Efficient Slurry-Phase Homopolymerization of Ethylene to Branched Polyethylenes Using α-Diimine Nickel(II) Catalysts Covalently Linked to Silica Supports

α-Diimine nickel(II) complexes covalently linked to a silica support were obtained by the reaction of an amino- or hydroxy-functionalized α-diimine nickel complex with silica particles treated with trimethyl aluminum. These silica-supported aryl α-diimine nickel(II) precatalysts linked via an amino ( 1a ) or hydroxy functionality ( 1b − c ) at the p -aryl position, and precatalysts linked via one ( 2a ) or two ( 2b ) hydroxy functionalities in the alkyl backbone were used in slurry polymerizations of ethylene to produce branched polyethylenes. Activation of precatalysts with ethylaluminum sesquichloride was effective even at very low Al/Ni ratios of 48. Initial polymerizations, performed at 60 °C and 150 psig ethylene, showed excellent productivities of up to 10.8 kg PE per gram of 1b (3.0 wt % nickel loading). Low productivities at temperatures above 60 °C can in part be overcome by increase in ethylene pressure. For example, a productivity of 6.0 kg PE per gram of 1b (3.0 wt % nickel loading) was obtained at 80 °C and 700 psig ethylene. The best polymerization productivities were obtained with trimethylaluminum as a traceless silica-linker, however, tetrachlorosilane and trichloroborane are attractive alternatives. Branching densities can be controlled by choice of ortho -aryl substituents. No reactor fouling occurs with these supported catalysts.