Synthesis of aromatic poly(amide-imide) copolymers containing para-meta benzoic structure

Thermostable poly(amide-imide)s containing para-meta benzoic structure were synthesized by reacting a para-meta benzoic polyamide prepolymer with vari ous diisocyanate-terminated polyimide prepolymers. The polyamide prepolymer s were prepared by first reacting m-phenylene diamine and isophthaloyl dich loride to form a poly(m-phenylphthalamide) prepolymer, then the terephthalo yl dichloride was subsequently added to form a para-meta benzoic polyamide prepolymer. The polyimide prepolymers were also prepared by using 4,4'-diph enylmethane disocyanate to react with pyromellitic dianhydride, 3,3',4,4'-b enzophenonetetracarboxylic dianhydride, or 3,3',4,4'-sulfonyldiphthalic anh ydride using the direct one-pot method to improve their solubility, but wit hout sacrificing thermal and physical properties. From the experimental res ults, the inherent viscosity of the copolymers was 0.72-1.15 dL/g and they were readily soluble in a wide range of organic hot solvents such as N-meth yl-2-pyrrolidone, dimethylimidazole, N,N-dimethylacetamide, dimethyl sulfo; dde, and N,N-dimethylformamide; however, some of the copolymers were not so luble in pyridine. The solubility was related to their chemical structure. Those copolymers with sulfonyl and high amide content displayed good solubi lity. All the poly(amide-imide)s had a glass transition temperature of 260- 324 degrees C, but the melting point did not vary much. The 10% weight loss temperatures were in a range of 463-580 degrees C in nitrogen and 450-555 degrees C in an air atmosphere. The tensile strength, elongation at break, and initial modulus of the copolymer films ranged from 59 to 102 MPa, 3.1 t o 5.1%, and 1.52 to 3.59 GPa, respectively. These copolymers, except those of high imide content (e.g., P-6, B-4, B-6 and D-6), which showed an amorph ous structure, mostly display a crystalline morphology. (C) 1999 John Wiley & Sons, Inc.