Commercial polystyrene has been modified by chemically attaching 6-methyl-1,3,5-triazine-2,4-dione moieties to it in the para position of the aromatic rings. Chlorination of this novel polymer in aqueous base yielded poly(1,3,5-trichloro-6-methyl-6-(4’-vinylphenyl)-1,3,5-triazine-2,4-dione) which functioned as a biocide against the bacterium Staphylococcus aureas in a water-filter application. Some preliminary characterization data have been presented.