Cyclic amine monomers and polymers and N-halamine biocidal polymer compounds are provided. Methods of making and using the same wherein the functional groups unhalogenated or halogenated hydantoins, triazine diones, imidazolidinones, and pyrimidinones are substituted onto inexpensive polymer units such as polystyrene, polyethylene, and modified polymethacrylamide are provided. The cyclic amine monomers and polymers can be utilized to form the biocidal N-halamine polymers. These N-halamine polymers are stable, insoluble biocides which release only small amounts of free halogen and other impurities. They can be useful as disinfectants for potable water, swimming pools, hot tubs, industrial water systems, cooling towers, air-conditioning systems, gas streams, paints, oils, ointments, fabrics, rubber materials, sterile bandages, coatings, hard surfaces, liners of containers, and the like.