Specific features of ethylene polymerization on self-immobilizing catalytic systems based on titanium bis(phenoxy imine) complexes

Article abstract of DOI:10.1134/S1070427211010204

The kinetics of ethylene polymerization on six methylalumoxane-activated self-immobilizing bis(phenoxy imine) complexes of titanium chloride with allyloxy groups in the m- and p-positions of the N-phenyl ring and with various substituents in the salicylal

Full text of DOI:10.1134/S1070427211010204

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2011, Vol. 84, No. 1, pp. 118−123. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © N.I. Ivancheva, V.K. Badaev, E.V. Sviridova, D.A. Nikolaev, I.V. Oleinik, S.S. Ivanchev, 2011, published in Zhurnal Prikladnoi Khimii,
2011, Vol. 84, No. 1, pp. 118−123.
MACROMOLECULAR COMPOUNDS
AND POLYMERIC MATERIALS
Specific Features of Ethylene Polymerization
on Self-Immobilizing Catalytic Systems
Based on Titanium Bis(phenoxy imine) Complexes
N. I. Ivancheva, V. K. Badaev, E. V. Sviridova,
D. A. Nikolaev, I. V. Oleinik, and S. S. Ivanchev
St. Petersburg Branch, Boreskov Institute of Catalysis, Siberian Branch,
Russian Academy of Sciences, St. Petersburg, Russia
Vorozhtsov Institute of Organic Chemistry, Siberian Branch,
Russian Academy of Sciences, Novosibirsk, Russia
Received November 30, 2010
Abstract—The kinetics of ethylene polymerization on six methylalumoxane-activated self-immobilizing
bis(phenoxy imine) complexes of titanium chloride with allyloxy groups in the m- and p-positions of the N-phenyl
ring and with various substituents in the salicylaldehyde fragment was studied. The activity of the complexes in
the temperature range 20–60°С and ethylene pressure of 0.4 MPa was evaluated.
DOI: 10.1134/S1070427211010204
A significant problem in commercial implementation
of catalytic polymerization is deposition of a polymer
layer on the reactor walls. The most widely and
successfully used way to overcome this problem is the
use of polymerization catalysts applied onto various
supports [1].
pyridine complexes.
Previously[9,10]westudiedethylenepolymerization
using six methylalumoxane (MAO)-activated titanium
chloride bis(phenoxy imine) complexes functionalized
with allyloxy groups. We revealed the kinetic features
of the polymerization and experimentally proved for
the first time the self-immobilization mechanism for the
catalytic systems studied.
In the past decades, some other approaches to het-
erogenization of catalytic systems directly in the course
of polymerization were suggested. Köppl and Alt [2]
suggested using a heterogeneous cocatalyst. Also Alt et
al. [3–5] studied catalytic systems based on functional-
ized metallocene complexes of Zr, Ti, and Hf, which al-
lowed the ethylene polymerization to be performed with
catalyst self-immobilization on the formed polyethyl-
ene (PE), owing to the possibility of copolymerization
with the functionalized catalytic complex via the double
bond in the functional group. In these papers, the cata-
lysts studied were termed self-immobilizing systems.
In this study we examined how the position of the
functional group in the N-phenyl ring affects the self-
immobilization, the polymerization kinetics, and the
molecular characteristics of the polymers formed. The
data obtained are useful for optimizing the structure of
self-immobilizing catalytic systems for polymerization
processes.
EXPERIMENTAL
The possibility of using the self-immobilization
of post-metallocene catalytic systems was later
demonstrated by Zhang et al. for Zr phenoxy imine
systems [6, 7] and by Alt et al. [8] for Fe bis(imino)
Ultrapure grade toluene was dried for 24 h over
calcinedAl2O3, distilled in an argon stream from sodium
metal, and stored in the presence of sodium metal in an
inert gas atmosphere. Chemically pure grade isopropyl
118

SPECIFIC FEATURES OF ETHYLENE POLYMERIZATION
119
alcohol was used without additional treatment.
The structures of the ligands and complexes were
confirmed by elemental analysis and by H NMR and
IR spectroscopy.
1
Ethylene containing no less than 99.5% main sub-
stance and higher grade argon prior to feeding into the re-
actor were dried by passing through columns packed with
calcined Al2O3, after which the moisture content of ethyl-
ene and argon did not exceed 10–20 and 10 ppm, respec-
tively. Methylalumoxane (CK Witko GmbH) was used as
10% toluene solution without additional treatment.
Ethylene polymerization was performed in a 150-ml
stainless steel reactor equipped with a detachable jacket
and a magnetically driven propeller stirrer operating at
pressures of up to 0.7 MPa and temperatures from 20
to 90°C. The pressure in the reactor was maintained
automatically, and the temperature, by feeding water
at the required temperature from an ultrathermostat to
the reactor jacket. Prior to starting the polymerization,
the reactor was evacuated to a residual pressure of 1 ×
10–1 mm Hg at 150–170°C for 1 h, with threefold purging
with dry argon. After cooling to room temperature, the
calculated amount of toluene and the components of the
catalytic system were loaded through the loading tube
in an argon counterflow using medical syringes. The
Phenoxy imine ligands were prepared by the reaction
of substituted salicylaldehydes with m- or p-allyl-
oxyanilinehydrochlorideinthepresenceoftriethylamine
in 87–97% yield. The corresponding complexes of
dichlorotitanium(IV) (1–3 with allyloxy group in
m-position, 4–6 with allyloxy group in p-position) were
prepared by the reaction of a TiCl2(OiPr)2 solution with
imines at room temperature1 [9, 10]. The synthesis
schemes are given below:
where R1 = CMe2Ph, R2 = H (1, 4); R1 = CMe2Ph, R2 = Ме (2, 5); R1 = t-Bu, R2 = Me (3, 6).
————————
1 Synthesized at the Vorozhtsov Institute of Organic Chemistry, Siberian Branch, Russian Academy of Sciences, Novosibirsk.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 1 2011

120
IVANCHEVA et al.
0.70
[η] = 6.2 × 10–4Mꢀ
.
reaction mixture was saturated with ethylene (0.4 MPa)
with simultaneous heating to the working temperature of
20–60°C. After a definite time, the reaction was stopped
by adding a mixture of isopropyl alcohol with 2% HCl.
The liquid phase was separated on a Büchner funnel,
and the polymer was washed twice with a mixture of
isopropyl alcohol and H2O and was vacuum-dried at
60°C to constant weight.
Thermal characteristics of the polymers were
determined by scanning calorimetry with a Shimadzu
DSM-60 device. The specific heats of phase transitions
and the characteristic temperatures were measured with
the same DSC device at a heating rate of 10 deg min–1
and a sample weight of 5–10 mg.
The content of terminal groups of the polymers was
determined by IR Fourier spectroscopy with a Shimadzu
FTIR-8300 device.
Themolecularweightofthepolymerswasdetermined
viscometrically and was calculated by the equation [11]
(a)
The results of ethylene polymerization on
bis(phenoxy imine) complexes functionalized with the
allyloxy group in the m- (structures 1–3) or p-position
(structures 4–6) are given in the table. Figures 1–3
show the kinetic curves of polymerization on the six
titanium complexes. Figure 4 shows how the molecular
weight of the polymers depends on the polymerization
temperature.
Experiments on polymerization at 20, 40, and
60°С (see table) on functionalized complexes 1 and
(b)
(a)
(b)
(c)
(c)
τ, min
Fig. 1. Kinetic curves of ethylene polymerization on
bis(phenoxy amine) complexes 1 and 4. (W) Polymerization
rate and (τ) time; the same for Figs. 2 and 3. Т, °С: (a) 20, (b)
40, and (c) 60; the same for Figs. 2 and 3.
τ, min
Fig. 2. Kinetic curves of ethylene polymerization on
bis(phenoxy amine) complexes 2 and 5.
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SPECIFIC FEATURES OF ETHYLENE POLYMERIZATION
121
Results of ethylene polymerization on complexes 1–6. Polymerization conditions: 50 ml of toluene, ethylene pressure 0.4 MPa,
МАО : Ti = 500 : 1, τpol = 60 min
Activity A,
Tpol
°С
,
Complex
(1)
Ti, μmol Yield, g kgPE (molcat)–1 Mη × 10–6
–CH3
–CH=CH2
Tm, °C
K, %
MPa–1 h–1
20
40
60
20
40
60
20
40
60
20
40
60
20
40
60
0.698
0.523
0.465
1.41
1.13
1.3
4.785
6.093
6.466
8.795
8.957
10.291
4.155
4.979
5.100
6.041
7.37
17140
29130
34760
15590
19820
19790
8800
4.3
3.0
2.5
3.0
2.8
3.7
2.4
1.8
1.3
2.8
5.9
8.7
4.0
6.21
8.2
0.05
0.05
0.2
~0
0.05
~0
0
0.065
0.09
0.09
0.06
0.07
0.08
0.035
0.04
0.06
0.05
0.04
0.03
0.04
0.035
0.025
142.7
142.3
142.7
142.0
142.8
143.2
142.2
143.4
141.6
141.7
144.3
144.1
143.3
143.2
143.2
76
79
80
78
75
77
80
81
79
75
77
78
76
80
81
(2)
(3)
(4)
(5)
1.18
0.917
0.917
0.523
0.523
0.47
1.0
13570
13900
28900
35230
31030
22470
29430
19170
0
~0
0
0
5.833
6.74
0
0
1.0
8.83
0
1.0
5.752
0
4 with the allyloxy group in the m- and p-positions of
the N-phenyl ring, respectively, and with the o-cumyl
substituent in the salicylaldehyde ring show that the
relative performance of the catalysts depends on the
polymerization conditions. At 20°C, the activity is lower
by 70% for the system with the allyloxy substituent in
the m-position, compared to the p-substituted derivative.
In addition, the course of kinetic curves in Fig. 1a
indicates that self-immobilization at low temperatures
occurs more intensely for catalytic systems with the
allyloxy group in the m-position, compared to the
p-substituted derivatives. At higher temperatures, the
self-immobilization rate and the catalyst activity depend
on the position of the allyloxy group less significantly
(see table; Figs. 1b, 1c).
(a)
(b)
(c)
τ, min
Figures 2 and 3 show the polymerization kinetic
curves for catalytic complexes differing in the nature
and position of substituents in the salicylaldehyde
ring. As can be seen, the kinetic curves at different
Fig. 3. Kinetic curves of ethylene polymerization on
bis(phenoxy amine) complexes 3 and 6. (W) Polymerization
rate, kg mol–1 min–1.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 1 2011

122
IVANCHEVA et al.
polymerization temperatures are fairly similar.
the highest catalytic activity. This can be seen when
considering complexes 1 and 4. Evaluation of the
capability of complexes 1 and 4 for self-immobilization
showed that, in ethylene polymerization at 20°C,
about 70% of the catalytic complex undergoes self-
immobilization on the PE formed (determined with
an SF-2000 spectrophotometer from variation of the
solution color in the range 400–500 nm [10]).
Of particular interest are data on the molecular weight
(MW) of the polymers obtained on the self-immobilizing
systems at different temperatures and different positions
of the allyloxy group in the N-phenyl ring (Fig. 4). As
can be seen, in going from m- to p-allyloxy derivatives,
the influence of temperature on the MW of the PE
formed changes cardinally (Fig. 4a). For the catalytic
systems with the allyloxy group in the p-position, MW
of the polymer increases with temperature, whereas for
the m-substituted derivatives it depends on temperature
insignificantly. For the complexes with different
substitution pattern in the salicylaldehyde ring (Fig. 4b,
compounds 2 and 5; Fig. 4c, compounds 3 and 6), the
molecular weight varies with temperature to a lesser
extent or is almost independent of temperature.
It is known that a bulky substituent in the o-position
of the salicylaldehyde ring in bis(phenoxy imine)
complexes ensures steric protection of these complexes
from the MAO cocatalyst always present in excess in the
polymerization system. It also favors efficient separation
of the active cationic species and anionic fragments of
the cocatalyst [12]. Therefore, an electron-donor methyl
group in the p-position of the salicylaldehyde phenoxy
group in complexes 2 and 5, which also contain a cumyl
group in the o-position, should not affect the catalyst
activity and the kinetic features of the polymerization
(see table; Figs. 2a–2c).
As shown in [12], among bis(phenoxy imine)
complexes substituted in the salicylaldehyde ring, the
complexes containing the o-cumyl substituent exhibit
Smaller substituents in the o-position of the
salicylaldehyde phenoxy group (e.g., tert-butyl group
insteadofcumyl),withthemethylgroupinthep-position,
decrease the catalyst activity and the polymerization
rate at 20, 40, and 60°C (Fig. 3, complexes 3 and 6). The
data obtained also showed that, at all the temperatures,
the MW of the product obtained with complex 6, as
well as with complex 3, is lower than with complexes 4
and 5. Evaluation of the capability of complexes 3 and
6 for self-immobilization also showed that, in ethylene
polymerization at 20°C, about 40% of the catalytic
complex is immobilized on the PE obtained [10]. This
fact determines a decrease in the activity and MW.
(a)
(b)
Experiments on ethylene polymerization on similar
complexes containing the allyloxy group in the
o-position failed to yield the polymer. Apparently, in
such complexes close location of the allyloxy group
prevents the monomer access to the active center.
Zhang and Jin [6] studied structurally related
bis(phenoxy imine) complexes of Zr and Ti and
(c)
suggested
a
self-immobilization mechanism in
formation of PE macrochains. They assume that
several catalytic complexes can be incorporated into
one PE macromolecule. To check this assumption,
we determined the molecular-weight distribution
of the isolated polymerized catalyst, which allowed
calculation of its “molar” yield. We found that, in all the
cases, there is approximately one number-average PE
Tpol, °C
Fig. 4. PE molecular weight Мη as a function of polymerization
temperature Тpol for complexes (a) 1 and 4, (b) 2 and 5, and (c)
3 and 6. Numerals at curves are complex nos.
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SPECIFIC FEATURES OF ETHYLENE POLYMERIZATION
123
macromolecule [Mw ~(150–300) × 103, Мw : Mn = 2.0–
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macromolecules per catalytic center can increase to two
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for performing polymerization experiments and to
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