An epoxy-group-containing monomer, glycidyl methacrylate (GMA), was grafted onto a porous hollow-fiber membrane made of polyethylene, by radiation-induced graft polymerization. Four kinds of alcohol, i.e., methanol, ethanol, 1-propanol, and 1-butanol, were employed as the solvents for GMA. Grafting rate of GMA was decreased with increasing carbon number of alcohols. The epoxy group of the GMA-grafted membrane with a degree of grafting of 90 or 120% was converted to a sulfonic acid group at a molar conversion of 10 to 12%. Hen-egg lysozyme (HEL) dissolved in carbonate buffer solution (pH 9.0) was forced to permeate through the pores of the sulfonic-acid-group-containing porous hollow-fiber membranes prepared with various alcohol solvents. The binding capacity of HEL onto the membrane in equilibrium with the feed concentration of 0.5 g-HEL/L increased with the increase in the carbon number of alcohols. For example, the binding capacities of the membranes prepared with methanol and 1-butanol were 0.18 and 0.38 g-HEL/g-membrane, respectively. In contrast, the flux of the protein solution was decreased with increasing carbon number of alcohols. This demonstrates that longer polymer brushes are formed on the pore surface of the membrane prepared with a higher carbon number of alcohol employed as the solvent for GMA.
