Living Radical Polymerization with Alkali and Alkaline Earth Metal Iodides as Catalysts

The generation of an alkyl radical (R^•) from an alkyl iodide (R-I) with NaI playing a catalytic role was experimentally demonstrated. This catalytic reaction was exploited as an activation process for living radical polymerization. Alkali metal iodides, NaI, KI, and CsI, and alkaline earth metal iodides, MgI₂ and CaI₂, were systematically studied as catalysts. 18-crown-6-Ether and a polyether, that is, diethylene glycol dimethyl ether (diglyme), were utilized to solvate these catalysts in hydrophobic monomers. Among the five catalysts, NaI exhibited a particularly high reactivity. The polymer molecular weight and its distribution (M_w/M_n = 1.2-1.4) were well controlled with high conversions (e.g., 80-90%) in reasonably short periods of time (3-6 h) at mild temperatures (60-70 °C) in the polymerizations of methyl methacrylate. NaI is also amenable to styrene, acrylonitrile, and functional methacrylates. In addition to homopolymers, NaI also afforded well-defined block copolymers, chain-end functional polymers, and a star polymer. The high monomer versatility and accessibility to a wide range of polymer architectural designs are desirable features of this polymerization system.