PROPYLENE POLYMERIZATION ON A TITANIUM-MAGNESIUM CATALYST IN THE PRESENCE OF VARIOUS ORGANOALUMINUM COMPOUNDS

The effect of organoaluminum compounds AlEt(3), Al-iso-Bu(3), and AlEt (2)H on the activity and stereospecificity of a titanium-magnesium cat alyst TiC14/MgC12/dibutylphthalate is investigated. The catalyst activ ity and the stereoregularity parameters of the isotactic polypropylene fraction that specify the maximum stereoregulating ability of isospec ific sites are shown to increase in the order AlEt(2)H > AlEt(3) > Al- iso-Bu(3). The isotacticity indices reflecting the site distribution i n stereospecificity vary in the opposite direction. The results obtain ed suggest that the active sites of the titanium-magnesium catalyst ha ve a bimetallic nature. In the presence of hydrogen, all three systems are activated. In this case, the decay of active sites is described b y a second-order formal kinetic equation. In the presence of AlEt(2)H, the decay of active sites follows the second-order kinetics even with out hydrogen. It is found that AlEt(2)H itself can activate the cataly st. The activation mechanisms for the reactions proceeding in the pres ence of hydrogen and AlEt(2)H are the same and comprise the reactivati on of ''sleeping sites'' due to a chain-transfer reaction.