Modification of the Acyl Chloride Quench-Labeling Method for Counting Active Sites in Catalytic Olefin Polymerization

Haoyang Yang,Wentao Zhong,Zhisheng Fu,Zhiqiang Fan,Biao Zhang

doi:10.3390/catal11060683

Haoyang Yang, Wentao Zhong + Show 3 more

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https://doi.org/10.3390/catal11060683

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Journal: Catalysts	Publication Date: May 28, 2021
Citations: 1	License type: CC BY 4.0

Affiliation: Zhejiang University, Zhejiang A & F University

Abstract

The reliable and efficient counting of active sites in catalytic olefin polymerization has been realized by using acyl chloride as the quench-labeling agent. However, the molar ratio of acyl chloride to the alkylaluminum cocatalyst must be larger than 1 in order to completely depress side reactions between the quencher and Al-polymeryl that is formed via chain transfer reaction. In this work, a tetrahydrofuran/thiophene-2-carbonyl chloride (THF/TPCC) mixture was used as the quenching agent when counting the active sites of propylene polymerization catalyzed by MgCl2/Di/TiCl4 (Di = internal electron donor)-type Ziegler–Natta catalyst activated with triethylaluminum (TEA). When the THF/TEA molar ratio was 1 and the TPCC/TEA molar ratio was smaller than 1, the [S]/[Ti] ratio of the polymer quenched with the THF/TPCC mixture was the same as that quenched with only TPCC at TPCC/TEA > 1, indicating quench-labeling of all active sites bearing a propagation chain. The replacement of a part of the TPCC with THF did not influence the precision of active site counting by the acyl chloride quench-labeling method, but it effectively reduced the amount of acyl chloride. This modification to the acyl chloride quench-labeling method significantly reduced the amount of precious acyl chloride quencher and brought the benefit of simplifying polymer purification procedures after the quenching step.

Highlights

In fundamental studies on catalytic reactions, speciation and counting of the catalytic active sites play key roles, especially when the reaction mechanism is to be disclosed through systematical analysis on the reaction kinetics [1,2,3,4,5,6]
At the end of 2 min polymerization, 2-thiophenecarbonyl chloride (TPCC) was added as a quenching agent to react with the Ti–polymeryl moieties of active sites and form polymer chains labeled with a 2-thiophenecarbonyl at chain end
To reduce the amount of TPCC, THF/TPCC mixtures of different compositions were used to quench the propylene polymerization conducted under the same conditions, wherein the THF/Al molar ratio was set at 1, 3 and 5, respectively

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. In fundamental studies on catalytic reactions, speciation and counting of the catalytic active sites play key roles, especially when the reaction mechanism is to be disclosed through systematical analysis on the reaction kinetics [1,2,3,4,5,6]. Ziegler–Natta (Z–N) catalysts that are widely used in the industry production of polyolefins, there is a long history of pursuing reliable and efficient methods of counting the number of polymerization active sites. For the presence of multiple active sites and their subtle changes in the reaction process, determining the number and variations of different active sites in

Methods

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Conclusion