Controlled soap-free emulsion polymerization stability using a novel cationic azo radical initiator with chloride or triflate counter anion

Abstract In our previous work, we developed a novel cationic azo radical initiator, 2,2’-azobis-[2-(1,3-dimethyl-4,5-dihydro-1H-imidazol-3-ium-2-yl)]propane triflate (ADIP) to prepare cationic and hydrophilic polymer particles for incorporation into cells. To apply this cationic radical initiator to hydrophobic polymer particles for a broader range of industrial applications, we attempted to synthesize polymethylmethacrylate (PMMA) latex via surfactant-free emulsion polymerization (SFEP). However, we found that the synthesized emulsion coagulated and contained a wide-size distribution of the particles, resulting in the failure of stable emulsion polymerization. In this study, we have successfully synthesized cationic PMMA particles with a narrow size distribution without any coagulation using ADIP-Cl which is an ADIP derivative in which the triflate counter anion was replaced with chloride. Compared to other halides and polyatomic anions, the triflate anion caused a significant aggregation of the PMMA particles. Furthermore, we confirmed that ADIP-Cl can be also applicable for the size-controlled synthesis of PMMA nanoparticles with sub-100 nm size in an acetone-water mixture. We envision that polymer particles prepared by ADIP-Cl via SFEP can contribute to the design of various functional materials.