Catalytic chain transfer polymerization (CCTP) of isobutylene in the presence of alcohol as an exo-enhancer with tert-butyl chloride/ethylaluminum dichloride (EADC)·bis(2-chloroethyl) ether (CEE) has been investigated in hexanes at 0 °C. Increasing exo-olefin content was observed with increasing steric bulkiness of the alkyl group of the alcohol, i.e., tert-butyl > isopropyl > methyl. Here, we report that tert-butanol (t-BuOH) is an excellent exo-enhancer compared to other tert-alcohols such as tert-amyl alcohol (AmOH), 2-methyl-2-pentanol (MPOH), and 3-ethyl-3-pentanol (EPOH). The aromatic tert-alcohol cumyl alcohol was not an exo-enhancer but acted as an initiator. In the reaction of EADC.CEE and t-BuOH, t-butoxyaluminum dichloride (t-BuOAlCl2) was formed, which is the real exo-enhancer and is not stable at room temperature. Molecular weights were virtually unchanged in the presence t-BuOAlCl2 with [t-BuOAlCl2]:[EADC.CEE] < 0.5, and exo-olefin content increased ∼15% relative to polymerization in the abs...

The rate constants of activation/deactivation for dormant oxonium/active carbenium ions have been measured and related to the increasing polymerization rate with increasing temperature.

ABSTRACTFast polymerization of isobutylene (IB) initiated by tert‐butyl chloride using ethylaluminum dichloride·bis(2‐chloroethyl) ether complex (T. Rajasekhar, J. Emert, R. Faust, Polym. Chem. 2017, 8, 2852) was drastically slowed down in the presence of impurities, such as propionic acid, acetone, methanol, and acetonitrile. The effect of impurities on the polymerization rate was neutralized by using two different approaches. First, addition of a small amount of iron trichloride (FeCl3) scavenged the impurity and formed an insoluble ·impurity complex in hexanes. The polymerization rate and exo‐olefin content were virtually identical to that obtained in the absence of impurities. Heterogeneous phase scavenger (FeCl3) exhibited better performance than homogenous phase scavengers. In the second approach, conducting the polymerization in wet hexanes, the fast polymerization of IB was retained in the presence of impurities with a slight decrease in exo‐olefin content. 1H NMR studies suggest that nucleophilic impurities are protonated in the presence of water, and thereby neutralized. Mechanistic studies suggest that the rate constant of activation (ka), rate constant of propagation (kp), and rate constant of β‐proton elimination (ktr) are not affected by the presence of impurities. To account for the retardation of polymerization in the presence of impurities, delay of proton transfer to monomer in the chain transfer step is proposed. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3697–3704

Stainless steel reactors are unsuitable for polymerizations catalyzed by EtAlCl2 due to a side reaction between Cr2O3 in stainless steel and EtAlCl2.

The kinetics and mechanism of the polymerization of isobutylene (TB) initiated by tert-butyl chloride and catalyzed by ethylaluminum dichloride (EADC)center dot bis(2-chlorethyl) ether (CEE) complex was studied in hexanes at 0 degrees C. The polymerization is first order in [TB] and in dry hexanes the slopes of the first order plots are independent of the [CEE]/[EADC] ratio in the range 1-1.5. From the slopes the steady state concentration of propagating cations [M-n(+)] = 1.8 x 10(-11) M was calculated, which suggests an equilibrium between dormant and active species. The olefin distribution is independent of TB concentration and conversion. At low conversion, the number average molecular weight (MO is proportional to the starting TB concentration. In hexanes saturated with water, the polymerization rate is 5 times higher at [CEE]/[EADC] = 1 compared to that in dry hexanes. However, at [CEE]/[EADC] = 1.5, the rates in dry or wet hexanes are identical. To account for the low concentration of active centers determined from the first order plots, an equilibrium between oxonium (dormant) and carbenium (active) ions is proposed. The existence of oxonium ions was confirmed by H-1 NMR studies and by polymerizations initiated from preformed oxonium ions. While identical rates and olefin distributions were obtained using EADC solutions in hexanes or toluene to form the EADC.CEE complex at short reaction times, at long reaction times, the exo-olefin content decreased when EADC solution in toluene was used. This was attributed to a slow tert-butylation of toluene yielding 95% para isomer and the concomitant formation of AlCl3.

In this study, the kinetics and mechanism of the polymerization of isobutylene catalyzed by FeCl3·ether complexes in hexane at 0 °C were investigated.

The polymerization of isobutylene (IB) to yield highly reactive polyisobutylene (HR PIB) with high exo-olefin content using GaCl3 or FeCl3 center dot 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 tertbutyl 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 degrees C polymerization was complete in S min at [t-BuCl] = [EADC.CEE] = 10 mM and resulted in PM with similar to 70% exo-olefin content. Studies on complexation using ATR FTIR and H-1 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 beta-proton abstraction. Density functional theory (DFT) studies on the Lewis acid center dot ether binding energies indicated a trend consistent with the polymerization results. The polymerization mechanism proposed previously for Lewis acid center dot ether complexes(1) adequately explains all the findings.

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.

The polymerization of isobutylene (IB) in hexanes at 0 degrees C initiated by tert-butylchloride (t-BuCl) and coinitiated by GaCl3 or FeCl3 center dot 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 center dot ether complex on the polymerization. Investigation of the properties of the FeCl3 center dot ether complexes possessing unique steric and electronic properties via attenuated total reflectance (ATR) 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. (C) 2013 Elsevier Ltd. All rights reserved.

The carbocationic polymerization of isobutylene (TB), co-initiated by AlCl3/ether complexes, has been reexamined and extended to different diallcyl ethers. In the absence of a proton trap, 2,6-di-tert-butylpyridine (DTBP), the polymerization of IB by the cumyl alcohol (CumOH)/AlCl3 center dot nBu(2)O initiator/co-initiator system in dichloromethane/hexanes (80/20 v/v) at -40 degrees C gave high conversion to polyisobutylene (PIB) comprising exo-olefins with high selectivity, similar to that reported before by Vasilenko et al.(1,2) However, in the presence of DTBP, polymerization was absent, suggesting that CumOH is not an initiator in conjunction with AlCl3 center dot Bu2O, and the true initiator is adventitious water. Similarly, in the presence of DTBP in exanes at 0 degrees C, polymerizations were absent not only with CumOH but with CumCl, tert-butanol, and 2-chloro-2,4,4-trimethylpentane. The polymerization of LB could be initiated only with adventitious water in the absence of DTBP, but monomer conversions and exo-olefin content (60-70%) were much lower than in a polar solvent and the PIBs exhibited M-n = 700-4200 with high polydispersities (PDI similar to 3-5). The separate addition of ether followed by AlCl3 to the polymerization mixture resulted in conventional PIE with high trisubstituted olefinic content. The previously proposed mechanism is inadequate, as it cannot explain all the observations. Mechanistic studies suggest that the reaction of water with AlCl3 center dot R2O yields H+AlCl3OH-, which initiates the polymerization, and free ether, which abstracts a beta-proton from the growing chain end before it diffuses from the immediate vicinity of the polymer cation. Accordingly, the role of the complex is to deliver the ether to close proximity of the propagating end.

The carbocationic polymerization of isobutylene (IB), co-initiated by 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 c...

The complex mechanism of the carbocationic rearrangements leading to a variety of olefin (exo-, endo-, tri-, and tetra-substituted) end groups in the cationic polymerization of isobutylene (IB) catalyzed by ethylaluminum dichloride (EtAlCl2) in nonpolar solvents in the temperature range of -40 to 25 degrees C was studied by model ionization experiments employing poly(isobutylene chloride) (PIB-Cl) of low molecular weight (M-n similar to 1000-2000) obtained by living cationic polymerization. Ionizations were performed with EtAlCl2 in hydrocarbon media to mimic a conventional cationic polymerization of IB, but in the presence of a proton trap to suppress reprotonation of the first formed olefin and subsequent decomposition of the resulting PIB cation. In the absence of a proton trap, ionization of PIB-Cl resulted in about 70% of tri-substituted olefin end groups in the studied temperature range. The exo and endo olefin end-group content was negligible. MALDI and APPI TOP MS indicated that the tri-substituted PIB olefins contained irregular carbon numbers, suggesting chain scission. Ionizations carried out in the presence of the proton trap 2,6-di-tert-butylpyridine (DTBP) at 0 and -40 degrees C also gave mainly the tri-substituted olefin; however, at 25 degrees C only exo-, endo-, and tetra-substituted olefins were formed with regular carbon numbers. Ionization of PIBd8(IB)(n)-Cl with n = 1-6 showed that on average 4 IB units are cleaved at -40 degrees C, which suggests that the tri-substituted olefins are formed by backbiting via hydride transfer followed by chain scission. A mechanism is proposed to account for the olefin structures involving a sterically hindered cation arising via hydride and methyde shifts, which either eliminates a proton to yield the tetra-substituted olefin or undergoes a distant hydride shift by backbiting followed by a methyde shift and chain scission to yield the tri-substituted olefin of irregular carbon number.