Copolymer gels were prepared by the radical copolymerization of N-hydroxymethyl acrylamide with itaconic acid and N-hydroxymethyl acrylamide with beta-methyl hydrogen itaconate. The ratios of both monomers were varied from 25 to 75 mol %, and the effects of external stimuli such as the pH and ionic strength of the swelling media were investigated. The gels were pH-responsive, and an increase in the ionic strength of the solutions caused a decrease in the equilibrium degree of swelling of the copolymer gels. The monomer reactivity ratios were determined with the Kelen-Tudos method. Moreover, the copolymer composition had a significant effect on the equilibrium swelling behavior of the two copolymers investigated. (c) 2006 Wiley Periodicals, Inc.