Polymerization of Isobutylene by AlCl3/Ether Complexes in Nonpolar Solvent

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• 作者：Philip Dimitrov ; Jack Emert ; Rudolf Faust
• 刊名：Macromolecules
• 出版年：2012
• 出版时间：April 24, 2012
• 年：2012
• 卷：45
• 期：8
• 页码：3318-3325
• 全文大小：316K
• 年卷期：v.45,no.8(April 24, 2012)
• ISSN：1520-5835

文摘

The carbocationic polymerization of isobutylene (IB), co-initiated by AlCl₃/ether complexes, has been reexamined and extended to different dialkyl ethers. In the absence of a proton trap, 2,6-di-tert-butylpyridine (DTBP), the polymerization of IB by the cumyl alcohol (CumOH)/AlCl₃路nBu₂O initiator/co-initiator system in dichloromethane/hexanes (80/20 v/v) at 鈭?0 掳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路Bu₂O, and the true initiator is adventitious water. Similarly, in the presence of DTBP in hexanes at 0 掳C, polymerizations were absent not only with CumOH but with CumCl, tert-butanol, and 2-chloro-2,4,4-trimethylpentane. The polymerization of IB could be initiated only with adventitious water in the absence of DTBP, but monomer conversions and exo-olefin content (60鈥?0%) were much lower than in a polar solvent and the PIBs exhibited M_n = 700鈥?200 with high polydispersities (PDI 3鈥?). The separate addition of ether followed by AlCl₃ to the polymerization mixture resulted in conventional PIB 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路R₂O yields H⁺AlCl₃OH^{鈥?/sup>, which initiates the polymerization, and free ether, which abstracts a 尾-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.}