Dual-functional interconnected pebble-like structures in highly crystalline poly(ethylene oxide) membranes for CO₂ separation

High-molecular-weight PEO (high-M_w PEO) has great potential for application in gas separation membranes owing to its low cost and great physical properties. However, high-M_w PEO-based membranes suffer from high crystallinity, which gives rise to nonselective structural defects or very low gas permeability. In this work, we synthesize defect-free, highly permeable high-M_w PEO-based membranes for CO₂ separation through a one-pot process using macromonomers, that is, poly(ethylene glycol) diglycidyl ether (PEGDE) and branched poly(ethyleneimine) (PEI). Because of the crosslinking between PEGDE and PEI via the epoxide-amine reaction, the interconnected pebble-like structure of PEGDE-PEI (named as PEGDEI) is formed within the PEO matrix, which was observed by scanning electron microscope. This unique structure induces confined crystallization of PEO between the PEGDEI networks, effectively suppressing the formation of spherulitic crystalline defects confirmed by small-angle X-ray scattering and optical microscopy. Moreover, the interconnected amorphous PEGDEI structure with a large number of amine groups acts as a CO₂ transport highway, thereby significantly improving the CO₂ permeability. As a result, the PEO/PEGDEI membrane achieved the best performance at 70 wt% of PEGDEI loading, showing CO₂ permeability of 201.1 barrer with CO₂/CH₄ selectivity of 15.7 and CO₂/N₂ selectivity of 49.3. This work suggests a facile strategy to apply low-cost high-M_w PEO as gas separation membranes by constructing dual-functional interconnected networks.