Effect of polyols on the interaction of p-hydroxybenzoic acid esters with polyoxyethylene dodecyl ether.

Abstract

The effect of polyols, i.e., glycerol, propylene glycol and 1, 3-butylene glycol, on the interaction between p-hydroxybenzoates and polyoxyethylene (15 units of oxyethylene) dodecyl ether was investigated by an ultrafiltration technique using a Diaflo membrane. Polyols had little effect on the binding of p-hydroxybenzoate to the primary class of sites in the nonionic surfactant micelles. In this binding process, bound preservative molecules are thought to be located at the oxyethylene-hydrocarbon interface, so it seems possible that polyols added to the system were too hydrophilic to penetrate deeply into the micelles and to compete effectively with this class of bound preservative. However, polyols modified the binding to the secondary class of sites to some extent ; namely, these compounds could displace a part of the bound preservative from the polyoxyethylene region of the micelles. 1, 3-Butylene glycol was the most effective polyol ; glycerol was somewhat less effective in enhancing the preservative activity.