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.