KCC-Seminar: Catalytic Chain Transfer in Carbocationic Polymerization

Mar 03 2015 12:00 AM - Mar 03 2015 01:30 AM

​Low molecular weight, terminal vinylidene (exo-olefin) functional polyisobutylene (HR PIB) is a valuable, highly reactive intermediate to PIB succinimides, which are employed as motor oil and fuel additives. In search of new catalysts for the polymerization of isobutylene (IB) to yield highly reactive PIB with high exo-olefin content, AlCl3, GaCl3 or FeCl3·ether complexes were studied. AlCl3·isopropyl ether catalyzed the polymerization only when water was used as an initiator. GaCl3 or FeCl3·branched alkyl ether complexes readily initiated the polymerization from t-butyl chloride (t-BuCl), which was explained by the increased chlorophilicity of GaCl3 or FeCl3 relative to that of AlCl3. The limitation of these systems is the low solubility of the complexes in nonpolar solvents. In an effort 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-BuCl 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 a 1:1 stoichiometry. 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 higher activation energy than b-proton abstraction. Density functional theory studies on the Lewis acid•ether binding energies indicated a trend consistent with the polymerization results.​