Two reaction routes for the preparation of aromatic polyoxadiazoles and polytriazoles: Syntheses and properties

Two reaction routes for the preparation of aromatic poly‐1,3,4‐oxadiazoles and poly‐1,2,4‐triazoles are studied and their influence on the physical properties, i.e., inherent viscosity, glass transition, degradation temperature, and film integrity of the final products are discussed. Aromatic poly‐1,3,4‐oxadiazoles are prepared by means of a polycondensation reaction of terephthaloyl chloride and isophthalic dihydrazide yielding a precursor polymer, poly(p, m‐phenylene) hydrazide, which is converted into the corresponding poly‐1,3,4‐oxadiazole by means of a cyclodehydration reaction. Poly‐1,3,4‐oxadiazoles are also prepared by means of a polycondensation reaction between terephthalic and isophthalic acid and hydrazine yielding poly‐1,3,4‐oxadiazoles with higher inherent viscosities. Flexible poly‐1,3,4‐oxadiazole films are obtained only if the inherent viscosities of the polymers used are higher than 2.7 dL/g. The thermal stability is found to increase with increasing content of p‐phenylene groups in the polymer backbone. Aromatic poly‐1,2,4‐triazoles are prepared using polyhydrazides with alternating para‐ and meta‐phenylene groups and poly‐1,3,4‐oxadiazoles with a random incorporation of para‐ and meta‐phenylene groups in the main chain as precursor polymers. The glass transition temperatures are found to increase with increasing content of p‐phenylene groups in the main chain of these polymers. Cold crystallization is observed only for the alternating polymer.