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Propene Polymerization with C(1)-Symmetric Fluorenyl-Metallocene Catalysts

Propene homopolymers have been produced by employing three C(1)-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 concentratio...

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Autores principales: Boggioni, Laura, Cornelio, Massimiliano, Losio, Simona, Razavi, Abbas, Tritto, Incoronata
Formato: Online Artículo Texto
Lenguaje:English
Publicado: MDPI 2017
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6418994/
https://www.ncbi.nlm.nih.gov/pubmed/30965886
http://dx.doi.org/10.3390/polym9110581
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author Boggioni, Laura
Cornelio, Massimiliano
Losio, Simona
Razavi, Abbas
Tritto, Incoronata
author_facet Boggioni, Laura
Cornelio, Massimiliano
Losio, Simona
Razavi, Abbas
Tritto, Incoronata
author_sort Boggioni, Laura
collection PubMed
description Propene homopolymers have been produced by employing three C(1)-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 (13)C 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 (1)H 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.
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spelling pubmed-64189942019-04-02 Propene Polymerization with C(1)-Symmetric Fluorenyl-Metallocene Catalysts Boggioni, Laura Cornelio, Massimiliano Losio, Simona Razavi, Abbas Tritto, Incoronata Polymers (Basel) Article Propene homopolymers have been produced by employing three C(1)-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 (13)C 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 (1)H 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. MDPI 2017-11-06 /pmc/articles/PMC6418994/ /pubmed/30965886 http://dx.doi.org/10.3390/polym9110581 Text en © 2017 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
spellingShingle Article
Boggioni, Laura
Cornelio, Massimiliano
Losio, Simona
Razavi, Abbas
Tritto, Incoronata
Propene Polymerization with C(1)-Symmetric Fluorenyl-Metallocene Catalysts
title Propene Polymerization with C(1)-Symmetric Fluorenyl-Metallocene Catalysts
title_full Propene Polymerization with C(1)-Symmetric Fluorenyl-Metallocene Catalysts
title_fullStr Propene Polymerization with C(1)-Symmetric Fluorenyl-Metallocene Catalysts
title_full_unstemmed Propene Polymerization with C(1)-Symmetric Fluorenyl-Metallocene Catalysts
title_short Propene Polymerization with C(1)-Symmetric Fluorenyl-Metallocene Catalysts
title_sort propene polymerization with c(1)-symmetric fluorenyl-metallocene catalysts
topic Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6418994/
https://www.ncbi.nlm.nih.gov/pubmed/30965886
http://dx.doi.org/10.3390/polym9110581
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