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Comparative Study on Kinetics of Ethylene and Propylene Polymerizations with Supported Ziegler–Natta Catalyst: Catalyst Fragmentation Promoted by Polymer Crystalline Lamellae

MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou 310027, China
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Polymers 2019, 11(2), 358; https://doi.org/10.3390/polym11020358
Received: 12 January 2019 / Revised: 1 February 2019 / Accepted: 6 February 2019 / Published: 19 February 2019
(This article belongs to the Special Issue Catalytic Polymerization)
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Abstract

The kinetic behaviors of ethylene and propylene polymerizations with the same MgCl2-supported Ziegler–Natta (Z–N) catalyst containing an internal electron donor were compared. Changes of polymerization activity and active center concentration ([C*]) with time in the first 10 min were determined. Activity of ethylene polymerization was only 25% of that of propylene, and the polymerization rate (Rp) quickly decayed with time (tp) in the former system, in contrast to stable Rp in the latter. The ethylene system showed a very low [C*]/[Ti] ratio (<0.6%), in contrast to a much higher [C*]/[Ti] ratio (1.5%–4.9%) in propylene polymerization. The two systems showed noticeably different morphologies of the nascent polymer/catalyst particles, with the PP/catalyst particles being more compact and homogeneous than the PE/catalyst particles. The different kinetic behaviors of the two systems were explained by faster and more sufficient catalyst fragmentation in propylene polymerization than the ethylene system. The smaller lamellar thickness (<20 nm) in nascent polypropylene compared with the size of nanopores (15–25 nm) in the catalyst was considered the key factor for efficient catalyst fragmentation in propylene polymerization, as the PP lamellae may grow inside the nanopores and break up the catalyst particles. View Full-Text
Keywords: ethylene; propylene; Ziegler–Natta catalyst; kinetics; morphology; catalyst fragmentation ethylene; propylene; Ziegler–Natta catalyst; kinetics; morphology; catalyst fragmentation
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Zhang, Z.; Jiang, B.; He, F.; Fu, Z.; Xu, J.; Fan, Z. Comparative Study on Kinetics of Ethylene and Propylene Polymerizations with Supported Ziegler–Natta Catalyst: Catalyst Fragmentation Promoted by Polymer Crystalline Lamellae. Polymers 2019, 11, 358.

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