Effects of “On-Water” on the Free Radical Polymerization of Methacrylates

Water-organic interfaces, referred to as "on-water", have recently attracted considerable attention because of their ability to accelerate various organic reactions. In this study, the effects of "on-water" interface on the conventional free radical polymerization of methacrylates were investigated. Polymerizations were carried out under various conditions, including variations in monomer, solvent, reaction time, and stirring speed, to evaluate the effects of heterogeneity and interfacial area at the water-monomer interface. The results clearly indicate that the "on-water" interface plays a significant role in increasing the polymer molecular weight. Specifically, the polymerizations of 2-methoxyethyl and 2-ethoxyethyl methacrylates in water/methanol mixtures at specific solvent volume ratios resulted in a bimodal molecular weight distribution, in which the higher-molecular-weight fraction increased as the polymerization proceeded. This polymerization behavior is attributed to a transition of the reaction medium from a homogeneous to a heterogeneous phase during polymerization, demonstrating the "on-water" interfacial effects.