Block copolymer that can be formed into an ion—Conductive membrane are provided. The block copolymer of the invention includes a first polymer block and a second polymer block attached to the first polymer block. The second polymer block has a main polymer chain and one or more side chains extending from the main polymer chain. The one or more side chains include at least one substitutent for proton transfer. Block copolymers utilizing phosphoric acid groups are also provided.