Synthesis of Highly Reactive Olefin Functional Polyisobutylene: A Precursor of Oil Additives and Lubricants

The carbocationic polymerization of isobutylene (IB), coinitiated 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 (AlC13• i-Pr2O) complexes reported previously, GaCl3• i-Pr2O and FeCl3•i-Pr 2O readily coinitiate 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 (i-Pr2O) complexes gave the highest polymerization rates, while non-branched 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.;Motivated by our studies on the polymerization of IB in hexanes at 0 °C initiated by t-BuCl and coinitiated by GaCl3 or FeCl3• i-Pr2O complexes and in an effort to further improve the efficiency of the catalytic system to produce highly reactive polyisobutylene (HR PIB) with increased amounts of exo-olefin, we have performed systematic studies on the effect of the nature of the ether used in the FeCl3•ether complex on the polymerization. Investigation into the complexes using several ethers possessing unique steric and electronic properties via attenuated total reflectance (ATR) FT-IR and solubility studies have revealed several interesting characteristics of FeCl 3•ether complexes that may be useful in further optimizing the present initiating system. For example, FeCl3•ether complexes with ethers possessing long alkyl chains hinders complex formation and results in decreased polymerization rates. Furthermore, the polymerization rate can be increased by incorporating electron-withdrawing groups on the ether, which affects both the complexation equilibrium and basicity of the ether. These investigations have been crucial in identifying key characteristics that should be present in the ether in order to increase reactivity while maintaining high levels of exo-olefin in HR PIB.;To synthesize PIB with high exo olefin content FeCl3• i-Pr2O as catalyst was prepared in dichloromethane (DCM). In an effort to replace DCM, an undesirable chlorinated solvent we have studied the feasibility of using non-chlorinated solvents. The 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. The 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 FeCl 3 to i-Pr2O dissolved in toluene.;To improve polymerization rates and exo olefin content, we have studied ethyl aluminum dichloride (EADC) complexes with diisopropyl ether, 2-chloroethyl ethyl ether (CEEE) and bis-(2-chloroethyl) ether (CEE) as catalysts in conjunction with t-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 olefins 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 isornerization has higher activation energy than beta-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 complexes adequately explains all the findings.