Microsuspension iodine transfer polymerization (ms ITP) for synthesis of micrometer-size, “hydrophilic” polymer particles

Microsuspension conventional radical polymerization ( ms CRP) of methyl acrylate (MA), which is more hydrophilic monomer than methyl methacrylate (MMA), was carried out at different benzoyl peroxide (BPO) concentrations (0.8–8.0 wt% relative to MA), gave not similar micrometer-size poly(MA) (PMA) particles as MA droplets but submicrometer-size ones. That is, emulsion polymerization proceeded in the ms CRP systems. When microsuspension iodine transfer polymerization ( ms ITP) with CHI 3 as chain transfer agent was carried out at 8.0 wt% BPO (relative to MA), at which micrometer-size poly(MMA) particles were successfully synthesized without submicrometer-size byproduct particles in a previous particle, only submicrometer-size PMA particles were formed, too. However, the percentage of the byproduct particles obviously decreased with a decrease in the BPO concentration, resulting in zero practically at 0.8 wt% BPO, where number-average molecular weight of the micrometer-size PMA particles was nearly equal to theoretical one and polydispersity was comparatively narrow ( M w / M n  = 1.43). Such experimental results were presumed based on the kinetic simulation study. Above results support the validity of the “radical exit depression (RED) effect” proposed and indicate a decisive effectiveness of ms ITP to improve a long-standing problem of ms CRP of “hydrophilic” monomer.