Abstract
Low-molecular-weight polymers formed by soap-free emulsion polymerization using a cationic initiator, styrene, and water are considered to be surfactants and consequently harmful to Micrococcus luteus. However, the effect of high-molecular-weight polymers, which form particulate materials in water, on M. luteus has not been elucidated. Herein, the influence of polymer morphology on toxicity against the indicator microorganism M. luteus was evaluated using polystyrene prepared by soap-free emulsion polymerization using 2,2′-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (VA-044), potassium persulfate (KPS), or 2,2′-azobis(2-methylpropionitrile) (AIBN) as the initiator. Low-molecular-weight polymers were removed from the suspension by centrifugation to ensure that only high-molecular-weight polymers were investigated in this study. Although particulate materials were formed in water, they were dissolved in toluene, which induced changes in morphology and size. The toluene solution of high-molecular-weight polystyrenes prepared using either VA-044 or KPS created an inhibition zone against M. luteus in the bioassay test. These results indicate that the morphology and size of the higher-molecular-weight polymer are closely related to antimicrobial activity. Particulate materials larger than 150 nm did not create inhibition zones in the bioassay test, although their toluene solutions were toxic to M. luteus. Therefore, the particulate or coagulated state in solution that avoids the formation of aggregates smaller than 20 nm is considered to be the environmentally safe polymer morphology.
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