NEW RESULTS IN THE ISOTACTIC POLYMERIZATION OF PROPENE PROMOTED BY HOMOGENEOUS METALLOCENE CATALYSTS

In this presentation, some mechanistic aspects of isotactic propene polymerization in the presence of homogeneous Group IV metallocene catalysts are analyzed in the light of new (and still largely unpublished) experimental results. In particular, the regiospecificity of catalyst systems based on two typical C-2-symmetric ansa-zirconocenes (i.e. rac-ethylenebis(1-indenyl)ZrCl2 and rac-dimethylsilylbis (1-indenyl)ZrCl2; co-catalyst, methylalumoxane) is discussed comparatively. An influence of propene concentration 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 observed polymerization behaviours are also proposed.