Highly Reactive Polyisobutylenes via Cationic Polymerization of Isobutylene by AlCl₃/Ether Complexes in Non‐Polar Media: Scope and Limitations

Abstract

Summary The cationic polymerization of isobutylene using AlCl 3 × OBu 2 and AlCl 3 × O i Pr 2 as co‐initiators in two non‐polar solvents (toluene and n ‐hexane) at different temperatures and monomer concentrations has been investigated. In toluene, highly reactive polyisobutylene (HR PIB) with desired low molecular weight (M n = 1,500–2,500 g mol −1 ) and high exo ‐olefin content (85–90%) were synthesized at high monomer concentration ([M] = 5.2–7.8 M) and high reaction temperature (0 °C–20 °C) with both of catalytic complexes. In n ‐hexane, AlCl 3 × O i Pr 2 showed considerably higher activity and selectivity towards β ‐H abstraction that AlCl 3 × OBu 2 and allowed to synthesize HR PIB with high functionality ( exo ≥ 80%) only at –20 °C, but the molecular weight of synthesized PIB is slightly higher (M n = 3,500–10,000 g mol −1 ) than required for the commercial application.