Methacrylic acid‐based amphiphilic block‐random copolymer stabilizers for emulsion polymerization

Abstract

AbstractThe emulsion polymerization of styrene was investigated using polystyrene‐b‐[polystyrene‐r‐poly(methacrylic acid)] amphiphilic block‐random copolymers (BRCs) of different compositions as stabilizers. These stabilizers with molar masses <20,000 g/mol, which possess unique dispersion behaviour (i.e., self‐assembly with low aggregation numbers) when dissolved in aqueous medium at alkaline pH, were prepared by the nitroxide‐mediated bulk polymerization of styrene to achieve a desired molar mass followed by chain extension by batchwise addition of styrene and methacrylic acid monomers to obtain the stabilizing group. Emulsion polymerizations of styrene stabilized by these BRCs yielded stable latexes with particle diameters that range between 30 and 150 nm. When different concentrations of the stabilizer (2–3.5 mM) were utilized for emulsion polymerization of styrene, a similar novel emulsion polymerization mechanism observed previously by our group for the acrylic‐acid based amphiphilic BRCs was also seen, further validating the difference between this class of polymeric surfactants and conventional small molecule surfactants, block copolymers, or alkali soluble resins. The performance of methacrylic‐acid based BRCs was more efficient and yielded higher surface coverage of the polystyrene latexes when compared to the acrylic‐acid based BRCs as a result of the more hydrophobic nature of the former.