ESR Study of Radicals in Conventional Radical Polymerizations Using Model Radicals Generated from Polymers Prepared by Atom Transfer Radical Polymerization

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Electron Spin Resonance(ESR) study of radicals in conventional radical polymerizations using model radicals generated from polymers prepared by atom transfer radical polymerization was done. I have carried out ESR study of propagating radicals in radical polymerizations by direct detection of the radicals. In the research works, clear and well-resolved spectra have been observed. However, no information on chain length of the observed radicals had been obtained in the experiments. Since the ESR spectra have been used for estimation of propagation rate constant (kp) of the radical polymerizations, information of chain length is extremely important. Combination of controlled radical polymerization technique and ESR spectroscopy provided information of chain lengths of propagating radicals of methacrylates. Atom transfer radical polymerization(ATRP) can produce polymers with given chain lengths and narrow polydispersity. Moreover, the resulting polymers prepared by ATRP have terminal carbon-halogen bonds. The carbon-halogen bonds can be cleaved by reaction with organotin compounds to form corresponding radicals. We can observe the radicals with well-known chain lengths as model of propagating radicals. In the experiments, shorter (mixture of oligomers with 2-7 monomer units) and longer (30 50,100-mers) model radicals showed different ESR spectra. From these results, we can distinguish the chain lengths of observed radicals by ESR spectroscopy. Model dimeric radical precursors with different methacrylate/acrylate monomer units can be prepared by ATRP for investigation of penultimate unit effects. Steric and electronic effect from the penultimate units were also observed by ESR.