The cation-exchange membranes (CEMs) were prepared from a graft-copolymer consisting of a polysulfone (PSF) main chain and styrene sulfonic acid side chains. The graft-copolymer was synthesized by grafting ethyl p-styrenesulfonate (Etss) on macro-initiators of chloromethylated polysulfone with different contents of chloromethyl (CM) groups, changing Etss content in the polymers by using atom transfer radical polymerization. The PSF based-CEMs show almost the same mechanical strength as commercially available CEMs. The CEMs with CM content = 16.6 mol% have higher transport properties (dynamic state transport number = 0.98, membrane resistance = 1.5 Omega cm(2)) than commercially-available CEMs. (C) 2014 Elsevier Ltd. All rights reserved.