Two series of heterocyclic aromatic polymers were synthesized from 4,4'-(4,4'-isopropylidenediphenoxy)-bis(phthaltic anhydride) and 2,2'-bis(3,4-dicarboxyphenyl)-hexafluoropropane dianhydride by two-step method. The inherent viscosities were in the range of 24-45 cm(3)/g. The effects of the rigid benzoxazole group in the backbone of copolymer on the thermal, mechanical, and physical properties were investigated. These polymers exhibit good thermal stability. The temperatures of 5% weight loss (T-5) of these polymers are in the range of 403-530 degrees C in air and 425-539 degrees C in nitrogen. The chard yields of these polymers are in the range of 15-24% in air and 54-61% in nitrogen. These polymers also have high glass-transition temperatures and a low coefficient of thermal expansion and good mechanical properties. The poly(benzoxazol imide) has a higher tensile strength and modulus than those of neat polyimide. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113:2301-2312, 2009