Rational Design and Synthesis of Poly(arylene ether)s for Membrane-Based Gas Separations

Industrial purification and separation processes account for 10–15% of the world's energy consumption and are responsible for 16% of the total CO₂ emissions. This is because we still rely on energy-intensive, century-old technologies such as amine absorption and distillation. Polymers are an attractive platform of materials for energy-efficient membrane-based separations. Membrane separation is a non-thermal separation technique that is capable of using 90% less energy than conventional distillation. Notably, the high free volume, which stems from their rigid and contorted backbone of polymers of intrinsic microporosity (PIMs), are attractive materials for gas separations. This work presents the rational design and synthesis of linear microporous poly(arylene ether)s (PAEs) via a Pd-catalyzed C-O polycondensation reaction. The scaffold of these microporous polymers consists of rigid three-dimensional triptycene and highly stereo-contorted spirobifluorene, generating high free volume and high porosity with angstrom-sized pores, ideal for gas separations. Unlike classic PIMs, this robust methodology for synthesizing PAEs allows facile incorporation of functionalities and branched linkers to control permeation and mechanical properties. CO₂-philic groups, such as nitrile and tertiary amine, can be incorporated into this microporous polymeric scaffold to enhance CO₂ separation performance. The exceptional structural flexibility also enables the incorporation of carboxylic groups, which facilitates the process of metal ion doping that might improve propane/propylene separation. Additionally, a solution-processable branched polymer prepared using this synthetic strategy showed good gas separation performance and enhanced mechanical properties, which allowed for the formation of a submicron defect-free film with comparable permeance-selectivity property sets to high-performance ultrathin polymer membranes reported in the literature. The structural flexibility, high physical stability, and ease of processing suggest that this synthetic strategy provides generalizable design strategies for membrane-based gas separation applications.