Activation of alkyl halides at the Cu0 surface in SARA ATRP: An assessment of reaction order and surface mechanisms

• Published in: Journal of polymer science. Part A, Polymer chemistry Polymer chemistry, 2017-09, Vol.55 (18), p.3048-3057
• Main Authors: Augustine, Kyle F., Ribelli, Thomas G., Fantin, Marco, Krys, Pawel, Cong, Yidan, Matyjaszewski, Krzysztof
• Format: Article
• Language: English
• Subjects: Activation; Activation analysis; Asymptotic properties; Cu0 RDRP; Halides; Ligands; Polymerization; polymerization kinetics; polymerization mechanisms; Reagents; Reducing agents; Solvents; surface reactions
• ISSN: 0887-624X; 1099-0518
• DOI: 10.1002/pola.28585

ABSTRACT The external order in reagents for the activation of alkyl halides by Cu0 was investigated in supplemental activator and reducing agents (SARA) ATRP. Using methyl 2‐bromopropionate (MBrP) or ethyl α‐bromophenylacetate (EBPA) and tris(2‐(dimethylamino)ethyl)amine (Me6TREN) in DMSO and MeCN, it was determined that the rate of activation scaled with (S/V)0.9 in both solvents. For MBrP, the rate was first order with respect to [MBrP]0 until a saturation in the rate was observed around 33 and 110 mM in DMSO and MeCN, respectively. For EBPA, the reaction was also first order until a maximum rate was observed at 33 mM in DMSO, whereas an inverse order was observed for concentrations above 66 mM in MeCN. At saturated concentrations of MBrP, it was found that the rate increased linearly with respect to [Me6TREN]0 for all systems but became asymptotic with a maximum rate of 2 × 10−6 and 4 × 10−5 M s−1 in DMSO and MeCN, respectively. Model polymerizations in the absence of ligand showed slow reaction rates, indicating the necessity for ligand. The results allow more accurate modeling and understanding of SARA ATRP under a large range of initiator concentrations. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3048–3057 Model studies of supplemental activator and reducing agent atom transfer radical polymerization (SARA ATRP) were conducted for the activation of alkyl halides by Cu0. Reaction orders with respect to initiators, ligand, and Cu0 were examined in acetonitrile (MeCN) and dimethyl sulfoxide (DMSO). The possible mechanisms of alkyl halide activation on the Cu0 surface were subsequently discussed. They include competitive adsorption of alkyl halides and ligands on Cu0 surface as well as ligand‐assisted desorption of CuI from the surface. These findings help to understand and optimize SARA ATRP.