Effects of substituents on chain‐transfer reactivities of p‐substituted cumenes in radical polymerization of p‐substituted styrenes

Abstract

AbstractIn order to study the effects of the substituents in both substrate and attacking radical on the chain‐transfer reactivities of nuclear‐substituted cumenes toward substituted polystyryl radicals, the polymerizations of p‐substituted styrenes in the presence of p‐substituted cumenes were carried out with α,α′‐azobisisobutyronitrile as an initiator at 60°C, and their chain‐transfer constants were determined. The relative chain transfer reactivities of p‐substituted cumenes toward given p‐substituted polystyryl radicals did not follow the Hammett equation, but were correlated with the modified Hammett equation, log(k/k0) = pρ + γER, which was proposed by the present authors for evaluating the substituent effects in radical reactions. On the other hand, the relative reactivities of poly‐(p‐substituted styrene) radicals toward given p‐substituted cumenes were correlated by the Hammett equation. Thus, it was concluded that the effects of the substituents in substrate cumene depended upon the contributions of both polar and resonance factors, while those in attacking polystyryl radical depended upon only a polar factor.