Living-Free-Radical Emulsion Photopolymerization of Methyl Methacrylate by a Surface Active Iniferter (Suriniferter)

A novel surface-active RAFT agent as a suriniferter, composed of the dithiobenzoyl main structure and a benzoic hydrophobic carboxylate hydrophilic moiety, was synthesized and applied to the living-radical emulsion polymerization of methyl methacrylate (MMA) initiated by UV irradiation in the absence of added surfactant and additional initiator at various temperatures. A stable spherical bead of PMMA was successfully obtained using the suriniferter, maintaining the living-radical polymerization characteristics. Monomer conversion, molecular weight evolution and distribution, and final particle sizes were characterized. The higher the iniferter concentration, the higher the conversion and the lower the molecular weight, final particle size, and molecular weight distribution (PDI) obtained. A linear increase in molecular weight with respect to conversion is observed, implying that this technique using the suriniferter follows living-radical polymerization. The PDI varies from 1.21 to 1.43, and the final particle sizes vary from 407 to 304 nm with an increase in the polymerization temperature from 60 to 80 °C. The ratios of the triad tacticity for syndiotactic, atactic, and isotactic configurations of the synthesized PMMA are 54.3, 38.6, and 7.1, respectively, and the glass-transition temperature (T_g) is 126.6 °C, which is much higher than that of commercial PMMA (T_g = 105 °C). Thus, it is believed that the suriniferter used in living-free-radical emulsion polymerization modifies the stereoregularity of the PMMA.