SG1 Nitroxide Analogues: a Comparative Study

Abstract

Due to a specific balance between steric, polar, and stabilization effects, SG1 nitroxide and its corresponding alkoxyamine BlocBuilder MA are now well recognized as two of the most potent compounds in nitroxide-mediated polymerization (NMP). In this work, alternatives to SG1, based on various aldehydes, were targeted using structure–reactivity relationships already developed by our group. Compared with SG1, we show that the substitution of the tert-butyl group on the carbon α to the aminoxyl function by a 2-ethylhexyl group led to a new nitroxide (ETHEXNO), which exhibited an half-life time at 120°C similar to SG1 and a slightly slower kd for the alkoxyamine (2–3 times lower than the SG1). The styrene polymerization mediated by the ETHEXNO nitroxide has a similar behaviour to the one mediated by the SG1 in terms of livingness and control but the kinetics is affected (2–3 times lower). Concerning the n-butyl acrylate polymerization, an unexpected overheating occurred at 120°C, which led us to perform the polymerization in toluene at 100°C. The slow kinetics impedes the use of this nitroxide as a good alternative to SG1 and shows that the structure of the SG1 nitroxide is already delicately optimized and finding good alternatives is not straightforward.