Impact of Interfacial Halogen Bonding with a Surfactant on Miniemulsion Reversible Chain Transfer-Catalyzed Polymerization

The application of reversible chain transfer-catalyzed polymerization (RTCP)─a type of reversible deactivation radical polymerization (RDRP)─in aqueous heterogeneous polymerization is important for the direct synthesis of functional polymer particles from monomeric species. In this study, RTCP using tetraiodomethane (CI₄) was demonstrated as a catalyst in a miniemulsion system in the presence of different types of surfactants to investigate the effects of surfactant species on polymerization control. We found that nonionic and cationic surfactants were suitable for successful miniemulsion RTCPs; however, the use of anionic surfactants led to poor control of the miniemulsion RTCP. Furthermore, the polymerization control worsened with an increase in the basicity of the functional groups of the anionic surfactants. The negative effect of the anionic surfactant on polymerization control was caused by the halogen bonding between the catalyst and the anionic surfactant. Furthermore, we found that the addition of a water-soluble salt (NaCl and NaI) to the miniemulsion RTCP with sodium dodecyl sulfate significantly improved the polymerization control, in which the interfacial halogen bonding between CI₄ and anionic surfactants was switched to electrostatic interactions between anionic surfactants and salts. Our findings provide valuable guidance for the synthesis of functional polymer particles using miniemulsion RTCP from the viewpoint of surfactant selection.