Imidazolium-functionalized polysulfone as a polymeric ionic liquid compatibilizer for ionic-liquid-based gas separation membranes

Functional polymers bearing ionic groups are attractive building blocks for membrane materials because they can simultaneously tailor chain mobility, interfacial interactions, and gas sorption. However, incorporating CO 2 -philic ionic liquids into glassy polymer matrices often leads to limited phase compatibility and morphological instability, which compromise transport performance and reproducibility. In this work, polysulfone was chemically functionalized with alkyl imidazolium pendants and employed as a polysulfone-derived polymeric ionic liquid (PIL) component in blended membranes containing pristine polysulfone and the ionic liquid 1-butyl-3-methylimidazolium succinimidate ([BMIM][Succ]). By systematically varying the pendant structure while keeping the fabrication protocol constant, we elucidate structure–property relationships linking functional group chemistry to membrane microstructure and gas transport. The imidazolium-functionalized polysulfone markedly improves ionic liquid dispersion and membrane homogeneity, enabling a concurrent increase in CO 2 permeability and CO 2 /N 2 selectivity compared to both pristine polysulfone and unmodified polysulfone/ionic liquid blends. CO 2 permeability values up to ∼ 290 Barrer at 0.8 bar and 30 °C were obtained. The observed behavior is consistent with an interplay between ionic-liquid-mediated CO 2 solubility and PIL-controlled diffusivity through improved phase compatibility. Overall, this study highlights polymeric ionic liquid engineering as a modular functional-polymer strategy to improve phase compatibility in ionic-liquid-containing membranes and tune gas-transport properties through controlled chemical design.