What are polymers (Что такое полимеры). Учебное пособие
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Unit 10
RESEARCH METHODS IN POLYMER CHEMISTRY
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A variety of lab techniques are used to determine the properties of polymers. Techniques such as wide angle X-ray scattering (WAXS), small angle X-ray scattering (SAXS) and small angle neutron scattering are used to determine the crystalline structure of polymers. Gel permeation chromatography is used to determine the number average molecular weight, weight average molecular weight, and polydispersity. Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and nuclear magnetic resonance (NMR) can be used to determine composition.
Thermal properties such as the glass transition temperature and melting point can be determined by differential scanning calorimetry and dynamic mechanical analysis. Pyrolysis followed by analysis of the fragments is one more technique for determining the possible structure of the polymer.
An important tool of the polymer chemist is infrared, or IRspectroscopy. IR-spectra are acquired on a special instrument, called an IRspectrometer. IR-spectroscopy is used to gather information about compound’s structure, to assess its purity, and sometimes to identify it.
The scanning electron microscopy (SEM) is especially useful for routine examination of plastics, elastomers and biopolymers.
There are many instruments that test the mechanical and viscoelastic properties of polymer materials. These instruments apply varied shear stress and shear rate to polymer samples to estimate their response to deformation and mechanical strength.
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to determine the properties of polymers
wide angle X-ray scattering small angle X-ray scattering gel permeation chromatography
number average molecular weight weight average molecular weight
Fourier transform infrared spectroscopy
Raman spectroscopy nuclear magnetic resonance infrared spectroscopy
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scanning electron microscopy
routine examination
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shear rate
mechanical strength
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Thermogravimetric analysis, or TGA, is a type of testing that is performed on samples to determine changes in weight in relation to change in temperature. Such analysis relies on a high degree of precision in three measurements: weight, temperature, and temperature change. As many weight loss curves look similar, the weight loss curve may require transformation before results may be interpreted. A derivative weight loss curve can be used to tell the point at which weight loss is most apparent.
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Again, interpretation is limited without further modifications and deconvolution of the overlapping peaks may be required.
TGA is commonly employed in research and testing to determine characteristics of materials such as polymers, to determine degradation temperatures, absorbed moisture content of materials, the level of inorganic and organic components in materials, decomposition points of explosives, and solvent residues. It is also often used to estimate the corrosion kinetics in high temperature oxidation.
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Wide angle X-ray scattering (WAXS) is an X-ray diffraction technique that is often used to determine the crystalline structure of polymers. According to this method the sample is scanned in a wide angle X-ray unit.
When X-rays are directed in solids they will scatter in predictable patterns based upon the internal structure of the solid. A crystalline solid consists of regularly spaced atoms (electrons) that can be described by imaginary planes. Every crystalline solid will have a unique pattern of X- ray scattering.
Small angle X-ray scattering is carried out at very low angles (typically, 0,1–10°). This method is used for the determination of the microscale or nanoscale structure of particle systems in terms of such parameters as averaged particle sizes, shapes and distribution.
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1.Small-angle X-ray scattering is used to study the structure of ordered systems like lamellar structures, fractal-like materials and etc.
2.Dynamic mechanical analysis is a technique used to study and characterize polymer materials and it is also useful for observing their viscoelastic nature.
3.Infrared spectroscopy is widely used in both research and industry as a simple and reliable technique for measurement, quality control and dynamic measurement.
4.Differential scanning calorimetry is a thermoanalytical technique in which the difference in the amount of heat required to increase the temperature of a sample and reference are measured as a function of temperature.
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5.The atmosphere inside the thermogravimetric analysis unit may be purged with an inert gas to prevent oxidation or other undesired reactions.
6.Oxidation stability of polymers is studied by heating them to a certain high temperature when they are oxidized much faster and then estimating their oxidation rate under normal conditions.
7.Liquid samples for IR-spectroscopy are placed between two plates of a high purity salt (commonly sodium chloride), that are transparent to the infrared light.
8.Differential thermal analysis curve provides data on the transformations that have occurred, such as glass transitions, crystallization, melting and sublimation.
9.Raman spectroscopy is a spectroscopic technique used in chemistry to study vibrational, rotational, and other low-frequency modes in a system.
10.Small angle neutron scattering is a laboratory technique similar to the light scattering that provides valuable information on chemical aggregation, colloids, proteins, viruses and macromolecules.
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1.What are the main methods to study the structure of polymers?
2.Which method will you use to study degradation of polymers?
3.What parameters of polymers are obtained by gel permeation chromatography?
4.Which structural property of solid matter forms the basis for X-ray scattering?
5.Which properties of polymers can be characterized by a high temperature oxidation?
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3 ! 1 «What are polymers?»
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natural polymer |
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chemical reactions |
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high molar mass |
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polymer of biological origin |
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a wide range of properties and uses |
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carbon-based monomers |
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backbone of alternating atoms |
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to be connected by covalent bonds |
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to be composed of |
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to be made from monomers |
2. Translate sentences into Russian:
1)Polymers are formed by chemical reactions in which a large number of molecules called monomers are joined sequentially, forming a chain.
2)Most addition polymers are made from monomers containing a double bond between carbon atoms.
3)Polymers are often named in terms of the monomer from which they are made.
4)Two industrially important polymeric materials are plastics and elastomers; most common classes of polymers are composed of hydrocarbons.
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5)Polymer signifies a chain of thousands of monomers that are covalently bonded together usually by the carbon atoms of the backbone, but the backbone can consist of other atoms such as silicon.
3. Translate sentences into English:
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3 ! 1 «What are polymers?»
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low-to-moderate molecular mass |
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elastomers |
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alternating silicon and oxygen atoms |
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industrially important polymers |
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three-dimensional structure |
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covalently bonded |
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to join together |
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to be linked to each other |
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to form a chain |
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to depend on the molecular weight |
2. Translate sentences into Russian:
1)Polymers are classified by the characteristics of the reactions by which they are formed.
2)Synthetic polymers are produced commercially on a very large scale and have a wide range of properties and uses.
3)A polymeric solid material may be considered to be one that contains many chemically bonded parts or units which themselves are bonded together to form a solid.
4)Examples of polymers include substances anywhere from proteins to stiff, high-strength Kevlar fibers.
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