A REINVESTIGATION OF BETA-TICL3 .2. CATALYTIC ACTIVITY IN PROPENE POLYMERIZATION

The catalytic behaviour in propene polymerization of "preformed" samples of beta(brown) TiCl3 was reinvestigated and compared with that of in situ TiCl4/AlR3 mixtures. Catalyst systems based on beta-TiCl3 produced highly regioregular polypropene samples with microstructures close to those of polymers obtained in the presence of violet TiCl3 [apart from a lower fraction of "highly isotactic" macromolecules (insoluble in boiling heptane)]. On the other hand, catalyst systems originating from the interaction of TiCl4 and an Al-trialkyl in the polymerization medium were found to contain, in addition to a heterogeneous beta-TiCl3 phase, homogeneous Ti species contributing substantially to the polymerization activity and responsible for the formation of a polymer fraction which is rather stereo- and regio-irregular and has low molecular weight.