A method for making single-site catalysts useful for olefin polymerization is
disclosed.
A nitrogen-functional heterocycle is first deprotonated with an alkyllithium compound,
followed by reaction of this anionic ligand precursor with about 0.5 equivalents
of a Group 4 transition metal tetrahalide in a hydrocarbon solvent at a temperature
greater than about 10 C. to give an organometallic complex-containing mixture.
When combined with exceptionally low levels of an activator (e.g., methyl alumoxane),
the mixture actively polymerizes olefins to give polymers with a favorable balance
of physical properties, including low density and narrow molecular weight distribution.
