Synthesis of hetero-bimetallic metallocene complexes and their catalytic activities for ethylene polymerization

Article abstract of DOI:10.1016/S1381-1169(02)00361-8

Five new hetero-bimetallic metallocene complexes were synthesized by the reaction of RCpTiCl₃ and a Si-bridged zirconocene complex in refluxing toluene. They were all well characterized. These complexes activated with methylaluminoxane (MAO) are highly active catalysts for the polymerization of ethylene. The molecular weight (M_w = 28,957-124,089) and the molecular weight distribution (MWD = 2.04-3.01) of the polymer generated from the bimetallic catalytic system were higher than that obtained by Cp₂ZrCl₂.

Full text of DOI:10.1016/S1381-1169(02)00361-8

Journal of Molecular Catalysis A: Chemical 189 (2002) 187–194
Synthesis of hetero-bimetallic metallocene complexes and their
catalytic activities for ethylene polymerization
Jiling Huanga, Zuofeng Fenga, Hong Wanga, Yanlong Qiana,∗, Junquan Sunb,
Yongjin Xub, Wei Chenc, Gang Zhengc
Laboratory of Organometallic Chemistry, East China University of Science and Technology,
a
130 Meilong Road, Shanghai 200237, PR China
Department of Chemical Engineering, Zhejiang University, Hangzhou 310027, PR China
b
c
Research Institute of Petroleum Processing, SINOPEC, 18 Xueyuan Road, Beijing 100083, PR China
Received 7 February 2002; received in revised form 9 May 2002; accepted 11 June 2002
Abstract
Five new hetero-bimetallic metallocene complexes were synthesized by the reaction of RCpTiCl3 and a Si-bridged zir-
conocene complex in refluxing toluene. They were all well characterized. These complexes activated with methylaluminoxane
(MAO) are highly active catalysts for the polymerization of ethylene. The molecular weight (Mw = 28,957–124,089) and
the molecular weight distribution (MWD = 2.04–3.01) of the polymer generated from the bimetallic catalytic system were
higher than that obtained by Cp2ZrCl2.
© 2002 Elsevier Science B.V. All rights reserved.
Keywords: Bimetallic; Zirconium; Titanium; Metallocene; Catalysis; Polyethylene
1. Introduction
On the other hand, another method to solve this prob-
lem is to combine two different metal centers in one
complex.
In recent years, much attention has been focused
on the formation of bimetallic metallocene complexes
due to their special features. Cooperative effect may
exist between the two metal centers that allow elec-
tronic interaction via the ligands, therefore, behav-
ing differently in catalysis when compared with the
mononuclear complex [6–14].
In our previous work, we found that differentially
substituted cyclopentadienyl (Cp) titanocenes gave
good result on the polymerization of olefins [15,16].
In the present research, we combined two metals
(Ti and Zr) with different substituent groups in one
complex in order to study their behaviors on the
polymerization of ethylene.
It is well known that metallocenes activated with
methylaluminoxane (MAO) are highly active homo-
geneous Ziegler–Natta catalysts that produce poly-
olefin with controlled stereoregularity and narrow
molecular weight distribution [1–4].
However, the molecular weight distributions of the
polymer produced by metallocene catalyst are so nar-
row to cause some disadvantages on the processability,
such as the high shear viscosity and low melt exten-
sional viscosity of the product. In order to overcome
those problems, some combined metallocene catalysts,
such as Cp2TiCl2/Cp2ZrCl2 [5] have been studied.
∗
Corresponding author. Fax: +86-21-6470-2573.
E-mail address: qianling@online.sh.cn (Y. Qian).
1381-1169/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S1381-1169(02)00361-8

188
J. Huang et al. / Journal of Molecular Catalysis A: Chemical 189 (2002) 187–194
We report here the synthesis and polymerization be-
The reaction of the known compound Me2Si(C5H5)2
with 2 eq. of n-BuLi in hexanes produced Li2[Me2Si
(C5H4)2], which was separated as a white powder.
Subsequent reaction of this dilithium salt with 1 eq.
of CpZrCl3·DME in toluene provided complex (X) as
yellow crystals (Scheme 1).
haviors of these new hetero-bimetallic metallocenes,
which combine the effects of having two active centers
and also the influence of having different substituent
groups on the Cp ligand.
All these complexes were characterized by
1HNMR, MS, IR and EA. They are soluble in CH2Cl2
and toluene, and are sensitive to air and moisture.
2. Results and discussion
2.1. Synthesis of complexes 1–5
2.2. Ethylene polymerization
The general method to prepare complexes 1–5 is
the reaction of 1 eq. of RCpTiCl3 with complex (X)
in refluxing toluene. Complex (X) was synthesized by
the procedure described by Ushioda et al. [8]. The
titanium complexes RCpTiCl3 were synthesized from
the reaction of RCpSiMe3 with TiCl4 in toluene as
reported in the literature [19].
The synthesized bimetallic complexes are suitable
as catalysts for the polymerization of olefins and were
used for the homogeneous polymerization of ethy-
lene. The catalytic system was formed by mixing the
complex with an excess of MAO.
Scheme 1. Complexes 1–5 were synthesized by the reaction of complex (X) with RCpTiCl3 in refluxing toluene, at 140 ◦C. Pure products
were obtained by recrystallization from toluene/hexane.

J. Huang et al. / Journal of Molecular Catalysis A: Chemical 189 (2002) 187–194
189
Table 1
The result of ethylene polymerization by complexes (1–5)
a
b
Number Catalyst
A (105 gPE/
Mn
Mw
Mw/Mn
mol cat h)
1
2
3
4
5
6
7
1
2
3
4
5
1.87
8.15
2.39
1.89
2.80
30894
11211
37201 109024 2.93
44120 124089 2.81
15999
14731
–
93137 3.01
28957 2.58
32641 2.04
24956 1.69
Cp2ZrCl2 2.33
Cp2TiCl2 1.03
–
–
Conditions: Al/M = 500, T = 60 ◦C, t = 60 min, V = 25 ml,
catalyst = 0.004 mmol.
a Number average molecular weight, determined by GPC.
b Weight average molecular weight, determined by GPC.
Fig. 3. GPC of polymerization of ethylene by complex 3.
The result of ethylene polymerization using these
bimetallic complexes (1–5) is shown in Table 1
and Figs. 1–6. All complexes gave high catalytic
activity ((1.87–8.15) × 105 gPE/mol cat h). Under
Fig. 4. GPC of polymerization of ethylene by complex 4.
Fig. 1. GPC of polymerization of ethylene by complex 1.
Fig. 5. GPC of polymerization of ethylene by complex 5.
Fig. 2. GPC of polymerization of ethylene by complex 2.

190
J. Huang et al. / Journal of Molecular Catalysis A: Chemical 189 (2002) 187–194
molecular weight distribution (2.04–3.01) is broader.
When complex 1 and MAO were used as the catalytic
system, the molecular weight distribution (3.01) of
the polymer is highest. We assume that there is more
than one active site or dormain during the polymeriza-
tion process. When complexes 3 or 4 with MAO were
used as the catalytic system, the molecular weight
of the polymer is about five times that produced us-
ing Cp2ZrCl2. This is a new catalytic system for the
production of high molecular weight polymers.
There is an interesting observation that at higher
activity levels Mw is lower. The lower Mw indicate
higher rate of ␤-hydride elimination. We think that
this higher rate constant for the ␤-hydride elimination
is the result of the different electronic environments
of the metal sites. The electron withdrawing effect
of one metal center reduces the electron density on
the Cp ligand at the adjacent metal center. This in
turn the reduced electron density at the other metal
center resulting in higher rate of ␤-hydride elimination
[13].
From the result of polymerization, we observe that
different substituent groups on the Cp would influ-
ence the polymerization behaviors remarkably. In gen-
eral, unsaturated substituent group (benzyl or allyl) on
Cp would improve the activity of polymerization. We
think that the electronic distribution on the Cp ring was
affected by the unsaturated substituent group. Conse-
quently, the coordination atmosphere around the metal
center was satisfied.
Fig. 6. GPC of polymerization of ethylene by complex Cp.
the same conditions, the activity of Cp2TiCl2 is
1.03×105 gPE/mol cat h and the activity of Cp2ZrCl2
is 2.33 × 105 gPE/mol cat h.
All the complexes gave high activity for the poly-
merization of ethylene. Under similar experimental
conditions, the title complexes show activities varying
between that of Cp2TiCl2 and Cp2ZrCl2. This illus-
trates the interaction between the two metal centers.
The activity is highest when R is benzyl (complex 2,
A = 8.15 × 105 gPE/mol cat h).
The molecular weight and molecular weight distri-
bution of the polymer generated from the bimetallic
complexes were different from that obtained from
Cp2ZrCl2 (Mw = 24956; MWD = 1.69). The molec-
ular weight (28,957–124,089) is much higher and the
Fig. 7. The effect of Al/M to the polymerization of ethylene.

J. Huang et al. / Journal of Molecular Catalysis A: Chemical 189 (2002) 187–194
191
Fig. 8. The effect of time to the polymerization of ethylene.
When the substituent groups are benzyl (complex
2) and allyl (complex 5), the activity (A) is some-
what higher (A2 = 8.15 × 105 gPE/mol cat h, A5 =
2.80×105 gPE/mol cat h). The benzyl substituted com-
plex 2 show the highest activity. We used complex 2 to
test the effect of different condition on the polymeriza-
tion of ethylene. The conditions varied in our study are
MAO/metal (Al/M) molar ratio, time of polymeriza-
tion, temperature and pressure of ethylene monomer.
The dependence of activity (A) on the Al/M molar
ratio is presented in Fig. 7. There is a direct relation-
ship between A and Al/M. The figure shows an initial
steep slope at Al/M = 250–500 that later normalized
as Al/M reached 500–1000. This implies that for prac-
tical purpose Al/M molar ratio roughly 500 is ideal
for polymerization, any further increase will have
very little impact on activity as we can see increasing
Al/M molar ratio from 500 to 1000 only increases the
activity from 8.15–10.38×105 gPE/mol cat h, i.e. less
than 25% increment for a 100% increase in Al/M mo-
lar ratio. This fact was observed by other researchers
and Koltzenburg [17] gave the explanation that it is
due to the mechanism of chain termination under
different aluminum concentrations. From Fig. 7 we
can also ascribe the slowing of rate of activity with
an increase in Al/M molar ratio to over-alkylation,
which drastically deactivates the metal centers
[18].
The result of the effect of time on polymeriza-
tion is presented in Fig. 8. From the figure it can be
seen that catalyst activity increases with time up to
a maximum (roughly 1 h) after which a steady de-
cline ensues, due probably to deactivation of catalyst.
Jüling et al. [13] reported one bimetallic metallocene,
when used as the catalyst for the propene polymeriza-
tion observed that the polymerization rate decreased
rapidly in a few minutes after initiation. Compared to
their system, the catalytic system we have employed
was much more stable. The length of time over
which the catalyst was stable is very impressive and
is very important for an industrial application of the
system.
The result on variation of activity with tempera-
ture is presented in Fig. 9. From where it is obvious
that 60 ◦C is an optimum point below or above which
the activity is lower. We supposed that the catalytic
system was not stable under high temperature, so the
activity decreased when the temperature was above
60 ◦C.
In order to fully understand the effect of all vari-
ants on the polymerization, we carried out a study
on the role of variation in pressure and the result
is presented in Table 2. Keeping all other condi-
tions constant, it is clear that activity increases di-
rectly with pressure. Increased pressure generally
implies much more monomer, since more monomer

192
J. Huang et al. / Journal of Molecular Catalysis A: Chemical 189 (2002) 187–194
Fig. 9. The effect of temperature to the polymerization of ethylene.
Table 2
were collected on a Nicolet Magna-IR550 (KBr). Mass
spectral data (EI) were collected on a Hewlett-Packard
model 5989A instrument. EA data was recorded from
an EA-1106 elemental analyzer.
Effect of pressure to the polymerization of ethylene
Number
Al/M
Pressure
(atm)
A (105 gPE/
mol cat h)
1
2
3
4
500
500
1000
1000
1
6
1
6
8.15
9.73
7.52
3.1. Synthesis of catalysts
10.90
(
)
3.1.1. Synthesis of complex X
Conditions: T = 65 ◦C, t = 60 min, V = 50 ml.
is converted per mole of catalyst by increasing the
pressure, i.e. making more monomer available for
polymerization.
Me2SiCp2 (5.0 g, 26.6 mmol) was dissolved in
80 ml hexane, and then 0.0532 mol n-BuLi was added
dropwise. This mixture was stirred overnight. Af-
ter removal of volatiles, 150 ml toluene was added.
CpZrCl3·DME (9.36 g) was then added to the sys-
tem, and the mixture was stirred at room temperature
overnight. The resulting yellow solution was then fil-
tered from solid residues, which was further extracted
with CH2Cl2 (50 ml × 2 ml). The combined filtrate
was concentrated under reduced pressure and cooled
to −20 ◦C to give pale yellow crystals of compound
X.
3. Experimental section
All operations were carried out under a dry argon at-
mosphere using standard Schlenk techniques. Toluene,
diethyl ether, tetrahydrofuran (THF) and hexane
were refluxed over sodium/benzophenone ketyl, from
which they were distilled prior to use. Polymerization-
grade ethylene was purified before use. CpꢀTiCl3
was prepared by the reaction of CpꢀSiMe3 with
TiCl4 in toluene according to literature methods [19].
CpZrCl3·DME was prepared by literature methods
[19].
3.1.2. Synthesis of complex 1 (R = CH3)
A mixture of compound X (511.3 mg, 1.35 mmol)
and CH3CpTiCl3 (315.2 mg, 1.35 mmol) was refluxed
in toluene (80 ml) for 20 h. The solution was then
filtered and concentrated in vacuo to half the orig-
inal volume. The filtrate was cooled to −20 ◦C to
1H NMR was recorded in CDCl3 on a Bruker
AVANCHE500 500 MHz NMR spectrometer. IR data

J. Huang et al. / Journal of Molecular Catalysis A: Chemical 189 (2002) 187–194
193
afford complex 1 as brown crystals (362.3 mg). Yield:
44.5%.
then filtered and concentrated in vacuo to half the
original volume. The filtrate was cooled to −20 ◦C
to afford complex 3 as a red solid (323.5 mg). Yield:
24.2%.
1HNMR: 6.83 (t, J = 2.4, 2H); 6.74 (t, J = 2.4,
2H); 6.59 (m, 4H); 6.43 (s, 5H); 6.31 (t, J = 2.6, 2H);
6.22 (t, J = 2.6, 2H); 2.35 (s, 3H); 0.64 (s, 6H).
IR: 3423.3w, 3104.5m, 2957.4w, 2920.2w, 2855.3w,
1499.7w, 1445.0w, 1409.1m, 1371.5w, 1351.9w,
1248.0m, 1176.3m, 1042.7m, 1017.6w, 933.4w,
905.7w, 818.6s, 781.6s,+730.0w, 675.9w.
1HNMR: 6.80 (t, J = 2.4, 2H); 6.74 (t, J = 2.4,
2H); 6.58–6.56 (m, 4H); 6.43 (s, 5H); 6.32–6.30
(m, 4H); 3.23 (m, 1H); 1.21 (d, J = 7.0, 6H); 0.64
(s, 6H).
IR: 3422.4w, 3105.2m, 2959.5m, 2923.9w,
2869.3w, 1491.9w, 1442.4w, 1408.1m, 1369.7w,
1317.7w, 1249.0m, 1175.7m, 1153.0w, 1073.0w,
1041.8m, 1018.3m, 907.1w, 817.5s, 782.4m, 730.7m,
673.7m.
MS: 573 (26.06, M• –Cl); 543 (9.61, M•+−Cp);
+
538 (16.42, M• –2Cl); 528 (12.05, M•+–MeCp);
313 (59.43, M•+–ZrCl2Cp–2Cl); 311 (54.61,
+
M• –TiCl2CpMe–Cl–Cp); 269 (56.24, M•+–ZrCl2
+
Cp–Cl–MeCp); 234 (100, M•+–ZrCl2Cp–2Cl–MeCp);
225 (8.55, ZrCl2Cp); 79 (10.67, MeCp).
E.A. calculated: C 45.17%; H 4.29%; found: C
45.19%; H 4.29%.
MS: 601 (52.18, M+• –Cl); 529 (41.58, M•+–C3H7
Cp); 566 (29.80, M• –2Cl); 376 (9.54, M•+–ZrCl2
Cp–Cl); 341 (14.84, M•+–ZrCl2Cp–2Cl); 311 (100,
+
+
–
M• –TiCl2[C3H7Cp]–Cl–Cp); 304 (20.73, M•
ZrCl2Cp–C3H7Cp); 276 (7.89, M•+–TiCl2[C3H7Cp]–
2Cl–Cp); 269 (73.62, M•+–ZrCl2Cp–Cl–C3H7Cp);
234 (61.72, M•+–ZrCl2Cp–Cl–C3H7Cp) 225 (50.41,
ZrCl2Cp); 107 (30.86, C3H7Cp).
3.1.3. Synthesis of complex 2 (R = CH2Ph)
A mixture of compound X (512.7 mg, 1.35 mmol)
and PhCH2CpTiCl3 (419.2 mg, 1.35 mmol) was re-
fluxed in toluene (80 ml) for 20 h. The solution was
then filtered and concentrated in vacuo to half the
original volume. The filtrate was cooled to −20 ◦C
to afford complex 2 as a red solid (354.2 mg). Yield:
38.2%.
E.A. calculated: C 46.95%; H 4.74%; found: C
46.76%; H 4.90%.
3.1.5. Synthesis of complex 4 (R = –
)
A mixture of compound X (530.4 mg, 1.41 mmol)
and (hexamethyleneCp)TiCl3 (423.1 mg, 1.40 mmol)
was refluxed in toluene (80 ml) for 20 h. The solution
was then filtered and concentrated in vacuo to half the
original volume. The filtrate was cooled to −20 ◦C
to afford complex 4 as a red solid (171.0 mg). Yield:
17.8%.
1HNMR: 7.32–7.17 (m, 5H); 6.82 (t, J = 2.3, 2H);
6.74 (t, J = 2.3, 2H); 6.56 (t, J = 2.2, 2H); 6.50 (t,
J = 2.2, 2H); 6.44 (s, 5H); 6.32 (d, J = 2.2, 2H);
6.29 (d, J = 2.2, 2H); 4.10 (s, 2H); 0.65 (s, 6H).
IR: 3442.8m, 3104.8m, 3024.4w, 2958.1w,
2923.1m, 2852.5w, 1736.9w, 1640.5w, 1600.9w,
1582.5w, 1492.8m, 1449.6m, 1409.8m, 1369.5m,
1351.2w, 1252.1s, 1175.7m, 1068.7w, 1039.8m,
900.1w, 814.5s, 788.6m, 728.5w, 702.3m, 674.2m
MS: 650 (7.05, M•+–Cl +1); 529 (12.79,
1HNMR: 6.78 (t, J = 2.4, 2H); 6.74 (t, J = 2.4,
2H); 6.57–6.55 (m, 4H); 6.42 (s, 5H), 6.30 (s, 4H);
2.88 (m, 1H); 2.00–1.98 (m, 2H); 1.77–1.68 (m, 3H);
1.43–1.37 (m, 2H); 1.28–1.16 (m, 3H); 0.64 (s, 6H).
IR: 3417.7w, 3106.6m, 2922.0m, 2849.2m,
1489.9w, 1445.1m, 1407.9m, 1370.1m, 1321.4w,
1249.9m, 1177.0m, 1051.3m, 1041.5m, 1016.8m,
956.5w, 933.4w, 909.5m, 895.6w, 829.7s, 819.8s,
782.7m, 730.9w, 675.6m.
+
M• –CpCH2Ph); 346 (51.16, M•+–TiCl2[CpCH2
Ph]–Cp); 311(100, M•+–TiCl2[CpCH2Ph]–Cl–Cp);
269 (45.02, M•+–ZrCl2Cp–Cl– CpCH2Ph); 234
(50.45, M•+–ZrCl2Cp–2Cl–CpCH2Ph); 225 (23.26,
ZrCl2Cp); 155 (19.34, CpCH2Ph).
E.A. calculated: C 50.65%; H 4.41%; found: C
50.60%; H 4.60%.
+
MS: 641 (22.51, M• –Cl); 606 (7.17, M•+–2Cl);
+
529 (52.03, M•
–
–Cp); 311 (63.10, M•+–TiCl2
3.1.4. Synthesis of complex 3 [R = CH(CH3)2]
A mixture of compound X (792.7 mg, 2.09 mmol)
and (CH3)2CHCpTiCl3 (546.2 mg, 2.09 mmol) was re-
fluxed in toluene (80 ml) for 20 h. The solution was
[
–Cp]–Cl); 304 (3.43, –ZrCl2Cp–
–Cp);
276 (4.96, M•+–TiCl2[
–Cp]–2Cl); 269 (79.96,

194
J. Huang et al. / Journal of Molecular Catalysis A: Chemical 189 (2002) 187–194
M•+–ZrCl2Cp–
–Cp–Cl); 234 (100, M•+–ZrCl2
time. The polymerization was quenched by venting
the ethylene and adding a small amount of ethanol.
The contents of the flask were transferred to a beaker
and using HCl was adjusted to pH 7. The polymer was
then separated from the solution then dried in vacuo
at 60 ◦C to constant weight.
Cp–
–Cp–2Cl); 225 (17.86, ZrCl2Cp); 147
(4.70,
–Cp).
E.A. calculated: C 49.48%; H 5.05%; found: C
49.29%; H 5.33%.
Acknowledgements
3.1.6. Synthesis of complex 5 (R = CH2CH = CH2)
A mixture of compound X (473.1 mg, 1.25 mmol)
and CH2=CHCH2CpTiCl3 (339.9 mg, 1.31 mmol)
was refluxed in toluene (80 ml) for 20 h. The solution
was then filtered and concentrated in vacuo to half the
original volume. The filtrate was cooled to −20 ◦C
to afford complex 5 as a red solid (145.0 mg). Yield:
18.2%.
We gratefully acknowledge financial support from
the Special Funds for Major State Basic Research
Projects (G 1999064801), the National Natural
Science Foundation of China (NNSFC) (20072004).
References
1HNMR: 6.83 (s, 2H); 6.73 (d, J = 5.8, 2H); 6.59
(s, 2H); 6.56 (s, 2H); 6.43 (s, 5H); 6.32 (d, J = 2.1,
2H); 6.28 (s, 2H); 5.95 (m, 1H); 3.51 (d, J = 6.5,
2H); 2.35 (s, 2H); 0.64 (s, 6H).
[1] W. Kaminsky, M. Miri, H. Sinn, R. Woldt, Makromol. Chem.
Repid Commun. 4 (1983) 417.
[2] J.A. Ewen, J. Am. Chem. Soc. 106 (1984) 6355.
[3] J.C.W. Chien, B.P. Wang, J. Poly Sci. Part A: Polym. Chem
26 (1988) 3089.
[4] F.R.W.P. Wild, L. Zsolnai, G. Huttner, H.H. Brintzinger, J.
Organomet. Chem. 232 (1982) 233.
[5] J.A. Ewen, in: T. Keii, K. Soga (Eds.), Proceedings of
the International Symposium on Catalytic Polymerization of
Olefins, Kondansha, 1986, p. 239.
[6] K.P. Reddy, J.L. Petersen, Organometallics 8 (1989) 2107.
[7] J.L. Huhmann, J.Y. Corey, N.P. Rath, Organometallics 15
(1996) 4063.
[8] T. Ushioda, M.L.H. Green, J. Haggitt, X.F. Yan, J. Organomet.
Chem. 518 (1996) 155.
[9] J.L. Huhmann, J.Y. Corey, N.P. Rath, J. Organomet. Chem.
533 (1997) 61.
[10] K. Soga, H.T. Ban, T. Uozumi, J. Mol. Cat. A: Chem. 128
(1998) 273.
IR: 3419.8w, 3106.6m, 3084.8m, 2956.9m,
2923.7m, 2901.4m, 2853.7w, 1638.6w, 1438.6m,
1409.2m, 1368.8m, 1315.1w, 1209.6w, 1250.3s,
1174.2m, 1126.1w, 1112.2w, 1089.3w, 1072.4w,
1046.5m, 1017.7m, 986.6m, 951.2m, 908.3m, 851.6m,
823.2s, 762.0m, 728.5m, 690.8m.
+
MS: 564 (9.71, M• –2Cl); 529 (14.51, M•+–C3H5
Cp); 494 (10.95, M•+–Cl–C3H5Cp); 376 (7.60,
+
M• –TiCl2[C3H5Cp]–Cl); 341 (15.46, M•+–TiCl2
[C3H5Cp]–2Cl–Cp); 311 (100, M•+–TiCl2[C3H5
Cp]–Cl–Cp); 304 (12.60, M•+–ZrCl2Cp–C3H5Cp);
269 (34.93, M•+–ZrCl2Cp–Cl–C3H5Cp) 234 (49.16,
M•+–ZrCl2Cp–2Cl–C3H5Cp); 225 (20.22, ZrCl2Cp).
E.A. calculated: C 47.09%; H 4.44%; found: C
47.29%; H 4.70%.
[11] S.K. Noh, G.G. Byun, G.S. Lee, D. Lee, K.B. Yoon, K.S.
Kang, J. Organomet. Chem. 518 (1996) 1.
[12] R. Feng, L.M. Su, D.W. He, B.Q. Wang, G.L. Tian, S.S. Xu,
X.Z. Zhou, Acta Polym. Sinica 6 (1998) 360.
[13] S. Jüling, R. Mlhaupt, H. Plenio, J. Organomet. Chem. 460
(1993) 191.
[14] J.C. Flores, T.E. Ready, J.C.W. Chien, M.D. Rausch, J.
Organomet. Chem. 562 (1998) 11.
[15] J. Liu, H. Ma, J. Huang, Y. Qian, A.S.C. Chan, Eur. Polym.
J. 35 (1999) 543.
[16] J. Liu, H. Ma, J. Huang, Y. Qian, Eur. Polym. J. 36 (2000)
2055.
3.2. Polymerization of ethylene
Ethylene was purified by passage through 4 Å
molecular sieves and Mn sieves. Polymerizations were
carried out in a reactor placed in a thermostatically
heated bath and equipped with a magnetic stirrer.
MAO, toluene solution of metallocene and more
toluene to bring the final volume to 25 ml were added
to the reactor in that sequence. The reaction mixture
was stirred vigorously at 60 ◦C and pre-dried ethylene
at atmospheric pressure was pumped in for a certain
[17] S. Koltzenburg, J. Mol. Cat. A: Chem. 116 (1997) 355.
[18] L. Jiang, Z. Shen, Y. Zhang, Eur. Polym. J. 36 (2000) 2513.
[19] E.C. Lund, T. Livinghouse, Organometallics
2426.
9 (1990)