Composite membranes and methods of use

A method of separating alcohol from a mixture of alcohol and gasoline, the method comprising contacting the mixture with an asymmetric composite membrane comprising:

• a porous substrate comprising opposite first and second major surfaces, and a plurality of pores;
• and
• a pore-filling polymer disposed in at least some of the pores so as to form a layer coating all of the first major surface of the porous substrate and having a thickness within the porous substrate, with the amount of the pore-filling polymer at or adjacent to the first major surface being greater than the amount of the pore-filling polymer at or adjacent to the second major surface;
• wherein the starting materials for the pore-filling polymer include a (meth)acrylate-containing monomer and/or oligomer, and the starting materials for the pore-filling polymer also comprise one or more polymeric additives that (a) have a strong affinity with the pore-filling polymer so that the pore-filling polymer is reinforced by the one or more polymeric additives and (b) enter pores of the porous substrate with the starting materials and thereby form an interpenetrating polymer network, the polymeric additive is selected from polyacrylic acid, polymethacrylic acid, polyacrylamide or its copolymers, polyethylene oxide, polyvinyl alcohol, poly(ethylene-co-vinyl alcohol) (EVAL), poly(N-vinylpyrrolidone), and mixtures or copolymers thereof, the amount of polymeric additive is in the range of from at least 0.20 wt-% up to 75%, based on the total amount of pore-filling polymer plus polymeric additive, the molecular weight (weight average) of the polymeric additive is in the range of from 1,000 to 500,000;
• and
• wherein the pore-filling polymer is more permeable to alcohol than gasoline but not soluble in alcohol or gasoline.