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Thermally resilient cobalt ethylene polymerization catalysts under the joint influence of co-catalyst, gem-dimethyl substitution and ortho-cycloalkyl ring size

journal contribution
posted on 06.05.2021, 14:50 by Randi Zhang, Yongfeng Huang, Yanping Ma, Gregory A Solan, Xinquan Hu, Tongling Liang, Wen-Hua Sun
The N,N,N′-chelated 2-(1-arylimino)ethyl-8-arylimino-7,7-dimethyl-5,6- dihydroquinoline-cobalt (II) chloride complexes, Co1 (aryl = 2-(C5H9)-6-MeC6H3), Co2 (aryl = 2-(C6H11)-6-MeC6H3), Co3 (aryl = 2-(C8H15)-6-MeC6H3), Co4 (aryl = 2-(C5H9)-4,6-Me2C6H2), Co5 (aryl = 2-(C6H11)-4,6-Me2C6H2) and Co6 (aryl = 2-(C8H15)-4,6-Me2C6H3), have been isolated in reasonable yield using a simple one-pot method. The molecular structures of Co1 and Co5 emphasize not only the gem-dimethyl-substitution present in the carbocyclic-fused tridentate ligand but also the substantial steric properties exerted by the ortho-cycloalkyl groups. Complexes Co1 – Co6, on interaction with MAO, were highly active catalysts for ethylene polymerization reaching a maximum level of 9.21 × 106 g PE mol−1 (Co) h−1 at 70 °C for cyclopentyl-containing Co1 and Co4. Strictly linear polyethylenes with low molecular weights (Mw range: 9.25–38.5 kg mol−1) and narrow dispersities were generated with selectivities for vinyl-terminated polymers approaching quantitative levels. By comparison, polymerizations conducted using Co1 – Co6 with MMAO as co-catalyst proved less thermally stable and less active, with vinyl chain-end selectivity proving temperature dependent. Common to both MAO and MMAO, the most sterically hindered precatalyst Co6 incorporating an ortho-cyclooctyl group gave the highest molecular weight polymer of the series.

History

Citation

Polymer Volume 222, 22 April 2021, 123684

Author affiliation

Department of Chemistry

Version

AM (Accepted Manuscript)

Published in

Polymer

Volume

222

Pagination

123684 - 123684

Publisher

Elsevier BV

issn

0032-3861

Acceptance date

20/03/2021

Copyright date

2021

Available date

24/03/2022

Language

en