Synthesis and thermal properties of copoly(1,4‐arylene‐1,2,4‐oxadiazole)s with dimethyl substituent

Abstract 2,5‐Dimethyl terephthalamide oxime (DTD) was prepared from 2,5‐dimethyl terephthalonitrile, and various mixtures of DTD and terephthalamide oxime (TD) were condensated with terephthaloyl chloride in dimethyl acetamide. The obtained homo‐ and copoly(terephthaloyl terephthalamide oxime)s with two methyl substituents were characterized and cyclodehydrated to give rise to corresponding homo‐ and copoly (1,4‐arylene‐1,2,4‐oxadiazole)s with two methyl substituents as the side branch. Thermal properties of the homo‐ and copoly(1,4‐arylene‐1,2,4‐oxadiazole)s were investigated and the effects of the methyl groups were determined and discussed. The introduction of methyl substituents improved the solubility of the copoly(1,4‐arylene‐1,2,4‐oxadiazole)s greatly, but lowered their thermal resistance. All the copolymers and the homopoly [1,2,4‐oxadiazole‐5,3‐diyl‐(2,5‐dimethyl‐1,4‐phenylene)‐1,2,4‐oxadiazole‐3,5‐diyl‐1,4‐phenylene] were found to be amorphous with no observable glass transition.