The monomer and polymer of the compound 3-(3-triethoxysilylpropyl)-7,7,9,9-tetramethyl-1,3,8-triaza spiro[4.5]decane-2,4-dione have been prepared and bonded to the surfaces of silica gel particles and cellulose, and the monomer has been copolymerized with a polyurethane formulation. Treatment of these polymers with dilute sodium hypochlorite solutions renders them antimicrobial. The oxidative chlorine immobilized on the materials is stable for extended periods and can be regenerated upon eventual loss by further exposure to dilute chlorine bleaching solutions. Data are presented showing that the treated materials are biocidal against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli O157:H7. The new siloxane is superior to previous N-halamine siloxane technology in that the N-halamine moiety contains two nitrogen binding sites for chlorine, one of which is a very stable hindered amine site.