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 Cu-0 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 Cu-I and Cu-0 species, disproportionation of Cu-I species, and comproportionation between Cu-II and Cu-0. Every relevant reaction was quantified by experimentally measured rate coefficients. The rates and contributions allow the exact roles of Cu-0 and Cu-I 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 Cu-I as the major activator and Cu-II 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 Cu-0 and Cu-II species dominates disproportionation of Cu-I species, with both reactions being relatively slow. The contribution of Cu-0 activation of alkyl halides to the overall reaction is very small, and plays only a supplemental role, since alkyl halides are predominantly activated by Cu-I species The effect of Cu-0 activity on polymerization rate and livingness were also studied by a series of simulations. In all cases, the rate of supplemental activation by Cu-0 was similar to the rate of radical termination, with both being relatively low in order to preserve the livingness of the chains. Cu-0 not only acts as a supplemental activator (SA), but also as a reducing agent (RA) and it is able to regenerate Cu-I from Cu-II, through comproportionation. Simulations based on experimentally measured rate coefficients showed that Cu-0 acts as a supplemental activator and reducing agent (SARA) and the results of an RDRP in the presence of Cu-0 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 Cu-I to the polymerization kinetics is negligible, and that the Cu-I species are predominantly involved in activation reactions The effect of the surface area of Cu-0, the effect of initially added Cu-II species, and other reaction parameters are discussed in light of SARA ATRP.