Recovery of compressive strain in atactic polystyrene

Abstract

Atactic polystyrene rods were compressed in an Instron universal testing machine to about 35% strain and then annealed near the glass transition temperature, T _g, (100° C) in a thermal mechanical analyser. The change of length during annealing was recorded and the compressive strain was found to recover obeying second-order kinetics at least during the later part of recovery. The activation enthalpy obtained from the temperature dependence of the second-order rate constant varied from 126 to 260 kcal mol⁻¹ as the annealing temperature decreased from 112 to 94° C. These activation enthalpies are attributed to the diffusion of positive or negative defects or configurations which annihilate during recovery. While these activation enthalpies agree with the findings of Andrews on retraction of hot-stretched filaments, they differ considerably from the spectrum obtained by Kimmel and Uhlmann using the data from Andrews' work. The reason for such differences is discussed.