Kinetic study of H‐atom transfer in imidazoline‐, imidazolidine‐, and pyrrolidine‐based alkoxyamines: Consequences for nitroxide‐mediated polymerization

The H-atom transfer reaction was studied for a series of imidazoline, imidazolidine, and pyrrolidine-based alkoxyamines containing either isobutyrate-2-yl or 1-phenylethyl alkyl fragments. The CO bond homolysis rate constants and activation energies were determined by 1H NMR product analysis as a function of temperature. Inter- and intramolecular H-atom transfer reactions were distinguished by examination of alkoxyamine thermolysis products in the absence and in the presence of a radical scavenger (thiophenol or deuterated styrene). A correlation between the structure of the nitroxyl fragment of alkoxyamine and the H-transfer reaction was found. The high steric demands of the substituents on the nitroxyl part of the isobutyrate-2-yl alkoxyamine decrease both types of reaction. For alkoxyamines containing the 1-phenylethoxyamines, neither inter- nor intramolecular H-atom transfer was observed. Controlled polymerization of methylmethacrylate initiated with imidazoline-based alkoxyamine was observed, although the polymer obtained was not living. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6579–6595, 2009