Alkoxyamine re-formation reaction. Effects of the nitroxide fragment: A multiparameter analysis.

A few years ago, Studer and co-workers (Macromolecules 2006, 39, 1347-1352) reported the dramatic effect of the reaction of re-formation of alkoxyamines on the fate of the nitroxide-mediated polymerization (NMP) of styrene. This prompted us to investigate more carefully the effects of the nitroxide structure on the re-formation rate constant k . Ten new values of k were obtained for the reaction of imidozalidine nitroxide and the phenethyl radical. These values were combined with the 21 values of k reported in the literature for a multiparameter analysis (log(k /M s ) = (10.22 ± 0.10) + (0.46 ± 0.02)E + (0.41 ± 0.17)σ ) using the electrical Hammett constant σ to describe both the stabilization and polar effects as well as the modified Taft steric constant E of the nitroxide. The same analysis was performed for the k values of the cross-coupling reaction of nitroxides with tert-butoxylcarbonyl-2-prop-2-yl radical (log(k /M s ) = (11.10 ± 0.25) + (0.57 ± 0.05)E + (1.42 ± 0.18)σ ) and tert-butoxycarbonylethyl radical (log(k /M s ) = (10.23 ± 0.16) + (0.35 ± 0.03)E + (0.93 ± 0.25)σ ). These correlations were applied for the analysis of the NMP of styrene controlled by 6π , 6θ , and 6ρ using a Fischer phase diagram. © 2012 American Chemical Society.