The reactivity of polynuclear aromatic hydrocarbons toward styryl radicals

Abstract

Recently, Belonovskaya(35) reported that anthracene and dibenzopyrene retarded the thermal polymerization of styrene, whereas naphthalene, phenanthrene, pyrene and chrysene had no effect. Among these: hydrocarbons J only dibenzopyrene is carcinogenic and possesses fairly high pi-electron density at its K-region. This would appear to bear out the expectation of seeking a correlation between carcinogenicity and free radical reactivity. However, the observed reactivity of anthracene destroys the possibility of seeking such a correlation as this hydrocarbon is non-carcinogenic and possesses no K-region. As will be seen later from our studies, several other non-carcinogenic hydrocarbons also retarded the polymerization of styrene. It can be implied that this chemical reactivity does not constitute a basis for differentiation between carcinogens and non-carcinogens. Thus, no correlation between carcinogenicity and their reactivity towards free radicals may be expected. Similar conclusions- may also be drawn from the studies of Szwarc(31) and Kooyman(32). However, a common feature among these compounds is that those hydrocarbons which possess a high pi-electron density in localized regions (K or L-regions), were also found to be reactive towards free radicals:, and as: will be seen later a correlation does exist between the pi-electron density of these regions and their chemical reactivity. Since the kinetics of inhibition and retardation of vinyl polymerization by condensed ring hydrocarbons has not yet been studied systematically, the research described in this thesis was undertaken to elucidate the mechanism of inhibition and retardation by these compounds. It was further hoped that the data obtained would provide experimental support for one or more of the existing theories relating pi-electron density and free radical reactivity.