Synthesis and degradation of cyano‐containing aramids

Abstract Various aramids having a cyano group on the diamine ring were synthesized. Aramids containing a cyano group ortho to the amide bond underwent thermal degradation via a two step mechanism, whereas those containing a cyano group meta to the amide bond did not. The first step represented the loss of HCN resulting in benzoxazole polymers, which degraded further in the second stage producing high char yield at 900°C. The thermal studied of copolyamides from m ‐phenylenediamine, 2,4‐diaminobenzonitrile, and iso‐ or terephthaloyl chloride showed that as the mole fraction of 2,4‐DABN increased the initial decomposition temperature decreased, but the char yield and glass transition temperature increased gradually from the poly(1,3‐phenylene isophthalamide) to the polycyanamide homopolymer. To confirm the nucleophilic displacement reaction mechanism rather than isomerization cyclization suggested by Barashkov et al. for aramids with the cyano group ortho to the amide bond, a high‐temperature cell attached to a FT‐IR spectrometer were employed. Model compound studies also showed evidence for the benzoxazole ring formation.