Methods for identifying polymers. Methods for studying the structure of polymers Polymer study methods
Ministry of Education and Science
RUSSIAN FEDERATION
GOU VPO "Saratov State University
name "
Institute of Chemistry
I argue:
vice-rector for educational and methodical work
d. Philol. n., Professor
"__" __________________20__
Working program discipline
Modern methods of research of polymers
Directional direction
020100 - Chemistry
Preparation profile
High molecular compounds
Qualification (graduate degree)
Bachelor
Form of study
Pupil
Saratov,
2011
1. Objectives of the development of discipline
The objectives of the discipline of the discipline, modern methods of polymer research "are:
- the formation of students' competences related to the understanding of the theoretical foundations of the main methods for the study of polymers used in domestic and foreign practice,
- formation of individual work skills when performing a chemical experiment;
- Formation of work skillson serial equipment used in analytical and physicochemical studies;
- acquisition of skills and skills in the process of mastering special methods for registering and processing the results of chemical experiments;
- development of computer equipment in order to use its capabilities for registration of laboratory work;
- Acquisition of skillsindependent Work with periodic chemical literature.
2. The location of the discipline in the structure of the UPO undergraduate
Discipline "Modern methods of polymer research" (B3.DV2) is a variable profile discipline of a professional (special) cycle B.3 of the preparation of bachelors in the direction020100 "Chemistry", profile of training "High molecular compounds" and is taught in the 8th semester.
The discipline material is based on knowledge, skills and skills acquired when mastering basic disciplines "Neorganic Chemistry, "Analytical Chemistry", "Organic Chemistry", "Physical Chemistry", "High Molecular Compounds", "Colloid Chemistry", "Ximic technology» professional (special) Cycle GEF VPO in the direction of training020100 "Chemistry", variabledisciplines "Numerical methods and programming in physicochemical polymers" mathematical and natural science cycle andvariable profile disciplines "Modern approaches to polymers synthesis», « Medico-biological polymers», « Synthesis and properties of water-soluble polymers», « Polymer Materials Science»OOP VPO in the direction of training020100 "Chemistry", profile "High molecular compounds".
For the successful development of the discipline, the learner must own knowledge aboutthe structure, properties and classification of high molecular weightcompounds, chemical properties and transformations of macromolecules, their behavior in solutions,have an idea of \u200b\u200bthe structure and basic physical properties of polymeric bodies, to own the skills of preparing solutions of polymers, carrying out reactions of polymerovalogical transformations,to be able to conduct tittometric, potentiometric, gravimetric, etc. Analyzes, metrological processing of the experimental results, be able to work on a computer, knowstandards and techniques for the design of educational and scientific texts, be able to conduct mathematical calculations in solving polymer-chemical problems.
Acquired in the framework of the discipline "Modern methods of research of polymers" knowledge, skills and skills are necessary for execution, design and successful protectiongraduation qualifying (bachelor's) work.
3. Competence of students, formed as a result of the development of the discipline "Modern methods of research of polymers"
Formulation of competence | The code |
Owns the skills of a chemical experiment, the main synthetic and analytical methods of obtaining and researching chemicals and reactions | PK-4. |
Owns work skills on modern educational and scientific equipment during chemical experiments | PK-6. |
Has experience in serial equipment used in analytical and physicochemical studies | PK-7. |
Owns methods for registering and processing the results of chemically experiments | PK-8. |
As a result of the development of the discipline "Modern methods of the study of polymers" students should
know:
– classification of polymer research methods,
- General methods of isolation and purification of natural polysaccharides (extraction, fractional deposition, ultrafiltration, dialysis, electrophoresis, ion exchange chromatography, gel filtering, ultracentrifugation, enzymatic cleaning, etc.),
- Basic methods for studying the structure and properties of polymers ;
be able to:
- allocate polysaccharides from plant or animal natural raw materials,
- apply the methods for cleaning polymers from low - and high molecular weight impurities,
- determine the humidity, fractional composition, solubility, molecular weight of the polymer, the degree of substitution of functional groups in the macromolecule,
- carry out the reactions of polymerovalogical transformations,
- identify the main physical and physicochemical characteristics of polymers,
- Work on serial equipment used in analytical and physicochemical studies,
- use computer technique when making laboratory work;
own:
- methods of selection of polysaccharides from natural raw materials,
- methods for cleaning polymers from impurities
- skills of the experimental reactions of polymer polymer transformations,
- skills of the experiment study of the structure and practically important properties of polymers,
- skills Comprehensive application of analyzing methods for polymer study
- the skills of individual work when performing a chemical experiment,
- receptions special methods for registering and processing the results of chemical experiments,
- skills independent Work with periodic chemical literature.
4. The structure and content of the discipline "Modern methods of research of polymers"
4.1. Total labor intensity of discipline Makes up 8 credit units (288 hours), of which lectures - 48 hours, laboratory work - 96 hours, independent work - 108 hours, of which 36 hours are given to the preparation for the exam.
Section of disciplines | Semester | Near-Seme | Types of study work, including independent work of students and labor intensity (in hours) | |||||
Lectures | Laboratory works | Independent work | Total |
|||||
General information on methods for studying polymers | ||||||||
General methods of isolation and purification of natural polymers | ||||||||
Chromatography methods | Written report in the laboratory journal. |
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Substances with electromagnetic radiation | Written report in the laboratory journal. Abstracts |
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Study of the structure and properties of polymers | Written report in the laboratory journal. Business games |
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final examination | An assessment exam |
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TOTAL: |
4.2. Contents of the lecture course
General information on the methods of research of polymers.
Characteristics of methods for studying polymers. Modern trends in the development of research methods. Classification of research methods. The choice of the optimal method of research. Study of the chemical composition of polymers. Determination of the content of various chemical elements in macromolecules.Analysis polymers thermal methods.Elemental analysis.Chemical analysis on the the content of individual elements. Analysis functional groups. Determination of unsaturation polymers.
General methods for the isolation and purification of natural polymers.
Filming, ultrafiltration, dialysis, electrodialysis. Centrifugation, ultracentrifugation. Fractional precipitation and extraction. Enzymatic cleaning. Chromatographic methods: ion exchange,adsorption Size-exclusive, affinity chromatography. Electrophoresis. Criteria for individuality and natural polysaccharides.
Chromatography methods.
Characteristics of chromatography methods. Gas chromatography. Capillary gas chromatography. Reaction gas chromatography. Facing gas chromatography. Pyrolytic gas chromatography. Selection of pyrolysis conditions. Choosing the conditions of gas chromatographic separation of pyrolysis products. Using PGS analysis of polymers.
Liquid chromatography. High-performance liquid chromatography. Capillary Electrosparation methods. Ion exchange liquid chromatography. Chromatomembrane division methods. Thin layer chromatography. Methods of analysis. Application areas of the method TLC. Gelproof chromatography. Equipment design of the method. Molecular weight determination and MMR polymers. Study of the kinetics of polymerization. Studying the composition of copolymers. Features of studying oligomers. Features of the study stitched polymers.
MACC spectrometric analysis method. Equipment design of the method.
Sample input methods. Methods of ionization of substance. Types Analyzers masses. MACC spectrometry with inductive-bound plasma. Scope of mass spectrometry. Analysis of the chemical composition of mixtures
Methods based on interaction Substances with electromagnetic radiation.
X-ray structural analysis and electronics. X-ray and x-rayelectronic spectroscopy. E. pelonography. Method of labeled atoms.
Methods using ultraviolet and visible shine. Spectrophotometric method of analysis in UV - and visible area. Basics of absorption spectrophotometry. Equipment registration.Methods preparation of samples. Conducting a quantitative analysis. Studying the kinetics of chemical reactions. Study of polymers and copolymers.Methods used optical laws. Reflection based methods sveta.Refractive methods sveta.Refractometry. Double bemprane. Scattering Methods sveta. The method of light scattering. Raman scattering spectroscopy. Photocolormetric analysis method.
Infrared spectroscopy. Equipment design of the method. Application method of IR spectroscopy. Definition of purity of substances. Study of the mechanism of chemical reactions. Studying composition and structures of polymers. Determining the composition of copolymers. Study microstructure, configuration and conformations of macromolecules. Study of surface layers of polymers. Determination of temperature transitions in polymers. Research oxidation and mechanodestruction 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.
Methods radio spectroscopy. Method of nuclear magnetic resonance. Physical basics of the method.Characteristics spectrum NMR. Equipment registration.Using method NMR. Studying the degree of transformation of monomers in the process polymerization.Conformational analysis of polymers. Study molecular movements in polymers.Study processes of aging rubbers. Study component compatibility and intermolecular interactions for mixing polymers. Study vulcanization nets in elastomers. Study deformations and polymer flows. Electronic paramagnetic resonance. Spectrum characteristics EPR. Equipment method design EPR. Application method EPR. Identification of paramagnetic particles. Research radicals in polymers. Study of molecular movements in polymers. Studying the structuring of elastomers. Nuclear quadrupole resonance.
Electrochemical analysis methods. Potentiometric analysis method.Conductometry method. Coulometric analysis method. INoltamperometric methods.Polarographic analysis method.Inversion electrochemical methods. High frequency methods.
Study of the structure and properties of polymers.
Study masses, branching and the interaction of macromolecules. Determination of the molecular weight of polymers. Non-average molecular weight. Midnomassian molecular mass. Other types of molecular masses. Definition MMR polymers. Analysis of the functionality of oligomers. The study of the branchedness of macromolecules. Study of intermolecular interactions in polymers.
Study of the supemolecular structure. Definition specific volume of polymers. Measure polymer density. Methods microscopy.Transmission electronic microscopy. Scanning electronic microscopy. Interference-diffraction methods. Research of crystallization method EPR. Determining the degree of crystallinity. Determination of crystallite sizes. Research orientation in polymers.
Methods for determining the glass transition temperature of polymers. FROM tatical methods.Dynamic methods. Dynamic mechanical methods. Electrical methods. Dynamic magnetic methods.
Evaluation of the resistance of polymers To external influences and efficiency actions stabilizers. The study of thermal aging processes. Thermogravimetric analysis method. Differential-thermal analysis. Differential scanning calorimetry. Oxidative aging of polymers. Investigation of oxygen absorption. Assessment of chemical resistance of polymers. Study mechanochemical destruction. Estimation of the stability of industrial elastomers. Study rubbers. The study of thermoelastoplasts. Study vulcanizats. Evaluation Weather resistance elastomers. Studying the effectiveness of action and selection of stabilizer.
Rheological and plasticoelastic properties of Kauchukov and rubber blends. Rotary viscomemetry. Capillary viscomemetry. Compressive plastometers. Dynamic methods of rheological tests.
Methods of studying the preparation of rubber mixtures. Definition of solubility of sulfur in elastomers. Analysis Microwaves B. rubber mixture. Evaluation of the quality of mixing. Quantitative evaluation of the quality of mixing.
Study of vulcanization processes and structures of volcanisites. Vulcanization evaluation properties.Vibration Retometry. Right riotters. Study structures of the vulcanization grid.
Examples Comprehensive application of analyzing methods for the study of polymers. Methods of research of polymer mixtures. Express Identification Methods polymers.Pyrolytic gas chromatography. Application IR - I. NMR spectroscopy. The use of thermal and dynamic analysis methods and data swelling . Study of the interfacial distribution of the filler. Type definition vulcanizing systems.
4.3. Structure and calendar plan of laboratory classes
Section of disciplines | Semester | Near-Seme | Types of academic work, including independent work of students and labor intensity (in hours) | Forms of current performance monitoring (semester weeks) |
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Laboratory works | Independent work | Total |
|||||
Isolation and quantitative determination of pectin substances from citrus peel. Selection of pectin from pumpkin pulp. Comparative analysis of the gel-forming capacity of citrus pectin with pumpkin pectin | Written report in the laboratory journal |
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Selection of chitin from crustacean shells. Conducting a chemical reaction of polymer-chip chitin chitosan. Determination degree of deacetylation and molecular weight of chitosan. Comparative analysis of solubility of chitin samples and chitosan in various environments (Provides 3 tasks) | Written report in the laboratory journal |
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Determination of the content of A -, B - and G-cellulose. Determination of penosenov. Determination of resins and fats. Determination of ash content of cellulose (Provides the execution of 2 tasks) | Written report in the laboratory journal. Interview on abstracts |
Study of the thermomechanical properties of polymers (Provides 3 tasks) | Written report in laboratory journal Business game number 1 |
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Physical and mechanical properties of polymers (Provide 4 tasks) | Written report in the laboratory journal. Business game number 2. |
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TOTAL: | Individual conversation with a teacher in dialogue |
5. Educational technologies
Along with traditional educational technologies (lectures, laboratory work), technologies based on modern information funds and methods of scientific and technical creativity, including training based on business games on topics "Termomechanical properties of polymers "," Physical and mechanical properties of polymers ", advanced independent work (abstracts), as well as training systems for professional skills and skills. There are meetings with representatives of Russian and foreign companies, scientists from the profile institutions of the Russian Academy of Sciences.
6. Educational and methodological support of independent work of students. Estimated means for current monitoring of academic performance, intermediate certification According to the results of the development of discipline.
Independent work of students suggests:
- preparation of supporting abstracts on the sections of the discipline,
- mastering theoretical material,
- preparation for laboratory work,
- registration of laboratory works,
- preparation for business games,
- writing an abstract,
– search for information on the Internet and libraries (SNB SSU, Cathedral Library, etc.),
– preparation for current and final control.
Final control form - exam (tickets in Appendix 1).
6.1. Questions for independent training
1. Optical research methods.
Spectrum of electromagnetic radiation. Theoretical foundations of the UV spectroscopy method. Chromophores, auxochromas. Types of displacement absorption bands. Electronic spectra of solutions and polymers films. Effect of solvent on electronic spectra of polymers solutions.
2. Oscillatory spectroscopy.
Theory of IR - and CR-absorption. Valentines, deformation oscillations (symmetric and asymmetric). Types of oscillations of individual groups.
3. NMR spectroscopy.
Basics of the theory of 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. Constant spin-spin interaction. Classification of spin systems: the first and higher spectra. Exchange interaction.
4. Heat movement in polymers.
The heat capacity of polymers. The heat capacity of solid polymers. Theoretical analysis of heat capacity. The heat capacity of polymer melts.
Energy transfer in polymers (thermal conductivity and temperature of polymers. Temperature dependence of thermal conductivity. Amorphous polymers. Crystalline polymers. Changes in thermal conductivity in the phase transition area. Heat conductivity and molecular parameters (molecular weight, branchedness and chain structure). The effect of thermal conductivity. Temperature Dependence of temperature ward. Teteropulation and molecular parameters.
Thermal features of transitions and relaxation processes in polymers. Melting and crystallization. Transformations in glassy condition and intermediate transformations.
5. Thermophysical processes in the deformation of polymers.
Reversible deformations. Thermal expansion of polymers. Thermodynamics of reversible deformations. Thermoelasticity of solid polymers. Thermoelasticity of rubber.
6. Reasonable deformations.
Orientation extracts of polymers. Destruction of polymers. Power softening of filled rubber.
6.2. Topics of abstracts
1. Structural features of polysaccharides.
2. Electrification of polysaccharide nanofolocon and non-woven materials.
3. Matriches and scaffolds from polysaccharides and their derivatives.
4. The effect of polysaccharide additives on the properties of a maccapsul of pharmacological purpose.
5. The effect of polysaccharides of plant and animal origin on the speed of germination of seeds.
6. Polysaccharides in biologically active systems.
7. The use of polysaccharides in pharmacology and medicine.
8. Polysaccharides as medicinal funds.
9. Polysaccharides in the food industry.
10. Sorbents of polysaccharides and their derivatives.
11. Polysaccharide plastics.
12. Composite materials based on polysaccharides and their derivatives.
6.3. Questions to the study discussion №1 "T.ermomechanical properties of polymers "
Deformation properties. Deformation of amorphous polymers. Elastic deformation. Forced elasticity. The effect of various factors on the glass transition temperature of polymers. Deformation of crystalline polymers. Deformation curves. Features of deformation of the stretching and twisting of polymers.
6.4. Questions to the educational discussion №2 "Physical and mechanical properties of polymers"
Strength and destruction. Theoretical strength. The strength of real polymers. The durability of polymers. Journal equation: analysis and value. Thermoflutting theory and mechanism for the destruction of polymers. The effect of macromolecular structures on the mechanical properties of polymers. Methods of physical and mechanical testing of polymer fibers and plastic masses.
7. Educational and methodological and informational support of the discipline "Modern methods of research of polymers"
Main literature
And others. Technology of polymeric materials. Under total. ed. . St. Petersburg: Profession. 20c.
Fedusenko Connections: Tutorial. Saratov: Publishing House Saratovsk. un-ta. 20c.
Methods for the allocation and properties of natural polysaccharides:Studies. benefit. Saratov: Publishing House "Cube". 20c.
additional literature
Henke H. Liquid chromatography / trans. with it. . Ed. . M.: Technosphere. 20c.
Scientific bases of chemical carbohydrate technology / ed. . M.: Publishing House. 20c.
Schmidt V. Optical spectroscopy for chemists and biologists. Per. from English . Ed. . M.: Technosphere. 20c.
Software and Internet resources
Programs Microsoft. Office 2007, with Hemdraw
Averco, bikmullin study of the structure and properties of polymers: studies. benefit. Kazan: KSTU. 20c.
http: // www. Himi. ***** / BGL / 8112.HTML
http: // download. ***** / NEHUDLIT / SELF0014 / AVERKO-ANTONOVICH. RAR
Shestakov Polymer research methods: educational and methods. benefit. Voronezh: VSU. 20c.
http: // window. ***** / WINDOW / CATALOG? p_rid \u003d 27245.
http: // www. / File / 149127 /
Annual methods of research of polymers. M.: Chemistry.http: // www. / File / 146637 /
Ageevat. BUT. Thermomechanical method of study of polymers: Methodology. Instructions to the laboratory workshop in chemistry and physics of polymers. Ivanovo: GOU VPO Ivan. State Him.-tehnol. un-t. 20c.
http: // www. ***** / E-LIB / NODE / 174
http: // window. ***** / WINDOW / CATALOG? p_rid \u003d 71432.
8. Material and technical support of the discipline "Modern methods of research of polymers"
1. A learning audience for lectures.
2. Overhead projector for demonstrating an illustration material.
3. Training laboratories №32 and 38 to perform laboratory work equipped with the necessary equipment
4. Samples of polymers, solvents and other chemical reagents.
5. Chemical dishes.
6. Personal computer.
7. Educational and methodological development for the study of theoretical material, preparation for practical work and reports on them.
8. Cathedral library.
The program is drawn up in accordance with the requirements of GEF VPO, taking into account the recommendations of the OOP HPE in the direction of preparation of 020100 - "Chemistry", the training profile "High molecular compounds".
h.N., head. Base department of polymers
The program is approved at the meeting of the base department of polymers
from "___" "______________" 20___, Protocol No. ____.
Head Base Department
Director of the Institute of Chemistry
Plastics products are made from various materials using a variety of technologies. It is almost impossible to identify material based on visual assessment or data of simple mechanical testing. In this case, there are many reasons that encourage identify the polymer. One of the most common is the desire to establish which material made a competing product. In addition, the defective products returned by the manufacturer often require reliable determination of their origin. Sometimes it is necessary to check whether the stated material is really used. The manufacturer of materials from secondary raw materials is also needed to determine which material it receives from various sources. Quite often, large amounts of raw materials with a lost identification mark fall into the processing, or in the warehouse material without proper label. In all these cases, even initial knowledge of the methods of identifying polymers will help save time and money.
Sometimes the consumer of finished products may have a desire to check whether the material used is responsible to the stated polymer type, and in this case it is possible to carry out the simplest identification of the material. The creation of new materials also requires the development of identification methods.
There are two approaches to identifying polymeric materials. The first one is quite simple, is performed quickly and inexpensively. It requires a very simple toolkit and a very small volume of knowledge about polymers. The second method is based on the implementation of systematic chemical and thermal analysis. In this case, a complex experimental technique is used; This approach requires high time and money, and the interpretation of the results obtained is available only to a professional who is familiar with the chemistry of polymers.
Polymeric materials are often copolymers, mixtures, and their properties are modified by using various additives or mixing with components such as flame retardant additives, foaming agents, lubricants and stabilizers. In these cases, the simplest identification methods will not give satisfactory results. The only way to get the right results is to use complex chemical and thermal analysis methods.
The first of these approaches is based on the use of the consistent elimination of possible options using the simplest tests. It is presented in the identification system of polymers ( Plastics Identification Chart.) shown below.
There are several basic instructions that should be guided in order to simplify the identification of the polymer.
First of all, it is necessary to establish whether the test polymer is thermoplastic or refers to the class of thermosetting resins. This separation on the main types of polymers is enough to simply implement, applying a heated soldering iron or a hot wand at a temperature of about 500 ºF. If the material softens, then this is a thermoplastic. If not, then - reactoplastic (thermosetting resin).
The next step is a burning test. To ignite the samples, it is desirable to use the Bunzen burner, which gives a colorless flame. Instead, you can use just a lighter. However, it is necessary to divide the smell from burning gas in the burner and the smell, formed during the combustion of the polymer. Before starting the burning tests, it is recommended to cook the next questionnaire to which it will be necessary to respond according to the test results.
Is it burning?
What is the color of the flame?
How smells burning material?
Are drops formed when burning the material?
Type and color of the formed smoke?
Is smoking at the process of burning?
Is the material by self-fighting or continues to burn after removing the source of the flame?
Does the burning happen quickly or slowly?
In order to identify the material, compare your observations with the estimates given in the polymer identification system. The reliability of the results obtained can be significantly improved if there is parallel tests of the known material. When implementing the procedure for identifying polymers, one should not forget about the compliance of safety regulations. Drops falling from a burning sample can be very hot and easily adhere to any surface. After the sample is walked, very carefully remove the smoke. Some plastics, such as polyacetals, form a toxic formaldehyde during combustion, which, inhaling the inhalation path, causes a burning sensation.
The results of the above-mentioned polymer tests described above should be further confirmed by the following tests:
determining the melting point;
solubility assessment;
test with copper wire;
measuring specific gravity.
Definition of melting point
A number of methods for determining the melting point of polymers are known.
In the first of them, Fischer-Jones is used. This method is most widely used now.
The device consists of a heating unit, the temperature in which is controlled by a rheostat, thermometer and a magnifying lens. A small granule or pinch of the polymer is placed in an electrically heated block together with several drops of silicone fluid. The sample is covered with coating glass, and the temperature gradually rises until the polymer is melted or does not soften enough so that it can be easily deformed.
Menisk formed by silicone fluid is clearly visible through a magnifying glass. The temperature in which the displacement of the meniscus occurs per melting point. The expected accuracy of the method is ± 5 ° F compared to literature data.
This method is applicable to both crystalline and amorphous polymers. For any crystalline polymers, the melting point is expressed sharply enough, so the transition is fixed very easily. Amorphous polymers, on the contrary, soften in a wide range of temperatures, which makes it difficult to determine their melting point.
The second method known as the method of the koflar method is used only for partially crystalline polymers. In this method, the sample is placed on the heated subject table of the microscope, and the polymer is considered through crossed polaroids. When the polymer melts, the characteristic double beamplan is disappeared due to the presence of crystalline formations. The temperature in which the double bemprane (usually in the form of all the rainbow colors) completely disappears, is taken as the melting point.
Solubility definition
The ratio of the polymer to one or another solvent often indicates the type of material. The solubility data that can be found in the literature is too common, and, therefore, they are quite difficult to apply in specific conditions. Partial solubility of some polymers in various solvents, as well as a high concentration of various additives, such as plasticizers, also make it difficult to identify the polymer by its solubility. Nevertheless, the solubility test may be very useful for establishing the difference between different derivatives of the same base polymer.
For example, this method can be distinguished by cellulose acetate from cellulose acetate-butirate, since the acetate is completely soluble in the furfuryl alcohol, and only partially dissolve butirate. Similarly, you can identify various types of polyamides and polystyrene.
Solubility test is most conveniently carried out by placing a small amount of polymer into the tube. Then the solvent is added to this tube and the tube shakes. For complete dissolution, it is sometimes necessary to quite significantly. .
Testing copper wire.
The presence of chlorine in the polymer, such as in polyvinyl chloride, can be easily installed with a copper wire. The tip of the wire heats up in flame to red. Conducting heated wire on the sample surface, you can capture a small amount of polymer. Next, the tip of the wire with polymers is again placed in the flame. If the flame is painted in green, this indicates the presence of chlorine atoms in the material.
Similarly, the presence of fluorine atoms in fluorinated hydrocarbons is proved.
Modern identification methods
As mentioned earlier, the complete and reliable identification of the polymer material is a complex and complex task that requires a long time and based on a deep understanding of analytical chemistry, experience and use of modern equipment. Polymeric materials are often copolymers, mixtures and contain various additives. The material modification changes its fundamental characteristics used to identify, such as the color of smoke and smell, which makes the simple identification methods not applicable. Moreover, very small amounts of material are often available, so the identification of the polymer becomes possible only on the basis of the use of modern methods described below in this chapter. Only a few milligrams of the substance are necessary in order to carry out research by methods of spectroscopy, thermal analysis, microscopy or chromatography.
To identify polymers and additives contained in compositions based on them, the following modern analytical methods are used:
Fourier infrared and infrared spectroscopy in the near region of the spectrum (F-X, B-X);
thermogravimetric analysis (THF);
differential scanning calorimetry (DSC);
thermomechanical analysis (TMA);
nuclear magnetic resonance spectroscopy (NMR);
chromatography;
mass spectroscopy;
x-ray structural analysis;
microscopy.
A list of modern methods used to identify polymers and adding additives contained in the table.
|
Method |
Region applications |
| Liquid chromatography | Distribution of macromolecules in size |
| Gel-penetrating chromotigraphia | Studies of mixtures, phosphorites, plasticizers, lubricants |
| Gas chromotigraphia |
Residual monomers Non-polymeric components Plasticizers |
| Infrared spectroscopy |
Type of polymer Nature additives |
| Thermal analysis |
Fillers Lubricants Molecular weight polymer |
| X-ray structural analysis |
Fillers Fireproof additives Stabilizers |
| Nuclear magnetic resonance |
Polyesters COLOSHORGANICAL CONNECTIONS Phenolic resins |
| Chemical analysis |
Lubricants Fireproof additives Catalysts |
Fourier infrared spectroscopy
Analysis based on the use of Fourier transform infrared spectrum is currently one of the most widely used both practitioners and scientists, methods for identifying polymers. Tests are that the flow of infrared radiation is directed to the sample, where it is partially absorbed, and partially passes through the material. The resulting infrared spectrum is the same individual reflection of the polymer as fingerprints. The results of the analysis are displayed in graphical form on the display. Since no two individual structures give completely identical spectra, the resulting spectrum is compared with well-known standards for previously studied materials, which allows you to unambiguously identify the analyzed polymer.
Fast infrared spectroscopy in the near region of the spectrum has become particularly popular lately. The sample is subjected to irradiation in the near infrared region lying in the wavelength range from 800 to 200 nm. Macromolecules absorb radiation in a different way, which ultimately gives a unique spectrum that allows you to identify the polymer studied. The spectrum measurement technology in the near infrared region is an inexpensive high-speed method, which has become an alternative method of Fourier infrared spectroscopy.
Thermogravimetric analysis
The thermogravimetric analysis method consists in measuring weight loss with a sample as it is continuous heating. The technique used to implement this method is quite simple. Typical equipment consists of analytical scales programmable electrically heated oven and recording device. This method is very useful for the study of polymers with various additives and fillers, the content of which is determined by weight. For example, the content of glass fibers and mineral fillers in the polymer can be determined by the complete combustion of the polymer in the inert atmosphere. The unlawful residue contains only glass and inert fillers.
The thermogravimetric analysis method is also used to identify ingredients in mixtures, which differ from the relative stability of the individual component.
Differential scanning calorimetry
According to the differential scanning calorimetry method, the amount of energy absorbed by the sample or separated from the sample is measured with a continuous increase or decrease in the temperature or when the material is shutter speed at a constant temperature. This method is one of the most effective ways to study melting, including the definition of glass transition, melting and crystallization temperatures, as well as thermal destruction temperatures. This method also gives useful information to determine the degree of crystalline crystallinity and crystallization kinetics. The use of the method of differential scanning calorimetry also allows you to judge the presence or absence of antioxidant in the polymer, since this affects the oxidative stability of the material. The method can also be used to determine the relative content of the component in mixtures, block and statistical copolymers, which affects the characteristics of the melting polymer.
The use of differential thermal analysis techniques also gives quantitative information about the content in the composition of various additives, such as fairy tales that contribute to the separation of the product from the form. Anti-static, ultraviolet radiation absorbers, impecker modifiers of material.
Consideration of typical thermograms makes it possible to judge the behavior of the material throughout the temperature range from the glass transition temperature to the degradation area, as well as about the changes occurring between these two extreme dots.
Thermomechanical analysis
Thermomechanical analysis is intended to determine the temperature dependence of the expansion or compression of the material, as well as for measuring the temperature dependences of the modulus of the elasticity and viscosity of the polymers. This method allows you to find a point of softening and characterize the viscoelastic properties of the material throughout the temperature range.
The implementation of the thermomechanical analysis method is very simple: it is carried out by an application of a constant load and measuring changes in the sample size in the vertical direction, and the experiment can be carried out both in the absence of external load and when the force is applied. The thermomechanical analysis method is very useful for the characteristics of the polymers: it allows you to accurately determine such physical properties of the material as the melting point, the glass transition temperature, the density of transverse strokes, the degree of crystallinity and the thermal expansion coefficient.
Nuclear magnetic resonance
The nuclear magnetic spectroscopy method is a powerful analytical method for identifying organic molecules and determine their structure. The nucleus of certain atoms in the molecule can be in various positions regarding the orientation of their back. If such a kernel is superimposed to impose a magnetic field, then the difference in the backs leads to the splitting of energy levels. Next, the molecule further affects the weak oscillating magnetic field. With some specific and accurately defined frequencies, the oscillation resonance occurs and this effect is registered and enhanced.
The method of nuclear magnetic resonance gives the complete characteristic of the structure of the chemical compound, as well as the reliable identification of ingredients in mixtures. This method allows you to determine the structure of functional groups that cannot be installed by other analytical methods.
In the study of polymers, the C13 atoms are most often used to identify the material. Determination of low molecular weight compounds, such as plasticizers, stabilizers, lubricants, are very easily and directly installed according to their NMR spectra.
Chromatography
Chromatography is an analytical method based on the separation of the mixture component, which pass at different speeds through the column filled with the same separating medium. Fixed material through which the mixture passes, is called a stationary phase and is usually a solid or gel. Moving medium (usually this is liquid, and sometimes gas) is called a movable phase. The mixture is dissolved in a solvent, called the eluent, and is pushed through a column or a set of columns. The separation of the component occurs due to the differences between the forces of the interatomic interactions between the molecules of the stationary phase, various separated components of the movable phase and eluent. As a result, individual components of the mixture are identified, and in some cases it can be determined quantitatively.
Both liquid and gas chromatography are used to identify substances. However, in the industry of polymeric materials, gel-penetrating chromatography received the greatest distribution.
Mass spectroscopy
Mass spectroscopy seems to be a very useful tool for obtaining detailed information on the structure of the polymer, and in this method, very small amounts of substance are used. The molecular weight of the polymer and the atomic structure of the compounds can be determined using spectral analysis. In combination with gas chromatography, mass spectroscopy, called chromato-mass spectroscopy, provides even greater identification capabilities than actually mass spectroscopy.
The analysis procedure is that the test substance is heated and placed in a vacuum chamber. The electron beam is affected by the pair, which ionizes either the molecule as a whole or its fragments. The formed ions are accelerated in the electric field, and when passing through the magnetic field, their movement lines are twisted, so that the direction of motion depends on the speed and the ratio of the mass to the charging. This eventually leads to a mass separation (electromagnetic separation). Due to the fact that the kinetic energy of larger ions is greater, they move along a longer arc compared to light ions, and this serves as a basic substance identification. On the outlet of the magnetic field, the ions are collected in traps.
X-ray analysis
X-ray structural analysis is used primarily for high-quality and quantitative identification of additives that are present in most polymer compositions, determining the presence of contaminants, as well as estimates of trace amounts of various elements in polymers and monomers.
For the implementation of X-ray analysis, the tools of two types are used - emission spectroscopy along the wavelength and by their energy.
Microscopy
Optical microscopy provides issues of obtaining information on surface morphology of samples, including the identification of pollution and analysis of the structure of mixtures and alloys. This technique is extremely useful for studying the structure of thin films.
Methods of optical microscopy include two class studies - scanning electron microscopy and translucent electron microscopy. In the latter case, a large allowing ability is achieved. The image can be obtained with an increase of more than 100,000 compared to the original.
The use of scanning electron microscopy is based on the fact that a well-focused beam moves along the surface, and the image with a high degree of resolution is created due to the scattering of secondary electrons from the surface of the sample. With translucent electron microscopy, the image is obtained by passing electrons through a specially prepared sample.
In modern cases, the most modern microscopy variants may also be used, in particular atomic force microscopy.
Study structure macromolecules Can be carried out by the following methods:
Chemical Methods involve the dismemberment of macromolecules to 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 the polymer to interact with the field of electromagnetic radiation, selectively absorbing energy at its particular area. At the same time, the energy state of such a macromolecule changes as a result of such intramolecular processes as electrons transitions, fluctuations in atomic nuclei, translational and rotational motion of the macromolecule as a whole. Absorption, UV, VI, IR spectroscopy and NMR, internal reflection spectroscopy are used.
6) viscomemetry.
7) Gelproof chromatography.
Research osm molecuular Structures can be carried out by the following methods:
1) light spectroscopy.
2) electron microscopy.
3) X-ray structural analysis
4) electronics.
Flexibility of polymers
Chain flexibility is a property characteristic only for polymers.
Flexibility - This is the ability of the macromolecule to change its conformation as a result of internal thermal motion or due to the action of external forces.
There are thermodynamic and kinetic flexibility.
Thermodynamic flexibility It 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 the rotary isomers ΔU. The smaller ΔU, the higher the probability of the transformation of the macromolecule from one conformation to another.
Thermodynamic flexibility is determined by the chemical structure of a repeating link and the conformation of the macromolecule, which also depends on the chemical structure.
Dienna Polymers:
CH 2 -C (R) \u003d CH-CH 2 - (R \u003d H, CH 3, CL)
characterized by high flexibility compared to vinyl row polymers:
CH 2 -CH- (R \u003d H, CH 3, CL, CN, C 6 H 5)
This is due to the fact that the difference between the energy of rotary isomers in the diene polymers is less than 100 times. Such a difference is associated with a decrease in exchange interactions (attraction-repulsion) between the CH 2 groups with a double bond group between them, which has a lower potential barrier. The same picture is observed for macromolecules containing Si-O or C-O bonds in the chain.
The nature of the substituents has a slight effect on thermodynamic flexibility.
However, if the polar substituents are located close to each other, their interaction reduces flexibility. The stringent are biopolymers, their stable spiral conformations are formed by hydrogen bonds.
Kinetic flexibility Reflects the transition rate of the macromolecule in the power field from one conformation with the energy U 1 to another with the energy U 2, and the activation barrier u 0 must be overcome.
Kinetic flexibility is estimated by the magnitude of the kinetic segment.
Kinetic segment - This is the part of the macromolecule, which responds to the external impact as a whole. Its value varies depending on the temperature and the rate of external influence.
Polymers consisting of links characterized by low values \u200b\u200bu 0 show high kinetic flexibility. These include:
1) carboards of unsaturated polymers and vinyl row polymers that do not contain functional groups - polybutadiene, polyisopene, polyethylene, polypropylene, polyisobutylene, etc.;
2) carbage polymers and copolymers with a rare arrangement of polar groups - polychloroprene, butadiene copolymers with styrene or nitrile of acrylic acid (the last content of up to 30-40%), etc.;
3) heteroacent polymers whose polar groups are separated by non-polar - aliphatic polyesters;
4) heteroacent polymers containing groups C-O, Si-O, Si-Si, S-S, etc.
The increase in the number of substituents, their volume, polarity, the asymmetry of the location reduces the kinetic flexibility.
CH 2 -CH 2 -; -CH 2 -CH-; -CH 2 -Che
If there is a double, kinetic flexibility next to the single bond increases. Polybutadiene and polyisoprene are flexible polymers that show flexibility at room and lower temperatures. Polyethylene and PVC show kinetic flexibility only at elevated temperatures.
In all cases, the temperature increase, increasing the kinetic energy of the macromolecule, increases the likelihood of overcoming the activation barrier and increases the kinetic flexibility.
The speed of external influence has a great influence on kinetic flexibility. Due to the large length of the macromolecule and intermolecular interaction for transition from one conformation to another, a certain time is necessary. The transition time depends on the structure of the macromolecule: the higher the level of the interaction, the more it is required to change the conformation.
If the time of force is larger than the transition time from one conformation to another, the kinetic flexibility is high. With very fast deformation, even a thermodynamically flexible macromolecule behaves like a tough.
Kinetic flexibility can be estimated by glass transition temperatures T C and fluidity t t.
Fiberglass temperature - This is the lower temperature limit for flexibility. With T.<Т from Polymer under any circumstances is not 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 polymer flexibility in a condensed state.
Temperature flow - This is the upper temperature limit of the change in conformations as a result of the inhibited rotation around the single bonds without changing the center of gravity of the macromolecule. With T\u003e t t, there is already a movement of individual segments, which causes the movement of the center of gravity of the entire macromolecule, i.e. Its current. The higher the ΔT \u003d T t. C, the higher the kinetic flexibility of the polymer in the condensed state.
Temperation and fiberglass temperature depend on the deformation mode, in particular, from its speed. With an increase in the speed (frequency) of mechanical exposure, both T C and T T, and the temperature range of the kinetic flexibility shifts towards higher temperatures.
Under the same external effects, the kinetic flexibility of polymers does not depend on the molecular weight of the macromolecule, since the activation barrier is determined only by the interaction of the neighbor. With increasing M increases the number of segments.
T C with the growth of m first grows, and then with a certain value of the M CR becomes constant. M cr matches M segment. For thermodynamically flexible polymers, the Mr CD is several thousand: polybutadiene - 1000, PVC - 12000; polyisobutylene - 1000; Polystyrene - 40000. Therefore, for polymers with a molecular weight of 100,000-1 million tons with practically independent of M.
To implement conformational transitions, it is necessary to overcome not only the potential barrier of rotation U 0, but also intermolecular interaction. Its level is determined not only by the chemical structure of the macromolecule, but also an ozm molecular structure. Thus, kinetic flexibility depends on the structure of the polymer at molecular and supemolecular levels.
Macromolecules in amorphous state are expressing greater flexibility than in crystalline. The crystalline state due to the dense packaging of macromolecules and far order in their location is characterized by an extremely high level of intermolecular interaction. Therefore, macromolecules of flexible polymers (polybutadiene, polychloroprene, polyethylene, etc.) in the crystalline state behave as tough not capable of changing the conformation. In the oriented state, the flexibility of polymers is also reduced, since when orientation occurs rapprochement of the chains and an increase in the density of the packaging. This increases the likelihood of the formation of additional nodes between the chains. This is especially characteristic of polymers with functional groups. Example: Cellulose and its derivatives. These polymers are characterized by medium thermodynamic flexibility, and in an oriented state, do not change the conformation under any conditions (t from above the decomposition temperature).
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lG M \u003d C1 - C.2 V.r. + S.3 V.2r. + (16).
Determination of distribution by the volume of eluent with (V.r.) and calibration curve V.r.(M) Allows you to easily obtain an integral and differential molecular weight distribution:
Vr.(M.)
F.w. (M.) F.(V.r. )from(V.r. )dVr.
f.w.dM.1 (17),
V.r. ( M.1 )
where M1 is the molecular weight of the lowest molecular weight component.
Those, the transition from the integral distribution by the volume of eluent F (V.r.) to integral distribution F (M) comes down to replacing the abscissa axis (V.r.) On the LGM axis by the LG M \u003d C1 - C2VR equation.
So The calibration procedure consists in consistent chromatography of standards and determining the retained volumes V. r. Maxims of peaks. Obtained for each standard V. r. Applicit LGPIKA \u003d F ( V. r. ) and combine the smooth line, which is a calibration curve, which is further used in the analysis of polymers with an unknown molecular weight.
Diluted solutions
The behavior of macromolecules in solution significantly depends on the thermodynamic quality of the solvent, the molecular weight of the polymer and the temperature of the solution. The change in these parameters affects the size and form of macromolecular balls, which leads to a change in the hydrodynamic properties of dilute polymers solutions. The main source of information about the molecular characteristics of polymers is to study their properties in dilute solutions by molecular optics and hydrodynamics. First of all, it static and dynamic methods light scattering, the use of which allows you to define mm, sizes I. conformation of dissolved objects. It should be noted that the use of these methods is particularly productive in the study of the properties of polymeric supramolecular structures, since it provides information about the system, unaffected by external influences. Another absolute method -
sedimentation-diffusion analysisallows you to reliably measure constants sedimentation S. and progressive diffusion coefficients D. In the region of strong dilution of polymeric solutions. The values \u200b\u200bobtained enable identify MM. and hydrodynamic radius R.h. The studied polymers.
Method of light scattering
The principle of the method of light scattering.The lighting method is based on the effect of scattering part of the light passing through the liquid medium. This scattering is due to the presence of density fluctuations and a substance concentration in a separate volume of the solution that exist due to a thermal motion. The difference in densities leads to the appearance of differences in refractive indices. Light passing through a liquid medium is refracted at the boundaries of areas with different density, deviates from the initial direction, i.e. scattered. Scattering the larger than the more fluctuation. If the medium is a solution of a polymer, then, in addition to the solvent density fluctuations, the polymer concentration fluctuations are located. These fluctuations are the more intense than less osmotic pressure inside the sections with a greater concentration, i.e. The larger mm dissolved substance.
The main use was obtained by methods based on measuring the intensity of light, scattered by solutions of polymers, and its angular dependence. Methods are distinguished static light scattering (elastic) or dynamic(quasisohibry) scattering. The main difference is the method measurement of the intensity of scattered light.
For elastic, or Rayleigh scattering Falling and scattered light have the same wavelength. As a result of the movement of the scattering centers, the scattered light ceases to be monochromatic, and instead of one line there is a Ralea peak. In this case, the total intensity averaged total intensity is measured as a function of the scattering angle. Using static light scattering, you can determine the mass and characteristic linear particle size in some systems.
For inelastic scattering The frequency of scattered light differs from the frequency of the falling light. In the method dynamic scattering Light is measured changing the intensity of time scattering. Where did the diffusion coefficients of the particles, the particle size and distribution of size are determined.
Ralea When studying the simplest case of scattering in the perfect low density gas in 1871, he proposed the theory of static (elastic) scattering. He considered scattering light by spherical dielectric particles with a diameter d., many smaller wavelengths l falling light ( d. < ? 20), и с коэффициентом преломления, близким к единице. В отсутствие поглощения и при использовании неполяризованного света rayleigh Equation It has the following form:
Molecular Theory of Light Scattering Liquids Designed Einstein. Considering scattering as a result of thermal fluctuations density, it received a liquid turbidity equation:
Debaapplicated Einstein theory to solutions of polymers. IN dilute solutions of polymers (with< 0.5 г/дл) рассеивающими центрами являются полимерные клубки. Если молекулярные клубки малы (h. 2 1 2 400 a) compared with the wavelength of the incident light (i.e. is 0.05 + 0.1 l.), the intensity of the scattered light does not depend on the angle of light scattering and the angular dependence - the ball (Fig. 1). In this case, the Debye equation is true.
Inqurement of refractive index, R.and - The number of Rayleigh or the scattering coefficient associated with the turbidity of the solution.
Substituting a debt expression to the equation for osmotic pressure
the value of the second virial coefficient (Fig. 1, a).
a B. Fig. one. The dissectivity of the scattered light does not depend on the angle of scattering (a);
concentration dependences of the inverse intensity of scattered light COP / R. = 90 for polystyreters obtained by the transmission reaction with tris- (pentafluorophenyl) by german with different molecular weight [(C6F5) 3GEH] \u003d 0.02 mol / l ( 1) and [(C6F5) 3GEH] \u003d 0.005 mol / l ( 2 ) in chloroform from concentration (b)
To determine mm polymers, the size of macromolecules of which is small compared to the wavelength (less l / 20), it is sufficient to find the value of the relative excess scattering at an angle of 90. Found by the method of light scattering MM corresponds to the average average value. All the above refers to small particles (compared with the wavelength of the falling light). With increasing dimensions, the patterns of light scattering change, the spherical asymmetry of the intensity of the scattered light appears, the degree of its polarity changes. Differences in scattering on small and large particles (? L / 20) can be demonstrated using vector diagrams (Fig. 2).
Fig. 2.MI diagrams for 0 small (a) and large (b) particles. The shaded part corresponds to the degree of polarization of the scattered light.
For large macromolecules, the intensity of the scattered light is spherically unshakened. This is due to the fact that electromagnetic oscillations that are excited by the macromolecule removed from each other are not phase. The difference between the phases of the waves of two induced dipoles turns out to be the greater the greater the size of the macromolecules and the greater the scattering angle and (Fig. 3).
In the direction of the primary light beam, the phase difference is zero, and in the opposite direction - the largest. The angular dependence of the intensity of the scattered light is an indication of scattering - used to determine the size and forms of macromolecules in solutions. In this regard, the Debye equation introduces the internal interference factor (or form factor - P.and): Sweet that will be searched
Fig. 3.Macromolecule light scattering
For macromolecules of any form P.and \u003d 1 and \u003d 0 s. With increasing and Value P.and decreases. The form factor is associated with the radius of inertia and depends on the shape of the particles (spheres, cylinders, thin sticks, etc.) in accordance with the Zimma equationform factor for particle with configuration of statistical tangle is equal:
1R 1 (8 2 9 2)h. 2 SIN 2 (/ 2) (26),
where h. 2 The average square of the distance between the ends of the polymer chain.
Substituting the equation (26) in (25) we get:
The average square of the distance between the edges of the polymer chain, determined from the equation (28) is z. - average value. Knowing h. 2 ,
h.2 6r. 2 (29).
To determine mm and other parameters of large molecules when the angular asymmetry of light scattering is observed, usually used double extrapolation technique(or the method of winter).
Winter showed that dependencies:
- Kc.R.from from, for and \u003d. const;
- Kc. R.from sin2 ( and 2), for from = const.;
- Kc.R.c. 0 from sIN2 (and / 2) and Kc.R.c. 0 from from represent straight lines.
Those. Direct, described by equations (30) and (31), cut off on the axis of the ordinate segment equal to 1 / M.w.. The magnitude of the corresponding angular coefficients can be found values A.2 and h. 2. The described extrapolation can be graphically portrayed on one diagram called diagram Zamma.(Fig. 4) representing addiction Kc.R.from (100from2 + sin (and / 2). To obtain this diagram, light scattering with a solution of one concentration at different angles is measured and, build a graph of dependencies in the fig. 4 coordinates, extrapolating the following dependence and \u003d. 0. Then receive a series of such dependencies for different concentrations. Across the points corresponding to one corner and different concentrations conduct lines that then extrapolate to from\u003d 0. Lines appropriate and= 0 and from= 0, intersect at one point (B), cutting off on the axis of the ordinate cut, according to which the average mmm polymer is found. From the tilt of the BS0 line at C \u003d 0, it is possible to determine the inertia radius of the macromolecule, and from the tilt line Bi0 at and \u003d 0 is the second virial coefficient.
Fig. four.General view of the diagram of the winter
Prerequisite for the use of light scattering methodsfor studying polymer solutions is the absence of multiple scattering, i.e. Each photon of incident radiation should experience interaction with only one polymer molecule in solution. This is achieved by the corresponding dilution of the system and a decrease in the volume of the sample under study.
Recently, the so-called "transport" methods based on the study of macroscopic transposher substance in a liquid medium under the action of external force were widely developed to determine the molecular weight characteristics. The basis of these methods is the dependence of the transport mobility of macromolecules from their molecular weight. These methods include sedimentation diffusion, electrophoresis I. chromatographic separationmacromolecules.
Selection and diffusion
Diffusiondirectly related to the mobility of molecules, consequently, its speed should depend on their size. Quantitative connection between diffusion coefficient D. and the dimension of the diffusing particle was obtained by Einstein:
This equation is valid for diffusing colloid particles, and for molecules. If the molecule has a spherical shape, then its volume V. 4 r.3 .
Multiplying this amount to density d., we obtain a mass of the molecule, and when multiplying the number of Avogadro N.A., we get a lot of 1 pray, i.e.
Expressing r. From the Einstein equation (32), and substituting it into equation (33), we obtain an expression for the molecular weight of a spherical molecule.
the ratio of the diffusion coefficients of spherical and non-souched particles moving at the same speed.
All existing equations of unfair for diffusion of macromolecules, and currently there is no equation that binds the coefficient of translational diffusion of macromolecules with their mm. Therefore, mm is calculated from empirical ratios. For this, the coefficient of translational diffusion of macromolecules is determined using second law fika:
Methods for determining the diffusion coefficient are based on measuring the breaking speed of the boundary between the solution of the polymer studied and the solvent. Distribution of concentration and gradient dCdX.near the border At various times, observation is expressed by the curves shown in Figure 5. DC DISTRIBUTIONdX.has a kind of a Gaussian curve with a maximum on The boundary between solution and solvent (x \u003d 0). It is described by the Wiener equation, obtained by the integration of the second law of the fic at certain assumptions:
where from0 - concentration of solution, g / cm3; t. - time from the beginning of the diffusion, C; x. - distance of the gradient under consideration from the border.
Fig. five.Concentration distribution curves (A), concentration gradient (b) playing refractive index (B)
For registration, usually use optical methods, for example, determine the refractive factor n. Solution and its gradient dN.dX.along Diffusion directions.
For working concentrations (0.5 g / ml) used in this method, the gradient of the refractive index is directly proportional to the concentration gradient:
After integrating equation (37) in the range of n.0 BE n.1 (Where n.0 and n.1 - Indicators of the refraction of the solvent and mortar) we get:
The distribution of the refractive index gradient is also expressed by a Gaussian curve (Fig. 5, B).
The simplest method of calculation is method of maximum ordinatewhich responds x. \u003d 0. In this expression x.2 4Dt. In equation (39), it turns to zero, and this equation is simplified:
Sedimentation method.As known, knowing the particle sedimentation speed determine their dimensions. The molecules in the centrifugal field occurs in the direction perpendicular to the axis of rotation. When settling the molecule (volume v.) Under the action of centrifugal force, its distance from the rotation axis is constantly changing ( x.). At the same time, the centrifugal force depends on the angular velocity of the centrifuge ( w.2 x.). The resistance force is expressed by the Stokes law (for spherical particles):
The diffusion coefficient is determined as shown in the diffusion method. The sedimentation constant is determined by ultracentrifuga. To do this, through a cuvette with a polymer solution, a light beam placed in an ultracentrifuge passes a beam that falls on a photoflastic for a cuvette. When the cuvette rotates, as the substance is precipitated, the boundary of the section between the solution and the solvent is gradually moved, and the light is absorbed in the height of the cuvette to varying degrees. On the photoplastic, strips of varying degrees of blackening are obtained. Photometrishing pictures made at certain intervals, you can get a sedimentation curve, i.e. The concentration gradient distribution curve along the height of the cuvette at different times.
Addiction lNX. from t. Must be expressed by the straight, on the angle of tilt which you can calculate the sedimentation coefficient S..
To exclude concentration effects find a value S.0 , extrapolating quantity S. on infinite dilution (i.e. building a graph of dependence 1 S F.(c.) ). Knowing values S.0 and D.0 find molecular weight Polymer according to formula (44).
The method of sedimentation in ultracentrifuge is an absolute method for measuring the molecular weight of the polymer, since It does not have any assumptions about the conformations of the macromolecule.
In combination, methods of light scattering, viscomemetry and sedimentation-diffusion analysis can provide complete information about the hydrodynamic and conformational properties of macromolecules in the solution, which is especially important for super-refundable polymers. Molecular hydrodynamic methods and optics in dilute solutions in chloroform were investigated by two series of superband copolymers of various topological structures based on perfluorinated hydrides of Germany (FG and DG). Variating the amount of DG, and its sequence of administration into the monomer mixture during the synthesis was obtained by polymers with different architectures. The first series is copolymers of various molecular weight (from 2.3 · 104 to 31 · 104) with rigid linear chains between branching points and different numbers of branching points in the cascades of a dendritic fragment, the second - copolymers, which, with a close degree of branching, they have more "loose" Structure for
the account of a larger number of linear links on the periphery of macromolecules with a molecular weight of 2.5 · 104 to 23 · 104 (Fig. 6).
Fig. 6.The schematic structure (CO) of tris- (pentafluorophenyl) polymers Herman Ebis- (pentafluorophenyl) Hermann of various architectures: copolymers with rigid linear chains between branching points and different numbers of branching points in cascades of a dendritic fragment (a), copolymers that are closely The branchings on average have a more "loose" structure due to a larger number of linear links on the peruphors of the macromolecules (b) and the superband perfluorine polyphenylenegerman (B).
The studied copolymers have very low characteristic viscosity. Values \u200b\u200bvary from 1.5 to 5 cm3 / g with an increase in mm from 1.4 · 104 to 25 · 104. For super-reflective polymers with flexible chains between branch points at such mm, it is usually possible in the range from 3 to 50 cm3 / g. Low values \u200b\u200bfor CO-PFG unequivocally indicate the compact dimensions of their macromolecules, on the high density of the polymer substance in the amount they are in the solution. In accordance with the Einstein ratio for a solid spherical particle SF \u003d 2.5 v. . Substituting, the value of the partial specific volume for CO-PFG, we have a PF 1.3 cm3 / g, which is somewhat less than the characteristic viscosity for the lowest molecular weight polymer - PFG (Table 1) obtained in the absence of bis- (pentafluorophenyl) German. Accordingly, it can be assumed that the form of its macromolecules is very slightly different from spherical. From Table 1 it can be seen that for PFG ratio / SF 1.2. Such a low value / SF is characteristic of dendrimers than for super-refundable polymers. For the latest usual / SF 1.5.
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Molecular mass |
hydrodynamic |
characteristics |
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superradicant copolymers based on FG and DG |
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M.SD. ·10 |
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R., nM |
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erg / hail / mol1 / 3 |
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According to the data obtained, it can be concluded that the macromolecules of the first series (Fig. 6, a) are characterized by a slightly more compact dimensions and a smaller form asymmetry compared to the second series molecules (Fig. 6, b). It is probably due to the fact that the copolymers of the first series have in their composition a dimer chain from the DG links to which "rolled" branched blocks, such molecules are tougher and in shape resemble a weakened ellipsoid, unlike the super-refined macromolecules of the second series for which it is characteristic The presence of a rigid spherical nucleus with a focal point -GE (C6F5) 3 and branches from DG and FG links, which ensures a generally more loose structure compared to super-refined PFG
So The molecular hydrodynamic methods and optics are shown that the macromolecules of the studied polymers have compact dimensions and are characterized by a high density of the polymer substance, and the asymmetry of their form is low. According to these characteristics, they are approaching dendrimems. With a fixed molecular weight, the copolymers with the "loose" structure are characterized by large sizes of macromolecules and higher characteristic viscosity values.
Concentrated solutions of polymers
Concentrated are solutions in which the molecules of the dissolved substance interact with each other. Interest in the rheological properties of such solutions is primarily due to the technology of polymers processing, many of which are processed through solutions and melts.
Consider features mechanical properties of polymers, located in fluid condition.Under polymers, located in Teaching (or viscous) state usually refer to the concentrated solutions of polymers, the melts of crystallizing polymers and amorphous polymers in such deformation modes and at such temperatures, when the deformation of the viscous flow is played in full deformation, i.e. irreversible component of complete deformation.
In addition to the main methods of thermomechanical research, for fluid polymers, we use a specific method consisting in measuring stresses in the constant deformation speed mode. Although, in principle, the constant deformation rate can also be carried out in mechanical tests of solid and highly elastic polymers, only for fluid polymeric systems, this method is crucial, because Only for them, complete deformation may be unlimitedly high and therefore monitoring the development of voltage in the constant deformation speed mode can be completed by the achievement of the steady flow mode. This flow regimen corresponds to its characteristic values \u200b\u200bof voltage and accumulated and persisting in the material of highly elastic deformation; The further development of deformation occurs only through a viscous course when the condition of the material does not change over time.
The viscosity of polymers depends on mm, temperature, pressure, as well as from the deformation mode (deformation and voltage velocity). For the overwhelming majority of polymeric systems, the effect of viscosity anomaly effect is characterized by the effect of viscosity anomaly, which consists in reducing efficient viscosity as the shear stress increases. When stretching, on the contrary, as the deformation and voltage rate increases, the longitudinal viscosity increases. The viscosity of polymers largely depends on temperature. For the high temperature range far from the temperature of the polymer, the viscosity curve on temperature is described by exponential addiction, which characterizes the amount of free energy activation of viscous flow U.. As MM increases, the activation energy becomes independent of MM, i.e. As the molecules lengthen the molecules, there is a segmental nature during the flow (for the implementation of a single flow act, only part of the molecule is required). Activation energy linear polymers Depends on the structure of the elementary link, increasing as the rigidity of the chain increases. Despite the fact that the mechanism and implementation of the elementary act of flow do not depend on the length of the macromolecule as a whole, the absolute viscosity values \u200b\u200bare significantly dependent on MM, since for irreversible movement of macromolecules it is necessary that the center of gravity of the macromolecule occurred through the independent movements of individual segments. The higher mm, the greater the number of agreed movements should occur in order to shift the center of gravity of the macromolecule. It follows that the dependence of viscosity from MM is folded from two sites. The first is the region of low MM values, where the viscosity is proportional to mm and the second section, this is the area where mm has a significant effect on viscosity and the condition begins to be performed. M.3.5 .
The appearance of highly elastic deformations is possible in polymers not only in highly elastic, but also viscous condition. Their development in both cases is due to the same mechanism - deviation
For high molecular weight polymers, the highlylastic module increases significantly as MMP expands.
Just as in polymers in highly elastic state, in fluid polymers, especially containing 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 increased mobility macromolecules, the process of thixotropic recovery proceeds faster than for polymers in highly elastic state.
The study of the viscoelastic properties of concentrated solutions is necessary to obtain valuable information on their structure, which is a spatial fluctuation grid formed by tightly packaged aggregates, or macromolecule associates, inside which are solvent molecules.
If we consider polymers of complex architecture, for example, ultra-standard polymers and dendrimers, then from the point of view of general problems of rheology, the spherical structure of the macromolecules allows them to consider them, on the one hand, as polymers, and on the other, as colloid dispersion.
Detailed studies of the rheological properties of the branched structural polymers in the block has now been practically not carried out, although it is precisely a detailed study of the viscoelastic properties of these polymers free of solvents, can provide useful information on the specifics of their behavior during the course of colloidal particles with flexible macromolecular fragments. To date, the main studies of the rheological (mainly viscous) properties were performed for diluted solutions of dendrimers in order to identify their molecular structure. In one of the works (Hawker C.J. with employees) devoted to the study of the rheological properties of dendrimers in the melt, an unusual dependence of viscosity from MM was discovered on the example of dendritic polyester. For lower generations of dendrimers, the indicator of the power dependence of viscosity from MM is significantly larger than the unit, and then when the mm is reached, this dependence becomes linear. The flow curves of dendrimers of different polybenzyl ether generations are newtonian character in a wide range of shear rates (0.1-100 C-1), which is uncharacteristic for polymers. Another situation takes place for the generations of polyamidoamine dendrimers: at temperatures that slightly different from the glass transition temperature, a decrease in dynamic viscosity is observed with an increase in the shift frequency (Wang H.).
The nature of the flow of dendrimers and super-refundable polymers depends on the nature of the end groups. Thus, the modification of polypropylenemy dendrimers amino and cyano groups led to an increase in viscosity while maintaining the Newtonian melt behavior. Tande B.M. With co-authors, it was also shown that the viscosity of the initial polypropylene dendrimers of the fourth and fifth generations is constant in a wide range of shear rates. At the same time, for these dendrimers modified with methyl and benzylcrylate, viscosity anomaly is observed. These results demonstrate an important impact of end groups on the rheological properties of the melts of dendrimers. It would be possible to believe that at temperatures above the glassware, it is already possible for dendrimers. However, the authors Smirnova N.N. and Tereshchenko A.S. Employees have established that for carbosilane dendrimers of high generations, in addition to glass, the second, high-temperature transition is observed. It was detected by the adiabatic high-resolution calorimetry method, which was associated with the nature of intermolecular contacts in the dendrimeters. With the aim of a detailed study of the nature of the high-temperature transition and the possible effect on this transition of end groups of dendrimers in a wide temperature range, viscoelastic properties of derivatives of carbosilane dendrimer were studied, differing in the type of terminal groups (Mironova M.V. et al.). It was shown that carbosilane dendrimers of high generations are able to form an ozm molecuular structure in the form of a physical grid of intermolecular contacts. The mesh destruction can be initiated by the shear deformation and temperature. The high-temperature transition in carbosilane dendrimeters of high generations caused by the destruction of the physical grid has a relaxation nature. It is determined by the specific intermolecular interaction of end groups of dendrimers and depends on their mobility. The presence of short siloxane substituents leads to the emergence of highly elastic properties above the fiber area, while the introduction of less flexible carbosilane and butyl substituents contributes to the manifestation of typical "polymer" properties. Thus, forming one or another type of surface layer of the molecular structure of the initial dendrimers, you can adjust their viscoelastic properties overwhered.
4. Methods for the study of the physicochemical and mechanical properties of polymeric materials
The chemical structure of polymers, i.e. Its chemical composition and method of connecting atoms in the macromolecule does not define the definite behavior of the 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 the polymer material from its structure. Here include: methods of thermal analysis (measurement of heat capacity, transition temperatures, differential thermal analysis), probe methods (thermodynamic parameters of the interaction of organic substances with polymers: solubility coefficients, sorption enthalpy, partial mole mixture enthalpies, solubility parameter, determination of the size of free volume in polymers etc.), mechanical (measurement of strength, deformation and relaxation properties), electrical (dielectric constant, dielectric losses) and dilatometric methods. Consider some of the listed methods.
4.1 Methods of thermal analysis of polymers
The thermal analysis methods include methods for which the properties of polymers can estimate during a change in temperature (cooling or heating). The most common is differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA).
Differential scanning calorimetry.This method is based on measure the difference in thermal flows coming from the test sample and sample comparison, which are formed as a result of changes in the physical or chemical properties of the material under study. The information obtained allows to determine the nature of the occurring processes and characterize the properties of the polymer material. The difference in thermal flows occurs due to such thermal effects as melting, crystallization, chemical reactions, polymorphic transformations, evaporation, etc. As a result, a specific heat capacity and heat capacity changes can be determined, for example during the glass transition of the polymer.
Thermogravimetric analysis.This is a method, which is based on permanent weighing of the sample, depending on the temperature at a constant heating rate, depending on the time. It allows using small amounts of substance, obtain information about the kinetics and the mechanism of the destruction of the polymer, its heat resistance, solid-phase reactions,
and also determine moisture, the content of residual materials in the polymer (monomer, solvent, filler), study the processes of sorption and composition of composite polymer materials. If you connect an IR Fourier or mass spectrometer to the TGA-analyzer, then the analysis of the excreted gases will give complete information about the mechanism of complex thermochemical processes, which go to the polymer with increasing temperature.
Dynamic mechanical analysisused for research dependencies of mechanical and viscoelastic properties (shear, stretching, compression, three-point and console bend) of polymeric materials from temperature, time and frequency when exposed to periodic loads. In detail, this method of analysis will be considered in section 4.3.
Currently, the modernization of methods of thermal analysis has led
to the appearance of modular systems with unique technical characteristics, unifying DMA, DSC and TGA methods. This allows you to simultaneously determine the various characteristics of the 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 on molecular rearring and arising structures in the material. This is exactly what opens up new opportunities to optimize the choice of polymer material and processing process, quality control, analysis of the destruction of the polymer, studying the reactions of stitching polymers, gelation, etc.
4.2 Transport and diffusion methods (probe methods)
The area of \u200b\u200bpractical use of polymers (for example, protective coatings, membranes, seals) is determined by their permeability.
Gas penetration mechanisms through solid bodies
Gas permeability of polymers, as well as other properties, are determined by such factors as the flexibility of the chain; intermolecular interaction; phase and physical condition of the polymer; Packing density macromolecules; Degree of stitching. Crucial for diffusion permeabilitywhich is mainly due to sorption and diffusion, has the flexibility of the polymer chain and interceptual interaction.
Gas sorption with polymers.Gases can adsorb on external and the inner surfaces of polymers or dissolve in micropores arising between their macromolecules. The total amount of absorbed or sorbed gas can be measured, for example, with the help of scales of McBene (sensitive spiral scales), and calculate the concentration from Gas in the polymer. It is the greater the more partial pressure p. Gas in the environment: from p. where proportionality coefficient
called sorption coefficient(gas volume, absorbed united polymer volume with partial pressure equal to one, and experience temperature). The sorption coefficient is expressed in cm3 / (cm3 kgf / cm2). When sorption of gases and vapors, they can condense in the polymer, i.e. Change your phase state, turning into a liquid. In some cases, the sorbed substance may form aggregates or associates in the polymer.
For an elastic non-patent polymer, in which only the gas dissolution process occurs (gas fills free volume, which has a fluctuation character, as a result of which gas molecules during sorption can exchange places with polymer links), this coefficient is called the solubility coefficient of Gaza, which depends on the partial gas pressure and temperature.
The process of sorption of non-thermal vapor polymers are considered as the process of mutual dissolution of components, which occurs according to different mechanisms, depending on the temperature:
1. T TS. A sorbitating polymer is in a highly elastic state for which the flexibility of the chain is characterized and the sorbate molecules and links or polymer chain segments are possible with very small pressure values. The type of sorption isotherms will depend on the thermodynamic affinity of the sorbate to the polymer and flexibility of the polymer chain. The smaller the affinity, the less sorption.
2. T TS. Due to the lack of segmental movement, the exchange between steam molecules and the polymer chain links is difficult. In this case, the steam molecules can only penetrate into micro-sheets available in the polymer, which have small-packed polymers. The amount of sorbed substance in this case is little, which lies outside the sensitivity of the sorption method.
Therefore, sorption processes are most noticeable when the system is in highly elastic state, i.e. It is possible to exchange between sorbate molecules and chain links, as a result of which, the polymer swelling is at first, which can then move into its dissolution in sorbate pairs.
Failed gas chromatography
To study the thermodynamics of sorption of gases and vapors in polymers and the determination of their physicochemical parameters, the method of transmitted gas chromatography (OGH) is used. For this, the polymer is applied to the surface of the porous solid carrier, and the sorbate is injected into the gas carrier stream. The OGM method is very informative to study the thermodynamics of sorption in polymers, which also increase the amount of free volume.
Theoretical foundations of the OGH method.In the OGM method, time is measured holding sorbitated t.r. and uncorrect t.a. Components. Value t.a.corresponding to the actual almost non-sorbed component (usually air) is needed to take into account the "dead" volume of chromatograph. Thus, you can find a clean retained volume V.N.: The length of the chromatographic column, and temperature T..
When cooking a column used in the OGM method, it is extremely important to know the mass (gr) of the polymer phase w.L.. Taking into account the magnitude w.L. A specific resistant volume can be obtained. V.g.: i.e. The main experimental value on which all the thermodynamic parameters are dependent.
Value p.0 (PA) - the inlet pressure of the column, and the parameter j.nm. It is a correction equal to the ratio of pressure averaged by the time of stay of the sample in the chromatographic column, to the pressure at the outlet of it.
Another thermodynamic parameter that can be found with infinite dilution:
The reduced activity coefficient characterizes the deviation from the ideality in the binary system of the polymer pairs (deviation from the ROUlyl's law to pressure the vapor vapor).
By the temperature dependence of the activity coefficient, it is possible to calculate the partial molar enthalpy of mixing, which characterizes the interaction of the sorbate with the polymer:
since sorption enthalpy can be represented as an amount H.s. H.c. H.m. where H.c. - Enthalpy condensation of various sorbates.
The experiment is carried out on gas chromatograph with thermal conductivity detector. The temperature of the column must be maintained with an accuracy of 0.5 ° C, the pressure at the inlet to the chromatograph is up to 0.6 kPa, which allows you to introduce amendments to equations (2) and (4), the output pressure was equal to the atmospheric. Helium helium is used as a carrier gas; Its speed is measured using a soap-film flow meter. Air peak is used to determine t.a..
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