Acid-catalyzed Cationic Polymerization and Oligomerization

The chloroaluminate(lll) ionic Hquids - [EMIM][Cl-AlCl3], for example (where EMIM is l-ethyl-3-methylimidazolium) - are liquid over a wide range of AICI3 concentrations [24]. The quantity of AICI3 present in the ionic Hquid determines the physical and chemical properties of the liquid. When the mole fraction, X(AlCl3), is below 0.5, the liquids are referred to as basic. When X(AlCl3) is above 0.5, the Hquids are referred to as acidic, and at an X(AlCl3) of exactly 0.5 they are referred to as neutral. 

Studies on the dimerization and hydrogenation of olefins with transition metal catalysts in acidic chloroaluminate(III) ionic liquids report the formation of higher molecular weight fractions consistent with cationic initiation [17, 20, 27, 28]. These 

Attempts to bring the benefits of ionic Hquid technology, drawing on this inherent ability of the chloroaluminate(lll) ionic liquids, to catalysis of cationic polymerization reactions, as opposed to their minimization, were patented by Ambler et al. of BP Chemicals Ltd. in 1993 [29]. They used acidic [EMlM][Cl-AlCl3] (X(AlCl3) = 

Ionic liquid-catalyzed polymerization of butene is not limited to the use of pure alkene feedstocks, which can be relatively expensive. More usefully, the technology can be applied to mixtures of butenes, such as the low-value hydrocarbon feedstocks raffinate I and raffinate If. The raffinate feedstocks are principally C4 hydrocarbon mixtures rich in butenes. When these feedstocks are polymerized in the presence of acidic chloroaluminate(III) ionic liquids, polymeric/oligomeric products with 

Reaction temperature Yield Molecular weight of product 

The ionic liquid process has a number of advantages over traditional cationic polymerization processes such as the Cosden process, which employs a liquid-phase aluminium(III) chloride catalyst to polymerize butene feedstocks [30]. The separation and removal of the product from the ionic liquid phase as the reaction proceeds allows the polymer to be obtained simply and in a highly pure state. Indeed, the polymer contains so little of the ionic liquid that an aqueous wash step can be dispensed with. This separation also means that further reaction (e.g., isomerization) of the polymer s unsaturated ot-terminus is minimized. In addition to the ease of isolation of the desired product, the ionic liquid is not destroyed by any aqueous washing procedure and so can be reused in subsequent polymerization reactions, resulting in a reduction of operating costs. The ionic liquid technology does not require massive capital investment and is reported to be easily retrofitted to existing Cosden process plants. 

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Acid-catalyzed Cationic Polymerization and Oligomerization 162J... 

Polymerization of 7V-vinylcarbazole catalyzed by dimethylglyoxime complexes of different metals immobilized on PVC follows the cationic mechanism. Lewis acids immobilized in a volume of swollen polymer gel catalyze cationic polymerization and oligomerization of vinyl ethers, etc. Cationic complexes of Pd(II) bound to modified PS initiate alternative copolymerization of fluorinated olefins (C F2 +i)(CH2)mCH=CH2 with carbon monoxide [112,113]. The product thus obtained was polyspiroketal rather than polyketone. 

The oligomerization of olefins is mostly catalyzed by cationic complexes which are very soluble in ionic liquids. The Pd-catalyzed dimerization of butadiene [36] and the Ni-catalyzed oligomerization of short-chain olefins [5, 37], which is also known as the Difasol process [1 d] if chloroaluminate melts are used, can be mn in imidazolium salts 1 [38, 39]. Here, the use of chloroaluminate melts and toluene as the co-solvent is of advantage in terms of catalyst activity, product selectivity, and product separation. Cp2TiCl2 [6] and TiCU [40] in conjunction with alkylaluminum compounds were used as catalyst precursors for the polymerization of ethylene in chloroaluminate melts. Neither Cp2ZrCl2 nor Cp2HfCl2 was catalytically active under these conditions. The reverse conversion of polyethylene into mixtures of alkanes is possible in acidic chloroaluminate melts without an additional catalyst [41]. 

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