Carbocation Rearrangement in Controlled/Living Isobutylene Polymerization

Abstract

Isobutylene polymerization was initiated using the cumyl chloride/TiCl4/2,4-dimethylpyridine system ([IB] = 1.0 M, [CumCl] = 2.3 × 10-2 M, [TiCl4] = 0.24 M, [DMP] = 2.4 × 10-3 M). Polymerization kinetics in 60/40 hexane/MeCl at −80 °C showed that an IB conversion of ∼98% was reached in 70 s. The active centers were monitored over time at high conversion, by 1H NMR after quenching with MeOH or allyltrimethylsilane (ATMS), and by GPC after a second addition of IB. Quenching with MeOH or ATMS at times up to 70 s yielded quantitative tert-chloride or allyl chain ends, respectively. For longer periods up to 12 h, MeOH-quenched PIB showed increasing depletion of tert-chloride chain ends of the normal structure (but no appearance of olefin) and ATMS quenching yielded a gradual reduction in allylation to 78% at 12 h. Real-time 1H NMR of an active polymerization mixture also indicated depletion of tert-chloride end groups. GPC results showed that coupling of PIB chains was not occurring and that a second charge of...