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

Abstract

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.

Realizing highly efficient blue photoluminescence of dimethylsilane-aryl (phenylene, diphenylene, fluorenyl) main-chain polymers with σ–π conjugation

“…51,54 In contrast, PFCS possesses redshifted bands in the region of 270-330 nm mainly involving p-p* transitions on the large conjugated fluorene groups. 51 Multi-bands (271, 300 and 329 nm) of PFCS are attributed to -CQC-at different environments in fluorene groups and several (two or three) fluorene groups coupled directly in the main chain, 51,55,56 which are consistent with experimentally estimated molecular structures. The absorption onsets (l onset abs ) and optical band gaps (E opt g ) of PPCS, PDCS and PFCS are determined as 347 nm (3.57 eV), 343 nm (3.62 eV) and 386 nm (3.21 eV) using the cut-off absorption wavelength.…”

Macrocyclic poly(methyl acrylate) and macrocyclic poly(methyl acrylate-block-styrene) synthesized by radical trap-assisted atom transfer radical coupling

“…As a consequence of the altered mechanistic sequence, RTA-ATRC ultimately accomplishes coupling in a stepwise fashion with both individual steps only first order with respect to the polymer radical chain ends (Scheme 1b). In addition to simply producing dimers of polystyrene (PS) from brominated precursors [33], RTA-ATRC has also been shown capable of producing diblocks by selectively capping one type of polymer radical in the first step, and the resulting nitroxidecapped polymer capturing a second type of polymer radical to form the diblock with an alkoxyamine at the junction of the segments [34]. Furthermore, the ability to couple polymer radicals that favor disproportionation as the major radicaleradical termination pathway, such as poly(methyl methacrylate) radicals [35], expands the scope of polymers that can participate in coupling reactions when RTA-ATRC is used instead of traditional ATRC.…”