Palladium catalysts metallocene polymers

Nickel-0- and palladium-O-complexes are very active catalysts for the polymerization of norbornene and also for cyclopentene [552-554], Nickel catalysts produce soluble polymers with a molecular weight of over one million while polymers obtained with palladium or metallocene complexes are insoluble. The soluble polymers have an atactic structure. The microstructure of the polynorbornene depends on the catalyst used and is isotactic by synthesis with chiral metallocenes. 

In contrast to what has been shown for metallocene catalysts, for most nickel and palladium catalysts there is no influence of the ligand stmcture on the polymer microstmcture... 

Brookhart et al. [57,58] described square planar nickel and palladium-diimine systems which are capable of polymerizing ethene to high molecular weight polymers with activities comparable to the metallocene catalyst systems when activated with methyl-aluminoxane. 

BF Goodrich s patents US 5,569,730 (29 Oct 1996) and US 5,571,881 (5 Nov 1996) further erode the mystique of metallocene catalysts in making specially polyolefins, specifically for norbornene-functional monomers. Unique catalyst systems that catalyze the insertion of chain-transfer agents exclusively at a terminal end of a polymer chain are used to produce addition polymers from norbornene-functional monomers. These catalyst systems, in common with DuPont s, are based on nickel or palladium. There are two noteworthy factors firstly, the nickel or palladium can be present as simple compounds such as the bromides, oxides, acetylacetonates, or 2-ethylhexanoates secondly, and perhaps more surprisingly, these catalysts are activated by the same activators as are the metallocenes. 

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