The strategy of remote bulky group substitution in modifying polyolefin catalysts has the potential to modulate catalytic behavior

a facet often overlooked in coordination insertion olefin polymerization reactions. In this study

a series of para-trityl substituted α-diimine nickel catalysts Ni1-Ni5 with different steric hindrances were synthesized and characterized. Upon activation with diethylaluminum chloride (Et2AlCl)

all Ni(II) catalysts were employed for ethylene chain-walking polymerization

and the effects of spatial steric hindrance were investigated. The research indicates that the introduction of trityl groups at the para-position can form remote rigid steric hindrance

thereby significantly enhancing the thermal stability of the nickel catalysts and exhibiting outstanding catalytic performance. The spatial steric effects of the catalysts

as well as changes in polymerization conditions

have a significant impact on ethylene polymerization activity

the molecular weight of the resulting polyethylene

branching degree

thermodynamic properties

and mechanical properties. The isopropyl-substituted Ni3-Ni5 exhibited extremely high catalytic activities of up to 1.26 × 107 g·PE·mol·Ni–1·h–1 toward ethylene polymerization

producing high molecular weight branched polyethylene

while maintaining excellent mechanical and elastic properties. Notably

even at a higher polymerization temperature of 120℃

the asymmetric structure of Ni5 still maintained high activity of up to 8.1 × 106 g·PE·mol·Ni–1·h–1.