244020-85-7Relevant articles and documents
Re-formation reaction of cyclic nitroxide-based alkoxyamines: Steric and polar/stabilization effects
Fischer, Hanns,Marque, Sylvain R. A.,Nesvadba, Peter
, p. 2330 - 2340 (2006)
In nitroxide-mediated radical polymerization, the polymerization times decrease with the increasing re-formation rate constant of the C-ON bond (→ alkoxyamine) between the growing polymer chain and the nitroxide radical. The factors influencing the re-formation rate constant are of considerable interest, but up to now, the polar/stabilization effects have not been addressed thoroughly. The combination of new data with previously reported data now showed that the re-formation rate constant kc increases with the increasing polar character of the substituents attached to the nitroxide moiety. The polar/stabilization effects are weaker for the re-formation than for the homolysis of the C-ON bond, and may be mainly attributed to the relocation of the odd electron onto the O-atom of the N-O moiety, i.e., the stabilization of the nitroxide moiety. Hence, it is possible to predict the values of k c by combining both the polar/stabilization (σ1) and steric effects (Es1), i.e., log(kc/M -1 s-1)=9.86+0.57·σ1+0. 40·Es.
