Evolutions of precision radical polymerizations from metal-catalyzed radical addition: living polymerization, step-growth polymerization, and monomer sequence control

Metal-catalyzed Kharasch addition or atom transfer radical addition (ATRA) is one of the most efficient radical reactions for controlled syntheses of organic molecules. This reaction proceeds via metal-catalyzed controlled generation of radical species from organic halides, subsequent addition of the radical species to vinyl groups, and capping of the resulting adduct radicals with halogens. Metal-catalyzed radical addition has evolved in various directions and resulted in the development of novel precision radical polymerizations, which allow control over many aspects of vinyl polymer structures, such as molecular weights, terminal groups, architectures, and monomer sequences. This review is focused on the development of metal-catalyzed living radical polymerizations via reversible activation of carbon-halogen bonds, metal-catalyzed step-growth radical polymerizations of designed monomers having an unconjugated vinyl group and a reactive carbon-halogen bond, simultaneous metal-catalyzed chain- and step-growth radical polymerization for syntheses of degradable vinyl copolymers, and vinyl monomer sequence control via combinations of iterative ATRAs and various controlled polymerizations. This review is focused on evolutions of precision radical polymerizations in various directions from metal-catalyzed Kharasch addition or atom transfer radical addition (ATRA). The developments include metal-catalyzed living radical polymerizations via reversible activation of carbon-halogen bonds, metal-catalyzed step-growth radical polymerizations of designed monomers having an unconjugated vinyl group and a reactive carbon-halogen bond, simultaneous metal-catalyzed chain- and step-growth radical polymerization for producing degradable vinyl copolymers with main-chain ester units, and vinyl monomer sequence control via combinations of iterative ATRAs and various controlled polymerizations.