The cyclotetrapolymerization of four diallylamine salt monomers, containing chelating motifs of aminocarboxylate, aminophosphonate, aminosulfonate and primary amine at the terminal of an alkyl chain (CH2)(12), has led to the synthesis of a tetrapolymer in excellent yield. A copolymer of methacrylate having acetyl acetate pendant has also been synthesized. The two polymers in aqueous solution is found to form gel because of covalent crosslinking via formation of imine bond by condensation of -NH2 groups of the tetrapolymer with the acetoacetate groups of the polymethacrylate copolymer. This is the first example of a cyclopolymer immobilized by covalent crosslinking with a polymethacrylate. The hydrogel, embedded with chelating motifs of aminoalkyl-carboxylate, phosphonate and sulfonate as well as imine motifs, demonstrated remarkable efficacies for the removal of Hg(II) ions at ppb levels. A 50 mg-dose of the hydrogel immersed in aqueous medium (20 mL) could reduce the concentration of Hg(II) from 200 and 500 ppb to 0.20 and 0.17 ppb, respectively, within 30 min. The hydrogel has also been shown to be remarkably effective in the removal of several toxic and priority metal pollutants from the matrix of an industrial wastewater.