A novel bis(epoxide)-functionalized ionic liquid (IL) monomer has been reacted with a commercially available amine monomer to produce cross-linked, epoxy-amine-based poly(ionic liquid) (PIL) resins and PIL/IL ion-gels via step-growth (S-G) polymerization. The degree of chemical functionality was controlled by manipulating the monomer stoichiometric ratios. The S-G PIL resins were investigated for CO2 sorption and have a relatively high equilibrium loading of 1.0 mmol CO2/(g resin). PIL/IL ion-gel membranes were subsequently prepared and tested for CO2/light gas permeation. These materials have CO2/ N-2 and CO2/CH4 permselectivity values near the Robeson upper bound. Analysis of their gas permeation data revealed that these materials exhibit a rare case of inverse CO2/CH4 diffusion selectivity (D-CO2/D-CH4 < 1). This phenomenon was attributed to the interaction of CO2 with residual and formed amine groups in the S-G PIL, resulting in a low CO2 diffusivity compared to that of non-interacting CH4. (C) 2014 Elsevier Ltd. All rights reserved.