alpha-Diimine nickel(II) complexes covalently linked to a silica support were obtained by the reaction of an amino- or hydroxy-functionalized alpha-diimine nickel complex with silica particles treated with trimethyl aluminum. These silica-supported aryl R-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 degrees 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 degrees 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 degrees 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.