Living/Controlled Radical Polymerization of Ethyl and n-Butyl Acrylates at 90 °C Mediated by β-Sulfinyl Nitroxides: Influence of the Persistent Radical Stereochemistry

Herein we report the living/controlled radical polymerization of ethyl and n -butyl acrylates mediated by β-sulfinyl nitroxides at temperatures below 90 °C. This study examined the effect of the persistent radical stereochemistry on the polymerization kinetics of ethyl acrylate. Experiments were carried out in the presence of alkoxyamines based on 1-phenylethyl transient radicals bearing a 4-hydrogen or a 4-(methyl carboxylate) group, and two enantiomerically pure mixtures of N - tert -butyl- N -(1- tert -butyl-2-ethylsulfinyl)propyl nitroxide (BESN); i.e., a 1:1 S S R β R α / R S S β S α and a 1:1 R S R β R α / S S S β S α racemic mixtures. The dissociation rate constants ( k d ) of the alkoxyamines and poly(ethyl acrylate) chains capped by both nitroxide racemic mixtures were determined by ESR spectroscopy measurements. Kinetic and ESR studies of ethyl acrylate polymerization experiments allowed the determination of the equilibrium constants ( K 90 ) and the rate constants of combination ( k c 90 ) for each system. The rate constants of combination were found to be slightly dependent on the nitroxide stereochemistry whereas an order of magnitude difference was observed for the rate constants of dissociation. Then, well-defined poly(ethyl acrylate) and poly( n -butyl acrylate) were prepared, at 90 °C, from alkoxyamines based on the R S R β R α / S S S β S α nitroxide diastereomers.