Copolymers of methyl methacrylate and 1,3-bis(methacryloxy methyl)-1,1,3,3-tetramethyl disiloxane were prepared by chemically induced copolymerization/crosslinking at 60°C and 49 mm Hg. Crosslinked, glassy copolymers were obtained with copolymer mole fraction of the silicon-containing monomer varying from 0.09 to 0.55. Oxygen transport studies were performed with thin films as prepared and after sub-Tg annealing. The results of this study indicated that an enhancement of both the steady state oxygen permeation rate and the oxygen diffusion coefficient was achieved through copolymerization. The oxygen diffusion coefficients through the copolymers were found, within experimental error, to be independent of silicon content and ranged from 0.80 × 10−7 to 1.90 × 10−7 cm2/s vs. oxygen diffusion coefficient for pure poly(methyl methacrylate) of 1.5 × 10−8 cm2/s. Sub-Tg annealing effected a reduction of approximately equal magnitude in both the oxygen diffusion coefficient and the steady state oxygen flux for the copolymers. In addition, the normalized oxygen flux data were predicted with Fick's law, assuming constant boundry conditions and diffusion coefficient. These results were explained in terms of the free volume theory and the combined effects of increased crosslinking density, chain mobility, and oxygen solubility with increased copolymer silicon content.