A tracer study of di- tert . butyl peroxide as an initiator for polymerization

Abstract

Di- tert . butyl peroxide labelled with carbon-14 has been used to initiate the polymerization of styrene, and the resulting polymers have been analyzed for fragments derived from the peroxide. Polymers prepared in benzene solution contain both tert . butoxy and methyl end-groups, the proportions depending upon the conditions prevailing during polymerization; except at low concentrations of styrene and high temperatures, initiation is chiefly by the tert . butoxy radical giving polymer molecules with ether end-groups. In some diluents, initiation is largely by an indirect process in which the primary radicals abstract hydrogen from the diluent. There is an isotope effect in the dissociation of the tert . butoxy radical; introduction of carbon-14 into the radical reduces by about 7% the velocity constant for dissociation to give acetone at 130°C. Allowance must be made for this effect when using the labelled peroxide as a source of tert . butoxy radicals to be used in competitive studies of the reactivities of substances towards these radicals.