Preformed Alkylaluminum-Titanium Tetrachloride Catalysts for the Polymerization of Isoprene

Catalysts prepared from TiCl4 and C1 to C8 trialkylaluminum compounds showed higher activity for cis-1,4 polymer formation with increasing chain length or branching of the alkyl group. Diisobutylaluminum hydride and triisobutylaluminum behaved similarly while diisobutylaluminum monochloride was a less efficient cocatalyst. Aging of catalysts prepared from the higher alkyls improved their stereospecificity. Separated and thoroughly washed solids (β-TiCl3) from preformed catalysts of 0.8-1.3 Al/Ti mole ratios exhibited catalytic activities which in most instances surpassed those of the corresponding unseparated catalysts. The variability in activity of catalysts examined in this study is explained in terms of the reducing power and adsorption characteristics of the various organoaluminum compounds toward TiCl3.