A theoretical study of the mechanism of cationic polymerization of isobutylene catalysed by EtAlCl2/t-BuCl with bis(2-chloroethyl)ether in hexanes

The mechanism of cationic polymerization of isobutylene catalyzed by t-BuCl/ethylaluminum dichloride (EADC) combined with bis(2-chloroethyl)ether (CEE) in n-hexane solvent has been investigated using ab initio molecular dynamics (AIMD) and metadynamics (MTD) simulations. The results indicated that the polyisobutylene (PIB) initiation stage involves a clear two-step mechanism. Calculation of the free energy landscapes of the other two ether reactions reveals that the energy barriers of diisopropyl ether (i-Pr2O) and 2-chloroethyl ethyl ether (CEEE) are much higher than those of CEE, which is consistent with the experimental results. During the chain propagation phase, the required free energy barrier gradually decreases and tends to reach equilibrium as the chain length increases. Finally, the oxonium mechanism during the chain initiation stage was investigated by calculating the 1H NMR spectra and MTD simulation. Our calculations can confirm that the existence of tert-butyloxonium ions during the reaction is possible. Their contribution to the whole reaction is further discussed.

Polyisobutylenes with Controlled Molecular Weight and Chain-End Structure: Synthesis and Actual Applications

The polymerization of isobutylene allows us to obtain a wide spectrum of polyisobutylenes (PIBs) which differ in their molecular weight characteristics and the chemical structure of chain-end groups. The bulk of the PIBs manufactured worldwide are highly reactive polyisobutylenes (HRPIBs) with -C(Me)=CH2 end-groups and low-molecular weights (Mn < 5 kDa). HRPIBs are feedstocks that are in high demand in the manufacturing of additives for fuels and oils, adhesives, detergents, and other fine chemicals. In addition, HRPIBs and CMe2Cl-terminated PIBs are intensively studied with the aim of finding biomedical applications and for the purpose of developing new materials. Both chain control (molecular weight and dispersity) and chemoselectivity (formation of exo-olefinic or -CMe2Cl groups) should be achieved during polymerization. This review highlights the fundamental issues in the mechanisms of isobutylene polymerization and PIB analysis, examines actual catalytic approaches to PIBs, and describes recent studies on the functionalization and applications of HRPIBs and halogen-terminated PIBs.

Recent advances in catalytic chain transfer polymerization of isobutylene: a review

This review presents the development of highly reactive polyisobutylene (HRPIB), a major commercial intermediate toward fuel and lubricant additives. Recent years have witnessed very substantial advances in the catalytic chain transfer polymerization (CCTP) of isobutylene/industrial Raffinate-1 (C4 Raffinate) to produce HRPIB, particularly in nonpolar solvents at elevated temperatures. The main subjects of this review are cationic polymerization of isobutylene, progress in HRPIB research and existing challenges, and recent advances of CCTP. New initiating/catalyst systems based on ionic liquids with Lewis acids are detailed, and this approach may open new views in the synthesis of HRPIB. Some current developments in CCTP of industrial Raffinate-1 and mechanistic studies are also described. This review strongly supports that the hydrocarbon soluble Lewis acid·ether (LA·ether) complex catalyzed CCTP will become the most popular technique for preparing HRPIB and could replace the traditional BF₃ catalyzed industrial method.

This review presents the development of highly reactive polyisobutylene (HRPIB), a major commercial intermediate toward fuel and lubricant additives.

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.

Effects of Ether on the Cationic Polymerization of Isobutylene Catalyzed by AlCl3

In this work, we prepared different initiator solutions containing ether and AlCl₃ by changing the addition sequence of ingredients, studied the interactions between ether and AlCl₃ from the evolution of the Fourier transform infrared (FTIR) spectra by comparison, and investigated the catalytic performances of AlCl₃ affected by ether for isobutylene polymerization. We observed that different preparation methods of initiator solutions could lead to two kinds of interactions between ether and H₂O/AlCl₃ in hexane. The strong interaction could stabilize carbenium ions and seriously decrease the catalytic performance, whereas the weak interaction could promote isomerization and proton elimination. Moreover, we found that the preparation method of initiator solutions was not a critical factor in CH₂Cl₂. Finally, a universal mechanism based on the AlCl₃-involved interactions in different solvents was proposed to understand the effects of ether on the cationic polymerization catalyzed by AlCl₃ thoroughly.

Synthesis of highly reactive polyisobutylene by catalytic chain transfer in hexanes at elevated temperatures; determination of the kinetic parameters

The rate constants of activation/deactivation for dormant oxonium/active carbenium ions have been measured and related to the increasing polymerization rate with increasing temperature.

Cationic polymerization of isobutylene catalysed by AlCl3 with multiple nucleophilic reagents

Adding the multiple nucleophilic reagents, iPr₂O and EB, in the initiation system is an effective way to attain the controlled polymerization of isobutylene.