Preparation of thermally rearranged (TR) copolybenzoxazoles with enhanced gas permeability

Gas transport properties of thermally rearranged polybenzoxazoles without fluorene rings (TR- co PBOs) were studied. Specific volumes ( V sp s) of the TR- co PBOs 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- co PBOs 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 CO 2 permeability by the copolymerization, the TR- co PBOs possessed high CO 2 /CH 4 selectivity. This fact demonstrated the TR- co PBOs could achieve simultaneously high CO 2 permeability and CO 2 /CH 4 selectivity, maintaining inherent high CO 2 /CH 4 permselectivity.