Water-soluble temperature-responsive polyelectrolytes and hydrogels have been synthesized by gamma-radiation copolymerization of [2-(methacryloyloxy)-ethyl]trimethylammonium chloride with N-isopropylacrylamide. Complex formation of soluble copolymers with potassium hexacyanoferrates (II, III) was studied in aqueous solutions. It was shown that, depending on the concentration and temperature, the formation of soluble or insoluble polycomplexes is observed. The hydrogels show good ability to absorb potassium hexacyanoferrates (II, III) from aqueous solutions. Sorption ability of hydrogels depends on the content of cationic monomer in copolymer and the nature of coordination ion. (C) 2003 Wiley Periodicals, Inc.