Fluorinated bis(phenoxy-imine)titanium complexes with methylaluminoxane for the synthesis of ultra high molecular weight polyethylene

Article abstract of DOI:10.1016/j.polymer.2013.04.060

Three fluorinated bis(phenoxy-imine)titanium complexes bearing ortho-halide substituents on the phenoxy rings [Cl (1), Br (2), I (3)] were synthesized, characterized and evaluated as precatalysts for the polymerization of ethylene in conjunction with methylaluminoxane (MAO) under atmospheric pressure. These C₂-symmetric catalysts exhibit high activity toward ethylene polymerization and produce ultra high molecular weight polyethylene (UHMWPE) (M_W > 3,000,000). The living polymerization was presented as evidenced by the narrow molecular weight distribution. The living nature of these catalysts is attributed to the interaction of a fluorine atom adjacent to the imine nitrogen and a β-hydrogen of a polymer chain resulting in the suppression of β-hydrogen transfer. The highest activity at 11.65 kg PE/mmol cat h was observed for the polymerization using complex 2. In comparison with complex 1, the more bulky bromo substituents can induce an effective ion-pair separation between the cationic active species and an anionic cocatalyst yielding a higher polymerization rate. However, in case of complex 3 with iodo substituents, the enhancement of the steric congestion at the metal center results in the decreased polymerization activity.

Full text of DOI:10.1016/j.polymer.2013.04.060

Polymer 54 (2013) 3217e3222
Contents lists available at SciVerse ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
Fluorinated bis(phenoxy-imine)titanium complexes with
methylaluminoxane for the synthesis of ultra high molecular weight
polyethylene
Supaporn Khaubunsongserm a, Pimpa Hormnirun b, Tanin Nanok b, Bunjerd Jongsomjit a,
,
Piyasan Praserthdam a
*
a Center of Excellence on Catalysis and Catalytic Reaction Engineering, Department of Chemical Engineering, Faculty of Engineering,
Chulalongkorn University, Bangkok 10330, Thailand
b Department of Chemistry, Faculty of Science, Kasetsart University, Bangkok 10900, Thailand
a r t i c l e i n f o
a b s t r a c t
Article history:
Three fluorinated bis(phenoxy-imine)titanium complexes bearing ortho-halide substituents on the
phenoxy rings [Cl (1), Br (2), I (3)] were synthesized, characterized and evaluated as precatalysts for the
polymerization of ethylene in conjunction with methylaluminoxane (MAO) under atmospheric pressure.
These C2-symmetric catalysts exhibit high activity toward ethylene polymerization and produce ultra
high molecular weight polyethylene (UHMWPE) (MW > 3,000,000). The living polymerization was
presented as evidenced by the narrow molecular weight distribution. The living nature of these catalysts
Received 21 February 2013
Received in revised form
23 April 2013
Accepted 26 April 2013
Available online 3 May 2013
is attributed to the interaction of a fluorine atom adjacent to the imine nitrogen and a
b-hydrogen of a
Keywords:
polymer chain resulting in the suppression of -hydrogen transfer. The highest activity at 11.65 kg
b
Ethylene polymerization
Ultra high molecular weight polyethylene
FI catalysts
PE/mmol cat h was observed for the polymerization using complex 2. In comparison with complex 1, the
more bulky bromo substituents can induce an effective ion-pair separation between the cationic active
species and an anionic cocatalyst yielding a higher polymerization rate. However, in case of complex 3
with iodo substituents, the enhancement of the steric congestion at the metal center results in the
decreased polymerization activity.
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
by Lewis acids, and increases effective ion-pair separation between
the active cationic species and an anionic cocatalyst. This provides
Group 4 metal non-metallocenes are among the highly active
homogenous catalysts reported to date [1e8]. The development of
this group of catalysts has shown a remarkable progress both in
academic and in industrial fields. Significant advances in ligand
design lead to the discovery of new active catalysts that can pro-
duce specialty polymeric materials otherwise unavailable [9e13].
Bis(phenoxy-imine) early transition metal complexes (known as
FI catalysts), discovered by scientists at Mitsui Chemicals, are one of
the groups of post-metallocene catalysts exhibiting high catalytic
more space for polymerization as well as increases the electrophi-
licity of the active species, yielding higher polymerization activity
[24]. The presence of the small substituent on the imine carbon is
reasoned for maintaining the sufficient space for polymerization
[24]. Recently, a new series of FI catalyst containing fluorine atom(s)
in the ligand framework (fluorinated FI catalyst) was discovered to
be remarkable catalysts for living ethylene and propylene poly-
merization [25e28]. The living polymerization was achieved by the
presence of the attractive interaction between the ortho-F and the
performance for
a-olefin polymerization [14e19]. The activity and
b-hydrogen of a growing polymer chain. This interaction can reduce
stereoselectivity of the catalyst systems are found to be significantly
affected by the structure of ligands. In general, the catalysts with a
sterically encumbered substituent on the phenoxy rings and a small
substituent on the imine carbon display very high catalytic activity
[20e23]. The large substituent ortho to the phenoxy oxygen provides
steric protection to the phenoxy oxygen against electrophilic attack
the rate of chain transfer to the aluminum cocatalyst, resulting
in living polymerization. Very recently, Weiser and coworkers re-
ported the synthesis and characterization of a fluorinated FIeTi
catalyst bearing 3,5-diiodosubstituents on the phenoxy rings and
2,6-difluoro moiety [29e31]. This catalyst is highly active catalyst in
living polymerization of ethylene and propylene. Ultra high molec-
ular weight polyethylene (UHMWPE), atactic polypropylene, and
block copolymer of ethylene and propylene were successfully
synthesized.
* Corresponding author. Tel.: þ66 2 218 6869; fax: þ66 2 218 6868.
E-mail address: piyasan.p@chula.ac.th (P. Praserthdam).
0032-3861/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.polymer.2013.04.060

3218
S. Khaubunsongserm et al. / Polymer 54 (2013) 3217e3222
Herein, we report the synthesis of the related fluorinated
2.2.2. Synthesis of N-(3,5-dibromosalicylidene)-20,60-difluroaniline
bis(phenoxy-imine)titanium complexes bearing halogen sub-
stituents on the phenoxy rings [Cl (1); Br (2); I (3)]. The effects of
ortho-phenoxyhalogen substituents on the polymerization activ-
ities of ethylene polymerization are investigated.
(L2H)
The same procedure was used as that described for L1H, starting
from 3,5-dibromosalicylaldehyde (2.00 g, 7.14 mmol) and 2,6-
difluoroaniline (0.92 g, 7.14 mmol), yielding orange crystals of
L2H in 91% yield (2.53 g). 1H NMR data (500.13 MHz, CDCl3, 298 K):
2. Materials ad methods
d
13.91 (s, 1H, OH), 8.34 (s, 1H, NCH), 7.63 (d, 4JHH ¼ 2.4, 1H, salicyl-
4
H), 7.48 (d, JHH ¼ 2.4, 1H, salicyl-H), 7.24e7.16 (m, 1H, aniline-H),
2.1. General procedures and materials
7.05e6.98 (m, 2H, aniline-H). 13C NMR data (125.77 MHz, CDCl3,
298 K):
d 166.30 (HCN), 157.61 (d, CF) 157.55 (COH), 155.60 (d, CF),
All manipulations with air- and/or water-sensitive compounds
were carried out under a dried nitrogen atmosphere using standard
Schlenk and cannula techniques in oven dried glassware or in a
glove box. Dried solvents (tetrahydrofuran (THF), toluene, hexane
and dichloromethane) used for the complex synthesis were puri-
fied by MBRAUN solvent purification system (MB-SPS-800-Auto).
All solvents were degassed prior to use unless stated otherwise.
139.07 (salicyl-CH), 134.23 (salicyl-CH), 128.17 (t, aniline-CN),
124.09 (t, CCHN),121.19 (aniline-CH),112.67 (dd, aniline-CH),112.55
(CBr), 110.80 (CBr). Elemental analysis for C13H7Br2F2NO: C, 39.93;
H, 1.80; N, 3.58%. Found C, 40.33; H, 1.90; N, 3.60%.
2.2.3. Synthesis of N-(3,5-diiodosalicylidene)-20,60-difluoroaniline
(L3H)
The same procedure was used as that described for L1H, starting
from 3,5-diiodosalicylaldehyde (1.00 g, 2.67 mmol) and 2,6-
difluoroaniline (0.34 g, 2.67 mmol), yielding orange crystals of
ꢀ
NMR solvents were dried over 4 A molecular sieves and degassed
prior to use. A 1.6 M solution of n-butyl lithium in hexanes (Aldrich)
was used without purification. 3,5-dichlorosalicylaldehyde (99%),
3,5-dibromosalicylaldehyde (98%), 3,5-diiodosalicylaldehyde (97%),
2,6-difluoroaniline (ꢀ97%), titanium tetrachloride (ꢀ99.995%),
methylaluminoxane (MAO) (10 wt.% in toluene) were purchased
from Aldrich and used as received. Ethylene was obtained from
Praxair Technology Inc. All other chemicals are commercially
available and were used as received unless otherwise stated.
1H and 13C nuclear magnetic resonance (NMR) spectra were
recorded on a Bruker Advance 500 MHz spectrometer. 1H and 13C
NMR spectra were referenced internally to the residual protio im-
L3H in 65% yield (0.84 g). 1H NMR data (500.13 MHz, CDCl3, 298 K):
4
d
8.75 (s, 1H, NCH), 8.13 (d, JHH ¼ 2.1, 1H, salicyl-H), 7.67
(d, 4JHH ¼ 2.1, 1H, salicyl-H), 7.24e7.16 (m, 1H, aniline-H), 7.06e6.96
(m, 2H, aniline-H). 13C NMR data (125.77 MHz, CDCl3, 298 K):
d
166.12 (t, HCN), 160.47 (salicyl-COH), 157.59 (d, CF), 155.57 (d, CF),
150.13 (salicyl-CH),141.29 (salicyl-CH),128.07 (t, aniline-CN),124.16
(t, CCHN), 121.17 (aniline-CH), 112.66 (dd, aniline-CH), 87.70 (CI),
80.46 (CI). Elemental analysis for C13H7I2F2NO: C, 32.19; H, 1.45; N,
2.89%. Found C, 32.18; H, 1.71; N, 3.01%.
purity peaks in the deuterated solvent (CDCl3: 1H, 7.26; 13C,
d d 77.0).
The following abbreviations have been used for multiplicities: s
(singlet); d (doublet); t (triplet); q (quartet); sept (septet); dd
(doubletof doublets); dt (doubletof triplets); td (triplet of doublets);
m (unresolved multiplet); br (board). Elemental analysis data (C, H,
N) were obtained from a LECO TruSpecÒ Micro Elemental Analyser.
Gel permeation chromatography (GPC) measurements were con-
ducted on a Polymer Laboratories PL-GPC-220 instrument equipped
2.3. Complex syntheses
2.3.1. Synthesis of bis[N-(3,5-dichlorosalicylidene)-20,60-
difluroanilinato]titanium(IV) dichloride (1)
To a stirred solution of L1H (5.00 g, 16.60 mmol) in THF (40 mL)
was slowly added n-butyl lithium (1.6 M solution in hexanes,
10.34 mL, 16.60 mmol) at 0 ꢃC. The solution was allowed to warm to
room temperature and stirred for 1 h. Then, to this resulting solu-
tion, a solution of TiCl4 (1.0 M solution in DCM, 8.27 mL, 8.27 mmol)
was added dropwise at 0 ꢃC. The reaction mixture was allowed to
warm to room temperature and stirred for 24 h. After removal of
the solvent, the product was extracted with DCM.
with PLgel10
m
m MIXED-B 300 ꢁ 7.5 mm columns, and 1,2,4-
trichlorobenzene was used as the eluent (flow rate: 1 mL minꢂ1 at
160 ꢃC). The number averaged molecular weights (Mn) and poly-
dispersity indice (Mw/Mn) were calibrated against polystyrene (PS)
standards. Transition melting temperatures (Tm) of the polymers
were determined by DSC with a Netzsch DSC 204 F1Phoe-
nixÒdifferential scanning calorimeter, measured upon reheating the
polymer sample to 200 ꢃC at a heating rate of 10 ꢃC/min.
LiCl was then isolated by filtration, followed by removal of the
volatile gave a dark red solid. The solid was recrystallized from a
mixture of toluene and hexane (4:1) at ꢂ20 ꢃC to give complex 1 as
orange crystals in 55% yield (3.27 g). 1H NMR data (500.13 MHz,
2.2. Ligand syntheses
CDCl3, 298 K):
d
8.20 (s, 2H, NCH), 7.49 (d, 4JHH ¼ 2.5, 2H, salicyl-H),
4
7.30 (d, JHH ¼ 2.5, 2H, salicyl-H), 7.28e7.00 (m, 4H, aniline-H),
2.2.1. Synthesis of N-(3,5-dichlorosalicylidene)-20,60-difluoroaniline
(L1H)
6.54e6.47 (m, 2H, aniline-H). 13C NMR data (125.77 MHz, CDCl3,
298 K):
d 170.3 (NCH), 136.1 (salicyl-CH), 132.1 (salicyl-CH), 129.0,
To a stirred solution of 3,5-dichlorosalicylaldehyde (2.00 g,
10.47 mmol) in ethanol (20 mL) was slowly added 2,6-
difluoroaniline (1.37 g, 10.47 mmol) at room temperature in the
presence of trace amount of formic acid as a catalyst. The reaction
mixture was stirred at room temperature for 3 h. Orange crystals
were formed and then filtered. The product was obtained in 64%
128.2, 125.3, 113.0, 112.8.
Elemental analysis for C26H12Cl6F4N2O2Ti: C, 43.31; H, 1.68; N,
3.89%. Found C, 48.11; H, 2.60; N, 3.57%.
2.3.2. Synthesis of bis[N-(3,5-dibromosalicylidene)-20,60-
difluroanilinato]titanium(IV) dichloride (2)
yield (2.74 g). 1H NMR data (500.13 MHz, CDCl3, 298 K):
d
13.77
The same procedure was used as that described for 1, starting
from L2H (3.00 g, 7.67 mmol), n-butyl lithium (1.6 M solution in
hexanes, 4.79 mL, 7.67 mmol), and TiCl4 (1.0 M solution in DCM,
3.84 mL, 3.84 mmol), yielding orange crystals of 2 in 48% yield
(s, 1H, OH), 8.87 (s, 1H, NCH), 7.48 (d, 4JHH ¼ 2.5, 1H, salicyl-H), 7.31
(d, 4JHH ¼ 2.5, 1H, salicyl-H), 7.23e7.16 (m, 1H, aniline-H), 7.06e6.98
(m, 2H, aniline-H). 13C NMR data (125.77 MHz, CDCl3, 298 K):
d
166.50 (HCN), 157.61 (d, CF), 156.22 (COH), 155.57 (d, CF), 133.61
(1.67 g). 1H NMR data (500.13 MHz, CDCl3, 298 K):
d 8.20 (s, 2H, NCH),
4
4
(salicyl-CH), 130.50 (salicyl-CH), 128.15 (t, aniline-CN), 124.14
(t, CCHN), 123.90 (CCl), 123.35 (CCl), 120.68 (aniline-CH), 112.64
(d, aniline-CH). Elemental analysis for C13H7Cl2F2NO: C, 51.68; H,
2.34; N, 4.64%. Found C, 51.89; H, 2.31; N, 4.66%.
7.79 (d, JHH ¼ 2.5, 2H, salicyl-H), 7.48 (d, JHH ¼ 2.5, 2H, salicyl-H),
7.28e7.00 (m, 4H, aniline-H), 6.56e6.47 (m, 2H, aniline-H). 13C NMR
data (125.77 MHz, CDCl3, 298 K):
141.6 (salicyl-CH), 135.9 (salicyl-CH), 128.3, 124.6, 113.0, 112.8, 110.7.
d 170.3 (NCH), 158.4 (salicyl-C),

S. Khaubunsongserm et al. / Polymer 54 (2013) 3217e3222
3219
Table 1
Results of ethylene polymerization with complexes 1e3/MAO at various
temperatures.a
b
b
b
c
Entry Complex Temp Yield Activity Mw
Mn
Mw/Mn Tm
(ꢃC)
(g)
kg PE/
mmol
cat h
(ꢁ10ꢂ6
)
( ꢁ 10ꢂ6
)
(ꢃC)
1
2
3
4
5
6
7
8
1
1
1
1
1
2
2
2
2
2
3
3
3
3
3
10
20
30
40
50
10
20
30
40
50
10
20
30
40
50
2.31 3.46
2.89 4.33
2.55 3.82
1.00 1.50
0.39 0.58
2.54 3.81
4.62 6.93
5.50 8.25
0.97 1.45
0.53 0.80
3.42 5.13
4.74 7.11
3.20 4.80
2.07 3.10
1.64 2.47
3.98
4.20
4.11
3.61
1.75
4.17
4.07
4.27
2.58
1.86
3.88
4.21
3.59
3.47
3.45
3.52
3.77
3.71
3.09
0.74
3.65
3.56
3.87
1.46
0.89
3.37
3.89
3.09
2.71
2.74
1.13
1.11
1.10
1.17
2.34
1.08
1.14
1.05
1.77
2.07
1.15
1.08
1.16
1.27
1.26
127.9
127.1
127.6
127.3
128.3
127.7
127.2
127.3
128.2
128.0
125.5
125.8
126.1
125.7
127.3
Scheme 1. Synthetic route for titanium complexes 1e3.
9
Elemental analysis for C26H12Br4Cl2F4N2O2Ti: C, 34.75; H, 1.35;
N, 3.12%. Found C, 35.12; H, 1.46; N, 2.92%.
10
11
12
13
14
16
2.3.3. Synthesis of bis[N-(3,5-diiodosalicylidene)-20,60-difluroanilinato]
titanium(IV) dichloride (3)
The same procedure was used as that described for 1, starting
from L3H (3.66 g, 7.56 mmol), n-butyl lithium (1.6 M solution in
hexanes, 4.72 mL, 7.56 mmol), and TiCl4 (1.0 M solution in DCM,
3.78 mL, 3.76 mmol), yielding orange crystals of 3 in 31% yield
a
Conditions: complex (2
mmol), cocatalyst MAO (1.25 mmol), 1 atm, toluene
250 mL.
b
c
Determined by GPC using polystyrene calibration.
Melting temperature of synthesized polyethylene determined by DSC.
(1.25 g). 1H NMR data (500.13 MHz, CDCl3, 298 K):
d 8.17 (d,
4
4JHH ¼ 2.1, 2H, salicyl-H), 8.15 (s, 2H, NCH), 7.67 (d, JHH ¼ 2.1, 2H,
salicyl-H), 7.20e7.00 (m, 4H, aniline-H), 6.55e6.46 (m, 2H, aniline-
H). 13C NMR data (125.77 MHz, CDCl3, 298 K): 170.3 (NCH), 161.4
(salicyl-C), 152.6 (salicyl-CH), 143.0 (salicyl-CH), 128.3, 124.3, 113.4,
113.2,110.9. Elemental analysis for C26H12I4Cl2F4N2O2Ti: C, 28.73; H,
1.11; N, 2.58%. Found C, 30.54; H, 1.50; N, 2.55%.
thermostated to a desired polymerization temperature, and then
the ethylene gas feed was started. After 20 min, polymerization was
initiated by adding a toluene solution of the cocatalyst and then a
toluene solution of catalyst into the reactor with vigorous stirring
(450 rpm). After a prescribed time, methyl alcohol (10 mL) was
added to terminate the polymerization, and the ethylene gas feed
was stopped. To the resulting mixture, the acidic methanol was
added. The polymer was collected by filtration, washed with
methanol (300 mL), and dried in vacuo at 80 ꢃC for 24 h.
2.4. Ethylene polymerization
Ethylene polymerization was carried out under atmospheric
pressure in toluene in a 500-mL glass reactor or a 1000-mL stainless
steel reactor equipped with a mechanical stirrer. To the 500 mL
glass reactor, toluene (250 mL) was introduced into the nitrogen-
purged reactor and stirred (450 rpm). In the case of the 1000-mL
reactor, toluene (500 mL) was used instead. The toluene was
2.5. DFT calculations
The geometry optimizations of complexes 1e3 were carried out
with no symmetry constraints by using the Gaussian 09 suite of
Fig. 1. B3LYP-DFT optimized structures of complexes (a) 1, (b) 2, and (c) 3: hydrogen atoms are omitted for clarity. Ti and I atoms are described by the LANL2DZ basis set while the
other atoms are treated by the 6-31G(d,p) basis set.

3220
S. Khaubunsongserm et al. / Polymer 54 (2013) 3217e3222
equimolar of TiCl4 in THF. [26]. The titanium complexes were ob-
10
8
tained as dark red solids in moderate yields (1: 55%, 2: 48%, 3: 31%).
1H NMR spectroscopic analyses of all complexes reveal a single
sharp peak of imine proton and three signals of aromatic protons
suggesting that these complexes exist as the C2-symmetric isomer
(see Supporting Information). In addition, according to previous
report on the observed X-ray crystal structures of complex 3, it is
reasonable to assume that complexes 1 and 2 have the same
octahedral geometry with a trans-O, cis-N, and cis-Cl disposition in
solution [29]. The optimized structures obtained from DFT calcu-
lations also support the proposed structures as shown in Fig. 1.
1
2
3
6
4
2
3.2. Ethylene polymerization using fluorinated TieFI catalysts 1e3
with MAO
0
Ethylene polymerizations with complexes 1e3 using methyl-
aluminoxane (MAO) as a cocatalyst was carried out at different
temperatures (10, 20, 30, 40, and 50 ꢃC) under atmospheric pres-
sure. The results are collected in Table 1. All the complexes are
active catalysts for ethylene polymerization and produce ultra high
molecular weight polyethylene (UHMWPE) under the given con-
ditions. The polyethylenes formed with these complexes exhibit
the Tm values in the range of 125.5e128.3 ꢃC. The constancy of the
melting temperature with increasing polymerization temperature
was also reported by Weiser and coworkers [29]. Plots of the cat-
alytic activities of complexes 1e3 versus the polymerization tem-
peratures are shown in Fig. 2. In the case of complex 1, the activity
increases from 3.46 kg PE/mmol cat h at 10 ꢃC to 4.33 kg PE/
mmol cat h at 20 ꢃC. Above 20 ꢃC, the activity gradually decreases
and at 50 ꢃC, the low activity of only 0.58 kg PE/mmol cat h is
observed. The increase of the activity when increasing the tem-
perature is attributed to the increase of the propagation rate of
transferring the monomer to the active metal center [37,38].
However, at high temperature, the chain transfer reactions are
promoted and the solubility of ethylene in the solvent decreases,
causing a decrease in the propagation reaction [39]. Changing the
temperature from 10 to 20 ꢃC resulted in the increase of the mo-
lecular weight due to the increase of the propagation rate. The
molecular weight of the resultant PE is slightly decreased when
increasing the temperature from 20 to 40 ꢃC, suggesting that no
significant effect of termination reaction operated in this temper-
ature range. In addition, the molecular weight distributions of the
resulting polymers produced from 10 to 40 ꢃC are relatively narrow
which indicate the living nature of complex 1. However, at tem-
perature of 50 ꢃC, a significant decrease in molecular weight and
the broadening of the molecular weight distribution were observed
(Mw ¼ 1.75 ꢁ 10ꢂ6, Mw/Mn ¼ 2.34). These results suggest that the
catalyst decomposition occurs at this temperature.
0
10
20
30
40
50
60
o
Temperature ( C)
Fig. 2. Relationship between the polymerization temperature and the polymerization
activity using complexes 1e3. Conditions: complex (2
(1.25 mmol), 1 atm, toluene 250 mL.
mmol), cocatalyst MAO
programs [32]. The electronic configurations of the molecular sys-
tems were described by the Los Alamos National Laboratory 2
double-z (LanL2DZ) effective core potential basis set [33]on the ti-
tanium and iodine atoms and the standard all-electron Pople basis
set 6-31G(d,p) [34] on the remaining atoms. Energies and geome-
tries were evaluated by means of the density functional theory (DFT)
method using the hybrid Becke’s three-parameter exchange func-
tional and the LeeeYangeParr correlation functional (B3LYP) [35].
3. Results and discussion
3.1. Synthesis of fluorinated bis(phenoxy-imine)titanium complexes
In this work, the influences of ortho phenoxy halide substituents
of titanium complexes on the polymerization activities of ethylene
polymerization (e.g. catalytic activity, molecular weight, molecular
weight distribution, and living characteristic) were examined.
Fluorinated bis(phenoxy-imine)titanium complexes (fluorinated
TieFI complexes) used in this study [R ¼Cl (1), Br (2), I (3)] are shown
in Scheme 1. Phenoxy-imine ligands (L1HeL3H) and titanium com-
plexes (1e3) were synthesized according to published procedures
[36]. All phenoxy-imine ligands were obtained in high yields
(L1H: 64%, L2H: 91%, L3H: 65%)by the Schiff base condensation of
2,6-difluoroaniline and the corresponding 3,5-dihalo substituent
salicylaldehyde derivatives. Complexes 1e3 were prepared by 2
steps: the formation of lithium salt by the reaction between the
phenoxy-imine ligand and n-butyl lithium and the complex for-
mation by treatment of two equivalents of the lithium salt with an
Changing the substituent R ortho to the phenoxy oxygen from Cl
(complex 1) to Br (complex 2) results in the enhancement of the
polymerization activity from the temperatures of 10e30 ꢃC. The
observed optimum polymerization temperature of this complex is
Table 2
Results of ethylene polymerization with complex 2/MAO at various catalyst concentrations.a
Mw (ꢁ10ꢂ6
)
Mnb (ꢁ10ꢂ6
)
Mw/Mn
b
b
c
Tm (ꢃC)
Entry
Complex (
m
mol)
[Al]/[Ti]
Yield (g)
Activity kg PE/mmol cat h
1
2
3
4
5
6
2 (1.0)
2 (2.0)
2 (3.0)
2 (4.0)
2 (5.0)
2 (6.0)
2500
1250
833
625
500
3.43
7.85
10.36
13.24
13.39
13.75
10.31
11.77
10.36
9.93
8.03
6.87
4.01
3.95
3.90
3.72
3.68
3.57
3.64
3.53
3.43
3.20
3.11
2.87
1.10
1.11
1.13
1.16
1.18
1.24
127.1
126.8
127.2
127.3
127.1
127.1
417
a
Conditions: cocatalyst MAO (2.50 mmol), 1 atm, toluene 500 mL, time 20 min, temperature 30 ꢃC.
Determined by GPC using polystyrene calibration.
Melting temperature of synthesized polyethylene determined by DSC.
b
c

S. Khaubunsongserm et al. / Polymer 54 (2013) 3217e3222
3221
30 ꢃC with the highest activity of 8.25 kg PE/mmol cat h. In com-
parison with complex 1, the increase of the polymerization activity
using complex 2 may arise from an effective ion-pair separation
between the cationic active species and an anionic cocatalyst by the
ortho substituent R group situated closely to the metal center [28].
At the temperatures above 30 ꢃC, the polymerization activity de-
creases significantly, and hence the decrease of molecular weight is
observed. The broadening of the molecular weight distribution
observed at elevated temperatures (entries 9 and 10, Table 1)
suggests the significant extent of the chain transfer termination.
In the case of complex 3 with the ortho iodo substituent, the
highest activity of 7.11 kg PE/mmol cat h is observed at 20 ꢃC.
Although the polymerization activity decreases at the temperature
above 30 ꢃC, the molecular weights of the resulting polymers are
relatively unchanged and the narrow molecular weight distributions
(Mw/Mn < 1.3) are observed. These results suggest that the increased
size of the substituent at the ortho position of the phenoxy rings
leads to the enhancement of the steric congestion at the metal
center, and hence decreasing in the polymerization activity. How-
ever, the chain transfer termination processes are diminished due to
the steric protection at the active site from the ortho substituent.
As the complex 2/MAO system displays a high potential for the
production of UHMWPE with the highest activity at 30 ꢃC
compared with the complexes 1 and 3/MAO systems at the same
condition, we, therefore, investigate the catalytic performance of
this catalyst in more details. The effects of the catalyst concentra-
tion, the catalystecocatalyst ratio and the polymerization time on
the ethylene polymerization are investigated in order to find the
optimum condition for the production of UHMWPE.
Table 4
Results of ethylene polymerization with complex 2/MAO at various polymerization
times.a
b
b
b
c
Entry Time Yield Activity
Mw
Mn
Mw/Mn Tm (ꢃC)
(min) (g)
kg PE/mmol cat h (ꢁ10ꢂ6
)
(ꢁ10ꢂ6
)
1
2
3
4
5
6
10
20
30
40
50
60
6.03 9.05
12.17 9.13
13.95 6.97
13.46 5.05
14.43 4.33
15.53 3.88
3.56
2.60
2.91
3.09
3.28
3.42
3.66
1.37
1.23
1.19
1.15
1.13
1.10
126.5
127.1
127.0
127.0
127.0
127.1
3.60
3.69
3.80
3.88
4.03
a
Conditions: complex (2
m
mol), cocatalyst MAO (1.65 mmol), [Al]/[Ti] ¼ 1825,
1 atm, toluene 500 mL, temperature 30 ꢃC.
b
Determined by GPC using polystyrene calibration.
Melting temperature of synthesized polyethylene determined by DSC.
c
the polarity of the medium with increasing MAO concentration
results in a better ion-pair separation, affording a higher poly-
merization rate. The decrease in the activity at the high Al/Ti con-
centration ratio (entry 1, Table 2) may be attributed to the result of
heterogenization of the system due to the high concentration of
MAO. In this system, the decrease of the activity and the molecular
weight due to chain transfer to aluminum seem not to be an
important reason [40]. This was supported by the observed narrow
molecular weight distribution, indicating the living nature of this
catalyst system.
Close examination of the Al/Ti concentration ratio reveals that
the optimum condition for the production of the UHMWPE with
the highest activity is the use of catalyst 2
mmol with the Al/Ti
concentration ratio of 1825 at 30 ꢃC (entry 5, Table 3).
4. Ethylene polymerization using complex 2 with MAO
4.2. Polymerization time
4.1. Cocatalystecatalyst concentration ratio ([Al]/[Ti])
To further investigate the living nature of complex 2, the poly-
merizations at 10, 20, 30, 40, 50, and 60 min were carried out. The
results are collected in Table 4. The increase of the polymer yield as
a function of polymerization time indicates that the complex
2/MAO catalyst system has a catalytic life time of at least 60 min
as shown in Fig. 3.The broadening of the molecular weight distri-
bution caused by the non homogeneity of the polymerization
MAO does not only act as a cocatalyst in homogenous poly-
merization, but also can be considered as a potential chain transfer
agent which is the drawback of the living polymerization system. In
general, a large amount of MAO is used in the polymerization, but
this can have an effect on the polymerization activity. Therefore, in
this study, the effect of the cocatalystecatalyst concentration ratio
was investigated. Table 2 shows the results of ethylene polymeri-
zation using complex 2/MAO at different catalyst concentrations.
The highest activity was observed when the concentrations of
20
15
10
5
catalyst and cocatalyst were 2.0 mmol and 2.50 mmol, respectively
([Al]/[Ti] ¼ 1250, entry 2, Table 1). Further increasing the catalyst
concentration resulted in decreasing the activity of ethylene poly-
merization and the molecular weight of the resulting polymers. On
the other hand, upon increasing the Al/Ti concentration ratio up to
[Al]/[Ti] ¼ 1250, the activity and the molecular weight of polymer
increase (entries 3e6, Table 2). These results were also observed
in the bis(pheneoxyimine)titanium catalyst containing penta-
fluoroaniline moiety by Rastogi and coworkers [39].The increase in
Table 3
Results of ethylene polymerization with complex 2/MAO at various MAO
concentrations.a
Entry
MAO (mmol)
[Al]/[Ti]
Yield (g)
Activity kg PE/mmol cat h
1
2
3
4
5
6
0.85
1.05
1.25
1.45
1.65
1.85
1025
1225
1425
1625
1825
2025
5.73
6.14
6.33
7.37
7.76
6.90
8.60
9.21
9.49
11.06
11.65
10.35
0
0
10
20
30
40
50
60
70
Time (min)
Fig. 3. Relationship between the polymerization time and the polymer yield obtained
a
Conditions: complex (2
m
mol), 1 atm, toluene 500 mL, time 20 min, temperature
with complex 2/MAO. Conditions: complex (2 mmol), cocatalyst MAO (1.65 mmol), [Al]/
30 ꢃC.
[Ti] ¼ 1825, 1 atm, toluene 500 mL, temperature 30 ꢃC.

3222
S. Khaubunsongserm et al. / Polymer 54 (2013) 3217e3222
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system due to excess polymer precipitation was not observed. The
living nature of polymerization was therefore, demonstrated by the
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5. Conclusions
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Three fluorinated bis(phenoxy-imine)titanium complexes
bearing halide substituents on the ortho position of the phenoxy
rings have been synthesized and tested as precatalysts for ethylene
polymerization in the presence of MAO as a cocatalyst. All com-
plexes are active toward ethylene polymerization and produce ultra
high molecular weight polyethylene (UHMWPE). The polymeriza-
tion activities are affected by the ortho-halide substituents on the
phenoxy rings. Complex 2 with ortho bromo substituents was
found to have the highest activity at 30 ꢃC and under atmospheric
pressure. In accordance with previous studies, the presence of a
fluorine atom adjacent to the imine nitrogen in the ligand is the
requirement for living polymerization through the suppression of
[25] Saito J, Mitani M, Mohri J, Yoshida Y, Matsui S, Ishii S, et al. Angew Chem Int Ed
2001;40:2918.
[26] Mitani M, Mohri J, Yoshida Y, Saito J, Ishii S, Tsuru L, et al. J Am Chem Soc
2002;124:3327.
b-hydrogen transfer. The living nature of all complexes is demon-
strated by the observed narrow molecular weight distributions.
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Chem 2005;690:4398.
[28] Furuyama R, Mitani M, Mohri J, Mori R, Tanaka H, Fujita F. Macromolecules
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Acknowledgments
We gratefully acknowledge materials and characterization in-
strument support from PTT Public Company Limited. The Support
from Office of the Higher Education Commission (CHE) and Higher
Education Promotion and National Research University Develop-
ment (AM1088A) are also appreciated.
[29] Weiser MS, Wesolek M, Mülhaupt R. J Organomet Chem 2006;691:2945.
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