Copper-mediated CRP of methyl acrylate in the presence of metallic copper: Effect of ligand structure on reaction kinetics

Abstract

The kinetics of copper-mediated controlled/living radical polymerization (CRP) of methyl acrylate (MA) in the presence of Cu 0 and two different ligands that form active catalyst complexes with copper-TPMA (tris(2-pyridylmethyl)amine) and Me 6TREN (tris(2-(dimethylamino) ethyl)amine)-are compared. The critical difference between the ligands is that TPMA forms a Cu I complex that undergoes essentially no disproportionation in a mixture of MA and dimethyl sulfoxide (DMSO), DMSO/MA (v/v = 1/2), while the complex with Me 6TREN undergoes disproportionation to a limited extent. Parameters such as the surface area of Cu 0 wire, the concentration of added Cu IIX 2/L, and ligand concentration were examined. Both the Me 6TREN- and TPMA-based catalysts efficiently controlled the polymerization of MA. The TPMA-based system showed a power law order of 0.47 for the apparent propagation rate constant with the Cu 0 surface area, very similar to the reported value for the Me 6TREN-based system, which showed a power law of 0.44. These results demonstrate that the polymerization of MA in DMSO in the presence of metallic copper can be explained by a core atom-transfer radical polymerization (ATRP) process in which the Cu 0 acts as a supplemental activator and reducing agent, rather than through the proposed single-electron-transfer living radical polymerization (SET-LRP) mechanism, which requires additional assumptions, such as complete and instantaneous disproportionation of Cu I/L species. © 2011 American Chemical Society.