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Application of spin trapping technique to radical polymerization, 15. Photo-decomposition of dibenzoyl disulfide and evaluation of relative reactivities of vinyl monomers toward the benzoylthiyl radical
Authors:Tsuneyuki Sato  Masao Abe  Takayuki Otsu
Abstract:The mechanism of photo-decomposition of dibenzoyl disulfide (DBDS) in benzene or in monomers, and the evaluation of relative reactivities of various vinyl monomers toward the benzoylthiyl radical ( 4 ) were investigated by means of the spin trapping technique using 2-methyl-2-nitrosopropane (BNO). When DBDS photo-decomposed in benzene at 22±2°C in the presence of BNO, both 4 and benzoyl radicals were trapped as their nitroxyl radicals, indicating that both S? S and C? S bonds in DBDS were decomposed during its photolysis. However, when the photo-decompositions were performed in the monomers, propagating radicals ( 7 ) were trapped, but no allyl-type radicals ( 11 ). The coupling constants of the nitroxyl radicals of various propagating radicals were determined. From the ESR spectra of the systems DBDS/vinyl monomers/methyl methacrylate (as reference)/BNO the relative concentrations of the nitroxyls, [8]/[10, X = COOCH3], were determined by computer simulation, and the relative reactivities of the vinyl monomers toward 4 were estimated. It was found that the relative reactivities of these monomers are correlated with their e values to give a linear relationship with a negative slope, similar to those toward the tert-butoxyl radical found in the previous paper.
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