A series of new soluble poly(amide-imide)s were prepared from the diimide-dicarboxylic acid, 3,3',5,5'-tetramethyl-2,2-bis [4-(4-trimel-litimidophenoxy)phenyl]propane (TBTPP), with various diamines by the direct polycondensation in N-methyl-2-pyrrolidinone using triphenyl phosphite and pyridine as condensing agents. The new diimide-dicarboxylic acid TBTPP bearing isopropylidene and methyl-substituted arylene ether units was synthesized by the condensation reaction of 3,3',5,5'-tetramethyl-2,2-bis[4-(4-aminophenoxy)phenyl]propane with trimellitic anhydride. All the polymers were obtained in quantitative yields with inherent viscosities of 0.58-1.03 dl g(-1). The polymers were amorphous and most of them were readily soluble in aprotic polar solvents such as N-methyl-2-pyrrolidinone, N,N-dimethylacetamide, and N,N-dimethylformamide, as well as in less polar solvents such as dimethyl sulfoxide, m-cresol, pyridine and gamma-butyrolactone, and also even in tetrahydrofuran. The glass transition temperatures of the polymers were determined by the differential scanning calorimetry (DSC) method and were in the range 240-278 degrees C. These polymers were stable up to 450 degrees C and lose 10% weight in the range of 454-484 degrees C and 448-482 degrees C in nitrogen and oxygen, respectively. The polymer films had a tensile strength range of 98-122 MPa and a initial modulus range of 2.7-3.8 GPa.