Effect of isotropization on the thermal behavior of two thermotropic copolyesters containing spirobicromane moieties

Two thermotropic copolyesters with inherent rigid spirobicromane (SPI) moie ties were prepared to evaluate their registry effects of neighboring chains in the mesomorphic state. Due to this chain registry effect, copolyester I -19, synthesized from polycondensation of terephthaloyl bis(4-oxybenzoyl ch loride) (TOBC), heptanediol (HD, 90 mol%), and SPI (10 mol%) exhibited diff erent thermal behavior between samples cooled from the mesomorphic and the isotropic liquid states. Chain arrangements in copolyester I-19, once rando mized by isotropization, can not be readily improved by a further annealing process. In contrast, crystallinity of copolyester II-19 prepared from rea ction of TOBC, HD (90 mol%), and bis(6-hydroxyhexanoxy)spirobicromane. 10 m ol%) (BHS) can be significantly enhanced by annealing even when previous th ermal treatment in the isotropic liquid state was performed. Suggestively, the minor component (i.e. SPI or BHS) in the corresponding copolyesters pla ys a decisive role in their responses toward annealing. The rigid, bent SPI moieties in copolyester I-19 efficiently retarded the crystallization proc ess. In contrast, the flexible 1,6-dioxyhexamethyl spacers introduced in th e BHS moieties greatly reduce the detrimental effect of the bent SPI moieti es on the crystallization behavior of copolyester II-19. (C) 2000 Elsevier Science Ltd. All rights reserved.