As part of a fractal pattern of gas transport processes revealed structural changes in the discrete and continuous phases of polydimethylsiloxane (PDMS) in the silane-siloxane block copolymers as compared to the homopolymer PDMS. The dimension of the PDMS structure in all three cases is the same, but the size of microcavities free volume varies quite widely (~ 5,12-13,5Å), due to the influence of the hard phase polyvinyltrimethylsilane. Reducing the size of microvoids free volume leads to a change in the mechanism of diffusion and, consequently, the diffusion coefficient. Fractal model allows prediction of the diffusion coefficients for discrete and continuous phase of siloxane block copolymers.