semipermeable membrane consisting of a polymer , embodying groups ; said groups may be present in the continuous polymer chains or may be present in links between continuous polymer chains . the membrane may have been formed either by in situ coagulation of a polymer solution in the pores of a porous substrate or by interfacial crosslinking of a water - soluble phenolic polymer with a sulphonyl halide compound to form an groups embodying polymer in the pores of a substrate .