Macromolecules, Vol.47, No.6, 1959-1965, 2014
Synthesis of Highly Reactive Polyisobutylene Catalyzed by EtAICI(2)/Bis(2-chloroethyl) Ether Soluble Complex in Hexanes
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.