Poly(ethylene glycol)-imidazolium-functionalized 6FDA-durene polyimides (PEG-Im-Pls) with various amounts of PEG-Im attached to the polyimide were synthesized. The structures and properties of these polymers were analyzed, as were the gas-separation properties of the various membranes made from each of these polymers. Attaching PEG and ionic imidazolium groups to the rigid polyimide backbone resulted in membranes that dissolved a lot of CO2 and hence showed excellent CO2/CH4 (up to 42.0) and CO2/N-2 (up to 37.1) permselectivity values. These membranes at the same time displayed good permeability levels, with values as high as 464 Barrer. (C) 2017 Elsevier B.V. All rights reserved.