Investigating the mechanism of copper(0)-mediated living radical polymerization in organic media

Single electron transfer living radical polymerization (SET-LRP) is a versatile polymerization tool that allows for the synthesis of functional materials for a range of potential applications. An interesting scientific debate has dominated the literature during the past few years regarding the mechanism of Cu(0)-mediated polymerizations in both aqueous and organic media. This article is the first part of a mechanistic study regarding the role of Cu(0) and CuBr in these systems with the aim of offering some increased level of understanding of the mechanism to aid application. In this current contribution, disproportionation and comproportionation studies reveal significant variations in the thermodynamic and kinetic equilibria depending on the solvent composition, the nature of the monomer and the ligand concentration. Interestingly, the sequence of reagent addition significantly affects the disproportionation equilibrium, which is attributed to competitive complexation reactions between monomer, solvent, ligand, and copper species. The Cu(0) generated via the in situ disproportionation of [Cu(Me₆TREN)]Br in DMSO prior to addition of monomer and initiator were demonstrated to contribute in different extents over the rate and control of the polymerization, depending on the equivalents of ligand employed. It was found that an increase in the concentration of the Cu(0) particles result in slower polymerization rates while when conditions that stabilize CuBr were employed, faster polymerization rates were observed. On the contrary, 5 cm of copper wire showed faster polymerization rates when compared with 9.4 mM of CuBr, highlighting that copper wire is essential for the efficient polymerization of acrylates in organic solvents.