Copper-Mediated CRP of Methyl Acrylate in the Presence of Metallic Copper: Effect of Ligand Structure on Reaction Kinetics

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-pyridylinethyl)amine) and Me(6)TREN (tris(2-(dimethylamino)ethyp amine) are compared. The critical difference between the ligands is that TPMA forms a Cu(I) complex that undergoes essentially no ciisproportionation in a mixture of MA and dimethyl sulfoxide (DMSO), DMSO/MA (v/v = 1/2), while the complex with Me6TREN undergoes disproportionation to a limited extent. Parameters such as the surface area of Cu wire, the concentration of added Cu(11)X(2)/L, and ligand concentration were examined. Both the Me(6)TREN- 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 surface area, very similar to the reported value for the Me(6)TREN-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 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(1)/L species.