Dk. Deak et al., Modification of randomness by transesterification of thermotropic liquid crystalline copolyesters, MACROMOLEC, 32(12), 1999, pp. 3867-3874
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.