Reduction and cyclization to form poly(benzimidazole amide imide) copolymers

Poly(amide imide) copolymers were synthesized with different molar ratios of 4,4‐diphenylmethane diisocyanate, two types of aromatic dianhydrides (pyromellitic dianhydride (PMDA) and 3,3′,4,4′‐sulfonyl diphthalic anhydride (DSDA)), and a diacid, which was derived from 3,3′‐dinitrobenzidine and isophthaloyl chloride in a previous work. In this study, the copolymers were further reacted with a reducing agent, and the nitro groups in the copolymers were hydrogenated into amine groups. Then, the amine‐group‐containing poly(amide imide) copolymers were cyclized at 180°C to form the poly(benzimidazole imide amide) copolymers in poly(phosphoric acid), which acted as a cyclizing agent. The resultant copolymers were soluble in sulfuric acid and poly(phosphoric acid) at room temperature and in sulfolane or N ‐methyl‐2‐pyrrolidone under heating to 100°C with 5% lithium chloride. According to wide‐angle X‐ray diffraction, all the copolymers were amorphous. According to thermal analysis, the glass‐transition temperature ranged from 270 to 322°C, and the 10% weight‐loss temperature ranged from 460 to 541°C in nitrogen and from 441 to 529°C in air. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 378–386, 2004