The first example of polymerization of isobutylene induced by a metallocene-like initiator, [(η ⁵ -C ₅ Me ₅ )TiMe ₂ [(µ-Me)B(C ₆ F ₅ ) ₃ ]

Addition of equimolar amounts of (η5-C5Me5)TiMe3 and B(C6F5)3 to solutions of isobutylene or isobutylene and isoprene (99 : 1 molar ratio) in toluene at –78 °C results in polymerization to give, respectively, isobutylene homopolymer with a high weight average molecular mass of ∼ 5 × 105 and a narrow polydispersity (2.1), or an isobutylene-isoprene copolymer exhibiting a composition, a molecular mass distribution and 1H and 13C NMR spectra identical to those of a sample of commercial butyl rubber.