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Article Dans Une Revue Macromolecules Année : 2005

Comparison of Bond Dissociation Energies of Dormant Species Relevant to Degenerative Transfer and Atom Transfer Radical Polymerization

Résumé

Density functional calculations are reported for the bond dissociation energy (BDE) of a number of dithioacetates, CH3C(S)S−R and selected dithiobenzoates, PhC(S)S−R, of relevance to reversible addition−fragmentation transfer (RAFT) controlled radical polymerization. In comparison with previously reported calculations [Gillies, M. B.; Matyjaszewski, K.; Norrby, P.-O.; Pintauer, T.; Poli, P.; Richard, R. Macromolecules2003, 36, 8551−8559] at the same level on corresponding R−X systems (X = Cl, Br, I, N3, S2CNMe2), the results reveal significant steric and polar effects on the BDE. Particularly bulky R groups (tBu, C(CH3)2COOMe) yield relatively weaker R−S2CZ (Z = Me, Ph) bonds, such that the radical transfer process to R‘−S2CZ where R‘ is less sterically encumbering (e.g., CH(CH3)COOMe) is less favorable, when compared to the same transfer to R‘−Cl (or R‘−Br). As indicated by an analysis of DFT computed natural charges, electronegative substituents in the α position of the R group (F, OMe, OAc, and also multiple substitution with Cl atoms) reinforce the ionic component of the R−X bond when X is a more electronegative group (i.e., Cl, Br) relative to S2CZ. Therefore, transfer of these radicals is also disfavored for R‘−S2CZ relative to R‘−Cl or R‘−Br. These effects rationalize experimental observations and can be used as a guiding tool for the rational design of ATRP initiators and RAFT transfer agents.
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hal-03277809 , version 1 (06-07-2021)

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Krzysztof Matyjaszewski, Rinaldo Poli. Comparison of Bond Dissociation Energies of Dormant Species Relevant to Degenerative Transfer and Atom Transfer Radical Polymerization. Macromolecules, 2005, 38 (19), pp.8093-8100. ⟨10.1021/ma0512049⟩. ⟨hal-03277809⟩
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