POSSIBLE MODEL FOR CHAIN END CONTROL OF STEREOREGULARITY IN THE ISOSPECIFIC HOMOGENEOUS ZIEGLER-NATTA POLYMERIZATION

A conformational study of a possible model for chain end control in the homogeneous isotactic specific Ziegler-Natta polymerization is presented. The model site consists of a complex with two ligands (olefin and growing chain) besides two cyclopentadienyl ligands. The geometries corresponding to the located energy minima are very similar to those of the chiral model previously proposed by us for the site control in the homogeneous isospecific Ziegler-Natta polymerization. In this case the diastereoisomeric intermediates for isotactic and syndiotactic propagation are energetically similar but, according to our assumptions, the insertion path for the propene would be easier in the case of isotactic propagation. © 1990.