Studies on Stereocontrol of Free-Radical Polymerization

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1. The presence of cobaltus complexes including (R,R)-N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediaminatocobalt (II) (1) was found to affect stereochemistry of free-radical polymerization of methyl, benzyl, isopropyl, and t-butyl methacrylates. In the polymerization of t-butyl ester, a decrease of 12% in rrrr pentad content was observed based on 1. Tacticity of polymers obtained from the other monomers such as vinyl acetate, stirene, and acrylates were also affected by the added radical complex where the magnitude of the effect varied depending on the combination of monomer and complex.2. Living-like propagation was demonstrated for the polymerization of methacrylates, acrylates, stirene, and vinyl acetate using cobaltus complexes although beta-hydrogen elimination (a termination reaction) took place in the methacrylate polymerization to give omega-end unsaturated polymers. In the case of acrylate polymerization, possibility of block copolymerization was suggested.3. Complexes including 1 was effective in regiochemistry control in sorbate polymerization which gives a relatively high-molecular-weight polymer with 1,4-trans structure in addition to oligomers with 1,2-or 3,4-structures having unreacted pendent vinyl group. The presence of the complex suppressed the production of the oligomers.4. Polymerization of 1-phenyldibenzosuberyl methacrylate using optically active peroxides (initiator) and thiols (chain transfer agent) based on chiral menthol gave optically active, helical polymer with excess single-handed helicity.5. Polymerization of 1-phenyldibenzosuberyl methacrylate in the presence of 1 resulted in optically active, helical polymer which gave purely single-handed helical fractions by GPC separation.