Unformatted post printPolymeric membranes either containing, or built from, ionic liquids (ILs) are of great interest for enhanced CO2/light gas separation due to the stronger affinity of ILs toward quadrupolar CO2 molecules, and hence, high CO2 solubility selectivity. Herein, we report the development of a series of four novel anionic poly(IL)-IL composite membranes via a photopolymerization method for effective CO2 separation. Interestingly, these are the first examples of anionic poly(IL)-IL composite systems, in which the poly(IL) component has delocalized sulfonimide anions pendant from the polymer backbone with imidazolium cations as “free” counterions. Two types of photopolymerizable methacryloxy-based IL monomers (MILs) with highly delocalized anions (–SO2–N(-)–SO2–CF3 and –SO2–N(-)–SO2–C7H7) and mobile imidazolium ([C2mim]+) counter cations were successfully synthesized and photopolymerized with two distinct amounts of free IL containing the same structural cation ([C2mim][Tf2N]) and 20 wt% PEGDA crosslinker, to serve as a composite matrix. The structure-property relationships of the four newly developed anionic poly(IL)-IL composite membranes were extensively characterized by TGA, DSC, and XRD analysis. All of the newly developed anionic poly(IL)-IL composite membranes exhibited superior CO2/CH4 and CO2/N2 selectivities together with moderate CO2/H2 selectivity and reasonable CO2 permeabilities. The membrane with an optimal composition and polymer architecture (MIL-C7H7/PEGDA(20%)/IL(1eq.)) reaches the 2008 Robeson upper bound limit of CO2/CH4, due to the simultaneous improvement in permeability and selectivity (CO2 permeability ~ 20 barrer and αCO2/CH4 ~119). This study provides a promising strategy to explore the benefits of anionic poly(IL)-IL composites to separate CO2 from flue gas, natural gas, and syngas streams and open up new possibilities in the polymer membrane design with strong candidate materials for practical applications.Partial support for this work provided by the United States Department of Energy (DE-SC0020282) and NASA Marshall Space Flight Center (80NSSC19K1314), is gratefully acknowledged. Liliana C. Tomé has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement no. 745734
