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Article Dans Une Revue Macromolecules Année : 2016

Effect of ligand structure on the Cu-II-R OMRP dormant species and its consequences for catalytic radical termination in ATRP

Résumé

The kinetics and mechanism of catalytic radical termination (CRT) of n-butyl acrylate (BA) in MeCN in the presence of Cu complexes with tridentate and tetradentate ligands was investigated both theoretically and experimentally. The tetradentate TPMA, TPMA*(1), TPMA*(2), TPMA*(3), and the newly synthesized tridentate N-propyl-N,N-bis(4-methoxy3,5-dimethylpyrid-2-ylmethyl)amine (BPMA*(Pr)) as well as tridentate BPMA(Me) were used as ligands. L/(CuX2)-X-II (X = Cl or OTf) complexs were characterized by cyclic voltammetry (CV), UV-vis-NIR, and X-ray diffraction. Polymerization of BA initiated by azobis(isobutyronitrile) (AIBN) in MeCN in the presence of a L/Cu-I complex showed higher rates of CRT for more reducing L/Cu-I complexes. The ligand denticity (tri- vs tetradentate) had a minor effect on the relative polymerization kinetics but affected the molecular weights in a way specific for ligand denticity. Quantification of the apparent CRT rate coefficients, kappa(app)(CRT) showed larger values for more reducing L/Cu-I complexes, which correlated with the L/Cu-II-R (R = CH(CH3)(COOCH3)) bond strength, according to DFT calculations. The bond strength is mostly affected by the complex reducing power and to a lesser degree by the ligand denticity. Analysis of kinetics and molecular weights for different systems indicates that depending on the ligand nature, the rate-determining step of CRT may be either the radical addition to L/Cu-I to form the L/Cu-II-R species or the reaction of the latter species with a second radical.
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hal-01929758 , version 1 (01-03-2021)

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Thomas G. Ribelli, S. M. Wahidur Rahaman, Jean-Claude Daran, Pawel Krys, K. Matyjaszewski, et al.. Effect of ligand structure on the Cu-II-R OMRP dormant species and its consequences for catalytic radical termination in ATRP. Macromolecules, 2016, 49 (20), pp.7749-7757. ⟨10.1021/acs.macromol.6b01334⟩. ⟨hal-01929758⟩
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