Synthesis and properties of organosoluble poly(amide-imide)s with propeller-shaped 1,1,1-triphenylethane units in the main chain

A dicarboxylic acid {1,1-bis[4-(4-trimellitimidophenoxy)phenyl]-1-phenylethane (II)} bearing two performed imide rings was prepared from the condensation of 1,1-bis[4-(4-aminophenoxy)phenyl]-1-phenylethane and trimellitic anhydride in a 1/2 molar ratio. A novel family of poly(amide-imide)s with inherent viscosities of 0.83–1.51 dL/g was prepared by triphenyl phosphite-activated polycondensation from the diimide-diacid II with various aromatic diamines in a medium consisting of N-methyl-2-pyrrolidinone (NMP), pyridine, and calcium chloride. Because the 1,1,1-triphenylethane group of II was unsymmetrical, most of the resulting polymers showed an amorphous nature and were readily soluble in polar solvents such as NMP and N,N-dimethylacetamide. All the soluble poly(amide-imide)s afforded tough, transparent, and flexible films, which had tensile strengths ranging from 88 to 102 MPa, elongations at break from 6 to 11%, and initial moduli from 2.23 to 2.71 GPa. The synthesized poly(amide-imide)s possessed glass-transition temperatures from 250 to 287 °C. The poly(amide-imide)s exhibited excellent thermal stabilities and had 10% weight losses from 501 to 534 °C under a nitrogen atmosphere. A comparative study of some corresponding poly(amide-imide)s is also presented.