Polymer-incorporated iron catalysts for ethylene polymerization - A new approach to immobilize iron olefin catalysts on polystyrene chains

Article abstract of DOI:10.1039/b202715c

2,6-Bis(imino)pyridyl iron catalysts bearing allyl groups [ArN=C(Me)][Ar′N=C(Me)]C₅H₃NFeCl₂ (Ar = Ar′ = 4-allyl-2,6-(i-Pr)₂C₆H₂ (Cat-1); Ar = 2,6-(i-Pr)₂C₆H₃, Ar′ = 4-allyl-2,6-(i-Pr)₂C₆H₃ (Cat-2)) have been synthesized and characterized. The corresponding polymer-incorporated iron catalysts PC-1, PC-2 and their SiO₂-supported core-shell structure catalysts SC-1 and SC-2 were obtained by the co-polymerization of the olefin groups of Cat-1 or Cat-2 with styrene in the presence of a radical initiator. All three types of catalysts (Cat-1 and Cat-2; PC-1 and PC-2; SC-1 and SC-2) have been investigated for ethylene polymerization. As a result, these catalysts were found to exhibit high activity using modified methylaluminoxane (MMAO) as a co-catalyst. Among them, the polymer-incorporated SiO₂ core-shell catalysts displayed very high activity (～3181 g (mmol Fe)^-1h^-1) with product molecular weights in the range 25-93 × 10⁴. The particle morphology of polyethylene produced by the core-shell structure catalysts (SC-1 and SC-2) was improved.

Full text of DOI:10.1039/b202715c

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Polymer-incorporated iron catalysts for ethylene polymerization—a
new approach to immobilize iron olefin catalysts on polystyrene
chains
Changkun Liua and Guoxin Jin*ab
a
State Key Laboratory of Macromolecular Physics and Chemistry, Changchun Institute
of Applied Chemistry, Changchun 130022, China
Chemistry Department, Fudan University, Shanghai 200433, China.
E-mail: gxjin@fudan.edu.cn; Fax: +86-21-65641740; Tel: +86-21-65643776
b
Received (in Montpellier, France) 14th March 2002, Accepted 16th May 2002
First published as an Advance Article on the web 20th August 2002
0
=
=
2,6-Bis(imino)pyridyl iron catalysts bearing allyl groups [ArN C(Me)][Ar N C(Me)]C5H3NFeCl2
(Ar ¼ Ar0 ¼ 4-allyl-2,6-(i-Pr)2C6H2 (Cat-1); Ar ¼ 2,6-(i-Pr)2C6H3 , Ar0 ¼ 4-allyl-2,6-(i-Pr)2C6H3 (Cat-2)) have
been synthesized and characterized. The corresponding polymer-incorporated iron catalysts PC-1, PC-2 and
their SiO2-supported core–shell structure catalysts SC-1 and SC-2 were obtained by the co-polymerization of
the olefin groups of Cat-1 or Cat-2 with styrene in the presence of a radical initiator. All three types of catalysts
(Cat-1 and Cat-2; PC-1 and PC-2; SC-1 and SC-2) have been investigated for ethylene polymerization. As
a result, these catalysts were found to exhibit high activity using modified methylaluminoxane (MMAO) as a
co-catalyst. Among them, the polymer-incorporated SiO2 core–shell catalysts displayed very high activity
(ꢀ3181 g (mmol Fe)ꢁ1 hꢁ1) with product molecular weights in the range 25–93 ꢂ 104. The particle morphology
of polyethylene produced by the core–shell structure catalysts (SC-1 and SC-2) was improved.
and distilled prior to use. Diacetylpyridine, 2,6-diisopropyl-
benzeneamine, SiO2 used as support were purchased from
Aldrich Chemical Co. Inc. Modified methylaluminoxane
(MMAO) was purchased from Acros Organics as 10% weight
of a toluene solution and used without further purification.
Styrene and divinylbenzene for co-polymerization were pur-
chased from Aldrich Chemical Co. Inc. and redistilled prior
to use.
1
Introduction
The polymerization of olefins by late transition metal com-
plexes is at an exciting juncture. Late transition metal catalysts
are particularly attractive because of their potential for tolerat-
ing heteroatomic functionalities, which may open up the pos-
sibility for copolymerizations of polar monomers.1,2 In prior
studies, Brookhart et al.,3–7 and Gibson et al.8–10 have reported
highly active ethylene and propylene polymerization catalysts
based on iron(II) and cobalt(II) bearing 2,6-bis(imino)pyridyl
ligands. We were attracted by the potential for using iron as
an ethylene polymerization active center due to its low cost
and high activity. However, practical considerations have indi-
cated that industrial ethylene polymerization is performed
usually in the heterogeneous mode with supported catalysts.
Traditional supports, such as high surface area silica or
alumina, have reactive surfaces11–13 that can lead to catalyst
deactivation and thus alternative supports are desirable.
Recently, on the basis of long experience in polymer-
supported metallocene catalysts for olefin polymerization,14a,b
we successfully developed a series of novel polymer-incorpo-
rated late transition metal catalysts for ethylene polymeriza-
tion. This article reports the preparation and characterization
of the polystyrene-incorporated iron catalysts and the more
practicable shell–core polystyrene-incorporated iron catalysts,
as well as the results on their use in ethylene polymerization
(Scheme 1).
2.2 Ligand and complex analyses
IR spectra of the complexes were measured on a Bio-Rad
FTS135 spectrometer. 1H-NMR spectra and 13C NMR spectra
were recorded on a Unity-400 spectrometer. EI-MS spectra
were recorded on a Finigan MAT 8500 spectrometer (70 eV),
and elemental analysis was performed on Perkin Elmer Series
II CHN/O Analyzer 2400.
2.3 Polymer characterization
13C NMR data for polyethylene were obtain using o-dichloro-
benzene as a solvent at 130 ꢃC. The intrinsic viscosity [Z] was
measured in Decalin at 135 ꢃC using an Ubbelohde viscometer.
Viscosity average molecular weight (Mv) were calculated by
using the following equation [Z] ¼ 2.3 ꢂ 10ꢁ4 Mv0.82. Molecu-
lar weight distribution (Mw/Mn) values of polyethylene were
determined using a PL GPC-220 gel permeation chromato-
graph at 150 ꢃC using narrow standards calibration and
equipped with three PL gel columns (sets of PL gel 10 mm
MIXED-B LS). Trichlorobenzene was employed as a solvent
at a flow rate of 1.00 mL minꢁ1. GPC characterizations of
the polystyrene-incorporated catalysts were made on a Waters
410 GPC Report at 35 ꢃC. Tetrahydrofuran (THF) was
2
Experimental
2.1 General considerations and materials
Dried solvents (hexane, toluene, tetrahydrofuran, methanol,
dichloromethane) used for complex synthesis and ethylene
polymerization were refluxed over an appropriate drying agent
employed as a solvent at a flow rate of 1.00 mL minꢁ1
.
Elemental analysis for Fe in polystyrene-incorporated catalysts
and shell–core iron catalysts was done using the ICP method
DOI: 10.1039/b202715c
New J. Chem., 2002, 26, 1485–1489
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Scheme 1 The synthesis of polystyrene-incorporated catalysts PC-1, PC-2 and shell–core polystyrene-incorporated catalysts SC-1, SC-2. a. Sty-
rene, AIBN, toluene, 79–80 ꢃC; b, SO2 , styrene, divinylbenzene, AIBN, toluene, 79–80 ꢃC.
with a TJA POEMS ICP analyzer after dry ashing and dilute
nitric acid dissolution.
(0.50 g, 1.55 mmol) was dissolved in 25 ml hot methanol, fol-
lowed by the addition of 5 ml CH2Cl2 , 2 ml formic acid and
excess 4-allyl-2,6-diisopropylaniline. The solution was stirred
in a sealed flask at 50 ꢃC for 2 days, and a yellow solid formed.
This solid was determined to be the deꢁsi1red ligand (L-2) (0.65
=
2.4 Synthesis
g, 80.4%). IR(KBr): n(C N) 1639 cm
.
1H-NMR (CDCl3):
All manipulations and reactions were performed with the
exclusion of oxygen and moisture under argon using standard
Schlenk technigues in oven-dried glassware. 4-Allyl-2,6-
diisopropylaniline was prepared from 2,6-diisopropylaniline
according to reference 15.
8.46–8.50 (br, 2H, Py-Hm), 7.90–7.96 (br, 1H, Py-Hp), 7.17
(d, 2H, Ph-Hm), 7.11 (t, 1H, Ph-Hp), 6.98 (s, 2H, Ph-Hm),
=
6.05 (br, 1H, –CH C), 5.10 (t, 2H, C CH2), 3.41 (d, 2H,
=
=
CH2–C C), 2.77 (br, 4H, CH(Me)2), 2.27 (s, 6H, CH3),
1.14–1.17 (br, 24H, C(CH3)2). 13C-NMR (CDCl3): 167.04
2.4.1 Synthesis of 2,6-diacetylpyridine bis(4-allyl-2,6-diiso-
propylaniline) (L-1). A solution containing 2,6-diacetylpyridine
(0.30 g, 1.84 mmol), 4-ally-2,6-diisopropylaniline (0.80 g, 3.68
mmol) and formic acid (2 ml) in 30 ml dry methanol was kept
to reflux under argon for 14 hours. The resulting yellow solid
was collected by filtration and washed with cold methanol
(3 ꢂ 5 ml). Yellow crystals (0.70 g, 68%) of L-1 were isolated
=
(C N), 155.21 (Py-C), 146.51 (Ph-C), 144.59 (Ph-C), 138.16
(Ph-C), 136.81 (Py-C), 135.77 (Ph-C), 135.71 (Ph-C), 134.78
=
(–CH ), 123.56 (Py-C), 123.17 (Py-C), 122.99 (Ph-C), 122.13
=
(Ph-C), 115.32 ( CH2), 40.26 (–CH2–), 28.33 (C(Me)2), 23.24
(CH3), 22.91 (CH3), 17.13 (CH3). C36H47N3 (521.79 g molꢁ1):
: Anal. Calcd.: C, 82.87; H, 9.08; N, 8.05. Found: C, 82.20; H,
9.13; N, 8.11%.
by recrystallization from CH2Cl2–hexane (1:4). IR (KBr):
1
n(C N) 1639 cmꢁ1. H-NMR (CDCl3): 8.47 (d, 2H, Py-Hm),
=
7.92 (t, 1H, Py-Hp), 6.98 (s, 4H, Ph-Hm), 6.04 (m, 2H,
2.4.3 Synthesis of 2,6-diacetylpyridine bis(4-allyl-2,6-diiso-
propylaniline) iron dichloride (Cat-1) and [2-[1-(2,6-diisopro-
pylphenylimino)ethyl]-6-[1-(4-allyl-2,6-diisopropylphenylimino)-
ethyl]pyridine] iron dichloride (Cat-2). A solution containing
FeCl2ꢄ4H2O (0.20 g, 1.00 mmol) and L-1 (0.60 g, 1.07 mmol)
in 40 ml THF was stirred for 5 h and then evaporated under
vacuum. The residue was washed with diethyl ether (3 ꢂ 10
ml), and recrystallized from CH2Cl2–hexane (3:1) at ꢁ20 ꢃC
to afford blue crystals of Cat-1 (0.66 g, 95.9%). IR(KBr):
=
CH C), 5.12 (m, 4H, C CH2), 3.40 (d, 4H, CH2-C C), 2.75
=
=
(m, 4H, CH(Me)2), 2.27 (s, 6H, CH3), 1.15 (d, 24H,
=
13
C(CH3)2); C-NMR (CDCl3): 167.04 (C N), 155.15 (Py-C),
144.57 (Ph-C), 138.12 (Ph-C), 136.79 (Py-C), 135.69 (Ph-C),
=
134.75 (–CH ), 123.16 (Py-C), 122.12 (Ph-C), 115.34
=
( CH2), 40.25 (–CH2–), 28.31 (C(Me)2), 23.24 (CH3), 22.92
(CH3), 17.14 (CH3). C39H51N3 (561.86 g molꢁ1): Anal. Calcd.:
C, 83.37; H, 9.15; N, 7.48. Found: C, 83.03; H, 9.13; N, 7.55%.
n(C N) 1621 cmꢁ1. EI-MS (70 eV): m/z 653 (M+ ꢁ Cl,
=
2.4.2 Synthesis of 2-[1-(2,6-diisopropylphenylimino)ethyl]-
6-[1-(4-allyl-2,6-diisopropylphenylimino)ethyl]pyridine (L-2). A
solution of 2,6-diacetylpyridine (0.30 g, 1.84 mmol), 2,6-diiso-
propylaniline (0.33 g, 1.84 mmol) and formic acid (2 ml) in 30
ml dry methanol was stirred at room temperature for two days.
The monosubstituted yellow solid product (0.52 g, 87.1%) was
collected by filtration, washed with cold methanol, and identi-
10%), 562 (M+ ꢁ FeCl2 , 100), 520 (M+ ꢁ FeCl2 ꢁ C3H6 , 5).
C39H51N3FeCl2 (688.61 g molꢁ1): Anal. Calcd.: C, 68.03; H,
7.47; N, 6.10. Found: C, 67.70; H, 7.39; N, 6.13%.
An analogous method was used for the preparation of Cat-2
(97.2%). IR(KBr): n(C N) 1619 cmꢁ1. EI-MS (70 eV): m/z
=
522 (M+ ꢁ FeCl2 , 100%), 576 (M+ ꢁ 2Cl, 20). C36H47N3FeCl2
(648.54 g molꢁ1): Anal. Calcd.: C, 66.67; H, 7.31; N, 6.48.
Found: C, 66.74; H, 7.27; N, 6.52%.
1
fied as the desired monoimine by H-NMR. This monoimine
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2.4.4 Preparation of polymer-incorporated catalysts PC-1
and PC-2. Under argon atmosphere, a solution containing
Cat-1 (0.34 g, 0.49 mmol), styrene (5 ml) and AIBN (0.20 g,
1.22 mmol) in 30 ml toluene was kept at 79–80 ꢃC under stir-
ring for 8 h. The solution was evaporated under reduced pres-
sure and the residue was washed with a mixed solution of
hexane–toluene (2:1) to afford the solid polymer-incorporated
catalyst PC-1. ICP-AES: 4.00 mg Fe/g poly.; GPC: Mw 22 598,
Mn 15 406, polydispersity index 1.446. An analogous method
was used for preparation of polymer-incorporated catalyst
PC-2. ICP-AES: 2.81 mg Fe/g poly.; GPC: Mw 17 959, Mn
13 000, polydispersity index 1.38.
2.4.5 Preparation of shell–core polymer-incorporated iron
catalysts SC-1 and SC-2. To a solution of 5 ml styrene in 10
ml toluene was added 2.0 g of SiO2 under nitrogen atmo-
sphere, followed by vigorous stirring at 40 ꢃC for 30 min. Then
the solution of 0.17 g (0.245 mol) Cat-l in 5 ml toluene and 0.25
ml of divinyl benzene were transferred to the above suspension
by syringe. 0.20 g of AIBN was added. The suspension was
kept at 79–80 ꢃC under stirring for 8 h. The precipitate was
separated and washed with toluene then dried under reduced
pressure to afford the shell–core polymer-incorporated iron
catalyst SC-1. ICP-AES: 1.69 mg Fe/g cat. An analogous
method was used for the preparation of shell–core polymer-
incorporated iron catalyst SC-2. ICP-AES: 1.44 mg Fe/g cat.
2.5 Ethylene polymerization
Scheme 2 The synthesis of Cat-1. a, Methanol, H+, heat; b,
FeCl2ꢄ4H2O, THF.
Ethylene polymerization was carried out under appropriate
ethylene pressure in toluene or hexane in a 500 mL glass reac-
tor equipped with a propeller-like stirrer. Solvent (100 mL)
was introduced into the argon-purged reactor and stirred
(800 rpm). The solvent was thermostated to a prescribed poly-
merization temperature, and the ethylene gas feed was started
after 20 min. Polymerization was initiated by adding a toluene
solution of co-catalyst (MMAO) and then catalyst (in a solu-
tion of toluene or as solid particles) into the reactor with vig-
orous stirring (800 rpm). After a prescribed time, the ethylene
gas feed was terminated. To the resulting mixture, ethanol (500
mL) and concentrated HCl (1 mL) were added. The polymer
was collected by filtration, washed with methanol (100 mL)
and dried in vacuo at 70 ꢃC for 15 h.
groups in Cat-1 and Cat-2 are also active and can be co-
polymerized with styrene in the presence of a radical initiator
(AIBN) resulting in the corresponding polymer-incorporated
catalysts PC-1 and PC-2. In order to co-polymerize the com-
plexes with styrene sufficiently, it was necessary to control
the temperature in the range of 79 ꢃC to 81 ꢃC. The higher
3
Result and discussion
3.1 Synthesis and characterization of the polymer-incorporated
iron catalysts and shell–core polymer-incorporated iron catalysts
The reaction of 2,6-diacetylpyridine and primary amine was
carried out in the presence of formic acid in methanol solution.
Different molar ratios of the starting materials gave two differ-
ent kinds of products. Treatment of 2,6-diacetylpyridine with
an excess of 4-allyl-2,6-diisopropylaniline led to the formation
of 2,6-diacetylpyridinebis(4-allyl-2,6-diisopropylaniline) (L-1)
(Scheme 2), while an equimolar ratio of 2,6-diacetylpyridine
with 4-allyl-2,6-diisopropylaniline or 2,6-diisopropylaniline
gave the monoimine product, which could further react with
the primary amine to form the unsymmetrical 2,6-diimine-
pyridine ligand (L-2) (Scheme 3). L-1 and L-2 can be used as
tridentate ligands and coordinated with FeCl2ꢄ4H2O in THF
solution to form complexes (Cat-1 and Cat-2) in high yields.
Cat-1 and Cat-2 were blue needle-like crystals, which were
obtained by recrystallization from CH2Cl2–hexane (3:1).
Alt et al. reported that metallocene catalysts with o-alkenyl
substituents showed self-immobilization in ethylene polymeri-
zation by the co-polymerization of the alkenyl group with
ethylene.16 Recently Herrmann et al. described that bis(imino)-
pyridyliron complexes with o-alkenyl groups acted as self-
immobilized catalysts for ethylene polymerization.17 The allyl
Scheme 3 The synthesis of Cat-2. a, Methanol, H+; b, 4-allyl-2,6-
diisopropylaniline, 2-propanol, H+, heat; c, FeCl2ꢄ4H2O, THF.
New J. Chem., 2002, 26, 1485–1489
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almost incorporated in polystyrene blocks. The rinsing time
of the solvent THF was affected by the tested samples so that
it was different in the three curves.
The shell–core iron incorporated catalysts SC-1 and SC-2
were prepared by using SiO2 beads to support the light
cross-linked polystyrene-incorporated iron catalysts. Co-poly-
merization among iron compounds, styrene and divinylben-
zene was controlled under similar condition to the
preparation of PC-1 and PC-2. The cross-linking degree of
the polystyrene-incorporated catalysts plays an important role
in the preparation of shell–core catalysts. Polymer-incorpo-
rated iron catalysts with high cross-linking degrees are insolu-
ble in toluene and can not cover the surface of the SiO2 beads,
whereas for the polystyrene-incorporated iron catalysts with
too low cross-linking degrees the shell–core catalysts will be
frail and easily disintegrated because of the swelling effect of
polystyrene in toluene. In this article, polystyrene-incorporated
catalysts with a cross-linking degree of 4.07% (calculated
according to the starting materials) were chosen.
Fig. 1 The results of GPC characterization.
3.2 Polymerization of ethylene
temperature would lead to enhancement of the rate of homo-
polymerization of styrene. When the co-polymerization is
complete, the mixed solvent hexane–toluene (2:1) was used
to precipitate the polymer-incorporated catalysts and wash
away the remnants of iron compounds, which did not co-poly-
merize with styrene. According to the results of ICP character-
ization, it was deduced that the molar ratios of the starting
materials (Cat-1:styrene and Cat-2:styrene) were 1:88.3 and
the corresponding copolymer unit ratios in PC-1 and PC-2
were 1:134 and 1:191. In the structures of the polymer-incorpo-
rated catalysts PC-1 and PC-2, the active center was connected
to the polystyrene chains through only one or two carbon–car-
bon bonds. The low content of active centers and the electronic
paramagnetism of Fe(II) make the IR and 1H NMR character-
ization inefficient. Further parallel GPC tests of three samples
(B, Cat-2; C, PC-2 mixed with trace of Cat-2, 4.67 mg Fe/g
poly.; D, PC-2, 2.81 mg Fe/g poly.) were carried out. Fig. 1
shows that the trace of Cat-2 in PC-2 (curve C) can be distin-
guished by the rinsing time (10.332 min for Cat-2, 9.386 min
for PC-2). No peak appears around 10.332 min in curve D
(9.438 min for PC-2, 10.859 min for THF solvent), demon-
strating that the iron content in PC-2 (2.81 mg Fe/g poly.) is
The results of ethylene polymerization tests are collected in
Table 1
Several features are noteworthy. Unlike the cases of Cat-1
and Cat-2, ethylene polymerization catalyzed by PC-1 and
PC-2 proceeds smoothly without an immediate exotherm
and a decrease in activity. The dispersion of iron complexes
among the polystyrene blocks did not approach too high con-
centrations of active centers in the polymerization system and
resulted in ethylene polymerization at a smooth pace. As a
result, PC-1 was found to display a activity of 430 kg of poly-
ethylene (mol Fe)ꢁ1 hꢁ1 at 25 ꢃC which was lower than the
activity of ethylene polymerization catalyzed by Cat-1 under
the same polymerization conditions (1590 kg of polyethylene
(mol Fe)ꢁ1 hꢁ1). However, PC-2 was found to display a higher
activity than Cat-2 under the same polymerization conditions
(at 13 ꢃC, PC-2: 2466 kg of polyethylene (mol Fe)ꢁ1 hꢁ1
Cat-2: 1588 kg of polyethylene (mol Fe)ꢁ1 ꢁ1). The different
polymer configuration of the polymer-incorporated catalysts
PC-1 and PC-2 may contribute to this observation.
Although the polymer-incorporated iron catalysts PC-1
and PC-2 are active for ethylene polymerization and avoid
;
h
Table 1 Results of ethylene polymerizationa
molecular weight
c
c
c
Entryb
Pro-catalyst
T/ꢃC
Pressure/MPa
Al/Fe (molar ratio)
Activity/g (mmol Fe)ꢁ1 hꢁ1
Mw
Mn
Mw/Mn
1
2
25
0
0.1
0.1
0.1
0.1
0.1
0.1
0.24
0.1
0.1
0.24
0.1
0.3
0.3
0.1
0.3
0.3
1600
1600
2200
2200
1200
1600
1600
1650
2200
2200
1200
1200
1200
1600
1600
1600
1590
1900
1588
4017
365
142 302
187 123
89 658
179 882
—
3001
8725
47.42
21.45
92.62
23.13
—
Cat-1
Cat-2
PC-1
3
13
0
968
7776
4
5
25
25
60
13
13
60
51
60
51
51
60
51
—
1456
6
430
99 935
182 427
—
68.64
27.09
—
7
3130
2233
2466
3900
636
6734
—
8
9
PC-2
SC-1
SC-2
129 216
153 632
2727
47.38
23.58
10
11
12
13
14
15
16
6514
31.24 ꢂ 104 d
25.47 ꢂ 104 d
93.97 ꢂ 104 d
30.56 ꢂ 104 d
28.13 ꢂ 104 d
86.98 ꢂ 104 d
3085
2507
1086
3181
2623
a
All of the pro-catalysts activated with MMAO; ethylene polymerization time, 1 h. b Entries 1–10, 50 ml of toluene solvent; entries 11, 13, 14, 16,
100 ml of hexane solvent; entries 12, 15, 100 ml of toluene solvent. c Determined by GPC at 135 ꢃC. d Polymer did not dissolve wholly in trichlor-
obenzene under GPC measurement conditions. The results were obtained from polyethylene soluble in Decalin under intrinsic viscosity measure-
ment conditions.
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reaction times. 13C-NMR analyses of the polyethylene gener-
ated by all the iron catalysts reveal that the resonances at
14.1 ppm, 22.85 ppm, 29.57 ppm, 29.69 ppm, 32.21 ppm are
obvious in all tests, by which the saturated end group in the
polymer chains is identified. This end group arises from chain
transfer to aluminium followed by hydrolysis during the acid
workup.19
In summary, the shell–core polymer-incorporated iron cata-
lysts described herein represent a significant polyolefin technol-
ogy, which may be applicable to some other olefin
polymerization catalysts based on late transition metals. To
the best of our knowledge, these are the first reported poly-
mer-incorporated and shell–core polymer-incorporated late
transition metal catalysts for olefin polymerization.
Fig. 2 (A) Scanning electron microscope image of a SC-1 particle
(scale bar, 10 mm). (B) Scanning electron microscope image of a poly-
ethylene bead resulting from the SC-1 catalyst (scale bar, 100 mm).
immediate exotherm, the morphology of the polyethylene cat-
alyzed by PC-1, PC-2 is a little poor, with particles of varied
and ill-defined shapes. The further synthesis of the shell–core
iron catalysts SC-1 and SC-2 is expected to control the particle
morphology.
Acknowledgements
Financial support by the National Natural Science Founda-
tion of China and by the Special Funds for Major State Basic
Research Projects (G 1999064800) is gratefully acknowledged.
The shell–core polymer-incorporated catalysts SC-1 and
SC-2 were prepared using SiO2 beads as the core to support
the polymer-incorporated catalysts so that fewer active centers
were enwrapped in the inner spherical particles to exhibit high
activity. As the result, SC-1 exhibited a very high activity of
3085 kg of polyethylene (mol Fe)ꢁ1 hꢁ1 at 60 ꢃC and 0.3
MPa of ethylene pressure with a viscosity average molecular
weight (Mv) value of 25.47 ꢂ 104 and SC-2 was found to dis-
play a very high activity of 3181 kg of polyethylene (mol
Fe)ꢁ1 hꢁ1 at 60 ꢃC and 0.3 MPa of ethylene pressure with a
viscosity average molecular weight (Mv) value of 28.13 ꢂ 104.
The most exciting fact was that the shell–core iron catalysts
SC-1 and SC-2 gave unexpectedly high molecular weight poly-
ethylene. Polyethylene with a very high viscosity average mole-
cular weight (Mv) value of 93.97 ꢂ 104 was obtained at 51 ꢃC
by using SC-1 as the catalyst, and polyethylene with a viscosity
average molecular weight (Mv) value of 86.98 ꢂ 104 was
obtained at 51 ꢃC by using SC-2 as catalyst. In comparison,
PC-2/MAO provided polyethylene with a viscosity average
molecular weight (MW) value of 18.24 ꢂ 104 at 60 ꢃC and
0.24 MPa of ethylene pressure,18 and 2,6-diacetylpyridine-
bis(2,6-diisopropylaniline)iron dichloride reported by Gibson
et al. provided polyethylene with a molecular weight (Mw)
value of 2.76 ꢂ 104 at 60 ꢃC and 1.33 MPa ethylene pressure.8
The explanation of such results is still under research.
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broad molecular weight distribution. The bimodality of poly-
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mechanism (chain transfer to aluminium), which predominates
at high concentrations of aluminium activator and at short
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