Semi-rigid thermotropic polyester containing a rigid, bent spirobicromane moieties - primary characterizations and the thermal behavior

Thermotropic copolyester TBH with inherent spirobicromane (SPI) moieties wa s prepared by polycondensation reaction between mixed diols of 4,4-bis(6-hy droxyhexanoyloxy)spirobicromane (BHS, 10 mol%), 1,7-heptanediol (HD, 90 mol %) and terephthaloyl bis(4-oxybenzoyl chloride) (TOBC). In addition, homopo lyester TH (or TB) synthesized from TOBC and HD (or BHS) diol was prepared for comparison. With the incorporated SPI moieties, polyester TB is a nemat ic material, in contrast to the smectic C-2 mesophase observed for polyeste r TH and copolyester TBH. The rigid, spiro SPI moieties in polyester TB are supposed to interrupt the ordered packing of the mesogenic triads required for a smectic C-2 mesophase. Under diffraction scanning calorimetry (DSC) scans, copolyester TBH exhibited multiple endothermic and exothermic peaks, which are different from the much simpler thermal behavior observed for ho mopolyesters TH and TB. The multiple melting and crystallization transition s for copolyester TBH was due to the facile crystallization of the inherent flexible spacers and the potential registry of neighboring chains in the m esomorphic state according to the results from isothermal, non-isothermal c rystallization experiments, and the X-ray diffraction study. Suggestively, the rigid, bent SPI moieties would impose a nonlinear geometry on the conne cted spacers and mesogenic units and consequently, influence its chain arra ngement in the mesomorphic state. (C) 2000 Elsevier Science Ltd. All rights reserved.