Positive Effect of Polar Solvents in Olefin Polymerization Catalysis

Olefin
polymerization that produces the world’s most important
plastic by scale is one of the most important chemical reactions.
Heteroatom-containing polar compounds are usually detrimental to olefin
polymerization because they are prone to deactivate catalysts. In
this contribution, we now report a desirable positive effect of polar
solvents in ethylene polymerization. Key is the finding of a sandwich-like
neutral salicylaldiminato nickel catalyst by the combination of 8-arylnaphthyl
and dibenzosuberyl groups. In comparison with toluene and xylene as
hydrocarbon solvents, tetrahydrofuran and 1,4-dioxane as polar solvents
bring about an increased polymer molecular weight, elevated turnover
frequency, narrower molecular weight distribution, and unaltered branching
density. This thus promotes ethylene polymerization in a living manner
(Mw/Mn <
1.10), enabling the generation of virtually linear ultrahigh molecular
weight polyethylene (UHMWPE, Mw = 6020
kDa) and particularly affording UHMWPE of Mw = 1002 kDa at a high temperature of 90 °C in polar solvents.