Copolymerization of ethylene with 1-hexene promoted by novel multi-chelated non-metallocene complexes with imine bridged imidazole ligand

Article abstract of DOI:10.1002/pola.23800

A series of novel bridged multi-chelated non-metallocene catalysts is synthesized by the treatment of N,N-imidazole, N,N-dimethylimidazole, and N,N-benzimidazole with n- BuLi, 2,6-dimethylaniline, and MCl₄ (M = Ti, Zr) in THF. These catalysts are used for copolymerization of ethylene with 1-hexene after activated by methylaluminoxane (MAO). The effects of polymerization temperature, Al/M molar ratio, and pressure of monomer on ethylene copolymerization behaviors are investigated in detail. These results reveal that these catalysts are favorable for copolymerization of ethylene with 1-hexene featured high catalytic activity and high comonomer incorporation. The copolymer is characterized by ¹³C NMR, WAXD, GPC, and DSC. The results confirm that the obtained copolymer features broad molecular weight distribution (MWD) about 33-35 and high 1-hexene incorporation up to 9.2 mol %, melting temperature of the copolymer depends on the content of 1-hexene incorporation within the copolymer chain and 1-hexene unit in the copolymer chain isolates by ethylene units. The homopolymer of ethylene has broader MWD with 42-46.

Full text of DOI:10.1002/pola.23800

Copolymerization of Ethylene with 1-Hexene Promoted by Novel
Multi-Chelated Non-Metallocene Complexes with Imine Bridged
Imidazole Ligand
LIFU MA,1 HONGLI WANG,1 JIANJUN YI,2 QIGU HUANG,1 KEJING GAO,3 WANTAI YANG1
1State Key Laboratory of Chemical Resource Engineering, Key Laboratory of Carbon Fiber and Functional Polymers, Ministry of
Education, The College of Material Science and Engineering, Beijing University of Chemical Technology, Beijing 100029
2Lab for Synthetic Resin Research Institution of Petrochemical Technology, China National Petroleum Corporation,
Beijing 100083, China
3Beijing Research Institute of Chemical Industry, Sinopec, Beijing 100013, China
Received 16 September 2009; accepted 26 October 2009
DOI: 10.1002/pola.23800
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: A series of novel bridged multi-chelated non-metal-
locene catalysts is synthesized by the treatment of N,N-imida-
zole, N,N-dimethylimidazole, and N,N-benzimidazole with n-
BuLi, 2,6-dimethylaniline, and MCl4 (M ¼ Ti, Zr) in THF. These
catalysts are used for copolymerization of ethylene with 1-hex-
ene after activated by methylaluminoxane (MAO). The effects of
polymerization temperature, Al/M molar ratio, and pressure of
monomer on ethylene copolymerization behaviors are investi-
gated in detail. These results reveal that these catalysts are
favorable for copolymerization of ethylene with 1-hexene fea-
tured high catalytic activity and high comonomer incorporation.
The copolymer is characterized by 13C NMR, WAXD, GPC, and
DSC. The results confirm that the obtained copolymer features
broad molecular weight distribution (MWD) about 33–35 and
high 1-hexene incorporation up to 9.2 mol %, melting tempera-
ture of the copolymer depends on the content of 1-hexene incor-
poration within the copolymer chain and 1-hexene unit in the
copolymer chain isolates by ethylene units. The homopolymer
C
V
of ethylene has broader MWD with 42–46. 2009 Wiley Periodi-
cals, Inc. J Polym Sci Part A: Polym Chem 48: 417–424, 2010
KEYWORDS: broad molecular weight distribution; copolyethy-
lene; copolymerization; metallocene catalysts; methylaluminox-
ane; non-metallocene complexes; Ziegler-Natta polymerization;
polyethylene
nature of the bridges. Petersen and coworkers20 reported
the synthesis of dinuclear metallocene titanium and zirco-
nium complexes bearing a bridged bis(cyclopentadienyl)
ligand. Huang and coworkers21 employed mono-bridged het-
ero-, or homo-binuclear complexes with different substituted
cyclopentadienyl ligands to promote the polymerization of
ethylene. Green and coworkers,22 Alt et al.,18 and Noh
et al.23 synthesized a lot of multinuclear metallocenes and
studied their behaviors in the polymerization of ethylene.
INTRODUCTION Mononuclear metallocene and constrained
geometry configuration (CGC) are excellent single site cata-
lyst for ethylene polymerization producing polymer ethylene
(PE) with excellent mechanical and optical properties.1–3
However, there still are some limitations in polymer process-
ing due to the narrow molecular weight distribution
(MWD).4 There are three approaches to control the MWD of
PE, using a series of reactors under different polymerization
conditions, employing different catalytic systems in one-
pot5,6 and designing metallocene precatalytic systems that
can produce multicatalytic species during the polymerization
process. In recent years, a variety of multinuclear bridged
metallocene complexes bearing polymethylene,7 polysiloxane
or sila,8–13 benzylene,14 p-bisbenzylene,15 polymethylene or
polysiloxane double bridges,16,17 and other ligands18,19 have
been prepared and used as catalysts in ethylene polymeriza-
tion due to their ability of MWD tailoring through the coop-
erative effect among metal centers, ligand structures and the
In our previous work,24 we reported a kind of novel bridged
non-metallocene catalysts for ethylene polymerization to pro-
ducing broad MWD and linear polyethylene. Herein, we syn-
thesize a series of novel bridged multi-chelated non-metallo-
cene catalysts bearing substituted or unsubstituted imidazole
ligands differed from the previous work. These catalysts ex-
hibit high catalytic activity for copolymerization of ethylene
with 1-hexene featured broad MWD and high comonomer
incorporation. The effects of performing conditions, such as
Correspondence to: Q. Huang, P.O. Box 82, Beisanhuan East Road No. 15, Beijing 100029, People’s Republic of China (E-mail: qgh96@yahoo.com.cn)
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Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 48, 417–424 (2010) 2009 Wiley Periodicals, Inc.
COPOLYMERIZATION OF ETHYLENE WITH 1-HEXENE, MA ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
SCHEME
1 The
synthesis
course of the non-metallocene
catalysts.
polymerization temperature, ratio of Al/M and monomer
pressure on the polymerization behaviors are investigated as
well.
Synthesis of Catalyst Precursors
Imidazole 5.00 g (0.0735 mol) was added in a 500-mL flask.
THF 100 mL was introduced into the flask and stirred it till
the imidazole totally dissolved. 29.4 mL (0.0735 mol) n-BuLi
was dripped into the solution at 5 ꢀC. The mixture was
EXPERIMENTAL
ꢀ
heated to 40 C and stirred for 6 h. Subsequently, the phos-
General Remarks
gene was introduced into the reactor and the mixture was
stirred for 2 h at 0 ꢀC. The ratio of imidazole to phosgene
was 2:1. The mixture was filtered and the filtrate was kept
All operations of air- and moisture-sensitive materials were
performed using the rigorous repellency of oxygen and mois-
ture in flamed Schlenk-type glassware on a dual manifold
Schlenk line under a nitrogen atmosphere. Toluene, benzene,
THF, and n-hexane were further purified by refluxing over
metal sodium under nitrogen for 48 h and distilled before
use. Toluene, benzene, n-hexane, THF, MCl4 (M ¼ Ti or Zr),
Methylaluminoxane (MAO) with 10% in toluene, and n-BuLi
with 2.5 M in n-hexane were purchased from Aldrich. The
ligands, 1, 2-R1, R2-N, N-imidazole (R1, R2 ¼ H, methyl), and
benzimidazole were purchased from Acros. 1-hexene (98%)
from Fluka was purified by distillation over CaH2 and stored
in a Schlenk tube containing 5A molecular sieves under
high-purity nitrogen.
ꢀ
in refrigerator at ꢁ15 C, 5.90 g white crystal N,N-carbonyl-
diimidazole (N,N-CDI) was obtained.
The imine bridged imidazole compound was synthesized as
following procedures. N,N-CDI (0.60 g) dissolved in 70 mL
anhydrous alcohol and 0.34 g of 2,6-dimethylaniline (2,6-
ꢀ
DMA) was introduced and stirred for 8 h at 60 C. The mix-
ture was filtered at room temperature and the filtrate was
crystallized at ꢁ10 ꢀC. Then the compound was recrystal-
lized from 50 mL petroleum ether at ꢁ10 ꢀC, from which
0.89
g 2,6-dimethylanilin-diimidazole (2,6-DMA-DI) was
obtained (Scheme 1), 1H NMR (DMSO): d ¼ 7.25 (s, 2H2),
418
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ARTICLE
TABLE 1 The Parameters for Cat.1 to Cat.6
Catalysts
Metals
Ti
Ligands
Microanalysis
1H NMR
Cat.1
2,6-DMA-DI
(C15N5H13TiCl2) (382): Calcd. C 44.05,
H 2.53, N 19.82; Found C 44.11, H
2.58, N 19.80
(DMSO): d ¼ 7.25 (s, 2H2), 7.18 (d, 2H4, 2H5,
J4,5 ¼ 3.6 Hz), 2.33 (s, 6H, dimethylaniline),
6.61 (d, 2H, dimethylaniline, J4,5 ¼ 3.0 Hz),
6.82 (m, 1H, dimethylaniline)
Cat.2
Cat.3
Zr
Ti
2,6-DMA-DI
(C15N5H13ZrCl2) (425): Calcd. C 42.27,
H 2.51, N 19.40; Found C 42.31, H
2.53, N 19.36
2,6-DMA-DI*
(C19N5H21TiCl2) (438): Calcd. C 52.05,
H 4.79, N 15.98; Found C 52.11, H
4.84, N 15.80
(DMSO):d ¼ 7.20 (s, 2H2), 3.90 (s, 12H,
methyl), 2.33 (s, 6H, dimethylaniline), 6.61
(d, 2H, dimethylaniline, J4,5 ¼ 3.0 Hz), 6.82
(m, 1H, dimethylaniline)
Cat.4
Cat.5
Zr
Ti
2,6-DMA-DI*
2,6-DMA-BDI
(C19N5H21ZrCl2) (481): Calcd. C 47.40,
H 4.37, N 14.55; Found C 47.45, H
4.42, N 14.59
(C23N5H17TiCl2) (482): Calcd. C 57.26,
H 3.53, N 14.52; Found C 57.31, H
3.58, N 14.57
(DMSO): d ¼ 8.25 (s, 2H2), 7.61 (d, 2H5, 2H8,
J5,6 ¼ 3.0 Hz), 7.18–7.21 (m, 2H6, 2H7), 2.33
(s, 6H, dimethylaniline), 6.61 (d, 2H, dime-
thylaniline, J4,5 ¼ 3.0 Hz), 6.82 (m, 1H,
dimethylaniline)
Cat.6
Zr
2,6-DMA-BDI
(C23N5H17ZrCl2) (525): Calcd. C 52.51,
H 3.24, N 13.33; Found C 52.56, H
3.29, N 13.38
2,6-DMA-DI: 2,6-dimethylanilin-diimidazole; 2,6-DMA-DI*: methyl substituted 2, 6-dimethylanilin-diimidazole; 2,6-DMA-DBI: 2,6-dimethylanilin-
dibenzimidazole.
7.18 (d, 2H4, 2H5, J4,5 ¼ 3.6 Hz), 2.33 (s, 6H, dimethylani-
line), 6.61 (d, 2H, dimethylaniline, J4,5 ¼ 3.0 Hz), 6.82 (m, H,
dimethylaniline); 2,6-DMA-DI (C15N5H15) (265): Calcd. C
66.38, H 3.85, N 29.81; Found C 66.40, H 3.87, N 29.79. The
ligand 2,6-DMA-DI was treated with n-BuLi in THF for 6 h at
40–50 ꢀC. 2,6-DMA-DI titanium complex (Cat.1) was pre-
pared by the treatment of ligand (0.60 g) with TiCl4 (0.31 g)
in 70 mL methylene chloride in the presence of 0.60 mL trie-
the reactor was heated to desired temperature by oil bath.
Under the desired ethylene pressure, the reaction system
was stirred for 60 min. Finally, the polymerization was ter-
minated with 10 wt % HCl in alcohol. The obtained copoly-
mer was filtered and washed with alcohol and water for
ꢀ
three times, then dried overnight in a vacuum oven at 80 C.
Characterization
13C NMR spectra of the copolymer samples were obtained
on an INOVA500 MHz (for hydrogen) instrument. The condi-
tions used for quantitative 13C NMR were 15 wt % samples
ꢀ
thylamine. The reaction lasted for 10 h at 40 C. The mixture
was filtrated and the solvent was removed. The residue was
dried by vacuum for 8 h at 40 ꢀC and 0.63 g Cat.1 was
obtained (Scheme 1). 2,6-DMA-DI and Cat. 1 were confirmed
by 1H NMR and microanalysis (Table 1). The ligand methyl
substituted 2,6-dimethylanilin-diimidazole (2,6-DMA-DI*)
derived from methyl substituted imidazole, 2,6- dimethylani-
lin-dibenzimidazole (2,6-DMA-DBI) from benzimidazole and
Cat.2–6 were synthesized according to the foregoing method.
Their 1H NMR and microanalysis data were compiled in
Table 1.
ꢀ
in ortho-dichlorobezene-d4 at 125 C. The average molecular
weight and MWD were measured by PL-GPC200 instrument
using standard polystyrene as reference and 1,2,4-trichloro-
benzene as solvent at 150 ꢀC. DSC thermograms were
recorded with a PA5000-DSC instrument at a rate of 10 K/
min. WAXD was recorded with an X-ray diffraction instru-
ment, using Ni films to sieve wave, using CuKa radiation (k
¼ 1.5405 ꢂ 10ꢁ10 m). WAXD intensities were recorded from
5 to 40ꢀ with a continuous scanning speed.
Polymerization Procedure
RESULTS AND DISCUSSION
All polymerizations were carried out in a 300 mL autoclave
with cooling and heating jacket, after purging all moisture
and oxygen by a high-vacuum pump, the reactor was sealed
under a nitrogen atmosphere. Freshly distilled toluene (80
mL), desired amount of non-metallocene catalyst and MAO
were added in order. The mixture was stirred for 15 min for
preactivation. After that, desired amount of 1-hexene was
added, ethylene was introduced up to desired pressure and
Copolymerization of Ethylene with 1-Hexene
The six newly synthesized non-metallocene catalysts (Cat.1
to Cat.6) are investigated for copolymerization of ethylene
with 1-hexene, using MAO as cocatalyst. These results are
compiled in Table 2.
From Table 2, it could be noticed that each of the six cata-
lysts exhibits high activity for homo and copolymerization of
COPOLYMERIZATION OF ETHYLENE WITH 1-HEXENE, MA ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
TABLE 2 The Copolymerization of Ethylene with 1-Hexene Mediated by Novel Non-Metallocene
Catalysts at 50 8C in 80 mL Toluene for 1 ha
Ab (ꢂ10ꢁ4
)
Mw (ꢂ10ꢁ6
)
Mw/Mn
1-hexd (mol %)
Tm
c
c
e
Run
Catalysts
1
Cat.1
Cat.2
Cat.3
Cat.4
Cat.5
Cat.6
Cat.1
Cat.2
Cat.3
Cat.4
Cat.5
Cat.6
1.46
1.88
2.42
3.21
2.86
3.32
0.61
0.84
1.64
2.01
1.86
2.12
1.11
1.21
1.12
1.28
1.17
1.27
1.06
1.12
1.08
1.18
1.12
1.17
33.2
33.6
34.5
35.2
33.2
33.9
42.0
43.0
43.5
46.0
43.2
43.9
4.6
6.7
5.1
9.2
4.3
6.8
_
118.1
_
2
3
112.2
_
4
5
122.8
_
6
7f
8f
9f
10f
11f
12f
a
128.8
129.0
129.2
129.7
130.8
129.8
_
_
_
_
_
M; Al/M, 200/1 in mol; 1-hexene, 4 mL; MAO as cocatalyst.
Catalytic activity, g PE/g M.h (M: Ti and Zr).
Measured by GPC, 1,2,4-trichlorobenzene as solvent, PS as reference.
The molar content of 1-hexene incorporation within copolymer chain.
Melting point, measured by DSC.
b
c
d
e
f
Homopolymerization of ethylene under the same conditions.
ethylene with 1-hexene. Non-metallocene titanium complexes
for copolymerization of ethylene with 1-hexene are less
effective than the zirconium analogues with the same ligand,
for example, the catalytic activity of 1.46 ꢂ 104 g PE/g Ti.h
for Cat.1 and 1.88 ꢂ 104 g PE/g Zr.h for Cat.2 (run 1, 2 in
Table 2). On the other hand, the complexes with methyl or
phenyl ring substituted ligands exhibit obviously higher cata-
lytic activity for homopolymerization of ethylene and copoly-
merization of ethylene with 1-hexene (runs 3–6 and runs 9–
12 in Table 2) than that with unsubstituted ones (runs 1–2
and runs 7–8 in Table 2). It exhibits that the replacement of
hydrogen by methyl or phenyl in this kind of catalysts is
more preferable for polymerization of ethylene and copoly-
merization of ethylene with 1-hexene. The results indicate
that the presence of methyl or phenyl ring moiety meets the
electronic coordination requirements for high activity; it
might be attributable to the electronic and steric effects of
methyl or phenyl ring substituent. Therefore, the overall cat-
alytic activity is enhanced. We can also notice from Table 2
that the positive ‘‘comonomer effective’’25,26 took place for all
these catalysts. The catalytic activity for copolymerization of
ethylene with 1-hexene was obviously higher than that of
the homopolymerization of ethylene catalyzed by the same
catalyst under the same conditions.
molecular weight of the obtained polymer by the catalysts
with methyl or phenyl substituted ligand and unsubstituted
ligand has the same change tendency. These results reveal
that the effects of ligand structure and transition metal on
weight average molecular weight of the polymer are nearly
unobservable. It also could be found from Table 2 that the
polyolefins promoted by these kinds of newly synthesized
non-metallocene catalysts feature outstanding broad Mw/Mn
ratio of 33.2–46.0. But the MWD of the copolymer is nar-
rower than that of the homopolymer. The result consists
with the report.27,28 The MWD of these copolymers aren’t
obviously relative to the content of 1-hexene incorporation.
From Table 2, one could notice that the melting point of
these homopolymers obtained is relatively low, ranged at
ꢀ
128.8–130.8 C (run 7–12 in Table 2). It is possible that the
lower molecular weight fraction of the polymer blends in the
higher molecular weight fraction as a lubricant in the poly-
mer, which impacts on the crystallization of polyethylene
and results in lower melting point of these polymers. How-
ever, the melting points of the copolymers considerably
depend on the content of 1-hexene incorporation. The higher
the content of 1-hexene incorporation, the lower the melting
points of the copolymers are. When the content of 1-hexene
incorporation is up to 6.7 mol % (run 2 in Table 2), the co-
polymer exhibits no endothermal phenomena on the DSC re-
cord. Wu and coworkers29 reports branched polyethylene
with branching degree of 62.5/1000C catalyzed by a-diimine
nickel (II) catalyst shows no melting endothermic character.
The thermal properties of the branched polyethylene depend
on the branching degree, distribution and structure. Li and
coworkers30 confirms that the copolyethylene with 1-hexene
incorporation content of 5.29 mol % promoted by bis(b-
enaminoketonato) titanium complexe/MAO obviously shows
It is shown in Table 2 that the weight average molecular
weight of the obtained polymers is relatively high, ranged in
1.06–1.28 ꢂ 106 g/mol. The high molecular weight mainly
attributes to the electron effect caused by the presence of
the bridged ligands with multi-nitrogen atoms, which results
in an increase of electron density at the metal center and
also at the b-carbon. Consequently, the b-hydrogen elimina-
tion and chain transfer to monomer reactions will be dimin-
ished during the polymerization process. Additionally, the
420
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ARTICLE
TABLE 3 Contents of Different Monomer Triads in 13C NMR of
TABLE 4 The Observed Signals Assignment for the Copolymer
the Copolymer (Run 4 in Table 2)
of Ethylene/1-Hexene (Run 4 in Table 2)
Mole
Chemical Shift
Peak
No.a
Carbon
Type
Monomer
Sequence
Fractions
Triad Distributions
Calculated
Found
[E]
[H]
9.2
[EHE]
8.8
[EHH]
0.47
[HHH]
0.18
[HEH]
0.36
[HEE]
16.35
[EEE]
73.84
1
aa
EHHE
40.18
38.13
35.85
35.00
34.90
34.54
34.13
33.47
30.94
30.47
29.98
29.51
29.34
29.18
27.28
23.36
14.12
40.35
38.26
36.03
35.13
35.04
34.65
34.25
34.03
32.17
30.50
30.20
29.66
29.56
29.44
27.36
22.84
14.06
90.8
2
CH
EHE
3
CH
HHE
4
ac
HHEHþEHEH
HHEEþHHE
EHEE
bad crystalline property with crystallinity of 8.9%.The crys-
tallinity of the copolymer considerably decreases with
increase of 1-hexene incorporation content.
5
adþþCH2(4)
6
adþ
The 13C NMR spectrum of the copolymer promoted by Cat.4
(run 4 in Table 3) is performed (Fig. 1). The chemical shift
assignments for the peaks are listed in Table 2.31 They are
obtained by comparing the observed ones to those calculated
with the empirical method of Grant and Paul.32
7
CH2(4)
CH
EHE
8
HHH
9
cc
cdþ
HEEH
10
11
12
13
14
15
16
17
a
HEEE
dþdþ
CH2(3)
CH2(3)
CH2(3)
bdþ
(EEE)n
EHE
As seen Table 3, the E–O copolymer contains the sequences
of EHHE, EHE, HHE, HHH, HEEH, HEE, EEE, and other
sequences. According to the 13C NMR spectrums of ethylene/
1-hexene copolymers obtained via these non-metallocene
catalysts, the signals content of the copolymer are high at d
38.31, 30.20, and 27.37 ppm, which are assigned to the
sequences of EHE, HEE, EEE. Moreover, these sequences
(HEH, HEEH) in which 1-hexene unit separated by one or
two ethylene units are appeared and the resonances ranging
from d 35.0 to 41.0 ppm and 34.03 ppm can confirm the
possibility of HH dyad and HHH triad sequences, indicating
the trend of 1-hexene toward forming relative long sequen-
ces in the ethylene/1-hexene copolymer. But, the signals of
long 1-hexene sequences are weak.
HHE
HHH
EHEE
CH2(2)
CH3
EHEþHHEþHHH
EHEþHHEþHHH
The peak numbers labeled in Figure 1.
in Table 4. As seen in Table 4, the ethylene/1-hexene copoly-
mer catalyzed by these non-metallocene catalysts mainly
contains the triad distributions of EHE, EEE, and HEE, but
these triad distribution concentrations (HHH, HHE, HEH) are
very low, indicating the trend of 1-hexene toward forming
isolated by one or more ethylene units and uniform sequen-
ces in the ethylene/1-hexene copolymer. The result of the
monomer reactivity ratio also confirms that the 1-hexene
units within the copolymer chain are mostly isolated by eth-
ylene units. Additionally, for the products of the comonomers
Based on the 13C NMR result, the microstructure of the
obtained copolymer is determined. Additionally, to determine
more precisely the microstructure of the analyzed copolymer,
the structural parameters, such as comonomer mole frac-
tions and the reactivity ratios of the comonomers are calcu-
lated using the Randall method.33 The results are presented
reactivity ratios, the values rE ¼ 13.51 for ethylene and rH
¼
0.059 for 1-hexene, with rEꢃrH ¼ 0.8. The value of rEꢃrH is
close to 1, reflecting a pronounced tendency for the random
distribution of the comonomers in the copolymer chain. Con-
sequently, unlike ethylene/1-hexene copolymers obtained by
metallocene catalysts, in which the copolymers with high 1-
octene content contained abundance of signals of HH dyad
and HHH triad sequences besides the alternating and iso-
lated H units. The ethylene/1-hexene copolymers obtained
by these non-metallocene catalysts are not only improved
the incorporation of 1-hexene into the polyethylene main
chain, but also optimized the uniformity for the whole co-
polymer molecular chain because of the copolymers mainly
containing the isolated and uniform H units.
Although the concentration of the comonomer in feed is the
same for these investigated catalysts (Cat.1 to Cat.6), the
results of the calculations show that the obtained copolymer
with these non-metallocene catalysts has a high contribution
of the comonomer in the product. Therefore, the
FIGURE 1 The 13C NMR spectrum of the copolymer promoted
by Cat.4 (run 4 in Table 2).
COPOLYMERIZATION OF ETHYLENE WITH 1-HEXENE, MA ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
TABLE 5 The Effect of Conditions on the Copolymerization of Ethylene with 1-Hexene Catalyzed with Cat.4 in 80 mL Toluene
for 1 ha
Pb (MPa)
h–fc (mL)
Ad (ꢂ10ꢁ4
)
Mw (ꢂ10ꢁ6
)
Mw/Mn
1-hexf (mol %)
Tm
e
e
g
Run
T (ꢀC)
Al/Zr (mol/mol)
13
4
40
50
60
50
50
50
50
50
5
200
200
200
150
250
200
200
200
200
200
200
0.5
0.5
0.5
0.5
0.5
0.1
0.25
0.3
0.5
0.5
0.5
4
4
4
4
4
4
4
4
1
2
6
2.42
3.21
2.61
2.01
2.56
1.48
1.77
2.45
2.85
2.98
3.01
e
1.06
1.28
1.02
0.98
1.03
0.92
0.94
1.03
1.06
1.03
0.96
31. 2
35.2
36.1
34.4
36.6
35.1
35.8
35.5
35.1
35.2
35.4
5.2
9.2
112.2
_
_
_
_
_
_
_
_
_
_
14
15
16
17
18
19
20
21
22
a
7.8
7.6
6.4
12.8
10.6
9.4
6.7
50
50
7.8
9.2
Polymerization conditions: the catalyst concentration, 1.0 ꢂ 10ꢁ4 M.
Pressure of the ethylene.
Determined by GPC.
b
c
f
The molar content of 1-hexene incorporation within copolymer chain.
Melting point determined by DSC.
g
The adding amount of 1-hexene in feed (mL).
Catalytic activity in g of PE/g of Zr.h.
d
incorporation of a-olefins into the polyethylene chain is
more effective in case of these non-metallocene catalysts
compared to the convenient Z–N catalyst.
polymerization temperature (40–60 ꢀC), at 50 ꢀC the peak
value of 1.28 ꢂ 106 g/mol is shown (run 4 in Table 5) and
the MWD of the obtained polymer becomes broader slightly
as increasing temperature (runs 13, 4, and 14 in Table 5).
But the 13C NMR spectrum of the homopolymer of ethylene
promoted by Cat.4 (run 10 in Table 2) exhibits only one sig-
nal at d 30.00 ppm, which attributes to the methylene of PE.
It is confirmed that the polymer features linear structure.
MAO is used as cocatalyst for alkylation, chain-transfer agent,
and deimpurifier. Trimethylaluminum (TMA) in MAO could
reduce oxidation state of Ti (IV) to Ti (III), Ti (IV) is favor-
able for a-olefin polymerization.35 From Table 4, it is found
that Cat.4 shows high activity at Al/Zr (mol/mol) ¼ 150–
250 (runs 15, 4, and 16 in Table 5) and exhibits a maximum
value of 3.21 ꢂ 104 g of PE/g of Zr/h at Al/Zr ¼ 200. How-
ever, the catalytic activity is obviously lower at higher or
lower ratio of Al/Zr, 2.1 ꢂ 104 g of PE/g of Zr.h at Al/Zr ¼
150 and 2.56 ꢂ 104 g of PE/g of Zr.h at Al/Zr ¼ 250 (runs
15 and 16 in Table 5), respectively. The weight average mo-
lecular weight of the obtained polymer increases from 9.8 ꢂ
105 to 12.8 ꢂ 105 g/mol with the increasing of the ratio of
Al/Zr from 150 to 200 (runs 15 and 4 in Table 5). When the
ratio of Al/Zr increases from 200 to 250, however, the value
of weight average molecular weight decreases slightly from
1.28 ꢂ 106 to 1.03 ꢂ 106 g/mol (runs 4 and 16 in Table 5).
In short, the catalytic activity of the non-metallocene com-
plexes and the molecular weight of the obtained polymer are
greatly depended upon the amount of MAO.
The WAXD pattern of the polyethylene catalyzed by these cat-
alysts (runs 1,3,5,7–12 in Table 2) shows three diffraction sig-
nals, which are at 2y ¼ 21.5, sharp, for (110) plane, 2h ¼ 23.9,
middle, for (200) plane, and 2y ¼ 31.5, weak, for (020) plane,
respectively. These signals attribute to the character of PE
crystal.34 But for those copolymers with high 1-hexene incor-
poration (runs 2, 4, 6 in Table 2), no sharp signal, just weak
and broad peaks are observed on their WAXD diffractograms.
Meanwhile, high catalytic activity of these six catalysts for
ethylene polymerization is exhibited even at fairly low Al/M
ratio of 200, which results in lower cost for industrial
production.
Comparing with other catalysts used in this work (in Table 2),
Cat.4 is preferable for ethylene polymerization. So the effects
of polymerization conditions, such as temperature, Al/Zr ratio,
and pressure of monomer on ethylene polymerization are
investigated in detail. The results are listed in Table 5.
Moreover, higher pressure of monomer leads to higher cata-
lytic activity and molecular weight (runs 17, 18, 19, and 4 in
Table 5). From Table 5, it could be also noticed that the
MWD of the obtained polyethylene is obviously broad but
changes slightly even at different polymerization conditions.
From Table 5 we could notice that the catalytic activity
increases with the increasing of temperature within the
ꢀ
range of 40–50 C (run 13 and run 4 in Table 5) and shows
a maximum value of 3.21 ꢂ 104 g of PE/g of Zr.h at 50 ꢀC.
However, it decreases to 2.61 ꢂ 104 g of PE/g of Zr.h at 60
ꢀC (run 14 in Table 5) because of both the lower monomer
concentration and the faster deactivation rate of the active
species at relatively high temperature. The weight average
molecular weight of the polymer is obviously relative to the
Broad Molecular Weight Distribution
Table 2 shows that the polyolefins catalyzed by these non-
metallocene catalysts have broader MWD, for example, the
polyethylene and the copolymer of ethylene with 1-hexene
422
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ARTICLE
obviously broader Mw/Mn ratio of 46.0 is obtained and the
processability of the polymer obtained might be improved.
CONCLUSIONS
The bridged multi-chelated non-metallocene catalysts consist-
ing of heterocyclic ligands (Cat.1 to Cat.6) exhibit high cata-
lytic activity for ethylene polymerization and copolymeriza-
tion of ethylene with 1-hexene. Zirconium complexes are
more favorable for ethylene polymerization and copolymer-
ization of ethylene with 1-hexene. Polymerization conditions,
such as temperature, pressure of ethylene and Al/M ratio
show considerable effects on the catalytic activity and weight
average of molecular weight of the obtained polymers. The
13C NMR results confirm that the homopolymer of ethylene
catalyzed by these bridged non-metallocene catalysts show
linear structure and the copolymers have high content of 1-
hexene incorporation within the copolymer chain. 1-hexene
units within the copolymer chain are isolated by one, two or
more units of ethylene. Block distribution of ethylene units
are dominant in the copolymer chain. The DSC results show
that the melting points of the obtained polymer are depended
on the content of 1-hexene incorporation, obviously decreased
with increasing of the content of 1-hexene incorporation. The
GPC results confirm that the obtained polymers feature rela-
tively high molecular weight and dramatic broad Mw/Mn ratio
of 42 to 46 for polyethylene, and 33 to 35.2 for copolymer of
ethylene with 1-hexene. The MWD of the obtained polymers
are independent of the polymerization conditions. The reac-
tivity ratio, rE is larger than rH. The result reveals that 1-hex-
ene unit within the copolymer chain is isolated by ethylene
units, but long sequence of ethylene units exists.
FIGURE 2 The GPC plots of the obtained polyolefins (a) run 10,
(b) run 4, and (c) run 3 (Table 2).
catalyzed by cat.4 (runs 10 and 4 in Table 2) exhibit broader
Mw/Mn ratio of 46.0 and 35.2, respectively, than the MWD of
the polymers promoted by traditional Z-N catalyst and met-
allocene complexes. Cat.3 having the same ligand as cat.4 for
the copolymerization of ethylene with 1-hexene produces the
copolymer with broader Mw/Mn ratio of 34.5. The GPC plots
of the obtained polymers are shown in Figure 2.
The value of Mw/Mn is relative large, indicating the forma-
tion of more than one active species and/or the changing na-
ture of the active species are taken place during the course
of the polymerization. This phenomenon is operative strong
evidence for the presence of different active species. It has
recently been provided by Barabanov et al.,36 who used 14CO
radiotagging to determine the number of active species and
propagation rate constant in homogeneous polymerization. It
is hard, at present, to specify the real active species in the
catalytic system. However, it is likely that the active species
would be [2,6-DMA-DITi(Zr)Me2]þ, [2,6-DMA-DI*Ti(Zr)Me2]þ,
and [2,6- DMA-DBITi(Zr)Me2]þ because [Cp*Ti(Zr)Me2]þ has
been proposed as an active polymerization catalyst37,38 and
the deactivation of [2,6-DMA-DITi(Zr)Me2]þ would take place
by the reduction of the central metal such as reductive elimi-
nation of the two alkyl groups.
Financial support for this work from the National Natural
Science Foundation of China (Grant No. 20574003), Major
Project for Polymer Chemistry, Physics Subject Construction
from Beijing Municipal Education Commission (BNEC)
(XK100100540, XK100100640) and IRT0706.
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