Blending and in situ thermally crosslinking of dual rigid polymers for anti-plasticized gas separation membranes

The polybenzimidazoles (PBI) has been employed as blends and macromolecular crosslinkers into bromomethylated polymers of intrinsic microporosity (PIM-Br) to prepare anti-plasticized gas separation membrane. Interestingly, the PBI showed excellent miscibility with PIM-Br probably due to the interaction between the benzimidazole and –CN groups, and thus a series of flexible, tough and transparent membranes were obtained by simply blending. After thermal treatment of the blending membrane, the crosslinked PIM-Br/PBI membranes with ionic and covalent crosslinking were achieved as confirmed by XPS results. Although the blending PIM-Br/PBI membranes showed the decreased gas permeabilities due to the lower gas permeability of PBI moieties, the increased gas permeabilities of PIM-Br/PBI membrane has been observed after crosslinking without significant sacrificing of selectivity. Moreover, higher crosslinking temperature induced the higher gas permeability. The PIM-Br/PBI membrane having PBI content of 5 wt% treated at 300 °C has a CO2 permeability of 3313.7 Barrer which is much higher than that of the PIM-Br/PBI blending membrane (1645.3 Barrer) probably due to the formation of more open matrix in membrane after crosslinking. However, comparable CO2/CH4 selectivity of ~13 were observed for all of the crosslinked membranes. Importantly, both of the blending and thermal crosslinking between PIM-Br and PBI resulted in the excellent CO2 anti-plasticization ability of the membrane. Particularly, a single gas plasticization pressure as high as more than 600 psi and mixed-gas plasticization resistance for crosslinked PIM-Br/PBI have been observed. This value is much higher than that of the pristine PIM-Br membrane (100 psi).