Highly Active Ethene Polymerization Catalysts with Unusual Imine Ligands - Late Transition Metal Polymerization Catalysis - page 88

Tab. 3.7 Ethene polymerization with iron diimine pyridine/MAO 66 - 69

Catalyst
(imine sub)

T pol [ C] Time

[min]

Activity tons
polymer
[mol h -1 bar -1 ]

M n
[g mol -1 ]

PDI T m

[ C]

H m
[Jg -1 ]

Cl,Cl 66 50-55 15 140 2800 3.0 130 245

Me,Me 68 50-60 15 110 3400 7.8

Br,Br 67 50 15 6 125 260

iPr,iPr 69 50 20 18

Polymerization in toluene, 2 bar ethene pressure, MAO co-catalyst, ratio Al/Fe=23100. PDI: polydis-
persity index M w / M n .

thus give in every aspect a more active catalyst. However, it does not mean a ma-
jor improvement with respect to a technical process.
The effects of introducing halogens in the 2 and 6 position of phenyl imine cat-
alysts was also studied in diimine pyridine iron dichloride/MAO systems [13].
These catalysts afford linear products with a low olefin content, generally less
than one (olefin) functionality per chain. The latter is due to a fast transfer of
iron bound alkyl groups to the aluminum compounds that are present in excess.
After hydrolysis, alkanes are obtained. When a high ratio of aluminum alkyl to
iron catalyst is used, polyethene waxes are obtained due to the statistically favored
alkyl group exchange between the metal species.
In Tab. 3.7 the results of polymerizing ethene with various bis(2,6-substituted
phenyl imine) derivatives of 2,6-diacetylpyridine are reported.
Polymerization was carried out at a pressure of 2 bar ethene in a 1 L autoclave.
The most active derivative with an activity of over 100 tons of polyethene wax per
mol iron catalyst carries chloro substituents (Fig. 3.11). In fact this catalyst is so
active that the temperature of the solution polymerization reaction could no
longer be controlled, even when using extremely small amounts of catalyst. The
activity is again higher than the sterically related methyl-substituted system. Also
the polydispersity of the product is smaller, probably due to a more dynamic ex-
change between aluminum and iron ( vide infra ).
In contrast, the bromo derivative readily deactivates under polymerization condi-
tions and has therefore a relatively low (but in absolute number still a very high)
activity. The polymers obtained with the catalyst with the halogen containing li-
gands differ somewhat in crystallinity and/or melting temperature. This is prob-
ably due to shorter polymer chains in the case of the bromo derivative. Analysis
by 13 C NMR spectroscopy shows that the waxes are linear within the detection
limit of branching.
Several experiments were performed with the 2,6-dichlorophenyl catalyst to ob-
tain insight into the polymerization behavior as a function of the Al/Fe ratio
[13b]. Experiments were run in a glass vessel at 1 bar ethene pressure. During po-
lymerization, aliquots were removed, precipitated in methanol, and the isolated
polymer was weighted and analyzed (Tab. 3.8).