Fluorinated-cardo-based Co-polyimide membranes with enhanced selectivity for CO2 separation

The application of fluorinated polyimides in the field of gas separation membranes is becoming increasingly widespread due to their strong thermal and chemical stability. However, overcoming the separation trade-off between gas permeability and selectivity of polyimides remains a key hurdle, requiring the design of new polyimides with tailorable free volume and microstructures. Herein, we synthesized a series of polyimides containing rigid cardo groups with C-F bonds (i.e. FFDA) to increase the packing efficiency of polymer chains and thus enhance the gas selectivity of membranes. Moreover, DAM segments were copolymerized with FFDA to finely regulate the fractional free volume and produce 6FDA-FFDA/DAM copolyimide to boost gas separation performance. The CO2 permeability and CO2/CH4 selectivity of fluorinated-cardo-based copolyimide 6FDA-FFDA/DAM (1:1) are 203.4 Barrer and 43.4, respectively, performing beyond the 2008 Robeson upper bound for CO2/CH4 separation. The design principles in this work lay the groundwork for fabricating desirable polymeric membranes with tailored microstructures and properties for selective CO2 separation.