Hydroxyl-functionalized microporous polymer membranes with tunable para position substituent benzaldehydes for gas separation.

We report hydroxyl-functionalized microporous polymers with tunable benzaldehyde groups for gas separation membranes. These polymers were synthesized via acid-catalyzed Friedel-Crafts polycondensation. The tunability in d-spacing and fractional free volume of these polymers depends on the para position substituents (-H, -F, -Cl, and -Br) of the benzaldehyde. Specifically, the size and polarity of the para position substituent influence the polymer chain-packing structure. Consequently, the hydroxyl-functionalized microporous polymer membrane with a larger para position substituent in the benzaldehyde group exhibited improved gas permeability. This improvement is due to enhanced gas diffusivity resulting from the inefficient polymer chain-packing structure. Furthermore, these membranes demonstrated enhanced CO plasticization resistance, attributable to the rigid, contorted polymer structure and the hydrogen bonding interactions between hydroxyl groups. This study provides insights into the relationship between the polymer chain-packing structure, tunable para position substituents, and molecular transport.