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

Abstract

Chloroaluminate ionic liquids as a medium of titanocene catalyst activated by alkyl aluminum compounds for ethylene polymerization Summary-1-Ethyl-3-methylimidazolium tetrachloroaluminate ([EMIM] + [AlCl4]-) and 1-n-butyl-3-methylimidazolium tetrachloroaluminate ([BMIM] + [AlCl 4 ]-) ionic liquids were applied in biphasic ethylene polymerization as a medium of Cp 2 TiCl 2 titanocene catalyst. The effects of alkylaluminum compound (MAO, AlEt 3 , AlEt 2 Cl, AlEtCl 2), 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.

Ionic Liquids in Biphasic Ethylene Polymerisation

“…This has been shown by experiments where the ionic liquid phase contained the Cp 2 TiCl 2 catalyst and the alkylaluminium compound was washed with hexane. Catalyst leakage was not detected, which indicates that the titanocene is firmly immobilised in the ionic liquid phase and remains during the entire duration of the polymerisation (Ochędzan-Siodłak, Pawelska, 2008). During the course of the polymerisation reaction, the polyethylene is progressively transferred to the hexane phase.…”

Comparison of imidazolium and pyridinium ionic liquids as the media for biphasic ethylene polymerization in the presence of titanocene catalyst

“…In our previous studies, a series of 1-n-alkyl-3--methylimidazolium tetrachloroaluminates (where alkyl = ethyl, butyl, hexyl, or octyl) [Formula (I)] was applied as a phase in biphasic ethylene polymerization [15][16][17].…”

“…In the biphasic system applied, the bottom phase was constituted by the ionic liquid, in which the catalyst and activator were dissolved. The upper phase was hexane (150 ml) with addition of activator (2 × 10 -4 mol of Al) acting as a scavenger of impurities [15,16]. It was a place where PE produced was gathered.…”

“…The previous studies of 1-n-alkyl-3-methylimidazolium tetrachloroaluminate ionic liquids as the media for Cp 2 TiCl 2 titanocene catalyst proved that ethylene polymerization carried out in a biphasic ionic liquid/hexane mode was possible [15][16][17]. It was found that [C 8 -mim] + [AlCl 4 ]ionic liquid having the longest (octyl) alkyl substituent at the imidazolium cation gave the best performance of ethylene polymerization, i.e.…”

“…The polymerization was carried out in the conditions elaborated previously for the imidazolium ionic liquids [15]. As an activator, AlEtCl 2 was applied, which was found to be the best for the biphasic ionic liquid/hexane polymerization [16,17]. The experiments showed that PE product, in the form of white powder, was present not only in the hexane phase but also remained in the ionic liquid phase.…”