Polybenzothiazoles. I. Synthesis and preliminary stability evaluation

Abstract

Abstract Completely aromatic polybenzothiazoles possessing superior oxidative and thermal stability have been prepared from aromatic bis( o ‐mercaptoamines) and aromatic dicarboxylic acids and benzothiazole forming derivatives thereof. The condensations were performed in N , N ‐diethylaniline and polyphosphoric acid. The former solvent gave meltable, low molecular weight prepolymers which were advanced to high molecular weight polybenzothiazoles by heating in the solid state. The course of the reaction was follwed by removing samples periodically and determining the polymer melt temperature, inherent viscosity, specific extinction coefficient and observing changes in the infrared spectrum. In polyphosphoric acid, relatively high molecular weight polybenzothiazoles were obtained after a short reaction period. The polybenzothiazoles exhibited average TGA weight losses of 6% to 600°C. in static air. The maximum glass transition temperature obtained for poly‐2,2′‐( m ‐phenylene)‐6,6′‐bibenzothiazole was 910°C. Most of the polybenzothiazoles were soluble in concentrated sulfuric acid and 0.3% solutions exhibited inherent viscosities as high as 1.51.