Sterically and Electronically Modified Aryliminopyridyl-Nickel Bromide Precatalysts for an Access to Branched Polyethylene with Vinyl/Vinylene End Groups

Muhammad Zada; Arumugam Vignesh; Liwei Guo; Randi Zhang; Wenjuan Zhang; Yanping Ma; Yang Sun; Wen-Hua Sun

doi:10.1021/acsomega.0c01208

Sterically and Electronically Modified Aryliminopyridyl-Nickel Bromide Precatalysts for an Access to Branched Polyethylene with Vinyl/Vinylene End Groups

ACS Omega. 2020 Apr 27;5(18):10610-10625. doi: 10.1021/acsomega.0c01208. eCollection 2020 May 12.

Authors

Muhammad Zada^{1

2}, Arumugam Vignesh¹, Liwei Guo^{1

3}, Randi Zhang^{1

2}, Wenjuan Zhang³, Yanping Ma¹, Yang Sun¹, Wen-Hua Sun^{1

2

4}

Affiliations

¹ Key Laboratory of Engineering Plastics and Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China.
² CAS Research/Education Center for Excellence in Molecular Sciences, University of Chinese Academy of Sciences, Beijing 100049, China.
³ Beijing Key Laboratory of Clothing Materials R&D and Assessment, Beijing Engineering Research Center of Textile Nanofiber, School of Materials Science and Engineering, Beijing Institute of Fashion Technology, Beijing 100029, China.
⁴ Key Laboratory of High-Performance Synthetic Rubber and Its Composite Materials, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China.

Abstract

A series of 2-((arylimino)ethyl)pyridine derivatives (L1-L5), each containing N-2,4-bis(dibenzocycloheptyl) groups with variations in the steric/electronic properties of the ortho-substituent in the aryl ring, and the corresponding nickel bromide precatalysts [2-N{2,4-(C₁₅H₁₃)-6-R-C₆H₂}C₇H₇N]NiBr₂ (R = Me (Ni1), Et (Ni2), ^i-Pr (Ni3), Cl (Ni4), or F (Ni5)), have been prepared in high yield. All the precatalysts are air-stable and characterized by Fourier transform infrared spectroscopy and elemental analysis. The molecular structures of Ni2 and Ni5 were proved through single-crystal X-ray diffraction analysis. The steric/electronic impact of the catalysts on ethylene polymerization and the resulting polymer properties were studied. Upon activation with either MAO or EASC, all the complexes displayed higher activities (up to 7.93 × 10⁶ g of PE (mol of Ni)^-1 h^-1 with MAO) in ethylene polymerization and produced moderate to highly branched unsaturated polyethylene with a molecular weight of up to 16.55 kg/mol with narrow dispersities (1.6-2.4). Significantly, the generated polyethylenes are branched and unsaturated with a major class of internal double bond (-CH=CH-) as compared to the terminal double bond (-CH=CH₂) (vinylene/vinyl = 9.8:1 to 1.8:1). Notably, their catalytic activities, types of unsaturation, and branches are highly affected by the nature of the ortho-substituent and reaction temperature. Moreover, the precatalysts Ni4 and Ni5 (with N-ortho = Cl and F) exhibited lower catalytic activities, produced low-molecular-weight polyethylene with a high melt temperature and the least number of branches with an increased level of terminal double bonds.