A series of new aromatic poly(amide-imide)s were synthesized by the triphenyl phosphite-activated polycondensation of the diimide-diacid, 1,4-bis(trimellitimido)-2,5-dichlorobenzene (I), with various aromatic diamines in a medium consisting of N-methyl-2-pyrrolidone (NMP), pyridine, and calcium chloride. The poly(amide-imide)s had inherent viscosities of 0.88-1.27 dL g(-1). The diimide-diacid monomer (I) was prepared from 2,5 -dichloro-p-phenylenediamine with trimellitic anhydride. All the resulting polymers were amorphous and were readily soluble in a variety of organic solvents, including NMP and N,N-dimethylacetamide. Transparent, flexible, and tough films of these polymers could be cast from N,N-dimethylacetamide or NMP solutions. Cast films had tensile strengths ranging from 92 to 127 MPa, elongations at break from 4 to 24%, and initial moduli from 2.59 to 3.65 GPa. The glass transition temperatures of these polymers were in the range of 256 degrees-317 degrees C, and the 10% weight loss temperatures were above 430 degrees C in nitrogen.