Composite poly(ionic liquid)-ionic liquid membranes containing copper (I) chloride (CuCl) have been successfully fabricated via photopolymerization of an IL monomer, 1-vinyl-3-butylimidazolium bistriflimide ([C(4)vim][Tf2N]), in the presence of CuCl and a non-polymerizable IL, 1-butyl-3-methylimidazolium chloride [C(4)mim][Cl]), forming the chlorocuprate anion ([CuCl2](-)) in situ. The influence of the metal salt content on the gas separation performance of the composite membranes was assessed. Results showed that increasing the content of non-polymerizable IL enhanced the permeabilities of CO2, H-2, N-2 and CO relative to those obtained in the pristine poly([C(4)vim][Tf2N]); whereas the addition of CuCl induced a general reduction of gas diffusivity. On the whole, an enhancement of both gas permeability and ideal gas pair selectivity were observed for CO2/N-2 and H-2/N-2 separations in the Cu-containing composite membranes with respect to the neat poly([C(4)vim][Tf2N]). (C) 2016 Elsevier B.V. All rights reserved.