Thermotropic copolyesters containing spirobicromane moieties: synthesis and primary characterizations

Spirobicromane (SPI) are supposed to have a drastic influence on the mesomo rphism due to their rigid, bent geometry and bulkiness; therefore, we attem pted to build the SPI unit into conventional thermotropic polyester and exa mine its effect on mesomorphism. In this study, thermotropic copolyester se ries I and II, with their SPI moieties aggregated or evenly distributed in the polymer chain, can be prepared according to single- and two-step polyco ndensation reactions of different amounts of SPI, 1,7-heptanediol (HD), and terephthaloyl bis(4-oxybenzoyl chloride) (TOBC), respectively. Thermal tra nsition temperatures (T-m and T-i) for both copolyester I and II series dec reased with the increasing SPI moieties incorporated and no liquid crystall ine properties were observed for copolyesters with SPI content more than 20 mol%. With more aggregated SPI moieties in the chain, copolyester I series possess higher isotropization temperature and better smectic order as comp ared to copolyesters II of the same composition, in which the detrimental S PI moieties are assumed to be evenly distributed to efficiently prevent an ordered chain packing in the mesomorphic state. (C) 1999 Elsevier Science L td. All rights reserved.