Tailoring the AlCl₃/iPr₂O/Et₂O initiation system for highly reactive polyisobutylene synthesis in pure n-hexane

This paper reports the flow synthesis of highly reactive polyisobutylenes (HRPIBs) in pure n-hexane using properly prepared AlCl₃·Et₂O crystals in conjunction with AlCl₃·iPr₂O solution as coinitiators. By preparing AlCl₃·iPr₂O solution and AlCl₃·Et₂O crystals separately, the cationic polymerization of isobutylene proceeded smoothly under a wide range of monomer concentrations (0.33-1.30 M) in the presence of H₂O as an initiator, affording a high yield (∼89%) and a moderate exo-olefin terminal group content (60-75%) in 10 min. The various functions of iPr₂O and Et₂O in the initiator solution were comprehensively revealed from the polymerization results, attenuated total reflection-Fourier transform infrared and ²⁷Al nuclear magnetic resonance spectra, and density functional theory simulations. AlCl₃·iPr₂O was confirmed to be the key component that stabilized carbenium ions. The AlCl₃·Et₂O complex was the key component to promote proton elimination. Free Et₂O should be removed to inhibit its negative effect on isomerization. This new strategy may lead to high commercial interest in HRPIB synthesis in pure green solvent and could potentially be extended to other initiation systems containing solid Lewis acids.