Modification of Randomness by Transesterification of Thermotropic Liquid Crystalline Copolyesters

Several different liquid crystalline copolyesters were thermally posttreated above their melt transition temperatures to increase their degree of randomness. Both poly(ethoxyphenylene terephthalate-co-ethylene terephthalate)s (poly(EPT-co-ET)) and poly(phenylphenylene terephthalate-co-ethylene terephthalate)s (poly(PPT-co-ET)) were prepared in 70:30 mole ratios of EPT:ET and PPT:ET and thermally randomized. The randomization reactions were controlled by variations in the duration and temperature of the reaction. The compositions of the copolymers remained constant in these reactions while the comonomer sequence distribution was changed. The inherent viscosities of the copolymers increased as a result of the reaction presumably because of increases in molecular weight. Increased randomness resulted in decreased crystallinities of the copolyesters, as observed by reduced enthalpies of fusion and crystallization, lower melt transitions, and lower crystallization temperatures.