Tailoring microstructure and gas transport pathways in copolymer membranes through monomer engineering and side-chain grafting

Achieving both high permeability and high selectivity in carbon dioxide (CO 2 ) separation membranes is essential for effective carbon capture. To address this challenge, a multiscale structural modulation strategy combining monomer engineering, post-grafting side-chain modification, and non-solvent-induced microstructure rearrangement (MSR) was developed. Different rigid and ether-rich structural units were incorporated into the copolymer backbone to simultaneously regulate chain packing and CO 2 affinity, while epoxy-containing side chains were further grafted to optimize gas transport pathways. Among the prepared membranes, the PEG-grafted membrane shows a marked increase in CO 2 permeability from 537.9 to 1640.9 Barrer without sacrificing CO 2 /N 2 selectivity. When further treated with ethanol-induced MSR, partial swelling-induced chain relaxation and rearrangement slightly increase the interchain spacing and generate more continuous gas transport pathways. Consequently, the optimized membrane shows a CO 2 permeability of 1865.4 Barrer and a CO 2 /N 2 selectivity of 39.75, approaching the 2019 Robeson upper bound. Long-term stability tests confirm the durability of the optimized membrane. Overall, this work demonstrates that the synergistic combination of monomer engineering, post-grafting, and MSR treatment provides an effective strategy for simultaneously enhancing CO 2 permeability and CO 2 /N 2 selectivity.