Poly(styrene-b-butadiene-b-styrene) (SBS) block copolymer has been recently demonstrated to be a polymer membrane material with high selectivity for CH₄/N₂ gas separation. In this study, two effective approaches of grafting and crosslinking have been explored to improve the gas permeability of SBS polymer by introducing polysiloxane (silicone) polymers to SBS backbone via hydrosilylation reaction. First, a series of novel poly(styrene-b-butadiene-b-styrene)-g-poly(dimethylsiloxane) (SBS-g-PDMS) graft copolymers were synthesized via the hydrosilylation reaction of SBS carbon double bonds and silanes (Si-H) from monohydride terminated PDMS. We found that CH₄ permeability was increased 40% by grafting only 1.24% PDMS in SBS. Second, to supplement additional silicone to SBS, the hydrosilylation reaction of SBS carbon double bonds and silanes from poly(methylhydrosiloxane) was used to prepare novel SBS-silicone cross-linked polymer membranes. It was demonstrated that CH₄ permeability could be improved by 214%, achieving 118 Barrer when 45 wt% silicone was incorporated in SBS. This successful example of improving gas permeation by molecular design could open up new avenues for researchers to develop future polymer membranes with both high selectivity and permeability for industrial applications including methane enrichment from coalbed gases.