Dielectric relaxation studies on a three component fully aromatic copolyester

The family of aromatic copolyesters based on the hydroxybenzoic acid (HBA) unit has been studied extensively by a number of groups. In particular the copolyesters of HBA and 2,6-hydroxynaphthoic acid (HNA) have received much of attention due to their superior physical properties. This paper, however , describes some detailed dielectric studies on a related fully aromatic co polyester, poly(p-oxybenzoate-co-p-phenylene isophthalate), known simply as HIQ. This polymer is of particular interest because it can be solvent cast in an amorphous form, with no apparent crystallinity or frozen liquid crystallin e texture and subsequently annealed, to increase the amount of crystalline and frozen liquid crystalline material. Dielectric measurements were theref ore made on tape and film samples with differing morphologies produced by d ifferent processing histories. Measurements were made from 1 Hz to 10 kHz o ver the temperature range - 100 degreesC to 150 degreesC. A low temperature gamma relaxation is observed which appears to be similar in nature to that which is observed in copolymers of HBA and HNA. An interm ediate temperature beta process is seen in isotropic samples which has a mu ch higher activation energy than that found in HBA/HNA polyesters for examp le. The intensity of this process, which is not seen in mechanical measurem ents on highly oriented samples, increases on annealing and it is therefore suggested that the process is the glass transition of the liquid crystalli ne phase, though why the process is not seen in mechanical measurements on oriented samples is unclear, Copyright (C) 2001 John Wiley & Sons, Ltd.