Properties of Copolymers Derived from 2,5-Dimethylterephthalamidoxime and Cyclodehydration to Copoly(1,3-arylene-1,2,4-oxadiazole)s

A series of copoly(1,3-arylene-1,2,4-oxadiazole)s was synthesized by thermal cyclodehydration of copoly(isophthaloylamidoxime)s, which were prepared by solution condensation from various mixtures of 2,5-dimethylterephthalamidoxime (DTD) and isophthalamidoxime (ID) with terephthaloyl chloride (TPC). The precursor copolymers containing mole ratios of 20% or more of DTD were soluble in N,N-dimethylacetamide (DMAc). Thermal properties of copoly(1,3-arylene-1,2,4-oxadiazole)s were investigated, and the effects of the methyl side groups are discussed. The introduction of dimethyl substituent improved solubility of copoly(1,2,4-oxadiazole)s greatly but lowered thermal resistance. All of the copolymers were found to be amorphous and glass transition could not be observed.