Synthesis and characterization of BTDA-based polyamide-imides

A series of thermally-stable, tough, linear polyimides containing amide linkages were prepared. These materials have potential as high temperature films and coatings as well as matrix resins in graphite reinforced structures. The new polyamide-imides were prepared by reacting a group of isomers of diaminobenzanilide (DABA) with 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) to form the polyamide-acid with subsequent thermal conversion to the polyamide-imide (PAI). Four polymers were synthesized from unsubstituted amide diamines and two others from N-substituted amide diamines. The properties of these polyamide-imides were compared to those of the polyimide of benzophenonetetracarboxylic dianhydride/3,3′-diaminobenzophenone (LARC–TPI) because their structures are similar, except for the presence of the more flexible amide linkages. These polymers exhibited high inherent viscosities and glass transition temperatures. They were made into tough, flexible films which showed good thermal stability and good resistance to organic solvents. Mechanical properties of the PAI films were better than those of LARC–TPI. Films of the 4,4′-isomer polyamide-imide exhibited an exceptionally high modulus and toughness during impact evaluation.