VISCOELASTIC PROPERTIES OF AMORPHOUS POLYMERS .1. DIFFERENT TEMPERATURE DEPENDENCES OF SEGMENTAL RELAXATION AND TERMINAL DISPERSION

Two drastically different temperature dependences of the segmental relaxation and terminal dispersion previously observed in entangled polystyrene, poly(vinylacetate), and polypropylene were explained before in the framework of the coupling model as due to the large difference between the segmental motion coupling parameter, n(alpha), and the entanglement coupling parameter, n(eta), in these polymers, with n(alpha) being significantly larger. The n(alpha) for a polyisobutylene was found recently to be the smallest among amorphous polymers, and its value is comparable to that of n(eta). As a consequence the coupling model requires that the temperature dependences for segmental relaxation (near the glassy level) and the terminal dispersion be similar. Viscoelastic measurements were carried out in a high molecular weight (entangled) polyisobutylene sample to verify this clear prediction. The experimental results presented here have borne out the theoretical expectations.