Organocatalyzed Living Radical Polymerization via in Situ Halogen Exchange of Alkyl Bromides to Alkyl Iodides

Halogen exchange of alkyl bromide (R–Br) with sodium iodide (NaI) was used for the transformation of R–Br to alkyl iodide (R–I) in situ in organocatalyzed living radical polymerization (LRP). R–Br was employed as a starting compound (precursor), and the R–I formed in situ was employed as an initiating dormant species for the polymerization. The efficiency of the transformation significantly depends on the R group of R–Br. By the rational selection of the R group and reaction temperature along with the use of tetrabutylammonium iodide (Bu₄NI) as a catalyst, low-polydispersity (M_w/M_n = 1.1–1.4) polymers were obtained with high conversions (e.g., 70–90%) in reasonably short periods of time (typically 3–10 h) in the polymerizations of methyl methacrylate, butyl acrylate, styrene, acrylonitrile, and functional methacrylates. Well-defined diblock and triblock copolymers and a chain-end functional polymer were also obtained. R–Br is generally much more stable than R–I upon storage. Various R–Br are commercially available. The use of simple, stable, and inexpensive R–Br as precursors of the dormant species is an attractive feature of this system. The high monomer versatility and the accessibility to a wide range of polymer structural designs demonstrated in this work show the capability of this system for use in a range of applications.