A new titanium (IV) complex bearing phenoxyimine-fluorene ligand and its use as catalyst for ethylene homo- and copolymerization

Article abstract of DOI:10.1002/pola.23927

A new titanium (IV) complex bearing phenoxyimine- fluorene ligand was prepared and its behaviors in ethylene homo- and copolymerization with 1-hexene, 1-octene, and norbornene in the presence of modified methylaluminoxane (MMAO) were studied respectively. The effects of various polymerization conditions including polymerization temperature, ethylene pressure and the concentration of comonomer on the catalytic activities and properties of the resultant polymer were investigated. The broad molecular weight distribution of resulting polymer indicated that the multiple active species were formed during polymerization. Such complex showed good catalytic activities in ethylene homo- and copolymerizations and good capabilities of incorporating various comonomers into polyethylene backbone.

Full text of DOI:10.1002/pola.23927

A New Titanium (IV) Complex Bearing Phenoxyimine-Fluorene Ligand
and Its Use as Catalyst for Ethylene Homo- and Copolymerization
LIANG ZHONG, KUN CUI, PENG XIE, JIAN-ZHUANG CHEN, ZHI MA
Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences (SIOC-CAS), 345# Lingling Road, Shanghai 200032,
People’s Republic of China
Received 26 October 2009; accepted 7 January 2010
DOI: 10.1002/pola.23927
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: A new titanium (IV) complex bearing phenoxy-
imine-fluorene ligand was prepared and its behaviors in ethyl-
ene homo- and copolymerization with 1-hexene, 1-octene, and
norbornene in the presence of modified methylaluminoxane
(MMAO) were studied respectively. The effects of various poly-
merization conditions including polymerization temperature,
ethylene pressure and the concentration of comonomer on the
catalytic activities and properties of the resultant polymer were
investigated. The broad molecular weight distribution of result-
ing polymer indicated that the multiple active species were
formed during polymerization. Such complex showed good
catalytic activities in ethylene homo- and copolymerizations
and good capabilities of incorporating various comonomers
C
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into polyethylene backbone.
2010 Wiley Periodicals, Inc. J
Polym Sci Part A: Polym Chem 48: 1617–1621, 2010
KEYWORDS: catalysts; copolymerization; ethylene copolymeriza-
tion; ethylene homopolymerization; polyolefins; titanium
complex
INTRODUCTION In recent years, numerous efforts are being
directed toward developing new postmetallocene catalysts1–4
for olefin polymerization, as well as allowing access to previ-
ously inaccessible polymers.5–7 Of the successful postmetallo-
cene catalysts developed,1–3 the complexes possessing phe-
noxyimine ligands are one of the promising examples.8–14
Tang et al. have reported that titanium (IV) catalysts bearing
phenoxyimine ligand with side-arm, i.e., [OꢀNP], [OꢀNO], or
[OꢀNS] tridentate ligands, were robust and highly active for
ethylene homo- and copolymerization with linear a-olefin
and cycloolefin, and so forth.15–19 Qian and coworkers20–22
and Lancaster and coworkers23,24 reported the synthesis of
half-titanocenes containing phenoxyimine ligands and their
use as catalysts for olefin polymerization. Recently, Jin and
coworkers25 reported the synthesis of titanium complexes
with monocyclopentadienyl and tridentate aryloxide or
arylsulfide and their use as catalysts in ethylene
polymerization.
mine ligands demonstrated their capability of copolymerizing
ethylene and linear a-olefin and cycloolefin.
Considering the steric and electronic effect in the design of cat-
alysts, both the combination of fluorene and phenoxyimine
would be expected to lead a new catalyst for olefin homo- and
copolymerization. Herein, we describe the synthesis of titanium
(IV) complex bearing phenoxyimine-fluorene ligand and its cat-
alytic behaviors in ethylene homopolymerization and copoly-
merizations with 1-hexene, 1-octene, and norbornene.
EXPERIMENTAL
Materials
All manipulations of air-sensitive and/or water-sensitive
compounds were performed under a dry nitrogen atmos-
phere by means of standard Schlenk techniques. 9-Amino-
fluorene hydrochloride was purchased from Aldrich (98%).
Toluene and THF were refluxed and distilled from sodium/
benzophenone ketyl under dry nitrogen prior to use. 1-Hex-
ene (Acros, 97%) and 1-octene (Aldrich, 98%) was distilled
from sodium/benzophenone ketyl before use. Norbornene
(Aldrich, 99%) was dried over sodium, vacuum-transferred,
and degassed by repeated freeze-pump-thaw cycles. Modified
methylaluminoxane (MMAO) was purchased from Akzo
Chemical as a 1.6 M toluene solution. All the other commer-
cial chemicals were used as received. Polymerization-grade
ethylene was purified before use.
The ethylene copolymers such as linear low density poly-
ethylenes and cycloolefin copolymers are high add-value
products. So, more attention were paid on the design and de-
velopment of catalysts which can incorporate comonomer
such as 1-hexene, 1-octene, long-chain a-olefin, cyclopentene,
and norbornene, and so forth into the backbone of polyethyl-
ene in a wide range of comonomer content. The constrained
geometry (linked cyclopentadienyl (Cp) -amide) catalysts26
and the titanium or zirconium complexes bearing phenoxyi-
Correspondence to: Z. Ma (E-mail: mazhi728@mail.sioc.ac.cn)
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Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 48, 1617–1621 (2010) 2010 Wiley Periodicals, Inc.
A NEW TITANIUM (IV) COMPLEX, ZHONG ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
Preparation of Ligand and Complex
temperature and the residual ethylene was released slowly.
Then the reaction mixture was poured into a solution of
HCl/ethanol (10 v/v %). The polymer was isolated by filtra-
tion, washed several times with ethanol, and dried at 60 ꢁC
overnight under vacuum.
To a solution of 9-aminofluorene hydrochloride (1.50 g, 6.9
mmol) in anhydrous ethanol (10 mL), triethylamine (Et3N,
0.7 g, 6.9 mmol) was added. After stirring for 2 h at room
temperature and standing for 0.5 h, the supernatant was
transferred to a solution of 3,5-di-tert-butylsalicyaldehyde
(1.87 g, 8.0 mmol) and 0.2-mL acetic acid in anhydrous etha-
nol (10 mL). After refluxing with stirring for 24 h, the result-
ing mixture was cooled to room temperature to afford a yel-
low solid. The solid was recrystallized from cold ethanol to
give pale yellow crystals as the desired product phenoxyi-
mine-fluorene (PIF), yield 1.43 g (52%).
Characterizations and Measurements
The 1H NMR and 13C NMR spectra of the ligand and the
complex were recorded on a Varian XL-300 MHz spectrome-
ter at ambient temperature with CDCl3 as the solvent and
TMS as the internal standard. 13C NMR spectra of copoly-
mers were performed with PROBHD 5 mm QNP 1H/13, PUL-
PROG zgig, gated decoupling at 125 MHz NMR on a solution
of polymer (20–40 mg) in 1, 2-dichlorobenzene-d4 (0.4 mL)
at 110 ꢁC. The interpulse relaxation delay was 4 s, and the
pulse width was 8.5 ls (90ꢁ flip-angle). Time domain data
points (64 K) were acquired with a sweep width of 43,859
Hz. Mass spectra were obtained using a HP5959A spectrom-
eter. Elemental analysis was performed by the Analytical
Laboratory of SIOC-CAS.
1H NMR (300 MHz, CDCl3, d, ppm): 13.36 (s, 1H, AOH), 8.82
(s, 1H, CH¼¼N), 7.78–7.21 (m, 10H, Ar-H), 5.43 (s, 1H,
NACHA), 1.38 (s, 9H, ACH3), 1.33 (s, 9H, ACH3). 13C NMR
(75 MHz, CDCl3, d, ppm): 167.6, 158.1, 144.3, 140.8, 140.1,
136.8, 128.6, 127.5, 127.2, 126.1, 125.3, 120.1, 117.8, 72.8,
35.0, 34.1, 31.5, 29.3. EI-MS (m/z): 398 [MþHþ]. Anal. Calcd.
for C28H31NO: C, 84.59; H, 7.86; N, 3.52. Found: C, 84.84; H,
7.88, N, 3.28.
Mw, Mn, and Mw/Mn of polymers were determined using a
gel permeable chromatography (GPC) (Waters Alliance 2000
series) at 135 ꢁC (using polystyrene calibration, 1,2,4-tri-
chlorobenzene as the solvent at a flow rate of 1.0 mL
minꢀ1). Polymer melting temperatures (Tm) were deter-
mined on a differential scanning calorimetry (DSC) (Perkin-
Elmer Instruments Pyris 1) calibrated with indium, using a
heatiꢁng rate of 10 ꢁC/min in the temperature range of 50–
200 C. The heating cycle was performed twice, but only the
results of the second cycle were reported, since the former
was influenced by the mechanical and thermal history of the
samples.
To a stirred suspension of NaH (0.24 g, 10.0 mmol) in THF
(10 mL), a solution of ligand PIF (0.795 g, 2.0 mmol) in THF
(30 mL) was added dropwise for 10 min at ꢀ78 ꢁC. The
resulting mixture was allowed to warm to room temperature
and stirred for 2 h. The solvent was removed under reduced
pressure, and the residue was dissolved in toluene (80 mL).
To this yellow, clear solution, a solution of titanium tetra-
chlorides (0.34 g, 1.8 mmol) in toluene (10 mL) was added
dropwise over a period of 10 min at room temperature. The
resulting mixture was stirred overnight and filtered, and the
solid was washed with dry toluene (20 mL ꢂ 3). The com-
bined organic filtrates were concentrated under reduced
pressure and kept at ꢀ30 ꢁC overnight. The reddish crystal
was collected and dried in vacuo to give complex titanium
(IV) complex of phenoxyimine-fluorene (TPIF), yield 55%.
1H NMR (300 MHz, CDCl3, d, ppm): 8.12 (s, 1H, CHAN),
7.62–6.81 (m, 10H, Ar-H), 1.23 (s, 9H, ACH3), 1.12 (s, 9H,
ACH3). 13C NMR (75 MHz, CDCl3, d, ppm): 168.63, 160, 153,
144.5, 140, 136.7, 132.7, 130.5, 129, 128.8, 128.6, 128.2,
126.9, 125.7, 118.9 91.8, 35.54, 34.42, 29.9, 29.8. EI-MS (m/
z): 513 [Mþ]. Anal. Calcd. for C28H29Cl2NOTi: C, 65.40; H,
5.68, N, 2.72. Found: C, 64.92; H, 6.19; N, 2.47.
RESULTS AND DISCUSSION
Preparation and Characterization of Titanium Complex
TPIF
The synthetic route to ligand PIF and catalyst TPIF was
shown in Scheme 1.
The ligand PIF was prepared by shiff-base condensation
reaction of 3,5-di-tert-butylsalicyaldehyde with 9-aminofluor-
ene hydrochloride after removing HCl with Et3N. The chemi-
1
cal structure of PIF was characterized by H NMR, 13C NMR,
and elemental analysis. After the hydrogen abstract by NaH
Ethylene Homopolymerization and Copolymerization
with 1-Hexene, 1-Octene, and Norbornene
A 250-mL stainless-steel autoclave equipped with magnetic
stirrer was dried under vacuum at 50 ꢁC or 80 ꢁC in an oil
bath for 1 h, subsequently cooled to the desired reaction
temperature, and then purged with ethylene three times.
Freshly distilled toluene was transferred to the reactor via a
gas-tight syringe. Then the comonomer (in the case of the
copolymerization) and MMAO were added into the autoclave.
After stirring for 5 min, the catalyst solution in toluene was
introduced into the autoclave. The system was maintained at
desired ethylene pressure throughout the polymerization run
with a continuous feed of ethylene gas. After the polymeriza-
tion run for 0.5 h, the autoclave was cooled quickly to room
SCHEME 1 Synthesis of titanium (IV) complex bearing phenox-
yimine-fluorene ligand.
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ARTICLE
TABLE 1 Results of Ethylene Polymerization and Copolymerization with TPIF/MMAOa
b
[TPIF]
Comonomer
Yield
Tr (ꢁC) (g)
Mw
Comonomer
Productivityb (104)
Mw/Mn
Incorporationd (mol-%) Tm (ꢁC)
c
e
Entry (lmol) PE (MPa) (mL)
1f
2f
3f
4f
5e
6h
7h
8i
5
5
0.1
0.1
0.1
0.5
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
0
0
30
50
80
50
50
50
50
50
50
50
50
50
0.10
0.11
0.06
1.97
3.66
2.21
2.08
2.00
1.57
1.31
2.39
3.04
0.39
0.44
0.24
3.94
7.32
4.42
4.16
4.00
3.14
2.62
4.78
6.08
n.d.g
15.6
n.d.g
n.d.g
n.d.g
5.18
n.d.g
n.d.g
0
n.d.g
132.7
n.d.g
n.d.g
134.7
120.0
121.8
122.2
119.8
120.7
124.5
122.5
0
5
0
0
10
10
10
10
10
10
10
10
10
0
0
0
116.7 15.2
0
10
20
10
15
20
50
100
86.9
n.d.g
64.1
9.98
1.34
2.04
0.82
n.d.g
1.76
2.82
3.53
n.d.g
8.28
n.d.g
8.37
n.d.g
8.84
9i
n.d.g
10i
11j
12j
a
47.6
n.d.g
132.5
f
Polymerization conditions: cocatalyst is MMAO, Al/Ti ¼ 2000; total vol-
Ethylene homopolymerization.
g
h
i
ume of reaction mixture ¼ 200 mL; t ¼ 0.5 h.
n.d. ¼ Not determined.
b
105 g Polymerꢃmolꢀ1 Ti hꢀ1
.
Ethylene/1-hexene copolymerization.
Ethylene/1-octene copolymerization.
Ethylene/norbornene copolymerization.
c
Determined by GPC.
d
e
j
Determined by 13C NMR.
Determined by DSC.
from fluorene and phenoxyl, ligand PIF was coordinated
with TiCl4 to form the targeted complex TPIF. The data of
1H NMR, 13C NMR, mass spectra, and elemental analysis con-
firmed the chemical structure of TPIF. The further confirma-
tion of solid-state structure of TPIF crystal by single-crystal
X-Ray diffraction is under investigation.
1 and Mw/Mn ¼ 15.2, entry 5, Table 1) indicated that more
than one active species were formed possibly as a result of
ligand dissociation and/or reconstruction during polymeriza-
tions. The similar phenomenon was also found in some post-
metallocene catalyst systems23,27 and copolymerizations in
this work (entries 6, 8, 10, and 13, Table 1). The study of
possible active species of TPIF/MMAO is under investigation.
Ethylene Homopolymerization and Copolymerization
The results of ethylene polymerizations and copolymeriza-
tions with TPIF as catalyst in the presence of MMAO
(MMAO/TPIF molar ratio was fixed at 2000) are summar-
ized in Table 1.
To test the capability of such novel catalyst in ethylene
copolymerizations which resulting the commercial copolymer
materials, two linear a-olefins (1-hexene and 1-octene) and a
bulky cycloolefin (norbornene) were used in the copolymer-
izations with ethylene.
The homopolymerizations at 0.1 MPa ethylene pressure were
firstly carried out at different temperature using the same
MMAO/Ti molar ration of 2000. The results indicated that
1-Hexene was copolymerized with ethylene using TPIF/
MMAO at 50 C and 1.0 MPa of ethylene pressure. A little bit
ꢁ
of decrease in catalytic activity (4.42 ꢂ 105 g Polymer molꢀ1
Ti hꢀ1 [entry 6, Table 1] versus 4.16 ꢂ 105 g Polymer molꢀ1
Ti hꢀ1 [entry 7, Table 1]) was present when increasing the
amount of 1-hexene from 10 mL to 20 mL. Although the
melting temperatures of the resulting copolymers were close,
the 1-hexene incorporation increased from 1.34 mol % to
2.04 mol % (entry 6 and entry 7, Table 1).
the highest catalytic activity (4.4 ꢂ 104 g PE molꢀ1 Ti hꢀ1
,
entry 2, Table 1) of titanium complex TPIF was reached at
50 ꢁC while the lowest activity (2.4 ꢂ 104 g PE molꢀ1 Ti
h
ꢀ1, entry 3, Table 1) was obtained at 80 ꢁC. So 50 ꢁC was
used as the polymerization temperature for all the other eth-
ylene and homo- or copolymerizations. The influence of eth-
ylene pressure on the catalytic activity of TPIF was further
studied by ethylene homopolymerizations at 0.5 MPa and 1.0
MPa, respectively. The catalytic activity increased obviously
up to 3.94 and 7.32 ꢂ 105 g PE molꢀ1 Ti hꢀ1 respectively,
(entry 4 and entry 5, Table 1) with the increase of ethylene
pressure because the higher concentration of ethylene would
benefit the coordination of ethylene with active center fol-
lowed by ethylene insertion to titanium-carbon bond and
chain propagation. The resulting polyethylenes have the
melting temperatures around 133 ꢁC. The broad values of
Mw/Mn of resulting polymer (Mw/Mn ¼ 5.18, entry 2, Table
TPIF also showed good capability of ethylene copolymeriza-
tion with 1-octene. ꢁThree experiments were performed using
TPIF/MMAO at 50 C and 1.0 MPa of ethylene pressure with
different amount of 1-octene (entries 8–10, Table 1.). The
catalytic activity decreased from 4.00 ꢂ 105 g Polymer
molꢀ1 Ti hꢀ1 to 2.62 ꢂ 105 g Polymer molꢀ1 Ti hꢀ1 when
the amount of 1-octene increased from 10 to 20 mL. The
melting temperatures of copolymers around 120 ꢁC showed
the characteristic of linear low density polyethylene. The 1-
octene incorporation can reach to 1.76 mol % (entry 10,
A NEW TITANIUM (IV) COMPLEX, ZHONG ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
TABLE 2 Dyad-Triad Sequence Distribution of Ethylene Copolymersa
b
Comonomer
Entry
X (mol %)
nE
[EE]
[EX]
[EEE]
[XEE]
[EXE]
1-Hexene
1-Hexene
1-Octene
1-Octene
Norbornene
Norbornene
a
6
7
1.44
2.04
0.82
1.76
2.82
3.53
68.3
55.9
80.3
48.3
35.5
16.6
94.3
97.5
97.9
96.2
96.9
96.3
5.7
2.5
2.1
3.8
3.1
3.7
94.9
95.8
96.7
94.2
92.2
85.4
3.8
3.0
1.3
1.2
0.8
1.7
2.3
2.9
8
2.5
10
11
12
4.1
5.5
11.7
X and E stand for comonomer and ethylene, respectively.
b
nE is the average sequence lengths for ethylene unit.
Table 1) from 0.82 mol % (entry 8, Table 1) in the per-
formed copolymerizations.
The microstructure of ethylene/norbornene copolymer
(entry 12, Table 1) is relatively simple according to the 13C
NMR spectrum depicted in Figure 1. The carbon signals of
the obtained ethylene/norbornene copolymers can be
assigned similarly according to literatures32–35 although the
conditions for 13C NMR determination or the polymers’
microstructures were different from one another. The signals
between 56 and 45 ppm can be assigned to C2 and C3
methine carbons (Fig. 1) in alternating-isotactic, alternating-
syndiotactic and isolated units, respectively. The signal at 42
ppm arises from alternating-isotactic C1 and C4 carbons. The
C7 carbon of norbornene unit appears at around 33 ppm.
The resonances at 30 ppm can be assigned to the carbons of
alternating-isotactic ethylene, successive ethylene, C5 and C6,
respectively. The calculated ethylene average sequence
lengths32–35 in copolymer from the 13C NMR data are 35.5
(entry 11, Table 2) and 16.6 (entry 12, Table 2), respectively,
indicating that the length between two norbonenes is
shorten with the increase of norbonene incorporation from
2.82 mol % to 3.53 mol %.
The copolymerizations of ethylene and norbornene were also
carried out to know the catalytic behavior of TPIF in the
incorporation of bulky comonomer into polyethylene. In con-
trary to ethylene copolymerization with 1-hexene and 1-
octene, the increase in the amount of norbornene resulted in
the higher catalytic activity for ethylene/norbornene copoly-
merization (6.08 ꢂ 105 g Polymer molꢀ1 Ti hꢀ1 [entry 12,
Table 1] versus 4.78 ꢂ 105 g Polymer molꢀ1 Ti hꢀ1 [entry
11, Table 1]). Such phenomenon was interesting and would
be explained after a systematic study on the ethylene/nor-
bornene copolymerization via TPIF/MMAO. The norbornene
incorporations of 2.82 mol % and 3.53 mol % were obtained
by addition of 50 and 100 mL norbornene in copolymeriza-
tion, respectively. The melting temperature of ethylene/nor-
bornene copolymer is around 123 ꢁC which is 10 ꢁC lower
than that of polyethylene obtained in this work.
Microstructure of the Resulting Ethylene Copolymers
The 13C NMR spectrum of the resulting ethylene/1-hexene
CONCLUSIONS
ꢁ
copolymer was performed in 1,2-dichlorobenzene-d4 at 110 C.
A new titanium (IV) complex (TPIF) bearing phenoxyimine-
fluorene ligand was synthesized and used as catalyst for eth-
ylene homo- and copolymerization with 1-hexene, 1-octene
and norbornene in the presence of modified methylaluminox-
ane (MMAO), respectively. The resulting polyethylenes and
ethylene copolymers have high molecular weight and broad
The presence of butyl branches is confirmed by a peak at
23.4 ppm, corresponding to the methylene carbons next to the
methyl carbons of branches. The signals at 14.1 ppm 38.0 ppm
are supposed to the signals of methyl carbons and methine
carbons in butyl branches. The microstructures of ethylene/
1-hexene copolymers are studied by 13C NMR spectroscopy
(entry 6 and entry 7, Table 2). The absence of [HHH], [HHE],
and [HEH] triads suggests random copolymerization. The
comonomer average sequence lengths were calculated28,29
from the 13C-NMR data and showed that copolymers are
formed by about 56–68 ethylene units between 1-hexene ones.
The calculation29–31 result of 13C NMR spectrum showed
that one 1-octene was inserted after 80.3 ethylene units into
the polymer backbone with 0.82 mol % 1-octene incorpora-
tion (entry 8, Table 2). While the length of sequential ethyl-
ene between two 1-octenes decreases to 48.3 units when the
1-octene incorporation goes up to 1.76 mol % (entry 10, Ta-
ble 2). Also, the copolymerization of ethylene and 1-octene is
random because there are no [OOO], [OOE] and [OEO] triads
according to the analysis result of 13C-NMR spectrum
(entries 8 and 10, Table 2).
FIGURE 1 13C NMR spectrum of ethylene/norbornene copoly-
mer (entry 12 in Table 1).
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ARTICLE
16 Wang, C.; Sun, X. L.; Guo, Y. H.; Gao, Y.; Liu, B.; Ma, Z.;
Xia, W.; Shi, L. P.; Tang, Y. Macromol Rapid Commun 2005, 26,
1609–1614.
Mw/Mn. The complex TPIF showed good catalytic activities
in ethylene homo- and copolymerizations and capabilities of
comonomer incorporation. The microstructure of copolymer
could be adjusted by changing comonomer amount.
17 Gao, M.; Tang, Y.; Xie, M.; Qian, C.; Xie, Z. Organometallics
The project is sponsored by the Scientific Research Foundation
for the Returned Overseas Chinese Scholars (State Education
Ministry) and the Knowledge Innovation Program of the Chi-
nese Academy of Sciences. Dr. Z. Ma would like to thank Prof.
Yong Tang (SIOC-CAS) for his great help and financial support
in this work. The authors thank Miss Zheng Wang (SIOC-CAS)
for assistance with GPC measurement.
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