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
first 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 substituent for proton transfer. Block copolymers
utilizing phosphoric acid groups are also provided.