Aqueous Reversible Addition-Fragmentation Chain Transfer (RAFT) Polymerization Using a Trithiocarbonate Chain Transfer Agent for Practical Applications

We focused on 4-[(2-carboxyethylsulfanylthiocarbonyl)sulfanyl]-4-cyanopentanoic acid (Rtt-17), a trithiocarbonate-type chain transfer agent (CTA) used for reversible addition-fragmentation chain transfer (RAFT) polymerization. Rtt-17 contains two carboxyl groups and showed higher apparent water solubility than the related CTA Rtt-16 under the present experimental conditions, making it a promising CTA for aqueous RAFT polymerization. To explore the practical applicability of aqueous RAFT polymerization, we evaluated the polymerization of several water-soluble monomers using Rtt-17 as CTA. In the polymerizations of acrylic acid, methacrylic acid (MAA), and sodium p-styrenesulfonate, the resulting polymers showed narrow molecular weight distributions (Mw/Mn < 1.3). When the molar ratio of MAA to Rtt-17 was varied from 100/1 to 1,000/1, the Mw/Mn values remained below 1.3. Furthermore, narrow Mw/Mn values were maintained regardless of whether degassing was performed and regardless of the type of water used, namely deionized water, tap water, or well water. In statistical copolymerization using two monomers, the polymerization rate varied depending on the monomer combination. However, for all monomer compositions, the resulting polymers exhibited narrow Mw/Mn values, indicating good control of the polymerization. In the synthesis of block copolymers by sequential polymerization, narrow Mw/Mn values were obtained when MAA was used as the first block. In contrast, Mw/Mn values tended to increase when MAA was introduced as the second block.