Synthesis of poly(1,3,4‐oxadiazole)s by direct polycondensation of dicarboxylic acids with hydrazine sulfate using phosphorus pentoxide/methanesulfonic acid as condensing agent and solvent

A convenient method for the synthesis of poly(1,3,4‐oxadiazole)s of high molecular weights has been developed. These polymers were prepared readily by the direct polycondensation of dicarboxylic acids with hydrazine sulfate (1) using phosphorus pentoxide/methanesulfonic acid (PPMA) as both a condensing agent and solvent. Polycondensation of aliphatic dicarboxylic acids with 1 proceeded even at room temperature and produced poly(1,3,4‐oxadiazole)s with inherent viscosities up to 1.4 dL/g. The synthesis of aromatic poly(1,3,4‐oxadiazole)s from aromatic dicarboxylic acids containing phenyl ether structures was carried out by a one‐pot procedure because the preactivation of dicarboxylic acids was required. The synthesis of 2,5‐disubstituted‐1,3,4‐oxadiazoles by the reaction of carboxylic acids with 1 in PPMA was studied to demonstrate the feasibility of the reaction for polymer formation. The thermogravimetry of the aromatic poly(1,3,4‐oxadiazole)s showed 10% weight loss both in air and in nitrogen at 440–490°C.