Improvement of biphasic polymerization by application of binary ionic liquid mixture

• Binary ionic liquid mixture intensifies the performance of the biphasic process.
• Problems with phase separation and mass transfer were resolved.
• Aralkyl ionic liquid can be applied in a broad range of temperatures.
• The physical properties of ionic liquids influence the polymer properties.

The mixture of two ionic liquids, 1-n-butyl-3-methylimidazolium and 1-(2-phenylethyl)-3-methylimidazolium chloroaluminates, [C4-mim][AlCl4] and [PhC2-mim][AlCl4], were applied as a medium to immobilize the Cp2TiCl2 titanocene catalyst for biphasic ionic liquid/hexane ethylene polymerization. The system makes possible to perform the reaction at lower temperatures, below the melting temperature of the aralkyl ionic liquid. A better separation of the ionic liquid phase was observed and an easier mass transfer of the polymer product from the ionic liquid to the hexane phase was obtained. The polyethylene reveals bimodal distribution of molecular weight. It is characterized by a high bulk density (500 g/dm3) and crystallinity degree (86%). The recycling of the ionic liquid medium containing the catalyst activated by AlEtCl2, results in the highest yield obtained in such systems (550 kg PE(mol Ti)−1).