Addition Polymerization of Norbornene-Type Monomers. High Activity Cationic Allyl Palladium Catalysts

A family of high activity catalysts for the vinyl addition polymerization of norbornene-type
monomers based on cationic η-allylpalladium complexes coordinated by phosphine ligands has been
discovered. The palladium complex [(η3-allyl)Pd(tricyclohexylphosphine)(ether)][B(3,5-(CF3)2C6H3)4] (2)
was found to copolymerize 5-butylnorbornene and 5-triethoxysilylnorbornene (95:5 molar ratio) with truly
high activity and is capable of producing more than a metric ton of copolymer per mole Pd per hour.
Multicomponent catalyst systems based on the addition of salts of weakly coordinating anions (e.g., Na[B(3,5-(CF3)2C6H3)4] or Li[B(C6F5)4]·2.5Et2O) to (η3-allyl)Pd(X)(PR3) (X = chloride, acetate, nitrate,
trifluoroacetate, and triflate) in the presence of norbornene-type monomers were developed. NMR tube
experiments confirm that Na[B(3,5-(CF3)2C6H3)4] abstracts the Cl ligand from the palladium complex
forming the cationic complex in situ. Control experiments confirmed that a high activity polymerization
system requires a palladium cation containing an allyl ligand, a neutral, two-electron-donor phosphine
ligand, and a weakly coordinating counterion. Those complexes where X contained electron-withdrawing
groups such as trifluoroacetate or triflate were found to be the most active catalyst precursors.
η3-Allylpalladium catalyst precursors with larger cone angle phosphine ligands yield lower molecular
weight polymers. The poly(norbornene) molecular weights can be further tuned by addition of α-olefin
chain transfer agents to the reaction mixture. The catalyst systems were also found to polymerize
norbornene-type monomers in aqueous media to high conversion at very low catalyst loadings. The effect
of molecular weight on thermomechanical properties was explored.