Effect Of The End-group Structures Of Dendritic Metal Complexes On Olefins Polymerization

Two new types of dendritic nickel complexes were synthetized from 1.0-generation poly(amidoamine) dendrimers, salicylaldehyde compounds(3,5-diclorosalicylaldehyde and 3-methylsalicylaldehyde) and nickel choride hexahydrate via Schiff base condensation and coordination reaction. The structures of dendritic 3,5-diclorosalicylaldehyde ligand, dendritic 3,5-diclorosalicylaldehyde nickel complex and dendritic 3-methylsalicylaldehyde nickel complexe were characterized by FT-IR, UV, 1H-NMR and ESI-MS. Furthermore, not only investigated the catalytic properties of these two dendritic catalysts in the ethylene oligomerization and ethylene/1-hexene copolymerization, we also explored the impact of the end-groups on catalytic properties.Two dendritic nickel complexes were evaluated as precursors in ethylene oligomerization, using methylaluminoxane as cocatalyst. The impact of the aromatic ring substituents of dendritic metal complexes on the ethylene oligomerization properties was explored by comparing the two dendritic nickel catalysts to previous dendritic butylsalicylaldehyde nickel catalyst. The results showed that, the maximum catalytic activity of dendritic 3,5-diclorosalicylaldehyde nickel complex could be 2.16×105 g ·(mol Ni · h)-1 and the maximum catalytic activity of dendritic 3-methylsalicylaldehyde nickel complex could be 2.50×105 g ·(mol Ni · h)-1. The end-group structures of dendritic metal complexes had important influence on catalytic properties. The catalyst which has the largest steric hindrance had the maximum catalytic activity and the highest selectivity for higher olefins.Dendritic 3,5-diclorosalicylaldehyde nickel complex, dendritic 3-methylsalicylaldehyde nickel complex and dendritic salicylaldehyde nickel complex were evaluated as precursors in ethylene/1-hexene copolymerization, using MAO as cocatalyst. The data showed that the selectivity for higher olefins(≥C10) was higher when 1-hexene was added to catalytic system. The selectivity for higher olefins of dendritic salicylaldehyde nickel complex could be increased from 51.95% to 59.43% at 25℃, 0.5MPa, 30 min and Al/Ni ratio of 500. At the same condition, the selectivity for higher olefins could be increased from 30.13% to 46.74% with 3,5-diclorosalicylaldehyde nickel complex as precatalyst while the value could be increased from 14.34% to 33.97% using dendritic 3-methylsalicylaldehyde nickel complex.