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ESR observation of propagating radical and estimation of propagation rate constant in the radical polymerization of vinyl chloride

Well-resolved electron spin resonance (ESR) spectra of propagating radicals in radical polymerizations of vinyl chloride have been detected under irradiation for the first time. Structure of propagating radicals of vinyl chloride was investigated on the basis of hyperfine splitting constants (hfc's) of the ESR spectrum. The spectrum was assisgned to a chain end propagating radical. The propagation rate constant (k p ) for the radical polymerization of vinyl chloride was also estimated by ESR spectroscopy. The value of k p for vinyl chloride was (5 400 ± 1 500) M -1 .s -1 at 25°C, which is in agreement within experimental error with one of those obtained by the rotating sector method.