A new diamine monomer containing noncoplanar methyl substitution, 2,2'-dimethyl-4,4'-bis(2-trifluoromethyl-4-aminophenoxy)biphenyl (DBTFAPB) was successfully synthesized and used in the preparation of a series of polyamides and polyimides by direct polycondensation with various aromatic dicarboxylic acids and tertacarboxylic dianhydrides. A new noncoplanar dicarboxylic acid monomer containing noncoplanar methyl substitution, 2,2'-dimethyl-4,4'-bis(2-trifluoromethyl-4-trimellitimidophenoxy)bipheny l (DBTFTPB) was also successfully synthesized by refluxing the diamine, DBTFAPB, with trimellitic anhydride in glacial acetic acid. A series of new poly(amide-imide)s were prepared directly from DBTFTPB with various diamines in N-methyl-2-pyrrolidinone (NMP). All the polymers exhibited excellent solubility in solvents, such as N-methyl-2-pyrrolidinone (NMP), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), pyridine, tetrahydrofuran (THF), cyclohexanone and gamma-butyrolactone at room temperature or upon heating at 70 degrees C. Inherent viscosities of the polymers were found to range between 0.60 and 1.34 dL g(-1). Gel permeation chromatography (GPC) of the polymers showed number-average and weight-average molecular weight up to 7.3 X 10(4) and 17.9 X 10(4), respectively. These polymers showed that the glass transition temperatures were between 230 and 265 degrees C, and the 10% mass loss temperatures were higher than 460 degrees C in nitrogen atmosphere. All the polymers could be cast into flexible and tough films from DMAc solutions. They had a tensile strength in the range of 82-124 MPa and a tensile modulus in the range of 1.9-2.9 GPa. These polymers exhibited low dielectric constants ranging from 2.87 to 4.03, low moisture absorption in the range of 0.29-3.20%, and high transparency with an ultraviolet-visible absorption cut-off wavelength in the 347-414 nm range. (c) 2006 Elsevier Ltd. All rights reserved.