This work concerns the relationships between structural characteristics and permeation properties of self-standing films made of cross-linked poly(ethylene oxide-co-epichlorohydrin) P(EO/EP) copolymers. Permeation experiments with CO2, N-2 and H-2 show high permeation rates and high selectivity towards CO2. The permeability remains almost constant for EO contents ranging between 50 mol% and 80 mol%. At higher EO content, the permeability increases rapidly up to a maximum around 90 mol% and then decreases abruptly. This particular behaviour was explained in terms of the evolution of polymers composition, crystallinity and cross-sectional concentration profile of chloromethyl groups. (C) 2009 Elsevier B.V. All rights reserved.