Novel thermally stable and soluble triarylamine functionalized polyimides for gas separation

A novel series of solution-processable aromatic polyimide membranes with trimethyl-substituted triphenylamine units for gas separation were prepared from a newly synthesized dianhydride, N,N-bis(3,4-dicarboxyphenyl)-2,4,6-trimethylaniline dianhydride (2), and various diamines via one-step high-temperature solution polymerization. The corresponding polyimides derived from structurally related dianhydrides with different pendant groups such as phenyl, naphthyl, and pyrenyl moieties were also prepared for comparison. All the polyimides were readily soluble in many polar solvents and showed useful levels of thermal stability associated with high glass-transition temperatures (Tg, 324–455 °C) and high char yields (higher than 58% at 800 °C in nitrogen). The noncoplanar triphenylamine-containing polyimides IV with pendant trimethyl-phenyl moieties exhibited an effective improvement of gas permeability with a minor decrease in permselectivity.