Effect of Phenols on the Free-Radical Photopolymerization of Vinyl Monomers in Aqueous Solution

Abstract

In this work, the effect of a series of p-substituted phenols on the photopolymerization of acrylamide in aqueous solution is reported. Millimolar concentrations of the phenols slightly reduce the polymerization rate, but decrease markedly the molecular weight of the formed polymers. Chain transfer constants were determined by a modified Mayo equation that takes into account variations in the polymerization rate. Chain transfer efficiencies were found to be highly dependent upon the donor-acceptor capability of the phenols, increasing with electron-donating p-substituents. The electron-donating ability is related to a charge transfer separation in the transition state. Fluorescence measurements of the phenols incorporated into the polymer chain indicate that the addition to the monomer involves the o-position of the phenoxyl radicals.