Polymerization of Isobutylene by GaCl₃ or FeCl₃/Ether Complexes in Nonpolar Solvents

Abstract

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...

Kinetic and Mechanistic Studies of the Polymerization of Isobutylene Catalyzed by EtAlCl2/Bis(2-chloroethyl) Ether Complex in Hexanes

“…At higher temperature, the equilibrium constant of oxoniumcarbenium ion is lower and polymerization may proceed as has been reported by the AlCl 3 , 28,30 GaCl 3 25 and FeCl 3 20,24,25,31 complexes with i-Pr 2 O. In addition to temperature, steric and electronic effects influence the stability of oxonium ions.…”

Highly efficient ring‐opening polymerization of tetrahydrofuran by anhydrous ferric chloride

“…This is the first report on the synthesis of PTMG using anhydrous FeCl 3 without additional solvent. This catalyst is particularly promising for the scalable and economical production of PTMG because FeCl 3 is a relatively nontoxic, environmentally benign, and abundant reagent . Moreover, no halogenated by‐products, which are difficult to separate from PTMG and have a detrimental effect on the polymer properties, are formed during the polymerization process.…”

“…This catalyst is particularly promising for the scalable and economical production of PTMG because FeCl 3 is a relatively nontoxic, environmentally benign, and abundant reagent. [23][24][25][26][27][28][29] Moreover, no halogenated by-products, which are difficult to separate Additional Supporting Information may be found in the online version of this article. from PTMG and have a detrimental effect on the polymer properties, are formed during the polymerization process.…”

Catalytic chain transfer polymerization of isobutylene: The role of nucleophilic impurities

“…The exo‐olefin terminated PIB is also referred to as “highly reactive” PIB (HR PIB), since it readily reacts with maleic anhydride in a thermal “ene” reaction to produce PIB succinic anhydride that can be converted to polyisobutenylsuccinimide, used as ashless dispersants. In the recent years, several research groups have reported on new catalyst systems for the synthesis of HR PIB . Some major drawbacks for the new HR PIB process systems include low process temperatures and/or use of polar chlorinated solvents that present serious limitations for industrial application .…”

“…In the recent years, several research groups have reported on new catalyst systems for the synthesis of HR PIB. [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] Some major drawbacks for the new HR PIB process systems include low process temperatures and/or use of polar chlorinated solvents that present serious limitations for industrial application. [26][27][28] Recently, we reported an ethylaluminum dichloride (EADC)Ábis(2-chloroethyl) ether (CEE) complex as a fully hydrocarbon soluble catalyst that in conjunction with tert-butyl chloride (t-BuCl) initiator in hexanes at 0-20 8C gave HR PIB with quantitative yields and up to 92% exo-olefin end-functionality.…”