Polybenzoxazoles and polybenzothiazoles

Polybenzoxazoles of high molecular weight were prepared easily by the solution polycondensation of 3,3′‐dihydroxybenzidine dihydrochloride or 3,3′‐diamino‐4,4′‐dihydroxybiphenyl dihydrochloride with both aromatic and aliphatic dicarboxylic acids in polyphosphoric acid. Polybenzothiazoles were prepared from 3,3′‐dimercaptobenzidine dihydrochloride and dicarboxylic acids by the same procedure. Aromatic polybenzoxazoles and polybenzothiazoles showed an excellent thermal stability up to 450°C. in air. They were insoluble in organic solvents.