Ethylene Polymerization and Copolymerization with Polar Monomers by Cationic Phosphine Phosphonic Amide Palladium Complexes

The synthesis, characterization,
and olefin (co)­polymerization
studies of a series of palladium complexes bearing phosphine phosphonic
amide ligands were investigated. In this ligand framework, substituents
on three positions could be modulated independently, which distinguishes
this class of ligand and provides a great deal of flexibilities and
opportunities to tune the catalytic properties. The palladium complex
with an o-MeO-Ph substituent on phosphine is one
of the most active palladium catalysts in ethylene polymerization,
with 1 order of magnitude higher activity than the corresponding classic
phosphine-sulfonate palladium complex. Meanwhile, the polyethylene
generated by this new palladium complex showed ca. 6 times higher
molecular weight in comparison to that by the classic phosphine-sulfonate
palladium complex. In ethylene/methyl acrylate copolymerization, the
new palladium complex showed lower activity, generating copolymer
with similar methyl acrylate incorporation and much higher molecular
weight. The new palladium complex was also able to copolymerize ethylene
with other polar monomers, including butyl vinyl ether and allyl acetate,
making it one of the very few catalyst systems that can copolymerize
ethylene with multiple industrially relevant polar monomers.