Reversible-Deactivation Radical Polymerization in the Presence of Metallic Copper. Comproportionation–Disproportionation Equilibria and Kinetics

Abstract

This article is the first in a series of papers, describing reversible-deactivation radical polymerization (RDRP) in the presence of metallic copper. The aim of these papers is to determine the proportions and roles of Cu0, CuIBr/L, and CuIIBr2/L, and the overall reaction mechanism. This paper is focused on the comproportionation and disproportionation equilibrium between Cu0, CuIBr/L and CuIIBr2/L in dimethyl sulfoxide (DMSO) for various surface areas of Cu0 and different ligand concentrations, in both the absence and presence of methyl acrylate (MA). Comproportionation dominated disproportionation when there was enough ligand present in the reaction medium to stabilize all soluble copper species. The relative amount of CuI at comproportionation/disproportionation equilibrium increased with ligand concentration. CuI represents approximately 99.95% of all soluble Cu species in MA/DMSO = 2/1 (v/v) at the ratio [Me6TREN]0:[CuIIBr2]0 = 6:1. Under typical polymerization conditions, there is essentially no disproportionation, since the ratio [Me6TREN]:[CuII] is very large, starting from infinity and decreasing down to 6.7, for ∼3% terminated chains under the initial conditions [MA]0:[MBrP]0:[Me6TREN]0 = 222:1:0.1, in 33.3% (v/v) DMSO, with excess Cu0. The kinetics of comproportionation and disproportionation were both slow, requiring hours to reach equilibrium. The apparent rate coefficients for comproportionation and disproportionation were calculated as k comp app = 9.0 × 10–4 cm s–1 and k disp app = 2.0 × 10–5 cm s–1 in DMSO, as well as 3.5 × 10–3 cm s–1 and 3.1 × 10–6 cm s–1 in MA/DMSO = 2/1 (v/v), respectively. The results of this study invalidate the assumption of instantaneous and complete disproportionation, proposed in single-electron transfer living radical polymerization (SET-LRP). These findings agree with Cu0 acting as a supplemental activator and reducing agent in atom transfer radical polymerization (SARA ATRP).

Investigating the Mechanism of Copper(0)-Mediated Living Radical Polymerization in Organic Media

“…These results are in agreement with that previously reported by both Percec 23 and Matyjaszewski. 34 Disproportionation of [Cu(Me 6 TREN)]Br in DMSO in the Presence of Monomer. As the polymerization occurs in the presence of initiator and a high concentration of monomer this is an important factor which may affect the extent of disproportionation.…”

Controlled Radical Polymerization: State-of-the-Art in 2014

“…In addition, Cu 0 serves as both a supplemental activator for alkyl halides and reducing agent for the Cu II via comproportionation (87). In SARA ATRP, the contribution of disproportionation to the kinetics of the polymerization is small and alkyl halide activation occurs exclusively by inner sphere electron transfer (ISET) by reaction with either Cu I or Cu 0 (87,(94)(95)(96).…”

“…Are alkyl halide activated by inner sphere electron transfer (102,103) or outer sphere electron transfer (97)? -Does disproportionation (86,97,98) or comproportionation (87,94,104) dominate during polymerization?…”

PSt-b-PU-b-PSt copolymers using tetraphenylethane-urethane macroinitiator through SARA ATRP

“…Taking into account the Matyjaszewski's researches [17,23,24] it can be stated that the SARA ATRP mechanism is correct. SARA ATRP/SET-LRP was successfully applied to relatively nonpolar monomers (e.g., styrene [25], butyl acrylate [26], methyl acrylate [14,24,26,27], 2-(diisopropylamino) ethyl methacrylate [26,28], methyl methacrylate [19,26,29]), as well as polar monomers (e.g., oligo(ethylene oxide) monomethyl ether acrylate [13], N-isopropylacrylamide [30]) for the preparation of a variety of polymeric materials with different structures and architectures, including homopolymers, and well-defined block copolymers. However, tri-block copolymers have sparked much interest and their potential has been realized in many areas.…”

“…Meanwhile, Percec group has proposed a single electron transfer living radical polymerization (SET-LRP) mechanism [18][19][20][21][22], which postulates Cu 0 as the major activator of alkyl halides, Cu II as the major deactivator and assumes that Cu I not participating in activation reactions and instead undergoing very rapid disproportionation to Cu 0 and Cu II [19]. Taking into account the Matyjaszewski's researches [17,23,24] it can be stated that the SARA ATRP mechanism is correct. SARA ATRP/SET-LRP was successfully applied to relatively nonpolar monomers (e.g., styrene [25], butyl acrylate [26], methyl acrylate [14,24,26,27], 2-(diisopropylamino) ethyl methacrylate [26,28], methyl methacrylate [19,26,29]), as well as polar monomers (e.g., oligo(ethylene oxide) monomethyl ether acrylate [13], N-isopropylacrylamide [30]) for the preparation of a variety of polymeric materials with different structures and architectures, including homopolymers, and well-defined block copolymers.…”