A series of crosslinked poly(propylene oxide) rubbers was prepared by UV photopolymerization of poly(propylene glycol) diacrylate (PPGDA) in the presence of varying amounts of poly(propylene glycol) methyl ether acrylate (PPGMEA). The polar ether oxygen linkages in the resulting copolymers interact favorably with CO2, imparting a high selectivity for CO2 over light, non-polar gases as required for CO2 separation applications. The introduction of mono-functional PPGMEA in the polymerization reaction mixture resulted in the insertion of short side branches along the copolymer network and a corresponding reduction in the effective crosslink density; the concentration of propylene oxide (PO) segments in the networks ranged from 60 to 85 wt.%, depending upon the initial reaction composition. The effect of PPGMEA content on the mass density, free volume, and viscoelastic relaxation properties of the polymer networks was studied, and these results were related to the gas transport performance of the rubbery films. Permeability measurements (35 degrees C) are reported for H-2, N-2, CH4, CO2, C2H6, and C2H4; solubility and diffusivity data are presented for CH4, CO2, C2H6, and C2H4. The physical and gas transport characteristics of the crosslinked PPGDA polymers were compared with those obtained for rubbery networks based on poly(ethylene glycol) diacrylate. (c) 2006 Elsevier B.V. All rights reserved.