Radical Generation and Termination in SARA ATRP of Methyl Acrylate: Effect of Solvent, Ligand, and Chain Length

Supplemental activator and reducing agent (SARA) ATRP is an efficient way to diminish the amount of Cu catalyst. A kinetic study of radical generation and termination in SARA ATRP was conducted to better understand and improve the livingness of the process. Monomer conversions and Cu-II/L concentrations were concurrently determined by UV-vis-NIR spectroscopy during polymerization of methyl acrylate in dimethyl sulfoxide (DMSO) or in acetonitrile (MeCN) with tris[2(dimethylamino)ethyl] amine (Me6TREN) or tris(2-pyridylmethypamine (TPMA) as ligands. The polymerization was well controlled in DMSO with either Me6TREN or TPMA and in MeCN with Me6TREN. However, when TPMA was used in MeCN, the rate of polymerization and the generation of Cu-II/L accelerated exponentially even using small surface area of Cu-0, rendering control over polymerization under such conditions difficult, plausibly due to excessive comproportionation. The study revealed that the rates of both activation of (macro)alkyl halide by Cu-0 and Cu-0 catalyzed radical termination remained constant during polymerization in low viscosity systems, with no chain length dependence.