A method for removing phosphate from a patient by ion exchange comprising orally administering to said patient a therapeutically effective amount of a composition comprising at least one polymer characterized by a repeat unit having the formula ##STR32## or a copolymer thereof, wherein n is an integer, each R1, R2 and R3, independently, is H, an unsubstituted C1 -C20 -alkyl, alkylamino, or aryl gr