Ambient Temperature Transition-Metal-Free Dissociative Electron Transfer Reversible Addition-Fragmentation Chain Transfer Polymerization (DET-RAFT) of Methacrylates, Acrylates, and Styrene

Inorganic sulfites as reducing agents were successfully used in combination with typical reversible addition-fragmentation chain transfer (RAFT) agents for the controlled DET-RAFT (DET: dissociative electron transfer) of methacrylates, methyl acrylate (MA), and styrene (Sty) near room temperature (30 °C). The polymerizations were first-order with respect to monomer conversion and polymers with narrow molecular weight distributions (D? < 1.2), and "living" features were obtained. MALDI-TOF experiments demonstrated the integrity of the chain-ends and clearly showed the absence of SO₂ in the polymer chains. Kinetic studies revealed that an increase of either temperature or concentration of sulfites provided faster reactions, without loss of control. Ab initio quantum chemistry calculations suggested that in the presence of the reducing agent the RAFT agent undergoes one-electron reduction to a stable radical anion that can then undergo fragmentation to yield the initiating carbon-centered radical. The new metal-free DET-RAFT developed proved to be versatile and robust, as it could be also used for the polymerization of different relevant monomers, such as glycidyl methacrylate (GMA), 2-(diisopropylamino)ethyl methacrylate (DPA), and 2-(dimethylamino)ethyl methacrylate (DMAEMA).