cocatalyst. The activity was on the order of one magnitude lower than for homogeneous polymerization under the same conditions (86–460 kg mol Fe
À1 h
À1 bar
À1 ).
The resulting products are bimodally distributed and show the usual dependence on
the aluminum concentration. At lower ratios of Al/Fe (to about 500), low molecular
weight products are thus progressively formed at higher ratios. Above a ratio of
Al/Fe of 1,000, the molecular weight of the high molecular weight fraction
increases as well as their relative weight. Chain transfer to aluminum thus becomes
less important, probably also as result of diffusion limitations for the aluminum
polymeryls formed in the process. The outcome of the reaction is thus very sensitive
to the course of the polymerization. A much more elaborate approach in an earlier
study, with tailoring of ligands that contain reactive entities towards silica surface
Si–OH bonds, gave high activities (up to 40 ton mol Fe
À1 h
À1 bar
À1 in the first
5 min) and bimodal distributions [71].
Zeolite SBA-15 [72], a silicate with large channels (up to 30 nm), was also used as a
support for BI
iPr2
P iron complexes [73]. The complexes were covalently anchored to
the surface by the action of butyl lithium. It is inferred that an iron–oxygen bond is
formed in the process as the molar ratio of Cl/Fe decreases from 2 to 0.29. The ironloaded zeolite could be activated for ethylene polymerization by the addition of MAO
in toluene solution. The activity of the system is at a high level of about 15% of the
homogeneous complex (range of 200 kg mol Fe
À1 h
À1 at 28
C). The molecular weight
decreases with the amount of MAO (Al/Fe ¼ 1,000–6,500), but the activity increases.
The catalyst does not deactivate after the first minutes as was observed on other
supports, and the system becomes thermally much more robust to allow excellent
activities and productivities at 75
C (390 kg PE mol Fe
À1 h
À1 at a Al/Fe ratio of 2,500).
The polyethylene is formed in bundles (Fig. 5), and is considered to be produced by
extrusion polymerization [74].
Magnesium dichloride has become a preferred support for Ziegler-type catalysts
for ethylene polymerization [75]. Several synthetic routes lead to useful magnesium
chlorides in the sense of supporting a Ziegler catalyst. Titanium chlorides for
example can be incorporated into the crystal surface of MgCl 2 . Subsequent treatment
with aluminum alkyls lead to highly productive ethylene polymerization catalysts.
BIP FeCl 2 was also screened as catalyst precursor in magnesium-supported systems.
BI
iPr2
P FeCl 2 was thus supported onto a MgCl 2 surface that was generated in situ
from butyl ethyl magnesium (BEM) in combination with ethyl aluminum
sesquichloride. Aluminum trialkyls (TEA, TIBA, DIBAL) were added to reach an
ethylene polymerization system [76]. The activity of the system reaches the level of
about 300 kg PE g Fe
À1 h
À1
. The catalyst system is more stable than the homogeneous
MAO-activated iron complex. It shows only a minor decay in activity at that level
after 60 min at temperatures as high as 60
C (at still higher temperature it does
rapidly deactivate). Concomitantly, the molecular weight decreases from M n
¼ 230–30 kg mol
À1 for polymerization temperatures of 40–80
C as a result of
both increased rate of transfer to aluminum and increased β-hydrogen elimination.
Typical support precursors like the ethanol adduct of magnesium dichloride
MgCl 2 ·xEtOH also yield good substrates for iron catalysts, i.e., after pretreating
by heating under vacuum and yielding alpha MgCl 2 types [77]. The activity of a
Iron Catalyst in the Preparation of Polyolefin Composites
353
À1 h
À1 bar
À1 ).
The resulting products are bimodally distributed and show the usual dependence on
the aluminum concentration. At lower ratios of Al/Fe (to about 500), low molecular
weight products are thus progressively formed at higher ratios. Above a ratio of
Al/Fe of 1,000, the molecular weight of the high molecular weight fraction
increases as well as their relative weight. Chain transfer to aluminum thus becomes
less important, probably also as result of diffusion limitations for the aluminum
polymeryls formed in the process. The outcome of the reaction is thus very sensitive
to the course of the polymerization. A much more elaborate approach in an earlier
study, with tailoring of ligands that contain reactive entities towards silica surface
Si–OH bonds, gave high activities (up to 40 ton mol Fe
À1 h
À1 bar
À1 in the first
5 min) and bimodal distributions [71].
Zeolite SBA-15 [72], a silicate with large channels (up to 30 nm), was also used as a
support for BI
iPr2
P iron complexes [73]. The complexes were covalently anchored to
the surface by the action of butyl lithium. It is inferred that an iron–oxygen bond is
formed in the process as the molar ratio of Cl/Fe decreases from 2 to 0.29. The ironloaded zeolite could be activated for ethylene polymerization by the addition of MAO
in toluene solution. The activity of the system is at a high level of about 15% of the
homogeneous complex (range of 200 kg mol Fe
À1 h
À1 at 28
C). The molecular weight
decreases with the amount of MAO (Al/Fe ¼ 1,000–6,500), but the activity increases.
The catalyst does not deactivate after the first minutes as was observed on other
supports, and the system becomes thermally much more robust to allow excellent
activities and productivities at 75
C (390 kg PE mol Fe
À1 h
À1 at a Al/Fe ratio of 2,500).
The polyethylene is formed in bundles (Fig. 5), and is considered to be produced by
extrusion polymerization [74].
Magnesium dichloride has become a preferred support for Ziegler-type catalysts
for ethylene polymerization [75]. Several synthetic routes lead to useful magnesium
chlorides in the sense of supporting a Ziegler catalyst. Titanium chlorides for
example can be incorporated into the crystal surface of MgCl 2 . Subsequent treatment
with aluminum alkyls lead to highly productive ethylene polymerization catalysts.
BIP FeCl 2 was also screened as catalyst precursor in magnesium-supported systems.
BI
iPr2
P FeCl 2 was thus supported onto a MgCl 2 surface that was generated in situ
from butyl ethyl magnesium (BEM) in combination with ethyl aluminum
sesquichloride. Aluminum trialkyls (TEA, TIBA, DIBAL) were added to reach an
ethylene polymerization system [76]. The activity of the system reaches the level of
about 300 kg PE g Fe
À1 h
À1
. The catalyst system is more stable than the homogeneous
MAO-activated iron complex. It shows only a minor decay in activity at that level
after 60 min at temperatures as high as 60
C (at still higher temperature it does
rapidly deactivate). Concomitantly, the molecular weight decreases from M n
¼ 230–30 kg mol
À1 for polymerization temperatures of 40–80
C as a result of
both increased rate of transfer to aluminum and increased β-hydrogen elimination.
Typical support precursors like the ethanol adduct of magnesium dichloride
MgCl 2 ·xEtOH also yield good substrates for iron catalysts, i.e., after pretreating
by heating under vacuum and yielding alpha MgCl 2 types [77]. The activity of a
Iron Catalyst in the Preparation of Polyolefin Composites
353