A Quantitative 1H NMR Method for the Determination of Alkoxyamine Dissociation Rate Constants in Stable Free Radical Polymerization. Application to Styrene Dimer Alkoxyamines

Abstract

A high-resolution 1H NMR method was developed and applied to the determination of the dissociation rate constants (kd values) of seven stable free radical polymerization (SFRP) model compounds, including three pairs of styrene dimer alkoxyamines, using oxygen as the alkyl radical scavenger. The efficiency and completeness of oxygen irreversible trapping were tested by taking advantage of the diastereoisomerism of the dimer alkoxyamines. The effects of alkoxyamine stereochemistry on the C−ON bond dissociation kinetics were also demonstrated. The 1H NMR method was validated by comparing kd values obtained by this method with ESR and HPLC results previously reported for 2,2,6,6-tetramethyl-1-(1-phenylethoxy)piperidine, a commonly studied alkoxyamine. In contrast to ESR methods, the 1H NMR procedure allows for the simultaneous determination of multiple kd values in a single experiment.