Nickel Polymerization Catalysts with Ylide Steering Ligands - Late Transition Metal Polymerization Catalysis - page 17

with ethylene, yields oligo-/polyethylenes, each chain with a highly reactive styryl
end group and a less reactive double bond in the chain. These styrenic macro-
mers can for example be copolymerized with other monomers using radical or an-
ionic initiators to create a whole array of new polymeric materials with interesting
properties.
1.4
Cycloolefin Polymerization [16, 17]
Cycloolefins such as norbornene can be polymerized with high efficiency (e.g.
18.6 tons (mol [NiPh(Ph 2 PCHCPhO)(Pr i PCHPh)]) -1 h -1 ) when the nickel catalysts
are used in combination with aluminoxanes such as MAO. The polynorbornenes
typically obtained are high molecular weight amorphous thermoplasts with very
high T g values and decomposition temperatures as high as 450-464 C. Softening
points vary between ca. 280 and 400 C and the polymers are soluble in chloroben-
zene. The situation changes when ylide palladium catalysts are used. Owing to
different microstructures the polymers become insoluble. However, the softening
temperature drops to ca. 250 C.
1.5
Butadiene Polymerization [18]
Ylide nickel catalysts can be activated with aluminum co-catalysts such as ethylalu-
minum chloride to oligomerize butadiene to low molecular weight oils. When the
catalyst is modified with boron trifluoride it produces high molecular weight poly-
butadiene rubber. The butadiene units are linked predominantly (95-99%) in a
1,4-fashion. Only 1-5% of the butadiene molecules are incorporated in a 1,2-fash-
ion, which create daugling vinyl Substituents on the polybutadiene main chain.
The configuration at the double bonds is medium to high cis (45-85%); - i.e. 45-
85% of the doubel bonds along the chain are cis -configured the others are trans -
configured.
1.6
Polar Monomer Polymerization [19]
The high polar group tolerance of co-catalyst-free ylide nickel catalysts makes
them interesting candidates for the polymerization of polar monomers. In fact,
quite a number of polar vinyl monomers can be homo- and copolymerized quite
effectively. The mechanisms of initiation and chain propagation have not been
elucidated yet. Especially, acrylic monomers are well suited. It is thus possible to
produce, for example, poly(methyl methacrylate), poly(ethyl acrylate) and poly-
(butyl acrylate) in high yield [Eq. (15)].