Exo-olefin End Groups Research Articles

Homogeneous and heterogeneous catalysts for the synthesis of highly reactive polyisobutylene: discovery, development and perspectives

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.

Liquid coordination complexes as a new class of catalysts for the synthesis of highly reactive polyisobutylene

A number of acidic liquid coordination complexes (LCCs) 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.

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

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.

Cationic Polymerization of Isobutylene and C4 Mixed Feed Using Complexes of Lewis Acids with Ethers: A Comparative Study

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.

Acidic imidazole-based ionic liquids in the presence of diisopropyl ether as catalysts for the synthesis of highly reactive polyisobutylene: Effect of ionic liquid nature, catalyst aging, and sonication

A number of imidazole-based acidic (χ(LA)≥0.6) ionic liquids (RmimCl-LA, where R = Et or Bu, LA = AlCl3, AlBr3, iBuAlCl2, FeCl3, GaCl3, and BBr3) has been synthesized and their activity in cationic polymerization of isobutylene has been assessed. Among different ionic liquids tested here, emimCl-AlCl3, emimCl-FeCl3 and emimCl-GaCl3 showed the best results in terms of monomer conversion, exo-olefin end group content and polydispersity. It was shown that reaction rate depended strongly on the rate of partial hydrolysis of corresponding ionic liquid and increased in the following order: emimCl-FeCl3<emimCl-GaCl3<emimCl-AlCl3. It was demonstrated that emimCl-FeCl3 is the most promising catalyst for the synthesis of HR PIB with desired low molecular weight (Mn < 2500 g mol−1) and polydispersity (Mw/Mn < 2.5) and high content of exo-olefin end groups (>85%). However, due to poor dispergation of emimCl-FeCl3 in n-hexane as well as its high stability toward hydrolysis, the catalyst aging and/or sonication of reaction mixture is required in order to provide acceptable polymerization rate.

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

Medium molecular weight polyisobutylenes (∼35 000 g mol−1) with exo-olefin end groups (&gt;80%) can be obtained by cationic polymerization of isobutylene in toluene using iBu2AlCl or iBuAlCl2·nOR2 (n = 0.6–0.8) as co-initiators.

Cationic polymerization of isobutylene catalyzed by iBuAlCl2 in the presence of ethers: Effect of catalyst pre-activation and mixture of two ethers

Abstract 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 ∼ 1000 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).

New catalysts for the synthesis of highly reactive polyisobutylene: chloroaluminate imidazole-based ionic liquids in the presence of diisopropyl ether

The use of [emim]Cl–AlCl3 in combination with iPr2O allowed the synthesis of HR PIB with high exo-olefin end group content (≥90%) and a relatively narrow MWD (Mw/Mn ≤ 2.0) at a high reaction temperature (&gt;0 °C) and monomer concentration (5.2 M–7.8 M).

Cationic polymerization of isobutylene by complexes of alkylaluminum dichlorides with diisopropyl ether: An activating effect of water

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, 52, 2386–2393

Synthesis of highly reactive polyisobutylenes with exo-olefin terminals via controlled cationic polymerization with H2O/FeCl3/iPrOH initiating system in nonpolar hydrocarbon media

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

Polyisobutylene with High exo-Olefin Content via β-H Elimination in the Cationic Polymerization of Isobutylene with H2O/FeCl3/Dialkyl Ether Initiating System

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 ...

A cost-effective process for highly reactive polyisobutylenes via cationic polymerization coinitiated by AlCl 3

The initiating system consisting of AlCl 3 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 –C H 3 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 M ns of 1300–2300 g mol −1 and monomodal molecular weight distribution ( M w/ M n = 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 BF 3-based initiating system at far below 0 °C.

End-Quenching of Quasiliving Carbocationic Isobutylene Polymerization with Hindered Bases: Quantitative Formation of exo-Olefin-Terminated Polyisobutylene

Polyisobutylenes possessing exclusively exo-olefin end groups were created by end-quenching TiCl4-catalyzed quasiliving isobutylene (IB) polymerizations with a hindered base at −60 to −40 °C. Polymerizations were initiated from either 2-chloro-2,4,4-trimethylpentane (TMPCl) or 1,3-bis(2-chloro-2-propyl)-5-tert-butylbenzene, in 60/40 hexane/methyl chloride in the presence of 2,6-dimethylpyridine, allowed to reach 98+% isobutylene conversion, and then reacted with either 2,5-dimethylpyrrole, 1,2,2,6,6-pentamethylpiperidine, or 2-tert-butylpyridine for various times ranging from 10 to 170 min. Typical reaction molar concentrations were [IB] = 0.5, [TMPCl] = 0.014, [26Lut] = 0.010, [TiCl4] = 0.083, and [hindered base] = 0.02−0.04 M. In some cases, minor amounts of coupled PIB were produced through reaction of carbenium ions with exo-olefin. Coupling was suppressed by higher temperature and lower chain end concentration. 2,5-Dimethylpyrrole was the most effective quencher under the conditions studied, yielding...