Thermostable aromatic poly(1,3,4-oxadiazole)s from multi-ring flexible diacids

A series of aromatic poly(1,3,4-oxadiazole)s, PODZs, was prepared either by direct polycondensation of dicarboxylic acids with hydrazine sulfate using the polyphosphoric acid/methanesulfonic acid mixture, or by thermal cyclodehydration of the corresponding poly(hydrazide)s. Various aromatic diacids containing flexible p-oxyphenylene joints and/or bulky isopropylidene or hexafluoroisopropylidene groups in the main chain were used to produce amorphous PODZs soluble in strongly polar organic solvents and having inherent viscosities up to 1.1 dl g(-1). The polymers were characterized by Fourier transform infrared and H-1 and C-13 nuclear magnetic resonance spectroscopy, and their thermal properties were investigated by differential scanning calorimetry and dynamic thermogravimetric analysis. The glass transition temperatures, T-g, lie in the range 190-295 degrees C, and depend both on the number of aryloxy groups and on the presence of bulky groups. The PODZs show good thermal resistance in nitrogen up to 440 degrees C. (C) 1998 Elsevier Science Ltd. All rights reserved.