A photo-cured cyclohexyl-substituted polysiloxane (PDCHS) film was prepared and compared with polydimethylsiloxane (PDMS) for the determination of permeability coefficients using various penetrants (H-2, N-2,O-2, CO2, CH4, C3H6, and C3H8). Penetrant sorption isotherms and local effective diffusion coefficients as a function of local Penetrant concentration were also determined. The crosslink density of the films was measured via dynamic mechanical thermal analysis and was found to be 6.46 X 10(4) mol/m(3) for PDMS and 1.82 x 10(3) mol/m(3) for PDCHS. Photo-differential scanning calorimetry was used to calculate percent conversion under the conditions used for curing and was found to be (99.6 +/- 0.3)% for PDMS and (98.4 +/- 0.3)% for PDCHS. When cured, the PDCHS films had a lower crosslink density and lower permeance. It was postulated that the cycloaliphatic substitution along the polysiloxane backbone may not have full rotational ability affording closer intermolecular interactions, thus reducing the available free volume. (c) 2006 Wiley Periodicals, Inc.