Direct Mechanistic Transformations from Isotactic or Syndiotactic Living Anionic Polymerizations of Methyl Methacrylate into Metal-Catalyzed Living Radical Polymerizations.

Abstract

The mechanistic transformations from living anionic polymerizations into living radical polymerizations were examined after halogenating the growing terminal during the stereospecific living anionic polymerization of methyl methacrylate (MMA), directly forming a macroinitiator with a covalent carbon-halogen terminal for subsequent transition metal-catalyzed living radical polymerizations. The quantitative halogenation of the living isotactic or syndiotactic PMMA anion, prepared using tBuMgBr in toluene or diphenylhexyllithium (DPHLi) in THF, respectively, was achieved using CCl3Br or CCl4 as a halogen source in the presence of strong Lewis bases, such as 1,8-diazabicyclo[5.4.0]undec-7-ene, to generate stereoregular PMMA with a C-X (X = Br or Cl) bond. The halogenated terminal was then transformed into the radical species through a one-electron redox reaction of the ruthenium catalysts to allow the living radical polymerization of styrene or MMA, resulting in block copolymers that consisted of stereoregular PMMA and polystyrene segments or stereoblock PMMAs.