Factors determining glass transition temperature and relaxation time of poly(vinyl chloride)

Abstract

Glass transition properties were obtained by measurements of the dilatometric glass transition temperature T g at elevated pressure by isobaric cooling at a constant rate. The properties include the pressure-volume-temperature ( P- V- T) relations of the liquid, the specific heat capacity and the dielectric properties for a single sample of poly(vinyl chloride). From the experimental results, various thermodynamic excess quantities such as the free volumes and the configurational entropy and energies were evaluated as factors determining T g and the relaxation time τ. Some empirical rules concerning T g, which have been proposed by Simha and Boyer, and Wunderlich, are also examined. The main conclusions are as follows: (1) the free volume is not an essential factor determining T g and τ; (2) the Adam-Gibbs parameter is slightly superior to the other excess entropy and energies defined as the difference of the entropy and energies between the liquid and the hypothetical crystal whose thermal expansivity and compressibility are the same as those of the corresponding glasses; and (3) the glass transition may not be treated as a quasi-equilibrium thermodynamic transition to which one of the Ehrenfest relations applies.