In this study, 3,3'-dinitrobenzidine was first reacted with excess isophthaloyl chloride to form a monomer with dicarboxylic acid end groups. Two types of aromatic dianhydride, [viz., pyromellitic dianhydride (PMDA) and 3,3',4,4'-sulfonyldiphthalic anhydride (DSDA)] also were reacted with excess 4,4'-diphenyl- methane diisocyanate (MDI) to form polyimide prepolymers terminated with isocyanate groups. The prepolymers were reacted further with the diacid monomer to form a nitro group- containing aromatic poly(amide imide) copolymers. The nitro groups in these copolymers were hydrogenated to form amine groups and cyclized at 180degreesC to form the poly(benzimidazote amide imide) copolymers in polyphosphoric acid (PPA), which acts as a cyclization agent. From the viscosity measurements, copolymer appeared to be a reasonably high molecular weight. From the differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) measurements it was shown that the glass transition temperature of copolymers was in the range of similar to270-322degreesC. The 10% weight loss temperatures were in the range of 460 similar to 541degreesC in nitrogen and similar to441-529degreesC in air, respectively. The activated energy and the integration parameter of degradation temperature of the copolymers were evaluated with the Doyle-Ozawa method. It indicated that these copolymers have good thermal and thermo-oxidative stability with the increase in imide content. (C) 2004 Wiley Periodicals, Inc.