Preparation of new types of poly(amide-imide)s with high thermal stability and improved solubility was investigated. Two new diimide-dicarboxylic acid containing pendent benzimidazole group, viz., 2-[3,5-bis(N-trimellitimidoyl)-phenyl] benzimidazole (DIDA-i) and 2-[3,5-bis(N-trimellitimidoyl)-phenyl] 5-methyl benzimidazole (DIDA-ii) from the condensation of 5-(2-benzimidazole)-1,3-phenylenediamine (DABI(A)) and 5-(5-methyl-2benzimidazole)-1,3-phenylenediamine (DABI(B)) with trimellitic anhydride in glacial acetic acid were synthesized, respectively. 1,3-bis(N-trimellitimidoyl)benzene (DIDA-iii, as a reference) was also synthesized in a similar manner to study the properties of the its structure. Three series of aromatic poly(amide-imide)s were prepared by triphenyl phosphite-activated polycondensation from diimide-dicarboxylic acid DIDA-i, DIDA-ii, and the reference monomer DIDA-iii with various aromatic diamines. The polymers were obtained in quantitative yields with inherent viscosities between 0.46 and 0.81 dL g(-1). The effects of the benzimidazole pendent groups on the polymer properties, such as solubility and thermal stability were investigated by comparison of the polymers. The polymers bearing benzimidazole pendent groups exhibited thermal stability and good solubility in common polar solvents higher than the reference polymers. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114: 185-192, 2009