Polysiloxanes With Quaternary Ammonium Salt Biocidal Functions and Their Behavior When Incorporated Into a Silicone Elastomer Network

Polysiloxanes of various structures having biocidal quaternary ammonium salt (QAS) groups pendant to the polymer chain were prepared. Their antibacterial activities were compared in aqueous solution. Selected polysiloxanes were linear polydimethylsiloxanes having 20% siloxane units substituted at silicon by 3(dimethyl-n-octylammonio)propyl chloride or 3(dimethyl-n-hexadecylammonio)propyl chloride and terminated by silanol functions at both chain ends. They were crosslinked and also incorporated by co-crosslinking into an RTV (room temperature vulcanized) silicone elastomer. Bacteriocidal activities of surfaces of the crosslinked biocidal polysiloxanes and of the elastomers having incorporated these polymers were determined by the colony count method. Thousand-fold reduction of Staphylococcus aureus in contact with the dimethyl-n-octylammonio substituted polymer was achieved in 2 min and in contact with the elastomer containing 20 wt% of this polymer in 15 min, although the density of the QAS was as low as 0.36 mmol/g. The surface structure and properties of the elastomers were studied by XPS, contact angle, AFM and model human serum protein (HSA) adsorption. Water sorption by this material was also studied. The concentration of QAS groups on the elastomer surface depended strongly on the material surroundings. No QAS was found on the surface in ultrahigh vacuum, while a strong enhancement of QAS presence on the surface was observed when it was in contact with water or water vapor. Hydrophobicity of the elastomer surface was little affected by the incorporated biocidal QAS-containing polysiloxane when the elastomer was kept in air. This material showed little ability to adsorb the HSA protein from its aqueous solution.