Synthesis and characterization of novel polyamide-imides containing noncoplanar 2,2?-dimethyl-4,4?-biphenylene unit

A new diimide-dicarboxylic acid, 2,2′-dimethyl-4,4′-bis(4-trimellitimidophenoxy)biphenyl (DBTPB), containing a noncoplanar 2,2′-dimethyl-4,4′-biphenylene unit was synthesized by the condensation reaction of 2,2′-dimethyl-4,4′-bis(4-minophenoxy)biphenyl (DBAPB) with trimellitic anhydride in glacial acetic acid. A series of new polyamide-imides were prepared by direct polycondensation of DBAPB and various aromatic diamines in N-methyl-2-pyrrolidinone (NMP), using triphenyl phosphite and pyridine as condensing agents. The polymers were produced with high yield and moderate to high inherent viscosities of 0.86–1.33 dL · g−1. Wide-angle X-ray diffractograms revealed that the polymers were amorphous. Most of the polymers exhibited good solubility and could be readily dissolved in various solvents such as NMP, N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), dimethyl sulfoxide, pyridine, cyclohexanone, and tetrahydrofuran. These polyamide-imides had glass-transition temperatures between 224–302 °C and 10% weight loss temperatures in the range of 501–563 °C in nitrogen atmosphere. The tough polymer films, obtained by casting from DMAc solution, had a tensile strength range of 93–115 MPa and a tensile modulus range of 2.0–2.3 GPa.