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.