Abstract
Gas transport properties of thermally rearranged polybenzoxazoles without fluorene rings (TR-coPBOs) were studied. Specific volumes (V sp s) of the TR-coPBOs were larger than the values predicted by the theoretical additive rule, stating that copolymerizing heterogeneous structures into a part of the rigid main chains caused inhibition of molecular chain packing. Gas permeability coefficients of the TR-coPBOs exceeded those predicted by the theoretical semi-logarithmic additivity and came to be maximized at the copolymerization of 10 mol% of heterogeneous units. The increasing gas permeability could be attributed to the increasing free volumes due to the copolymerization of heterogeneous units. Despite the specific increase in CO2 permeability by the copolymerization, the TR-coPBOs possessed high CO2/CH4 selectivity. This fact demonstrated the TR-coPBOs could achieve simultaneously high CO2 permeability and CO2/CH4 selectivity, maintaining inherent high CO2/CH4 permselectivity.
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