The carbocationic polymerization of isobutylene (IB), co-initiated by AlCl3/ether complexes, has been reexamined and extended to different dialkyl ethers. In the absence of a proton trap, 2,6-di-tert-butylpyridine (DTBP), the polymerization of IB by the cumyl alcohol (CumOH)/AlCl3·nBu2O initiator/co-initiator system in dichloromethane/hexanes (80/20 v/v) at −40 °C gave high conversion to polyisobutylene (PIB) comprising exo-olefins with high selectivity, similar to that reported before by Vasilenko et al. , However, in the presence of DTBP, polymerization was absent, suggesting that CumOH is not an initiator in conjunction with AlCl3·Bu2O, and the true initiator is adventitious water. Similarly, in the presence of DTBP in hexanes at 0 °C, polymerizations were absent not only with CumOH but with CumCl, tert-butanol, and 2-chloro-2,4,4-trimethylpentane. The polymerization of IB could be initiated only with adventitious water in the absence of DTBP, but monomer conversions and exo-olefin content (60–70%) were much lower than in a polar solvent and the PIBs exhibited M n = 700–4200 with high polydispersities (PDI ∼ 3–5). The separate addition of ether followed by AlCl3 to the polymerization mixture resulted in conventional PIB with high trisubstituted olefinic content. The previously proposed mechanism is inadequate, as it cannot explain all the observations. Mechanistic studies suggest that the reaction of water with AlCl3·R2O yields H+AlCl3OH–, which initiates the polymerization, and free ether, which abstracts a β-proton from the growing chain end before it diffuses from the immediate vicinity of the polymer cation. Accordingly, the role of the complex is to deliver the ether to close proximity of the propagating end.

The carbocationic polymerization of isobutylene (IB), co-initiated by GaCl 3 or FeCl 3 ·dialkyl ether 1:1 complexes has been investigated in hexanes in the −20 to 10°C temperature range. In contrast to AlCl 3 ·diisopropyl ether (AlCl 3 ·i-Pr 2 O) complexes, 1 GaCl 3 ·i-Pr 2 O and FeCl 3 ·i-Pr 2 O readily co-initiate polymerization with 2-chloro-2,4,4-trimethylpentane (TMPCl) or tert-butyl chloride (t-BuCl) in the presence or absence of proton trap. In the absence of proton trap, chain transfer to monomer readily proceeded, resulting in close to complete monomer conversion and up to 85% exo-olefinic end group content. Diisopropyl ether complexes gave the highest polymerization rates, while nonbranched alkyl ether complexes were completely inactive. A polymerization mechanism is proposed to involve ether-assisted proton elimination to yield PIB exo-olefin, and the abstracted proton can subsequently start a new polymer chain by protonation of IB. Alternatively PIB + may be deactivated by ion collapse to yield PIBCl, which can be reactivated by the Lewis acid. The reasons for the difference in behavior between the Ga and Fe catalysts and the Al-based catalysts are described. ■ INTRODUCTIONLow molecular weight (M n ∼ 500−5000 g/mol) olefin end functional PIB is a precursor to motor oil and fuel additives. Currently two major industrial methods are utilized to produce low molecular weight IB homo or copolymers with olefinic end groups. The "conventional" method uses a C4 mixture and AlCl 3 or EtAlCl 2 based catalyst systems, which provides polybutenes with high trisubstituted olefinic content. 2,3 The other method employs pure IB and uses BF 3 complexes with either alcohols or ethers as catalysts, yielding highly reactive PIB (HR PIB) with high exo-olefinic end-group content. 4 In contrast to the trisubstituted olefins of conventional polybutenes, PIB exo olefins readily react with maleic anhydride in a thermal ene reaction to produce PIB succinic anhydride and subsequently polyisobutenyl succinimide ashless dispersants. Since chlorination is not necessary for maleation of HR PIB, the final product does not contain any chlorine, making HR PIB more desirable than conventional polybutenes.In recent decades, several new methods for the synthesis of HR PIB have been reported. For example, PIBCl was selectively dehydrochlorinated by a bulky base, e.g., potassium tertbutoxide to yield HR PIB. 5 Storey et al. used living cationic polymerization of IB at −80°C to obtain living PIB, which was then end-quenched with sterically hindered bases 6 or sulfides. 7 Another method used to produce HR PIB, developed by Kuhn and co-workers, involves inorganic/organometallic catalysts with weakly coordinating anions in dichloromethane (DCM). 8 Recently, Kostjuk and Wu independently reported that at moderate temperatures AlCl 3 ·dibutyl ether 9 (AlCl 3 ·Bu 2 O) and AlCl 3 ·i-Pr 2 O 10 complexes in DCM or DCM/hexanes 80/20 (v/ v) mixtures give HR PIB with exo-olefinic end-groups in excess of 90%. Shortly thereafter, Wu and co-workers also rep...

The exploration of pseudorotation paths involves the migration of a specific carbon atom from a corner to an adjacent noncorner position (an elementary process)2•3 or series of such migrations. As a result of an elementary process three torsional angles change by about 120°: ±60 to T60, ±60 to 180, and 180 to ±60, where these values are approximate and may vary by 10-20°in some cases. One torsional angle passes through 0°and the other through 120°In a sequential rather than simultaneous fashion.