The rate of ethylene polymerization with the BI
iPr2 P FeCl 2 /(M)MAO was
originally reported to increase linearly with the ethylene concentration
[29, 47]. This was found in other catalysts too and is consistent with the mechanism
of a rate-determining ethylene insertion into the iron–carbon bond. For example,
the average rate of polymerization over 30 min was found to be linearly dependent
on the ethylene concentration in the case with the BI
Me2 P FeCl 2 /MAO system as
catalyst (Al/Fe ¼ 400–1,400) [62]. The products had molecular weights in the
range of waxes (Table 1), with PDI substantially below 2, showing that a typical
single-site catalysis was operative. The rate in this system as well as with BI
iPr2 P
FeCl 2 also increases linearly with the MAO concentration, probably on account of
the linear increase in the number of active centers. The rate decreases with
temperature.
We have used BI
Cl2 P FeCl 2 /MAO [55] as catalyst system to address the reaction
order in the catalyst and MAO at high concentration [49, 63]. Ethylene batch
polymerizations with a ratio Al/Fe of 10,000 were evaluated on the basis of the
time-dependent pressure drop to show that the reaction order in the catalyst is close
to 1 (0.9 Æ 0.2). The reaction order in MAO was close to zero (À0.2 Æ 0.1) at a
ratio of Al/Fe over 10,000. A decrease in overall activity with higher MAO
concentrations has also been reported [50]. The overall rate of the BIP FeCl 2
(MAO)-catalyzed ethylene polymerization is thus likely to follow (3a) at “low”
MAO concentrations. The dependence is explained by the increase in the number of
active sites with increasing MAO concentration and a rate-determining ethylene
insertion into an iron–carbon bond. At high concentration of cocatalyst, where the
maximum concentration of active catalyst is reached, an inhibition may result
because of coordination of aluminum alkyls to the active site (Scheme 1). The
rate laws in (3) are thus indicative of a single catalyst species performing the
ethylene polymerization [39].
0
100
200
300
400
500
20
24
28
32
36
40
temperature [∞C]
flow rate [mL/min]
0
2 0
4 0
6 0
reaction time [min]
flow rate
temperature
Fig. 3 Typical progress
of a semibatch ethylene
polymerization with BIP
FeCl 2 /TEA catalyst mixture
Iron Catalyst in the Preparation of Polyolefin Composites
349
iPr2 P FeCl 2 /(M)MAO was
originally reported to increase linearly with the ethylene concentration
[29, 47]. This was found in other catalysts too and is consistent with the mechanism
of a rate-determining ethylene insertion into the iron–carbon bond. For example,
the average rate of polymerization over 30 min was found to be linearly dependent
on the ethylene concentration in the case with the BI
Me2 P FeCl 2 /MAO system as
catalyst (Al/Fe ¼ 400–1,400) [62]. The products had molecular weights in the
range of waxes (Table 1), with PDI substantially below 2, showing that a typical
single-site catalysis was operative. The rate in this system as well as with BI
iPr2 P
FeCl 2 also increases linearly with the MAO concentration, probably on account of
the linear increase in the number of active centers. The rate decreases with
temperature.
We have used BI
Cl2 P FeCl 2 /MAO [55] as catalyst system to address the reaction
order in the catalyst and MAO at high concentration [49, 63]. Ethylene batch
polymerizations with a ratio Al/Fe of 10,000 were evaluated on the basis of the
time-dependent pressure drop to show that the reaction order in the catalyst is close
to 1 (0.9 Æ 0.2). The reaction order in MAO was close to zero (À0.2 Æ 0.1) at a
ratio of Al/Fe over 10,000. A decrease in overall activity with higher MAO
concentrations has also been reported [50]. The overall rate of the BIP FeCl 2
(MAO)-catalyzed ethylene polymerization is thus likely to follow (3a) at “low”
MAO concentrations. The dependence is explained by the increase in the number of
active sites with increasing MAO concentration and a rate-determining ethylene
insertion into an iron–carbon bond. At high concentration of cocatalyst, where the
maximum concentration of active catalyst is reached, an inhibition may result
because of coordination of aluminum alkyls to the active site (Scheme 1). The
rate laws in (3) are thus indicative of a single catalyst species performing the
ethylene polymerization [39].
0
100
200
300
400
500
20
24
28
32
36
40
temperature [∞C]
flow rate [mL/min]
0
2 0
4 0
6 0
reaction time [min]
flow rate
temperature
Fig. 3 Typical progress
of a semibatch ethylene
polymerization with BIP
FeCl 2 /TEA catalyst mixture
Iron Catalyst in the Preparation of Polyolefin Composites
349