The distribution of configurations in (predominantly) isotactic polypropylene samples obtained with heterogeneous Ziegler-Natta catalyst systems, investigated by means of high-field 13C NMR, reveals deviations from that predicted by the simple "enantiomorphic-site" model commonly used to describe it. Such deviations suggest that the "active socket" in these systems is similar to that of the new homogeneous isotactic-selective catalysts based on C1-sym. ansa-metallocenes of the 4th column. This provides, inter alia, a common explanation for the increase of stereoselectivity with decreasing monomer concn. obsd. for both catalyst classes.
New Evidence on the Nature of the Active Sites in Heterogeneous Ziegler-Natta Catalysts for Propene Polymerization / Busico, Vincenzo; Cipullo, Roberta; Talarico, Giovanni; Segre Anna, Laura; Chadwick John, C.. - In: MACROMOLECULES. - ISSN 0024-9297. - STAMPA. - 30:(1997), pp. 4786-4790. [10.1021/ma9704673]
New Evidence on the Nature of the Active Sites in Heterogeneous Ziegler-Natta Catalysts for Propene Polymerization
BUSICO, VINCENZO;CIPULLO, ROBERTA;TALARICO, GIOVANNI;
1997
Abstract
The distribution of configurations in (predominantly) isotactic polypropylene samples obtained with heterogeneous Ziegler-Natta catalyst systems, investigated by means of high-field 13C NMR, reveals deviations from that predicted by the simple "enantiomorphic-site" model commonly used to describe it. Such deviations suggest that the "active socket" in these systems is similar to that of the new homogeneous isotactic-selective catalysts based on C1-sym. ansa-metallocenes of the 4th column. This provides, inter alia, a common explanation for the increase of stereoselectivity with decreasing monomer concn. obsd. for both catalyst classes.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
