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Remote dibenzocycloheptyl substitution on a bis(arylimino)pyridyl-iron ethylene polymerization catalyst; enhanced thermal stability and unexpected effects on polymer properties

journal contribution
posted on 19.08.2021, 15:12 by Liwei Guo, Wenjuan Zhang, Furong Cao, Youshu Jiang, Randi Zhang, Yanping Ma, Gregory A Solan, Yang Sun, Wen-Hua Sun

Four examples of para-dibenzocycloheptyl-substituted 2,6-bis(arylimino)pyridyl-iron(II) chloride complexes, [2,6-{(2-R1,4-(C15H13),6-R2C6H2)N[double bond, length as m-dash]CMe}2C5H3N]FeCl2 (R1 = R2 = Me Fe1, Et Fe2, iPr Fe3, R1 = Me, R2 = Et Fe4), have been synthesized and characterized by a combination of IR spectroscopy, elemental analysis and single crystal X-ray diffraction. The molecular structures of Fe2 and Fe4 highlight not only their pseudo-square pyramidal geometries but also the variation in configuration of the two remote dibenzo-fused cycloheptyl rings. When activated with MAO or MMAO, Fe1–Fe4 displayed very high activities for ethylene polymerization by operating effectively at 70 °C/10 atm [up to 7.14 × 107 g(PE) mol−1(Fe) h−1] producing high molecular weight linear polyethylene (as high as 98.7 kg mol−1) with a single melting temperature (Tm: >129.7 °C) as well as various levels of vinyl unsaturation. Even at temperatures up to 100 °C, the polymerization activity remained high [up to 1.46 × 107 g(PE) mol−1(Fe) h−1] underlining the good thermal stability of this catalyst class. By contrast at PC2H4 = 1 atm, all polyethylenes produced using Fe1–Fe4 at run temperatures between 20–60 °C exhibited two melting point values with either MAO (Tm1 93.5–116.2 °C, Tm2 124.9–130.0 °C) or MMAO (Tm1 65.1–85.9 °C, Tm2 116.8–122.8 °C) in line with the bimodality of the lower molecular weight polymers. In particular, when MMAO was employed as a co-catalyst, the polyethylene displayed a wax-like composition and displayed a very narrow dispersity (Mw/Mn range: 1.1–1.6).

History

Citation

Polym. Chem., 2021,12, 4214-4225

Author affiliation

Department of Chemistry

Version

AM (Accepted Manuscript)

Published in

Polymer Chemistry

Volume

12

Issue

29

Pagination

4214-4225

Publisher

Royal Society of Chemistry (RSC)

issn

1759-9954

eissn

1759-9962

Acceptance date

06/07/2021

Copyright date

2021

Available date

06/07/2022

Language

English