Triptycene-containing poly(benzoxazole-co-imide) membranes with enhanced mechanical strength for high-performance gas separation

Herein, a series of novel triptycene-containing thermally rearranged poly(benzoxazole-co-imide) membranes (TPI-PBOs) with enhanced mechanical properties and gas separation performance are reported. The effects of chemical structures and poly(benzoxazole-co-imide) composition on the fractional free volume, polymer chain packing, microcavity size and size distribution, mechanical properties, and gas transport properties have been comprehensively investigated. Due to the incorporation of triptycene-containing non-TR-able polyimide segments, the resulting poly(benzoxazole-co-imide) films exhibited good mechanical properties even after being treated at 450 °C. The incorporation of bulky and rigid triptycene units led to significantly improved fractional free volume and gas transport properties compared to previously reported poly(benzoxazole-co-imide)s. Several triptycene-containing poly(benzoxazole-co-imide) films displayed excellent gas separation performance for H2/CH4, H2/N2, and CO2/CH4 gas pairs that exceeded the 2008 upper bounds.