Thermophysical Properties of PolymersAmong various branches of polymer physics an important position is occupied by that vast area, which deals with the thermal behav ior and thermal properties of polymers and which is normally called the thermal physics of polymers. Historically it began when the un usual thermo-mechanical behavior of natural rubber under stretch ing, which had been discovered by Gough at the very beginning of the last century, was studied 50 years later experimentally by Joule and theoretically by Lord Kelvin. This made it possible even at that time to distinguish polymers from other subjects of physical investigations. These investigation laid down the basic principles of solving the key problem of polymer physics - rubberlike elasticity - which was solved in the middle of our century by means of the statistical thermodynamics applied to chain molecules. At approx imately the same time it was demonstrated, by using the methods of solid state physics, that the low temperature dependence of heat capacity and thermal expansivity of linear polymers should fol low dependencies different from that characteristic of nonpolymeric solids. Finally, new ideas about the structure and morphology of polymers arised at the end of the 1950s stimulated the development of new thermal methods (differential scanning calorimetry, defor mation calorimetry), which have become very powerful instruments for studying the nature of various states of polymers and the struc tural heterogeneity. |
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accompanied adiabatic amorphous polymers amorphous regions anisotropy block copolymers calculated calorimeter calorimetry chains Chem cold drawing compression constant corresponding crack crystallization curve decrease degree of crystallinity drawing rate drawn crystalline polymers elasticity modulus elastomers elongation energy contribution entropy equation estimate experimental extension filler films fracture function glass transition glass transition temperature glassy and crystalline glassy polymers Godovsky YuK Gruneisen parameter HDPE heat capacity increase interchain interfibrillar internal energy internal energy change intrachain inversion lattice LDPE low temperature macromolecules measurements mechanical methods modes modulus molecular neck propagation negative thermal expansion networks obtained oriented phonon plastic deformation PMMA Polym Sci Polym pressure rupture sample Sci Polym Phys shown in Fig solid polymers stored energy strain stretching structure studied temperature changes temperature dependence temperature rise thermal conductivity thermal effects thermal expansion coefficient thermocouple thermodynamic thermoelastic thermomechanical behavior typical undrawn values velocity vibrations