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RESEARCH PRODUCT

Ionic Liquids in Biphasic Ethylene Polymerisation

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Over the past several years there has been a considerable increase in the interest of ionic liquids as versatile reaction media for a wide variety of synthetic processes. The popularity of ionic liquids has been related primarily to their unique physical and chemical properties, which can be tailored by the judicious selection of cations and anions. These properties make it possible to use ionic liquids as solvents for many organic, inorganic, and organometallic compounds, including catalysts and co-catalysts, for various types of reactions. In particular, the polar but weakly coordinating character of ionic liquids enables them to be applied as mediums in catalysis, to immobilize various kinds of catalyst precursors which contain transition metals. Recently, ionic liquids have also been viewed as a “green” replacement to conventional organic solvents (Olivier-Bourbigou, 2002; Wasserscheid et al., 2004; Wilkes, 2004; Welton, 2004; Kubisa, 2004; Jain, 2005 ; Parvulescu et al., 2007; Chowdhury et al., 2007; Ochedzan-Siodlak, 2009). Amongst many reactions carried out in an ionic liquids environment, dimerisation and oligomerisation reactions catalyzed by nickel complexes should be noted. In the majority of cases, an improvement in the activity and selectivity of the processes as well as the limitation of undesirable side reactions were achieved. Due to the good solubility of transition metal compounds in the ionic liquid phase, and simultaneously, a poor miscibility of the produced olefins, the reaction is commonly performed in a biphasic mode. The product creates a separate phase over the ionic liquid phase containing the dissolved catalyst. Thus, it becomes possible to easily separate the product from the reaction mixture, to minimize the waste of the expensive transition metal compound, and to use the catalyst repeatedly (recycling) (Chauvin et al.,1990; 1995; 1997; Einloft et al. 1996; Simon et al., 1998; Ellis et al., 1999; Pinheiro et al., 2001; Wasserscheid et al., 2001; Bernando-Gusmao et al., 2003; Wasserscheid et al., 2004). The successful application of ionic liquids in the oligomerisation of 1-olefins inspired us to investigate the biphasic technique in polymerisation reactions using metallocene catalysts, which constitute the next generation of organometallic catalysts for olefin polymerization. Metallocenes in the past gained a considerable interest due to their high activities up to several tons of the polymer product per gram of the transition metal. Unfortunately, it was found that such high activities can only be obtained for homogenous catalyst systems dissolved in carcinogenic solvents and activated by a great excess of expensive methylaluminoxane (MAO). Furthermore, the homogenous systems reveal low stabilities