Electron transfer reactions relevant to atom transfer radical polymerization

Polystyrene with Improved Chain‐End Functionality and Higher Molecular Weight by ARGET ATRP

“…The catalyst undergoes an inner sphere one-electron oxidation to abstract a halogen atom, X, from the dormant species, R-X. [10][11][12] The growing radicals propagate and react reversibly with the oxidized metal complex, Cu II -X 2 /ligand (deactivator), to reform the dormant species and the activator. This process occurs with the rate constants of activation, k a , and deactivation, k da , respectively (where k a /k da ¼ K ATRP ).…”

“…These side reactions are based on outer sphere electron transfer (OSET) processes where the radical is oxidized to a carbocation in the presence of Cu II or reduced to a carbanion in the presence of Cu I . [10,11] The other possibility for loss of halide chain-end functionality, particularly during ATRP of styrene (St)-type monomers, is a b-H elimination reaction catalyzed by the Cu II deactivator. [16] Scheme 2 presents two possible mechanisms for the elimination process.…”

“…Nevertheless, OSET-induced side reactions can be decreased by the proper choice of catalyst and by decreasing the amount of copper in an ATRP. [11,20] We have recently improved the ATRP process by employing a very active copper catalyst which can be used in minute amounts in the presence of excess reducing agent. The new system is called activators regenerated by electron transfer (ARGET) ATRP.…”

“…[17,19] Catalytic systems that are more active, and have a lower redox potential, such as Me 6 TREN/CuBr are less likely to oxidize polystyryl radicals and participate in b-Helimination reaction. [5,11] Thus, comparison of normal ATRP with less reductive dNbipy/CuBr complex versus ARGET ATRP is not ideal. Nevertheless, the present results Polystyrene with Improved Chain-End Functionality and Higher Molecular Weight .…”

Exploring the first steps of an electrochemically-triggered controlled polymerization sequence: Activation of alkyl- and benzyl halide initiators by an electrogenerated FeIISalen complex

“…Several parallel studies have been undertaken to delimit the redox properties of M nþ1 t -X=M n t ATRP catalysts, with respect to the recurrent equilibrium which is commonly invoked to explain the regulation of the concentration between radical and dormant species. In particular, an overview of the electrochemistry of copper complexes currently used by Matyjaszewski and his group or school has given a rational representation of the thermodynamical boundaries within which these copper complexes favor either the activation of dormant chains (forward sense in the above equilibrium) or the deactivation of radicals (backward sense) [16,17]. The apparent standard potentials of the Cu II /Cu I complexes used optimally in ATRP generally lie in a [À0.4 V to +0.3] V (vs. SCE) window, and may be adjusted depending on the nitrogen ligand associated to the metal.…”