are low spin cobalt(II) complexes and organo-cobalt(III) species, which function as latent storage sites for organo-radicals required to obtain living radical polymerization by several pathways. The major products of catalytic chain transfer polymerization are vinyl terminated polymer chains. One of the major drawbacks of the process is that catalytic chain transfer polymerization does not produce macromonomers of use in free radical polymerizations, but instead produces addition-fragmentation agents. When a growing polymer chain reacts with the addition fragmentation agent the radical end-group attacks the vinyl bond and forms a bond. However, the resulting product is so hindered that the species undergoes fragmentation, leading eventually to telechelic species. These addition fragmentation chain transfer agents do form graft copolymers with styrenic and acrylate species however they do so by first forming block copolymers and then incorporating these block copolymers into the main polymer backbone. While high yields of macromonomers are possible with methacrylate monomers, low yields are obtained when using catalytic chain transfer agents during the polymerization of acrylate and styrenic monomers. This has been seen to be due to the interaction of the radical centre with the catalyst during these polymerization reactions. Utility The catalytic chain transfer process was commercialized very soon after its discovery. The initial commercial outlet was the production of chemically reactive macromonomers to be incorporated into paints for the automotive industry. Federally mandated VOC restrictions are leading to the elimination of solvents from the automotive finishes and the lower molecular weight chain transfer products are often fluids. Incorporation of monomers such as glycidyl methacrylate or hydroxyethylmethacrylate (HEMA) into the macromonomers aid curing processes. Macromonomers incorporating HEMA can be effective in the dispersion of pigments in the paints. The chemistry is very effective under emulsion polymerisation conditions and has been used in the printing industry since 2000. The vinylic end group acts as an addition fragmentation agent and has been utilised to make multi block copolymers and derivatives used as stress relief agents in dental restoration by 3M. See also Radical polymerization Living polymerization Cobalt Mediated Radical Polymerization References Polymer chemistry Chemical processes