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<span style="font-family: Calibri;"><span style="font-size: medium;">Two late transition metal catalysts based on 2,6-bis(imino)pyridine iron(II) were synthesized by introducing methyl substitution (catalyst A) and <em>t</em></span><span style="font-size: medium;">-Butyl substitution (catalyst B) at the </span><em><span style="font-size: medium;">ortho</span></em><span style="font-size: medium;"> position of</span><span style="font-size: medium;"> the aryl rings of the ligand. Comparative ethylene polymerizations using the catalysts showed quiet different behaviors. The activity of catalyst A was higher than that of catalyst B in all of the polymerization conditions used. The highest activities of these catalysts were obtained at almost 25°C. Activities of the </span><span style="font-size: medium;">catalysts increased </span><span style="font-size: medium;">with increasing both monomer pressure and [Al]: [Fe] molar ratio. Multi modal peaks were appeared in the DSC analysis of oligomers obtained by catalyst A, while in the DSC analysis of the polymer obtained using catalyst B unimodal peaks were appeared. It is suggested that catalyst A containing less bulkier substitution produced polymer with different molecular weight fractions and different melting</span><span style="font-size: medium;"> points. Besides, the t-butyl group in catalyst B resulted in producing polyethylene (PE) </span><span style="font-size: medium;">with single sharp DSC peaks; the latter is due to the formation of highly linear polyethylene. Polymerization</span><span style="font-size: medium;"> temperatures affected the pattern of DSC thermograms in terms of number and shape of the peaks </span><span style="font-size: medium;">of the obtained polymers by catalyst A. Catalyst A produced linear oligomers contained liner</span><span style="font-size: medium;"> olefinic part with a number average molecular weight in the range of 260 to 361</span><span style="font-size: medium;">.</span></span>