Copper-Mediated Controlled/"Living" Radical Polymerization in Polar Solvents: Insights into Some Relevant Mechanistic Aspects

• Published in: Chemistry : a European journal Vol. 18; no. 15; pp. 4607 - 4612
• Main Authors: Guliashvili, Tamaz, Mendonça, Patrícia V., Serra, Arménio C., Popov, Anatoliy V., Coelho, Jorge F. J.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 10.04.2012; WILEY‐VCH Verlag; Wiley Subscription Services, Inc
• Subjects: Activation; Chemistry; copper; Disproportionation; heterogeneous catalysis; Ligands; Polymerization; radical reactions; Radicals; Reducing agents; Solvents; transition metals; Wire
• ISSN: 0947-6539; 1521-3765; 1521-3765
• DOI: 10.1002/chem.201102183

The field of transition‐metal‐mediated controlled/“living” radical polymerization (CLRP) has become the subject of intense discussion regarding the mechanism of this widely‐used and versatile process. Most mechanistic analyses (atom transfer radical polymerization (ATRP) vs. single‐electron transfer living radical polymerization (SET‐LRP)) have been based on model experiments, which cannot correctly mimic the true reaction conditions. We present, for the first time, a determination of the [CuIBr]/[L] (L=nitrogen‐based chelating ligand) ratio and the extent of CuIBr/L disproportionation during CLRP of methyl acrylate (MA) in dimethylsulfoxide (DMSO) with Cu0 wire as a transition‐metal catalyst source. The results suggest that Cu0 acts as a supplemental activator and reducing agent of CuIIBr2/L to CuIBr/L. More importantly, the CuIBr/L species seem to be responsible for the activation of SET‐LRP. Copper(I) is the activator! The CuIBr/Me6TREN ratio (Me6TREN=tris[2‐(dimethylamino)ethyl]amine) and the extent of CuIBr/Me6TREN disproportionation were determined, for the first time, under real polymerization conditions. The results (see figure) clearly revealed that [CuIBr/Me6TREN] species are the most probable activators of single‐electron transfer living radical polymerization (SET‐LRP), whereas Cu0 acts as a supplemental activator and reducing agent of CuIIBr2/Me6TREN.