Studies of the Breakdown Mechanisms of Polymers. VI. The Thermal Decomposition of Polybenzoxazoles and Polybenzothiazoles.

Abstract : The thermal breakdown of three polybenzoxazoles and three polybenzothiazoles was studied in vacuum between 450 and 660 C. Two model compounds corresponding to the two basic polymer systems were subjected to flash pyrolysis. The polybenzoxazoles lost most of the oxygen up to 660 C as carbon monoxide and carbon dioxide, with the carbon atom of the benzene ring adjacent to the oxygen participating in the reaction. The structure of the residual polymer is possibly that of a crosslinked, Schiff base structure, with only out of six C=N linkages being eliminated as hydrogen cyanide. Polybenzothiazoles became highly crosslinked, but were essentially unchanged, after heating to 625 C. (Author, modified-PL)