The bridged cyclopentadienyl indenyl (fluorenyl) zirconocene complexes for polyethylene macromonomers

Article abstract of DOI:10.1002/aoc.1674

The synthesis of long-chain branched polyethylene includes the generation of vinyl-terminated polyethylene macromonomers and the copolymerization of these macromonomers with ethylene. Four new bridged cyclopentadienyl indenyl (fluorenyl) zirconocene compl

Full text of DOI:10.1002/aoc.1674

Full Paper
Received: 10 November 2009
Revised: 27 February 2010
Accepted: 17 April 2010
Published online in Wiley Online Library: 28 June 2010
(wileyonlinelibrary.com) DOI 10.1002/aoc.1674
The bridged cyclopentadienyl indenyl
(fluorenyl) zirconocene complexes
for polyethylene macromonomers
Wenzhong Huang, Fengbo Li, Haiyan Ma and Jiling Huang∗
The synthesis of long-chain branched polyethylene includes the generation of vinyl-terminated polyethylene macromonomers
and the copolymerization of these macromonomers with ethylene. Four new bridged cyclopentadienyl indenyl (fluorenyl)
zirconocene complexes 1a–b, 2a–b were prepared and showed high activities for ethylene homopolymerization upon the
activation of methylaluminoxane. The steric bulk of bridged substituent has a profound effect on the catalytic activity as well
as on the molecular weight of resulting polyethylene. Complex 1b showed the highest activity of up to 5.32 × 106 g PE/(mol
Zr h) for ethylene homopolymerization at 70 ◦C, which was higher than that of Cp2ZrCl2. The polyethylenes produced with
complexes 1a–d/MAO are mostly vinyl-terminated, possess low molecular weight and fit as macromonomers. The (p-MePh)2C-
bridged cyclopentadienyl indenyl zirconocene complex 1a could produce polyethylene macromonomer with selectivity for the
c
vinyl-terminal as high as 94.9%. Copyright ꢀ 2010 John Wiley & Sons, Ltd.
Keywords: zirconocene; ethylene polymerization; polyethylene macromonomer
Introduction
after the macromonomer is produced but not separated (tandem),
or the two catalysts are added simultaneously to the reactor
(simultaneous).
Metallocene catalysts have attracted considerable attention due
to their high catalytic activities for olefin polymerizations and fine
control over polyolefin size dimensions and microstructure.[1,2]
Modification of the ligand environment on the catalyst affords
polymers with different physical characteristics such as molecular
weight (Mw), molecular weight distribution and branch length.[3,4]
The length of branches dramatically affects the processability and
rheological properties of polyolefin[5] and the frequency of long-
chain branches in the range of 0.01–3 long chain branches per
1000 carbon atoms can be a remarkable influence on the physical
properties of polyolefin.[6]
It is difficult to incorporate α-olefins with more than eight
carbon atoms into growing chains by Ziegler–Natta catalysts,[7]
but metallocene catalysts can copolymerize α-olefins with
vinyl end-group chains to form long chain branched (LCB)
polymers.[8–10] These vinyl end-group chains can be considered
as macromonomers.[11] Dow Chemical Company[10] first used the
constrained geometry catalyst (CGC) to get LCB polyethylene
up to 0.34 long chain branches/1000 carbon atoms. Then some
metallocenes such as Et(Ind)2ZrCl2[11] and Cp2ZrCl2[12] were used
as single catalysts to produce LCB polyethylene with narrow
molecular weight distribution. In comparison with the single-
site nature of metallocene complexes, the non-metallocene
nickel complex, {[2-C6H4(C6H5)]–N C(CH3)–C(CH3) N-[2-C6H4
(C6H5)]}NiBr2,[13] afforded LCB polyethylene but with a broad or
bimodal molecular weight distribution.
In order to obtain LCB PE, it is necessary to obtain vinyl-
terminated PE macromonomers of suitable molecular weights.
Becausestudiesshowedthatonlyvinyl-terminatedoligomerswere
incorporated into growing polymer chains,[15] longer branches did
not benefit incorporation and shorter branches were found not
to influence the rheological properties,[6,16] the branch length of
LCB polymer must exceed the entanglement molar mass (Me) of
around 1300 g/mol for polyethylene.[4] The PE macromonomers
were produced by Markel et al.[17] with Cp2ZrCl2/MAO in hexane.
Sperber and Kaminsky[14] reported that bridged metallocene
systemof[Me2C(Cp2)]ZrCl2/MAOproducedmacromonomerswith
Mw ranging from 1200 to 4500 g/mol and terminal double
bond contents up to 96–98%. In addition, Fujita et al.[18] used
thenon-metallocenecomplexes[(2-OH-3-R1-5-R2)–C6H3 –CH N-
R3]2ZrCl2 to synthesize PE macromonomers with vinyl-terminal
content of 90–96% and Mw of 2000–14 000 g/mol.
Recently, we reported[19,20] that the bridged cyclopenta-
dienyl indenyl zirconocene complexes [(R-Ph)2C(Cp)(Ind)]ZrCl2
showed high activities for ethylene polymerization and afforded
polyethylenes of low molecular weights. Further analysis showed
that the obtained PEs possessed a high percentage of vinyl-
terminal groups. The results implied that these zirconocene
complexes can homopolymerize ethylene to provide polyethy-
lene macromonomers. In order to obtain PE macromonomers
Besides the method utilizing one catalyst, two different metal
complexes are often combined to produce LCB PE. In this method,
one is the catalyst for producing PE macromonomer and the other
is the catalyst for copolymerization. There are also three ways to
carry out the copolymerization:[14] the separated macromonomer
copolymerizeswithethyleneinthepresenceofthesecondcatalyst
(copolymerization), orsecondcatalystisaddedtothesamereactor
∗
Correspondence to: Jiling Huang, Laboratory of Organometallic Chemistry,
East China University of Science and Technology, 130 Meilong Road, Shanghai
200237, People’s Republic of China. E-mail: jlhuang@ecust.edu.cn
Laboratory of Organometallic Chemistry, East China University of Science and
Technology, 130 Meilong Road, Shanghai 200237, People’s Republic of China
c
Appl. Organometal. Chem. 2010, 24, 727–733
Copyright ꢀ 2010 John Wiley & Sons, Ltd.

W. Huang et al.
of various molecular weights as well as with high vinyl-terminal
content, in the work described herein we take advantage of
two reported ansa-cyclopentadienyl indenyl zirconocene com-
plexes and synthesize two new analogous complexes to examine
their ethylene polymerization behavior. In addition, two new
ansa-cyclopentadienyl fluorenyl zirconocene complexes were also
synthesizedanditwasfurtherattemptedtocopolymerizeethylene
with PE macromonomers using three different copolymerization
methods.
for 3 days. Then the reaction was slowly quenched by addition of
water(50 ml)at0 ◦C;theorganiclayerwaswashedwithwaterthree
times and dried over MgSO4, filtered and concentrated in vacuo
to produce yellow viscous oil. The crude product was purified by
chromatography on silica gel with petroleum ether as eluant. A
pale yellow solid powder was obtained (1.8 g, yield 49.7%).
(p-CH3-Ph)[p-C(CH3)3-Ph]C(C5H5)(C9H7)
The compound was obtained as a pale yellow solid powder using
a similar procedure (2.4 g, yield 32.8%).
Experimental
(p-CH3-Ph)2C(C5H5)(C13H9)
General Procedures
A solution of fluorenyl lithium (1.32 g, 7.7 mmol) in 20 ml of Et2O
was added dropwise to a solution of (p-CH3-Ph)2C (C5H4) (2.0 g,
7.7 mmol) in 30 ml of Et2O. After being stirred for about 24 h, the
reaction solution was hydrolyzed with 20 ml of water. The white
solid (p-CH3-Ph)2C(C5H5)(C13H9) precipitated (1.9 g, yield 57.8%).
All manipulations were carried out under a dry argon atmosphere
using standard Schlenk techniques unless otherwise indicated.
Toluene, diethyl ether (Et2O) and tetrahydrofuran (THF) were
refluxed over sodium benzophenone. Dichloromethane (CH2Cl2)
was refluxed over CaH2. Chloroform-d was dried over calcium
hydride under argon and stored in the presence of activated 4 Å
molecular sieves. n-BuLi (2.5 M in n-hexane) was purchased from
Chemetall. The cocatalyst methylaluminoxane (MAO, 1.53 M in
toluene) was purchased from Witco. Polymer-grade ethylene was
directly used for polymerization.
(p-CH3-Ph)[p-C(CH3)3-Ph]C(C5H5)(C13H9)
Similarly, fluorenyl lithium salt (1.15 g, 6.7 mmol) and (p-CH3-
Ph)[p-C(CH3)3-Ph]C (C5H4) (2.0 g, 6.7 mmol) gave (p-CH3-Ph)[p-
C(CH3)3-Ph]C(C5H5)(C13H9) as a white solid (1.8 g, yield 57.9%).
1H NMR spectra were recorded on a Bruker Avance-500
1
spectrometer with CDCl3 as solvent. Chemical shifts for H NMR
Synthesis of Complex [(p-CH3-Ph)2C(C5H4)(C9H6)]ZrCl2 (1a)
spectra were referenced internally using the residual solvent
resonances and reported relative to tetramethylsilane (TMS).
Elemental analyses were carried out on an EA-1106 type analyzer.
Differential scanning calorimetry analyses (DSC) were performed
on a Universal V2.3C TA instrument at a heating rate of 10 ◦C/min.
13C NMR spectra of polymers were recorded on a Bruker Avance-
500 spectrometer with 1,2-dichlorobenzene-d at 100 ◦C. Intrinsic
viscosities were determined in decahydronaphthalene at 135 ◦C
A hexane solution of n-butyllithium (2.50 mol/l, 1.9 ml, 4.8 mmol)
was added to a solution of (p-CH3-Ph)2C(C5H5)(C9H7) (0.9 g,
2.4 mmol) in Et2O (30 ml) at 0 ◦C. The resulting suspension was
stirred for 12 h at room temperature. After removal of solvent in
vacuo, the dilithium salt was obtained as a white solid. The solution
of dilithium salt in CH2Cl2 (50 ml) was added dropwise into the
suspension of ZrCl4 (0.56 g, 2.4 mmol) in CH2Cl2 (30 ml) at 0 ◦C. The
mixture was stirred at room temperature overnight. The solvent
was removed invacuo to yield a yellow solid which was redissolved
in n-hexane leaving a precipitate of LiCl. The filtrate was reduced
to 80 ml in vacuo and stored at −20 ◦C to give a yellow powder
(312 mg, yield 24.3%). 1H NMR (500 MHz, 298 K, CDCl3): δ 7.76
and viscosity average molecular weights of PEs were calculated
0.67
according to the equation:[21] [η] (dl/g) = 6.77 × 10−4 Mη
.
Synthesis of Fulvenes
3
3
4
(p-CH3-Ph)2C (C5H4)
(d, 2H, J = 8.1 Hz, Ph), 7.73 (dd, 1H, J = 8.0, J = 1.5 Hz, Ph),
7.65 (d, 1H, 3J = 8.7 Hz, Ind), 7.58 (dd, 1H, 3J = 8.0, 4J = 1.5 Hz,
Cyclopentadienyl sodium (27 ml, 1.56 mol/l, 42.1 mmol) in THF
was added to a solution of (p-CH3-Ph)2CO (7.1 g, 33.8 mmol) in
Et2O (30 ml). The solution was stirred at room temperature for
3 days. The reaction was slowly quenched by addition of water
(50 ml) at 0 ◦C; the organic layer was washed with water and dried
over MgSO4, filtered and concentrated in vacuo to produce red
viscous oil. The crude product was purified by chromatography
on silica gel with petroleum ether as eluant. A red crystal was
obtained (4.12 g, yield 47.1%).
3
Ph), 7.32 (quasi t, 1H, Ind), 7.20 (d, 1H, J = 8.3 Hz, Ph), 7.18 (d,
2H, 3J = 8.1 Hz, Ph), 7.14 (d, 1H, 3J = 8.3 Hz, Ph), 6.90 (d, 1H,
3J = 3.3 Hz, Ind), 6.78 (quasi t, 1H, Ind), 6.58–6.54 (m, 2H, Cp), 6.40
(d, 1H, 3J = 8.9 Hz, Ind), 6.26 (d, 1H, 3J = 3.3 Hz, Ind), 5.87 (dd, 1H,
3J = 5.4 Hz, 4J = 2.4 Hz, Cp), 5.72(dd, 1H, 3J = 5.4 Hz, 4J = 2.4 Hz,
Cp), 2.33 (s, 6H, CH3), 1.33-1.26 (m, 4H, hexane-CH2), 0.88 (t, 3H,
3J = 6.5 Hz, hexane-CH3); IR (KBr, cm−1): 3089m, 3023m, 2954s,
2921s, 2856m, 1608 w, 1509s, 1459s, 1409m, 1379m, 1234 w,
1211 w, 1189m, 1124m, 1051m, 1041m, 1021m, 1002 w, 867 w,
806s, 784s, 747s, 724m, 580s, 520m, 468s; MS (m/z): 532 (100, M+),
496 (24, M+− Cl), 441 [41, M+− (CH3-C6H4)], 372 (12, M+− ZrCl2).
Anal. calcd for C29H24ZrCl2·0.5C6H14: C, 66.53; H, 5.41. Found: C,
67.44, H, 5.40%.
(p-CH3-Ph)[p-C(CH3)3-Ph]C (C5H4)
This compound was obtained as a viscous oil by using a similar
procedure (4.24 g, yield 54.8%).
Synthesis of Complex {(p-CH3-Ph)[p-C(CH3)3-Ph]C(C5H4)(C9
H6)}ZrCl2 (1b)
Following the procedure described for complex 1a, 2.50 mol/l n-
butyllithium in hexane (1.8 ml, 4.50 mmol), (p-CH3-Ph)[p-C(CH3)3-
Ph]C(C5H5)(C9H7) (0.9 g, 2.24 mmol) and ZrCl4 (0.52 g, 2.24 mmol)
were used to give 1b as a yellow crystal (132 mg, yield 10.3%).
Synthesis of Preligands
(p-CH3-Ph)2C(C5H5)(C9H7)
Indenyl lithium (1.05 g, 12.9 mmol) in Et2O (20 ml) was added to a
solution of (p-CH3-Ph)2C (C5H4) (2.5 g, 12.9 mmol) in Et2O (20 ml)
at 0 ◦C. The mixture was warmed to room temperature and stirred
c
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Copyright ꢀ 2010 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2010, 24, 727–733

Bridged cyclopentadienyl indenyl (fluorenyl) zirconocene complexes
Two diastereomers existed. 1H NMR (500 MHz, 298 K, CDCl3): δ
7.79 (d, 0.8H, 3J = 8.1 Hz, Ph), 7.78 (d, 1.2H, 3J = 8.6 Hz, Ph), 7.76
M+−Cl),535[53,M+−(CH3-C6H4)],491{14,M+−[C(CH3)3-C6H4]},
491 (13, M+− ZrCl2). Anal. calcd for C36H32ZrCl2·C7H8: C, 71.84; H,
5.61. Found: C, 71.60; H, 5.92%.
3
4
(dd, 1H, J = 8.1 Hz, J = 2.1 Hz, Ph), 7.65 (d, 1H, 3J = 8.7 Hz,
3
4
Ind), 7.58 (dd, 1H, J = 8.1 Hz, J = 2.1 Hz, Ph), 7.40 (dd, 0.4H,
3J = 8.0, 4J = 2.1 Hz, Ph), 7.37 (d, 1.2H, 3J = 8.6 Hz, Ph), 7.34–7.30
(m, 1.4H, 1H-Ind, 0.4H-Ph), 7.23 (d, 3J = 8.0 Hz, 0.6H, Ph), 7.20
(d, 3J = 8.1 Hz, 0.8H, Ph), 7.14 (d, 3J = 8.0 Hz, 0.6H, Ph), 6.89 (m,
1H, Ind), 6.72–6.68 (m, 1H, Ind), 6.58–6.54 (m, 2H, Cp), 6.38 (dd,
Homopolymerization
A 100 ml autoclave, equipped with a magnetic stirrer, was
evacuated under vacuum, and then filled with ethylene. Toluene
was injected into the reactor. After equilibrating, the appropriate
volume of catalyst solution and cocatalyst were injected to start
the reaction. The ethylene pressure was kept constant during the
reaction. The polymerization was carried out for 30 min and then
quenched with 30 ml 3% HCl in ethanol. The collected polymer
was washed to neutral with ethanol and then dried overnight in a
vacuum oven at 60 ◦C to constant weight.
3
4
3
0.6H, J = 8.9 Hz, J = 0.7 Hz, Ind), 6.31 (dd, 0.4H, J = 8.9 Hz,
4J = 0.7 Hz, Ind), 6.29 (d, 0.6H, 3J = 3.5 Hz, Ind), 6.25 (d, 0.4H,
3J = 3.5 Hz, Ind), 5.89 (dd, 0.4H, 3J = 5.3 Hz, 4J = 2.8 Hz, Cp), 5.86
(dd, 0.6H, 3J = 5.3 Hz, 4J = 2.8 Hz, Cp), 5.74 (dd, 0.6H, 3J = 5.3 Hz,
4J = 2.8 Hz, Cp), 5.72 (dd, 0.4H, 3J = 5.3 Hz, 4J = 2.8 Hz, Cp), 2.35
(s, 1.8H, CH3), 2.34 (s, 1.2H, CH3), 1.2 (s, 9H, C(CH3)3); IR (KBr, cm−1):
3049m, 3028m, 2959s, 2867m, 1608 w, 1510s, 1461m, 1409m,
1362m, 1266m, 1130m, 1111m, 1078m, 1041s, 952 w, 866 w, 825s,
803s, 742s, 723m, 589s, 508s, 468s; MS (m/z): 574 (100, M+), 538
(11, M+− Cl), 483 [14, M+− (CH3-C6H4)], 442 {13, M+− [C(CH3)3-
C6H4]}. Anal. calcd for C32H30ZrCl2: C, 66.64; H, 5.24. Found: C,
66.97; H, 5.81%.
Copolymerization
All copolymerizations were carried out in a 100 ml autoclave
reactor. According to the conventional copolymerization, the
macromonomer was first added to the dry reactor, then toluene
and MAO were introduced. After equilibrating, the appropriate
catalystsolutionof2awasinjectedtoinitiatethecopolymerization.
For the tandem copolymerization, a conventional ethylene
polymerization was done using the toluene solution of complex
1a after the reactor was set with the toluene, MAO, temperature,
and ethylene pressure and stirred for 30 min. Then a solution of
complex 2a in toluene was added to start the copolymerization.
The simultaneous copolymerization was carried out by injecting
a mixture of 1a and 2a after the reactor was set. The polymer
product was then quenched with 30 ml of 3% HCl in ethanol.
The precipitated polymer was filtered, and extracted with hot
toluene for 24 h in a Soxhlet apparatus to separate the residue
macromonomer from high molecular weight component. Then
the macromonomer and polyethylene were dried overnight in a
vacuum oven at 60 ◦C.
Synthesis of Complex [(p-CH3-Ph)2C(C5H4)(C13H8)]ZrCl2 (2a)
To a solution of (p-CH3-Ph)2C(C5H5)(C13H9) (1.0g, 2.4 mmol)
in 30 ml of Et2O, 1.75 mol/l n-butyllithium in hexane (2.8 ml,
4.9 mmol) was added dropwise at −78 ◦C. After being stirred
overnight, ZrCl4 (0.55 g, 2.4 mmol) was added directly to the
solution as a solid. The resulting suspension was stirred for 8 h
at room temperature, and then filtered. The solid residue was
recrystallized in toluene to give complex 2a as a red crystal
(350 mg, yield 25.4%). 1H NMR (500 MHz, 298 K, CDCl3): δ 8.19
3
3
4
(d, 2H, J = 8.3 Hz, Flu), 7.80 (dd, 2H, J = 8.3 Hz, J = 1.9 Hz,
Ph), 7.77 (dd, 2H, 3J = 8.3 Hz, 4J = 1.9 Hz, Ph), 7.56 (quasi t, 2H,
Flu), 7.27–7.21 (m, 4H, 2H-toluene-Ph, 2H-Ph), 7.18–7.15 (m, 3H,
toluene-Ph), 7.13 (d, 2H, 3J = 8.3 Hz, Ph), 7.01 (quasi t, 2H, Flu), 6.45
(d, 2H, 3J = 8.3 Hz, Flu), 6.37 (quasi t, 2H, Cp), 5.79 (quasi t, 2H, Cp),
2.35 (s, 3H, toluene-CH3), 2.34 (s, 6H, CH3); IR (KBr, cm−1): 3112m,
3083m, 3024s, 2968 w, 2918s, 1590m, 1512m, 1504m, 1494m,
1462s, 1427s, 1326s, 1212m, 1126m, 1082m, 1042s, 1018m, 952 w,
896 w, 823s, 786m, 753s, 730s, 695m, 473s; MS (m/z): 582(63, M+),
546 (14, M+− Cl), 491 [100, M+− (CH3-C6H4)], 422 (14, M+− ZrCl2).
Anal. calcd for C33H26ZrCl2·C7H8: C, 70.98; H, 5.06. Found: C, 71.30;
H, 5.42%.
Results and Discussion
Synthesis of Zirconocene Complexes
The new ansa-cyclopentadienyl indenyl (or fluorenyl) zirconocene
complexes 1a–b and 2a–b were synthesized as illustrated
in Scheme 1. For comparison purposes, complexes 1c–d were
synthesized according to our previous paper.[19]
Synthesis of Complex {(p-CH3-Ph)[p-C(CH3)3-Ph]C(C5H4)(C13
H8)}ZrCl2 (2b)
The bridged cyclopentadienyl indenyl (or fluorenyl) preligand
compounds were synthesized analogously to the literature.[22,23]
Thesubstituteddiphenylfulveneswerepreparedbythereactionof
substitutedbenzophenonswithcyclopentadienylsodiuminether.
Then the indenyl (or fluorenyl) lithium salt was allowed to react
with the fulvenes. After hydrolysis, the preligand compounds were
precipitatedfromdiethyletheraswhitesolids.Thepreligandswere
treated with two equivalents of n-butyl lithium in diethyl ether
and reacted respectively with one equivalent of zirconium tetra-
chloride to afford zirconocene complexes 1a–b and 2a–b after
recrystallization from toluene. All the complexes were character-
ized by 1H NMR spectroscopy and elemental analysis methods.
Following the procedure described for 2a, (p-CH3-Ph)[p-C(CH3)3-
Ph]C(C5H5) (C13H9) (1.1 g, 2.36 mmol), 2.50 mol/l n-butyllithium
in hexane (1.9 ml, 4.75 mmol) and ZrCl4 (0.55 g, 2.36 mmol) were
used to give 2b as an orange crystal (226 mg, yield 15.3%). 1H NMR
(500 MHz, 298 K, CDCl3): δ 8.19(d, 2H, 3J = 8.4 Hz, 4J = 0.9 Hz, Flu),
7.80 (d, 2H, 3J = 8.3 Hz, Ph), 7.77 (dt, 2H, 3J = 8.3 Hz, 4J = 2.3 Hz,
Ph), 7.58–7.55 (m, 2H, Flu), 7.41 (dd, 1H, 3J = 8.3 Hz, 4J = 2.1 Hz,
Ph), 7.36 (dd, 1H, 3J = 8.3 Hz, 4J = 2.1 Hz, Ph), 7.27–7.22 (m, 2H,
toluene-Ph), 7.18–7.14 (m, 5H, 3H-toluene-Ph, 2H-Ph), 7.03–6.99
(m, 2H, Flu), 6.45 (d, 1H, 3J = 8.3 Hz, Flu), 6.37 (d, 1H, 3J = 8.3 Hz,
Flu), 6.35 (m, 2H, Cp), 5.82-5.78 (m, 2H, Cp), 2.36 (s, 3H, CH3), 2.35
(s, 3H, toluene-CH3), 1.32 (s, 9H, C(CH3)3); IR (KBr, cm−1): 3115m,
3031m,2959s,2865m,1595 w,1510s,1493m,1460s,1428s,1409m,
1328m, 1214m, 1128m, 1081m, 1043m, 1017m, 823s, 808m,
753s, 730s, 695m, 587s, 475s; MS (m/z): 626 (100, M+), 588 (14,
Synthesis of Polyethylene Macromonomer
Vinyl-terminated PE macromonomers were usually obtained with
low Al : Zr molar ratios.[18] In this work, an Al : Zr molar ratio of
c
Appl. Organometal. Chem. 2010, 24, 727–733
Copyright ꢀ 2010 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

W. Huang et al.
O
NaCp
Et2O
R
R'
R
R'
Zr
R
R
Cl
Cl
1a: R = R' = CH3
1b: R = CH3, R' = tBu
1c:* R = R' = tBu
C9H7Li
Et2O
nBuLi
ZrCl4
CH2Cl2
1d:* R = R' = OCH3
R'
R'
* Reported by Yang et al.[19]
R
R
Cl
nBuLi
C13H9Li
Et2O
Zr
ZrCl4
2a: R = R' = CH3
2b: R = CH3, R' = tBu
Cl
CH2Cl2
R'
R'
Scheme 1. Synthetic route of substituted ansa-zirconocene complexes.
Markel et al.[17] reported that Cp2ZrCl2 catalyzed ethylene
polymerizationtogetPEmacromonomerswithMn of12 933 g/mol
and 89.5% vinyl-terminated group in hexane, and with Mn of
25 154 g/mol and 91.4% vinyl-terminated group in toluene. In
comparison with that, complexes 1a–d afforded polyethylenes
with lower molecular weights. Complex 1b displayed higher
catalytic activities than Cp2ZrCl2, but with similar selectivity for
vinyl-terminated groups (Table 1: runs 4 and 11).
10000
5 bar
10 bar
8000
6000
M
From Table 1, it is clear that low catalyst concentration (run
4 vs 5) and high polymerization temperature (run 3 vs 4 and
run 8 vs 9) were favorable for producing vinyl-terminals and
macromonomers with low molecular weight. These results are
similar to other reported ansa-metallocene catalyst systems.
Rulhoff and Kaminsky[24] used [CMe2(Cp)2]ZrCl2 to produce PE
and also found that high polymerization temperature of 90 ◦C and
low ethylene concentration of 0.05 mol/l were of benefit to the
formation of low-molecular-weight macromonomers.
The influence of polymerization temperature on catalytic
activity differed for individual complexes. The newly synthesized
complexes 1a–b displayed higher catalytic activities than those of
complexes 1c–d, as shown in Fig. 2. Furthermore, polymerization
temperature for maximal catalytic activities of complexes 1a–c
decreased from 90 to 70 and 60 ◦C, indicating that the increase
in the steric bulk of the para-substituent led to a decrease in the
thermal stability of corresponding zirconocene complex.
End group analyses using 1H NMR[25] revealed that the majority
of the unsaturated oligomer chains obtained with individual ansa-
complexes 1a–d ended in a vinyl group, with the rest ending in
a vinylidene group, whereas Cp2ZrCl2/MAO system produced
macromonomers mainly with vinyl-terminal and a few with
vinyleneendgroups.Itispossiblethatthetwokindsofmetallocene
complexes experience different transition states (Scheme 2).[26]
4000
2000
0
1a
1b
1c
Complexes
Figure 1. Influence of ethylene pressure on molecular weight (polymer-
ization conditions: [Zr] = 50 µmol/l, Al : Zr = 500, 90 ◦C, 30 min, 25 ml
toluene).
500 was adopted for most of the polymerization runs. Upon the
activation of methylaluminoxane, all complexes are effective for
the polymerization of ethylene in toluene.
The molecular weight and high vinyl-terminal content
of macromonomer are particular important to synthesize
LCB polyethylene. From Fig. 1, in the presence of MAO
complexes 1a–c catalyzed ethylene polymerization to give
polyethylenes with molecular weight ranging from 3300
to 10 300 g/mol by changing ethylene pressure from 5 to
10 bar. The obtained polymers/oligomers possessed high
vinyl-terminal percentages of 80.7–94.9%, as depicted in
Table 1.
c
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Copyright ꢀ 2010 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2010, 24, 727–733

Bridged cyclopentadienyl indenyl (fluorenyl) zirconocene complexes
Table 1. Ethylene polymerization by complex 1a–d/MAO catalyst systema
Terminal selectivity (%)
c
[Catalyst]
(10−4 mol/l)
Mn,NMR
Run
Catalyst
Al : Zr
Pethylene (bar)
TP (◦C)
Activityb
(g/mol)
Vinyl
Vinylidene
Vinylene
1
1a
1a
0.5
0.5
0.5
0.5
1.0
0.5
0.5
0.5
0.5
0.5
0.5
500
500
500
500
500
200
2000
500
500
500
500
10
5
90
90
60
90
90
90
90
60
90
90
90
19.7
9.49
38.0
44.1
39.2
21.4
77.2
12.7
9.52
15.3
25.1
3 300
8 900
7 300
4 400
5 600
4 500
7 500
5 300
4 900
2 700
28 000
80.7
94.9
68.8
88.9
83.5
84.3
86.9
74.2
85.8
80.0
89.7
19.3
5.1
2
3
1b
10
10
10
10
10
10
10
10
10
31.2
11.1
16.5
15.7
13.1
25.8
14.2
20.0
4
1b
5
1b
6
1b
7
1b
8
1c
9
1c
10
11
1d
Cp2ZrCl2
10.3
a Polymerization runs were performed in 25 ml of toluene over 30 min.
b 105 g PE/(mol Zr h)
c Calculated by the data of 1H NMR assuming each polymer chain is olefin terminated.[25]
Table 2. Ethylene polymerization by complex 2a–b/MAO systema
50
40
30
20
10
0
Run
Catalyst
TP (◦C)
Yield (g)
Activityb
Mηc (g/mol)
12
13
14
15
2a
2a
2b
2b
60
90
60
90
0.330
0.965
0.096
0.871
5.28
15.44
1.54
300 000
232 000
161 000
109 000
1a
1b
1c
1d
13.94
a Polymerization runs were performed with [Zr] = 5.0 × 10−5 mol/l,
Al : Zr = 500, 10 bar of ethylene pressure in 25 ml of toluene over
30 min.
b 105 g PE/(mol Zr h)
c Intrinsic viscosity was determined in decahydronaphthalene at 135◦C
and viscosity average molecular weight was calculated using the
60
70
80
90
0.67
relation:[21] [η] = 6.77 × 10−4 Mη
.
T
(°C)
P
Figure 2. Influence of polymerization temperature on activity (polymer-
ization conditions: [Zr] = 50 µmol/l, Al : Zr = 500, 30 min, 10 bar ethylene,
25 ml toluene).
ization to provide PE macromonomers (Table 2). The 13C NMR
spectroscopic analyses indicate that these polymers are linear
polyethylenes with double bond end-groups.
Complex 2a showed higher catalytic activity than complex
2b but both complexes reached the highest activity at the
polymerization temperature of 90 ◦C (Fig. 3), which indicates that
The possible mechanism of forming a vinyl end group is β-H
transfer to the metal center as reported by Chien et al.[26] The
vinylene end group is formed by β-H transfer after isomerization
from propagating chains containing ethylene as a terminal unit
under the Cp2ZrCl2/MAO system.[27] In addition, as Seppa¨la¨ et al.
has reported,[11] the small number of vinylidene end groups
formed in the system of complexes 1a–d/MAO perhaps may
result from the insertion of macromonomer. This mechanism can
explain why high catalyst concentration is disadvantageous for
forming vinyl-terminated groups (run 4 vs 5).
the two complexes exhibit highly thermal stability. In comparison
[28]
with the analogous complex of [(p-tBu-Ph)2C(Cp)(Flu)]ZrCl2
,
complexes 2a and 2b displayed higher catalytic activities.
Obviously, increasing the steric bulk of substituted phenyl leads
to a fall of catalytic activity.
Copolymerization Attempt of Macromonomer with Ethylene
For ansa-zirconocene complexes 1a–d, the substituents on the
phenyl groups of bridge carbon had a significant effect on the
activity. Complex 1b with para-tBu and para-Me substituents
on phenyl groups exhibited the highest catalytic activity of
5.23 × 106 g PE/(mol Zr h), which is about 2.5 times more active
than complex 1a with two para-Me substituents on phenyl under
the same conditions.
Comparedwiththebridgedcyclopentadienylindenylzirconium
complexes, the bridged cyclopentadienyl fluorenyl zirconium
complexes (2a–b) could not catalyze ethylene homopolymer-
Kaminsky et al.[24] reported that ansa-cyclopentadienyl fluorenyl
zirconium complex [Ph2C(Cp)(Flu)]ZrCl2 can catalyze the copoly-
merization of PE macromonomer with propylene to give LCB
polypropylene. In this work, with the aim of synthesizing LCB PE,
complex2awaschosenasthecatalystforcopolymerizationdueto
itshaving ahighercatalyticactivityandaffording highermolecular
weight PE than those of complex 2b; complex 1a was selected to
synthesize polyethylene macromonomers. All results are listed in
Table 3.
c
Appl. Organometal. Chem. 2010, 24, 727–733
Copyright ꢀ 2010 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

W. Huang et al.
(1) Vinyl end group
H2
H
PE
PE
H
H
β-H transfer
C
C
Zr
Zr
C
PE
C
PE
Zr
H2
H2
(2) Vinylidene end group
R
H2
C
H2
C
H2
R
C
H2
H
C
R
H2
C
PE
H
C
R
PE
R
PE
β-H transfer
C
C
Zr
C
Zr
C
H
Zr
C
C
C
PE
PE
C
H2
H2
H2
H2 H2
Zr
H2 H2
R = polyethylene macromonomer
(3) Vinylene end group
H
H
H2
C
H
H2
C
PE
H2
C H
H2
C
H
C
PE
H
C C
H3C
H
β-H transfer
H
C
C
C
Zr
Zr
Zr CH
C H
PE
H2
Zr
PE
C
C
C
C
H2 H2
H2 H2
H
H2
H2C PE
Scheme 2. The β-H transfer reaction in ethylene polymerization.
16
Table 3. Different copolymerization methods with the complex 1a,
2a/MAO systema
60 °C
70 °C
80 °C
90 °C
Insoluble polymer
12
c
b
Mη
Ccat 1a
Ccat 2a
Yield mInsol
(g) (g)
Run (mmol/l) (mmol/l) Al : Zr
(×105) Tmd (◦C)
16e
17e
18f
0.5
0.5
0.5
0.5
0.5
0.5
500 1.137 0.455
250 0.782 0.447
1.74
1.05
133.9
133.0
8
4
0
500 2.111
0
a Polymerization conditions: ethylene pressure = 10 bar; TP = 90 ◦C, in
25 ml of toluene; 30 min.
b The insoluble polymer was obtained by extracting the bulk polymer
sample with hot toluene for 24 h in a Soxhlet apparatus
c Intrinsic viscosity was determined in decahydronaphthalene at 135◦C
and viscosity average molecular weight was calculated using the
2a
2b
equation:[21] [η] = 6.77 × 10−4 M0η.67
.
Complexes
d Melting point was determined by differential scanning calorimetry.
e Copolymerization with the ‘simultaneous’ method: 1a and 2a were
added simultaneously.
Figure 3. Influence of polymerization temperature on activity (polymer-
ization conditions: [Zr] = 50 µmol/l, Al : Zr = 500, 30 min, 10 bar ethylene,
25 ml toluene).
f Copolymerization with the ‘tandem’ method: after 1a/MAO had been
polymerized for 30 min, 2a/MAO was added.
The method of ‘copolymerization’ was attempted to produce
LCB PE first. The separated polyethylene macromonomer sample
from run 1 was copolymerized with ethylene using 2a/MAO
system, but the weight of recovered macromonomer was equal to
input and the molecular weight of the polymer fraction was similar
to that of run 13 (with the melting point of 134.2 ◦C), suggesting
thatmacromonomerdoesnotcopolymerizewithethylene.Further
studies show that the ‘tandem’ method just gives macromonomer
and does not produce any high molecular weight PE (run 18).
Finally, the method of ‘simultaneous’ polymerization was carried
out. In comparison with the homopolyethylene obtained with
2a/MAO (run 13), polymer samples obtained in runs 16 and
17 possessed rather low viscosity average molecular weight.
Meanwhile, the melting points of these polymers had almost
the same value. Sperber and Kaminsky reported[14] that the
melting point of the synthesized LCB PE decreases with increasing
the side-chain percentage. For that reason, LCB PE might not
have been produced in this work. The low molecular weights of
isolate polymers are probably a result of the interaction of mixed
complexes.
Conclusion
Four new bridged cyclopentadienyl indenyl (fluorenyl) zir-
conocenecomplexes,1a–band2a–b,werepreparedandshowed
moderate to high activities for ethylene homopolymerization. The
steric bulk of the bridging group displays an important influ-
ence on the catalytic activity and thermal stability. The bridged
c
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Copyright ꢀ 2010 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2010, 24, 727–733

Bridged cyclopentadienyl indenyl (fluorenyl) zirconocene complexes
cyclopentadienyl indenyl zirconocene complexes 1a–d can cat-
alyze ethylene homopolymerization to afford vinyl-terminated PE
macromonomer in high percentages (68.8–94.9%) with molecular
weights ranging from 2.7 × 103 to 10.3 × 103 g/mol. Polymer-
ization conditions such as ethylene pressure, polymerization
temperature and catalyst concentration dramatically influence
the vinyl selectivity and the molecular weight of obtained
macromonomer.
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Acknowledgments
This work is subsidized by the National Basic Research Program
of China (2005CB623801), National Natural Science Foundation
of China (NNSFC, 20604009, 20774027), the Program for New
Century Excellent Talents in University (for H. Ma, NCET-06-0413)
and the Key (Keygrant) Project of Chinese Ministry of Education
(no. 109064). All the financial support is gratefully acknowledged.
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c
Appl. Organometal. Chem. 2010, 24, 727–733
Copyright ꢀ 2010 John Wiley & Sons, Ltd.
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