Polypropylene supported polyaniline membranes photografted with 2-hydroxyethyl methacrylate and glycidyl methacrylate to produce hydrophilicity and reactivity and then reacted with diamines to provide basicity, have been prepared and used for the separation of carbon dioxide and methane. After solvation with water, these membranes exhibited a permeability of around 3400 Barrers and a separation factor up to 490. Examination by scanning electron microscopy and atomic force microscopy confirmed the absence of undesired cracks and pinholes in these membranes. The primary amine groups were further modified with 2-ethyl-2-thiopseudourea to form guanidine functionalities producing membranes with a notable permeability of 3460 Barrers and a separation factor of 540. The presence of water in these membranes promotes permeation of carbon dioxide via the facilitated transport mechanism in which both the fixed carrier amine moieties and water play the major role. (c) 2012 Elsevier B.V All rights reserved.