Biocidal Poly(styrenehydantoin) beads for disinfection of water

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Introduction

Work in these laboratories since 1980 has focused on the development of novel biocidal N-halamine derivatives. 1 Water-soluble cyclic N-halamine derivatives such as 1,3-dihalo-5,5-dimethylhydantoin and halogenated isocyanurates (e.g., Trichlor and Dichlor) have been employed as biocides for industrial and recreational water uses for many years, but the water-soluble N-halamine compounds produced in these laboratories (oxazolidinones and imidazolidinones) are superior because of their long-term stabilities in aqueous solution and in dry storage. This exceptional stability is a result of their chemical structures; all have electron-donating alkyl groups substituted on the heterocyclic rings adjacent to the oxidative N-Cl or N-Br moieties which hinder the release of “free halogen” into aqueous solution. The combined N-halamines thus serve as the contact biocides.

Although combined N-halamine monomers generally require longer contact times at a given halogen concentration than does “free halogen” to inactivate pathogens, it has been demonstrated in these laboratories that it is possible to concentrate N-halamine moieties on insoluble polymers, thus producing a substantial reservoir of combined halogens for enhanced disinfection purposes. Furthermore, the functionalized N-halamine polymers may be superior in overall performance (taking into account biocidal efficacy, stability at varying pH’s and in the presence of organic receptors, rechargeability, lack of toxicity, and cost) to other biocidal polymers which have been developed over the years, some of which are in the commercial sector, such as halogenated poly(styrene-divinylbenzenesulfonamides),2 polymeric phosphonium materials,3 and polymeric quaternary ammonium compounds.4

Several commercial polymers have been functionalized with N-halamine moieties, rendering them biocidal upon surface contact with pathogens. These include cellulose,5,6 nylon,6,7 poly(ethylene terephthalate),6,8 Kraton rubber,9 and various surface coatings.10 However, to date, the most important N-halamine polymers developed, because of their potential for economical disinfection of potable water, thus improving world health, are the N-halogenated poly(styrenehydantoins) (Figure 1).11-15 In previous work it was shown that the biocidal polymers poly[1,3-dichloro-5-methyl-5-(4¢-vinylphenyl) hydantoin] (Poly1-Cl) and poly[1,3-dibromo-5-methyl-5-(4¢-vinylphenyl)hydantoin] (Poly1-Br) could be prepared by a three-step procedure.11,12 In the first step commercial polystyrene having low cross-linking was dissolved in an organic solvent such as carbon disulfide, and a Friedel-Crafts acylation was performed utilizing acetyl chloride and the catalyst aluminum chloride. The  poly(4-vinylacetophenone) thus produced was then dissolved in an ethanol/water mixture, and it was reacted in the second step with potassium cyanide and ammonium carbonate in a pressure reactor to produce poly[5-methyl-5-(4¢-vinylphenyl)hydantoin] (PSH). This product was a granular solid which was insoluble in water, but it could be chlorinated or brominated at 10 °C by slowly adding free chlorine or free bromine, respectively, under alkaline conditions. The final products were amorphous solids which were insoluble in water and could be packed into glass columns which functioned as cartridge filters.

It was observed that the filters inactivated numerous species of bacteria, fungi, and even rotavirus in only seconds of contact time in flowing water.11-15 Also, it was observed that the columns did not leach out decomposition products into the water14 and that the free chlorine and bromine concentrations leached into the flowing water were less than 0.1 mg/L and less than 2.0 mg/L, respectively. Furthermore, once the halogen supply was exhausted through various loss processes, it could be replenished on the polymers by simply exposing them to flowing aqueous free halogen (e.g., sodium hypochlorite bleach for Poly1-Cl). It appeared that the chlorinated polymer would be useful for potable water disinfection applications throughout the world and that the brominated polymer would work well in disinfecting recreational water sources.

However, there were limitations inherent in the polymers produced as described above. First, the particle size could not be controlled in the three-step synthesis; the particles varied in diameter from less than 10 ím to several hundreds of microns. A large portion of the particles were small; these migrated to the end of the filter, causing plugging and some deposition into the disinfected effluent water. Also, larger particles tended to break into smaller particles over an extended use period. Second, the irregular particle distribution led to flow reproducibility problems from batch to batch. Third, the dried solids exhibited a noticeable halogen odor when stored in enclosed containers as many commercial halogenated resin materials do. A buildup of free halogen in the storage container could lead to occupational exposure for workers in an industrial setting.

The limitations have now been circumvented by converting highly cross-linked polystyrene porous beads of uniform size into biocidal polymers while maintaining particle size control and by carefully controlling the halogenation conditions by appropriate pH adjustments. The methods and some performance data will be described herein.

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