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

Abstract

Single electron transfer living radical polymerization (SET-LRP) is a versatile polymerization tool that allows for the synthesis of functional materials for a range of potential applications. An interesting scientific debate has dominated the literature during the past few years regarding the mechanism of Cu(0)-mediated polymerizations in both aqueous and organic media. This article is the first part of a mechanistic study regarding the role of Cu(0) and CuBr in these systems with the aim of offering some increased level of understanding of the mechanism to aid application. In this current contribution, disproportionation and comproportionation studies reveal significant variations in the thermodynamic and kinetic equilibria depending on the solvent composition, the nature of the monomer and the ligand concentration. Interestingly, the sequence of reagent addition significantly affects the disproportionation equilibrium, which is attributed to competitive complexation reactions between monomer, solvent, ligand, and copper species. The Cu(0) generated via the in situ disproportionation of [Cu(Me 6 TREN)]Br in DMSO prior to addition of monomer and initiator were demonstrated to contribute in different extents over the rate and control of the polymerization, depending on the equivalents of ligand employed. It was found that an increase in the concentration of the Cu(0) particles result in slower polymerization rates while when conditions that stabilize CuBr were employed, faster polymerization rates were observed. On the contrary, 5 cm of copper wire showed faster polymerization rates when compared with 9.4 mM of CuBr, highlighting that copper wire is essential for the efficient polymerization of acrylates in organic solvents.

Activation of alkyl halides at the Cu0 surface in SARA ATRP: An assessment of reaction order and surface mechanisms

“…The activity of specific copper species has previously been assessed by analyzing the overall rates of polymerization using different activators (Cu 0 vs. L/Cu I ) . However, polymerization rate does not directly correlate to activity of Cu 0/I since RDRP in the presence of Cu 0 exhibits steady‐state kinetics while L/Cu I follows the persistent radical effect (PRE) .…”

Synthesis of star-glycopolymers by Cu(0)-mediated radical polymerisation in the absence and presence of oxygen

“…As previously reported the complex Cu(I)/Me 6 -TREN possess the best disproportionation efficiency in H 2 O, and efficiently mediated the polymerisation process. 45,46 Considering the solubility of the initiator and disproportionation efficiency of catalyst, the experiments were carried out in the mixed solvents of DMF/H 2 O or DMSO/H 2 O. In order to determine the optimal condition for the synthesis of four-arm star glycopolymers, polymerisations with different solvent compositions and ratios of bromine/cuprous bromide/ligand (Br/Cu/L) ratios were conducted in the present work.…”

Synthesis of phosphorescent iridium‐containing acrylic monomers and their room‐temperature polymerization by Cu(0)‐RDRP

“…Now widely explored for the polymerization of (meth)acrylates, styrenes, and acrylamides among others, this technique affords polymers with low dispersity while retaining near‐quantitative end‐group fidelity at conversions >90%. Though some debate persists regarding the mechanistic details of Cu(0)‐RDRP, the technique offers many advantages with respect to scalability and cost. For example, many Cu(0)‐RDRP processes proceed efficiently at room temperature or with only mild heating, and use simple Cu(0) powder or wire as catalyst.…”