Two families of rubbery polymers, commercial hydrogenated nitrile rubbers and synthesized poly (acrylonitrile-co-butadiene)-based polyurethanes with different amount of nitrile groups were studied as CO2 selective membrane materials. The polymers were characterized by the techniques of FTIR, gel permeation chromatography, WAXD, and differential scanning calorimetry. The permeabilities of pure CO2 and N-2 were measured using constant pressure/variable volume method at a feed pressure of 6 atm. With a higher amount of polar nitrile group within a given family of polymers, the permeability coefficient (P) was found to decrease, while the permselectivity (alpha) of these membranes was found to increase. The trade-off between both transport parameters was less severe for the polyurethanes, which also showed much higher permeabilites. The results obtained were also discussed with respect to the polymer structure, and some relationships were found between P and T-g values. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 2690-2696, 2011