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-pyridyl­methyl)­amine (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 Cu⁰, 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 Cu⁰ and Cu⁰ catalyzed radical termination remained constant during polymerization in low viscosity systems, with no chain length dependence