Using cationic and anionic polymerization of 1,1,3,3-tetramethyl-2-oxa-1,3-disilacyclopentane ( I ) and 1,1,3,3-tetramethyl-2-oxa-1,3-disilacyclohexane ( II ), α,ω-dihydroxypolydimethylsildimethyleneand α,ω-dihydroxypolydimethylsiltrimethylenedimethylsiloxanes ( III and IV , respectively) were synthesized. The polymer materials for the flat membranes MI and MII with stable mechanical properties were produced via crosslinking condensation of tetraethoxysilane and the terminal hydroxyl groups of III and IV . Methane and butane were applied to demonstrate the gas transport properties of these membranes. It was shown that compared to PDMS, the synthesized MI and MII have a higher butane/methane ideal selectivity at high permeability coefficients (7800 and 6600 Barrer, respectively). An increase in butane/methane selectivity is achieved due to the high coefficients of butane solubility in the membrane materials.