Propylene polymerization on a titanium-magnesium catalyst in the presence
of various organoaluminum compounds (in English)
Polimery 1998, No 4, 235
The effect of organoaluminum compounds AlEt3, Al(isoBu)3, and AlEt2H on the activity and stereospecificity of a titanium—magnesium catalyst TiCl4/MgCl2/dibutyl phthalate was investigated. The catalyst activity and the stereoregularity parameters of the isotactic polypropylene fractions that specify the maximum stereo regulating ability of isospecific sites, were shown to vary in the descending order AlEt2H > AlEt3 > Al(isoBu)3. The isotacticity indexes reflecting the distribution of sites with respect to stereospecificity vary in the reverse order. The results obtained suggest the active sites on the titanium—magnesium catalyst to be bimetallic in nature. In the presence of hydrogen, each of the three systems was activated. In this case, the decay of active sites followed the second-order kinetics. AlEt2H alone could activate the catalyst. In contrast to other cocatalysts, with AlEt2H, polymerization followed the second-order kinetics even without hydrogen. For the reactions proceeding in the presence of hydrogen and AlEt2H the activation mechanisms are the same and comprise the reactivation of "sleeping sites" owing to a chain transfer reaction.
Keywords: polymerization of propylene, titanium-magnesium catalysts, organoaluminum compound catalysts, kinetics, active center types