Measurements of the temperatwe dependence of volume resistivity of a variety of polymers are used to elucidate polymer structure and the mechanism of electrical conduction ne of the more important measurements made by 0 those investigating high polymers is that of the magnitude and temperature dependence of the electrical volume resistivity. Such data can be used to calculate the activation energy, E,, for the electrical conduction process in the polymer and to estimate the extent of polymerization. The magnitude and temperature dependence of the electrical resistivity (or conductivity) of a polymer is a function of the molecular structure of the polymer, the nature and number of the current carriers, and the temperature. Resistivity determinations have been used for many years by physicists in studying the structure of both elements and inorganic compounds (1), and more recently they have been applied to solid organic compounds ( 2 ) . However, the use of this measurement on high polymers has not been widespread. A number of years ago studies by Fuoss (3) and by Baker and Yager (4) utilized the temperature dependence of the resistivity as an aid in studying the molecular structure of polymers. Following their work, use of the technique has slowly become more widespread. However, the literature still does not contain any significant amount of accurate data on the magnitude and temperature dependence of the electrical resistivities of thermoplastic and thermosetting polymers. Such information is of great importance not only in technological applications of these materials but also in theoretical investigations. The values reported here and the experimental technique are of interest to those considering the possibility of employing modified polymers (5) as organic semiconductors. These data could also serve as an index for the characterization of polymers. In addition to the experimental work and data reported here, the available literature values for the temperature dependence of the resistivity of various polymers are also included. TheoreticalThe theoretical basis for calculating the activation energy, E,, of the electrical conduction process has been developed by Glasstone, Laidler, and Eyring ( 6 ) who have shown that the concepts used in chemical kinetic 80 studies can be successfully applied to physical processes. The change in the electrical resistivity of a polymer with temperature can be considered to be a rate process similar to those encountered in chemical kinetic studies and the same equations can be applied to both chemical and physical rate processes.Equation ( 1 ) is used to calculate the activation energy for the conduction process.where p is the resistivity, A, is a temperature independent constant, R is the molar gas constant 1.987 cal/degmole, T is the absolute temperature, and E, is the activation energy for the conduction process. Many investigators have studied the electrical conduction process in high polymers, (3, 7) and the evidence is that conduction is an ionic process. Ions stem from t...
A Tarassov function has been used to estimate the specific heat of polystyrene between 0° and 60°K. These data, together with published Cp data, have been used to calculate the entropy, enthalpy, and free energy of styrene and polystyrene from 0° to 298.16°K. The entropy of polymerization of styrene at 298.16°K. was found to be 26.69 cal./mole°.The thermodynamic function Cp/T versus T as calculated for polystyrene, increases to a maximum at 65°K. and then increases again at the glass transition temperature. The Tarassov function, which is shown to be useful in estimating the specific heat of amorphous polymers, should be combined with a T3 Debye function to yield more accurate cv data at low temperatures. The number of classically vibrating units per repeating unit of polystyrene was found to be 6.57. The difference Cp – Cv was calculated at 273°K. and found to be 2.0 cal./mole°.
Electrical volume resistivity techniques hare been employed to study the polymerization characteristics and the nature of solid amorphous crosslinked polymers. It is shown that this experimental approach yields data which can be related to structural parameters. Use of these techniques to investigate the rate and extent of polymerization, the magnitude and temperature dependence of the resistivity, glass transition and thermal stability is described and discussed.The Compensation Law is observed to hold for the electrical conduction process for the polymers considered -per.A linear relationship was also found to exist between the logarithm of the magnitude of the resistivity a t 25°C. and the activation energy for the electrical conduction process. A possible explanation of the significance of this relationship is given. ZUSAMMENFASSUNG:Die Methode der elektrischen Widerstandsmessung wird zur Untersuchung des Polymerisationsverlaufs und der Eigenschaften fester, vernetzter Polymerer angewandt. Es wird gezeigt, daB sich mit dieser Methode MeBgroBen ergeben, die in Beziehung zu Strukturparametern der Polymeren gesetzt werden konnen. Die Anwendung des Verfahrens zur Untersuchung der Polymerisationsgeschwindigkeit, des AusmaBes der Polymerisation, der GroBe und der Temperaturabhlngigkeit des spezifischen Widerstandes, der Einfriertemperatur und der thermischen Stabilitat wird beschrieben und diskutiert.Die Giiltigkeit des Kompensationsgesetzes fiir die elektrische Leitfahigkeit wird fur die in dieser Arbeit untersuchten Polymeren nachgewiesen. Es wird ferner eine lineare Beziehung zwischen dem Logarithmus der GroBe des spezifischen Widerstandes bei 25 "C und der Aktiviemngsenergie fiir die elektrische Leitfahigkeit gefunden. Eine mogliche Erklamng fiir die Bedeutung dieser Beziehung wird gegeben.
Epoxy, polyester, and styrene isothermal polymerizations have been monitored electrically. Sample resistivity—time records at different temperatures are reported for each class of polymer. These plots suggest that relative rates of reaction could be conveniently obtained if a correlation between extent of polymerization and electrical resistivity were known for the particular resins studied. Qualitative agreement between changes in infrared absorption and changes in volume resistivity as a measure of the extent of polymerization has been obtained.
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