Enhanced mechanical robustness and separation performance in triptycene modulated thermally rearranged copolyimide membranes

Thermally rearranged (TR) polymers have seen a growing role in gas separation membranes. Further exploitation of TR membranes with enhanced mechanical properties and gas separation performance are urgently demanded. Herein, a new series of TR polymers incorporating rigid triptycene units were prepared containing amino-functionalized neighbored benzene propellers and thermally rearrangeable o-hydroxy groups. The resultant TR membranes exhibit increased chain d-spacing and gas permeability with the increase of thermal arrangement temperatures. Moreover, the presence of triptycene enhances the mechanical strength of TR polymers due to the π-π stacking effect of triptycene moieties. The 400 °C TR polymer 6FDA-6FAP:DAT(2:1) displays a H2 permeability of 345.3 Barrer with a H2/CH4 selectivity of 83.6, 440% and 118% higher than the precursor, respectively, exceeding the latest Robeson upper bound. The design principle of TR membranes in this work provides an alternative route for the development of mechanically robust and high performance membranes with potentials for energy efficient gas separations.