Leveled steric effect in alkoxyamines of SG1-type

During nitroxide mediated polymerization (NMP) the polymerization time decreases with the increasing rate constant of the cleavage of the NO-C bond of the dormant alkoxyamines. Hence, the knowledge of the factors influencing this cleavage is of considerable interest. Recently, we demonstrated that the influence of the nitroxyl moieties of 24 alkoxyamines on the values of the rate constant for the homolysis of the C-ON bond of the alkoxyamine (k(d)) was accounted for by a biparametric equation log k(d) = -3.07 x sigma(U) - 0.88 x E-S - 5.88, with sigma(U) for the universal electrical effect and E-S for the steric demand of the substituents bound to the nitroxyl function. During the course of the work, it was assumed for a number of molecules that the steric effect was leveled. We present herein three new SG1-based alkoxyamines with sufficiently different steric strains to confirm the leveled steric effect.