BIOCIDAL POLYMERS ACTIVE BY CONTACT .3. AGING OF BIOCIDAL POLYURETHANE COATINGS IN WATER

Polyurethane coatings prepared from hydroxytelechelic polybutadiene wi th pendant quaternary ammonium salts (QAS) are able to kill microorgan isms only by contact. In order to determine the time of protection aga inst microorganisms, these biocidal polymers were submitted to various ageing conditions. The activity remained constant after exposure to a very high number of bacteria (Escherichia coli). Nevertheless immersi on in water caused a slow decrease of activity with time whatever the QAS examined (-N+R2R' with R = Me or Bu and R' = n-octyl to n-hexadecy l). The phenomenon can be analysed in two stages. The first one, short (5-10 days) and limited, is due to the diffusion of a water-soluble s ynthesis residue. At the end of this period, the samples are still act ive and the activity is only due to a contact polymer-bacteria. The se cond stage is much slower and is accompanied by a transformation of QA S in amine. This is attributed to an equilibrium between QAS, amine, a nd alkyl bromide slowly shifted toward the formation of amine because of a weak solubility of alkyl bromide in water. Increasing the lipophi licity and bulkiness of the QAS substituents improves the durability o f the biocidal activity. Some samples still exhibit a good activity af ter more than 1 year of ageing in harsh conditions. (C) 1993 John Wile y & Sons, Inc.