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

In this presentation, some mechanistic aspects of isotactic propene po lymerization in the presence of homogeneous Group IV metallocene catal ysts are analyzed in the light of new (and still largely unpublished) experimental results.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 influen ce of propene concentration on the ratio between 2,1 and 1,3 monomer e nchainments and surprisingly - on the stereoregularity of the produced polymers is pointed out. Tentative kinetic explanations of the observ ed polymerization behaviours are also proposed.