Pure gas permeability coefficients of a series of copolymers based on polar hydrophilic poly(ethylene glycol) dimethacrylate n = 14 (PEGDMA) and siloxane-based co-monomer [methyl bis(trimethylsiloxy) silyl] propyl glycerol methacrylate (SIGMA) are reported SIGMA is miscible with PEGDMA and able to form homogeneous films SIGMA contains a bulky siloxane-based end group which acts to increase permeability and an -OH pendant group which Increases miscibility with polar co-monomers such as PEGDMA As the SIGMA content in these copolymers Increases to 53 vol% CO2 permeability increases from 95 to 255 barrer while CO2/N-2 and CO2/H-2 pure gas selectivities decrease from 58 to 20 and 64 to 3 2 respectively At the same time fractional free volume of the copolymer increases from 0 118 to 0 140 Comparisons to a similar copolymer system are made to rationalize the permeability and selectivity trends of this series of copolymers (C) 2010 Elsevier Ltd All rights reserved