Thermal behavior of copolyimides containing bisbenzoylamine groups

In an effort to improve the processibility of full aromatic polyimides, copolybisbenzoylamine imides were synthesized. As this study is a continuation of our work on flexibilization of the polyimide main chain, the bisbenzoylamine group was introduced stepwise into the polyimide main chain. Mixtures of pyromellitic anhydride, the rigid component, and a bisbenzoylamine-3,3′, 4,4′-tetracarboxylic acid dianhydride, the flexible component, were polymerized with aromatic diamines in a two-step procedure. The thermal stability of the four series of resulting copolyimides shows parallel changes that depend on the dianhydride ratio. The functional dependence of glass transition temperature (T_g) on copolymer composition differs for hydrogen or alkyl group substitution on the nitrogen in the bisbenzoylamine group. The solubility of the copolyimides in dimethylformamide changes from 0 to 33 wt %; there is a nonlinear dependence between solubility and the dianhydride ratio.