Reversible Generation of a Carbon-Centered Radical from Alkyl Iodide Using Organic Salts and Their Application as Organic Catalysts in Living Radical Polymerization

A new method of producing carbon-centered radicals was discovered through the reaction of an alkyl iodide (R-I) with organic salts to reversibly generate the corresponding alkyl radical (R^•). Via this new reaction, the organic salts were used as new and highly efficient organic catalysts in living radical polymerization. The catalysts included common and inexpensive compounds such as tetrabutylammonium iodide and methyltributylphosphonium iodide. Notably, the catalysts were highly reactive. They enabled the synthesis of high-molecular-weight polymers (up to M_n = 140 000) and the control of acrylate polymerization, which had been difficult with other organic catalysts. The organic salt catalysts were highly versatile, reacting with methacrylate, acrylate, styrene, acrylonitrile, and functional methacrylate monomers. Well-defined block copolymers were also prepared by using this method. A kinetic study quantitatively confirmed the high reactivity of these catalysts. Attractive features of this system include its low cost, its ease of operation, and its ability to access a wide range of polymer designs.