particular, on its speed. With an increase in the speed (frequency) of mechanical action, both T s and T t increase, and the temperature region of manifestation of kinetic flexibility shifts towards higher temperatures.

Under the same external action conditions, the kinetic flexibility of polymers does not depend on the molecular weight of the macromolecule, since the activation barrier is determined only by the short-range order interaction. As M increases, the number of segments increases.

T with increasing M first increases, and then at a certain value of M kr becomes constant. M cr corresponds to M segment. For thermodynamically flexible polymers, M cr is several thousand: polybutadiene - 1000, PVC - 12000; polyisobutylene - 1000; polystyrene - 40,000. Therefore, for polymers with a molecular weight of 100,000-1 million T, practically does not depend on M.

To implement conformational transitions, it is necessary to overcome not only the potential barrier of rotation U 0 , but also the intermolecular interaction. Its level is determined not only by the chemical structure of the macromolecule, but also by the supramolecular structure. Thus, the kinetic flexibility depends on the structure of the polymer at the molecular and supramolecular levels.

Macromolecules in the amorphous state are more flexible than in the crystalline state. The crystalline state due to the dense packing of macromolecules and long-range order in their arrangement is characterized by an extremely high level of intermolecular interaction. Therefore, the macromolecules of flexible polymers (polybutadiene, polychloroprene, polyethylene, etc.) in the crystalline state behave as rigid ones, unable to change conformation. In the oriented state, the flexibility of polymers also decreases, since the orientation brings the chains closer together and increases the packing density. This increases the likelihood of additional nodes forming between chains. This is especially true for polymers with functional groups. Example: cellulose and its derivatives. These polymers are characterized by medium thermodynamic flexibility, and in the oriented state they do not change conformation under any conditions (T c above the decomposition temperature).

MINISTRY OF EDUCATION AND SCIENCE

RUSSIAN FEDERATION

GOU VPO "Saratov State University

name »

Institute of Chemistry

APPROVE:

Vice-Rector for Educational and Methodological Work

d. philol. n., professor

"__" __________________ 20__

Work program of the discipline

Modern methods of polymer research

Direction of training

020100 – Chemistry

Training profile

Macromolecular compounds

Qualification (degree) of the graduate

Bachelor

Form of study

full-time

Saratov,

2011

1. The goals of mastering the discipline

The objectives of mastering the discipline "Modern Methods for the Study of Polymers" are:

– the formation of students' competencies related to understanding the theoretical foundations of the main methods for studying polymers used in domestic and foreign practice,

– formation of skills of individual work when performing a chemical experiment;

– formation of work skillson serial equipment used in analytical and physico-chemical studies;

– acquisition of skills and abilities in the process of mastering special methods registration and processing of results of chemical experiments;

- the development of computer technology in order to use its capabilities for the design of laboratory work;

– acquisition of skillsindependentwork with periodical chemical literature.

2. The place of the discipline in the structure of the BEP of the bachelor's degree

The discipline "Modern Methods of Polymer Research" (B3.DV2) is a variable profile discipline of the professional (special) cycle B.3 of training bachelors in the direction 020100 "Chemistry", training profile "High-molecular compounds" and is taught in the 8th semester.

The material of the discipline is based on the knowledge, skills and abilities acquired during the development of the basic disciplines "NInorganic Chemistry”, “Analytical Chemistry”, “Organic Chemistry”, “Physical Chemistry”, “High Molecular Compounds”, “Colloid Chemistry”, “Xchemical technology» professional (special) cycle of the Federal State Educational Standard of Higher Professional Education in the direction of training020100 "Chemistry", variablediscipline "Numerical methods and programming in the physical chemistry of polymers"mathematical and natural science cycle andvariable profile disciplines "Modern approaches to polymer synthesis», « Biomedical polymers», « Synthesis and properties of water-soluble polymers», « Polymer materials science» BEP HPE in the direction of training 020100 "Chemistry", profile "High-molecular compounds".

For the successful mastering of the discipline, the student must have knowledge ofstructure, properties and classification of macromolecularcompounds, chemical properties and transformations of macromolecules, their behavior in solutions,have an idea about the structure and basic physical properties of polymeric bodies, master the skills of preparing polymer solutions, carrying out reactions of polymer-analogous transformations,be able to carry out titrimetric, potentiometric, gravimetric and other analyses, metrological processing of experimental results, be able to work on a computer, knowstandards and techniques for the design of educational and scientific texts, be able to carry out mathematical calculations when solving polymer-chemical problems.

The knowledge, skills and abilities acquired within the framework of the discipline "Modern Methods of Polymer Research" are necessary for the implementation, design and successful defensefinal qualifying (bachelor's) work.

3. Competencies of the student, formed as a result of mastering the discipline "Modern methods of polymer research"

Statement of Competence	Code
Possesses the skills of a chemical experiment, basic synthetic and analytical methods for obtaining and studying chemicals and reactions	PC-4
Has the skills to work on modern educational and scientific equipment when conducting chemical experiments	PC-6
He has experience of working on serial equipment used in analytical and physico-chemical studies.	PC-7
Owns the methods of registration and processing of the results of chemical experiments	PC-8

As a result of mastering the discipline "Modern Methods for the Study of Polymers", the student must

know:

– classification of polymer research methods,

– general methods for the isolation and purification of natural polysaccharides (extraction, fractional precipitation, ultrafiltration, dialysis, electrophoresis, ion-exchange chromatography, gel filtration, ultracentrifugation, enzymatic purification, etc.),

– basic methods for studying the structure and properties of polymers ;

be able to:

– isolate polysaccharides from plant or animal natural raw materials,

– apply methods of purification of polymers from low- and high-molecular impurities,

- determine the moisture content, fractional composition, solubility, molecular weight of the polymer, the degree of substitution of functional groups in the macromolecule,

– carry out reactions of polymer-analogous transformations,

– to determine the main physical and physico-chemical characteristics of polymers,

- work on serial equipment used in analytical and physico-chemical studies,

- use computer equipment in the design of laboratory work;

own:

– methods for isolating polysaccharides from natural raw materials,

– polymer purification methods from impurities,

– the skills of the experiment of carrying out reactions of polymer-analogous transformations of polymers,

– experimental skills in studying the structure and practically important properties of polymers,

– skillscomprehensive application of analysis methods at polymer research,

– skills of individual work when performing a chemical experiment,

- tricks special methods for recording and processing the results of chemical experiments,

– skills independentwork with periodical chemical literature.

4. The structure and content of the discipline "Modern methods for the study of polymers"

4.1. The total complexity of the discipline is 8 credit units (288 hours), of which lectures - 48 hours, laboratory work - 96 hours, independent work - 108 hours, of which 36 hours are devoted to preparing for the exam.

	Section of discipline	Semester	Week-la-semester	Types of educational work, including independent work of students and labor intensity (in hours)
Lectures	Laboratory works	Independent work	Total

	General information about polymer research methods
	General methods for isolation and purification of natural polymers
	Chromatography methods				Written report in the laboratory journal.

	substances with electromagnetic radiation				Written report in the laboratory journal. Abstracts
	Study of the structure and properties of polymers				Written report in the laboratory journal. business games
	final examination				Graded Exam
Total:

4.2. The content of the lecture course

General information about the methods of studying polymers.

Characterization of polymer research methods. Modern trends in the development of research methods. Classification of research methods. The choice of the optimal research method. Study of the chemical composition of polymers. Determination of the content of various chemical elements V macromolecules. Analysis polymers thermal methods. elemental analysis. Chemical analysis on content of individual elements. Analysis functional groups. Definition of unsaturation polymers.

General methods for isolation and purification of natural polymers.

Filtration, ultrafiltration, dialysis, electrodialysis. Centrifugation, ultracentrifugation. Fractional precipitation and extraction. Enzymatic cleaning. Chromatographic methods: ion exchange, adsorption, size exclusion, affinity chromatography. Electrophoresis. Criteria of individuality and nativeness of natural polysaccharides.

Chromatography methods.

Characteristics of chromatography methods. Gas chromatography. Capillary gas chromatography. Reaction gas chromatography. reversed gas chromatography. Pyrolytic gas chromatography. Choice of pyrolysis conditions. Choice of conditions for gas chromatographic separation of pyrolysis products. Usage UHT at polymer analysis.

liquid chromatography. highly efficient liquid chromatography. Capillary electroseparation methods. Ion exchange liquid chromatography. Chromatomembrane separation methods. Thin layer chromatography. Analysis technique. Fields of application of the method TLC. Gel penetrating chromatography. Hardware method design. Determination of molecular weight and MMR polymers. Study of polymerization kinetics. Study of the composition of copolymers. Features of the study of oligomers. Research features stitched polymers.

Mac-spectrometric analysis method. Hardware method design.

Sample injection methods. Ways to ionize a substance. Types analyzers wt. Mass spectrometry with inductively coupled plasma. Fields of application of mass spectrometry. Analysis of the chemical composition of mixtures

Interaction based methods substances with electromagnetic radiation.

X-ray diffraction analysis and electronography. X-ray and X-ray spectroscopy. E electronography. Labeled atom method.

Methods using ultraviolet and visible light. Spectrophotometric method of analysis in UV and visible area. Absorption Fundamentals spectrophotometry. Hardware decor. Ways sample preparation. Carrying out quantitative analysis. Study of the kinetics of chemical reactions. Polymer Research And copolymers. Methods using optical laws. Reflection Based Methods Sveta. Refraction based methods Sveta. Refractometry. Double refraction. Scattering methods Sveta. Light scattering method. Raman Spectroscopy. Photocolorimetric analysis method.

infrared spectroscopy. Hardware method design. Application IR spectroscopy method. Determination of the purity of substances. Study of the mechanism of chemical reactions. Composition study And polymer structures. Determination of the composition of copolymers. Studying microstructures, configuration And conformations of macromolecules. Study of surface layers of polymers. Definition of temperature transitions V polymers. Oxidation study And mechanical degradation of polymers. Study of mixing processes And vulcanization. Study of the structure of vulcanizates. Other applications of IR spectroscopy. laser analytical spectroscopy. Laser-induced emission spectral analysis (LIESA). laser fluorescent analysis.

Methodsradiospectroscopy. Method of nuclear magnetic resonance. Physical the basics of the method. Characteristics spectrum NMR. Hardware decor. Usage method NMR. Study of the degree of conversion of monomers in progress polymerization. conformational polymer analysis. Study molecular movements V polymers. Studying rubber aging processes. Study component compatibility And intermolecular interactions at mixing polymers. Studying vulcanizing nets in elastomers. Studying deformations And polymer flows. Electronic paramagnetic resonance. Spectrum characteristics EPR. Hardware method design EPR. Application of the method EPR. Identification of paramagnetic particles. Radical research V polymers. Study of molecular motions V polymers. Study of the structuring of elastomers. Nuclear quadrupole resonance.

Electrochemical methods of analysis. Potentiometric analysis method. Conductometry method. Coulometric analysis method. IN oltammetric methods. Polarographic analysis method. Inversion electrochemical methods. high frequency methods.

Study of the structure and properties of polymers.

Studyingmasses, branching And interactions of macromolecules. Determination of the molecular weight of polymers. Number average molecular weight. Medium mass molecular mass. Other types of molecular weights. Definition MMR polymers. Analysis of the functionality of oligomers. Study of the branching of macromolecules. Research of intermolecular interactions V polymers.

Study of the supramolecular structure. Definition specific volume of polymers. Measurement density of polymers. Methods microscopy. transmission electronic microscopy. scanning electronic microscopy. Interference-diffraction methods. Crystallization study by method EPR. Determination of the degree of crystallinity. Determination of the sizes of crystallites. Orientation study V polymers.

Methods for determining the glass transition temperature of polymers. WITH tactic methods. dynamic methods. Dynamic mechanical methods. electrical methods. Dynamic magnetic methods.

Evaluation of the resistance of polymers to external influences And efficiency actions stabilizers. Study of thermal aging processes. thermogravimetric analysis method. Differential thermal analysis. Differential scanning calorimetry. Oxidative aging of polymers. Study of oxygen uptake. Evaluation of the chemical resistance of polymers. Studying mechanochemical destruction. Evaluation of the stability of industrial elastomers. Study rubbers. Study of thermoplastic elastomers. Study vulcanizates. Grade weather resistance elastomers. Studying the effectiveness of action And choice of stabilizer.

Rheologicaland plastoelastic rubber properties And rubber compounds. Rotational viscometry. Capillary viscometry. Compressive plastometers. dynamic rheological test methods.

Methods for studying the processes of preparation of rubber mixtures. Determination of the solubility of sulfur in elastomers. Analysis microinclusions in rubber compound. Evaluation of the quality of mixing. quantitative mixing quality assessment.

Study of vulcanization processes And structures of vulcanizates. Evaluation of vulcanizing properties. Vibrational rheometry. Rotorless rheometers. Studying vulcanization mesh structures.

Examplescomprehensive application of analysis methods at polymer research. Methods for the study of polymer mixtures. Express identification methods polymers. Pyrolytic gas chromatography. Application IR - and NMR spectroscopy. The use of thermal And dynamic methods of analysis And swelling data . Study of the interfacial distribution of the filler. Type definition vulcanizing systems.

4.3. Structure and schedule of laboratory classes

	Section of discipline	Semester	Week-la-semester	Types of educational work, including independent work of students and labor intensity (in hours)	Forms of current progress control (by week of the semester)
Laboratory works	Independent work	Total

	Isolation and quantitative determination of pectin substances from citrus peel. Isolation of pectin from pumpkin pulp. Comparative analysis gelling ability of citrus pectin with pumpkin pectin					Written report in the laboratory journal
	Isolation of chitin from crustacean shells. Carrying out a chemical reaction of a polymer-analogous transformation of chitin–chitosan. Determination of the degree of deacetylation and molecular weight of chitosan. Comparative analysis of the solubility of chitin and chitosan samples in various media (provided for the implementation of 3 tasks)					Written report in the laboratory journal
	Determination of the content of a -, b - and g -cellulose. Determination of pentosans. Determination of resins and fats. Determination of the ash content of cellulose (provided for the implementation of 2 tasks)					Written report in the laboratory journal. Interview on abstracts


	Study of thermomechanical properties of polymers (provided for the implementation of 3 tasks)		Written report in the laboratory journal Business game №1
	Physical and mechanical properties of polymers (provided for the implementation of 4 tasks)		Written report in the laboratory journal. Business game №2
Total:		Individual conversation with the teacher in the interactive mode

5. Educational technologies

Along with traditional educational technologies (lectures, laboratory work), technologies based on modern information tools and methods of scientific and technical creativity are widely used, including training based on business games on the topics "Tthermomechanical properties of polymers”, “Physical and mechanical properties of polymers”, advanced independent work (abstracts), as well as training systems for professional skills and abilities. Meetings are planned with representatives of Russian and foreign companies, scientists from specialized institutions of the Russian Academy of Sciences.

6. Educational and methodological support for independent work of students. Evaluation tools for current monitoring of progress, intermediate certification based on the results of mastering the discipline.

Independent work of students involves:

– compiling reference notes for sections of the discipline,

– development of theoretical material,

- preparation for laboratory work,

- preparation of laboratory work,

- preparation for business games,

- writing an abstract

– search for information on the Internet and libraries (ZNL SSU, the cathedral library, etc.),

– preparation for the current and final control.

Form of final control - exam(tickets in attachment 1).

6.1. Questions for self-study

1. Optical research methods.

The spectrum of electromagnetic radiation. Theoretical foundations of the UV spectroscopy method. Chromophores, auxochromes. Types of absorption band shifts. Electronic spectra of solutions and films of polymers. Influence of the solvent on the electronic spectra of polymer solutions.

2. Vibrational spectroscopy.

Theory of IR and Raman absorption. Valence, deformation vibrations (symmetric and asymmetric). Types of fluctuations of individual groupings.

3. NMR spectroscopy.

Fundamentals of the theory of the NMR spectroscopy method from the point of view of classical and quantum mechanics. Chemical shift, standards in NMR spectroscopy. Shielding constants, atomic, molecular, intermolecular shielding. Spin-spin interaction. Spin-spin interaction constant. Classification of spin systems: spectra of the first and higher order. exchange interaction.

4. Thermal motion in polymers.

Heat capacity of polymers. Heat capacity of solid polymers. Theoretical analysis of heat capacity. Heat capacity of polymer melts.

Energy transfer in polymers (thermal conductivity and thermal diffusivity of polymers. Temperature dependence of thermal conductivity. Amorphous polymers. Crystalline polymers. Changes in thermal conductivity in the region of phase transitions. Thermal conductivity and molecular parameters (molecular weight, branching and chain structure). Anisotropy of thermal conductivity. Effect of pressure on thermal conductivity. Temperature dependence of thermal diffusivity Thermal diffusivity and molecular parameters.

Thermal features of transitions and relaxation processes in polymers. melting and crystallization. Transformations in the glassy state and intermediate transformations.

5. Thermophysical processes during the deformation of polymers.

reversible deformations. Thermal expansion of polymers. Thermodynamics of reversible deformations. Thermoelasticity of solid polymers. Thermoelasticity of rubbers.

6. Irreversible deformations.

Orientation stretching of polymers. Destruction of polymers. Power softening of filled rubbers.

6.2. Essay topics

1. Structural features of polysaccharides.

2. Electrospinning of polysaccharide nanofibers and nonwovens.

3. Matrices and scaffolds from polysaccharides and their derivatives.

4. The effect of polysaccharide additives on the properties of the shell of macrocapsules for pharmacological purposes.

5. Influence of polysaccharides of plant and animal origin on the rate of seed germination.

6. Polysaccharides in biologically active systems.

7. The use of polysaccharides in pharmacology and medicine.

8. Polysaccharides as therapeutic agents.

9. Polysaccharides in the food industry.

10. Sorbents from polysaccharides and their derivatives.

11. polysaccharide plastics.

12. Composite materials based on polysaccharides and their derivatives.

6.3. Questions for educational discussion No. 1 "Tthermomechanical properties of polymers"

deformation properties. Deformation of amorphous polymers. Elastic deformation. Forced elasticity. Influence various factors on the glass transition temperature of polymers. Deformation of crystalline polymers. Deformation curves. Peculiarities of tensile and torsion deformation of polymers.

6.4. Questions for educational discussion No. 2 "Physical and mechanical properties of polymers"

Strength and destruction. theoretical strength. Strength of real polymers. durability of polymers. Zhurkov's Equation: Analysis and Significance. Thermofluctuation theory and the mechanism of destruction of polymers. Influence of macromolecular structures on the mechanical properties of polymers. Methods of physical and mechanical testing of polymer fibers and plastics.

7. Educational, methodological and information support of the discipline "Modern methods of polymer research"

Main literature

et al. Technology of polymeric materials. Under total ed. . SPb.: Profession. 20s.

Fedusenko connections: textbook. Saratov: Publishing House Saratovsk. university 20s.

Isolation methods and properties of natural polysaccharides:Proc. allowance. Saratov: Publishing House "KUBiK". 20s.

additional literature

Henke H. Liquid chromatography / Per. with him. . Ed. . Moscow: Technosphere. 20s.

Scientific foundations of the chemical technology of carbohydrates / Ed. . Moscow: LIKI Publishing House. 20s.

Schmidt V. Optical spectroscopy for chemists and biologists. Per. from English. . Ed. . Moscow: Technosphere. 20s.

Software and Internet Resources

Programs Microsoft Office 2007, With hemDraw

Averko-, Bikmullin study of the structure and properties of polymers: Proc. allowance. Kazan: KSTU. 20s.

http://www. himi. *****/bgl/8112.html

http://download. *****/nehudlit/self0014/averko-antonovich. rar

Shestakov Methods for the study of polymers: Educational and methodical. allowance. Voronezh: VSU. 20s.

http://window. *****/window/catalog? p_rid=27245

http://www. /file/149127/

Godovskiy methods of research of polymers. M.: Chemistry. http://www. /file/146637/

AgeevaT. A. Thermomechanical method for the study of polymers: Methodical. instructions for the laboratory workshop on chemistry and physics of polymers. Ivanovo: GOU VPO Ivan. state chemical-technological un-t. 20s.

http://www. *****/e-lib/node/174

http://window. *****/window/catalog? p_rid=71432

8. Material and technical support of the discipline "Modern methods of polymer research"

1. Classroom for lecturing.

2. Overhead projector for demonstrating illustrative material.

3. Educational laboratories No. 32 and 38 for laboratory work, equipped with the necessary equipment

4. Polymer samples, solvents and other chemicals.

5. Chemical glassware.

6. Personal computer.

7. Educational and methodological developments for the study of theoretical material, preparation for practical work and reports on them.

8. Cathedral Library.

The program was drawn up in accordance with the requirements of the Federal State Educational Standard of the Higher Professional Education, taking into account the recommendations of the Educational Program of the Higher Professional Education in the direction of preparation 020100 - "Chemistry", the training profile "High-molecular compounds".

Doctor of Chemistry, Head. base department of polymers

The program was approved at a meeting of the Basic Department of Polymers

dated "___" "______________" 20___, protocol No. ____.

Head base department

Director of the Institute of Chemistry

"Methods for the study of modern polymeric materials Educational and methodological manual Recommended by the Methodological Commission of the Faculty of Chemistry for UNN students studying in the discipline..."

-- [ Page 1 ] --

FEDERAL AGENCY FOR EDUCATION

Nizhny Novgorod State University N.I. Lobachevsky

Research methods of modern

polymer materials

for UNN students studying in the discipline DS R.01 "Methods

polymer research", in the direction of preparation 020100 "Chemistry" and

specialties 020101 "Chemistry", 020801 "Ecology"

Nizhny Novgorod UDC 678.01:53 BBC 24.7 З-17

H-17 METHODS FOR INVESTIGATION OF MODERN POLYMER

MATERIALS: Compiled by: Zamyshlyaeva O.G. Teaching aid. - Nizhny Novgorod: Nizhny Novgorod State University, 2012. - 90 p.

Reviewer: Candidate of Chemical Sciences, Associate Professor Markin A.V.

The educational and methodical manual (UMP) corresponds to the subject of the educational and scientific innovative complex UNIK-1 - "New multifunctional materials and nanotechnologies". The UNIK-1 complex is being developed as part of the priority direction for the development of UNN as a national research university"Information and telecommunication systems: physical and chemical foundations, advanced materials and technologies, mathematical software and application", which is of interest for the development of the education system and improving the quality of training of specialists at UNN.

This UMP outlines the possibilities of physicochemical research methods in relation to modern polymeric materials, in addition, some problems of modern chemistry of macromolecular compounds are touched upon, one of which is the creation of functional polymeric materials with a given set of properties.

UMP is intended for 4th and 5th year students of the Faculty of Chemistry studying in the direction of preparation 020100 "Chemistry" and specialties 020101 "Chemistry" and 020801 "Ecology", who are familiar with the basic concepts and laws of chemistry and physics of macromolecular compounds, methods of their synthesis, kinetic and thermodynamic regularities of polymerization and polycondensation, phase and physical states of polymers, their supramolecular structural organization. The material presented in the UMP will acquaint students with the specifics of physical and chemical methods of analysis in relation to modern polymeric materials, and the implementation of practical work on modern equipment will help future graduates acquire work skills that can be further used in scientific and industrial laboratories.

UDC 678.01:53 LBC 24.7

Table of contents…………………………………………………………… 3 Introduced

– – –

INTRODUCTION

Polymers have recently found wide application in modern world due to its unique consumer properties. In this connection, responsible tasks are often assigned to polymeric materials in the creation of structurally complex materials, for example, membranes for ultrafine purification and separation of substances at the molecular level, anisotropic media with a reconfigurable architecture, in the manufacture of complex elements of various devices and devices (microelectronics), creation of wood-polymer composites.

The ability to use the described methods is necessary for a future specialist to assimilate the theoretical material studied at the university and develop practical skills.

The purpose of the UMP is to briefly introduce students to the use of the most well-known physical and chemical methods for studying polymers. This development does not contain the theoretical foundations of all physical research methods, since they were considered in detail in the course "Physical Research Methods" taught at the Faculty of Chemistry. Only the fundamentals of the methods used to study polymers (methods of light scattering, sedimentation and diffusion, gel permeation chromatography, probe methods, dynamic-mechanical analysis, the wetting method, the behavior of amphiphilic polymers in Langmuir monolayers and in solid Langmuir-Blodgett films) are considered in detail, which is due to both by the diversity and structural features of the objects of study, and by the continuous development and improvement of analytical equipment, as well as by the increasing requirements for the quality of polymeric materials. The last chapter of the training manual contains recommendations for the implementation of practical work within the framework of a special workshop, with a description of the equipment and methods for conducting the experiment.

The main tasks of the UMP:

To acquaint with the features of the application of physico-chemical methods for studying the kinetic laws of radical polymerization and activated polycondensation;

Show the possibilities of various physical and chemical methods for identifying polymeric materials, studying the structure of polymers and their chemical structure;

Familiarize yourself with modern methods for studying dilute and concentrated solutions of polymers of various architectures;

Illustrate methods for studying the physicochemical and mechanical properties of polymeric materials. To acquaint with the methods of studying the processes of transfer of gases and vapors through polymeric materials, and determining the value of the free volume (by the method of inverted gas chromatography and positron annihilation), which can be used to quantitatively describe the transfer processes in polymers and is an urgent task in modern materials science;

Show the possibilities of methods that can not only characterize the heterogeneity of the surface of polymer films (atomic force microscopy), but also determine the energy characteristics of films by the wetting method using various methods (Zisman method, Owens-Wendt method);

To demonstrate the possibilities of methods for studying the colloidal-chemical properties of amphiphilic polymers in monomolecular layers at the water-air phase boundary and in solid Langmuir-Blodgett films.

CHAPTER 1. STUDY OF KINETIC

REGULARITIES OF THE SYNTHESIS OF HIGH MOLECULAR

CONNECTIONS

Let us consider some of the physicochemical methods used to describe the processes of synthesis of macromolecular compounds.

The main characteristic of polymerization and polycondensation reactions is the rate of monomer-to-polymer conversion, which can be expressed by the polymer yield, the monomer concentration in the reacting mixture, and the degree of monomer-to-polymer conversion.

In addition, the degree of conversion of a monomer into a polymer can also be controlled by chemical methods by the number of unreacted double bonds:

brommetric, mercurimetric and hydrolytic oximation method.

1.1. Physical Methods

1.1.1. thermometric method

If we consider the case when the use of the steady state method does not introduce a significant error (for example, the polymerization of methyl methacrylate (MMA) up to 20–50% conversion), then taking into account the change in kinetic parameters, polymerization can be quantitatively described to high degrees of conversion. In this case, attention should be paid to the possible change in the rate of initiation already at the initial stages of the transformation.

It is well known that the rate of polymerization is described by the equation:

d M k р 1 2 fk spread I M (1).

If the decay of the initiator is a first order reaction, then:

d I k spread I (2) d

– – –

IR spectroscopy. IR spectroscopy is the most applicable for studying polymerization kinetics, since it is characterized by a large set of absorption bands corresponding to vibrations of almost all functional groups (from 12500 to 10 cm-1). The main conditions for the use of IR spectroscopy for the study of kinetic regularities is the presence of spectrally separated characteristic absorption bands of the monomer, initiator, and solvent. At Tomsk Polytechnic University Sutyagin V.M. et al. studied the polymerization of vinylcarbazole using the stopped jet method with registration of the spectrum in the IR region. The setup consisted of reservoirs with reagent solutions connected to a jet block through which the reagents were supplied to the observation chamber (with an opening for the passage of IR rays), where polymerization takes place. The method consists in successive recording of the kinetic curve as a dependence of the transmittance on time for a solution of a certain concentration of monomer and initiator.

The recording of the curve was carried out in a wide time interval, the start of the recording system was automatically switched on with the supply of reagents to the observation chamber. After the recording device showed that the reaction was completely completed, the monomer mixture was removed through the drain hole and the measuring cell was washed. Further, using the Lambert-Beer equation, the extinction coefficient of the absorption band of the stretching vibrations of the vinyl bond of vinylcarbazole was found, and taking into account the thickness of the cuvette, the reaction rate constant was determined.

UV spectroscopy. This method can also be used to obtain data on the kinetics of chemical reactions. The starting materials and reaction products are capable of absorbing in various regions of the UV spectrum. Spend quantitative analysis to build calibration curves, with which you can build kinetic curves of changes in the concentration of the substances under study over time. After processing these curves determine the rate constant of the reaction.

1.1.4. Calorimetry One of the informative methods for studying the kinetic regularities of the polycondensation reaction is heat-conducting reaction calorimetry. This method has found wide application in the study of hyperbranched polymers. The measurements are carried out on a Calve microcalorimeter, in which the main part of the energy released in the reaction chamber is removed from the reaction zone through a system of thermopiles. For example, the Calve DAK-1A calorimeter automatically registers the value of the integral heat flux coming from the reaction calorimetric cell through differentially connected thermopiles to the massive central block of the calorimeter thermostat.

The sensitivity of its measuring thermopiles is at least 0.12 V/W. The electrical circuit provides measurements of heat release energy of at least 98%.

Using this method, it is possible to study not only polymerization processes, but also reactions of activated polycondensation. For example, the activated polycondensation of trispentafluorophenyl)germane (FG) and bis-(pentafluoro)phenylgermane (DG) in THF solution using triethylamine as an activator has been studied in detail.

The loading of the studied substances and the process of their mixing in the calorimeter were carried out in an argon atmosphere. One of the substances (Et3N) was placed into a sealed evacuated glass ampoule with a thin-walled bottom. This ampoule was placed in the upper part of the Teflon reaction cell (height 0.11 m, diameter 0.01 m) of the calorimetric block of the calorimeter thermostat using a special device. Another substance (solution of FG and DG in THF) was preliminarily introduced into the cell in an argon atmosphere. After thermal equilibrium was established between the calorimetric block of the calorimeter thermostat and the cell with the substances under study, the reagents were mixed by breaking the lower part of the glass ampoule against the bottom of the cell.

The device mentioned above ensured complete mixing of the components and their intensive mixing. A correction was introduced into the final result, which took into account the breaking of the glass ampoule, the mixing of the resulting mixture, and the evaporation of the solvent into the volume of the ampoule not filled with the sample. Blank experiments were performed to determine the correction value. The measurement temperature was 25C. All obtained heat release curves had 2 maxima, the intensity of which was determined by the ratio of components in the reaction mixture. To analyze the obtained data, it was necessary to carry out similar measurements for the polycondensation of each of the monomers (FG and DG) under the same conditions.

As a result, it was shown that FG is more reactive than DG in the copolycondensation reaction; in addition, using the 19F NMR method, it was possible to establish the mechanism for the formation of branched macromolecules with different architectures and to determine the degree of branching (Section 2.2).

1.1.5. polarography

– – –

consumption curves of each of the monomers in the copolymerization process (C concentration, I d - change in the height of the polarographic wave). In addition, the value of E1/2 is related to the parameters of the reactivity of the monomers, which can be used to find the relative activities of the monomers r1 and r2.

1. 2. Chemical methods

1.2.1. The bromide-bromate method uses KBr and KBrO3. When the components interact, bromine is released, which adds to the double bond of the monomer:

5KBr + KBrO3 + 6HCl 6KCl + 3H2O +3Br2, Br2 + CH2=CHCOOH CH2BrCHBrCOOH, Br2 + 2KI 2KBr + I2, I2 + 2Na2S2O3 2NaI + Na2S4O6.

1.2.2. The method of mercurimetric titration of the reagent is based on the addition of mercury (II) nitrate at the site of the double bond of the monomer (acrylic or methacrylic acid), followed by titration of excess mercury (II) nitrate with Trilon B. The reactions proceed according to the following equations:

Hg(NO3)2 + CH2=CHCOOH CH2(HgNO3)CH(ONO2)COOH, C10H14O8N2Na2 + Hg(NO3)2 C10H12O8N2Na2Hg + 2HNO3.

1.2.3. The hydrolytic oximation method is based on the reaction of acetaldehyde released during the hydrolysis of, for example, vinyl ether with hydroxylamine hydrochloride and subsequent tiation of hydrochloric acid alkali:

CH2=CHR + H2O CH3CHO + HOR, CH3CHO + NH2OHHCl CH3CH=NOH + HCl + H2O, HCl + KOH KCl + H2O.

The kinetics of polymerization can also be studied using gravimetric and dilatometric methods. The gravimetric method (weight) is one of the simplest and most accessible, but its significant drawback is that one experiment gives only one point on the graph. More accurate is the dilatometric method based on the decrease in the volume of the reaction mass during polymerization. One of the advantages of this method is the possibility of obtaining kinetic curves at a certain temperature without isolating the polymer.

CHAPTER 2. STUDYING THE STRUCTURE AND COMPOSITION OF POLYMERS

Let us consider the physicochemical methods used to study the microstructure, chemical structure, and composition of copolymers, which, in combination with methods for controlling kinetic processes, can be useful in establishing the mechanism for the formation of complex macromolecular structures.

2.1. EPR - spectroscopy

The method is based on the phenomenon of resonant energy absorption electromagnetic waves paramagnetic particles placed in a constant magnetic field. Absorption is a function of the unpaired electrons present in the polymer sample. The nature of the radical can be identified from the shape, intensity, position, and splitting of the spectrum using atlases of EPR spectra. This method is the only method of "direct" observation of unpaired electrons. Instruments give the first derivative of the energy absorption curve. The line intensity of an EPR spectrum is the area under its curve, which is proportional to the number of unpaired electrons in the sample. The position of the line in the spectrum is taken to be the point at which the first derivative of the spectrum crosses the zero level.

In polymer chemistry, this method is widely used to study free radicals formed during the oxidation and degradation of polymers (including mechanical destruction), polymerization (photo-, radiation initiation, etc.), which is associated with a high sensitivity of the method, which allows detecting the concentration radicals of the order of 10-9-10-11 mol/l.

General principles for the interpretation of EPR spectra. After registration of the EPR spectrum, it is necessary to interpret it.

The following rules are used to interpret isotropic EPR spectra:

1. The positions of the lines of the spectrum must be symmetrical with respect to some center of the spectrum. The asymmetry may be due to the superposition of the two spectra, and is related to the difference in the corresponding g factors. If the hyperfine splitting constants are large, then second-order splittings can lead to asymmetry in line positions. The differences in linewidths can be caused by the slow rotation of the radical. This can also be the reason for the appearance of spectrum asymmetry;

2. If there is no intense central line in the spectrum, then this indicates the presence of an odd number of equivalent nuclei with half-integer spins.

The presence of a central line does not yet exclude the presence of an odd number of nuclei.

3. For nuclei with I=1/2, the sum of the absolute values of the hyperfine splitting constants for all nuclei should be equal to the distance (in gauss) between the extreme lines, which can be very weak and even not be observed at all. This sum is equal to ni ai, where ni is the number of nuclei with i hyperfine splitting ai.

4. The reconstruction of the spectrum, if it is correct, must correspond to the experimental positions of the lines, especially at the edges of the spectrum.

If the line widths are equal and the overlap is negligible, then the relative line amplitudes should correspond to the degeneracy multiplicity.

5. The distance between two adjacent lines most distant from the center is always equal to the smallest value of the hyperfine splitting.

6. The total number of energy levels in the system for one value of MS n is given by the expression 2 I i 1, where ni is the number of nuclei with spin I i.

– – –

equivalent nuclei with spin I i.

There are currently many computer programs to simulate EPR spectra, and therefore, the task of analyzing the hyperfine structure has been greatly simplified. For example, the WINEPR SimFonia software package allows you to download the experimental spectrum, determine the value of the g factor, and approximately measure some of the most obvious CFS constants. By introducing the measured parameters of the spectrum (g-factor, type of nuclei and their number, values of the HFI constants), setting the width and shape of the line, one can construct a theoretical spectrum. Then the simulated spectrum is subtracted from the experimental one. Adjusting the parameters of the theoretical spectrum, one achieves the minimum difference between it and the experimental spectrum.

2.2. NMR - spectroscopy

The NMR method is based on the ability of polymers placed in an external magnetic field to absorb electromagnetic radiation in the radio frequency range (1…..500 MHz). In this case, absorption is a function of the magnetic properties of the atomic nuclei in the macromolecule. Active in NMR, i.e.

those objects that contain magnetic nuclei appear, for example, 11H, 1 H, 9 F, 7 N, 15 P, etc. The NMR spectrum is the dependence of the intensity of electromagnetic radiation on frequency (Hz). The shift of NMR signals under the influence of different electronic environment is called chemical shift, which is proportional to the electromagnetic field and is measured in relation to the signal of a reference substance, which has a signal in a stronger field than most protons.

Interpretation of the NMR spectra of polymers must begin with establishing the chemical shifts of various atoms in molecules (H, C, F, etc.) using chemical shift correlation tables and catalogs of NMR spectra.

study of the configuration and conformation of polymer chains; distinguishing between block copolymers, alternating polymers and polymer blends, determining the structure of the polymer.

To determine the structure of polymers, the value of the chemical shift between the peaks and the value of the hyperfine splitting constants, which determine the structure of the absorption peak itself, are used. Different groupings correspond to a certain value of the chemical shift, which is determined by the electronic screening of the nuclei. These characteristics indicate the environment of this group.

To analyze the structure of a polymer, it is necessary:

Determine which spin-spin interaction leads to hyperfine splitting of each of the peaks;

Having assumed the structural formula of a macromolecule unit, it is necessary to calculate the intensity of the peaks and determine the ratio of the numbers of protons in the groups. For example, if the total number of protons is known (from elemental analysis), the number of protons in each group can be determined, which finally helps to establish the structure of the substance.

NMR spectra can also be used to characterize the branching of polymers of complex architecture. For example, we studied the 19F NMR spectra of copolymers based on FG and DG. In this case, fluorine atoms of different generations are distinguishable due to the polarizing effect of the ion pair at the focal point of the hyperbranched macromolecule.

Six signals were found in the spectra in the ratio 2:2:1:1:1:2 (Fig.

1). The signals at 158.5, 146.6, and 125.8 ppm correspond to the fluorine atoms of the terminal phenyl groups in the meta, para, and ortho positions, respectively. 127.1 ppm

Fluorine atoms of C6F4 groups located between two equivalent germanium atoms. Signals 128.2. and 136.3 ppm correspond to the fluorine atoms of the C6F4 groups located between the germanium atom with pentafluorophenyl ligands and the germanium atom bonded to the hydrogen atom.

Rice. Fig. 1. 19F NMR spectrum of the copolymer of FG and DG obtained in the presence of 20% DG (Table 1).

The degree of branching of copolymers based on FG and DG was estimated from the relative content of fluorine para-atoms (the outer shell of a hyperbranched macromolecule) - Fp from the total number of fluorine atoms calculated for a third-generation hyperbranched macromolecule.

Fi=si/s, where si is the effective area in the absorption spectrum corresponding to each type of aromatic fluorine. 19F NMR spectra were recorded on a Bruker AM-500 Fourier NMR spectrometer, 470.5 MHz (reference hexafluorobenzene).

Table 1. Characteristics of copolymers obtained by light scattering methods (solvent - chloroform) and 19F NMR

– – –

For perfluorinated polyphenylenegermane (PFG) obtained in the absence of DH, Fp(D3)=0.144 was found, which practically corresponds to the calculated value.

For the polymer obtained from DG, the calculated value of Fp(D3) = 0.1176; for the copolymer at [FG]/[DG]=1/3 Fp(D3) =0.1386. In all cases, we proceeded from a branched structure with a branching index on the germanium atom equal to 3 and 2 for FG and DG, respectively. It can be seen from the table that the copolymers are characterized by an underestimated value of Fp compared to PFG, which can only be achieved by crosslinking, due to the participation of the hydrogen atom of the DG units in the crosslinking reactions. Calculations were carried out for a copolymer of the composition [FG]/[DG]=1/3, in which half of the DG units underwent crosslinking (16.5%). In this case Fp(D3)=0.126 is found. It should be noted that the calculations were carried out on the basis of a common mechanism for intra- and intermolecular cross-linking associated with a change in the ratio between the number of C6F5 and C6F4 groups.

The main advantages of the NMR method are its comparative simplicity and the possibility of carrying out absolute quantitative determinations (without calibration); the condition of sufficient polymer solubility (a solution of at least 3–5%) should be a limitation.

2.3. IR spectroscopy

This method can largely complement NMR spectral studies. Currently, there are automated search systems that can identify any compound if it was previously known. But, unfortunately, the main problems solved in the chemistry of macromolecular compounds are associated with the synthesis and study of the properties of polymers, the structure of which has not been previously studied.

Absorption in the infrared region of any substance is due to vibrations of atoms, which are associated with a change in interatomic distances (valence vibrations) and angles between bonds (deformation vibrations). The IR spectrum is a fine characteristic of a substance. To identify polymers, it is necessary to record the spectrum of the polymer (in the form of a film, in tablets with KBr, in the form of a solution) on an IR spectrometer in the form of a dependence of the relative intensity of transmitted light, and hence the absorbed light, on the wavelength or wave number. The spectrum of the polymer must be well resolvable. When identifying polymeric materials, as a rule, the presence of absorption bands in the valence region is first analyzed.

1 vibrations of the double bond (3000 and 1680….1640 cm) and the area of deformation vibrations of these bonds (990..660 cm-1). If they are in the IR spectrum, then the polymer can be attributed to the class of unsaturated polymers. Further, using the tables of characteristic frequencies, the other absorption bands are completely assigned to certain atomic groups that make up the link of the macromolecule.

The interpretation of the spectrum is complicated by the fact that the absorption bands of different groups may overlap or shift as a result of a number of factors. Table 1. shows the characteristic frequency ranges of some groups.

Table 1. Characteristic frequencies of some groups

– – –

Using the method of IR spectroscopy, it is also possible to determine and study intermolecular and intramolecular hydrogen bonds, because

their education leads:

To shift the band towards lower frequencies;

Broadening and increase in the intensity of the band corresponding to the stretching vibration of the group involved in the formation of hydrogen bonds.

To study hydrogen bonds, the spectra of polymers are usually taken at several concentrations in a nonpolar solvent.

2.4. Capabilities of the mass spectrometry method

This method is based on the study of the chemical structure, composition, and properties of polymers by determining the ratio of mass to charge me and the number of ions obtained by ionization of volatile decomposition products of the analyzed polymer. Due to the high sensitivity and speed of analysis (hundreds of analyzes per 1 s), as well as the possibility of observing a single substance in a mixture, this method has found wide application in studying the initial stages of polymer degradation in degradation processes.

In addition, this method makes it possible to determine the molecular weights of polymers with high accuracy. Since the mass of an electron is negligible compared to the mass of a molecule, the problem of identifying the mass spectrum is reduced to revealing the lines of molecular ions and determining their mass numbers. Lines of molecular ions are observed only in 90% of the mass spectra.

If you analyze the mass spectra of a polymer of unknown structure, you may encounter a number of difficulties. First, it is necessary to determine the molecular weight and elemental composition based on the mass numbers of characteristic lines in the spectrum, then, it is necessary to try to guess which class of compounds this polymer belongs to and the possibility of the presence of any functional groups. To do this, consider the difference in the mass numbers of the line of molecular ions and characteristic lines closest to it or the difference in the elemental compositions of molecular and fragment ions.

In the case when the nature of the polymer is known, and it is necessary to establish some details of its structure according to the known patterns of dissociation upon electron impact, the mass spectrum data is sufficient to write the structural formula of the compound.

– – –

2 sin crystalline regions), I c (s) is the intensity of coherent X-ray scattering from the crystalline region.

The application of this method of analysis in the study of the structure of polymers is complicated by the fact that the polymer usually consists of crystalline regions distributed in the mass of an amorphous substance, which leads to obtaining X-ray diffraction patterns of a crystalline substance against a broad blurred background.

Analyzing such an X-ray pattern, one can determine the percentage of the crystalline phase.

2.6. Chemical Methods

One of the common methods for analyzing the composition of nitrogen-containing copolymers is the Keldahl analysis.

Keldahl method. This method consists in the fact that nitrogen-containing organic matter is decomposed by heating with a sufficient amount of concentrated H2SO4 to quantitatively form (NH4)2SO4. Carbon is then oxidized to carbon dioxide (H2CO3), and nitrogen is converted to ammonia (NH3), which remains in solution in the form of sulfate salt.

1. Decomposition:

– – –

CHAPTER 3. POLYMER SOLUTIONS

Molecular weight distribution is one of the most important characteristics of macromolecular compounds, which reflects the kinetic process of polymerization and determines the operational characteristics of polymers, predicting the ways of its processing. In this section, we consider the concept of the molecular weight distribution of polymers and possible methods for their fractionation.

3.1. Molecular weight characteristics of polymers

– – –

It follows from expression (3) that the number average MM is equal to the total mass of macromolecules divided by their number.

In the experimental study of MMPs, one usually deals with continuous curves and distribution functions. The value of the continuous differential numerical distribution function fn(M) is equal to the numerical fraction of macromolecules with MM from M to M+dM, divided by dM; the value of the continuous mass distribution function fw(M) is equal to the mass fraction of macromolecules with MM from M to M+dM divided by dM.

Continuous differential numerical and mass functions are interconnected, like the corresponding discrete functions, by a simple relationship:

f w (M) (M M n) f n (M) (5).

In addition to differential, integral distribution functions are widely used:

the value (ordinate) of the integral numerical distribution function Fn(M) is equal to the numerical fraction of macromolecules with MM from the minimum to the specified M;

the value (ordinate) of the integral mass distribution function Fw(M) is equal to the mass fraction of macromolecules with MM from the minimum to the specified M.

An important characteristic of a polydisperse polymer is the MWD width. The ratio M w M n, which characterizes the MMD width, is called the Schulz polydispersity coefficient. Often, in the ratios characterizing the MWD of a polymer, the degree of polymerization p M M 0 is used instead of MM, where M and M0 are the molecular weights of the polymer and monomer.

The average molecular weights M n and M w are determined using absolute methods, since their calculations are carried out without any assumptions about the shape and size of macromolecules. The number average molecular weight M n can be determined by any method based on measuring the colligative (i.e., depending only on the number of particles) properties of polymer solutions: osmometry, ebullioscopy, cryoscopy, isothermal distillation, measurement of the thermal effects of condensation, as well as from quantitative determination data terminal functional groups of macromolecules by any physical or chemical methods.

The mass-average value of M w can be determined, for example, by the method of light scattering.

In practice, MWD curves are obtained as a result of fractionation of polymers, i.e. performing various methods of separating a polymer sample into fractions with different molecular weights.

– – –

The separation of the polymer into fractions is based on the fact that the critical dissolution temperatures of polymers depend on their molecular weight. Despite the fact that the polymer solution is a multicomponent system (due to the presence of macromolecules with different molecular masses in the polymer), it can be considered as a quasi-binary system, since the formation and coexistence of only two phases is usually observed during phase separation of such a multicomponent system.

The compositions of the phases formed during the separation of the polymer solution are not the same and can be determined from the equilibrium condition z, z

– – –

In addition, the actual separation of the polymer depends not only on the degree of polymerization, but also on the ratio of the volumes of the resulting phases. If the volume of the concentrated phase is small, then the low molecular weight product will remain entirely in the dilute phase.

For fractionation, it is necessary to take very dilute solutions with a concentration below the critical one. When such a solution is cooled (Fig. 1, point A), the phases separate with the formation of a more concentrated second phase. A solution above the critical concentration is not suitable for fractionation (Point B, Fig.

The critical concentration can be determined by the 2, crit formula:

2, crit 1 z For example, at a number average molecular weight of 106 z104 and 2, crit 0.01. Those. the initial concentration of a solution of this 2,cr. 2 polymer during fractionation should be much less than 0.01.

Fractionation methods. Most fractionation methods are based on the dependence of the solubility of the polymer on its MW. The more MM, the worse the solubility. Solubility can be influenced by changing the temperature of the solution or by changing the composition of the solvent.

There are two types of fractionation: preparative (in which fractions are isolated so that their properties can be studied), and analytical, in which a distribution curve is obtained without isolating individual fractions.

Preparative methods include methods of fractional precipitation and fractional dissolution. The most commonly used method of fractional precipitation consists in successive precipitation of a number of fractions from a polymer solution, the molecular weights of which decrease monotonically.

This can be done in various ways:

By adding a precipitant to the polymer solution;

Evaporation of the solvent, if the polymer was previously dissolved in the solvent-non-solvent mixture;

A change in the temperature of the solution, which leads to a deterioration in the quality of the solvent.

The fractional dissolution method consists in successive extraction of a polymer with a series of liquids, the dissolving power of which with respect to a given polymer gradually increases.

The starting polymer can be solid, in the form of a coacervate, a film, on an inert or active carrier. The resulting fractions have a consistently increasing molecular weight.

analytical methods

Fractionation includes:

ultracentrifugation, turbidimetric titration, gel permeation chromatography, etc.

Turbidimetric titration consists in measuring the turbidity of a polymer solution when a precipitant is added to it. If the polymer solution is sufficiently diluted, then the macromolecules of the polymer released when the precipitant is added remain in the form of a stable suspension, causing the solution to become cloudy. As the precipitant is added, the turbidity of the solution increases until all the polymer is separated, after which the turbidity remains constant. The results of the titration are presented as a dependence of the optical density of the solution, which is proportional to the turbidity, on the volume fraction of the precipitant.

This method has two main assumptions:

It is assumed that the amount of precipitant required to initiate polymer precipitation (critical volume of precipitant or precipitation threshold) depends on the concentration of the polymer at the time of precipitation (C) and its molecular weight (M) according to the equation:

cr k lg C f M (10), where cr is the volume fraction of the precipitant at the settling threshold, k is a constant, f M is some MM function, the value of which is determined from calibration titrations of narrow polymer fractions with known MM;

It is believed that the turbidity is proportional to the amount of precipitated polymer, and when a small amount of precipitant () is added, the increase in turbidity () is associated only with the release of macromolecules of a certain length z.

The value of the method is its speed and the ability to work with very small amounts of polymer (several mg). The method turns out to be very useful in selecting precipitant-solvent systems for preparative fractionation, in determining the solubility limits of copolymers, in qualitatively assessing the MWD of polymers in studying the polymerization mechanism, etc.

Fractionation by the method of gel permeation chromatography is carried out according to the principle of a molecular sieve (chromatographic separation of molecules occurs only in size, due to their different ability to penetrate into the pores, and does not depend on the chemical nature of the components). This method combines continuous sample fractionation, which is based on the difference in the interfacial distribution of substances moving with the solvent (mobile phase) through a highly dispersed stationary phase medium, and subsequent analysis of the fractions.

The principal feature of the method is the possibility of separating molecules according to their size in solution in the range of molecular weights from 102 to 108, which makes it indispensable for the study of synthetic and biopolymers.

The principle of the GPC method. During fractionation by this method, a solution of a polydisperse polymer is passed through a column filled with particles of a porous sorbent in a solvent, while the molecules tend to diffuse into the solvent, which is in the pores, i.e. penetrate into the pores. With a constant solvent flow, the solute moves along the column, and macromolecules will penetrate into the pores only when their concentration outside the pores is greater than in the pores. When the solute zone leaves this area of the sorbent, the concentration of the sample inside the sorbent becomes greater than outside it, and the macromolecules again diffuse into the flow of the mobile phase. This process is repeated cyclically along the entire length of the column. In a polydisperse polymer, there is always a fraction of "short" macromolecules that easily penetrate into all pores of the sorbent, a fraction of "larger" macromolecules that can penetrate only some of the pores, and "large" macromolecules that do not penetrate into the pores at all are "forbidden" for pores of this size. According to different pore penetration ability, macromolecules are retained in the column different time: the “forbidden” large macromolecules are washed out of the column first, the smallest ones are the last. This separation in the chromatographic column is called the "spatial inhibition" method. The time during which the polymer molecules are held in the pores is called the retention time tr. Those. this is the average time for a macromolecule to pass through the column from the moment the sample is injected to a certain distance equal to the length of the column. The retention time tr is the main experimentally determined characteristic of the chromatographic process.

Another parameter that is most often used in chromatography

– "retained volume" - Vr, which is related to the retention time:

Vr = trv (11), where v is the volumetric flow rate of the solvent through the column (mL/min), which is set at the beginning of the experiment.

The retention volume is the number of milliliters of solvent that must be passed through the column to flush the sample out of the pores of the sorbent. This value is related to the size of macromolecules similarly to the retention time: Vr is minimal for “forbidden” molecules and maximal for macromolecules that completely penetrate into the pores.

The volume of the exclusion column can be expressed as the sum of three terms:

V = Vо + Vs + Vd (12), where Vо is the “dead” intermediate volume of the column, i.e. solvent volume between sorbent particles (mobile phase volume); Vs is the volume of pores occupied by the solvent (the volume of the stationary phase); Vd is the volume of the sorbent matrix, excluding pores.

The total solvent volume in the column, Vt (total column volume), is the sum of the volumes of the mobile and stationary phases:

Vt = Vo + Vs (13).

The equilibrium distribution coefficient of macromolecules between the mobile and stationary phases k characterizes the probability of diffusion of macromolecules into pores and depends on the ratio of the sizes of molecules and pores, and also determines the retention of molecules in the exclusion column:

k = Cs/Co (14), where Cs is the concentration of the substance in the stationary phase; Co - in the mobile phase.

Since the mobile and stationary phases have the same composition, then k of the substance for which both phases are equally accessible is equal to 1. This situation is realized for molecules with the smallest sizes (including solvent molecules), which penetrate into all pores and therefore move through the column most slowly. Their retained volume is equal to the total volume of the solvent.

All molecules larger than the pore size of the sorbent cannot enter them (complete exclusion) and pass through the channels between the particles.

They elute first from the column with the same retention volume equal to the volume of the mobile phase (Vo). The distribution coefficient k for these molecules is 0.

Molecules of intermediate size, capable of penetrating only some part of the pores, are retained in the column according to their size.

The distribution coefficient k of these molecules varies from 0 to 1 and characterizes the proportion of pore volume available for molecules of a given size.

Their retained volume is determined by the sum of Vo and the available part of the pore volume:

Vr = Vo + k Vs (15).

This is the basic equation that describes retention in a chromatographic process.

The convenience of the GPC method lies in the fact that the main parameter of the method, the retained volume Vr, is a single-valued function of the molecular weight (M).

In the general case, the dependence Vr(M) is expressed:

log M = C1 – C2Vr + С3V2r + … (16).

Determining the volume distribution of the eluent with (Vr) and the calibration curve Vr(M) makes it easy to obtain the integral and differential molecular weight distributions:

Vr (M) M (17), c(Vr)dVr Fw (M) F (Vr) f dM 1 w Vr (M 1) M1

– – –

The behavior of macromolecules in solution essentially depends on the thermodynamic quality of the solvent, the molecular weight of the polymer, and the temperature of the solution. A change in these parameters affects the size and shape of macromolecular coils, which leads to a change in the hydrodynamic properties of dilute polymer solutions. The main source of information about the molecular characteristics of polymers is the study of their properties in dilute solutions by the methods of molecular optics and hydrodynamics. First of all, these are the methods of static and dynamic light scattering, the use of which makes it possible to determine the MM, dimensions, and conformation of dissolved objects. It should be noted that the use of these methods is especially productive in studying the properties of polymeric supramolecular structures, since it provides information about a system that is not subject to external influences. Another absolute method, sedimentation-diffusion analysis, makes it possible to reliably measure sedimentation constants S and translational diffusion coefficients D in the region of strong dilution of polymer solutions. The obtained values make it possible to determine the MM and hydrodynamic radius Rh of the polymers under study.

3.2.1.1. Light scattering method

The principle of the light scattering method. The light scattering method is based on the scattering effect of part of the light passing through a liquid medium. This scattering is due to the presence of fluctuations in the density and concentration of the substance in a separate volume of the solution, which exist due to thermal motion. The difference in densities leads to differences in the refractive indices. Light passing through a liquid medium is refracted at the boundaries of sections with different densities, deviates from the original direction, i.e. dissipates. The greater the scattering, the greater the fluctuation. If the medium is a polymer solution, then, in addition to fluctuations in the density of the solvent, there are fluctuations in the concentration of the polymer. These fluctuations are the more intense, the lower the osmotic pressure inside the areas with a higher concentration, i.e. the greater the molecular weight of the solute.

Methods based on measuring the intensity of light scattered by polymer solutions and its angular dependence have received the main application. There are methods of static light scattering (elastic) or dynamic (quasi-elastic) scattering. The main difference lies in the method of measuring the scattered light intensity.

In elastic or Rayleigh scattering, the incident and scattered light have the same wavelength. As a result of the movement of scattering centers, the scattered light ceases to be monochromatic, and a Rayleigh peak is observed instead of a single line. In this case, the time-averaged total intensity is measured as a function of the scattering angle. Using static light scattering, it is possible to determine the mass and characteristic linear size of particles in some systems.

In inelastic scattering, the frequency of the scattered light differs from the frequency of the incident light. In the dynamic light scattering method, the change in the scattering intensity with time is measured. From where the particle diffusion coefficients, particle size and size distribution are determined.

Rayleigh, in studying the simplest case of scattering in an ideal gas of low density, in 1871 proposed the theory of static (elastic) scattering. He considered the scattering of light by spherical dielectric particles with a diameter d much smaller than the wavelength of the incident light (d 20) and with a refractive index close to unity.

In the absence of absorption and using unpolarized light, the Rayleigh equation is:

9 2 V 2 F 4 2 (1 cos2) I 0 (20), I R where I0 is the incident light intensity; I is the intensity of light scattered at an angle with respect to the incident beam; F is a function of refractive indices; is the number of particles per unit volume; V is the particle volume; is the wavelength of the incident light; R is the distance from the scatterers at which the intensity I is measured. The function F is defined as n 2 n0 (21), F 21 n 2n 2

– – –

b a Fig. 1. The intensity of the scattered light does not depend on the scattering angle (a);

concentration dependences of reciprocal intensity of scattered light Кс/R=90 for polystyrenes obtained by chain transfer reaction with tris-(pentafluorophenyl)germane with different molecular weights [(C6F5)3GeH]=0.02 mol/l (1) and [(C6F5)3GeH] =0.005 mol/l (2) in chloroform versus concentration (b) average value. All of the above applies to small particles (compared to the wavelength of the incident light). With an increase in size, the laws of light scattering change, a spherical asymmetry of the scattered light intensity appears, and the degree of its polarization changes. Differences in scattering by small and large particles (/20) can be demonstrated using vector Mie diagrams (Fig. 2).

– – –

For large macromolecules, the scattered light intensity is spherically nonsymmetric. This is due to the fact that the electromagnetic oscillations that are excited in the regions of the macromolecule that are remote from each other are out of phase. The difference in the phases of the waves of two induced dipoles is the greater, the larger the size of the macromolecules and the larger the scattering angle (Fig. 3).

In the direction of the primary light beam, the phase difference is zero, and in the opposite direction it is the largest. The angular dependence of the intensity of scattered light - the scattering indicatrix - is used to determine the size and shape of macromolecules in solutions.

In this regard, the internal interference factor (or form factor - P) is introduced into the Debye equation:

– – –

For macromolecules of any shape P = 1 at = 0С. As the value of P increases, it decreases.

The form factor is related to the radius of gyration and depends on the shape of the particles (spheres, cylinders, thin sticks, etc.) According to the Zimm equation, the form factor for a particle with a statistical coil configuration is:

1 P 1 (8 2 92)h 2 sin 2 (/ 2) (26), where h 2 is the average square of the distance between the ends of the polymer chain.

Substituting equation (26) into (25) we get:

– – –

with one polymer molecule in solution. This is achieved by appropriately diluting the system and reducing the volume of the test sample.

Recently, the so-called "transport" methods based on the study of the macroscopic transfer of a substance in a liquid medium under the action of an external force have been widely developed to determine the molecular mass characteristics. These methods are based on the dependence of the transport mobility of macromolecules on their molecular weight. Such sedimentation, diffusion, electrophoresis and methods include chromatographic separation of macromolecules.

– – –

For registration, optical methods are usually used, for example, the refractive index n of the solution and its gradient dn dx along the direction of diffusion are determined.

For the working concentrations (0.5 g/mL) used in this method, the refractive index gradient is directly proportional to the concentration gradient:

– – –

The distribution of the refractive index gradient is also expressed as a Gaussian curve (Fig. 5c).

The simplest calculation method is the maximum ordinate method, which corresponds to x = 0.

In this case, the expression x 2 4 Dt in equation (39) vanishes, and this equation is simplified:

– – –

where r is the radius of the settling spherical molecule; dx dt - sedimentation rate, dch and d0 - particle and medium density.

If macromolecules settle, then vdh N A M and v2, where v2 is the partial dh specific volume of the polymer in solution. Then RTS0 (44), M D0 v2d 0 where S0 is the sedimentation constant; D0 is the diffusion coefficient.

The diffusion coefficient is determined as shown in the diffusion method. The sedimentation constant is determined using an ultracentrifuge. To do this, a beam of light is passed through a cuvette with a polymer solution placed in an ultracentrifuge, which falls on a photographic plate located behind the cuvette. As the cell rotates, as the substance is deposited, the interface between the solution and the solvent gradually moves, and light is absorbed along the height of the cell to varying degrees. On the photographic plate, stripes of varying degrees of blackening are obtained.

By photometrically taking photographs taken at certain time intervals, one can obtain a sedimentation curve, i.e. distribution curve of the concentration gradient along the cuvette height at different times.

dx dt d ln x (45), S 2 w2 x w dt, then the dependence of lnx on t should be expressed as a straight line, from the slope of which the sedimentation coefficient S can be calculated.

To exclude concentration effects, the value of S0 is found by extrapolating the value of S to an infinite dilution (i.e., plotting the dependence 1 S f (c)). Knowing the values of S0 and D0, the molecular weight of the polymer is found using formula (44).

The ultracentrifuge sedimentation method is an absolute method for measuring the molecular weight of a polymer, since it does not make any assumptions about the conformations of macromolecules.

In combination, the methods of light scattering, viscometry, and sedimentation-diffusion analysis can provide complete information about the hydrodynamic and conformational properties of macromolecules in solution, which is especially important for hyperbranched polymers. Using the methods of molecular hydrodynamics and optics in dilute solutions in chloroform, we studied two series of hyperbranched copolymers of different topological structures based on perfluorinated germanium hydrides (FG and DG). By varying the amount of DG and its sequence of introduction into the monomer mixture during the synthesis, it was possible to obtain polymers with different architectures. The first series is copolymers of various molecular weights (from 2.3 104 to 31 104) with rigid linear chains between branch points and a different number of branch points in the cascades of the dendritic fragment, the second is copolymers that, with a close degree of branching, on average have a more “loose” structure due to a larger number of linear units on the periphery of macromolecules with a molecular weight from 2.5 104 to 23 104 (Fig. 6).

– – –

c) Fig. Fig. 6. Schematic structure of (co)polymers based on tris-(pentafluorophenyl)germane and bis-(pentafluorophenyl)germane of various architectures: copolymers with rigid linear chains between branch points and a different number of branch points in cascades of the dendritic fragment (a), copolymers that with a close degree of branching, on average, they have a more “loose” structure due to a larger number of linear units at the periphery of macromolecules (b) and hyperbranched perfluorinated polyphenylene german (c).

The studied copolymers have very low intrinsic viscosities. The values change from 1.5 to 5 cm3/g as the MM increases from 1.4 104 to 25 104. For hyperbranched polymers with flexible chains between branching points at such MWs, typically in the range of 3 to 50 cc/g. The low values for co-PFG unambiguously indicate the compact size of their macromolecules and the high density of the polymeric substance in the volume they occupy in solution. In accordance with the Einstein relation for a solid spherical particle, cf = 2.5 v. Substituting the value of the partial specific volume for co-PFG, we have sf 1.3 cm3/g, which is slightly less than the intrinsic viscosity for the lowest molecular weight polymer, PFG (Table 1), obtained in the absence of bis-(pentafluorophenyl)germane. Accordingly, it can be assumed that the shape of its macromolecules differs very slightly from spherical. Table 1 shows that for PFG the ratio /sf is 1.2. Such a low /sf value is more typical for dendrimers than for hyperbranched polymers. For the latter, usually /sf 1.5.

– – –

Based on the data obtained, it can be concluded that the macromolecules of the first series (Fig. 6, a) are characterized by somewhat more compact sizes and less asymmetric shape compared to the molecules of the second series (Fig. 6, b). This is probably due to the fact that the copolymers of the first series contain a dimeric chain of DG units, on which branched blocks are "strung", such molecules are more rigid and resemble a slightly elongated ellipsoid in shape, in contrast to the hyperbranched macromolecules of the second series, which are characterized by the presence of a rigid spherical core with a focal point –Ge(C6F5)3 and branches of DG and FG units, which generally provides a looser structure compared to hyperbranched PFG (Fig. 6c).

That. The methods of molecular hydrodynamics and optics have shown that the macromolecules of the studied polymers have compact dimensions and are characterized by a high density of the polymer substance, while the asymmetry of their shape is low. According to these characteristics, they approach dendrimers.

At a fixed molecular weight, copolymers with a “loose” structure are characterized by larger macromolecular sizes and higher intrinsic viscosities.

3.2.2. Concentrated polymer solutions

Concentrated solutions are those in which the solute molecules interact with each other. Interest in the rheological properties of such solutions is primarily due to the technology of processing polymers, many of which are processed through solutions and melts.

Let us consider the features of the mechanical properties of polymers in a fluid state. By polymers in a fluid (or viscous) state, they usually mean concentrated solutions of polymers, melts of crystallizing polymers, and amorphous polymers in such deformation modes and at such temperatures, when the viscous flow deformation plays a decisive role in their complete deformation, i.e.

irreversible component of the total deformation.

In addition to the main methods of thermomechanical research, a specific method is applicable for flowing polymers, which consists in measuring stresses in the constant strain rate mode. Although, in principle, it is possible to achieve a constant strain rate during mechanical testing of solid and highly elastic polymers, this method becomes crucial only for fluid polymer systems, since only for them, the total deformation can be infinitely large, and therefore the observation of the development of stress in the constant strain rate regime can end with the achievement of the steady flow regime. This flow regime corresponds to its characteristic values of stress and accumulated and retained in the material of highly elastic deformation; further development of deformation occurs only through a viscous flow, when the state of the material does not change in time.

The viscosity of polymers depends on MM, temperature, pressure, and also on the deformation mode (strain rate and stress). For the vast majority of polymer systems, the dependence of velocity on stress in shear flow is characterized by the effect of viscosity anomaly, which consists in a decrease in effective viscosity with increasing shear stress.

In tension, on the contrary, as the strain rate and stress increase, the longitudinal viscosity increases. The viscosity of polymers is highly dependent on temperature. For the region of high temperatures, far from the glass transition temperature of the polymer, the viscosity versus temperature curve is described by an exponential dependence that characterizes the value of the free activation energy of the viscous flow U. As the MM increases, the activation energy becomes independent of the MM, i.e.

as the molecules lengthen, their movement during the flow has a segmental character (for the implementation of a single flow event, only a part of the molecule needs to move). The activation energy of linear polymers depends on the structure of the elementary unit, increasing as the chain rigidity increases. Despite the fact that the mechanism and implementation of the elementary flow act do not depend on the length of the macromolecule as a whole, the absolute values of viscosity depend significantly on the MM, since for the irreversible movement of macromolecules it is necessary that the center of gravity of the macromolecule be mixed by independent movements of individual segments. The higher the MM, the more number coordinated movements must occur in order to shift the center of gravity of the macromolecule. Hence it follows that the dependence of viscosity on MM consists of two sections. The first is the area of low MM values, where the viscosity is proportional to MM, and the second section is the area where MM has a significant effect on viscosity and the condition M 3.5 begins to be satisfied.

The appearance of highly elastic deformations is possible in polymers not only in the highly elastic state, but also in the viscous flow state. Their development in both cases is due to the same mechanism – the deviation of the distribution of conformations from the equilibrium one.

A typical character of the dependence of el highly elastic deformations in shear flow on shear stress in a steady flow is shown in Fig. . 7, from which it follows that the modulus of high elasticity increases with increasing shear stress. This is typical for flowable polymers. The state of the Newtonian flow, in which elastic flows can also develop. 7. Dependence of highly elastic deformations, corresponds to the value of deformations (el) in the regime of the steady-state initial (lowest) modulus of flow of solutions with different viscosities () on highly elastic.

stress () For high molecular weight polymers, the modulus of high elasticity increases significantly as the MWD expands.

Just as in polymers in a highly elastic state, in fluid polymers, especially those containing a solid filler, the effects of reversible destruction of their structure are possible, which leads to a thixotropic change in the properties of the system. For fluid polymers, due to the increased mobility of macromolecules, the processes of thixotropic recovery proceed faster than for polymers in a highly elastic state.

The study of the viscoelastic properties of concentrated solutions is necessary to obtain valuable information about their structure, which is a spatial fluctuation network formed by densely packed aggregates, or associates of macromolecules, inside which there are solvent molecules.

If we consider polymers of complex architecture, for example, hyperbranched polymers and dendrimers, then from the point of view of general problems of rheology, the spherical structure of macromolecules allows us to consider them, on the one hand, as polymers, and on the other, as colloidal dispersions.

Detailed studies of the rheological properties of polymers with a branched structure in a block have hardly been carried out to date, although it is a detailed study of the viscoelastic properties of these solvent-free polymers that can provide useful information about the specifics of their behavior during flow as an ensemble of colloidal particles with flexible macromolecular fragments. To date, the main studies of rheological (mainly viscous) properties have been performed for dilute solutions of dendrimers in order to reveal their molecular structure. In one of the works (Hawker C.J. et al.) devoted to the study of the rheological properties of dendrimers in the melt, an unusual dependence of viscosity on MM was found using the example of dendritic polyester. For the lower generations of dendrimers, the exponent of the power dependence of viscosity on MM is much greater than unity, and then, when the MM reaches about 104 (starting from the fifth generation), this dependence becomes linear. The flow curves of dendrimers of different generations of polybenzyl ether are Newtonian in a wide range of shear rates (0.1–100 s–1), which is uncharacteristic of polymers. Another situation occurs for generations of polyamidoamine dendrimers: at temperatures slightly different from the glass transition temperature, a decrease in dynamic viscosity is observed with increasing shear frequency (work by Wang H.).

The nature of the flow of dendrimers and hyperbranched polymers depends on the nature of the end groups. Thus, the modification of polypropyleneimine dendrimers with amino and cyano groups led to an increase in viscosity while maintaining the Newtonian behavior of the melt. Tande B.M. et al. also showed that the viscosity of the initial polypropyleneimine dendrimers of the fourth and fifth generations is constant over a wide range of shear rates. At the same time, for these dendrimers modified with methyl- and benzyl acrylate, an anomaly in viscosity is observed. These results demonstrate the important influence of end groups on the rheological properties of dendrimer melts. It could be assumed that at temperatures above the glass transition point, the flow of dendrimers is already possible. However, the authors Smirnova N.N. and Tereshchenko A.S. co-workers found that for high-generation carbosilane dendrimers, in addition to glass transition, a second, high-temperature transition is observed. It was detected by high-resolution adiabatic calorimetry, which was associated with the nature of intermolecular contacts in dendrimers. In order to study in detail the nature of the high-temperature transition and the possible influence of the end groups of dendrimers on this transition in a wide temperature range, the viscoelastic properties of carbosilane dendrimer derivatives that differ in the type of end groups were studied (Mironova M.V. et al.).

It was shown that high-generation carbosilane dendrimers are capable of forming a supramolecular structure in the form of a physical network of intermolecular contacts. Grid failure can be initiated by shear deformation and temperature. The high-temperature transition in high-generation carbosilane dendrimers, caused by the destruction of the physical network, has a relaxation nature. It is determined by the specific intermolecular interaction of the end groups of dendrimers and depends on their mobility. The presence of short siloxane substituents leads to the appearance of highly elastic properties above the glass transition region, while the introduction of less flexible carbosilane and butyl substituents promotes typical “polymeric” properties. Thus, by forming one or another type of the surface layer of the molecular structure of the initial dendrimers, one can control their viscoelastic properties over a wide range.

CHAPTER 4. METHODS FOR INVESTIGATION OF PHYSICOCHEMICAL AND MECHANICAL PROPERTIES

POLYMER MATERIALS

The chemical structure of polymers, i.e. its chemical composition and the method of connecting atoms in a macromolecule does not unambiguously determine the behavior of a polymer material. The properties of polymers depend not only on the chemical, but also on their physical (supramolecular) structure. Structural processes are studied using methods that are based on measuring the dependence of any indicator of the physical properties of a polymer material on its structure. These include: thermal analysis methods (measurement of heat capacity, transition temperatures, differential thermal analysis), probe methods (thermodynamic parameters of the interaction of organic substances with polymers: solubility coefficients, sorption enthalpies, partial molar enthalpies of mixing, solubility parameter, determination of the free volume in polymers etc.), mechanical (measurement of strength, deformation and relaxation properties), electrical (dielectric permittivity, dielectric losses) and dilatometric methods. Let's take a look at some of these methods.

4.1. Methods for thermal analysis of polymers

Thermal analysis methods include methods by which it is possible to evaluate the properties of polymers during temperature changes (cooling or heating). The most common are differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA).

Differential scanning calorimetry. This method is based on measuring the difference in heat flows from the test sample and the reference sample, which are formed as a result of changes in the physical or chemical properties of the material under study. The information obtained makes it possible to determine the nature of the ongoing processes and characterize the properties of the polymer material. The difference in heat flows arises due to such thermal effects as melting, crystallization, chemical reactions, polymorphic transformations, evaporation, etc. As a result, it is possible to determine the specific heat and changes in heat capacity, for example, during the glass transition of a polymer.

Thermogravimetric analysis. This is a method based on the constant weighing of the sample as a function of temperature at a constant heating rate as a function of time. It allows, using small amounts of a substance, to obtain information on the kinetics and mechanism of polymer degradation, its thermal stability, solid-phase reactions, as well as to determine moisture, the content of residual materials in the polymer (monomer, solvent, filler), to study sorption processes and the composition of composite polymer materials. If an IR-Fourier or mass spectrometer is connected to the TGA analyzer, then the analysis of the released gases will provide complete information about the mechanism of complex thermochemical processes that occur in the polymer with increasing temperature.

Dynamic mechanical analysis is used to study the dependence of mechanical and viscoelastic properties (shear, tension, compression, three-point and cantilever bending) of polymeric materials on temperature, time and frequency under periodic loads. This method of analysis will be discussed in detail in Section 4.3.

At present, the modernization of thermal analysis methods has led to the emergence modular systems with unique technical specifications combining DMA, DSC and TGA methods. This allows you to simultaneously determine various characteristics polymer material in a wide range of frequencies and temperatures, which makes it possible to obtain information not only about the mechanical properties (determining the scope of the polymer), but also about the molecular rearrangements occurring in the material and the resulting structures. It is this that opens up new opportunities for optimizing the choice of polymeric material and the processing process, quality control, analysis of polymer degradation, studying polymer crosslinking reactions, gelation, etc.

– – –

The gas permeability of polymers, as well as other properties, is determined by factors such as chain flexibility; intermolecular interaction; phase and physical state of the polymer; packing density of macromolecules; degree of crosslinking. Of decisive importance for diffusion permeability, which is mainly due to sorption and diffusion, is the flexibility of the polymer chain and interchain interaction.

Sorption of gases by polymers. Gases can be adsorbed on the outer and internal surfaces polymers or dissolve in micropores that appear between their macromolecules. The total amount of absorbed or sorbed gas can be measured, for example, using a McBain balance (sensitive spiral balance), and the concentration c of the gas in the polymer can be calculated. It is the greater, the greater the partial pressure p of the gas in the environment: with p, where the proportionality coefficient is called the sorption coefficient (the volume of gas absorbed by a unit volume of the polymer at a partial pressure equal to one and the temperature of the experiment). The sorption coefficient is expressed in cm3/(cm3kgf/cm2). During the sorption of gases and vapors, they can condense in the polymer; change its phase state, turning into a liquid. In some cases, the sorbed substance can form aggregates or associates in the polymer.

For an elastic non-porous polymer, in which only the process of gas dissolution occurs (gas fills the free volume, which has a fluctuation character, as a result of which, during sorption, gas molecules can exchange places with polymer units), this coefficient is called the gas solubility coefficient, which depends on the partial pressure gas and temperature.

The process of sorption of non-inert vapors by polymers is considered as a process of mutual dissolution of components, which occurs according to different mechanisms depending on temperature:

T Ts. The sorbent polymer is in the highly elastic 1.

a state characterized by chain flexibility and possible permutations of sorbate molecules and units or segments of the polymer chain even at very low pressures. The type of sorption isotherms will depend on the thermodynamic affinity of the sorbate for the polymer and the flexibility of the polymer chain. The lower the affinity, the lower the sorption.

T Ts. Due to the lack of segmental movement, the exchange between 2.

vapor molecules and polymer chain links is difficult. In this case, vapor molecules can only penetrate into the microvoids present in the polymer, which are small in close-packed polymers.

The amount of sorbed substance in this case is small, which is beyond the sensitivity of the sorption method.

Therefore, sorption processes are most noticeable when the system is in a highly elastic state, i.e. exchange between sorbate molecules and chain links is possible, as a result of which, at first, swelling of the polymer occurs, which can then turn into its dissolution in sorbate vapor.

4.2.1. Reversed gas chromatography

To study the thermodynamics of the sorption of gases and vapors in polymers and determine their physicochemical parameters, the method of inverted gas chromatography (WGC) is used. To do this, the polymer is applied to the surface of a porous solid carrier, and the sorbate is introduced into the carrier gas flow. The WRC method is very informative for studying the thermodynamics of sorption in polymers, which also makes it possible to estimate the value of the free volume.

Theoretical foundations of the WRC method. In the WRC method, the retention time of the sorbed tr and nonsorbed ta components is measured. The value of ta, which actually corresponds to almost no sorbed component (usually air), is necessary to take into account the “dead” volume of the chromatograph.

Thus, one can find the net retained volume VN:

– – –

where p10 (Pa) is the saturated vapor pressure of the sorbate at the experimental temperature T; M1 (g/mol) is the molecular weight of the sorbate. The reduced activity coefficient characterizes the deviation from ideality in the polymer–vapor binary system (deviation from the Raoult law for the vapor pressure over the solution).

From the temperature dependence of the activity coefficient, one can calculate the partial molar enthalpy of mixing, which characterizes the interaction of the sorbate with the polymer:

H m R (1 T) The same value can be estimated from the temperature dependence of the solubility coefficient:

H s (7), S S0 exp RT since the sorption enthalpy can be represented as the sum of H s H c H m, where H c is the enthalpy of condensation of various sorbates.

The experiment is carried out on a gas chromatograph with a thermal conductivity detector. The temperature of the columns must be maintained with an accuracy of 0.5°C, the pressure at the chromatograph inlet is up to 0.6 kPa, which makes it possible to introduce corrections into equations (2) and (4), the outlet pressure was equal to atmospheric. Helium is used as the carrier gas; its velocity is measured using a soap-film flow meter. The air peak is used to determine ta.

The gas chromatographic experiment is started after stabilization of the temperature and pressure of the gas in the column. The temperature of the evaporator is set to 30° C. above the boiling point of the sorbate. The amount of sorbate in the sample should be sufficient to identify the peak on the chromatogram (~0.01 µl). For each sorbate at each temperature, 7-10 parallel experiments are carried out.

When studying the sorption of gases and vapors in polymers by the WRC method, it is extremely important to control whether volumetric sorption is established in the entire layer of the polymer phase in the course of a chromatographic experiment. For this purpose, in special experiments, the influence of the carrier gas velocity (it varies from 2.5 to 30 cm3/min) on the observed retention time and volume is studied. For example, when using n-octane at 45°C and n-nonane at 50°C on an LKhM-80 gas chromatograph, it was found that at a rate below 5 cm3/min, there is no noticeable effect of the carrier gas velocity, so all measurements in the work at different temperatures and with different sorbates, it was carried out at this speed. Obviously, at a higher temperature during the chromatographic experiment, a higher diffusion coefficient is realized. This is also evidenced by the linearity of the dependence of the specific retention volume on the reciprocal temperature. The thermodynamic parameters found in this way correspond to the conditions of infinite dilution during bulk sorption in the polymer.

Saturated vapor pressure of sorbates is found using the Antoine equation and (or) the equation lnPVP = AlnT + B/T + C + DT2, the parameters of which are tabulated in special databases.

If the sorbate retention diagrams, i.e. Since the dependences of the logarithm of the specific retention volume on the reciprocal temperature are linear over the entire range of temperatures studied (30–115°C), this indicates the constancy of the internal sorption energy in the studied temperature range.

As the size of the adsorbed molecule (MM sorbate) increases at a particular temperature, the specific retention volume increases. The linear nature of the dependences may be another confirmation of the fact that under the experimental conditions, volumetric sorption in the film of the polymer deposited on the carrier is completely established. Thus, the measured values of Vg can be used to calculate the thermodynamic parameters of sorption. The values of Vg according to the formula (4) calculate the coefficient of solubility of various sorbates in the polymer.

Diffusion restrictions leading to deviations from equilibrium sorption in a chromatographic experiment are the reason for the S-shaped retention diagrams.

The partial molar enthalpy of mixing, which is calculated by equation (6), passes through a minimum depending on the molecular size of the sorbate, while the coordinates of the minimum correspond to the average size of the free volume element in the glassy polymer. Those. in the process of sorption (at low concentrations of the dissolved substance), the sorbate molecules fill predominantly the vacancies present in the glassy polymer (elements of the free volume). As a result, the heat of mixing turns out to be sharply negative, since in this case the sorbate molecules do not do the work of pushing the polymer chains apart. Therefore, the WRC method is successfully used as a probe method for estimating the free volume in glassy polymers, and its results are in good agreement with the data of other probe methods, for example, with the positron annihilation method.

4.2.2. Spectroscopy of positron annihilation times

The positron annihilation method is used to obtain information about the size and size distribution of the free volume elements, their concentration, as well as the influence of such factors as temperature, pressure, mechanical deformations, and the phase composition of the polymer on the free volume.

Using this method, it is possible to follow the changes in the free volume during the physical aging of polymers, as a result of sorption and swelling, in the course of crosslinking. The parameters of the spectra of the positron annihilation times strongly depend on the structure of the polymers and are practically independent of the MM.

This method is based on measuring the lifetimes of positrons in matter. In a polymer, positrons can exist both in the free state (e+) and in the bound state. The latter is possible in the form of a hydrogen-like positronium atom, i.e. electron-positron pair (Ps or e-e+). The singlet state of this p-Ps particle has antiparallel spins and a short lifetime (0.125 ns in vacuum), while the triplet state (o-Ps) with parallel spins has a much longer lifetime (142 ns in vacuum). It is believed that the long-lived o-Ps particle enters the region with a low electron density, i.e. in the ESO. As a result of the overlapping of the wave functions of o-Ps and the electrons of the atomic orbitals that form the walls of the POE, the lifetimes of o-Ps are greatly shortened compared to vacuum annihilation and usually range from 1.5 to 4.0 ns. The observed lifetimes strongly depend on the size of the POE: the larger the POE, the longer the lifetime of the positron in the polymer. The lifetime spectrum is a set of experimental characteristics of times i (ns) and corresponding statistical weights or intensity I i (%). It is assumed that the intensity of the positronium component depends on the POE concentration.

The source of positrons is usually the 22Na isotope (half-life

2.6 years). The resulting positrons have an energy of 0-0.5 MeV with a distribution maximum of 0.2 MeV and a path length of 1 mm in conventional polymers. In matter, positrons rapidly thermalize, and all subsequent processes proceed with the participation of particles with thermal energies.

The experimental setup for measuring positron annihilation times is shown in Fig.1. It consists of a source of positrons placed between two samples of the polymer under study. The lifetimes are measured by an electronic system operating on the principle of converting time intervals into the amplitude of electrical impulses. The scheme registers the time between two events: the appearance of primary quanta from the source, and quanta accompanying the annihilation of positrons. After registering 105-107 such events (i.e. registered by a photomultiplier

Quanta) build an experimental positron lifetime distribution curve y(t), showing the number of events y depending on the measured time t.

– – –

Large sizes of free volume elements were found in polymeric sorbents and organic clusters. Using this method, it was found that in hypercrosslinked polystyrene sorbents there are cavities with a pore radius of 14 Å, which account for about 20% of the total number of free volume elements in the material.

Thus, the positron annihilation method gives a microscopic description of the free volume in terms of the average POE radii and the corresponding volumes f. To relate these values to the macroscopic parameters of polymers, it is necessary to know the average concentrations of free volume elements N (cm-3), after which it is possible to estimate the free volume fraction as a product of fN.

The traditional method of positron annihilation is aimed at studying the free volume inside the polymer matrix. However, there are many objects for which the surface properties of polymers (membrane), coatings on the surface of various materials, etc. are important rather than volumetric ones. Such properties of polymer layers as glass transition temperature, density, chain mobility, and others can differ greatly inside the polymer matrix and at the interface.

The positrons with an average energy of 200 keV used in the traditional technique have a stopping distance of 1 mm. This value is many orders of magnitude larger than the characteristic thickness of the surface layers; therefore, the positron lifetimes in such experiments carry information about the free volume in the matrix. To study the free volume in the near-surface layer, it is necessary that the energy of the positron beam be significantly lower than the indicated value (positrons should not penetrate deep into the sample volume and annihilate in the near-surface layers). For this, low-energy monochromatic positron beams with a much lower (0.2-20 keV) controlled positron energy are used, which makes it possible to probe the free volume in thin polymer layers (several nanometers) and construct a free volume profile in them.

The methods listed above for studying the free volume in polymers are probe methods; are based on the fact that certain probe molecules are introduced into the polymer and its behavior is monitored, on the basis of which conclusions are drawn about the structure of the free volume. These methods differ in the nature and size of the chosen probes. Thus, in the method of positron annihilation for the study of polymers, the probe is an electron-positron pair - a positronium atom. In reversed gas chromatography, rows of structurally related compounds act as probes. The 129Xe NMR method, in which a single probe, the 129Xe atom, “examines” the free volume in different polymers, has also found wide application.

In addition to experimental methods for studying the free volume in polymers, methods of computer simulation of the nanostructure of polymers have become increasingly important in recent years in order to predict the properties of a polymer material (diffusion coefficients, solubility, etc.). When analyzing computer simulation data, the results of probe methods are used to confirm the reliability of calculations.

At the same time, computer simulation opens up new additional possibilities for studying the free volume in polymers, which are basically inaccessible to probe methods for studying it:

visualization of free volume; free volume connectivity analysis (cluster size, closed or open porosity); building a size distribution of POEs; study of mobility (dynamics) of free volume elements in polymers.

At present, Monte Carlo methods, molecular mechanics, as well as the transition state theory and related approaches are widely used to model free volume.

Knowledge of a number of thermodynamic parameters and other physicochemical quantities obtained by probe methods for polymers is necessary to determine the potential area of their practical application. For example, perfluorinated polymers have high gas permeability and a large free volume, increased chemical resistance (the ability to separate aggressive media), and high thermal stability. To date, fluorinated polymers Hyflon (a random copolymer of 2,2,4-trifluoro-5-trifluoromethoxy-1,3-dioxalane and tetrafluoroethylene) and Cytop have already found application in materials science, the structure of which is presented in Table 1.

Table 1. Structure of some amorphous perfluorinated polymers

– – –

These perfluorinated polymers are characterized by reduced gaseous hydrocarbon solubility, are insoluble in common organic solvents, and do not swell or break down on contact with petroleum products. These properties can be important when using these polymers as a material for gas separation membranes: the low solubility of common organic compounds in perfluorinated polymers is manifested in a reduced ability to plasticize, and it is this phenomenon that causes a significant deterioration in the selectivity of gas separation and pervaporation membranes.

The nature of the large free volume in amorphous perfluorinated polymers is related to the high rigidity of the chains in these polymers, which hinders their close packing of chains under the condition of weak interchain interactions.

Even now, there are data in the literature on the effectiveness of membranes based on amorphous AF 2400 Teflon for organoselective pervaporation (separation of mixtures of chlorine derivatives of methane and purification of wastewater containing them). The objects of such division are the field of petrochemistry and chemistry of heavy organic synthesis. However, the use of pervaporation to separate numerous azeotropic mixtures is limited by the solubility of existing pervaporation membranes in organic mixtures to be separated and by low permeability.

A significant problem is the very limited range of available perfluorinated polymers as membrane materials.

– – –

where Mt is the amount of sorbed or desorbed substance by the time t; M is the equilibrium amount of the sorbed substance.

Based on the data obtained, a graph of the dependence M t / M = f (t1/2) is built. For systems obeying Fick's second law ("Fick systems"), this graph has the form of an L-shaped curve with an initial straight section in the region of M t / M, 0.6 (Fig. 4, curve 1).

An L-shaped dependence is observed when D is a function of concentration only and does not depend on time. In many cases, anomalous “non-Fickian” diffusion is observed, which manifests itself in a different character of the dependence М t / М = f(t1/2), which has the form of S-shaped or two-step curves (Fig. 4, curve 3). Deviations from Fick's second law are usually associated with a change in the conformation of macromolecules, as well as with displacements of the structural elements of the polymer resulting from the interaction of its macromolecules with the molecules of the diffusing gas. Both of these processes have a relaxation character. If the relaxation time is short, which is observed for polymers in the elastic state, then conformational and structural changes occur fairly quickly. In this case, D depends only on the speed of movement of gas molecules. At T Tc, the mobility of the segments is low, and the rate of conformational and structural transformations may be lower than the rate of gas diffusion. The net carryover effect is determined by the rate of the first processes, and D is a function of time.

– – –

Dynamic Mechanical Analysis (DMA). This method of analysis is used to study the dependence of mechanical and viscoelastic properties of materials on temperature. As a result of the research, it is possible to determine the Young's modulus and shear modulus, data on the structure and morphology of polymers, relaxation characteristics and viscoelastic properties, material defects, and also analyze the destruction of polymers. The use of the DMA method has now greatly helped to optimize and maximize the efficiency of the polymer processing process due to the correlation between technological conditions and the molecular structure of the polymer.

This method is a sensitive method for determining the mechanical response of a polymer material by monitoring the change in properties as a function of temperature and the frequency of an applied sinusoidal voltage.

The uniqueness of modern equipment is:

In simultaneous measurement of load and displacement, which allows obtaining very accurate values of the modulus of elasticity;

Measurement capabilities in a wide range of load amplitudes (from 1 mN to 40 N), which allows you to study both soft and hard materials and in a wide range of loading frequencies (from 0.001 Hz to 1000 Hz).

In this method, a force is applied to the sample and the amplitude and phase of the resulting displacement are measured. The DMA uses a linear actuator in which the force (voltage) applied to the sample is calculated from the signal applied to the motor's electromagnetic coils. A sinusoidal voltage that is applied to the sample creates a sinusoidal strain or displacement. This applied stress (force) is chosen so small as not to change the analyzed material. By measuring both the strain amplitude at the peak of the sine wave and the phase difference between the stress and strain sine waves, quantities such as modulus, viscosity, and damping can be calculated. When the response of the material to the applied vibrations is perfectly elastic, the input signal is in phase with the output, then a phase delay = 0? is observed, if the viscous response gives a phase divergence, then = 90?. Viscoelastic materials fall between these two extremes, i.e. 0? 90?.

This method separates the dynamic response of materials into two different parts - the elastic part D" and the viscous component D"".

The complex modulus D* is defined as the instantaneous ratio of the phase or elastic response D" (which is proportional to the recoverable or stored energy) to the viscous response D"" (which is proportional to the unrecoverable or dissipated energy) D* = D" + iD"".

Force and Displacement Sensor

– – –

The mechanical loss tangent tg is another important parameter for comparing the viscoelastic properties of different materials: tg = D""/D", where tg (damping factor) is the ratio of dissipated and stored energy. The presence of a maximum in the temperature dependence of tg is a sign of a relaxation transition, and also phase transformations.This is due to the fact that in the processes of phase and relaxation transitions from one state to another, the structure is rearranged, at which the losses typical of both states are summed.The dynamic method is very convenient for assessing the process of structuring and vulcanization of polymers, which corresponds to the expansion of the zone high elasticity and reduced losses in the low frequency region.

This method has gained great popularity due to its speed and high accuracy, as well as the ability to scan materials in a wide range of temperatures and frequencies.

In addition, this method is currently used as an alternative approach to the study of branched polymers in viscous flow in combination with rheometric measurements, which can measure the creep of a polymer material. This is due to the limitations of standard methods in relation to polymers of complex architecture, since their relaxation properties are due not to intermolecular interactions such as entanglements (as in the case of linear polymers), but to intramolecular rearrangements, i.e. are directly related to their topological structure. Thus, a group of researchers (Vrana K. et al.), using the example of branched copolymers based on ethylene, propylene, and vinyl norbornene, showed that by combining the two methods listed with the help of special diagrams (Van Gurp-Palmen diagram), it is possible to trace not only the influence of the chain structure on the fluidity of polymers, but also to determine the degree of their branching.

On fig. Figure 6 shows the dependences of the shear modulus of copolymers obtained on the basis of tris-(pentafluorophenyl)germane and bispentafluorophenyl)germane of various degrees of branching. The most characteristic is the increase in the value of the modulus with temperature, which may be associated with an increase in the interaction of macromolecules due to the interpenetration of fragments of the outer sphere. Apparently, the unfreezing of the conformational mobility of this sphere is responsible for the high-temperature relaxation transition, which can be taken as the glass transition temperature. It can be seen from the figure that Тс of the copolymers increases to 252С (maximums on the curves) as the content of bispentafluorophenyl)germane increases to 50.7%. For branched perfluorinated polyphenylenegermane, a polymer obtained from tris-(pentafluorophenyl)germane by activated polycondensation Tc=163C. The effect of an increase in Tc may be due to inter- and intramolecular cross-linking of dendrons, and, as a consequence, limitation of rotation around the Ge-C bonds.

– – –

TS Strength characteristics of polymers. The widespread use of polymeric materials is also determined by their valuable mechanical properties and high strength, combined with the ability to large reversible deformations. The creation of new polymeric materials with predetermined functional properties is one of the main problems of modern polymer science. The fulfillment of this task requires knowledge of the fundamental laws that relate the physicochemical properties of polymeric materials with their molecular structure, as well as the development of methods for controlling the properties of composite systems on this basis. It is well known that blending of polymers makes it possible to create materials whose characteristics are intermediate between those of the original components. Composite materials are an example of such miscible polymer systems.

Consider wood-polymer compositions (WPC), which have recently found wide application in construction as a decking (terrace board). The market demand for WPC is due to some of the disadvantages of natural wood, such as high water absorption, high microbial degradation and low durability. In this connection, WPC has already found application not only for the manufacture of terrace boards, but also for the manufacture of foundations, plank sidewalks, siding, pallets, and roofing tiles. In addition, automotive products are made from composite materials with long-fiber cellulose ( internal panels, spare tires, etc.). WPC can be made from any type of thermoplastic polymers in combination with fillers (cellulose fiber) and other components.

Wood-polymer composites are made from a polymer filled with cellulose fiber and other components by extrusion or molding. The main requirement for the polymer is thermoplastics, with a processing temperature below 200C, which is due to the low heat resistance of wood. An important criterion in the production of WPC is the melt flow characteristics, which is associated with processing modes during production and can lead to defects on the surface of extruded profiles, surface roughness. Such problems may arise from poor formulation flow at given processing temperatures and may be identified in advance by taking into account the rheology of the filled composition or the polymer itself at the selection stage. That.

a decisive role in the creation of WPC formulations is played by the rheological features of selected thermoplastic polymers (shear rate, shear stress, dynamic viscosity, limiting viscosity).

The most studied thermoplastics are polyethylene, polypropylene, polyvinyl chloride, copolymers of styrene with acrylonitrile and butadiene, polyamide, etc. The use of compositions with polyvinyl alcohol and polyacrylate has led to the creation of biodegradable WPC. To improve the compatibility of polymers and fillers in the production of WPC, binders are used that can chemically bond with cellulose fiber and (or) copolymers, which contributes to the formation of a homogeneous system.

The mechanical properties of WPC are largely determined by the nature of the filler and polymer.

Consider the main mechanical characteristics related to the scope of the WPC:

Flexural strength, which determines the breaking load (ultimate load), up to which the given composition can be operated;

Modulus of elasticity and flexural deflection. This characteristic is closely related to the breaking load, and its value is determined by the requirements of building codes. Deflection under a uniformly distributed load is determined by the load, the width of the board, the flexural modulus, the moment of inertia (a measure of the board's strength and stiffness, or stiffness factor), and the span between the supports.

In addition to the listed mechanical properties, thermal expansion-contraction, shrinkage, slip resistance, water absorption, microbial degradation, combustibility, oxidation and fading are important criteria.

Calcium carbonate, silica, talc are used as mineral fillers, which increase the stiffness of the filled product and give the polymer a higher fire resistance, in addition, their introduction usually improves both the flexural strength (usually by 10-20%) and the flexural modulus (200-400%) filled with WPC. The use of cellulose as a filler in thermoplastic compositions was previously difficult (1970s) because it is poorly distributed in polymer formulations during molding and compounding. In this connection, a number of researchers have obtained a composite material, including thermoplastic PVC and cellulose fiber in the form of wood pulp or cotton fluff (US Patent No. 3 943 079). This problem has also been solved by using cellulose fibers derived from materials such as sawdust, flax, straw and wheat, and a binder mixed with a filler (US Patent No. 6 939496). A patent search has shown that in order to improve the mechanical properties of WPC, during production, moisture is removed from cellulose fibers (wood pulp, paper waste, etc.) before they are mixed with thermoplastic polymers (polypropylene, polyethylene, polyvinyl chloride, etc.), which results in molded products without cavities and bubbles, and improves physical properties molded products (US Patent No. 4,687,793).

4.4. Electrical Methods

The method is based on studies of the temperature-frequency dependence of the dielectric loss tangent (tg) and dielectric permittivity (). The permittivity is determined by the ratio of the capacitance of an electric capacitor filled with this substance to the capacitance of the same capacitor in vacuum at a certain frequency of the external field. This value is related to polarization, i.e. with the appearance of a certain electric moment in a unit volume of the dielectric when it is introduced into electric field. Part of the energy of the electric field, which is irreversibly dissipated in the dielectric in the form of heat (energy dissipation) is called dielectric losses. The angle, which is determined by the phase shift between the vectors of the electric field applied to the dielectric and the polarization arising under the action of this field, is called the dielectric loss angle -, and its tangent is the dielectric loss tangent.

Because the dielectric properties of polymers depend on the chemical structure and structure of the repeating unit, the structure of macrochains and the way they are stacked, this method is used to study the molecular structure and thermal motion in polymers.

A feature of polymers is the independent movement of chain segments consisting of a large number of segments. In addition to the movement of segments in the polymer, the movement of smaller and more mobile kinetic units (side chains, for example, polar substituents) is possible. The relaxation time of the orientational moment of such groups is shorter than the relaxation time of the main chain segments; therefore, they can retain mobility at lower temperatures, at which the segments no longer exhibit it. If a polymer containing polar groups is placed in an electric field, at certain ratios of relaxation times and field frequency, the orientation of segments and smaller kinetic units will occur, which causes some values of the permittivity and dielectric losses. In this case, not only the polarity of the groups in the polymer is important, but also the way they enter the monomer unit.

Those. the chemical structure of the repeating unit has a significant effect on intra- and intermolecular interactions, i.e. on the mobility of the links and the relaxation time. The stronger the intra- and intermolecular interactions, the more mobile the units, the higher the temperature at which the maximum tg is observed, and the longer the relaxation time.

Dielectric properties are also affected by:

Repeating unit isomerism (for example, the method of adding ethereal oxygen in polymethyl methacrylate and polyvinyl acetate);

the presence in the macromolecule of sites of syndiotactic or isotactic structure. Their length and quantitative ratio significantly affect the mobility of segments and groups, and, consequently, the dielectric characteristics of polymers.

In addition to the above factors, the dielectric properties are also affected by the orientational stretching of macromolecules. Polymer stretching can lead to both an increase and a decrease in the relaxation time of dielectric losses associated with orientational rotations of the polar units of the macromolecule under conditions where segmental motion (highly elastic state) is possible, depending on whether the packing of macromolecules is compacted or loosened during stretching.

CHAPTER 5. PROPERTIES OF POLYMERS IN LANGMUIR MONOLAYERS AND THIN FILMS

Some characteristics of polymer films and monolayers (surface tension, contact angle, surface topography, self-organization at the water-air interface) are important parameters, for example, for controlling the cleaning processes of surfaces contaminated with oil products, when studying the properties of biomaterials (lenses, implants) and pharmaceutical preparations (powders, tablets, capsules).

5.1. Study of the colloid-chemical properties of amphiphilic macromolecules in monolayers and Langmuir-Blodgett films At present, in the development of polymer chemistry, much attention is paid to the study of amphiphilic polymers, which have blocks of various nature in their composition. The appearance of new interesting properties in them is associated with the ability of macromolecules to self-organize in solution and in bulk. The decisive role in self-organization in thin films is played by the incompatibility of covalently bonded blocks. The main factors that will determine the surface morphology of the copolymer films are the ratio of the lengths of different blocks and the nature of the interaction between them. Such block copolymers are predominantly characterized by structures such as spheres, cylinders, and lamellae. In addition, hydrophobic and hydrophilic groups in the macromolecules of block copolymers impart amphiphilic properties to the molecule, which is necessary condition for the formation of stable monomolecular films at the interface.

Moreover, the nature of the processes occurring during the formation of films at the water-air phase boundary primarily depends on the hydrophilic-hydrophobic balance in block copolymer molecules.

Significant advances in the field of molecular architecture achieved in the last two decades are largely due to the use of such a method for obtaining films of amphiphilic compounds as the Langmuir-Blodgett method. This method is a convenient and efficient way to disperse a substance to the molecular level, study surface properties, and form ultrathin mono- and multimolecular films, including analogues of lipid membranes. In addition, the Langmuir-Blodgett technology makes it quite easy to change surface properties and form high-quality film coatings due to precise control of the film thickness (number of applied layers) in the process of isolation, coating uniformity, low roughness, and high (if appropriate conditions are selected) adhesion of the film to the surface. . The properties of the films can also be easily varied by changing the structure of the polar block of the amphiphilic macromolecule, the composition of the monolayer (two- and multicomponent mixtures of molecules), as well as the isolation conditions (composition of the subphase and surface pressure). Those. By controlling the size and shape of macromolecules, it is possible to impart completely new functional qualities to materials, which differ sharply from those of ordinary polymers.

Surface pressure isotherms and monolayer transfer. The formation of an ordered monolayer on the subphase surface proceeds as follows. A certain volume of a solution of the test substance in a highly volatile solvent is applied to the surface of the subphase. After evaporation of the solvent, a monomolecular film is formed on the water surface, the molecules in which are arranged randomly. At a constant temperature T, the state of the monolayer is described by the compression isotherm -A, which reflects the relationship between the surface pressure of the barrier and the specific molecular area A (Fig. 1, a).

b a Fig. Fig. 1. Langmuir isotherm (a) and the behavior of macromolecules at the water-air interface (b) Using a movable barrier, the monolayer is compressed to obtain a continuous film with dense packing of molecules, in which the specific molecular area A is approximately equal to the area cross section molecules, and hydrocarbon radicals are oriented almost vertically (Fig.

1b). The linear segments on the dependence -A, corresponding to the compression of the monolayer in different phase states, are characterized by the value A0 - the area per molecule in the monolayer, obtained by extrapolating the linear segment to the A axis (= 0 mN/m). The phase state of an amphiphilic substance monolayer localized at the “subphase-gas” interface is determined by the adhesive-cohesive balance of forces in the “subphase-monolayer” system and depends on the nature of the substance and the structure of its molecules, temperature T, and subphase composition. Gaseous G, liquid L1, liquid-crystalline L2 and solid-crystalline S monolayers are isolated (Fig. 1, b).

Using a Brewster microscope, which is a video camera with a laser drive, one can observe in real time Langmuir films at the water-air interface or on a dielectric substrate.

The formed monolayer, consisting of close-packed molecules, is transferred to a solid substrate moving up and down through the water surface. Depending on Fig. 2. A microscope for observing the type of substrate surface with the Brewster angle for the state of the monolayer (hydrophilic or hydrophobic) and the sequence of crossing the substrate surface of the subphase with a monolayer and without a monolayer, it is possible to obtain Legnmuir-Blodgett (PLB) films symmetric (Y) or asymmetric (X, Z ) structures (Fig. 3).

The Langmuir-Blodgett technology for producing thin films, which can be used to easily control the size and shape of macroobjects, has recently been actively developed, since it can be used to impart new functional properties to polymeric materials.

The main problem in the creation of nanostructured polymer films is related to the selection of optimal conditions for the formation of films, which to a certain extent depend on the molecular weight of the hydrophilic and hydrophobic blocks, on the degree of branching of the dendritic fragment in hybrid block copolymers, and on the nature of the linear block. The PLB is a multilayer, a fundamentally new object of modern physics, and therefore any of its properties (optical, electrical, acoustic, etc.) are completely unusual. Even the simplest structures composed of identical monolayers have a number of unique features, not to mention specially constructed molecular ensembles.

The value of the surface pressure at which the monolayer is transferred to the substrate is determined from the compression isotherm of the given amphiphilic copolymer and corresponds to the state with close packing of molecules in the monolayer. During the transfer, the pressure p is kept constant by reducing the area of the monolayer by moving barriers.

The criterion for the degree of coverage of the substrate with a monolayer is the transfer coefficient k, which is determined by the formula:

– – –

To obtain a Langmuir-Blodgett film uniform in thickness, the substrate surface must have a roughness Rz of 50 nm. From the surface pressure isotherms, one can extract information both about the universal effects of intermolecular interaction in a monolayer and about the specific behavior of a complex amphiphilic molecule with a change in surface pressure (its reorientation, conformational rearrangements, etc.). As a rule, the destruction of a monolayer of such molecules occurs at high surface pressures (up to 30 mN/m). The low values of the surface pressure may be associated with the association of amphiphilic molecules with each other (the formation of dimers, trimers, etc.), which leads to a decrease in the number of particles forming a two-dimensional gas, with the formation of macroscopic islands of the solid phase at low pressures. In addition, when interpreting the obtained -A isotherms, it is necessary to take into account steric repulsions and dispersive attraction between hydrocarbon chains, as well as Coulomb and dipole-dipole interaction forces between polar groups. It should also be remembered that amphiphilic molecules can interact strongly with water, forming hydrogen bonds.

Consider the surface pressure isotherm of the block copolymer poly-(N-vinylpyrrolidone-2,2,3,3-tetrafluoropropyl methacrylate) (Fig. 4). The section of the obtained isotherm, at a pressure close to zero, corresponds to the region of a two-dimensional gas, in which the block copolymer molecules lie on the interface and do not contact each other. With further compression of the film, the molecules begin to contact in the region of a two-dimensional liquid, and the first increase in surface pressure is observed, with a sufficiently large decrease in the area of the film.

– – –

Rice. Fig. 4. Surface pressure isotherm of the amphiphilic block copolymer poly-(Nvinylpyrrolidone-2,2,3,3-tetrafluoropropyl methacrylate), Mw = 1.7410-5, nitrogen content in the block copolymer (Kjeldahl analysis) = 12 wt.%, planting volume = 120 µl In the region of the phase transition on the isotherm at almost constant pressure, there is a linear section (plateau), where the macromolecules begin to rearrange and change shape: the hydrophilic groups are immersed in water, while the hydrophobic ones remain on the surface and line up perpendicular to the phase boundary. With further barrier compression, a second, sharp increase in surface pressure occurs with a small decrease in the film area, which gives grounds to speak of the formation of a “two-dimensional solid body” and the end of the rearrangement of surface groups.

In this region of the isotherm, the film is in the maximum compressed state, and its further compression leads to the destruction of the monolayer.

In some cases, the non-horizontal “plateau” region can be observed on the surface pressure isotherms, which is apparently associated with the escape of molecules from the surface into the volume of the aqueous phase. In addition, the discrepancy between the compression and expansion isotherms indicates some aggregation of blocks of macromolecules during compression.

5.2. Surface properties of films

The phenomena observed on the surface of solids are determined by the physicochemical interactions of the phases at the interface. Recently, the most common method for studying surface properties is wetting, in which the intensity of these interactions is characterized, first of all, by the value of the contact angle between the surfaces of a liquid and a solid at the boundary with the environment.

Depending on the number of phases involved in wetting, two main cases are distinguished. Wetting when a solid is completely immersed in a liquid (immersion wetting), in which only two phases, a liquid and a solid, are involved, and contact wetting, in which, along with a liquid, a third phase, a gas or other liquid, contacts the solid. In the first case, the intensity of interactions on the surface of solids is characterized by the heat of wetting. In the second - the value of the contact angle (the angle between the surfaces of liquids and solids at the boundary with the environment).

The main characteristic of the state of the surface of solids is surface tension, which characterizes the uncompensated intermolecular interaction at the interface and causes an excess of surface energy. It is defined as the work of a reversible isothermal process of formation of a unit area of the phase separation surface, provided that the thermodynamic parameters of the state of the system (temperature, pressure, chemical potentials of the components) do not change.

According to the Fawkes approach, the value of surface tension consists of 3 components: polar (induction) (p), dispersion (d) and orientational (0). d - effective surface tension due to intermolecular interaction of a liquid with a solid surface, p - surface tension due to inductive (polar) interaction at the liquid-solid interface.

The orientation component is small and is usually not considered.

The dispersion and polar components of surface tension can be determined by the Zisman method, according to which the contributions p T - G and d T - G are determined by the change in 0 in the system solid - water (l1) - hydrocarbon (l2).

For this system, Young's equation will have the following form:

Т-Ж1= Т-Ж2 +Ж1-Ж2 cos 0, (2) where - Т-Ж1, Т-Ж2 andЖ1-Ж2 - surface tensions at the phase boundaries:

solid - liquid 1, solid - liquid 2, liquid 1 - liquid 2, respectively. Then the Fawkes equations will be written in the form:

T-F2= T-G + F2-G - 2(dT-G x dF2-G)1/2 - 2(RT-G x RJ2-G)1/2, (3) T-F1= T-G + Zh1-G - 2(dT-G x dZh1-G)1/2 - 2(RT-G x RZh1-G)1/2, (4) where Т-Ж1, Т-Ж2, Zh1-Ж2 are surface tensions at the boundaries: solid - water, solid - hydrocarbon, water - hydrocarbon;

Zh1-G, dZh1-G, RZh1-G, Zh2-G, dZh2-G, RZh2-G, T-G, dT-G, RT-G - surface tensions and their dispersion and polar components of pure substances at the boundary with air .

Subtracting equations (3) - (4) taking into account the fact that for hydrocarbons Р

L2-G= 0 (L2-G = dЖ2-G) we get:

S-Zh2- S-Zh1=Zh2-G -Zh1-G +2(dT-G)1/2 [(dZh1-G)1/2 –(Zh2-G)1/2] +2(RT-G x РЖ1-Г)1/2, (5) taking into account Young's equation (2), we finally obtain:

Zh1-G - Zh2-G + Zh1-Zh2cos0 = 2(dТ-Г)1/2 [(dЖ1-Г)1/2 – (Ж2-Г)1/2] + +2(RT-G x РЖ1- G)1/2, (6) where the values of Zh1-G, Zh2-G, Zh1-G2, dZh1-G, Zh2-G, RZh1-G are reference values.

The dependence in coordinates: (Ж1 -Ж2 +Ж1-Ж2cos) on 2 [(dЖ1-Г)1/2Ж2-Г)1/2] is described by a straight line equation of the type y = x tg + b (Fig. 5.).

– – –

It should be noted that this approach is valid only when water displaces the hydrocarbon on the surface of the solid, i.e., the following inequality is satisfied:

T-W1 - T-W2 - W1-W2 0 (10).

As an example, tables 1 and 2 show the data of the wetting method and calculations of the surface tension and its constituents by the Zismann method for films of a PMMA-PFG block copolymer obtained from various solvents (chloroform, THF).

Table 1. Average values of contact angles for films of PMMA-PFG block copolymers (chloroform film).

– – –

1.5 -1.0 -0.5 0.0 0.5 1.0 2. Determination of the polar and dispersion components for PMMA-20% PFG copolymer films, solvent chloroform (1), THF (2).

Table 2. Energy characteristics of the surface of the studied films of the PMMA-PFG block copolymer (20 wt.

% PFG) formed from chloroform and THF.

– – –

For polymer films, when both dispersion and polar interactions are possible, the most reliable results in estimating the free surface energy of a polymer film are given by the Owens-Wandt equation, which relates the experimentally determined wetting angle and the energy characteristics of a liquid and a solid as follows:

(1 cos()) lv (sd)1 2 (sp)1 2 (lp)1 2 (ld)1 2 (11), 2(ld)1 2 with saturated steam, and ld, lp and sd, sp are the dispersion and polar components of the free energies of the liquid and solid polymer. The total free surface energy of a solid body s is defined as the sum of the dispersion and polar components:

This method uses test liquids of various nature, such as water, glycerin, dimethyl sulfoxide, hexane, dodecane.

This method is widely used for films of fluorinated polymers, and for block copolymers based on them, with a predominant content of a hydrophobic block, where dispersion forces mainly predominate due to the formation of hydrogen bonds and dipole-dipole interactions.

Currently, there are fully automated and computer-controlled devices (for example, an optical tensiometer, Fig. 3), which greatly simplify the work of researchers. They can simultaneously determine a number of parameters, such as contact angles, surface and interfacial tension, free surface energy, film surface porosity, and interfacial rheology.

Rice. 3. Optical tensiometer

Recently, the attention of researchers has been directed to obtaining structured surfaces with a given two-dimensional organization on the nano- or microscale. Such surfaces, which have interesting physical and biological properties, can be used as platforms for assembling more complex functional nanostructures and nanodevices. In this connection, at present, there are many methods for the formation of nanostructured surfaces, for example, the Langmuir-Blodgett method, obtaining nanoparticles modified by organic molecules from their colloidal solutions by precipitation, as well as an approach based on controlled interaction (self-organization) of molecules and/or nanoparticles , acting as "building blocks", such surfaces can serve in the future to create more complex structures. In all cases, an indispensable method for studying the nature of the film surface is atomic force microscopy.

5.3. Atomic force microscopy (AFM)

The AFM method makes it possible to obtain unique information about the surface structure and to determine the deformation-strength and relaxation properties of individual macromolecules. In addition, this method can be used to measure the energy of a specific interaction between various functional groups of organic and biological macromolecules. In recent years, there has been a tendency to use in situ AFM in studies of the melting of crystalline and liquid crystal phases.

As an example, in fig. 4 shows the topography of the film surface of a mechanical mixture of polymethyl methacrylate and perfluorinated polyphenylene german (60%-40%). It can be seen from the figure that the reliefs of the film of the mechanical mixture and the film of the linear-denrite block copolymer, which is characterized by a uniform heterogeneous surface, are significantly different. The topography of the film of the mechanical mixture is due to the segregation of macromolecules of the branched polymer into the surface layer of the film. In the case of a block copolymer, a similar separation of the components is hindered by the chemical bonding of the blocks.

– – –

A variety of materials used in various new technologies sets the task of creating universal research methods that have a wide practical application, high resolution and at the same time allow you to reliably determine the various local properties of the objects under study, in connection with which, the hardware solution of a number of devices is currently being improved. to study surface properties, in order to expand the experimental possibilities.

CHAPTER 6. PRACTICAL WORKS

Work 1. Study of the kinetics of radical polymerization of butyl methacrylate (BMA) in the presence of small amounts of hyperbranched polymer on a thermographic unit

– – –

1 – cell body, 2 – metal sleeve, 3 – Plexiglas sleeve, 4 – resistance thermometer, 5 – strain gauge amplifier and electronic potentiometer, 6 – computer.

The change in temperature during polymerization causes a change in the resistance of the resistance thermometer of the working cell, while the resistance of the reference cell remains constant. The registering and reference resistance thermometers are connected to the arms of the bridge, the imbalance from which is fed to the TA-5 amplifier, then the signal from the amplifier is fed to the electronic potentiometer and then to the personal computer (PC).

The use of an installation of this type makes it possible to record with great accuracy minor temperature changes during the reaction of the order of 10-4 degrees per millimeter of the chart recorder scale, which makes it possible to record a polymerization rate of the order of 0.01% per minute and higher.

Preparation of cells for studying the kinetics of radical polymerization up to deep conversions Prepare monomer mixtures for 4 cells of different composition (PBMA, 1.

and its mixture with hyperbranched perfluorinated polyphenylenegermane in the amount of 0.01%, 0.05%, 1% and 5%). The volume of the monomer mixture is prepared based on the volume of the cells.

Fill the cells with monomer mixtures and degas them three times 2.

refreezing in vacuum. Solder the ampoules.

The sequence of work on the thermographic installation Turn on the thermostat, and after reaching the temperature at which 1.

polymerization is carried out, warm up the cells for 1-1.5 hours to establish a working temperature in the center of the cells.

Turn on the strain gauge TA-5 and let it warm up for 15-20 minutes.

When the unit has entered the mode (data for each of the channels is not 3.

very different), load the ampoules with monomer mixtures by inserting them into the sample holders of the working cells. A reference ampoule (PBMA) is inserted into the sample holder of the reference cell. The ampoules are placed in the appropriate cells, preheating for 3-5 minutes at the temperature of the experiment in glass beakers.

Instrument readings on the computer are recorded every 2 minutes, 4.

then every 5 minutes. The data are entered into a table (Table 1).

Table 1. Calculation data for kinetic data from thermographic curves

– – –

After that, for each of the samples, the dependence T f () is built.

– – –

Rice. Fig. 2. Dependence of the degree of transformation. Fig. 3. Dependence of the MMA conversion rate on time in the presence of various MMAs on time in the presence of various amounts of PFG. amount of PFG.

After polymerization is completed, the ampoules are removed from the thermographic unit, the polymer is purified by threefold reprecipitation with hexane from chloroform. After that, the isolated polymers are dried in a vacuum cabinet at 40C to constant weight.

Work 2. Qualitative analysis of PBMA-PFG copolymers by IR spectroscopy Theoretical part As discussed above, IR spectroscopy is not only qualitative, but also quantitative.

Thus, it can be used to determine the composition of the copolymer by first constructing the calibration dependences of the corresponding mechanical mixtures of various ratios. For example, the compositions of PMMA-PFG, PNVP-PFG copolymers, and other linear-dendritic block copolymers were previously determined using a calibration curve constructed from absorption bands of –C6F5 groups and absorption bands characteristic of one of the groups of vinyl polymers.

To construct a calibration curve on the IR absorption spectra, it is necessary to isolate the bands characteristic of each of the polymers included in the block copolymer. Thus, in the case of a linear-dendritic block copolymer PNVP-PFG, the composition was determined from the absorption bands of groups - C6F5 (960 cm-1, 1075 cm-1, 1220 cm-1) and the absorption bands of PNVP.

– – –

PURPOSE OF THE WORK: Qualitative analysis of PBMA-PFG copolymers by IR spectroscopy Apparatus and equipment Infralum-FT801 IR spectrometer, polymer films. Before measurement, it is necessary to prepare films by pouring from 8-10% solutions (depending on MW) in chloroform. In the course of the work, it will be necessary to take the IR spectra of PBMA, PFG, isolated PBMA-PFG block copolymers and analyze the obtained spectra (correlate the absorption bands to the corresponding groups of linear and branched polymers).

IR spectrometer 4.

"Infralum-FT801"

Completing of the work

1. Connect the device to a personal computer.

2. Turn on the device with the button on the left side panel.

3. Warm up the device for 10-20 minutes (until the green light flashes).

4. Before starting work, create a folder to save the IR spectra.

5. Take reference spectrum (air).

6. Fix the polymer film in the cell, insert it into the device.

7. Take the spectrum of the PBMA polymer film in the transmission mode (selecting the T-transmission mode, after taking the spectrum "remove CO2 peaks", "normalization 100%").

8. Remove films of PFG and block copolymers in the same way.

9. Compare the obtained IR spectra with the data library (select the data library and start the spectrum search).

The report must provide the analyzed IR spectra, with the correlation of the characteristic frequencies to the groups of the copolymer.

Work 3. Determination of MWD of copolymers by GPC.

Analysis of integral and differential distribution curves Theoretical part When working in the GPC method, refractometric and spectrophotometric detectors are usually used. The principle of operation of a refractometric detector is based on measuring the difference between the refractive indices n of the eluate (polymer solution) and eluent (solvent), the flows of which, after the columns, enter the comparative and working chambers of the cuvette. The working and reference chambers are a combination of two adjacent prisms separated by a transparent partition and forming a plane-parallel plate. If liquid flows with the same refractive index pass through the chambers, for example, pure tetrahydrofuran, then the light beam passing through the chambers is not refracted at their interface. In this case, a “zero” line is registered.

If, however, the eluent passes through the comparative chamber, and the working solution of the polymer, which has a higher refractive index, i.e. there is a difference in the refractive indices n, then the light beam at the interface between the chambers is refracted and exits at a certain angle relative to its initial direction, proportional to n. The refractometric detector is the most versatile and widely used, since for polymers it is almost always possible to choose a solvent in which the refractive index increment dn/dc is sufficiently large (dn/dc 0.1).

To obtain additional data on polymer impurities, along with a refractometric detector, a spectrophotometric detector can be used (it records the absorption of UV radiation in the region = 254 nm, 340 nm - via two channels), which is connected to the system in series after the refractometric one and data can be recorded simultaneously from two detectors. This detector is qualitative and does not carry any quantitative information.

Also recently, a viscometric detector and a flow laser nephelometer (small-angle laser light scattering detector) have been widely used for the analysis of polymers. These detectors, in combination with a refractometer, make it possible to determine the MW of hyperbranched polymers, as well as their degree of branching.

Determination of MWD and average MW of polymers. Primary information about MWD is obtained in the form of a chromatogram, which is the dependence of the recorded detector signal on the retention parameters - retention volume (Vr) or retention time (tr). The chromatogram is a superposition of a large number of overlapping peaks of individual polymer homologues, the height of the signal on the chromatogram is directly proportional to the concentration of chromatographed macromolecules at the column outlet.

The refractometric detector determines the mass concentration of the polymer, so the chromatogram gives the mass distribution function. From which, using the calibration dependence and the corresponding calculations using the LCSoluthon software, the values of the average molecular characteristics and MWD of the polymer are determined in differential or integral form.

EXPERIMENTAL PURPOSE OF THE WORK: To determine the molecular weight of PBMA-PFG copolymers by GPC method Instrumentation and equipment

1. Liquid chromatograph LC-20 (Shimadzu).

2. Computer with LCsolution software (LCSolution software - GPC Software for MMP data processing).

3. Vials with screw caps with a capacity of 7-10 cm3.

4. Analytical balance.

5. Sample filtration discs, diameter 13 mm, with PTFE membranes, pore size 0.45 µm.

METHODOLOGICAL INSTRUCTIONS for conducting seminars on the course Methods for the study of waste from industrial processing of vegetable ... "

“The unique territories of Gorny Altai are treated with dignity by the city of Gorno-Altaisk Editorial Board: Mishurova V.V. Engoyan O.Z. Kondrashova T.V. Shpunt A.A. From the Editor Dear readers! This collection includes materials that make up the main ... "

"Kazakh Agrotechnical University named after S.Seifullin CATALOG OF ELECTIVE DISCIPLINES for undergraduates in the specialty 6M070100 - "Biotechnology" Astana 2014 UDC 574 Compiled by: Doctor of Science, Professor Bulashev A.K., Doctor of Biological Sciences. Associate Professor Kukhar E.V., Associate Professor Doctor of Biological Sciences Bekkuzhina S.S., Ph.D., Senior Lecturer Serik...»

«Biomap of Paramesotriton chinensis Chinese Warty Newt Paramesotriton chinensis Chinese Warty Newt Compiled by: Nunikyan E.F. Last update date: 10/29/11 1. Biology and field data 1.1 Taxonomy Order Caudates Caudata Salamander family...» BOLYUGININ IDARESI RESOLUTION dated 08/03/2015 No. 197 Sovetsky On the liquidation of the Municipal State Institution "Department of Images..." Nunikyan E. F. Date of last update: 29.10.11 1. Biology and field data 1.1 Taxonomy Order Anura Anura Family Horned frogs (?) Ceratophryidae Genus Horned frogs Ceratophrys Russian name (if...» 612.776.1:796 This work was supported by Ulyanovsk Regional Branch of the Academy of Sciences of the Republic of Tatarstan (URO AS RT) Reviewers: Doctor of Biological Sciences, Corresponding Member of the Russian Academy of Education V.K ... "resources and protection environment Samara region at the expense of the regional target budgetary environmental fund of the Samara region. Performers: Fund for Social and Environmental Rehabilitation ... "SUMMARY OF THE LESSON ON THE ECOLOGICAL TRAIL (middle group) Purpose: In a playful way, continue monitoring the objects of the ecological trail during the period late autumn. Develop mental activity, memory, observation. Exercise in the education of the mind ... "

"Belarusian State University APPROVED Vice-Rector for Academic Affairs of BSU BASICS OF INDUSTRIAL ASEPTHICS Curriculum for the specialty 1-31 05 01 Chemistry (according to directions) Specialty direction: 1-31 05 01-03 Chemistry (pharmaceutical activity) Specialization 1-31 05 01-03 -02 "Drug technology 2..."

«Ecology ECOLOGY UDC 576.85 S.S. Baksheeva INFLUENCE OF ADVERSE ENVIRONMENTAL FACTORS ON ANTIBIOTIC RESISTANCE OF STAPHYLOCOCCI ISOLATED FROM RESIDENT BACTERION CARRIERS The article presents the results of studying the antibiotic resistance of staphylococcus cultures vegetating on the sl...»

2017 www.site - "Free electronic library - various documents"

The materials of this site are posted for review, all rights belong to their authors.
If you do not agree that your material is posted on this site, please write to us, we will remove it within 1-2 business days.

Send your good work in the knowledge base is simple. Use the form below

Students, graduate students, young scientists who use the knowledge base in their studies and work will be very grateful to you.

Posted on http://www.allbest.ru/

FEDERAL AGENCY FOR EDUCATION

Nizhny Novgorod State University N.I. Lobachevsky

"Methods of polymer research", in the direction of preparation 020100 "Chemistry" and specialties 020101 "Chemistry", 020801 "Ecology"

Teaching aid

Methods for the study of modern polymeric materials

Compiled by: Zamyshlyaeva O.G.

Reviewer: Ph.D., Associate Professor Markin A.V.

Nizhny Novgorod

2012

Introduction

1. Studying the kinetic regularities of the synthesis of macromolecular compounds

1.1 Physical methods

1.2 Chemical methods

2. Study of the structure and composition of polymers

2.1 EPR method

2.2 NMR method

2.3 IR spectroscopy method

2.4 Capabilities of the mass spectrometry method

2.5 Method of X-ray diffraction analysis

2.6 Chemical analysis (Keldahl method)

3. Polymer solutions

3.1 Molecular weight characteristics of polymers

3.2 Methods for polymer fractionation

4. Methods for studying the physicochemical and mechanical properties of polymeric materials

4.1 Methods for thermal analysis of polymers

4.2 Transport and diffusion methods (probe methods)

4.3 Mechanical methods

4.4 Electrical methods

5. Properties of polymers in Langmuir monolayers and thin films

5.1 Study of the colloid-chemical properties of amphiphilic macromolecules in monolayers and Langmuir-Blodgett films

5.2 Surface properties of films

5.3 Atomic force microscopy

6. Practical work

6.1 Work 1. Study of the kinetics of radical polymerization of butyl methacrylate in the presence of small amounts of hyperbranched polymer in a thermographic setup

6.2 Work 2. Qualitative analysis of PBMA-PFG copolymers by IR spectroscopy

6.3 Work 3. Determination of the MWD of copolymers by GPC. Analysis of integral and differential distribution curves

6.4 Work 4. Determination of the strength characteristics of PBMA-PFG copolymer films

6.5 Work 5. Obtaining isotherms of surface pressure compression-expansion for amphiphilic polymers

Literature

Introduction

In this UMP the possibilities of physicochemical research methods in relation to modern polymeric materials are outlined, in addition, some problems of modern chemistry of macromolecular compounds are touched upon, one of which is the creation of functional polymeric materials with a given set of properties.

Polymers have recently found wide application in the modern world due to their unique consumer properties. In this connection, responsible tasks are often assigned to polymeric materials in the creation of structurally complex materials, for example, membranes for ultrafine purification and separation of substances at the molecular level, anisotropic media with a reconfigurable architecture, in the manufacture of complex elements of various devices and devices (microelectronics), creation of wood-polymer composites.

The development of the chemistry of macromolecular compounds is largely due to physicochemical methods of analysis. These methods are actively involved in various stages of obtaining polymeric materials, where usually only chemical methods prevail. The UMP considers the most common physicochemical methods for studying polymeric materials in the practice of scientific and industrial laboratories. The ability to use the described methods is necessary for a future specialist to assimilate the theoretical material studied at the university and develop practical skills.

The purpose of the UMP is to briefly introduce students to using the most well-known physico-chemical methods for studying polymers. This development does not contain the theoretical foundations of all physical research methods, since they were considered in detail in the course "Physical Research Methods" taught at the Faculty of Chemistry. Only the basics of the methods used to study polymers(methods of light scattering, sedimentation and diffusion, gel permeation chromatography, probe methods, dynamic-mechanical analysis, wetting method, behavioral features of amphiphilic polymers in Langmuir monolayers and in solid Langmuir-Blodgett films), which is due both to the diversity and structural features of the objects of study, and continuous development and improvement of analytical equipment, as well as increasing requirements for the quality of polymeric materials. The last chapter of the training manual contains recommendations for the implementation of practical work within the framework of a special workshop, with a description of the equipment and methods for conducting the experiment.

The main tasks of the UMP:

To acquaint with the features of the application of physico-chemical methods for studying the kinetic laws of radical polymerization and activated polycondensation;

Show the possibilities of various physical and chemical methods for identifying polymeric materials, studying the structure of polymers and their chemical structure;

Familiarize yourself with modern methods for studying dilute and concentrated solutions of polymers of various architectures;

To demonstrate the possibilities of methods for studying the colloid-chemical properties of amphiphilic polymers in monomolecular layers at the water-air interface and in solid Langmuir-Blodgett films.

1. Studying the kinetic regularities of the synthesis of macromolecular compounds

Let us consider some of the physicochemical methods used to describe the processes of synthesis of macromolecular compounds.

In practice, the polymerization rate can be determined by various methods, for example, gravimetric, dilatometric, thermometric, spectrophotometric, chromatographic, calorimetric, by measuring dielectric losses, etc. In addition, the degree of conversion of a monomer into a polymer can also be controlled by chemical methods by the number of unreacted double bonds: bromometric, mercurimetric, and hydrolytic oximation.

1.1 Physical methods

thermometric method

Bulk polymerization of a number of vinyl monomers is characterized by a sharp increase in the reaction rate at certain degrees of monomer-to-polymer conversion. This phenomenon is called the "gel effect". Moreover, the course of the kinetic curves is determined by the nature of the monomer, the concentration of the initiator and the conditions of the process. The theory of the gel effect was developed in the late 30s and early 40s of our century. It was proved that the peculiarity of deep polymerization is associated with a change in a number of kinetic parameters (kob, V, kр, ), which are variables. If we consider the case when the use of the steady state method does not introduce a significant error (for example, the polymerization of methyl methacrylate (MMA) up to 20–50% conversion), then taking into account the change in kinetic parameters, polymerization can be quantitatively described to high degrees of conversion. In this case, attention should be paid to the possible change in the rate of initiation already at the initial stages of the transformation.

The applicability of the equation for many systems during polymerization both in bulk and in solution at low degrees of conversion is beyond doubt. However, during polymerization in viscous media, this equation is not satisfied. As polymerization proceeds, the rate of initiation and the magnitude f become variable due to the diffusion mechanism of the initiation reaction.

Experimental and theoretical data characterizing the change in all kinetic parameters of polymerization in viscous media make it possible to describe polymerization to high degrees of conversion with sufficient accuracy. The polymerization process is accompanied by a significant release of heat. In this case, each released portion of heat exactly corresponds to one or another number of reacted bonds, i.e. degree of conversion of monomer to polymer. The thermographic method for studying the kinetics of exothermic reactions is based on measuring the rate of heat release in the reacting system by recording self-heating ( T) of the reaction mixture during the transformation, and the process must be carried out in such a way that the value T at any time did not exceed 1-2 C. Only under this condition, the measurement error due to the distortion of the kinetic curve due to an increase in the conversion rate with increasing T according to the Arrhenius law, does not exceed 3-5%. To study long-term processes, a thermographic setup is usually used, in which the substance under study is placed in a measuring cell with poor conditions for heat exchange between the reaction volume and the thermostatic shell. The inclusion of some thermal resistance between the reaction volume and the thermostatic shell leads to the fact that the temperature gradients in the test substance are reduced to a minimum, which allows the temperature sensor to be moved from the center of the reaction mass to its surface. The location of the temperature sensor on the surface of the reaction volume not only greatly simplifies the design of the measuring cell, but also makes it possible to neglect the possible change in the heat capacity of the test substance during the process.

Study of polymerization by measuring dielectric losses

This method can also be used to study the kinetics of radical polymerization up to deep conversions.

Spectroscopic methods

IR spectroscopy. Most applicable to the study of kinetics polymerization is IR spectroscopy, since it is characterized by a large set of absorption bands corresponding to vibrations of almost all functional groups (from 12500 to 10 cm-1). The main conditions for the use of IR spectroscopy for the study of kinetic regularities is the presence of spectrally separated characteristic absorption bands of the monomer, initiator, and solvent. At Tomsk Polytechnic University Sutyagin V.M. et al. studied the polymerization of vinylcarbazole using the stopped jet method with registration of the spectrum in the IR region. The setup consisted of reservoirs with reagent solutions connected to a jet block through which the reagents were supplied to the observation chamber (with an opening for the passage of IR rays), where polymerization takes place. The method consists in successive recording of the kinetic curve as a dependence of the transmittance on time for a solution of a certain concentration of monomer and initiator. The recording of the curve was carried out in a wide time interval, the start of the recording system was automatically switched on with the supply of reagents to the observation chamber. After the recording device showed that the reaction was completely completed, the monomer mixture was removed through the drain hole and the measuring cell was washed. Further, using the Lambert-Beer equation, the extinction coefficient of the absorption band of the stretching vibrations of the vinyl bond of vinylcarbazole was found, and taking into account the thickness of the cuvette, the reaction rate constant was determined.

UV spectroscopy. This method can also be used to get data on the kinetics of chemical reactions. The starting materials and reaction products are capable of absorbing in various regions of the UV spectrum. Quantitative analysis is carried out to construct calibration curves, with the help of which it is possible to construct kinetic curves of the change in the concentration of the substances under study over time. After processing these curves determine the rate constant of the reaction.

Calorimetry

One of the informative methods for studying kinetic

regularities of the polycondensation reaction is heat-conducting reaction calorimetry. This method has found wide application in the study of hyperbranched polymers. The measurements are carried out on a Calve microcalorimeter, in which the main part of the energy released in the reaction chamber is removed from the reaction zone through a system of thermopiles. For example, the Calve DAK-1A calorimeter automatically registers the value of the integral heat flux coming from the reaction calorimetric cell through differentially connected thermopiles to the massive central block of the calorimeter thermostat. The sensitivity of its measuring thermopiles is at least 0.12 V/W. The electrical circuit provides measurements of heat release energy of at least 98%.

Using this method, it is possible to study not only polymerization processes, but also reactions of activated polycondensation. For example, there was a solution of THF, when used as an activator of triethylamine. The loading of the studied substances and the process of their mixing in the calorimeter were carried out in an argon atmosphere. One of the substances (Et3N) was placed into a sealed evacuated glass ampoule with a thin-walled bottom. This ampoule was placed in the upper part of the Teflon reaction cell (height 0.11 m, diameter 0.01 m) of the calorimetric block of the calorimeter thermostat using a special device. Another substance (solution of FG and DG in THF) was preliminarily introduced into the cell in an argon atmosphere. After thermal equilibrium was established between the calorimetric block of the calorimeter thermostat and the cell with the substances under study, the reagents were mixed by breaking the lower part of the glass ampoule against the bottom of the cell. The device mentioned above ensured complete mixing of the components and their intensive mixing. A correction was introduced into the final result, which took into account the breaking of the glass ampoule, the mixing of the resulting mixture, and the evaporation of the solvent into the volume of the ampoule not filled with the sample. Blank experiments were performed to determine the correction value. The measurement temperature was 25 C. All obtained heat release curves had 2 maxima, the intensity of which was determined by the ratio of components in the reaction mixture. To analyze the obtained data, it was necessary to carry out similar measurements for the polycondensation of each of the monomers (FG and DG) under the same conditions.

polarography

This method is based on the ability of dissolved compounds to be oxidized or reduced on an inert electrode when a certain potential is applied. As a result of the occurrence of redox reactions, a current will flow through the solution, which is measured with a milliammeter. According to the data obtained, the dependence of the current strength on the applied voltage (or the potential of the working electrode), called the polarogram, is built.

	in magnitude
polarography	is
potential		half-wave


relevant
half the distance between

	final

		get
parameter information
reactionary	capabilities
monomers.
control	concentration

polarographically active monomer during polymerization allows you to determine the conversion of monomer to polymer. On the other hand, polarographic control of the flow rate of the initiator (in the presence of data on the kinetics of the process) makes it possible to obtain information about the termination mechanism

and the chain transfer constant. The most convenient initiators for this method are peroxide compounds and azo- bis-isobutyric acid

This method is also very convenient for polycondensation processes, when one of the monomers (bi- or trifunctional compound) has polarographic activity and for copolymerization. So if the monomers 1

And 2 polarographically active and their E1/2 differ significantly, then by values of half-wave potentials of reduction of monomers using calibration plots WITH 1 f (Id 1) and C 2 f (Id 2) , you can go to the kinetic

consumption curves of each of the monomers in the copolymerization process ( WITH- concentration, Id- change in the height of the polarographic wave). In addition, the value E1/2 is related to the reactivity parameters of the monomers, which can be used to find the relative activities of the monomers r1 And r2 .

1.2 Chemical methods

IN bromide -bromate method KBr and KBrO3 are used. When the components interact, bromine is released, which adds to the double bond of the monomer:

5KBr + KBrO3 + 6HCl 6KCl + 3H2O +3Br2,

Br2 + CH2=CH?COOH CH2Br?CHBr?COOH,

Br2 + 2KI 2KBr + I2,

I2 + 2Na2S2O3 2NaI + Na2S4O6.

Method mercurimetric titration reagent is based on addition of mercury (II) nitrate at the double bond site of the monomer (acrylic or methacrylic acid), followed by titration of excess mercury (II) nitrate with Trilon B. The reactions proceed according to the following equations:

Hg(NO3)2 + CH2=CH?COOH CH2(HgNO3)?CH(ONO2)?COOH,

C10H14O8N2Na2 + Hg(NO3)2 C10H12O8N2Na2Hg + 2HNO3.

Method hydrolytic oximation based on reaction acetaldehyde released during hydrolysis, for example, vinyl ester with hydrochloric acid hydroxylamine and subsequent titration of hydrochloric acid with alkali:

CH2=CH?R + H2O CH3CHO + HOR,

CH3CHO + NH2OH HCl CH3CH=NOH + HCl + H2O,

HCl + KOH KCl + H2O.

The kinetics of polymerization can also be studied using gravimetric and dilatometric methods. . gravimetric method(weight) - one of the most simple and accessible, but its significant drawback is that one experiment gives only one point on the graph. More accurate is dilatometric method, based on the decrease in the volume of the reaction mass during polymerization. One of the advantages of this method is the possibility of obtaining kinetic curves at a certain temperature without isolating the polymer.

2. Study of the structure and composition of polymers

2.1 EPR method

The method is based on the phenomenon of resonant absorption of the energy of electromagnetic waves by paramagnetic particles placed in a constant magnetic field. Absorption is a function of the unpaired electrons present in the polymer sample. The nature of the radical can be identified from the shape, intensity, position, and splitting of the spectrum using atlases of EPR spectra. This method is the only method of "direct" observation of unpaired electrons. Instruments give the first derivative of the energy absorption curve. The line intensity of an EPR spectrum is the area under its curve, which is proportional to the number of unpaired electrons in the sample. The position of the line in the spectrum is taken to be the point at which the first derivative of the spectrum crosses the zero level.

General principles for the interpretation of EPR spectra. After registering the EPR-

spectrum needs to be interpreted. The following rules are used to interpret isotropic EPR spectra:

1. The positions of the lines of the spectrum must be symmetrical with respect to some center of the spectrum. The asymmetry may be due to the superposition of the two spectra, and is related to the difference in the corresponding g-factors. If the hyperfine splitting constants are large, then second-order splittings can lead to asymmetry in line positions. The differences in linewidths can be caused by the slow rotation of the radical. This can also be the reason for the appearance of spectrum asymmetry;

2. If there is no intense central line in the spectrum, then this indicates the presence of an odd number of equivalent nuclei with half-integer spins.

The presence of a central line does not yet exclude the presence of an odd number of nuclei.

3. For nuclei with I=1/2, the sum of the absolute values of the hyperfine splitting constants for all nuclei must be equal to the distance (in gauss) between the extreme lines, which can be very weak and even

not be observed at all. This amount is equal to niai , Where ni - number of cores i hyperfine splitting ai .

4. The reconstruction of the spectrum, if it is correct, must correspond to the experimental positions of the lines, especially at the edges of the spectrum. If the line widths are equal and the overlap is negligible, then the relative line amplitudes should correspond to the degeneracy multiplicity.

5. The distance between two adjacent lines most distant from the center is always equal to the smallest value of the hyperfine splitting.

6. The total number of energy levels in the system for one value of MS is given by the expression 2 Ii 1 ni, Where ni is the number of nuclei with spin Ii . i

7. The maximum possible number of lines (with unresolved splittings of the second order) is 2 ni Ii 1 , where ni - number i equivalent nuclei with spin Ii .

Currently, there are many computer programs for simulating EPR spectra, and therefore, the task of analyzing the hyperfine structure has been greatly simplified. For example, the WINEPR SimFonia software package allows you to download the experimental spectrum, determine the value of the g-factor, and approximately measure some of the most obvious CFS constants. By introducing the measured parameters of the spectrum (g-factor, type of nuclei and their number, values of the HFI constants), setting the width and shape of the line, one can construct a theoretical spectrum. Then the simulated spectrum is subtracted from the experimental one. Adjusting the parameters of the theoretical spectrum, one achieves the minimum difference between it and the experimental spectrum.

2.2 NMR method

The NMR method is based on the ability of polymers placed in an external magnetic field to absorb electromagnetic radiation in the radio frequency range (1..500 MHz). In this case, absorption is a function of the magnetic properties of the atomic nuclei in the macromolecule. Active in NMR, i.e. those objects that contain magnetic nuclei appear, for example, 11 H , 12 H , 199F, 147N, 1531P and etc. The NMR spectrum is the dependence of the intensity electromagnetic radiation from frequency (Hz). The shift of NMR signals under the influence of different electronic environment is called chemical shift, which is proportional to the electromagnetic field and is measured in relation to the signal of a reference substance, which has a signal in a stronger field than most protons.

This method is very widely used in polymer chemistry, since it can be used to solve many problems: the study of crosslinking processes; determination of tacticity in polymers and copolymers; study of molecular interactions in polymer solutions; diffusion in polymer films; compatibility of polymers and polymer blends; study of the configuration and conformation of polymer chains; distinguishing between block copolymers, alternating polymers and polymer blends, determining the structure of the polymer.

Determine which spin-spin interaction leads to hyperfine splitting of each of the peaks;

Six signals were found in the spectra in a ratio of 2:2:1:1:1:2 (Fig. 1). The signals at 158.5, 146.6, 125.8 ppm correspond to the fluorine atoms of the terminal phenyl groups in meta-, pair- And ortho-provisions, respectively. 127.1 ppm - fluorine atoms of ?С6F4 groups located between two equivalent germanium atoms. Signals 128.2. and 136.3 ppm correspond to the fluorine atoms of the ?С6F4 groups located between the germanium atom with pentafluorophenyl ligands and the germanium atom bonded to the hydrogen atom.

Rice. 1.19FNMR spectrum of the copolymer of FG and DG obtained in the presence of 20% DG (Table 1).

The degree of branching of copolymers based on FG and DG was estimated from the relative content pair- fluorine atoms (outer shell of a hyperbranched macromolecule) - Fp of the total number of fluorine atoms calculated for the hyperbranched macromolecule of the third generation. Fi=si/ s, where si is the effective area in the absorption spectrum corresponding to each type of aromatic fluorine. 19F NMR spectra were recorded on a Bruker AM-500 Fourier NMR spectrometer, 470.5 MHz (reference hexafluorobenzene).

Table 1 Characteristics of copolymers obtained by light scattering methods (solvent - chloroform) and 19F NMR

	Rh,	Fp
(luminous)

For perfluorinated polyphenylenegermane (PFG) obtained in the absence of DH, we found Fp(D3)=0.144, which corresponds to the calculated value. For a polymer derived from DG, the calculated value Fp(D3) = 0.1176; for copolymer at

[FG]/[DG]=1/3

Fp(D3)=0.1386.

In all cases, we proceeded from a branched structure with a branching index on the germanium atom equal to 3 and 2 for FG and DG, respectively. The table shows that copolymers are characterized by an underestimated value Fp, in comparison with PFG, which can be achieved only by crosslinking, due to the participation of the hydrogen atom of DG units in crosslinking reactions. Calculations were carried out for a copolymer of the composition [FG]/[DG]=1/3, in which half of the DG units underwent crosslinking (16.5%). In this case found Fp(D3)=0.126. It should be noted that the calculations were carried out on the basis of a common mechanism for intra- and intermolecular cross-linking associated with a change in the ratio between the number of αC6F5 and αC6F4 groups.

2.3 IR spectroscopy method

If they are in the IR spectrum, then the polymer can be attributed to the class of unsaturated polymers. Further, using the tables of characteristic frequencies, the other absorption bands are completely assigned to certain atomic groups that make up the link of the macromolecule. The interpretation of the spectrum is complicated by the fact that the absorption bands of different groups may overlap or shift as a result of a number of factors. Table 1. shows the characteristic frequency ranges of some groups.

Table 1. Characteristic frequencies of some groups

Wavenumber range	group of atoms
	hydroxyl, primary and secondary amino groups
	triple С?С, С?N or С=С=С bonds
	carbonyl groups (aldehydes, carboxylic acids and their
	derivatives), absorption bands of alkenes, aromatic
	compounds and heterocycles, and containing C=C, C=N bonds,

	bands of stretching vibrations of CH bonds in fragments =CH2 and
	СH?, aromatic and heterocyclic rings
	absorption bands of CH-bonds of alkyl groups
	corresponds to vibrations of the C=N bond
	C=O stretching vibrations in ester groups

Using the method of IR spectroscopy, it is also possible to determine and study intermolecular and intramolecular hydrogen bonds, because their education leads:

To shift the band towards lower frequencies;

Broadening and increase in the intensity of the band corresponding to the stretching vibration of the group involved in the formation of hydrogen bonds.

To study hydrogen bonds, the spectra of polymers are usually taken at several concentrations in a nonpolar solvent.

2.4 Capabilities of the mass spectrometry method

This method is based on the study of the chemical structure, composition and properties of polymers by determining the ratio of mass to charge me And the amount of ions obtained during the ionization of volatile decomposition products of the analyzed polymer. Due to the high sensitivity and speed of analysis (hundreds of analyzes per 1 s), as well as the possibility of observing a single substance in a mixture, this method has found wide application in studying the initial stages of polymer degradation in degradation processes. In addition, this method makes it possible to determine the molecular weights of polymers with high accuracy. Since the mass of an electron is negligible compared to the mass of a molecule, the problem of identifying the mass spectrum is reduced to revealing the lines of molecular ions and determining their mass numbers. Lines of molecular ions are observed only in 90% of the mass spectra.

2.5 Method of X-ray diffraction analysis

The method is based on the analysis of the diffraction pattern obtained by scattering electromagnetic X-ray (λ 0.1 nm) radiation by scattering centers - electron shells of atoms. The X-ray diffraction analysis method makes it possible to unambiguously determine all the details of the crystal structure (atomic coordinates, bond lengths, bond angles, etc.). Polymers are studied by X-ray diffraction at small angles. This method is widely used to determine the degree of crystallinity of polymers, which is understood as the ratio of the total scattering of crystallites to the total scattering from amorphous and crystalline regions. For this, the scattering intensity curves for the amorphous reference sample, the crystalline reference sample and the polymer sample are examined separately.

with unknown crystallinity. The degree of crystallinity is calculated by the formula:

2.6 Chemical analysis (Keldahl method)

One of the common methods for analyzing the composition of nitrogen-containing copolymers is the Keldahl analysis.

Keldahl method. This method is that nitrogen-containing the organic matter is decomposed by heating with sufficient concentrated H2SO4 to quantitatively form (NH4)2SO4. Carbon is then oxidized to carbon dioxide (H2CO3), and nitrogen is converted to ammonia (NH3), which remains in solution in the form of sulfate salt.

1. Decomposition:

2. Distillation:

(NH4)2SO4 + 2NaOH Na2SO4 + 2NH3 + 2H2O

3. Titration:

(NH4)3BO3 + 3HCl 3 NH4Cl + H3BO3

The decomposition reaction is accelerated by adding a mixed catalyst consisting of mercury sulfate, magnesium sulfate and selenium. After decomposition is completed, the liquid is supersaturated with NaOH, ammonia is distilled off and titrated with HCl solution.

3. Polymer solutions

3.1 Molecular weight characteristics of polymers

The main molecular weight characteristics of polydisperse polymers are average molecular weights (MW), molecular weight distribution functions (MWD) and distribution curves corresponding to these functions.

In order to quantitatively characterize the molecular weight distribution of a polymer, it is necessary to calculate the relative amount of fractions containing macromolecules of the same molecular weight. This can be done in two ways - based on the number or total mass of macromolecules. having MM equal to Mi; ni Mi is the total mass of the polymer.

The average MW of a polydisperse polymer is a weighted average, the contribution to which of each of the fractions is determined by its MW and relative amount. From the latter it follows that a polydisperse polymer is characterized by two average molecular masses - number average molecular mass M n :

It follows from expression (3) that the number average MM is equal to the total mass of macromolecules divided by their number.

In the experimental study of MMPs, one usually deals with continuous curves and distribution functions. The value of a continuous differential numerical distribution function fn(M) is equal to the numerical fraction of macromolecules with MM from M before M+dM divided by dM; value of the continuous mass distribution function fw(M) is equal to the mass fraction of macromolecules with MM from M before M+dM divided by dM.

Continuous differential numerical and mass functions are interconnected, like the corresponding discrete functions, by a simple relationship:

fw (M) (M Mn )fn (M)(5).

In addition to differential, integral distribution functions are widely used:

value (ordinate) integral numerical function distribution Fn(M) is equal to the numerical fraction of macromolecules with MM from the minimum to the specified M;

value (ordinate) integral mass function distribution Fw(M) is equal to the mass fraction of macromolecules with MM from the minimum to the specified M.

An important characteristic of a polydisperse polymer is the width

MMR. Attitude M wMn , which characterizes the MMD width, called Schulz polydispersity coefficient. Often, in the ratios characterizing the MWD of the polymer, instead of the MM, the degree of polymerization is used p MM 0 , Where M And M 0 - molecular weights of the polymer and monomer.

Average molecular weights M n, And M w are determined using absolute methods, since their calculations are carried out without any assumptions about the shape and size of macromolecules. Number average molecular weight M n can be determined by any method based on measuring the colligative (i.e., depending only on the number of particles) properties of polymer solutions: osmometry, ebullioscopy, cryoscopy, isothermal distillation, measurement of the thermal effects of condensation, and also according to the quantitative determination of terminal functional groups of macromolecules by which either by physical or chemical means. Mass average value M w, can be determined, for example, by the method of light scattering.

In practice, MWD curves are obtained as a result of fractionation of polymers, i.e. performing various methods of separating a polymer sample into fractions with different molecular weights.

Polymer Fractionation Methods

The compositions of the phases formed during the separation of the polymer solution are not the same and can be determined from the equilibrium condition z z, meaning that the chemical potentials z-measure in coexisting phases are the same. Let z refers to the more concentrated phase, and to the more dilute phase. Expressions for and z can be obtained from the equation for the isobaric-isothermal potential of the polymer solution

For any value for different z- measures ratio zz will different, i.e. phase separation is accompanied by fractionation of the polymer;

Usually > 0 and I > z, i.e. any z-measures regardless of z present in

more concentrated phase, i.e. low molecular weight macromolecules are always contained in the high molecular mass fraction; each fraction has its own molecular mass distribution, of course, narrower than the original polymer;

adding a precipitant to the polymer solution;

Evaporation of the solvent, if the polymer was previously dissolved in the solvent-non-solvent mixture;

A change in the temperature of the solution, which leads to a deterioration in the quality of the solvent.

Fractional dissolution method is in succession extraction of the polymer with a series of liquids, the dissolving power of which in relation to a given polymer increases sequentially. The starting polymer can be solid, in the form of a coacervate, a film, on an inert or active carrier. The resulting fractions have a consistently increasing molecular weight.

TO analytical methods fractionation include: ultracentrifugation, turbidimetric titration, gel permeation chromatography, etc.

Turbidimetric titration is to measure the turbidity polymer solution when a precipitant is added to it. If the polymer solution is sufficiently diluted, then the macromolecules of the polymer released when the precipitant is added remain in the form of a stable suspension, causing the solution to become cloudy. As the precipitant is added, the turbidity of the solution increases until all the polymer is separated, after which the turbidity remains constant. The results of the titration are presented as a dependence of the optical density of the solution, which is proportional to the turbidity, on the volume fraction of the precipitant. This method has two main assumptions:

It is assumed that the amount of precipitant required to initiate polymer deposition (the critical volume of precipitant or the threshold of deposition) depends on the concentration of the polymer at the time of deposition ( WITH) and its molecular weight ( M) according to the equation:

kr k lg C f M (10),

Where kr- volume fraction of the precipitant at the settling threshold, k - constant, f M -

some MM function, the value of which is determined from calibration titrations of narrow polymer fractions with known MM;

Fractionation By method gel penetrating chromatography

carried out according to the principle of a molecular sieve (chromatographic separation of molecules occurs only in size, due to their different ability to penetrate into the pores, and does not depend on the chemical nature of the components). This method combines continuous sample fractionation, which is based on the difference in the interfacial distribution of substances moving with the solvent (mobile phase) through a highly dispersed stationary phase medium, and subsequent analysis of the fractions. The principal feature of the method is the possibility of separating molecules according to their size in solution in the range of molecular weights from 102 to

108, which makes it indispensable for the study of synthetic and biopolymers.

The principle of the GPC method. When fractionated by this method through a column filled with particles of a porous sorbent in a solvent is passed through a solution of a polydisperse polymer, while the molecules tend to diffuse into the solvent, which is in the pores, i.e. penetrate into the pores. With a constant solvent flow, the solute moves along the column, and macromolecules will penetrate into the pores only when their concentration outside the pores is greater than in the pores. When the solute zone leaves this area of the sorbent, the concentration of the sample inside the sorbent becomes greater than outside it, and the macromolecules again diffuse into the flow of the mobile phase. This process is repeated cyclically along the entire length of the column. In a polydisperse polymer, there is always a fraction of "short" macromolecules that easily penetrate into all pores of the sorbent, a fraction of "larger" macromolecules that can penetrate only some of the pores, and "large" macromolecules that do not penetrate into the pores at all are "forbidden" for pores of this size. In accordance with the different ability to penetrate into the pores, the macromolecules are retained in the column for different times: the "forbidden" large macromolecules are washed out of the column first, the smallest ones are the last. This separation in the chromatographic column is called the "spatial inhibition" method. The time during which polymer molecules are held in pores is called time holding tr. Those. is the average transit time for a macromolecule column from the moment of sample injection to a certain distance equal to the length of the column.

retention time tr is the main experimentally determined characteristic of the chromatographic process.

Another parameter that is most often used in chromatography

- "retained volume" - Vr, which is related to retention time:

Vr= trv(11),

Where v- volumetric flow rate of the solvent through the column (ml/min), which is set at the beginning of the experiment.

The retention volume is the number of milliliters of solvent that must be passed through the column to flush the sample out of the pores of the sorbent. This value is related to the size of macromolecules in a similar way to the retention time: Vr is minimal for "forbidden" molecules and maximal for macromolecules that completely penetrate into the pores.

The volume of the exclusion column can be expressed as the sum of three terms:

V = VO+Vs+Vd (12),

Where VO- "dead" intermediate volume of the column, i.e. solvent volume between sorbent particles (mobile phase volume); Vs is the volume of pores occupied by the solvent (the volume of the stationary phase); Vd is the volume of the sorbent matrix, excluding pores.

Total volume of solvent in the column Vt(total column volume), is the sum of the volumes of the mobile and stationary phases.

Equilibrium distribution coefficient of macromolecules between mobile and stationary phases k characterizes the probability of diffusion of macromolecules into pores and depends on the ratio of the sizes of molecules and pores, and also determines the retention of molecules in the size exclusion column:

k = Cs/CO (14),

Where WITHs is the concentration of the substance in the stationary phase; CO- in the mobile phase. Since the mobile and stationary phases have the same composition,

That k for which both phases are equally accessible is 1. This situation is realized for molecules with the smallest sizes (including solvent molecules), which penetrate into all pores and therefore move through the column most slowly. Their retained volume is equal to the total volume of the solvent.

All molecules larger than the pore size of the sorbent cannot enter them (complete exclusion) and pass through the channels between the particles. They elute first from the column with the same retention volume equal to that of the mobile phase (VO) . Distribution coefficient k for these molecules is 0.

Molecules of intermediate size, capable of penetrating only a certain part of the pores, are retained in the column according to their size. Distribution coefficient k of these molecules varies from 0 to 1 and characterizes the fraction of pore volume available for molecules of a given size. Their retained volume is determined by the sum VO and the accessible part of the pore volume:

This is the basic

Vr= VO+ kVs (15).

Retention in an equation describing the chromatographic process.

The convenience of the GPC method is that the main parameter of the method is the retention volume Vr is an unambiguous function of molecular weight (M).

In general, the dependency Vr(M) is expressed:

...