Tailoring Pendant Group Chemistry and Thiol–Ene Network Structure of Thin-Film Composite Membranes to Optimize CO ₂ Gas Separation

Carbon dioxide (CO₂) capture is critical to mitigating the anthropogenic emissions that contribute to global warming. Polymer membranes can be applied in energy efficient gas separation methods, where chemical and structural features can be tuned to co-optimize selectivity and permeability. In this work, we developed a modular thiol-ene network platform to independently tune cross-link density and functionality to explicitly understand the impact of network architecture and polymer chain functionality on separation performance. By varying the pendant functional groups in the networks, we investigated how molecular substitutions affect the selectivity of CO₂/N₂ and CO₂/O₂ selectivity. These membranes were subsequently applied as a selective layer in a thin-film composite membrane system. In pure gas testing, the network with pendant aromatic rings elevated the CO₂/N₂ selectivity from ≈10 to 34 and CO₂/O₂ selectivity from ≈5 to 17 compared to bare polydimethylsiloxane (PDMS) membranes, with a CO₂ permeability of 1426 barrer. Furthermore, the topologically regular and predictable cross-linking density features in this modular network system allowed us to unravel their effect on CO₂ selectivity and permeability. We demonstrate that these functionalized thiol-ene network-based membranes can be used in a pseudomultistage gas separation configuration to concentrate CO₂ from gas mixtures of industrially relevant composition.