Quasiliving carbocationic polymerization of isobutylene using FeCl3 as an efficient and water-tolerant Lewis acid: synthesis of well-defined telechelic polyisobutylenes

Abstract

Quasiliving cationic polymerization of isobutylene with dicumyl chloride (DiCumCl)/FeCl₃/ⁱPrOH in CH₂Cl₂/n-hexane 40/60 v/v at −80 °C has been investigated. It was shown that this initiating system afforded well-defined difunctional low molecular weight polyisobutylenes (M_n from 1250 g mol⁻¹ to 21 000 g mol⁻¹, Đ ≤ 1.28) possessing predominantly chlorine end groups (>90%) with a small fraction of exo-olefin end groups. A one-step approach to convert this difunctional polymer to an exclusively exo-olefin-terminated polyisobutylene by end quenching the quasiliving polyisobutylene with ⁱPr₂O was developed. In addition, the synthesized polymers were successfully converted into phenol-terminated difunctional polyisobutylenes via one-step alkylation of phenol by quasiliving polyisobutylene chains at room temperature. Remarkable, FeCl₃-based initiating systems required a much lower concentration of Lewis acid and displayed much higher water tolerance as compared to widely used TiCl₄-based initiating systems. The mechanistic studies revealed that complexes of FeCl₃ with alcohols (ⁱPrOH, BuOH) or ethers (ⁱPr₂O, Bu₂O), not a free Lewis acid, participate in the initiation and propagation steps of the polymerization. The polymerization needs to be conducted at a low polymerization temperature (−80 °C) to suppress the formation of a free base, which induced undesirable β-H abstraction leading to the formation of olefinic end groups and admixtures of monofunctional PIB chains.