New results in the isotactic polymerization of propene promoted by homogeneous metallocene catalysts

In this presentation, some mechanistic aspects of isotactic propene polymn. in the presence of homogeneous Group IV metallocene catalysts are analyzed in the light of new (and still largely unpublished) exptl. results. In particular, the regiospecificity of catalyst systems based on two typical C2-sym. ansazirconocenes [i.e. rac-ethylenebis(1-indenyl)ZrCl2 and rac-dimethylsilylbis(1-indenyl)ZrCl2; cocatalyst, Me aluminoxane] is discussed comparatively. An influence of propene concn. on the ratio between 2,1 and 1,3 monomer enchainments and - surprisingly - on the stereoregularity of the produced polymers is pointed out. Tentative kinetic explanations of the obsd. polymn. behaviors are also proposed.