Chloroaluminate ionic liquids as a medium of titanocene catalyst activated by alkyl aluminum compounds for ethylene polymerization

摘要

1-Ethyl-3-methylimidazolium tetrachloroaluminate ([EMIM]~+[AlCl4]~- and 1-n-butyl-3--methylimidazolium tetrachloroaluminate ([BMIM]~+[AlCl4]~-) ionic liquids were applied in biphasic ethylene polymerization as a medium of Cp2TiCl2 titanocene catalyst. The effects of alkylaluminum compound (MAO, AlEt3, AlEt2Cl, AlEtCl2), the activator/catalyst molar ratio, polymerization time, ethylene pressure, catalyst recycling and the volume of the ionic liquid/hexane medium on the polymerization yield were investigated. Physical properties of polyethylene (PE) obtained are presented. It was shown that AlEtCl2 is the best activator investigated so far. The [BMIM]~+[AlCl4]~- ionic liquid is a better medium for the titanocene catalyst than [EMIM]~+[AlCl4]~- one. The product obtained is characterized primarily by its high crystallity degree and shows the properties of a typical linear polyethylene. Thus, biphasic ionic liquid polymerization of ethylene can be a potential alternative to that with a metallocene catalyst immobilized on a solid carrier.