Linear/branched Block Polyethylene Produced by α-Diimine Nickel(II) Catalyst and Bis(phenoxy-imine) Zirconium Binary Catalyst System in the Presence of Diethyl Zinc

In order to promote development of linear/branched block polyethylenes based on new catalytic systems, we synthesized a novel alpha-diimine nickel(II) complex with isopropyl substituents on ortho-N-aryl and hydroxymethyl phenyl substituents on para-N-aryl structures. The activity of alpha-diimine nickel(II) catalyst was 3.02x10(6) g center dot mol(Ni)(-1)center dot h(-1) at 70 degrees C, and resultant polyethylene possessed 135/1000C branches. The linear/branched block polyethylenes were synthesized from ethylene polymerization catalyzed by the alpha-diimine nickel(II) complex/bis(phenoxyimine) zirconium in the presence of diethyl zinc. With the addition of ZnEt2 (from 0 to 400), the melting peak of resultant polyethylene changed from a single melting peak to bimodal melting peaks. The molecular weights of resultant polyethylene ranging from 26.8 kg/mol to 17.1 kg/mol and PDI values varying gradually from 24.4 to 15.2 were obtained via adjusting ZnEt2 equiv. and molar ratio of two catalysts. In addition, the branching degree of the polyethylene increased from 13/1000C to 56/1000C with the increase of the proportion of alpha-diimine nickel(II) catalyst. Using this binary catalyst system, the reaction temperature of chain shuttling polymerization can be carried out at 70 degrees C, which is more conducive to industrial application.