THERMOTROPIC POLYESTERS - SYNTHESIS AND PROPERTIES OF MODIFIED POLY(4-OXYBENZOATE-CO-1,4-PHENYLENE ISOPHTHALATE)S

The constitution of poly(4-oxybenzoate-co-1,4-phenylene isophthalate)s , consisting of rod-like 4-oxybenzoyl and 1,4-phenylenedioxy units and angular isophthaloyl units, is modified by gradually replacing (i) th e 1,4-phenylenedioxy units with chloro-1,4-phenylenedioxy units, and ( ii) the angular isophthaloyl units with rod-like terephthaloyl units. The former modification results in a gradual decrease of the melting t emperature, while the latter one has the opposite effect. When both mo difications are employed simultaneously, their effects essentially com pensate each other. Thus, a fully aromatic nematogenic copolyester con sisting of equimolar quantities of rod-like 4-oxybenzoyl, chloro-1,4-p henylenedioxy and terephthaloyl units melts at 313 degrees C, more tha n 100 degrees C below its thermal stability limit. Although the meltin g behaviour of the materials investigated is strongly affected by anne aling, the changes can be reversed by remelting.