Interfacially initiated polymerization of epoxides: a thin-film synthesis platform for XLPEO gas separation membranes

Crosslinked poly(ethylene oxide) (XLPEO) membranes are leading candidates for membrane post-combustion carbon capture, because of their high CO2/N2 selectivity and CO2 permeability. However, their crosslinked nature makes it difficult to process them into thin films through conventional coating techniques. In this study, interfacially initiated chain growth polymerization of epoxides is used to circumvent the XLPEO processing challenge whilst allowing in-situ crosslinking. The interfacial design strategy yields intrinsically crosslinked, epoxide-based PEO (eXLPEO) thin-film composite gas separation (GS) membranes consisting fully of CO2-philic ether bonds. An eXLPEO selective layer made from poly(ethylene glycol) diglycidyl ether was successfully deposited on a PAN support and, after introduction of densification steps and a PDMS sealing, gas selective membranes were obtained. Synthesis-structure-performance analysis revealed that multiple reaction condition combinations result in highly selective membranes with a tunable chemical structure. The best performing membranes showed CO2/N2 separation factors of 58 at 35°C, with a stable operation at pressures from 2-10 bar, and retaining a separation factor of 30 at 65°C. However, all membranes had a low CO2 permeance (<10 GPU), probably due to pore impregnation of the support layer. This work demonstrates for the first time the viability of interfacial polymerization for the synthesis of thin film eXLPEO GS membranes.