Influence of ziegler-natta catalyst regioselectivity on polypropylene molecular weight distribution and rheological and crystallization behavior

John C. Chadwick, Frank P.T.J. Van Der Burgt, Sanjay Rastogi, Vincenzo Busico, Roberta Cipullo, Giovanni Talarico, Johannes J.R. Heere

Research output: Contribution to journalArticlepeer-review

74 Scopus citations

Abstract

Fundamental implications of occasional secondary (2,1-) insertions in propene polymerization with different MgCl2-supported Ziegler-Nȧtta catalysts are discussed, with reference to the properties of the polymers obtained. The relatively narrow molecular weight distribution of polypropylene prepared using catalysts of type MgCl2/TiCl 4/diether-AlR3 is ascribed to the fact that the active species in this system are relatively uniform, in the sense that significant 2,1-insertion takes place at both highly isospecific and weakly isospecific active species. In contrast, the isospecific species in the catalyst system MgCl2/TiCl4/diisobutyl phthalate-AlEt3- alkoxysilane undergo less 2,1-insertion and are therefore less responsive to chain transfer with hydrogen. The presence of (some) highly regiospecific active sites in such catalysts will therefore lead to the formation of a high molecular weight polymer fraction and, overall, a broad molecular weight distribution. The presence of high molecular weight chains leads to relatively slow molecular relaxation and a more rapid onset of crystallization of the polymer from the melt, as evidenced by rheological studies of polypropylenes prepared using different catalysts and having different molecular weight distributions.
Original languageEnglish (US)
Pages (from-to)9722-9727
Number of pages6
JournalMacromolecules
Volume37
Issue number26
DOIs
StatePublished - Dec 28 2004
Externally publishedYes

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