STRUCTURAL ANALOGIES BETWEEN HOMOGENEOUS AND HETEROGENEOUS CATALYSTS FOR THE STEREOSPECIFIC POLYMERIZATION OF 1-ALKENES

The stereospecificity of 1-alkene polymerization in the presence of Ziegler-Natta catalysts is discussed comparatively for heterogeneous and homogeneous systems. In particular, from molecular mechanics calculations on model catalytic sites, it is proposed that nonbonded interactions at the active center play a major role in determining the catalyst stereocontrol; in all cases, the chiral orientation assumed by the first C-C bond of the growing polymer chain seems to be crucial for the onset of the enantioselectivity.