Nitroxide-Mediated Surfactant-Free Emulsion Polymerization of n-Butyl Methacrylate with a Small Amount of Styrene

Abstract

Nitroxide-mediated emulsion polymerization of n-butyl methacrylate (BMA) can produce highly living and well-controlled polymer chains when polymerized in the presence of 10 mol % styrene (St) using a one-pot, differential monomer addition technique. When n-BMA-co-St is polymerized in the presence of a surfactant above the critical micelle concentration, bimodal particle size distributions are obtained, likely as a result of combined micellar and aggregative nucleation mechanisms. This phenomenon is not observed for the more hydrophilic monomer system of methyl methacrylate and styrene. In the absence of surfactant, however, it is possible to prepare stable, monomodal latexes. Using N-tert-butyl-N-(1-diethylphosphono-2,2-dimethylpropyl) nitroxide (SG1), we report the first nitroxide-mediated polymerization of n-butyl methacrylate with a small amount of styrene in a facile surfactant-free emulsion polymerization system. The surfactant-free system requires no separate macroinitiator synthesis step and produces highly living polymers with monomodal particle size distributions. The initiator efficiency can be increased by the addition of methyl acrylate or by the addition of surfactant at concentrations below the critical micelle concentration in the absence of methyl acrylate.