COMPARISON OF THE COUPLING BEHAVIOR OF DIISOCYANATE AND BISOXAZOLINESIN MODIFICATION OF LIQUID-CRYSTALLINE POLY(ETHYLENE TEREPHTHALATE-CO-OXYBENZOATE)S

Methylene-4,4'-diphenyldiisocyanate and two different bisoxazolines we re used for coupling reactions in carboxy-terminated liquid crystallin e poly(ethylene terephthalate-co-oxybenzoate). In order to guarantee d efined conditions, copolyesters with different carboxylic group concen trations were synthesized. The determination of the carboxylic group c ontent is described. The coupling behaviour of both types of chain ext enders has been compared. It was evidenced that the bisoxazolines reac ted significantly faster than the diisocyanate. A slight excess of bis oxazoline in the reaction mixture prevented thermomechanical degradati on. Depending on the amount of coupling agent added, an oxazoline term ination of the copolyester was observed. Additionally, probable crossl inking reactions and the thermal stability have been discussed.