Synthesis and properties of soluble colorless poly(amide–imide)s based on N,N′-bis(3-carboxyphenyl)-4,4′-oxydiphthalimide and various aromatic diamines

The diimide–diacid monomer, N,N′-bis(3-carboxyphenyl)-4,4′-oxydiphthalimide (I), was prepared by azeotropic condensation of 4,4′-oxydiphthalic anhydride and m-aminobenzoic acid at a 1:2 molar ratio in polar solvent and toluene. A series of organosoluble and colorless poly(amide–imide)s with inherent viscosities ranging from 0.95 to 1.70 dl/g were synthesized from diimide–diacid I and various aromatic diamines by the direct polycondensation using triphenyl phosphite and pyridine as condensing agents. From UV–visible spectrum and resulting parameters of Macbeth Color-eye colorimeter, these polymers were much lighter in color than other analogous polymers. All the poly(amide–imide)s were readily soluble in a variety of organic solvents such as NMP, DMAc, DMF, and DMSO, and some even could be dissolved in less polar solvents such as m-cresol and pyridine. The cast films exhibited tensile strengths ranging from 82 to 106 MPa, elongations to break from 10 to 15%, and initial moduli from 1.9 to 2.3 GPa. Poly(amide–imide)s had glass transition temperatures of 221–276°C and 10% weight loss temperatures of 551–570°C in nitrogen and 548–578°C in air indicating excellent thermal stability.