FROM CONFORMATIONAL TRANSITIONS IN A POLYMER-CHAIN TO SEGMENTAL RELAXATION IN A BULK POLYMER

The local segmental dynamics of a polymer chain are governed by the one-dimensional connectivity of the chain and are known to be well described by the Hall-Helfand model. In this paper, a theoretical model is developed which relates the local Hall-Helfand processes of a chain to the segmental motions in bulk polymers as revealed by mechanical, dielectric and light-scattering techniques. With the conformational transitions of each chain described by the Hall-Helfand correlation function, interactions between chains are included by the method of the coupling model. Previous applications of the coupling model had assumed a constant local rate and had obtained a Kohlrausch-Williams-Watts (KWW) decay function in the presence of intermolecular interactions. In the present work, the time-dependent Hall-Helfand rate is used as the local rate. The resulting decay function for bulk polymers generally differs from the KWW function but approaches it for times long compared with the Hall-Helfand correlated relaxation time, tau-1. The coupling model relation between the observed relaxation time and the local relaxation time is found to hold between the KWW relaxation time, tau*, and the Hall-Helfand uncorrelated relaxation time, tau-2. The decay functions for Hall-Helfand with coupling and the corresponding frequency loss response functions are presented and discussed.