Novel pH-sensitive polymers were synthesized by copolymerizing a monomer derivatized from 4-amino-N-[4,6-dimethyl-2-pyrimidinyl]benzene sulfonamide with N,N-dimethylacrylamide. The linear copolymers showed pH-sensitive solubility, while chemically crosslinked hydrogels exhibit a relatively sharp transition in swelling around physiological pH. These changes were found to be reversible. By varying the type of sulfonamide and the copolymer composition, a new class of pH-sensitive polymers with a broad range of transition pH can be synthesized.