Enhancement of the Rate of Atom Transfer Radical Polymerization in Organic Solvents by Addition of Water: An Electrochemical Study

Addition of water to organic solvents enhances the rate of atom transfer radical polymerization (ATRP). To understand the origin of this rate enhancement, the effects of H2O on the redox properties of [CuIITPMA]2+ and [BrCuIITPMA]+ (TPMA=tris(2-pyridylmethyl)amine), and on the ATRP equilibrium (KATRP) and activation rate (kact) constants of methyl -bromopropionate by [CuITPMA]+ were investigated in CH3CN, DMF and DMSO and their mixtures with methyl acrylate (MA). E°s of the complexes allowed evaluation of the relative halidophilicities of [CuIITPMA]2+ and [CuITPMA]+, KII Br and KI Br, respectively. KII Br/KI Br dropped in pure solvents and solvent/MA mixtures when 11% (v/v) H2O was added, uggesting that H2O hampers the stability of the deactivator [BrCuIITPMA]+. Conversely, both kact and KATRP were enhanced by the presence of water. In solvent/MA mixtures (50/50, v/v), addition of 11% (v/v) H2O increased KATRP by a factor of 2–3, which could explain the accelerating effect of H2O on ATRP in organic solvents.