1. Designing of imine thiophene-ligated metal-complexes and implication in ethylene polymerization.
- Author
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Shaikh, Maulali H, Ramekar, Rohan V, Jawoor, Shailaja, Dash, Soumya R, Birajadar, Rajkumar S, Pawal, Sandip B, Thenmani, Nandakumar, Vanka, Kumar, and Chikkali, Samir H
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HIGH density polyethylene , *MOLECULAR weights , *LIGANDS (Chemistry) , *TRANSITION metals , *POLYETHYLENE - Abstract
Polyethylene is the single largest volume polymer produced globally using Ziegler-type catalysts. Numerous modifications have been reported in search of a better catalyst that can control molecular weight, polydispersity, and branching. In our attempts to identify a suitable imine thiophene-ligated chromium complex, we examined 9 different titanium complexes computationally. The DFT investigations considered barriers for insertion, propagation, and termination by β-H elimination or chain transfer, and identified N-(4-methoxyphenyl)-2-phenyl-1-(thiophen-2-yl)ethan-1-imine(L9) as the most suitable ligand. Subsequently, L9 was prepared in good yield (70%) by condensing 2-phenyl-1-(thiophen-2-yl)ethan-1-one with 4-methoxyaniline. Ligand L9 was treated with early transition metal precursors (Ti, Cr, Zr) to generate a homogenous catalyst. The identity of these catalysts was unambiguously ascertained using a combination of NMR, ICP, FT-IR, UV-Vis spectroscopy, and ESI-MS. The performance of L9-ligated titanium complex [Cat.1] was examined in ethylene polymerization using MMAO as a co-catalyst. Insertion of ethylene was tracked using high-pressure NMR experiments and Cat.1 was found to be active in the polymerization. Ethylene polymerization conditions were optimized to obtain high activity and molecular weight polyethylene. The chromium complex [Cat.2] outperformed the Ti and Zr-derived catalysts with the highest TOF of 6294 mol of PE/mol of Cr/h. Cat.2 produced high molecular weight, high-density polyethylene. SYNOPSIS TOC: Rational designing and synthesis of imine thiophene-ligated Ti, Cr, and Zr-complexes and their performance in ethylene polymerization is presented. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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