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Polymers 2017, 9(11), 581;

Propene Polymerization with C1-Symmetric Fluorenyl-Metallocene Catalysts

CNR Istituto per lo Studio delle Macromolecole (ISMAC), Via E. Bassini, 15-20133 Milano, Italy
Total Petrochemicals Research, Zone Industrielle C, B-7181 Feluy, Belgium
Author to whom correspondence should be addressed.
Received: 11 October 2017 / Revised: 30 October 2017 / Accepted: 31 October 2017 / Published: 6 November 2017
(This article belongs to the Special Issue Olefin Polymerization and Polyolefin)
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Propene homopolymers have been produced by employing three C1-symmetric metallocene molecules (1, 2 and 3), each having t-butyl substituent(s) on the Cp, on the fluorenyl or on both aromatic moieties activated with methylaluminoxane at different polymerization temperatures and monomer concentrations. Polymers’ microstructures determined by 13C NMR spectroscopy suggest that the otherwise dominant alternating mechanism governed by the chain migratory insertion is largely replaced by the competing site epimerization mechanism, as a direct result of the imposing steric bulk of the t-butyl substituent on one of the distal positions of the Cp moiety. This phenomenon is more pronounced with 3 when a second t-butyl is present in the same half-space of the molecule making the site epimerization mandatory. The lower activity of catalyst 3 with respect to catalyst 2 is also in line with the necessity for the polymer chain to back-skip (or the site to epimerize) to its original position before the subsequent monomer insertion. Chain end group analyses by 1H NMR spectroscopy have revealed that the formation of vinylidene end groups, either via β-H elimination or as a result of direct chain transfer to the monomer after an ordinary 1,2-insertion is the prevailing chain termination route. A correlation between the relative concentrations of vinylidene end groups of polypropene (PP) polymers produced with each catalyst and the corresponding polypropenes’ molar masses was found, indicating the lower the relative concentrations of vinylidene end groups, the higher the molar masses. View Full-Text
Keywords: propene; metallocene catalysts; microstructure propene; metallocene catalysts; microstructure

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Boggioni, L.; Cornelio, M.; Losio, S.; Razavi, A.; Tritto, I. Propene Polymerization with C1-Symmetric Fluorenyl-Metallocene Catalysts. Polymers 2017, 9, 581.

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