Effects of orientation on the mechanical and dielectric relaxation behavior of cycloaliphatic polyester networks

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AbstractThe mechanical and dielectric relaxation behavior of strained and unstrained networks, prepared from hydroxyl‐terminated poly(diethylene glycol‐trans‐1,4‐cyclohexane dicarboxylate) (PDGC), is studied over a wide interval of frequencies and temperatures. The mechanical relaxation spectrum exhibits a glass‐rubber absorption, designated β, located in the vicinity of 0°C at 0.1 Hz, followed by a β relaxation which appears to be the result of two overlapping peaks centered at −80°C (β1) and −110°C(β2). These two peaks coalesce into a single peak in the case of strained networks. The dielectric relaxation spectrum also exhibits an α absorption followed by a subglass β relaxation whose width decreases as the elongation ratio λ increases. The activation energy associated with the mechanical β1 appears to increase as λ increases. However, the activation energy of the dielectric β 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 Ccy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 ration increases, suggesting that the entropic effects overcome the volume effects. The glass‐rubber transition is interpreted in terms of the free volume theory.