Hydrogen abstraction followed by nitroxide-mediated polymerization: Synthesis of 2,7-dibromofluorene-labeled polystyrene

摘要

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.