EFFECTS OF ORIENTATION ON THE MECHANICAL AND DIELECTRIC-RELAXATION BEHAVIOR OF CYCLOALIPHATIC POLYESTER NETWORKS

The mechanical and dielectric relaxation behavior of strained and unstrained networks, prepared from hydroxyl-terminated poly (diethylene glycol-1,4-cyclohexane dicarboxylate) (PDGCZ), is studied over a wide interval of frequencies and temperatures. The mechanical relaxation spectrum exhibits a glass-rubber absorption, designated alpha, located in the vicinity of 0-degrees-C at 0.1 Hz, followed by a beta-relaxation which appears to be the result of two overlapping peaks centered at -80-degrees-C (beta-1) and -110-degrees-C (beta-2). These two peaks coalesce into a single peak in the case of strained networks. The dielectric relaxation spectrum also exhibits an alpha-absorption followed by a subglass beta-relaxation whose width decreases as the elongation ratio lambda increases. The activation energy associated with the mechanical beta-1 appears to increase as lambda increases. However, the activation energy of the dielectric beta-process does not show a clear dependence on the elongation ratio. The analysis of the conformational characteristics of PDGC chains indicates that rotational transitions through the C(cy)-C* bonds of the acid residue would give rise to high dielectric activity. Conformational changes about the CH2-CH2 bonds of the glycol residue would produce significant mechanical activity but, comparatively, low dielectric activity. The glass-rubber absorption is slightly displaced toward the high-temperature side as the elongation ratio increases, suggesting that the entropic effects overcome the volume effects. The glass-rubber transition is interpreted in terms of the free volume theory.