Polymer, Vol.159, 124-137, 2018
Nitro-functionalized bis(imino)pyridylferrous chlorides as thermo-stable precatalysts for linear polyethylenes with high molecular weights
Electronically and sterically enhanced Fe (II) chloride complexes (Fe1 - Fe6) bearing 2-(1-(2,6-dibenzhydryl-4-nitrophenylimino)ethyl)-6-(1-(arylimino)ethyl)pyridine (aryl = 2,6-Me2Ph L1, 2,6-Et2Ph L2, 2,6-(Pr2Ph)-Pr-i L3, 2,4,6-Me3Ph L4 and 2,6-Et-2-4-MePh L5) and 2,6-bis(1-(2,6-dibenzhydryl-4-nitrophenylimino)ethyl)pyridine (L6) ligands have been prepared. In addition to the elemental and spectroscopic analysis of all new compounds; the molecular structures of Fe1, Fe2 and Fe6 have been subject of the X-ray diffraction. The catalytic potential of all the complexes was investigated for ethylene polymerization and compared with the results of prototypal precatalyst, 2,6-bis(1-(2,6-diisopropylphenylimino)ethyl)pyridyliron chloride (Fe0). On treatment with MAO and MMAO co-catalysts, Fe6 was essentially inactive, while the iron complexes (Fe1 - Fe5) displayed exceptionally high activities as high as 2.53 x 10(7) g(PE) (mol of Fe)(-1)h(-1 )at 50 degrees C and 3.86 x 10(6) g(PE) (mol of Fe)(-1) h(-1) at 100 degrees C, and afforded high molecular weight polyethylene up to 610.6 kg/mol. By comparing with catalytic performance of the reported bis(imino)pyridine-iron precatalysts bearing non-nitro para-substituents (CH3, Cl) including Fe0, these values of activity and molecular weight are found to be the highest reported up to date. Additionally, the resultant polyethylenes are characteristically linear as being confirmed by DSC (T-m = 125.3-135.6 degrees C) and high-temperature C-13 NMR measurments.