Aging resistant, fluorinated aromatic polymers with ladderized, rigid kink-structured backbones for gas separations

Abstract

A facile, robust and scalable one-pot synthesis of easily processable, film-forming, shape persistent polymers became a great challenge in membrane separation technologies. Herein, we report for the first time a simple methodology of engineering off main chain ether-bond-free, ladderized, fluorinated aromatic polymers with rigid kink-structured backbones by polymerization of planar dibenzofuran (DBF) possessing multiple competitive reactive sites with carbonyl compounds. Five polymers incorporating rigid planar dibenzofuran isomer moieties with different bulky pendant trifluoromethyl- and aryl fragments were synthesized by one-pot, room temperature, non-stoichiometric superacid catalyzed step-growth polymerization. These solution processable aromatic polymers with ladderized, rigid kink-structured backbones provided membranes with tunable gas separations, physical aging resistance, and good mechanical and thermal properties. The membranes displayed CO2 permeability between 203 and 401 Barrer and H2 permeability between 210 and 472 Barrer, with CO2/CH4 and H2/CH4 selectivity close to 2008 Robeson's upper bound. Their gas permeability is due to a high FFV caused by packing of their kink-structured backbones, bulky pendant groups and to a strong interaction between CO2 and the ring fused oxygen atoms in the polymeric structure. Physical aging, measured in 30–40 μm films after 500 days, resulted in permeability drops from 17% to 39% with improved selectivity. The results obtained also demonstrate the versatility of this synthetic strategy based on superacid catalyzed polymerization to fabricate well-defined macromolecules with designed shape-persistent architecture for advanced membrane applications.