In-situ nitroxide mediated polymerization of styrene promoted by the N-tert-butyl-á-isopropylnitrone/BPO pair: ESR investigations

Abstract

The styrene polymerization initiated by benzoyl peroxide (BPO) in the presence of N-tert-butyl-á-isopropylnitrone as nitroxide precursor is well-controlled provided that a pre reaction between the nitrone and BPO is carried out in suitable conditions prior to polymerization at a higher temperature. Electron Spin Resonance (ESR) spectroscopy was implemented to probe the nitroxides formed during both steps; i.e. the pre-reaction and polymerization, and to get crucial information regarding the structure of the nitroxides responsible for the polymerization control. ESR studies combined with first principles calculations have evidenced that nitroxides observed during the pre-reaction in the presence of styrene and during the polymerization steps consist of a mixture of two macronitroxides. One is formed by the addition of a growing polystyrene chain to the nitrone as would be expected. However, the second one results from the addition of a polystyrene chain to tert-butyl nitroso that is in-situ formed presumably by decomposition of the first macronitroxide type.