Highly Reactive Polyisobutylenes via Cationic Polymerization of Isobutylene by AlCl_3/Ether Complexes in Non-Polar Media: Scope and Limitations

摘要

The cationic polymerization of isobutylene using AlCl_3×OBu_2 and AlCl_3×O~iPr_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]=5.2–7.8M) and high reaction temperature (0 °C–20 °C) with both of catalytic complexes. In n-hexane, AlCl_3×O~iPr_2 showed considerably higher activity and selectivity towards b-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.