Reversible-Deactivation Radical Polymerization in the Presence of Metallic Copper. Kinetic Simulation

Reversible-deactivation radical polymerization (RDRP) of methyl acrylate in DMSO in the presence of Cu0 was studied by kinetic simulations. Kinetic simulations give access to the rates and contributions of all reactions, including those of activation of alkyl halides by CuI and Cu0 species, disproportionation of CuI species, and comproportionation between CuII and Cu0. Every relevant reaction was quantified by experimentally measured rate coefficients. The rates and contributions allow the exact roles of Cu0 and CuI species to be evaluated. These simulations show that the control over the polymerization is due to the atom transfer radical polymerization (ATRP) dynamic equilibrium with CuI as the major activator and CuII as the major deactivator. The ATRP equilibrium is maintained throughout the entire process. The simulations confirmed earlier experimental findings that in dimethyl sulfoxide (DMSO) with tris[2-(dimethylamino)ethyl]amine (Me6TREN) ligand comproportionation between Cu0 and CuII species dominates disproportionation of CuI species, with both reactions being relatively slow. The contribution of Cu0 activation of alkyl halides to the overall reaction is very small, and plays only a supplemental role, since alkyl halides are predominantly activated by CuI species. The effect of Cu0 activity on polymerization rate and livingness were also studied by a series of simulations. In all cases, the rate of supplemental activation by Cu0 was similar to the rate of radical termination, with both being relatively low in order to preserve the livingness of the chains. Cu0 not only acts as a supplemental activator (SA), but also as a reducing agent (RA) and it is able to regenerate CuI from CuII, through comproportionation. Simulations based on experimentally measured rate coefficients showed that Cu0 acts as a supplemental activator and reducing agent (SARA) and the results of an RDRP in the presence of Cu0 are consistent with the SARA ATRP mechanism, and in direct conflict with the single electron transfer-living radical polymerization (SET-LRP) mechanism. The kinetic analysis also revealed that the contribution of disproportionation of CuI to the polymerization kinetics is negligible, and that the CuI species are predominantly involved in activation reactions. The effect of the surface area of Cu0, the effect of initially added CuII species, and other reaction parameters are discussed in light of SARA ATRP.