3,3'-Dinitrobenzidine was first reacted with excess in-chlorophenyl acid to form a monomer with dicarboxylic acid end groups. Two types of aromatic dianhydrides (Pyromellitic diconhydride (PMDA) and 3,3',4,4'-sulfonyl diphthalic anhydride) were also reacted with excess 4,4'-diphenylmethane diisocyanate to form polyimide prepolymers terminated with isocyanate groups. The prepolymers were further extended with the diacid monomer to form nitro groups containing aromatic poly(imide amide). The nitro groups in these copolymers were hydrogenated to form amine groups and then were cyclized at 180degreesC to form poly(imide amide benzimidazole) in poly(phosphoric acid), which acted as a cyclization agent. The resultant copolymers were soluble in sulfuric acid and poly(phosphoric acid), in sulfolane under heating to 100degreesC, and in the polar solvent N-methyl-2-pyrrolidone under heating to 100degreesC with 5% lithium chloride. According to wide-angle X-ray diffraction, all the copolymers were amorphous. According to thermal analysis, the glass-transition temperatures of the copolymers were 270-322degreesC. The 10% weight-loss temperatures were 460-541degreesC in nitrogen and 441-529degreesC in air. (C) 2003 Wiley Periodicals, Inc.