We present measurements of the rate constants (k_d) of the C−ON bond cleavage in new alkoxyamine models containing the N-(2-methyl-2-propyl)-N-(1-diethylphosphono-2,2-dimethylpropyl)-N-oxyl (SG1) moiety. The homolysis rate constants of 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO)- and SG1-based alkoxyamines are analyzed in terms of polar inductive/field (σ_U), steric (υ), and radical stabilization (σ_RS) contributions of the leaving alkyl radicals, using a multiparameter equation, i.e., log(k_d/k_d,0) = ρ_Uσ_U + δυ + ρ_RSσ_RS. The rate constants increase with increasing electron withdrawing, steric, and stabilization demands of the leaving alkyl radicals. Good correlations are found for TEMPO (log(k_d/k_d,0) = 13.6σ_U + 6.6υ + 13.9σ_RS) and SG1 (log(k_d/k_d,0) = 19.5σ_U + 7.0υ + 15.3σ_RS) derivatives, highlighting the polar sensitivity of the leaving alkyl radical to the nitroxyl moiety. Such correlations should facilitate the design of new alkoxyamines as initiators/regulators and help to improve the tuning of NMP experiments.