No abstract

No abstract

No abstract

No abstract

Cobalt(II) porphyrin complexes ((por)Co II •) are used to illustrate how metalloradicals (Μ•) can function to control radical polymerization through both chain transfer catalysis and living polymerization. Chain transfer catalysis (CTC) is best achieved when there are minimal steric demands. This allows β-hydrogen abstraction from oligomer radicals by Μ•, as illustrated by the radical polymerization of methyl methacrylate in the presence of tetraanisylporphyrinato cobalt(II). When β-Η abstraction from the oligomer radical is precluded by sterics, then a metalloradical mediated living radical polymerization (LRP) can occur. Radical polymerization initiated and mediated by organo-cobalt tetramesitylporphyrin complexes manifest high living character as shown by the linear increase in M n with conversion, formation of block copolymers and relativity low polydispersity homo and block copolymers. Kinetic studies provide rate and activation parameters for the living radical polymerization process.Bond homolysis of an organometallic complex (M-C(CH 3 )(R)X) in solution proceeds through the intermediacy of a caged radical pair (M e »C(CH 3 )(R)X) that can recombine, separate into freely diffusing radicals, or react by Μ· abstracting a β-Η from the organic radical to form a metal hydride (M-H) and an olefin ( 7).In the absence of events that irreversibly terminate radicals and metal hydride, the homolytic dissociation of an organo-metal complex can potentially provide a constant equilibrium source of both an organic radical and a metal hydride. The broad objectives of this program are to evaluate the kinetic and thermodynamic factors that