Oligomerization of olefins in a chloroaluminate ionic liquid

Linear 1-olefins are oligomerized to dimers, trimers and tetramers by the Lewis acidic (excess of 0.1 mol equivalent AlCl3) ionic liquid [1-butyl-3-methylimidazolium][tetrachloroaluminate], even in the presence of ethylaluminiumdichloride. Addition of titaniumtetrachloride, however, generates branched, atactic polymers with narrow monomodal polydispersities as waxy or oily compounds in high yields. Molar masses vary from M-w = 650 to 1620 g/mol (M-n = 440-970 g/mol) independent of the monomer used. Predominantly 1,1,2-trisubstituted double bonds are formed by a migration mechanism in the termination step of the oligomerization process. In contrast, polymerization of ethene by titaniumtetrachloride in the conventional solvent toluene, affords mainly linear polyethene with a broader polydispersity and a higher molar mass. (C) 2002 Elsevier Science B.V. All rights reserved.