Hydrogen Abstraction Followed by Nitroxide-Mediated Polymerization: Synthesis of 2,7-Dibromofluorene-Labeled Polystyrene



Chromophore end-labeled polystyrene is synthesized using nitroxide-mediated polymerization (NMP) by decomposing 2-2′-azoisobutyronitrile (AIBN) or benzoyl peroxide (BPO) in the presence of fluorene or fluorene derivatives. End-labeling is dependent on the thermally produced radical species selectively abstracting a hydrogen atom from the 9-position of the fluorene species prior to initiation of styrene. From gel permeation chromatography (GPC) data and UV–Vis analysis, it is found that AIBN initiation, compared to BPO, leads to a more controlled polymerization system, producing polymers with predictable molecular weights, narrower polydispersity index (PDI) values (<1.3), and higher amounts of fluorene end-labeling. In terms of the reaction parameters, no consistent trend is observed as a function of the timing of styrene's addition or the temperature at which the hydrogen abstraction phase is performed. Analysis of the chromophore content by UV–Vis spectroscopy demonstrated that the presence of bromine atoms on the 2- and 7-position of the fluorene species leads to higher percent labeling of the chromophore species, presumably due to a more facile abstraction of the hydrogen at the 9-position.