Synthesis of thermostable Nomex copoly(amide-imide) and their properties

Abstract

Thermostable Nomex copoly(amide–imide)s with inherent viscosity of 0.72–1.31 dL/g were synthesized by reacting diacid-terminated Nomex prepolymer with various diisocyanate-terminated polyimide prepolymers. The polyimide prepolymer was prepared by using 4,4′-diphenylmethane diisocyanate to react with 3,3′,4,4′-benzophenonetetracarboxylic dianhydride, pyromellitic dianhydride, or 3,3′,4,4′-sulfonyl diphthalic anhydride using a direct one pot method in order to improve their solubility. The copolymers, except B-1, P-1, P-2, D-1, and D-2, could be dissolved in N, N-dimethylacetamide +5% lithium chloride at room temperature or dimethyl sulfoxide at high temperature but were not soluble in N,N-dimethylformamide or pyridine. The solubility is considered to be related to their crystallinity. Those copolymers with crystalline structure displayed poor solubility. All the Nomex copoly(amide–imide)s had glass transition temperatures in the range of 223–352°C and showed a 10% weight loss temperature of 438–574°C in air and 441–585°C in nitrogen atmosphere. The tensile strength, elongation at break, and initial modulus of polymer films ranged 63–118 MPa, 4–9% and 1.67–2.53 GPa, respectively. From the X-ray diffraction studies, copolymers of B-1, P-1, P-2, D-1, and D-2 with high content of PmIA showed a crystalline structure, but the others only displayed an amorphous morphology. © 1996 John Wiley amp; Sons, Inc.