Introduction of taurine into polymer brush grafted onto porous hollow-fiber membrane

Two types of sulfonic-acid-group-containing porous hollow-fiber membranes were prepared by radiation-induced graft polymerization of an epoxy-group-containing monomer, glycidyl methacrylate, and the subsequent addition of taurine (NH2CH2CH2SO3H) and sodium sulfite (Na2SO3) to some epoxy groups. The remaining epoxy groups were quantitatively hydrolyzed into a diol group. The taurine-introduced porous hollow-fiber membrane (TAU-diol fiber) bound hen egg lysozyme (HEL) in approximately six multilayers while maintaining its flux at 60% of the starting porous hollow-fiber membrane, whereas the sodium sulfite-introduced porous hollow-fiber membrane (SS-diol fiber) showed a negligible flux. This difference can be explained by the fact that the amphoteric moieties, i.e., amino and sulfonic acid groups of taurine, suppress the extension of the graft chain. HEL adsorption caused the graft chain to shrink by tangling the graft chain and thereby increasing flux. The equilibrium binding capacity of the TAU(25)-diol fiber for HEL, where the number 25 denotes the molar conversion of the addition of taurine to the epoxy group, was 130 mg/g of the TAU-diol fiber. Furthermore, a high-throughput adsorption of HEL onto the TAU-diol fiber in the permeation mode was demonstrated because of the negligible diffusional mass-transfer resistance of HEL to the sulfonic acid group of the graft chain originating from the addition of taurine to the epoxy group. The diol group adjacent to the sulfonic acid group prevented the nonselective adsorption of HEL onto the TAU-diol fiber.