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 various diisocyanate‐terminated polyimide prepolymers. The polyamide prepolymers were prepared by first reacting m ‐phenylene diamine and isophthaloyl dichloride to form a poly( m ‐phenylphthalamide) prepolymer, then the terephthaloyl dichloride was subsequently added to form a para – meta benzoic polyamide prepolymer. The polyimide prepolymers were also prepared by using 4,4′‐diphenylmethane disocyanate to react with pyromellitic dianhydride, 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride, or 3,3′,4,4′‐sulfonyldiphthalic anhydride using the direct one‐pot method to improve their solubility, but without sacrificing thermal and physical properties. From the experimental results, 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 ‐methyl‐2‐pyrrolidone, dimethylimidazole, N , N ‐dimethylacetamide, dimethyl sulfoxide, and N , N ‐dimethylformamide; however, some of the copolymers were not soluble in pyridine. The solubility was related to their chemical structure. Those copolymers with sulfonyl and high amide content displayed good solubility. All the poly(amide‐imide)s had a glass transition temperature of 260–324°C, but the melting point did not vary much. The 10% weight loss temperatures were in a range of 463–580°C in nitrogen and 450–555°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 to 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 amorphous structure, mostly display a crystalline morphology. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2671–2679, 1999