a membrane is produced by dissolving , in a water - miscible solvent , a water insoluble copolymer of acrylontrile with at least one monomer selected from the group consisting of an aminostyrene , a vinyl pyridine and an n - hydroxy - containing - substituent - acrylamide , casting said solution to form a thin layer of solution , contacting said solution with water thereby to coagulate the copolymer into a film , and washing away from the copolymer film the solution of solvent and water . the amine or hydroxy group of the copolymer is then activated and coupled with a ligand such as glucose isomerase , chymotrypsin or protein a . the coupled membranes can then be used for biological separations and reactions .