Study of Polymer Glass Transition and Segmental Motions in Partially Crystallized Poly(ethyl acrylate)∕p-xylene Mixtures

Abstract

A poly(ethyl acrylate network), PEA, was swollen with several contents of p‐xylene, cpx, from xerogel until saturation (0≤cpx≤0.86). Differential Scanning Calorimetry (DSC), Thermally Stimulated Depolarization Currents (TSDC) and Dielectric Relaxation Spectroscopy (DRS) were performed to probe the thermal transitions and the polymer molecular dynamics in these mixtures. The results show, that the mixtures are homogeneous in the whole temperature range studied for p‐xylene contents cpx<0.20, whereas are partially crystallized for cpx≥0.20 (co‐existence of homogeneous PEA/p‐xylene phase and p‐xylene crystallites). For 0.20≤cpx≤0.30, the mixtures are partially crystallized only on heating (above the glass transition temperature, cold crystallization), while for cpx>0.30 during cooling. The partially crystallized mixtures exhibit a critical p‐xylene content estimated at 0.12–0.15 that remains un‐crystallized regardless of the p‐xylene composition. The respective polymer glass transition temperature remains constant at −47±2° C due to the presence of this specific amount of un‐crystallized p‐xylene for cpx>0.30, whereas it decreases significantly with increasing cpx(0<cpx<0.30). The α relaxation polymer segmental dynamics, related with the polymer glass transition, sustains its cooperative nature in the partially crystallized mixtures, whereas the distribution of α process relaxation times exhibit a slight broadening compared to the xerogel and homogeneous mixtures, ascribed to the spatial concentration fluctuations induced by the presence of p‐xylene crystallites. Finally, the α process dielectric strength as well as the heat capacity increment of glass transition undergo significant depression compared to the homogeneous mixtures once the p‐xylene crystallites are present.