Hafnium vs. Zirconium, the Perpetual Battle for Supremacy in Catalytic Olefin Polymerization: A Simple Matter of Electrophilicity?
The performance of C-2-symmetric ansa-hafnocene catalysts for isotactic polypropylene typically deteriorates at increasing temperature much faster than that of their zirconium analogues. Herein, we analyze in detail a set of five Hf/Zr metallocene pairs-including some of the latest generation cataly...
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Veröffentlicht in: | Polymers 2021-08, Vol.13 (16), p.2621, Article 2621 |
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Format: | Artikel |
Sprache: | eng |
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Zusammenfassung: | The performance of C-2-symmetric ansa-hafnocene catalysts for isotactic polypropylene typically deteriorates at increasing temperature much faster than that of their zirconium analogues. Herein, we analyze in detail a set of five Hf/Zr metallocene pairs-including some of the latest generation catalysts-at medium- to high-polymerization temperature. Quantitative structure-activity relationship (QSAR) models for stereoselectivity, the ratio allyl/vinyl chain ends, and 2,1/3,1 misinsertions in the polymer indicate a strong dependence of polymerization performance on electrophilicity of the catalyst, which is a function of the ligand framework and the metal center. Based on this insight, the stronger performance decline of hafnocenes is ascribed to electrophilicity-dependent stabilization effects. |
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ISSN: | 2073-4360 2073-4360 |
DOI: | 10.3390/polym13162621 |