Polystyrene end-labeled with 2,7-dibromofluorene synthesized using an adaptation of reverse atom transfer radical polymerization

Polystyrene with high amounts of end-labeling was synthesized using iniuating systems comprised of conventional radical initiators and 2,7-dibromofluorene or other fluorene derivatives in an adaptatioo of reverse atom transfer radical polymerization (RATRP). Benzoyl peroxide (BPO) or 2,2′-azoisobutyronitrile (AIBN) were decomposed and allowed to react with 2,7-dibromofluorene, 2-bromofluorene, or fluorene in the presence of ligand-bound CuX₂ allowing for abstraction of the 9-H from the flouorenyl species and the establishment of an equilibrium between the subsequent active radical and the dormant alkyl halide. Gel permeation chromatography (GPC) traces indicated CuCl₂-catalyzed reactions produced polymers possessing narrow polydispersity index (PDI) values <1.3 with AIBN and 2,7-dibromofluorene systems, while analogous reactions catalyzed using CuBr₂ were less controlled (PDI > 1.7). Analysis of the polymers using UV-vis spectroscopy and UV-GPC demonstrated competition between initiation from both the conventional radical initiator and fluorenyl species generating polymers end-labeled with both the 2,7-dibromofluorene and isobutyronitrile groups. Fluorene or 2-bromofluorene as co-initiators led to lowered amounts of end-labeling, but the polymers generally possessed lower PDI values compared to 2,7-dibromofluorene systems.