a permselective graft polymer is disclosed that is formed by converting into intermediate reactive sites a portion of the cyano groups of a backbone polymer containing — ch 2 — ch — units , and grafting polyalkylene oxide polymer chains to the backbone polymer through the reactive sites . either the backbone polymer of a polymer resin or a permselective polymer membrane can be grafted . when a resin is used , it is formed into a permselective polymer membrane using known methods . the resulting permselective membrane can be formed into hollow fibers or flat sheets for the encapsulation of living cells . the encapsulated cells are then implanted into a patient in need of the biologically active factors produced by the cells . the permselective graft polymer membrane exhibits good molecular diffusion with minimal protein adsorption .