Macromolecules, 2014, 47 (6), pp 1959–1965.
Rajeev Kumar †, Bin Zheng ‡, Kuo-Wei Huang ‡,Jack Emert §, Rudolf Faust *†
† Polymer Science Program, Department of Chemistry,University of Massachusetts Lowell, One University Avenue, Lowell, Massachusetts 01854, United States and
‡ KAUST Catalysis Center and Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal 2355-6900, Saudi Arabia and
§Infineum USA, 1900 E. Linden Avenue, Linden, New Jersey 07036,United States.
Abstract
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 {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 complexes1 adequately explains all the findings.
Copyright © 2014 American Chemical Society.