3-[Tris-(trimethylsiloxy)silyl] propyl acrylate (TRIS-A) was copolymerized with poly(ethylene glycol) diacrylate (PEGDA), and the gas transport and physical properties of the resulting copolymers were characterized. Introduction of IRIS-A led to increased polymer fractional free volume and strong broadening of the glass-rubber relaxation without a significant shift in glass transition temperature in samples containing up to 80 wt% TRIS-A. Gas permeability increased significantly as TRIS-A content increased: for instance, addition of 80 wt% TRIS-A increased CO(2) permeability from 110 to 800 barter. The strongly non-polar character of TRIS-A, however, resulted in progressively lower CO(2) affinity for the polymer network, leading to decreased CO(2)/light gas selectivity with increasing TRIS-A content. (C) 2010 Elsevier B.V. All rights reserved.