Reevaluation of the Formation and Reactivity of Midchain Radicals in Nitroxide-Mediated Polymerization of Acrylic Monomers

Abstract

In radical polymerization of acrylic monomers, intramolecular transfer to polymer, and the reactions of the resulting midchain radical, can have a strong impact on both the kinetics and microstructure of the resulting polymer. It has previously been stated that, in nitroxide-mediated polymerization, a substantial proportion of midchain radicals reacts with free nitroxide to form a capped species and that this can lead to a reduction in branch points, in the resulting polymer. In this article, we show that, contrary to previous evidence, the nitroxide capped midchain species cannot be observed in nitroxide-mediated polymerization of butyl acrylate. In addition, we show that, in nitroxide-mediated polymerization, lower than expected concentrations of products arising from transfer to polymer are observed.