Tailoring the AlCl/iPrO/EtO initiation system for highly reactive polyisobutylene synthesis in pure -hexane.

This paper reports the flow synthesis of highly reactive polyisobutylenes (HRPIBs) in pure -hexane using properly prepared AlCl·EtO crystals in conjunction with AlCl·iPrO solution as coinitiators. By preparing AlCl·iPrO solution and AlCl·EtO 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 HO 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 iPrO and EtO in the initiator solution were comprehensively revealed from the polymerization results, attenuated total reflection-Fourier transform infrared and Al nuclear magnetic resonance spectra, and density functional theory simulations. AlCl·iPrO was confirmed to be the key component that stabilized carbenium ions. The AlCl·EtO complex was the key component to promote proton elimination. Free EtO 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.