Abstract
The model previously proposed for the heterogeneous isospecific Ziegler-Natta polymerization, which agrees with a large number of experimental facts, has been examined in more detail. In particular a semiquantitative evaluation of the discriminating effects between the two faces of the co-ordinated prochiral l-propene molecule at the insertion step has been attempted. This study is presented together with a re-examination of the model at the co-ordination step, which considers in more detail the influence of the assumed values for the metal-carbon bond lengths on the stereospecificity. In agreement with previous suggestions, the analysis indicates the presence of enantioselectivity ( si olefin favoured on a Λ site independently of the configuration of the growing chain) at the insertion step also in the absence of enantioselectivity at the co-ordination step.
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