Polystyrene End‐Labeled with 2,7‐Dibromofluorene Synthesized Using an Adaptation of Reverse Atom Transfer Radical Polymerization

Summary: Polystyrene with high amounts of end‐labeling was synthesized using initiating systems comprised of conventional radical initiators and 2,7‐dibromofluorene or other fluorene derivatives in an adaptation 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 fluorenyl 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.