the invention is a process of making a chemically and uv treated polymer of intrinsic microporosity membrane comprising preparing a polymer of intrinsic microporosity , chemically cross - linking said polymer of intrinsic microporosity with a cross - linking compound to produce a chemically cross - linked polymer of intrinsic microporosity and then treating said chemically cross - linked polymer with uv radiation for a period of time sufficient to provide a product membrane . this product membrane is useful in the separation of c3 and higher hydrocarbons , as well as co 2 , from natural gas and other gas streams .