Homolysis of N‐alkoxyamines: A Computational Study

10.1002/cphc.200500308.absDuring nitroxide‐mediated polymerization (NMP) in the presence of a nitroxide R2(R1)NO., the reversible formation of N‐alkoxyamines [PON(R1)R2] reduces significantly the concentration of polymer radicals (P.) and their involvement in termination reactions. The control of the livingness and polydispersity of the resulting polymer depends strongly on the magnitude of the bond dissociation energy (BDE) of the CON(R1)R2bond. In this study, theoretical BDEs of a large series of model N‐alkoxyamines are calculated with the PM3 method. In order to provide a predictive tool, correlations between the calculated BDEs and the cleavage temperature (Tc ), and the dissociation rate constant (kd ), of the N‐alkoxyamines are established. The homolytic cleavage of the NOC bond is also investigated at the B3P86/6‐311++G(d,p)//B3LYP/6‐31G(d), level. Furthermore, a natural bond orbital analysis is carried out for some N‐alkoxyamines with a OCON(R1)R2fragment, and the strengthening of their CON(R1)R2bond is interpreted in terms of stabilizing anomeric interactions. Nitroxide‐mediated polymerization (NMP): The relative bond dissociation energy (BDE) of the NOC bond within a series of N‐alkoxyamines is estimated. Good correlations between the calculated BDE (NOC) and the experimental cleavage temperatures and the dissociation rate constants are obtained. These correlations are a predictive tool for finding new nitroxide controllers for the NMP of acrylic or styrenic monomers (see figure).