Phase heterogeneity in poly(methyl acrylate)-polystyrene sequential interpenetrating polymer networks studied by thermally stimulated recovery

Abstract

The aim of this work is to explore the ability of a mechanical thermal sampling (TS) technique to study the glass transition of heterogeneous polymer systems. Poly(methyl acrylate) and polystyrene are immiscible. Sequential interpenetrated polymer networks (IPNs) were prepared with these components with two varying cross-linking densities. The dynamic mechanical analysis shows, in the case of the loosely cross-linked IPN, two clearly separated main x-relaxations in a similar position as in the pure network components while in the highly cross-linked IPN the two peaks overlap. The thermally stimulated recovery (TSR) technique, using the TS procedure allows a more detailed analysis of the glass transition region. With this technique it is possible to determine the temperature dependence of the apparent activation energy of the conformational mobility in the range of the glass transition. A peak appears at a temperature very close to the glass transition temperature. The presence of differentiated peaks in the heterogeneous system allows one to reveal the phase separation or the presence of interphases with differentiated mechanical behaviour. More details related with phase heterogeneity are observable by the low-frequency TSR technique relatively to the conventional dynamic methods.