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 (Me 6 TREN) 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.