A comparative study of the kinetic and thermodynamic approaches to the glass transition phenomenon in high polymers

Abstract

The effect of thermal history on the glass transition temperature T g of polystyrene, polyvinylchloride and polyethyleneterephthalate was studied using differential scanning calorimetry (DSC). Parameters such as the hole energy E h, the activation energy E j for the disappearance of holes, the activation enthalpies Δ h1 ∗ and Δ h2 ∗ for structural relaxation and the activation energy E for the glass transition process were calculated. The increase in E h value with increasing T g showed that there exists a distribution of hole sizes. The E j value calculated according to Wunderlich's treatment, the Δ h1 ∗ parameter obtained using Moynihan's procedure and the E value derived from Barton and Critchley's method agreed with one another for polystyrene and polyvinylchloride. The Δ h2 ∗ quantity obtained using Moynihan's formula increased as the rate of heating was increased, a result similar to the variation in E h value with heating rate. The validity of the Δ C p- T g criteria proposed by Wunderlich and by Simha and Boyer were also investigated for the three polymers concerned. The variations in kinetic parameters such as Δ Ha, the cohesive energy density (CED) and the thermodynamic quantity Δμ (Adam-Gibbs) were also calculated and their variation is discussed in the light of structure-property relationships.