Highly Active Ethene Polymerization Catalysts with Unusual Imine Ligands - Late Transition Metal Polymerization Catalysis - page 86

Tab. 3.4 Types of branching (methyl endgroups/1000C).

Precatalyst Methyl

branches

Ethyl
branches

Butyl
branches

C 6
branches

Total methyl
branches

61a 19 71 11 80 181

Double bonds (mol%)

Precatalyst Vinyl Vinylidene Cis/trans -CH=C<

61a 1.1 0.2 4.3 0.6

catalysts yield strictly linear oligomers [3d] here a significant degree of
branching is observed. The polymer obtained is a complex mixture of differ-
ent, low molecular weight oligomers. As shown in Tab. 3.4 the amount of
double bonds, especially the internal double bonds, is remarkable. Obviously,
no single termination pathway is responsible for the formation of the poly-
mers.

From the results discussed above one might speculate on the pathways accessible
for the oligomerization and polymerization reaction of ethene. As in the initial
studies with late transition metal catalysts [8, 11], there is a delicate balance be-
tween insertion of the monomer resulting in a linear polyethene and -hydride

elimination and re-addition, resulting in branching and olefinic products. The
branched polyethene produced by catalysts 53a - 62 suggests that the latter pro-
cess, “chain-walking”, is quite important. This is in marked contrast to Broo-
khart's and Gibson's bis(imino)pyridyl Fe and Co complexes which produce highly
linear PE, [12, 13], but more like the 1,2-diimine Ni and Pd complexes which
yield mainly branched polymers [11]. We can only offer a description of this be-
havior of catalysts 53a - 62b ; it is interesting to note that in essence electronic
modification of the peripheral substituents (N-azolyl versus N-phenyl) has such a
dramatic effect on the microstructure and physical properties of the polymers.

Polymerization of Propylene The active complex 54a served as the test case for
the polymerization of propylene. Under similar experimental conditions as de-
scribed above (with propylene as monomer) 15 g of an oily polymer was obtained,
corresponding to an activity of 300 g PP/mmol Fe·h. The 13 C-NMR spectrum of
the polymer shows its atactic nature. In addition, a variety of saturated and unsa-
turated end-groups could be observed, indicating that again several termination
pathways are accessible.