Interaction of Propyl p-Hydroxybenzoate with Polyoxyethylene Dodecyl Ethers

Abstract

The interaction of propyl p-hydroxybenzoate (PP) with polyoxyethylene dodecyl ethers (PDE) having various numbers of oxyethylene units in a homogeneous chain was studied by means of ultrafiltration and nuclear magnetic resonance spectrometry. The results indicate that PP molecules are bound to two distinct loci within the surfactant micelles. The primary class of sites had high affinity but a low capacity for PP molecules, whereas the secondary class of sites exhibited low affinity and a large binding capacity. In the primary class of sites, it seems probable that the PP molecules are situated at the interface of the hydrocarbon core and the polyoxyethylene mantle of the micelles. The interaction of the secondary class of sites is probably a simple partitioning of PP molecules into the polyoxyethylene region of the micelles. The interaction of PP with PDE was much greater than that of methyl p-hydroxybenzoate with PDE.