Synthesis and Their Thermal and Thermo-Oxidative Properties of Poly(benzimidazole amide imide) Copolymers

Abstract

In this study, the 3′-dinitrobenzidine was first reacted with excess isophthaloyl chloride form a monomer with dicarboxylic acid end group. Two types of aromatic dianhydride (viz. pyromellitic dianhydride (PMDA) and 3,3′,4,4′-sulfonyldiphthalic anhydride (DSDA)), were also reacted with excess 4,4′-diphenyl-methane diisocyanate to form polyimide prepolymers terminated with an isocyanate group. The prepolymers was further extended with the diacid monomer to form a nitro group containing aromatic poly(amide-imide) copolymers. The nitro groups in these copolymers were hydrogenated to form amine groups and cyclized at 180 ^○C, to form the poly(benzimidazole amide imide) copolymers in polyphosphoric acid which acted as a cyclization agent. The resulting copolymers can be soluble in sulfuric acid and polyphosphoric acid, in sulfolane under heating to 100 ^○C, and in polar solvent N-methyl-2-pyrrolidone under heating to 100 ^○C with 5% lithium chloride. From the DSC and TGA measurements, it demonstrated that the glass transition temperature of copolymers exhibits a range of 270∼322 ^○C. The 10% weight loss temperatures exhibits a range of 460∼541 ^○C in nitrogen, and 441∼529 ^○C in air, respectively. The activation energy and the integration parameter of degradation temperature of the copolymers were evaluated by the Doyle–Ozawa method. It indicated that these copolymers exhibited good thermal and thermo-oxidative stability with the increase of imide content.