Modification of randomness by transesterification of thermotropic liquid crystalline copolyesters

Several different liquid crystalline copolyesters were thermally posttreate d above their melt transition temperatures to increase their degree of rand omness. Both poly(ethoxyphenylene terephthalate-co-ethylene terephthalate)s (poly(EPT-co-ET)) and poly(phenylphenylene terephthalate-co-ethylene terep hthalate)s (poly(PPT-co-ET)) were prepared in 70:30 mole ratios of EPT:ET a nd PPT:ET and thermally randomized. The randomization reactions were contro lled by variations in the duration and temperature of the reaction. The com positions of the copolymers remained constant in these reactions while the comonomer sequence distribution was changed. The inherent viscosities of th e copolymers increased as a result of the reaction presumably because of in creases in molecular weight. Increased randomness resulted in decreased cry stallinities of the copolyesters, as observed by reduced enthalpies of fusi on and crystallization, lower melt transitions, and lower crystallization t emperatures.