The equilibrium between propagating radicals and dormant chains in Atom Transfer Radical Polymerization (ATRP) is regulated by a Cu catalyst. The activator CuIL+ (L = polydentate amine ligand) reductively cleaves the C-X chain ends (X = Br, Cl), thereby generating radicals and the deactivator X-CuIIL+. However, we recently discovered that CuIL+ can also react with the generated radicals, forming the organometallic species R-CuIIL+. This species disclosed uninvestigated equilibria and pathways for Cu catalyzed radical polymerizations. For instance, in the presence of relatively high amount of CuIL+, acrylate radicals changed their termination mode. Indeed, saturated products were observed besides expected coupling products. Moreover, the reversible formation of R-CuIIL+ can contribute to the control over the polymerization, by offering an additional radical (de)activation pathway. In order to minimize or take advantage of these processes, it is necessary to reach a complete mechanistic understanding of the formation and the fate of the organocopper species. To this end, the formation and the reactivity of R-CuIIL+ were studied by using cyclic voltammetry combined with digital simulations, spectroelectrochemistry, NMR, and spectrophotometry. The obtained thermodynamic and kinetic parameters will be discussed, with focusing on the effect of i) the ATRP activity of Cu catalysts, ii) the structure of radical initiators, iii) the solvent, and iv) the temperature. Finally, the properties of R-CuIIL+ will be correlated to the control over the growth of polymer chains.

Defining the role of organometallic species in atom transfer radical polymerization

2019 Spring National Meeting

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