Pervaporation composite membranes

A composite membrane comprising

• (a) a support member that has a plurality of pores extending through the support member, wherein the support member is an ultrafiltration membrane comprising a first layer having smaller pores and a second layer having larger pores;
• and
• (b) a cross-linked copolymer comprising:
• (i) an anionic monomer that is an unsaturated carboxylic acid or anhydride or salt thereof, or an unsaturated sulfonic acid or anhydride or salt thereof;
• (ii) a cationic monomer that is an unsaturated amine or an unsaturated ammonium salt;
• (iii) a cross-linking agent selected from the group consisting of di(ethylene glycol) diacrylate, N,N′-methylenebisacrylamide and trimethylolpropane trimetharylate;
• which cross-linked copolymer fills the pores of the support member,
• the cross-linked copolymer having a permeability for a fluid that is dependent on the polarity of the fluid, wherein the permeability increases with increasing polarity;
• and wherein the support member has a void volume that is not completely occupied by the cross-linked copolymer, and the amount of cross-linked copolymer is greater at or adjacent to a first major surface of the support member than the amount at or adjacent to a second major surface of the support member, wherein said first major surface is defined by said first layer of said support member and said second major surface is defined by said second layer of said support member.