Gas transport through interfacially formed poly(N, N-dimethylaminoethyl methacrylate) membranes was investigated. The membrane performance for the separation of binary CO2/N-2, CO2/CH4 and CO2/H-2 mixtures was studied, and the coupling effects between the permeating species were evaluated by comparing the permeance of individual components in the mixture with their pure gas permeance. For the permeation of these binary gas mixtures, the presence of CO2 was shown to influence the permeation of the other components (i. e., N-2, H-2 and CH4), whereas the permeation of CO2 was not affected by these components. In consideration that water vapor is often encountered in applications involving CO2 separation, the presence of water vapor on the membrane permselectivity was also studied. When hydrated, the membrane was shown to be more permeable to CO2, while the membrane selectivity did not change significantly. Unlike membranes based on size-sieving of penetrant molecules, the present membranes exploit the favorable interactions between the hydrophilic quaternary amines in the membrane and CO2, especially in the presence of water vapor in the feed. (C) 2009 Elsevier B. V. All rights reserved.