New soluble poly(amide–imide–imide)s based on tetraimide-dicarboxylic acid condensed from 4,4′-oxydiphthalic anhydride, 2,2-bis[4-(4-aminophenoxy)phenyl]sulfone, and p-aminobenzoic acid, and various aromatic diamines

A new-type tetraimide-dicarboxylic acid (I) was synthesized starting from the ring-opening addition of p-aminobenzoic acid, 4,4′-oxydiphthalic anhydride, and 2,2-bis[4-(4-aminophenoxy)phenyl]sulfone (BAPS) at a 2:2:1 molar ratio in N-methyl-2-pyrrolidone (NMP), followed by cyclodehydration to the diacid I. A series of poly(amide–imide–imide)s (IIIa–i) with inherent viscosities of 0.71–0.99 dl/g was prepared by triphenyl phosphite-activated polycondensation from the tetraimide-diacid I with various aromatic diamines (IIa–i) in a medium consisting of NMP, pyridine, and calcium chloride. All of the polymers were readily soluble in a variety of organic solvents such as NMP, N,N-dimethyl acetamide, dimethyl sulfoxide, and even in less polar m-cresol. Compared with those of the corresponding poly(amide–imide)s IVa–i, the solubilities of poly(amide–imide–imide)s IIIa–i were greatly improved. Most of the polymers III afforded tough, transparent, and flexible films, which had a tensile strength ranging from 94 to 100 MPa, elongation at break from 7 to 9%, and initial tensile modulus from 2.0 to 2.3 GPa. The glass transition temperature of polymers was recorded at 265–291 °C. They had 10% weight loss at a temperature above 550 °C and left more than 50% residue even at 800 °C in nitrogen.