The carbon dioxide separation performance of a new series of polymeric ionic liquid composite membranes based on poly(diallyldimethylammonium) bis(trifluoromethylsulfonyl)imide, poly([pyr(11)] [NTf2]), by the addition of 0, 20, 40, 60, 80 and 100 wt% of 1-Butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide [pyr(14)][NTfz]) were measured in order to establish the feasibility of using these composites as membranes for flue gas separation and natural gas purification. This study evaluates membranes within the whole range of compositions, from pure ionic liquid to pure polymer. The results show that the permeability of the three gases, carbon dioxide, methane and nitrogen, in the ionic liquid is two orders of magnitude higher than that of the polymeric ionic liquid. The preparation of composite membranes increases the permeability of all three gases, overcoming the hindered diffusion of gas in the polymer. The composites also promote increased permselectivity for CO2/N-2, while the opposite behavior was found for CO2/CH4. Robeson plots were used to evaluate and understand the performance of the prepared membranes for the two selected gas separations. The addition of free ionic liquid to the polymer system has the main role in the permselectivity of the prepared composites. (C) 2012 Elsevier B.V. All rights reserved.