Article

Cationic polymerization of isobutylene co-initiated by chloroferrate imidazole-based ionic liquid: The advantageous effect of initiator and aromatic compounds

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Abstract

The effect of different initiators (tert-butyl chloride (t-BuCl) and 2-chloro-2-phenylpropane (CumCl) on the cationic polymerization of isobutylene co-initiated by acidic chloroferrate imidazole-based ionic liquid emimCl-FeCl3 (emimCl: 1-ethyl-3-methylimidazolium chloride, molar fraction of FeCl3 (χ(FeCl3)) ≥ 0.6) in the presence of diisopropyl ether at 0 °C and [IB] = 5.2 M has been investigated. Generally, the use of all above-mentioned initiators results in increase of the monomer conversion from 30% to 60% as well as in decrease of molecular weight from 2500 g mol⁻¹ to 1100 g mol⁻¹ and polydispersity from 2.6 to 1.7, respectively, but does not influence the content of exo-olefin end group. It was demonstrated that CumCl does not initiated directly the polymerization at 0 °C or −20 °C, rather, it decomposed with the formation of the proton, a true initiator of the polymerization. It was also found that addition of small amounts (1% by volume) of benzene or its derivatives into the polymerization system leads to further increase of the monomer conversion (>90%). The rate of isobutylene polymerization depends on basicity of aromatic compounds added and increases in the following order: benzene < toluene ≈ mesitylene.

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... [44] Alternatively, acidic ionic liquids were found to be very efficient heterogeneous catalysts for the synthesis of HR PIB. [45][46][47] 2.3.1. Acidic ionic liquids Despite of wide using of haloaluminate acidic ionic liquids (ILs) as catalysts in the reaction of Friedel-Crafts alkylation (acylation) of aromatic compounds, [48,49] their application in the cationic polymerization was limited to the polymerization of a-pinene [50] and IB. ...
... The low efficiency of the last strategy is consistent with the rather poor miscibility of emimCl-FeCl 3 and n-hexane that results in relatively slow initiation due to slow hydrolysis of catalyst. [46] An interesting strategy for the fast synthesis of HR PIB with low polydispersity ( -D < 2.5) using IL as catalyst under mild conditions (room temperature, high monomer concentration) was developed by Kostjuk et al. [47] Exploiting the chlorophilic nature of FeCl 3 -based IL, [21] the use of t BuCl as initiator results in anticipated increase the reaction rate due to the faster and more efficient cationiation as compared to H 2 O, on the one hand. On the other hand, HR PIB with much lower polydispersity was generated with t BuCl/ emimCl-FeCl 3 initiating system as compared to H 2 O/ emimCl-FeCl 3 system ( -D ¼ 1.7 vs. 2.2-2.5, see Table 2). ...
... The rate of reaction depends on basicity of aromatic compounds added and increases in the following order: benzene < toluene % mesitylene, while properties of HR PIB (M n , -D and exo-olefin content) do not depend significantly on the nature of aromatic compound used. [47] A great advantage of using ILs as heterogeneous catalysts for the synthesis of HR PIB as compared to alkylaluminum dichlorides (vide supra) is quite low polydispersity ( -D < 2.5), which could be obtained even at high monomer concentration and high polymerization temperature. Therefore, to explain the unique behavior of acidic ILs in the synthesis of HR PIB, the following mechanism has been proposed (Scheme 7). ...
Article
In this article, the current state and future perspectives in the application of complexes of Lewis acids with ethers in the synthesis of highly reactive polyisobutylene (HR PIB) were critically reviewed. The complexes of metal halides with ethers showed good activity and regioselectivity in the synthesis of HR PIB only in polar solvents due to their poor solubility in hydrocarbons. In strong contrast, HR PIB with high exo-olefin end group content was synthesized in non-polar n-hexane using fully soluble in hydrocarbons complexes of alkylaluminum dichlorides as catalysts. The further improvement in the synthesis of HR PIB was achieved using heterogeneous catalysts (acidic ionic liquids or liquid coordination complexes), which provides polyisobutylenes with high exo-olefin end group content in conjunction with low polydispersity.
... These authors also investigated the effect of different initiators and ethers or aromatic compounds on the cationic polymerization of isobutylene co-initiated by emimCl-AlCl 3 20 and emimCl-FeCl 3 . 21 Low-molar-mass poly-(isobutylene) (M̅ n = 1.3 kg·mol −1 ), showing molar-mass dispersity close to 2.0 and high content of exo-olefin end groups (88%), were synthesized using tert-butyl chloride (t-BuCl)/ emimCl-FeCl 3 in the presence of toluene. 21 Due to the potential of IL catalysts in polymerization reactions, we investigated in this work the synthesis of a series of metal-containing ILs and their application as catalysts for styrene bulk polymerization. ...
... 21 Low-molar-mass poly-(isobutylene) (M̅ n = 1.3 kg·mol −1 ), showing molar-mass dispersity close to 2.0 and high content of exo-olefin end groups (88%), were synthesized using tert-butyl chloride (t-BuCl)/ emimCl-FeCl 3 in the presence of toluene. 21 Due to the potential of IL catalysts in polymerization reactions, we investigated in this work the synthesis of a series of metal-containing ILs and their application as catalysts for styrene bulk polymerization. The synthesized iron-, indium-, copper-, zinc-, tin-, manganese-, nickel-, niobium-, cobalt-, or chrome-containing catalysts showed to be effective for the polymerization of styrene, thus leading to the formation of tailored polystyrene with different macromolecular properties. ...
... The most convenient way to obtain PIB-sulfonates is the sulfonylation of hydroxyl-terminated PIBs (PIB-OHs) by the corresponding sulfonyl chlorides, e.g., tosyl chloride (TsCl) or nosyl chloride (NsCl) as shown in Scheme 1. PIB-OHs are usually prepared by hydroboration/oxidation of olefin-terminated PIBs [31,32]. While commercial PIBs with relatively broad molecular weight distributions (MWD) have about 80% reactive exo-olefin functionality [1,[4][5][6]8,9] (PIB-Exo), the inifer method [33] and quasiliving carbocationic polymerization (QLCCP) results in PIB-Exo with quantitative vinylidene endgroups [34,35]. In situ allylation by endquenching of QLCCP of isobutylene with allyltrimethylsilane yields PIBs directly with allyl termini (PIB-All) [32]. ...
... In situ allylation by endquenching of QLCCP of isobutylene with allyltrimethylsilane yields PIBs directly with allyl termini (PIB-All) [32]. It has to be noted that significant efforts have been made to increase the exo-olefin functionality in PIB-Exo by conventional carbocationic polymerization in recent years [1,[4][5][6]9,[24][25][26][27][28][29]. Both PIB-Exo and PIB-All were converted to 32,36], which in principle can be converted to PIB-sulfonates, e.g., tosylates, nosylates and mesylates. ...
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Endfunctional polymers possess significant industrial and scientific importance. Sulfonyl endgroups, such as tosyl and nosyl endfunctionalities, due their ease of substitution are highly desired for a variety of polymer structures. The sulfonylation of hydroxyl-terminated polyisobutylene (PIB-OH), a chemically and thermally stable, biocompatible, fully saturated polymer, with tosyl chloride (TsCl) and nosyl chloride (NsCl) is presented in this study. PIB-OHs derived from commercial exo-olefin-ended PIB (PIBexo-OH) and allyl-terminated polymer made via quasiliving carbocationic polymerization of isobutylene (PIBall-OH) were tosylated and nosylated in the presence of 4-dimethylaminopyridine (DMAP), pyridine and 1-methylimidazole (1-MI) catalysts and triethylamine (TEA). Our systematic investigations revealed that the end product distribution strongly depends on the relative amount of the components, especially that of TEA. While PIBexo-OTs with quantitative endfunctionality is readily formed from PIBexo-OH, its nosylation is not as straightforward. During sulfonylation of PIBall-OH, the formed tosyl and nosyl endgroups are easily substituted with chloride ions, formed in the first step of sulfonylation, leading to chloride termini. We found that decreased amounts of TEA afford the synthesis of PIBall-OTs and PIBall-ONs with higher than 90% endfunctionalities. These sulfonyl-ended PIBs open new ways for utilizing PIB in various fields and in the synthesis of novel PIB-containing macromolecular architectures.
... The uses of ethylaluminum dichloride (EADC), GaCl 3 and other Lewis acid catalyst systems have also been reported by considerable fractions of the analyzed papers, as shown in Figure 4 [74,77]. The many Lewis acid compounds that have been tested to produce PIB materials, especially in the last two decades, illustrate the efforts that are still being made to select more efficient and viable alternatives to replace the more conventional catalysts in these processes [68,71,72,[78][79][80]. Generically, the development of new catalysts pursues the combination of high activity and selectivity, cost reduction, easy handling and possible operation at mild conditions [59,65,76,81]. ...
Article
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Polyisobutylenes (PIB) constitute a versatile family of polymer materials that have been used mainly as fuel and lubricant additives. Particularly, the current commercial demand for highly reactive polyisobutylene (HR-PIB) products motivates the development of new processes and procedures to produce PIBs with high polymer yields, narrow molar mass distributions and high vinyl contents. For this reason, a bibliometric survey is presented here to map and discuss important technical aspects and technological trends in the field of solution cationic polymerization of isobutylenes. It is shown that investigations in this field are concentrated mainly on developed countries and that industrial initiatives indicate high commercial interest and significant investments in the field. It is also shown that use of catalyst systems based on AlCl3 and ether cocatalysts can be very beneficial for PIB and HR-PIB manufacture. Finally, it is shown that investigations search for cheaper and environmentally friendly catalysts and solvents that can be employed at moderate temperatures, particularly for the production of HR-PIB.
... In this direction, it is worth highlighting the controlled cationic polymerizations of styrene in the presence of water [3,13] and the polymerizations of other cationically polymerized monomers in the presence of ionic liquids, such as p-methyl styrene [14] , vinyl ether and its derivatives [15,16] , and isobutylene [17][18][19] . We recently described the efficient encapsulation of hexadecane in high molar mass polystyrene nanoparticles obtained through cationic miniemulsion polymerization [20] , and the synthesis of several ILs catalysts intended to produce tailored polystyrene through bulk polymerization process [21] . ...
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The kinetics and mechanism of the polymerization of isobutylene (IB) using ethylaluminum dichloride (EADC)•bis(2-chloroethyl) ether (CEE) complex as catalyst in conjunction with tert-butyl chloride (t-BuCl) as initiator in hexanes at 0 °C have been previously reported.1 In an effort to further study the catalyst performance, we have investigated the polymerization at elevated temperatures. Polymerization rates increased while molecular weights and exo-olefin contents (90-78 %) decreased with increasing temperature. At elevated temperatures the first-order plots are curved upward, suggesting that the formation of the tert-butyloxonium ion is slower at higher temperatures. 1H NMR studies confirmed that the t-butyloxonium ion is stable up to 15 oC but slowly decompose at 20 °C. Linear first order plots were obtained when the polymerization was carried out with tert-butyloxonium ion preformed at 10 °C. The slope of the first order plots that is proportional to the steady state concentration of carbenium ions increased 2, 3 and 4 fold at 10, 15 and 20 °C relative to that at 0 °C. Kinetic parameters of activation-deactivation were determined using model reactions. The rate constant of activation at 0 oC (ka = 3x10-4 s-1) increased 2, 3.4 and 4 fold at 10, 15 and 20 oC, respectively, in line with the rate increases. The deactivation rate constant, kd = 1010 L mol-1 s-1 was at the diffusion-limit.
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There has recently been a wide range of trends in the use of ionic liquids (ILs) as reaction solvent for various polymerization processes. A series of cationic polymerizations of styrene in 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim][PF6]) had been achieved using a variety of coinitiators combined with a,a-dimethylbenzyl chloride (CumCl) as a initiator at −15 °C. Experiments were carried out to observe the influence of solvent polarity and viscosity on polymerization rate. Compared with those in organic solvents, the cationic polymerization of styrene in [Bmim][PF6] proceeded in a milder exothermic manner. The end-group structures of the polystyrenes were identified by ¹H NMR spectroscopy and MALDI-TOF-MS. The corresponding elementary reactions and mechanism of styrene cationic polymerization in [Bmim][PF6] were also discussed.
Article
The use of [emim]Cl–AlCl3 in combination with diisopropyl ether allowed us to synthesize highly reactive polyisobutylene with an exceptionally high exo-olefin end group content (≥90%) and a relatively narrow molecular weight distribution (Mw/Mn ≤ 2.0) at a high reaction temperature (0 °C–10 °C) and monomer concentration ([IB] = 5.2 M–7.8 M).
Article
The cationic polymerization of isobutylene using pre-activated by the wet argon or salts hydrates iBuAlCl2 as catalyst in the presence of diisopropyl ether in n-hexane at 10 °C as a starting temperature and high monomer concentration ([IB] = 5.8 M) has been investigated. It was shown that pre-activated iBuAlCl2 possessed high activity (>90% of monomer conversion in 10 min) and unexpectedly high regioselectivity of β-H abstraction at rather low ether to Lewis acid ratio (iPr2O/iBuAlCl2 = 0.4). The use of pre-activated iBuAlCl2 as a co-initiator leads to formation of more uniform active species that results in narrowing of molecular weight distribution as compared to polyisobutylenes synthesized with non-pre-activated iBuAlCl2. Much better control over polydispersity can be achieved by using of mixture of two ethers of different basicity and steric structure (diethyl and diisopropyl ethers) as additive instead of one (diisopropyl ether) during IB polymerization co-initiated by pre-activated iBuAlCl2. Under optimized conditions ([iBuAlCl2 pre-act.] = 38 mM, [Et2O] = [iPr2O] = 7.6 mM, [H2O] = 0.033 M, time: 15 min), desired low molecular weight (Mn ∼ 1,000 g mol−1) highly reactive polyisobutylenes in high yield (>90%) with high content of exo-olefin end groups (>80%) and relatively low polydispersity (Mw/Mn = 2.4–2.7) were readily synthesized at high reaction temperature (10 °C) and monomer concentration ([IB] = 5.8 M).
Article
Cationic polymerization of p-methylstyrene (p-MeSt) in imidazolium-based [NTf2-1] ionic liquids (ILs) was investigated. The effects of the anions, cations, and alkyl chain length of ILs on p-MeSt solubility and viscosity were comprehensively studied. The COSMO-RS method, which is a valuable tool for screening and selecting ILs, was also applied to identify the most suitable solvent for p-MeSt cationic polymerization. The results revealed that p-MeSt cationic polymerization proceeded in a milder exothermic manner in ILs than in a traditional organic solvent. Controlled polymerizations were achieved in [Bmim][NTf2] with a CumOH/BF3OEt2 initiating system at -25 degrees C when 2,6-di-tert-butylpyridine was introduced. The cationic polymerization mechanism of p-MeSt in ILs was proposed on the basis of the results of density functional theory and the terminal structures of polymers.
Article
Ionic liquid with acidic properties is an important branch in the wide ionic liquid field and the aim of this article is to cover all aspects of these acidic ionic liquids, especially focusing on the developments in the last four years. The structural diversity and synthesis of acidic ionic liquids are discussed in the introduction sections of this review. In addition, an unambiguous classification system for various types of acidic ionic liquids is presented in the introduction. The physical properties including acidity, thermo-physical properties, ionic conductivity, spectroscopy, and computational studies on acidic ionic liquids are covered in the next sections. The final section provides a comprehensive review on applications of acidic ionic liquids in a wide array of fields including catalysis, CO2 fixation, ionogel, electrolyte, fuel-cell, membrane, biomass processing, biodiesel synthesis, desulfurization of gasoline/diesel, metal processing, and metal electrodeposition.
Article
The polymerization of alpha-pinene was investigated in the presence of Lewis acidic ionic liquids (ILs). The results indicated that ILs 1-(1-ethyl acetate-yl)-3-methylimidazolium chloroaluminates ([EtOCOCH2-mim]Cl-AlCl3), especially molar fraction of AlCl3 x = 0.67, had excellent catalytic performance for the polymerization of alpha-pinene. The yield and softening point of solid resin reached to 52.0% and 115 degrees C, respectively, when the polymerization was carried out at -5 degrees C for 4 h. IL was reused for five times without a decrease in the catalytic performance. Compared with the traditional catalyst AlCl3, IL exhibited some advantages such as simplicity and efficiency of the product isolation, higher yield and softening point of the product, and excellent reusability.
Article
In this work, with the AlCl3 addition in the range from 4 to 10 mmol L-1 and enough isopropyl ether (iPr2O) addition, we suc-cessfully synthesized high reactivity polyisobutylene (HRPIB) using a microflow system within 12 s or less. The temperature window was extended from -20 oC to 50 oC, and the molecu-lar weight (Mn) was ad-justable between 500 to 15000. The evolutions of HRPIBs and the effects of reaction conditions were carefully investigated, revealing multiple effects of an excess of iPr2O over AlCl3 including: 1) decreas-ing the intensive isomeri-zation coinitiated by free AlCl3; 2) inhibiting the chain termination to pre-sent chain transfer domi-nated kinetics; 3) weaken-ing the temperature sensi-tivity of Mn as a restriction on temperature elevation; 4) retarding the chain propagation to slow the reaction and increase the probability of isomeriza-tion. A key access to fast synthesis of high quality HRPIB is proposed to make a compromise of these effects by properly selecting iPr2O:AlCl3.
Article
Friedel–Crafts alkylation of benzene with 1-dodecene, which is an important reaction of synthetic detergent, was studied using the catalyst [bmim][TFSI]/AlCl3 (1-butyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)imide/AlCl3). These ionic liquid catalysts show biphasic behaviors at a specific condition. Active site species and Lewis acidity were determined by NMR and acetonitrile probe FT-IR. NMR spectroscopy investigations indicated that “coordinated” and “uncoordinated” [TFSI]− existed in the ionic liquid catalyst system simultaneously, while tetrahedral 4-coordinate Al2Cl7− was the main active species for Friedel–Crafts alkylation. The complex [AlClx(TFSI)y]− tends to decompose and release 4-coordinated Al2Cl7− and [TFSI]−. The phase behavior study of the ionic liquid [bmim][TFSI]/AlCl3 demonstrated that the upper phase could be used as an efficient heterogeneous catalyst when AlCl3/IL ≥ 1.5. Due to the presence of the anion [TFSI]− around the active sites, especially [TFSI]− at the “uncoordinated” state, the ionic liquid formed a stable and hydrophobic chemical environment, which enhanced catalyst durability. The influence of various reaction conditions including catalyst reusability on the alkylation reaction was studied, and the potential reasons for catalyst deactivation were discussed. The highest 2-LAB selectivity was more than 50% when 1-dodecene conversion was nearly 100%. Compared with liquid or solid acid catalyst, ionic liquid catalysts have many advantages concerning energy and the environment.
Article
The synthesis of highly reactive polyisobutylene (HR PIB) using FeCl3·diisopropyl ether (i-Pr2O) as catalyst prepared in dichloromethane (DCM), to produce polyisobutylene with high exo-olefin content (HR PIB), has been previously reported [1]. The use of chlorinated solvent for complex preparation is a major disadvantage for industrial-scale production of HR PIB. In an effort to replace DCM, an undesirable chlorinated solvent, we have studied the feasibility of using non-chlorinated solvents. Polymerization was absent when the complex preparation was attempted in hexanes, nitrobenzene or acetonitrile. When the complex was prepared in benzene the conversion was similar to that observed with DCM. Conversions decreased when a complex was prepared in toluene or o-xylene, due to a side reaction involving chlorination of the aromatic ring by FeCl3. This side reaction was suppressed by changing the addition order, i.e., adding an equivalent amount of FeCl3 to i-Pr2O dissolved in toluene.
Article
When synthesis of highly reactive polyisobutylene (HR PIB) via cationic polymerization of isobutylene (IB) using ethylaluminum dichloride•bis(2-chloroethyl) ether (EADC•CEE) complex were carried out in metal reactors made of 316 stainless steel (SS), PIB olefin with up to 20% lower exo-olefin content were obtained compared to that obtained in glass reactors (upto 90%). In an effort to investigate this reduction in exo-olefin selectivity in SS reactors, we have studied the polymerization of IB using EADC•CEE complex in SS (minimum of 10.5% chromium content by mass), carbon steel (CS) (0% chromium content by mass), monel alloy 400 (M400) (0% chromium content by mass) and glass reactors. The latter was examined in the presence and absence of SS balls. Mechanistic studies using ATR-FTIR and 1H NMR spectroscopy suggest that this decrease in exo-olefin selectivity is due to a side reaction of EADC with Cr2O3 involving the loss of the ethyl group from EADC and decomplexation of the EADC•CEE complex which hinders the selective abstraction of the β-proton from the growing chain end. In the absence of chromium (CS and M400 reactors), the exo-olefin content is virtually identical to that obtained in glass reactors. Therefore, CS and M400 reactors are suitable to produce HR PIB with high exo-olefin content.
Article
Living cationic polymerization of isobutylene (IB) with 1-chlorine-2,4,4-trimethyl pentane (TMPCl)/TiCl4/isopropanol (iPrOH) or isoamylol (iAmOH) has been achieved in the presence of 2,6-di-tert-butylpyridine (DtBP) at −80°C. Polyisobutylenes with nearly theoretical Mn based on TMPCl molecules and more than 90% of tert-chlorine-end groups could be obtained at high [TMPCl]. The β-proton elimination from CH3 in growing chain ends increased with increasing polymerization temperature and decreasing solvent polarity. A chain-transfer-dominated cationic polymerization process with H2O/TiCl4/iAmOH could be achieved in n-hexane at −30°C. The monomer conversion and content of exo-olefin end groups increased while molecular weight decreased with increasing [iAmOH]. To the best of our knowledge, this is the first example to achieve the direct synthesis of highly reactive polyisobutylene with low Mn of 1200∼1600, carrying more than 80% of exo-olefin terminals by a single-step process via cationic polymerization co-initiated by TiCl4 in nonpolar hydrocarbon. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42232.
Article
The polymerization of isobutylene (IB) in hexanes at 0 °C initiated by tert-butylchloride (t-BuCl) and coinitiated by GaCl3 or FeCl3•diisopropyl ether (i-Pr2O) complexes to produce polyisobutylene with high exo olefin content (HR PIB) has been previously reported [1]. In an effort to further improve the efficiency of the catalytic system, we have performed systematic studies on the effect of the nature of the ether used in the FeCl3•ether complex on the polymerization. Investigation of the properties of the FeCl3•ether complexes possessing unique steric and electronic properties via attenuated total reflectance (ATR) FT-IR, and solubility studies have revealed several interesting characteristics that may be useful in further optimizing the present initiating system. For example, long alkyl chains reduce the solubility of the catalyst resulting in decreased polymerization rates. On the other hand, the polymerization rate can be increased by incorporating electron-withdrawing groups on the ether, which affects both the complexation equilibrium and the basicity of the ether. These investigations have identified key characteristics that should be present in the ether in order to increase reactivity while maintaining high levels of exo-olefin in HR PIB.
Article
The cationic polymerization of isobutylene using AlCl3 × OBu2 and AlCl3 × OiPr2 as co-initiators in two non-polar solvents (toluene and n-hexane) at different temperatures and monomer concentrations has been investigated. In toluene, highly reactive polyisobutylene (HR PIB) with desired low molecular weight (Mn = 1,500–2,500 g mol−1) and high exo-olefin content (85–90%) were synthesized at high monomer concentration ([M] = 5.2–7.8 M) and high reaction temperature (0 °C–20 °C) with both of catalytic complexes. In n-hexane, AlCl3 × OiPr2 showed considerably higher activity and selectivity towards β-H abstraction that AlCl3 × OBu2 and allowed to synthesize HR PIB with high functionality (exo ≥ 80%) only at –20 °C, but the molecular weight of synthesized PIB is slightly higher (Mn = 3,500–10,000 g mol−1) than required for the commercial application.
Article
An initiating system composed of GaCl3 and an alkylbenzene was demonstrated to be highly effective for the controlled cationic polymerization of a plant-derived monomer, beta-pinene. Alkylbenzenes such as pentamethylbenzene and hexamethylbenzene were shown to function as suitable additives for the polymerization of beta-pinene, an alkene monomer with low reactivity, although the alkylbenzenes are much less basic than conventional additives such as esters and ethers for base-assisting living cationic polymerization. For example, when two equivalents of hexamethylbenzene were added to GaCl3 in conjunction with 2-chloro-2,4,4-trimethylpentane as an initiator, cationic polymerization of beta-pinene successfully proceeded in a living manner at -78 degrees C. Successful control over the reaction, i.e., control of an active-dormant equilibrium, was attributed to the formation of a complex between GaCl3 and the alkylbenzene, as confirmed by UV-vis and Ga-71 NMR analyses.
Article
This article reviews recent approaches toward the synthesis of exo-olefin terminated polyisobutylene (PIB) or so-called highly reactive PIB (HR PIB). The advantages and disadvantages of methods based either on living cationic polymerization or using complexes of Lewis acids with ethers are discussed here from the point of view of their industrial relevance. The first method is unique in terms of the synthesis of well-defined di- or trifunctional exo-olefin terminated polyisobutylenes. The second one could be an alternative route towards HR PIB, which is currently obtained at the industrial scale via BF3-coinitiated polymerization of isobutylene. Special focus is laid on the recent progress in the cationic polymerization of 1,3-dienes (isoprene, 1,3-pentadiene) allowing us to synthesize well-defined low molecular weight poly(1,3-diene)s with a high degree of unsaturation of the polymer chain (>85%). This review article shows that the Lewis acid-co-initiated cationic polymerization of isobutylene and 1,3-dienes has still not been fully explored, and new innovative initiating systems of high commercial interest can be discovered.
Article
The polymerization of isobutylene (IB) to yield highly reactive polyisobutylene (HR PIB) with high exo-olefin content using GaCl3 or FeCl3·diisopropyl ether complexes has been previously reported.1 In an effort to further improve polymerization rates and exo-olefin content, we have studied ethylaluminum dichloride (EADC) complexes with diisopropyl ether, 2-chloroethyl ethyl ether (CEEE), and bis(2-chloroethyl) ether (CEE) as catalysts in conjunction with tert-butyl chloride as initiator in hexanes at different temperatures. All three complexes were readily soluble in hexanes. Polymerization, however, was only observed with CEE. At 0 °C polymerization was complete in 5 min at [t-BuCl] = [EADC·CEE] = 10 mM and resulted in PIB with 70% exo-olefin content. Studies on complexation using ATR FTIR and 1H NMR spectroscopy revealed that at 1:1 stoichiometry a small amount of EADC remains uncomplexed. By employing an excess of CEE, exo-olefin contents increased up to 90%, while polymerization rates decreased only slightly. With decreasing temperature, polymerization rates decreased while molecular weights as well as exo-olefin contents increased, suggesting that isomerization has a higher activation energy than β-proton abstraction. Density functional theory (DFT) studies on the Lewis acid·ether binding energies indicated a trend consistent with the polymerization results. The polymerization mechanism proposed previously for Lewis acid·ether complexes1 adequately explains all the findings.
Article
Acid catalysts are used in the production of several commercially important lubricant additives, including dispersants and antioxidants. While the use of conventional mineral and Lewis acids still dominate existing production, heterogeneous solid acid catalysts provide a future option for cost reduction and pollution prevention. The heteropolyacids discussed in this presentation are based on the parent phosphotungstic acid, H3PW12O40, which has been studied for many years as solid acid catalysts especially by Japanese researchers. A particular class of heterpolyacid salts of the formula (M+)2.5H0.5PW12O40 exhibit enhanced catalytic activity, which is believed to be due to the formation of a phase with nano-sized crystallites, as has been reported by Misono and coworkers. This class of heteropolyacid salts has been successfully applied by Lubrizol researchers to the production of high-reactivity polyisobutylene, a polymer used in the production of dispersants for commercial lubricants. Most notably, the catalyst of the formula (NH4+)2.5H0.5PW12O40 provides high conversion to the desired reactive vinylidene isomer and a unique polymer molecular weight distribution, which results in improved performance characteristics when compared to existing commercial AlCl3 and BF3 catalysts. Catalyst performance is effectively optimized by catalyst concentration in a slurry reactor, catalyst calcination temperature and loading on a silica support. This class of catalysts has also been successfully applied to a number of other acid-catalyzed processes for the production of additives, including for the antioxidant nonyl diphenylamine.
Article
The scope of the univalent gallium salts [Ga(C6H5F)2]+[Al(ORF)4]– and the new completely characterized [Ga(1,3,5 Me3C6H3)2]+[Al(ORF)4]– (RF = C(CF3)3) was investi-gated in terms of initiating or catalyzing the synthesis of highly reactive poly(2-methylpropylene) – highly reactive polyisobutylene (HR PIB) – in several solvents. A series of polymerization reactions proved the high efficiency and quality of the univalent gallium salts for the polymerization of isobutylene. Best results were obtained using very low concentrations of [Ga(C6H5F)2]+[Al(ORF)4]– (down to 0.007 mol%) while working at reaction temperatures of up to ±0 °C and in the non-carcinogenic and non-water hazardous solvent toluene. Under these conditions, HR PIB with an α content of terminal olefinic double bonds up to 91 mol% and a molecular weight of 1,000 to 2,000 g mol–1 was obtained in good yields. Upon changing [Ga(C6H5F)2]+[Al(ORF)4]– for the electron richer [Ga(1,3,5 Me3C6H3)2]+[Al(ORF)4]–, polymerization temperatures could be increased to +10 °C. The reactivity of the gallium(I) cations therefore seems to be tunable through ligand exchange reactions. Experimental results, density functional theory calculations, and mass spectrometric investigations point towards a coordinative polymerization mechanism.
Article
The RAlCl2 × OiPr2-co-initiated (R = iBu or Et) cationic polymerization of isobutylene in the presence of externally added water (0.016–0.1 mM) in nonpolar n-hexane at 10 °C and high monomer concentration ([IB] = 5.8 M) has been investigated. It was shown that the sequence of H2O introduction into the system had the crucial effect on the polymerization rate, saturated monomer conversion, and, to a lesser extent, the content of exo-olefin end groups. Particularly, the highest polymerization rate (>70% of monomer conversion in 10 min) and acceptable exo-olefin end groups content (∼83%) were observed when iBuAlCl2 × 0.8OiPr2 reacted with suspended in n-hexane H2O before the monomer addition. Better functionality can be obtained when H2O is introduced into the system in the course of the polymerization (after 3–10 min since the initiation of reaction). Under these conditions, highly reactive polyisobutylenes (exo-olefin content is 86–89%) with desired low molecular weight (Mn = 1000–2000 g mol−1) in a high yield (75–90% of monomer conversion in 20 min) were readily synthesized. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014
Article
Cationic polymerizations of isobutylene (IB) with H2O/FeCl3/isopropanol (iPrOH) initiating system were conducted in nonpolar hydrocarbon media, such as n-hexane or mixed C4 fractions at −40 to 20 °C. This cationic polymerization is a chain-transfer dominated process via highly selective β-proton elimination from CH3 in the growing chain ends, leading to formation of highly reactive polyisobutylenes (HRPIBs) with large contents (> 90 mol %) of exo-olefin end groups (structure A). The content of structure A remained nearly constant at about 97 mol % during polymerization and isomerization via carbenium ion rearrangement could be suppressed in nonpolar media. First-order kinetics with respect to monomer concentration was measured for selective cationic polymerization of IB in the mixed C4 fraction feed at −30 °C and the apparent rate constant for propagation was 0.028 min−1. High polymerization temperature (Tp) or [FeCl3] accelerate β-proton elimination or isomerizations and simultaneously decrease selectivity of β-proton abstraction from CH3. Molecular weight decreased and molecular weight distribution (MWD) became narrow with increasing Tp or [FeCl3]. To the best of our knowledge, this is the first example to achieve high quality HRPIBs with near 100% of exo-olefin terminals and relatively narrow MWD (Mw/Mn = 1.8) by a single-step process in nonpolar hydrocarbon media. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4200–4212
Article
exo-Olefin-terminated polyisobutylene was obtained directly from living isobutylene polymerizations by addition of a quenching compound to the living chain ends. Three broad classes of compounds were evaluated including hindered bases such as hindered pyridines and piperidines, N-hydro-2,5-disubstitutedpyrroles, and sulfides, ethers, and silylethers. The proposed mechanism of quenching unique to each class was discussed, with supporting kinetic, spectroscopic, and structure-based evidence presented. Hindered bases were proposed to operate by E2 elimination reaction of free base at the carbenium ion. N-Hydro-2,5-disubstitutedpyrroles were proposed to form the η5-2,5-disubstitutedpyrrolyltrichloro-titanium(IV) coordination complex, which serves as the true quencher. Sulfides, ethers, and silylethers were proposed to operate by first converting the PIB chain ends quantitatively to the onium adduct, which is then decomposed to form exo-olefin PIB. Sulfides and ethers were the best performing quenchers of all the types studied, particularly bulky ones such di-tert-butylsulfide and diisopropyl ether.
Article
Addition of excess dialkyl ether, e.g., diisopropyl ether (DIPE) or di-sec-butyl ether (DSBE), to a TiCl4-co-initiated, living carbocationic polymerization of isobutylene (IB) results in capping of the chain ends with oxonium cations, as evidenced by cessation of polymerization. Structure of PIB diisopropyl oxonium cations was determined using 500 MHz 1H NMR, by introducing DIPE to a mixture of TiCl4 and 2-chloro-2,4,4-trimethylpentane (TMPCl), a model for the PIB chain end, at −70 °C in CS2/CD2Cl2 (50/50, v/v). One-pot, two-step quantitative synthesis of mono- and telechelic (difunctional) exo-olefin-terminated polyisobutylene (PIB) was achieved by quenching living PIB with DIPE, followed by termination with methanol at −60 °C. TMPCl and 1,3-bis(1-chloro-1-methylethyl)-5-tert-butylbenzene (bDCC) were used as mono- and difunctional initiators, respectively. 1H NMR spectroscopy was used to characterize end-group composition of PIBs. Percent formation of exo olefin was directly related to the steric bulk of the ether, i.e., sec-butyl (100%) ≈ isopropyl (100%) > n-alkyl (68.5–81.5%). Coupled PIB and tert-chloride PIB were the principle side products observed when exo olefin was <100%. To prevent coupling, molar ratio of Lewis acid/chain ends ([TiCl4]/[CE]) should be at least about 2.2. To prevent tert-Cl PIB, [TiCl4] ≤ [CE] + [ether]. For [TiCl4]/[CE] = 2.2 and [DIPE]/[CE] ≥ 3, quantitative mono- and telechelic (difunctional) exo-olefin-terminated PIB was observed at [CE] ≤ 0.1 M, for reaction volumes about 1 dL. However, the end group composition of difunctional PIB was 96.2% exo olefin and 3.8% coupled, when the reaction was up-scaled to about 4 L (0.66 kg of PIB). Study of various quenching methods for production of exo-olefin-terminated PIB, including ether, sulfide, hindered base, and methallyltrimethylsilane, showed that ether and sulfide quenching were superior to other methods with regard to maximizing exo-olefin end groups at high [CE].
Article
This review highlights recent approaches toward polyisobutylene (PIB) by an energy efficient room temperature cationic polymerization. Special focus is laid on our own work using modified Lewis acids and nitrile-ligated metal complexes associated with weakly coordinating anions. In both cases, suitable conditions have been found for efficient production of PIB characterized by medium to low molar masses and a high content of exo double bonds as end groups—the typical features of highly reactive PIB, an important commercial intermediate toward oil and gasoline additives. These and other approaches demonstrate that the cationic polymerization of isobutylene is still not fully explored, and new innovative catalyst systems can lead to surprising results of high commercial interest. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013
Article
Nitrile-ligated copper(II) and zinc(II) complexes comprising (fluoroalkoxy)aluminates as weakly coordinating anions (WCAs) have been synthesized and applied for the polymerization of isobutylene at room temperature (30°C). The polymers obtained are in the low and moderate molecular weight range and show characteristics of the highly reactive polyisobutylene. Results indicate that the fluoroalkoxy aluminate WCAs have even a higher tolerance toward water in IB polymerization than the earlier tested perfluoroborate WCAs. Studies showed that water plays an important role in the polymerization process, which indicates a polymerization mechanism similar to a proton-initiated carbocation polymerization. The role of the WCAs and their importance for the room-temperature polymerization process was re-examined, and the effect of the addition of proton and electron donors including proton traps (2,6-di-tert-butyl-4-methylpyridine or DTBP) was studied in detail. The polymerization reaction seems to be dominated by transfer reactions that lead to the high content of exo double bonds while propagation proceeds via conventional cationic polymerization. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013
Article
The carbocationic polymerization of isobutylene (IB), co-initiated by GaCl3 or FeCl3·dialkyl ether 1:1 complexes has been investigated in hexanes in the −20 to 10 °C temperature range. In contrast to AlCl3·diisopropyl ether (AlCl3·i-Pr2O) complexes,(1) GaCl3·i-Pr2O and FeCl3·i-Pr2O 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.
Article
The cationic polymerization of isobutylene using 2-phenyl-2-propanol (CumOH)/AlCl3OBu2 and H2O/AlCl3OBu2 initiating systems in nonpolar solvents (toluene, n-hexane) at elevated temperatures (−20 to 30 °C) is reported. With CumOH/AlCl3OBu2 initiating system, the reaction proceeded by controlled initiation via CumOH, followed by β-H abstraction and then irreversible termination, thus, affording polymers (Mn = 1000–2000 g mol−1) with high content of vinylidene end groups (85–91%), although the monomer conversion was low (≤35%) and polymers exhibited relatively broad molecular weight distribution (MWD; Mw/Mn = 2.3–3.5). H2O/AlCl3OBu2 initiating system induced chain-transfer dominated cationic polymerization of isobutylene via a selective β-H abstraction by free base (Bu2O). Under these conditions, polymers with very high content of desired exo-olefin terminal groups (89–94%) in high yield (>85%) were obtained in 10 min. It was shown that the molecular weight of polyisobutylenes obtained with H2O/AlCl3OBu2 initiating system could be easily controlled in a range 1000–10,000 g mol−1 by changing the reaction temperature from −40 to 30 °C. The MWD was rather broad (Mw/Mn = 2.5–3.5) at low reaction temperatures (from −40 to 10 °C), but became narrower (Mw/Mn ≤ 2.1) at temperatures higher than 10 °C. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012
Article
Ionic liquids with chlorometallate anions may not have been the first ionic liquids, however, it was their development that lead to the recognition that ionic liquids are a distinct, and useful, class of (functional) materials. While much of the phenomenal interest and attention over the past two decades has focussed on 'air and water stable' ionic liquids, research and application of chlorometallate systems has continued unabated albeit largely out of the main spotlight. The defining characteristic of chlorometallates is the presence of complex anionic equilibria, which depend both on the type and on the concentration of metal present, and leads directly to their characteristic and individual properties. Here, we review the experimental techniques that can be applied to study and characterise the anion speciation in these ionic liquids and, using recent examples, illustrate how their applications base is evolving beyond traditional applications in Lewis acidic catalysis and electrochemistry through to uses as soft and component materials, in the ionothermal synthesis of semiconductors, gas storage systems and key components in the development of biomass processing.
Article
The cationic polymerizations of isobutylene (IB) with H2O/FeCl3/dialkyl ether initiating system were conducted in dichloromethane (CH2Cl2) at temperatures from −20 to +20 °C, in which the dialkyl ether includes diethyl ether (Et2O), dibutyl ether (Bu2O) or diisopropyl ether (iPr2O). The highly reactive polyisobutylenes (HRPIBs) with high content of exo-olefin end groups (−CH2−C(CH3)═CH2) 82−91 mol % and acceptable monomodal molecular weight distribution (Mw/Mn = 1.7−2.3) could be successfully synthesized at low concentration of FeCl3 at 0.005 mol·L−1 at 0 or even 10 °C. These results are comparable to those of commercial HRPIBs produced industrially at far below 0 °C. The directly rapid β-proton elimination from −CH3 of the growing chain ends and chain transfer reaction to monomer were dependent on concentration of iPr2O·FeCl3 complex (1:1), concentration of free iPr2O ([free iPr2O] = [iPr2O] − [FeCl3]) if (iPr2O·FeCl3> 1) and polymerization time. The much higher concentration of PIB chains formed in the polymerization system (CPIB) than that of components in initiating system indicates a chain-transfer dominated caionic polymerization process. To the best of our knowledge, this is the first example to achieve HRPIBs with such high exo-olefin end groups by FeCl3-based initiating system.
Article
The cationic polymerization of isobutylene co-initiated by a number of complexes of AlCl3 with linear (Et2O, Bu2O, Am2O, Hex2O, MeOPh) and branched (iPr2O, tBuOMe) ethers in toluene or CH2Cl2 at −20 °C has been investigated. Among them, the complexes with ethers of moderate basicity (AlCl3 × OBu2 and AlCl3 × OiPr2) afforded polyisobutylenes with the highest exo-olefin terminal groups content (80–95%) and monomer conversion, while the use of such weak ether as anisole led to the conventional polyisobutylenes containing mainly tri- and tetra-substituted olefinic end groups (90–95%). The complexes of AlCl3 with tert-butyl methyl ether or tetrahydrofuran are characterized by low stability at room temperature due to the ether cleavage by such strong Lewis acid as AlCl3. The polymerization of isobutylene in the presence of AlCl3 × OBu2 or AlCl3 × OiPr2 as co-initiators could be successfully performed in n-hexane at elevated temperatures (−20 °C to 10 °C) and at high monomer concentrations (up to [M] = 7.8 M) to afford low molecular weight polyisobutylenes (Mn = 1000–8000 g mol−1) with relatively broad MWD (Mw/Mn = 2–4) containing high amount of exo-olefin terminal groups (exo = 70–85%).
Article
This review gives a survey on the latest most representative developments and progress concerning ionic liquids, from their fundamental properties to their applications in catalytic processes. It also highlights their emerging use for biomass treatment and transformation.
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There has been a recent upsurge in interest in use of ionic liquids as reaction media for various chemical processes. Until recently, ionic liquids were considered as highly polar solvents. Our earlier investigation indicated that cationic polymerization of styrene initiated by aryl (alkyl) chlorides in ionic liquids may proceed even in the absence of coinitiator (Lewis acid). Polymerization, however, did not conform to controlled polymerization scheme. More recently, it has been claimed that ionic liquids are not as polar as it was previously assumed. Independently, high solubility of sulfur dioxide in ionic liquids was noticed. As sulfur dioxide displays a high ionizing power toward organic halides, we applied ionic liquid/sulfur dioxide mixture as a solvent in cationic polymerization of styrene initiated by aryl (alkyl) chlorides. Results show that in this reaction medium ionization of the CCl bond is facilitated, and the contribution of chain transfer reaction can be reduced as compared with polymerization in ionic liquid alone. Ionization of the CCl bond, however, is still not sufficiently fast to ensure conditions of controlled polymerization. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5251–5257, 2009
Article
Alkoxybenzenes were used to end-quench TiCl4-catalyzed quasiliving isobutylene polymerizations initiated from 2-chloro-2,2,4-trimethylpentane or 5-tert-butyl-1,3-di(1-chloro-1-methylethyl)benzene at −70 °C in 40/60 (v/v) hexane/methyl chloride. The alkoxybenzene/chain end molar ratios were in the range 2.5−4. Effective alkoxybenzene quenchers included those with simple alkyl groups, such as anisole and isopropoxybenzene, haloalkyl tethers, such as (3-bromopropoxy)benzene and (2-chloroethoxy)benzene, and even those with hydroxyl and amine functionality, such as 4-phenoxy-1-butanol and 6-phenoxyhexylamine. Alkylation was generally quantitative and occurred exclusively in the para position; multiple alkylations on the same alkoxybenzene were not observed. The alkylation reactions were tolerant of temperatures ranging from −70 to −30 °C and were unimpeded by the presence of endo- or exo-olefin termini. In situ cleavage of the ether linkage of anisole and isopropoxybenzene termini allowed single pot syntheses of phenol-terminated polyisobutylenes.
Article
The quantity kp/k-i was measured from first-order kinetic data for cationic quasiliving polymerization of styrene and isobutylene initiated with 5-tert-butyl-1,3-bis(2-chloro-2-propyl)benzene (bDCC)/TiCl4 in 60/40 MCHex/MeCl, via analysis of an initiation event termed rapid monomer consumption (RMC). RMC is characterized by an initial period of high polymerization rate followed by slower first-order decay in monomer concentration and is due to a larger ionization rate for the initiator compared to the polymer chain end. The value of kp/k-i was used in conjunction with the apparent rate constant for propagation, kapp, to calculate apparent rate constants of chain-end ionization, ki, for both monomers at −60, −70, −80, and −90 °C, independently of kp. Rate constants of ion-pair collapse and ionization equilibrium were calculated assuming published values of kp. Apparent energies of activation for kp/k-i of −2.4 and −4.6 kcal/mol were determined for styrene and IB, respectively. Apparent energies of activation for ionization, propagation, and ionization equilibrium were calculated for both monomers. Rates of chain-end ionization and ion-pair collapse were both higher and more sensitive to temperature for polyisobutylene than polystyrene.
Article
The run number (RN), the average number of monomer units added per ionization−termination cycle, was measured at −70 °C from first-order kinetic data for cationic quasi-living polymerization of styrene and isobutylene initiated with 5-tert-butyl-1,3-bis(2-chloro-2-propyl)benzene (bDCC)/TiCl4 in 60/40 MCHex/MeCl, via analysis of an initiation event termed rapid monomer consumption (RMC). RMC is characterized by an initial period of high polymerization rate followed by slower first-order decay in monomer concentration and is due to a larger ionization rate for the initiator compared to that for the polymer chain end. Styrene RN was found to decrease with increasing initiator concentration while that for isobutylene remained relatively unchanged; the dependence of styrene RN on initiator concentration was attributed to chain transfer to initiator during RMC. RN in the limit of zero initiator concentration was determined to be 39 and 4.7 for 0.5 M styrene and isobutylene, respectively. Apparent rate constants of chain-end ionization, ki, of 1.3 and 15 M-2 s-1 and rate constants of ion-pair collapse of 1.9 × 107 and 7.5 × 107 s-1 for styrene and isobutylene, respectively, were calculated. The latter were calculated using a value for kp of 1.5 × 109 M-1 s-1 for styrene and 7 × 108 M-1 s-1 for IB; apparent rate constants of chain-end ionization were determined independently of kp, from k-i/kp and kapp.
Article
The initiating system consisting of AlCl3 with dialkyl ether such as di-n-butyl ether or diisopropyl ether has been successfully developed for providing a cost-effective process of synthesis of highly reactive polyisobutylenes (HRPIBs) with large proportion of exo-olefin end groups up to 93 mol% at temperatures ranging from −20 to +20 °C. The above dialkyl ethers played very important roles in promoting the directly rapid β-proton elimination from –CH3 of the growing chain ends to create exo-olefin end groups and decreasing or even suppressing the carbenium ion rearrangements to form the double bond isomers. Very importantly, the highly reactive PIBs with 80–92 mol% of exo-olefin end groups, having low Mns of 1300–2300 g mol−1 and monomodal molecular weight distribution (Mw/Mn = 1.7–2.0) could be achieved at 0–20 °C. These results are comparable to those of commercial HRPIBs produced industrially by the best BF3-based initiating system at far below 0 °C.
Article
Friedel-Crafts reactions in the ionic liquid system 1-methyl-3-ethylimidazolium chloride-aluminium(III) chloride can be performed with excellent yields and selectivities, and in the case of anthracene, have been found to be reversible.
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Isobutenyl-telechelic polyisobutylenes (PIBs) were synthesized by reacting tert-chlorine-telechelic and living PIBs with isobutenyltrimethylsilane (IBTMS) in the presence of TiCl4 in CH2Cl2/hexane (40/60 v/v) solvent mixtures at −78°C. In order to obtain PIB oligomers, living polymerization of isobutylene was induced by the di-(2-hydroxy-2-propyl)-5-tert-butylbenzene (tBuDiCumOH)/BCl3 combination in CH2Cl2 followed by addition of required amounts of hexane and TiCl4 to avoid polymer precipitation and permanent termination. Although quantitative end-quenching of living PIB was achieved with IBTMS, chain coupling between the living PIB chains and isobutenyl-ended polymers also occurred. This side reaction was avoided by isobutenylation of tert-chlorine-telechelic PIB with IBTMS in the presence of TiCl4. The resulting isobutenyl-telechelic PIB contains exclusively exoCH2C(CH3)CH2 endgroups, and is free from CHC(CH3)2 endo olefins usually obtained in small quantities (∼3–8% of total double bonds) as a side product of other methods used in the past.