Radical‐cationic photoinitiated copolymerization of isobutylene with isoprene in the presence of vanadium (IV) chloride

Abstract

AbstractEPR spectra of isoprene and isobutylene‐isoprene mixture has been studied in the presence of VCl4 in dark and under irradiation, respectively. Analogously, as with isobutylene, a radical‐cation of isoprene is formed under irradiation, and in a mixture of both monomers radical‐cations of isobutylene and isoprene are formed side by side. Formation of the isoprene radical‐cation prevails even in an excess of isobutylene, that is, in an isobutylene‐isoprene ratio of 8:1. Peroxy radicals which inhibit the photochemical copolymerization of isobutylene with isoprene were recorded in the presence of oxygen in isoprene and in the isobutylene‐isoprene mixture. The copolymers of isobutylene with isoprene prepared photochemically (unsaturation 1.5–2 mole %) at −30 to −78°C had a considerably higher viscometric molecular weight than copolymer samples prepared under the same conditions with AlCl3 or BF3 catalysts. According to NMR measurements of butyl rubber samples prepared by photochemical copolymerization, all isoprene is incorporated in the polymer chain as 1,4‐structural units.