Article

Cationic polymerization of isobutylene in toluene: toward well-defined exo-olefin terminated medium molecular weight polyisobutylenes under mild conditions

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Abstract

The cationic polymerization of isobutylene with H2O/ⁱBu2AlCl and H2O/ⁱBuAlCl2·nOR2 (n = 0-1; R2O = Bu2O, Hex2O, ⁱPr2O) initiating systems in toluene as a solvent at -20 °C has been investigated. The H2O/ⁱBu2AlCl initiating system induced slow cationic polymerization of isobutylene to afford polyisobutylenes with high molecular weight (up to Mn = 55 000 g mol⁻¹) with relatively low polydispersity (Mw/Mn < 2.5) and high exo-olefin end group content (>85%). The introduction of additional water into the system allowed increasing the reaction rate, but almost did not influence the molecular weight and exo-olefin content. The use of stronger Lewis acid ⁱBuAlCl2 results in a significant increase of the intensity of side reactions such as chain transfer to solvent (toluene) and isomerization of the growing macrocations, leading to the formation of ill-defined products. However, the addition of 0.6-1.0 equivalents of ethers to Lewis acid allowed conducting the polymerization in a controlled fashion in terms of chain end functionality. In addition, the molecular weight can be efficiently controlled by either the ether/Lewis acid ratio or the nature of the electron donor additive. Based on the obtained results, the polymerization mechanism, the key features of which are complex formation between Lewis acid and toluene and possible stabilization of active species through their interaction with toluene, was proposed.

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... Consequently, AlCl 3 constitutes a promising alternative to replace the BF 3 catalyst in the near future. It is important to recall that the isobutylene polymerization catalyzed by AlCl 3 is usually very fast, and consequently highly exothermic and difficult to control, requiring the association with weak bases for selective electron abstraction and production of HR-PIB [60][61][62][63]. On the other hand, it offers convenient operation at relatively mild temperatures [43,60]. ...
... It is important to recall that the isobutylene polymerization catalyzed by AlCl 3 is usually very fast, and consequently highly exothermic and difficult to control, requiring the association with weak bases for selective electron abstraction and production of HR-PIB [60][61][62][63]. On the other hand, it offers convenient operation at relatively mild temperatures [43,60]. ...
... Ether compounds (38%) have been largely used as Lewis base co-catalysts for synthesis of HR-PIB, although diisopropyl ether (Pr 2 O) [58][59][60]94,95], bis(2-chloroethyl) ether (CEE) [96] and dibutyl ether (Bu2O) [59,60] are the ones cited most often, usually in association with the AlCl 3 co-catalyst. This is probably due to the fact that ethers are known to form well-defined complexes with AlCl 3 [97]. ...
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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.
... [13,18,21] The solubility issue was addressed by using complexes of alkylaluminum dichlorides with ethers, which are fully soluble in n-hexane and other non-polar sol-vents. [22][23][24][25][26][27][28][29][30] These new initiating systems, under optimized conditions, induced fast cationic polymerization of isobutylene at high temperature (0−20 °C) and monomer concentration (up to 5 mol·L -1 ) to afford HR PIB with desired low molecular weight (Mn < 2500 g·mol -1 ) and high content of exo-olefin end groups (> 80%). [22][23][24][25][26][27][28][29][30] However, the polydispersity of obtained PIBs was typically high (Mw/Mn = 3−5), which is detrimental for the application. ...
... [22][23][24][25][26][27][28][29][30] These new initiating systems, under optimized conditions, induced fast cationic polymerization of isobutylene at high temperature (0−20 °C) and monomer concentration (up to 5 mol·L -1 ) to afford HR PIB with desired low molecular weight (Mn < 2500 g·mol -1 ) and high content of exo-olefin end groups (> 80%). [22][23][24][25][26][27][28][29][30] However, the polydispersity of obtained PIBs was typically high (Mw/Mn = 3−5), which is detrimental for the application. [1] The polydispersity can be improved (Mw/Mn = 2.3−3.5) by using the mixture of two ethers of different basicities and steric structures (diethyl and diisopropyl ethers) instead of i Pr2O [31] or micromixing conditions. ...
... [1,2,3] Therefore, the polymerization of C 4 mixed feed to yield polyisobutylene with high content of exo-olefin end groups is challenging. Despite the huge progress achieved in the synthesis of HR PIB from neat isobutylene using complexes of Lewis acids with ethers as catalysts, [2,3,[22][23][24][25][26][27][28][29][30][31][32][33][34] considerably less attention has been paid to polymerization of C 4 mixed feed. [16,28,35,36] Most of examples reporting the cationic polymerization of C 4 mixed feed deal with application of the first generation of catalysts, namely complexes of metal halides with ethers. ...
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The cationic polymerization of C4 mixed feed and isobutylene co-initiated by AlCl3×OⁱPt2, ⁱBuAlCl2×nOⁱPr2, and [emim]Cl-FeCl3×nOⁱPr2 ([emim]Cl: 1-ethyl-3-methylimidazolium chloride) has been investigated. AlCl3×OⁱPr2 co-initiated cationic polymerization of C4 mixed feed proceeds at a lower rate than polymerization of isobutylene affording polymers with higher molecular weight. Complexes of ⁱBuAlCl2 with diisopropyl ether of different compositions are more suitable co-initiators than AlCl3×OⁱPr2 for the synthesis of highly reactive polyisobutylene (HR PIB) from C4 mixed feed due to their higher activity in the polymerization as well as possibility to prepare polyisobutylenes with lower molecular weight and higher content of exo-olefin end groups. However, ⁱBuAlCl2 needs activating via addition of external water (initiator) and/or interaction with salts hydrates in order to increase the reaction rate and the saturated monomer conversion. [Emim]Cl-FeCl3/ⁱPr2O is a quite promising catalyst for the preparation of HR PIB with high exo-olefin end group content (> 80%) and relatively low polydispersity (Mw/Mn < 2.8) via cationic polymerization of C4 mixed feed. The sonication of reaction mixture in case of using [emim]Cl-FeCl3 allowed increasing the reaction rate and decreasing the molecular weight.
... 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.
... Kostjuk and coworkers found H 2 O/iBu 2 AlCl/toluene was able to afford PIB with high M w at T p = −20 • C because of the weak basicity of toluene, which would help to stabilize the active species. While for iBuAlCl 2 with stronger Lewis acidity, additional ether was needed to suppress side reactions and obtain HPIBs [24]. The same group also disclosed that alkoxy aluminum chlorides-based systems H 2 O/(RO) 0.8+n AlCl 2.2−n /n-hexane (R = Bu, Hex or iPr; n = 0-0.4) ...
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A complexed initiating system AlCl3·phenetole/TiCl4·H2O was prepared by simply compounding AlCl3/phenetole and TiCl4/H2O and used for cationic polymerization of isobutylene. It was found AlCl3·phenetole/TiCl4·H2O exhibited activities 1.2–3 times higher than those of AlCl3/phenetole, and more than an order of magnitude higher than those of TiCl4/H2O, which indicated a notable synergistic effect produced in the complexed system. In addition, due to the higher activity of AlCl3·phenetole/TiCl4·H2O, lower coinitiator concentration and polymerization temperature, as well as higher monomer concentration were more favored for this complexed initiating system to produce polyisobutylene (PIB) with reasonable molecular weight (Mw) and molecular weight distribution (MWD). Furthermore, high molecular weight polyisobutylene (HPIB) with Mw = 1–3 × 105 g·mol−1 could be successfully produced by the complexed catalyst system at Tp = −60 to −40 °C. As a whole, the high activity as well as the simple preparation procedures of the complexed initiating system offer us a unique approach for the production of HPIB with improved efficiency.
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Macromolecular engineering is defined as the total synthesis of tailor‐made macromolecules. The ultimate goal of this technology is to obtain a high degree of control over compositional and structural variables that affect the physical properties of macromolecules, including molecular weight, molecular weight distribution, end functionality, tacticity, stereochemistry, block sequence, and block topology, where the parameters of molecular characterization are well represented by the ensemble average. This review article summarizes the use of carbocationic polymerization for macromolecular engineering.
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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.
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A number of acidic liquid coordination complexes (LCC) based on phosphorus-containing electron donors such as tri-n-octylphosphine oxide (POct3O), triphenylphosphine oxide (PPh3O) or triphenylphoshine (PPh3), and Lewis acids (AlCl3, FeCl3, TiCl4) have been synthesized and tested as catalysts of cationic polymerization of isobutylene. Among different LCCs studied, POct3O–AlCl3 and POct3O–FeCl3 (χ(MCl3)=0.60) in combination with bis(2-chloroethyl)ether (CE) and ⁱPr2O, respectively, showed best results in terms of monomer conversion, exo-olefin end group content and polydispersity. POct3O–AlCl3/CE catalytic system afforded highly reactive polyisobutylene (HR PIB) with high exo-olefin end group content (75–90%) and low polydispersity (Đ≤2.0) in high yield (70 – 90%) at 20 °C and high monomer concentration ([IB]=5.2 M) in n-hexane, although the number-average molecular weight (Mn=2.500–3.500 g mol–1) is slightly higher than required for application. POct3O–FeCl3/ⁱPr2O catalytic system showed higher activity and regioselectivity in the cationic polymerization of isobutylene as compared to POct3O–AlCl3/CE giving desired low molecular weight HR PIB (Mn=1500 g mol⁻¹, Đ=2.1, Fn(exo)=91%) in quantitative yield at lower catalyst concentration (22 mM for POct3O–FeCl3 vs. 44 mM for POct3O–AlCl3) at room temperature.
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The AlCl3×OPh2-co-initiated cationic polymerization of anethole, a biomass-derived vinyl monomer, in toluene and α,α,α-triflurotoluene as less toxic solvents as compared to traditionally used chlorinated ones has been reported. The investigations of the effect of temperature, solvent nature, proton trap addition as well as co-initiator concentration allowed to establish optimal conditions for the synthesis of relatively high molecular weight polymers. Polyanethole with Mn up to 21,000 g mol–1 with moderate polydispersity (Đ ≤ 3.5) were obtained in toluene at –20 °C in the presence of 2,6-lutidine as a proton trap at low co-initiator concentration (13 mM). It was shown that all synthesized polymers contain high molecular weight fraction, which is generated due to the chain transfer to monomer via its alkylation followed by the copolymerization of obtained macromonomers with anethole. The content of high molecular weight fraction can be successfully reduced down to < 7% by the increase the reaction temperature and a use of less polar solvent (toluene). The synthesized polyanetholes showed high glass transition temperature values (Tg > 237 °C), high thermal stability (Td5 > 383.5 °C) and high Young modulus (E = 3.1±0.6 GPa) that makes the polymer perspective for the application as high-performance materials.
Article
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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The cationic polymerization of isobutylene using RAlCl2 × nOiPr2-based initiating systems (R = Me, Et, iBu; n = 0.6–1) in non-polar n-hexane at 10 °C and with high monomer concentrations ([M] = 2.8–5.8 M) has been investigated. Among the complexes of alkylaluminum dichlorides with diisopropyl ether the best results in terms of exo-olefin content and monomer conversion were obtained with EtAlCl2 × nOiPr2 and iBuAlCl2 × nOiPr2 where n = 0.8–0.9. These initiating systems afforded polyisobutylenes with the desired low molecular weight (Mn = 1000–1500 g mol−1) and high exo-olefin terminal group content (85–95%) in a moderate yield (30–60%). The use of a “delayed proton abstraction” approach, i.e. when the polymerization of IB is co-initiated by RAlCl2 and separately added ether, allowed an increase in both the reaction rate and the ultimate monomer conversion (70% in less than 15 min), while the exo-olefin end group content remained high (85%). In addition, RAlCl2 × OiPr2-based initiating systems showed high activity and selectivity towards the polymerization of mixed C4 feed.
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The polymerization of β-pinene is efficiently prompted by AlCl3 etherates to afford relatively high molecular weight polymers (Mn = 9000–14000 g mol−1) with good thermal properties (Tg = 82–87 °C) at room temperature and low catalyst content (2.5–5.5 mM).
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This highlight is about my metamorphosis from a cationic polymerization chemist to a biomaterialist (no pun intended) and some of the main events on the road. My earlier career faded away with the discovery of living cationic polymerizations, chronicled in my 1999 highlight, but it also put me on the road to designed biomaterials. My new career started with, and still focuses on, the creation of new polymeric architectures, mainly by cationic techniques, for toughened bone cements, injectable intervertebral discs, nonclogging artificial blood vessels, and amphiphilic networks for controlled drug delivery and immunoisolatory membranes. The enormous complexities of immunoisolation of pancreatic islets are now center stage, and lately we have been using all kinds of techniques to make unique membranes to correct type 1 diabetes. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2951–2963, 2005
Article
In this work, by exploiting the perfect performances of microflow reactors in mixing and residence time control, we systematically investigated the cationic polymerization of isobutylene (IB) catalysed by AlCl3 with multiple nucleophilic reagents, isopropyl ether (iPr2O) and ethyl benzoate (EB). Through properly introducing iPr2O and EB, the polymerization of IB could produce PIBs with a narrow molecular weight distribution (PDI < 2.0), a relatively high molecular weight (>40 000 g mol⁻¹), and a high content of exo-olefin (w > 70%) at relatively high temperatures (-30 °C), during which most of the monomer conversion (>70%) could be fulfilled within 0.5 s and the chain scission mainly takes place after seconds. The expression [2[EB] + [iPr2O]]/[AlCl3] being equal to 1 is recognized as a quantitative criterion for achieving these outcomes, corresponding to H⁺iPr2OAlCl3(OH)⁻ initiating polymerization with inhibited chain transfer by introducing EB(AlCl3)n, but eliminating free AlCl3. Increasing the flow capacity in a certain microflow system provides the potential to increase the molecular weight further and facilely tailor it for particular applications. This work verifies the various functions of multiple nucleophilic reagents and their ability to break the trade-off of conversion rate and propagation chain stability in cationic polymerization and develop new functional products of PIBs.
Article
Phenoxyalkyl acrylates and methacrylates were studied as quenching (capping) agents for living carbocationic polymerization of isobutylene (IB) at −70 °C in 40/60 (v/v) hexane/methyl chloride, catalyzed by TiCl4. Quenching reactions were carried out by reactivation by TiCl4 of preformed difunctional tert-chloride-terminated polyisobutylene (PIB) or by a one-step method in which IB polymerization and quenching were conducted sequentially in the same reactor. Chain-end concentrations ranged from 0.02 to 0.1 M, and quenchers were used at concentrations of 1.5–2.5 times the chain ends. The phenoxyalkyl (meth)acrylates were synthesized by reaction of (meth)acryloyl chloride with the corresponding phenoxyalkanol; alkylene tethers from two to eight carbons were examined. Quenched polymers were characterized by 1H and 13C NMR, MALDI-TOF mass spectrometry, and size exclusion chromatography (SEC). Alkylation was observed to occur exclusively at the para position of the phenoxy moiety, and SEC showed no coupling or molecular weight degradation as a result of quenching. For short tethers of two or three carbons, quenching was slow and incomplete due to competing loss of living chain ends presumably by carbocation rearrangement. For tethers of four, six, or eight carbons, quenching was much faster and yielded quantitative (meth)acrylate chain-end functionality (number-average functionality ≥1.98 by 1H NMR). MALDI-TOF-MS results were consistent with the expected end group structures. The carbonyl group of the quencher consumes one equivalent of Lewis acid in formation of a 1:1 complex; thus, the highest rate of quenching at a given Lewis acid concentration is achieved by using only a modest excess of quencher relative to living chain ends.
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
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
Alkoxybenzenes, including (3-bromopropoxy)benzene, anisole, and isopropoxybenzene, were used to end-quench polyisobutylene, activated with either AlCl3 or TiCl4 at different temperatures (-50, -25 and 0°C) in 70/30 and 55/45 (v/v) hexane/methylene chloride (Hex/CH2Cl2). Quenching reactions were performed on pre-formed difunctional tert-chloride PIB, which was produced from 5-tert-butyl-1,3-di(1-chloro-1-methylethyl)benzene/TiCl4 at -70°C in 40/60 (v/v) hexane/methyl chloride. For (3-bromopropoxy)benzene and anisole, quantitatively end-capped products were achieved if the alkoxybenzene/AlCl3 molar ratio was greater than unity. Under these conditions, alkylations were generally quantitative and occurred exclusively in the para position; neither multiple alkylations on the same alkoxybenzene nor polymer chain degradation were observed. Carbocation rearrangement was observed if the alkoxybenzene/AlCl3 molar ratio was less than unity. No such specific alkoxybenzene/Lewis acid molar ratio was required to obtain quantitatively alkylated products using TiCl4 catalyst. The alkylation rate of (3-bromopropoxy)benzene with AlCl3 was 2.6 times faster than with TiCl4 under the same reaction conditions. The alkylation rate of (3-bromopropoxy)benzene was faster than that of anisole using AlCl3. For isopropoxybenzene quencher only, using AlCl3 catalyst, a small fraction of exo-olefin was formed during the initial stage of reaction, and the quenching reaction failed to reach completion. Chain end functionality, a mixture of para and meta isomers (3:1), reached only 1.72 (86.4% conversion) after 45 h. Increasing temperature to -25 and 0°C did not greatly affect the rate of alkylation, but it did increase carbocation rearrangement and decreased regioselectivity; at 0°C, 25% alkylation occurred at the meta or ortho positions of (3-bromopropoxy)benzene. Increasing solvent polarity to 55/45 (v/v) Hex/CH2Cl2 also did not greatly affect alkylation rate but increased carbocation rearrangement.
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
Polyisobutylene-b-poly(N,N-diethylacrylamide) (PIB-b-PDEAAm) well-defined amphiphilic diblock copolymers were synthesized by sequential living carbocationic polymerization and reversible addition-fragmentation chain transfer (RAFT) polymerization. The hydrophobic polyisobutylene segment was first built by living carbocationic polymerization of isobutylene at −70 °C followed by multistep transformations to give a well-defined (Mw/Mn = 1.22) macromolecular chain transfer agent, PIB-CTA. The hydrophilic poly(N,N-diethylacrylamide) block was constructed by PIB-CTA mediated RAFT polymerization of N,N-diethylacrylamide at 60 °C to afford the desired well-defined PIB-b-PDEAAm diblock copolymers with narrow molecular weight distributions (Mw/Mn ≤1.26). Fluorescence spectroscopy, transmission electron microscope, and dynamic light scattering (DLS) were employed to investigate the self-assembly behavior of PIB-b-PDEAAm amphiphilic diblock copolymers in aqueous media. These diblock copolymers also exhibited thermo-responsive phase behavior, which was confirmed by UV-Vis and DLS measurements. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015
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
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 cyclopolymerizations of 2,2-bis(vinyloxymethyl)bicyclo[2.2.1]heptane (1), 5,5-bis(vinyloxymethyl)-2-bicyclo[2.2.1]heptene (2), and 2,2-bis(vinyloxymethyl)tricyclo[3.3.1.1]3, 7decane (3), divinyl ethers with a norbornane, norbornene, or adamantane unit, respectively, were investigated with the HCl/ZnCl2 initiating system in toluene and methylene chloride at −30 °C. All the reactions proceeded quantitatively to give gel-free, soluble polymers in organic solvents. The number-average molecular weight (Mn) of the polymers increased in direct proportion to monomer conversion and further increased on addition of a fresh monomer feed to the almost completely polymerized reaction mixture. The contents of the unreacted vinyl groups in the produced soluble polymers were less than ∼10 mol %, and therefore, the degree of cyclization of the polymers was determined to be over ∼90%. These facts show that cyclopolymerization of 1, 2, and 3 exclusively occurred and the poly(vinyl ether)s with the cyclized repeating units and polycyclic pendants were obtained with their molecular weights being regulated. BF3OEt2 initiator also caused cyclopolymerization of 1, 2, and 3 to give the corresponding high-molecular-weight cyclopolymers quantitatively. Glass transition temperatures (Tg's) of poly(1) and poly(2) were 165–180 °C, and Tg's of poly(3) were 211–231 °C; these values are very high as vinyl ether polymers. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2445–2454
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
A new design perspective on initiating systems for living cationic polymerization was gained by thorough examination of various metal chlorides as catalysts in conjunction with a weak Lewis base in the cationic polymerization of p-methoxystyrene. The Lewis acids clearly differed in controllability, in contrast to the findings of a previous report on the polymerization of isobutyl vinyl ether (IBVE) using various catalysts (all the metal chlorides used in the present study induced the controlled polymerization of IBVE, although the reaction rates depended on the chlorophilic and oxophilic nature of the central metals: Macromolecules 2009, 42, 3965). Metal tetrachlorides and dichlorides such as SnCl4, TiCl4, ZrCl4, HfCl4, and ZnCl2 induced controlled polymerizations to produce polymers with predetermined molecular weights and very narrow molecular weight distributions (MWDs). In contrast, frequent side reactions (β-proton elimination and the Friedel—Crafts reaction) occurred with the trichlorides FeCl3 and GaCl3, yielding polymers with molecular weights lower than the theoretical values and with broad MWDs. Another trichloride, AlCl3, produced polymers with very high molecular weights owing to its very low initiation efficiency. NbCl5, a pentachloride, was also unable to control the polymerization. The structures of the counteranions with or without a coordinating weak Lewis base were shown to be responsible for the difference in the controllability between the metal chlorides.
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
The low-cost essentially quantitative methods for the synthesis of novel polyisobutylenes (PIBs) fitted with terminal primary -Br, -OH, -NH2, or a methacrylate end group have been developed. The primary -Br was synthesized by quantitative anti-Markovnikov hydrobromination of the readily available allyl-terminated PIB. To synthesize primary bromo-terminated PIB, allyl-terminated PIB dissolved in hexane were placed in a three-necked flask. The system was refluxed and air was bubbled through the solution for 30 min., followed by cooling the system to 0°C. HBr gas was bubbled into the solution for 5 min. and sodium bicarbonate was added to neutralize the mixture. After washing the system with water, the organic layer was separated, washed, and dried and hexane were removed. The product, bromo-terminated PIB was dried in vacuum and the same procedure was employed to convert Glissopal® 2300 to the primary bromide terminated derivative.
Article
The ternary catalytic system AlBui 3-TiCl4-CCl4 initiates the cationic polymerization of isobutylene in toluene at room temperature, whereas the binary combinations of these components do not induce isobutylene polymerization. At low CCl4 concentrations, the polymerization rates decrease sharply with time, and the quantitative yield of the polymer is achieved at an excess of CCl4 with respect to the titanium and aluminum components. The molecular weights of the polymers range within 1300–4000, and the index of polydispersity, as a rule, does not exceed 2.7. The influence of the conditions of component mixing (order of addition, duration of exposure prior to addition of the third component) on the yield and molecular weight of the polymerization product was found.
Article
The kinetics of the reactions of the carbocations CH3[C(CH3)2CH2]nC+Ph2 (1a+−1d+, n = 0, 1, 2, 34) with allyltrimethylsilane (4) and dimethylphenylsilane (5) have been investigated. It is found that the carbocation 1a+ (n = 0) is 102 times more reactive than the more highly substituted analogues 1b+−1d+, which hardly differ in their electrophilic reactivity. We, therefore, conclude that the (CH3)3CCH2 and (CH3)3CCH2C(CH3)2CH2 groups are suitable to mimic the polyisobutylene chain in a growing carbocation.
Article
N-(2-tert-Butoxyethyl)pyrrole was used to end-quench TiCl4-catalyzed quasiliving isobutylene polymerizations initiated from 2-chloro-2,2,4-trimethylpentane and 5-tert-butyl-1,3-di(2-chloro-2-propyl)benzene at −60 °C in 60/40 (v/v) hexane/methyl chloride. End-capping was near-quantitative except for the formation of <5% exo-olefin chain ends, with alkylation occurring in both the C-3 (57%) and C-2 (38%) position on the pyrrole ring. Coupling was not observed for the monofunctional polymers; however, quenching of difunctional polymers resulted in small amounts of coupling due to dialkylation at the pyrrole ring. The terminal tert-butyl group of the N-(2-tert-butoxyethyl)pyrrole-capped polyisobutylene was rapidly and quantitatively removed in situ by addition of ethylaluminum dichloride and sulfuric acid to the reaction mixture. Furthermore, heating the reaction mixture to reflux (69 °C) forced alkylation by the residual exo-olefin chain ends and induced isomerization of the pyrrole-capped chain ends to yield exclusively [3-polyisobutyl-N-(2-hydroxyethyl)]pyrrole. The primary hydroxy-terminated polyisobutylenes showed excellent, unimpeded reactivity with carboxylic acid and isocyanates typically used in block copolymer synthesis.
Article
Epoxy telechelic polyisobutylenes (EP-PIB-EP), potentially useful to obtain flexible epoxies, were synthesized by reacting bromoallyl end-functional PIB with glycidol in the presence of NaH. The epoxy end-capped macromonomers were mixed with bisphenol A diglycidyl ether (DGEBA) and triethylenetetramine as curing agent and cured at elevated temperature. Field emission scanning electron microscopy (FESEM) indicated nanophase segregation of rubbery domains at EP-PIB-EP ≤ 15 wt %, and the fracture toughness increased by 100% relative to the unmodified epoxy network, while the tensile and flexural strengths remained adequate. However, at EP-PIB-EP ≥ 20 wt % macrophase separation resulted in a drastic reduction in toughness along with other mechanical properties. Use of oligo(tetramethylene oxide) modified epoxy telechelic PIB (EP-oTHF-PIB-oTHF-EP) as soft segment significantly improved the miscibility, and cured materials with excellent fracture toughness were obtained even at 40 wt % rubber content. Thermal stability of the amine cured epoxy resin was not affected by the incorporation of PIB. These flexible networks possess superior mechanical properties compared to poly(ethylene glycol)/DGEBA networks commercialized by Dow Chemical Company.
Article
The application of the 2-phenyl-2-propanol (CumOH)/AlCl3OBu 2 initiating system to the synthesis of highly reactive polyisobutylene containing 86-95% of exo-olefin end groups. Isobutylene was dried in the gaseous state by passing through the column packed with CaCl 2. Ethyl acetate and pyridine were distilled twice from CaH 2 under an inert atmosphere. Diphenyl ether was distilled from CaH2 under reduced pressure. Size exclusion chromatography (SEC) was performed on a PL-GPC 50 integrated GPC system with two columns and one precolumn thermostated at 30°C. The detection was achieved by differential refractometer. Tetrahydrofuran (THF) was eluted at a flow rate of 1.0 mL/min. diphenylthiocarbazone as an indicator. The polymerization reactions were carried out in glass tubes under an argon atmosphere at different temperatures. It is evident that the molecular weight of polymers synthesized with the CumOH/AlCl3OBu2 initiating system is controlled by the concentration of free base (Bu2O), not by [isobutylene]/[CumOH] ratio.
Article
The carbocationic polymerization of isobutylene (IB) was studied in conjunction with AlBr3, MeAlBr2, Me1.5AlBr1.5, and Me2AlBr coinitiators in hexanes(Hex)/methyl chloride (MeCl) 60/40 (v/v) solvent mixtures at −80 °C in the presence of a proton trap, 2,6-di-tert-butylpyridine. The observed Mns were directly proportional to monomer-to-initiator ratio with 2-chloro-2,4,4-trimethylpentane (TMPCl) as initiator and MeAlBr2, Me1.5AlBr1.5, and Me2AlBr coinitiators; however, with AlBr3 the Mns are much lower than the theoretical values. Chain extension “incremental monomer addition” (IMA) experiments resulting in bimodal distributions demonstrate that termination is operational with Me2AlBr. With MeAlBr2 the chain-extended PIBs exhibited close to theoretical Mns, but the molecular weigh distribution was broad. Using Me1.5AlBr1.5, Mn of the polymers increased in direct proportion and the molecular weight distributions remained narrow. 1H and 13C NMR spectroscopy of the polyisobutylene (PIB) obtained with Me1.5AlBr1.5 suggested virtually quantitative bromo end functionality. With MeAlBr2 and Me2AlBr the bromo functionality was lower (0.8−0), decreasing with the increase of Lewis acid concentration and polymerization time. The capping reaction of living polyisobutylene cation (PIB+) with 1,3-butadiene (BD) in Hex/MeCl 60/40 (v/v) solvent mixtures at −80 °C was also studied in conjunction with methylaluminum bromide coinitiators. Quantitative crossover reaction from living PIB chain end to BD followed by instantaneous termination and selective formation of 1,4-addition product bromoallyl functional PIB (PIB-AllylBr) was obtained only with Me1.5AlBr1.5 coinitiator.
Article
The cationic polymerization of isobutylene with weak Lewis acids, such as BBr3 and FeBr3, has been studied. These halides are unable to induce individually the polymerization in nonpolar solvents, such as heptane or toluene, or they only initiate the polymerization to low conversions in polar media, such as dichloromethane. The complex compounds, formed by interaction of both Lewis acids, initiate a fast polymerization of isobutylene, which proceeds up to high conversions. The coinitiation effect of HBr in the mixture with BBr3 and FeBr3 was also investigated. The hypothetic formation of efficient initiators and the initiation mechanism of olefin polymerization are discussed on the basis of the ionogenic action of both Lewis acids.
Article
This study briefly surveys a variety of new advanced polymeric materials and controlled synthetic processes available by carbocationic macromolecular engineering techniques and having potential commercial interest. These recent developments, mainly by living carbocationic polymerization, have led to new opportunities in polymerization process control, and in designing microstructure, functionality, molecular weight and molecular weight distribution (MWD) and thus properties of a wide variety of unique polymer systems. The fundamentals of these new emerging technologies and the novel materials offered by them, such as macromonomers, telechelics, polymers with pendant functional groups (liquid crystalline homo- and co-polymers, non-linear optical materials etc.), star-shaped macromolecules, block and graft copolymers, high temperature polymers, and specialty networks (amphiphilic networks and rubber toughened bone cements) as potential biomaterials will be overviewed.
Article
This paper describes the synthesis of highly reactive polyisobutene (PIB), a special type of PIB used as a component in the production of lubricant and fuel additives. The reactivity and the chemical structure are described in detail, in relation to the nature of the product and its uses as an additive component.
Article
This article highlights the biomaterial-related research of the Macromolecular Engineering Research Centre (MERC). The MERC group concentrated on polyisobutylene (PIB)-based biomaterials. In this article, first the unique properties of PIB are discussed, followed by a review of PIB-based potential biomaterials. MERC's systematic research program aimed to develop novel PIB-based biomaterials is then highlighted, including surface modification and biocompatibility studies. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3091–3109, 2004
Article
Copper(II) complexes with weakly coordinating counter anions can be utilized as highly efficient catalysts for the synthesis of poly(2-methylpropene) ("polyisobutene") with a high content of terminal double bonds. These copper(II) compounds are significantly more active than the manganese(II) complexes described previously, can be applied in chlorine-free solvents such as toluene, are easily accessible, and can be handled at room temperature and in laboratory atmospheres for brief periods, but they are sensitive to excess water, thereby losing their catalytic activity. Replacing the acetonitrile ligands by benzonitrile ligands improves the solubility and catalytic activity in nonpolar and nonchlorinated solvents. However, the benzonitrile copper(II) compounds have lower thermal stability than their acetonitrile congeners.
Article
Polyisobutylene (PIB)-based block copolymers have attracted significant interest as biomaterials. Poly(styrene-b-isobutylene-b-styrene) (SIBS) has been shown to be vascularly compatible and, when loaded with paclitaxel (PTx) and coated on a coronary stent, has the ability to deliver the drug directly to arterial walls. Modulation of drug release from this polymer has been achieved by varying the drug/polymer ratio, by blending SIBS with other polymers, and by derivatizing the styrene end blocks to vary the hydrophilicity of the copolymer. In this paper, results are reported on the synthesis, physical properties, and drug elution profile of PIB-based block copolymers containing methacrylate end blocks. The preparation of PIB-poly(alkyl methacrylate) block copolymers has been accomplished by a new synthetic methodology using living cationic and anionic polymerization techniques. 1,1-Diphenylethylene end-functionalized PIB was prepared from the reaction of living PIB and 1,4-bis(1-phenylethenyl)benzene, followed by the methylation of the resulting diphenyl carbenium ion with dimethylzinc (Zn(CH(3))(2)). PIB-DPE was quantitatively metalated with n-butyllithium in tetrahydrofuran, and the resulting macroinitiator could initiate the polymerization of methacrylate monomers, yielding block copolymers with high blocking efficiency. Poly(methyl methacrylate-b-isobutylene-b-methyl methacrylate) (PMMA-b-PIB-b-PMMA) and poly(hydroxyethyl methacrylate-b-isobutylene-b-hydroxyethyl methacrylate) (PHEMA-b-PIB-b-PHEMA) triblock copolymers were synthesized and used as drug delivery matrixes for coatings on coronary stents. The PMMA-b-PIB-b-PMMA/PTx system displayed zero-order drug release, while stents coated with PHEMA-b-PIB-b-PHEMA/PTx formulations exhibited a significant initial burst release of PTx. Physical characterization using atomic force microscopy and differential scanning calorimetry of the formulated PMMA-b-PIB-b-PMMA coating matrix indicated the partial miscibility of PTx with the PMMA microphase of the matrix.
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