Structural Relaxation of Glass-Forming Polymers Based on an Equation for Configurational Entropy. 1. DSC Experiments on Polycarbonate

Abstract

A phenomenological model for the process of structural relaxation in glass-forming materials is discussed. The model is based on an expression for the evolution of the configurational entropy of the material when subjected to an arbitrary thermal history and contains four fitting parameters. The prediction of the model is presented in terms of heat capacity c p (T) curves, which are compared with the experimental DSC heating scans. Experimental results on polycarbonate with a broad series of thermal histories are presented, and the routine employed to fit the parameters of the model is described. The procedure permits the determination of material parameters (independent of thermal history) of the polymer : a curve of calorimetric equilibrium relaxation times as a function of temperature and a value for the width parameter of the Kohlrausch-Williams-Watts relaxation function. The possibility that the limit states of the structural relaxation process do not coincide with the states obtained from the extrapolation of the experimentally determined liquidus curve is also discussed.