During nitroxide-mediated polymerization, the polymerization time decreases with an increasing rate constant of the cleavage of the NO-C bond of dormant alkoxyamines. Thus, knowledge of the factors influencing this cleavage is of considerable interest. We have prepared a series of SG1 2-[N-tert-butyl-N-(1-diethoxyphosphoryl-2,2-dimethylpropyl)aminoxyl] based alkoxyamines [SG1-CH(Me)CO2R] with various R groups (alkyl or aryl) and measured the homolysis rate constants (k(d)). k(d) decreases with the bulkiness and increases with the polarity of the R group. (C) 2004 Wiley Periodicals, Inc.