Active site selectivity of 2,3-Bis[(2,6-diisopropylphenylimino)butane] nickel/MAO/ZnEt2 system toward ethylene polymerization for modulating polyethylene microstructure

Abstract

2,3-Bis[(2,6-diisopropylphenylimino)butane] nickel/MAO system toward ethylene polymerization displays two active sites with ultraviolet absorption bands at 456 nm and 492 nm to produce branched polyethylenes, respectively. It is surprising that adding ZnEt2 results in selective catalyst active site to modulate polyethylene microstructure. 200 equiv. of ZnEt2 causes a more than 30% decrease of branching degree from 140 to 97. The UV,EPR and CV results suggest that the active site at 456 nm is easily reduced by ZnEt2. However, the active site at 492 nm still exhibits high catalytic activity, producing polyethylenes with a relatively low branching degree.