ISSN 15600904, Polymer Science, Ser. B, 2010, Vol. 52, Nos. 7–8, pp. 443–449. © Pleiades Publishing, Ltd., 2010. Original Russian Text © M.Yu. Vasil’eva, S.P. Fedorov, D.A. Nikolaev, I.I. Oleinik, S.S. Ivanchev, 2010, published in Russian in Vysokomolekulyarnye Soedineniya, Ser. B, 2010, Vol. 52, No. 8, pp. 1483–1490.
CATALYSIS
Polymerization of Ethylene in the Presence of Bis(phenoxyimine) Complexes of Titanium Chloride That Contain Various Substituents in a Phenoxy Group1 M. Yu. Vasil’evaa, S. P. Fedorova, D. A. Nikolaeva, I. I. Oleinikb, and S. S. Ivancheva a
Boreskov Institute of Catalysis (St. Petersburg Branch), Siberian Branch, Russian Academy of Sciences, pr. Dobrolyubova 14, St. Petersburg, 197198 Russia b Vorozhtsov Institute of Organic Chemistry, Siberian Branch, Russian Academy of Sciences, pr. Akademika Lavrent’eva 9, Novosibirsk, 630090 Russia email:
[email protected] Received November 13, 2009; Revised Manuscript Received January 25, 2010
Abstract—The kinetic features of ethylene polymerization with six methylaluminoxaneactivated bis(phe noxyimine) complexes of titanium chloride that are distinguished by the electronic properties of substituents in the phenoxy group are studied in the temperature range 30–80°C and at an ethylene pressure of 0.3 MPa. It is shown that, in the presence of an electrodonor or electronacceptor substituent in the phenoxy group, −1 −1 the catalytic systems under study exhibit high activity (up to ~700 tPE mol cat h–1) and form high mol ethylene molecularmass PE samples (Mη = (500–900) × 103) with different molecularmass distributions. In the case of titanium bis(phenoxyimine) complexes containing donor substituents at the para position of the phenoxy group, the polymerization of ethylene follows the livingchain mechanism, while the introduction of accep tor substituents diminishes the contribution of this mechanism to the reaction.
DOI: 10.1134/S1560090410070080 1
INTRODUCTION
Many studies [1–6] have been devoted to searching for new highly efficient catalysts of ethylene polymer ization through variation in the nature of substituents in the ligands of bis(phenoxyimine) complexes. These papers mostly concern the influence of steric effects of hydrocarbon substituents at the imine nitrogen, and substituents, which are situated in the ortho position of the phenol group of ligands, on the catalytic activity of complexes. However, the data on the catalytic activ ity of complexes containing halide substituents in the phenoxy groups and the properties of the resulting polymers are scanty. In this study, the effects of electronic properties of substituents of various natures and structures that are situated in ortho and para positions of the phenoxy group with the fixed substituent at the imine nitrogen (phenyl) on their catalytic activity, the kinetic features 1 This
work was supported by the Siberian Branch of the Russian Academy of Sciences within the framework of complex integra tion project no. 123.
and mechanism of ethylene polymerization, and the properties of the polymers being formed are com pared. The general structure of the bis(phenoxyimine) complexes of titanium is outlined below. (Catalytic −1 −1 activity А was expressed in kgPE mol cat h–1.) mol ethylene
R2
N O R1
C 6H5 Cl Ti
Cl N C 6H 5
R1 O
, R2
1–6
Here, R1 = R2 = tertBu (1), R1 = tertBu and R2 = Br (2), R1 = tertBu and R2 = Cl (3), R1 = tertBu and R2 = OCH3 (4), R1 = Br and R2 = tertBu (5), and R1 = Br and R2 = OCH3 (6).
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EXPERIMENTAL Reagents and Materials and Their Preparation Before experiments, ethylene was passed through columns packed with calcined aluminum oxide. The content of ethylene was no less than 99.9%; the con densation point was from –45 to –60°С. Argon of the highpurity grade was additionally passed through columns packed with calcined alumi num oxide to remove moisture traces. After purifica tion, the condensation point did not exceed –60°С. Polymethylaluminoxane (Aldrich) was used as a 10% solution in toluene. Toluene of the specialpurity grade was dried two times over calcined aluminum oxide and distilled over metallic sodium in a flow of argon. Isopropyl alcohol and hydrochloric acid were used as received. Decalin (Merck) containing small amounts of Irganox 1010 as a stabilizer, which hindered the ther mal degradation of polymers, was used without any additional treatment at 135°С. 1,2,4Trichlorobenzene (Merck) containing small amounts of Ionol as a stabilizer, which hampered the thermal degradation of polymers, was employed with out any additional treatment at 150°С. Synthesis of Bis(phenoxyimine) Complexes of Titanium Phenoxyimine ligands were prepared via the inter action of corresponding aldehyde with aniline hydro chloride in the presence of triethylamine. Complexes 1–6 were synthesized through the action of a solution of TiCl2(OisoPr)2 on the corresponding phenoxyimines at room temperature [7–9]. The com position and structure of ligands and of corresponding titanium complexes were studied by elemental analysis and 1H NMR and IR spectroscopy. Polymerization of Ethylene The polymerization of ethylene was conducted in a 150ml stainlesssteel reactor equipped with a dis mountable shirt and a propeller stirrer with a magnetic drive. The process was performed at a pressure of up to 0.5 MPa and in the temperature range from 30 to 80°С. The pressure in the reactor was maintained automatically throughout the experiment, and the desired temperature was set via feeding of water of the appropriate temperature from an ultrathermostat to the reactor jacket. Before polymerization, the reactor was evacuated for 1 h at 150–170°С and washed three times with anhydrous argon. When the reactor was cooled to room temperature, calculated amounts of toluene and catalytic system components were loaded through the loading con necting pipe in a counterflow of argon with the aid of medical syringes and the reaction mixture was satu
rated with ethylene; simultaneously, it was heated to the operating temperature and the calculated pressure. After a certain time, the reaction was stopped via addi tion of an isopropyl alcohol–hydrochloric acid mix ture (10%) to the reaction mixture. The liquid phase was separated on a Büchner funnel, and the resulting polymer was washed with isopropyl alcohol and dried at 60°С in vacuum to a constant weight. Analytical Procedures The molecular mass of the polymers was calculated through the equation [η] = 6.2 × 10–4М0.70 [10] on the basis of viscometry measurements. The molecular mass characteristics of the polymers (Mw and Mw/Mn) estimated by gelpermeation chromatography on an Alliance GPCV2000 (Waters, United States) chro matograph equipped with styrogel HT3 and HT5 (Waters) columns at a temperature of 150°С. 1,2,4Trichlorobenzene was used as a solvent; the elu tion rate was 0.5 ml/min. Chromatograms were treated with the use of the universal calibration curve plotted relative to PS standards (Waters) with Мp = 9.0 × 103–5.5 × 106. The thermal characteristics (melting temperature and enthalpies of phase transitions) of the polymers were studied by DSC on a Shimadzu DSC60 instru ment. The crystallinity of the polymers α (%) was cal culated from the formula α = ΔH/ΔHmax (–ΔHmax = 293 J/g). The structure of the polymers was studied by FTIR spectroscopy on a Shimadzu FTIR8300 instrument. The absorption spectra were measured in the absorp tion range 500–2500 cm–1. RESULTS AND DISCUSSION Table 1 and Fig. 1 show the data on the polymeriza tion of ethylene with bis(phenoxyimine) complexes of titanium 1–6, the molecularmass characteristics of PE samples, and the temperature dependence of cata lytic activity for complexes 1–4, respectively. It is seen that, depending on the electronic and steric properties of substituents R2 in the para position of the phenoxy group, titanium complexes manifest the highest catalytic activity А at various temperatures. Thus, for catalysts 1, 3, and 4 (R2 = tertBu, Cl, OCH3, respectively), the highest catalytic activity is observed at 50°C; in the case of catalyst 2 (R2 = Br), the greatest catalytic activity is found at 30°C. Com plexes 1 and 4 containing tertBu and OCH3 substitu ents in the para position of the phenoxy group, respec tively, possess higher thermal stability in polymeriza tion than their analogs 2 and 3 with halide substituents. These data are in agreement with the results from [11], where the introduction of electron donor substituents into the ligand environment of bis(phenoxyimine) complexes of Zr increased their thermal stability.
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Table 1. Polymerization of ethylene with bis(phenoxyimine) complexes 1–6 –1
–1
–1
Catalyst
T, °C
olymer yield, g
1
30
8.8
390
890
50
11.7
650
670
70
10.0
714
660
80
5.1
425
600
30
13.1
582
500
50
10.1
561
480
70
6.7
478
470
80
3.3
275
460
30
11.3
502
550
50
11.9
661
540
70
8.0
571
530
80
3.1
258
530
30
6.8
302
800
50
7.7
428
700
70
5.6
400
650
80
3.6
300
600
5
30
0.2
9
–
6
30
0.7
31
–
2
3
4
А × 10–3, kg PE mol cat mol ethylene h
Mη × 10–3
Note: Here and in Tables 2 and 3, the conditions of polymerization are a toluene volume of 50 ml, an ethylene pressure of 0.3 MPa, [Ti] = 1 × 10–6 mol, [polymethylaluminoxane] : [Ti] = 500, and a time of ethylene polymerization of 1 h.
Catalyst 5 carrying the acceptor substituent in the ortho position of the phenoxy group is characterized by a very low activity since not bulky Br does not pro tect the cationic Ti center from the interaction with the anionic form of the cocatalyst that leads to the loss of the active center (Table 1). A strong electrondonor substituents, the methoxy group, was introduced into the para position of the phenoxy group (catalyst 6) to improve the catalytic activity due to the electronic effect of the substituent. In fact, the catalytic activity increased appreciably (by a factor of more than 4); however, the steric effect of the ortho substituent of the methoxy group remained decisive. As is seen from Table 1, the values of Mη for the polymers prepared with complexes 1 and 4 containing electrondonor substituents tertBu and OCH3 in the para position of the phenoxy group are higher (Mη = (890–600) × 103) than molecular masses of the poly POLYMER SCIENCE
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mers obtained with complexes 2 and 3 carrying elec tronacceptor substituents Br and Cl (Mη = (540–460) × 103). Figure 2 displays the temperature dependence of the molecular mass of PE samples prepared with complexes 1–4. It is seen that the molecular mass of polymers prepared with these complexes containing electrondonor substituents in the para position of the phenoxy group decreases with temperature by a factor of ~1.5, while the molecular mass of the polymers pre pared with complexes 2 and 3 containing electron acceptor substituents turns out to be almost tempera tureindependent. It is known [5, 12] that, in the case of bis(phenox yimine) complexes of titanium, the polymerization of ethylene obeys the livingchain mechanism. Up to now, little is known of the effect of the structure of ligands in bis(phenoxyimine) complexes of titanium chloride lacking fluorinated substituents at the imine 2010
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–3
–1
A × 10 , kg PE mol cat mol ethylene h 800
600
–1
2 3
400
1 4
200
30
40
50
60
70
80 T, °C
Fig. 1. Temperature dependence of catalytic activity of complexes 1–4. Here and in Figs. 2–5, the conditions of polymerization are as follows: a toluene volume of 50 ml, an ethylene pressure of 0.3 MPa, [Ti] = 1 × 10–6 mol, [polymethylaluminoxane] : [Ti] = 500, and a time of ethylene polymerization of 1 h.
Mη × 10−3 1000 1 800 600
400
4
3 2 30
40
50
60
70
80 T, °C
Fig. 2. Variation in the molecular mass of PE prepared with complexes 1–4 with temperature.
nitrogen on the feasibility of living polymerization of ethylene. We examined how the molecular mass of PE samples, which were prepared with complexes 1–4 with different electronic and steric properties of sub stituents situated in the para position of the phenoxy group, varied with time (Fig. 3). The molecular mass of PE prepared with com plexes 1 and 4 containing electrondonor substituents tertBu and –OCH3 in the para position of the phe noxy group increases with time, thus indicating the living mechanism of polymerization. Already 2 min after the onset of ethylene loading, the Mη of the poly mers obtained with catalysts 2 and 3 that carry elec tronacceptor substituents attains ~(500–550) × 103 and then remains unchanged. Hence, the mechanism of polymerization changes with electronic and steric properties of substituents in the para position of the phenoxy group.
We studied whether the living polymerization can be catalyzed by complexes 1 and 4 at high tempera tures –50, –70°C (Fig. 4). As is seen, in the case of complex 1, living polymerization at these tempera tures is less typical than that for complex 4. This result is due to the fact that the rate of elementary chain transfer events, which defines the feasibility of living polymerization, depends on the structure of substitu ents in the ligand of the bis(phenoxyimine) complex of titanium chloride. In accordance with [1, 13], bis(phenoxyimine) cat alysts occur in solution in the form of a mixture of five isomers with different cis and trans arrangements of ligands relative to the central metal atom. Depending on the structure of ligands in the bis(phenoxyimine) catalyst and the temperature of the process, the ratio of isomers changes. This effect may be responsible for deterioration of the multicentered nature of the cata
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Mη × 10−3 1
690 1
4
850
3
590
4 750
2 490
650 390 550
3 2
290
450 0 20
40
60 Time, min
Fig. 4. Molecular mass of PE prepared at (1, 3) 50 and (2, 4) 70°С with complexes (curves 1, 2) 1 and (curves 3, 4) 4 vs. time of polymerization.
Fig. 3. Molecular mass of PE prepared at 30°С with com plexes 1–4 vs. time of polymerization.
lytic system being formed and may lead to the synthe sis of uni, bi, and trimodal PEs. Table 2 shows the molecularmass characteristics of PE samples prepared with complexes 1–4 at 30 and 70°C. A comparison of differential molecularmass distributions is shown in Fig. 5. The bimodal molecu larmass distribution functions are the linear superpo sition of differential distribution functions for two fractions of polymer macromolecules, which are plot ted as dashed lines. The ratio of molecular fractions with respect to the numerical concentration of PE macromolecules in the samples is shown in Table 2. As is seen from Fig. 5a, the polymers prepared in the presence of complex 1 containing the electron donor substituent tertBu in the para position of the phenoxy group at 30 and 70°C are characterized by a unimodal molecularmass distribution peaking at Mp ~ 480 × 103 (30°C) and ~290 × 103 (70°C), respec tively. This implies that, in the case of catalyst 1, the growth of polymer chains continues with time on the same number of active centers of similar nature at both 30 and 70°C. When complexes 2 and 3 containing electron acceptor substituents Br and Cl in the para position of the phenoxy group are used, PE formed at 30°C is characterized by a unimodal distribution with Mp ~ 330 × 103, while the polymer obtained at 70°C shows the bimodal distribution with the quantitative pre dominance of lower molecular mass fractions (Table 2). Thus, the PE sample synthesized with com plex 2 contains two fractions, with Mp ~ 250 × 103 POLYMER SCIENCE
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60 Time, min
(93%) and ~ 2000 × 103 (7%) (Fig. 5b), while the sam ple prepared with complex 3 contains fractions with Mp ~ 200 × 103 (93%) and ~1500 × 103 (7%) (Fig. 5c). This fact implies that, at 70°C, the growth of polymer
Table 2. Molecularmass characteristics of polymers prepared with complexes 1–4
Catalyst
Т, °С
Mw × 10–3
Mw /Mn
Ratio between peak areas of differential molecularmass distribution curves
0
40
20
1
30
600
2.00
100 : 0
70
460
2.13
100 : 0
30
434
2.23
100 : 0
70
421
2.67
93 : 7
30
470
2.25
100 : 0
70
403
2.29
93 : 7
30
537
3.57
78 : 22
70
446
3.64
69 : 31
2
3
4
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dn/d(logM) 1.0
(a)
Ph
1
2
N
Ti O
0.8
dn/d(logM) 1.0 (b)
Cl Cl
0.6 0.4
0.4
0.2
0.2
0
0
N
1 2
Ti O
0.8
Ti O
Cl
2
Ph
(d)
Cl
N
0.7
2
Cl
0.6
0.5
0.4
0.3
0.2
Cl
2
Br
0.9
Ph
1.0
Cl
N
1
0.8
2
0.6
(c)
Ph
1
Ti O
2
Cl Cl
2
O
0.1
0 4.5
5.0
5.5
6.0
6.5
7.0 logM
4.5
5.0
5.5
6.0
6.5
7.0 logM
Fig. 5. Differential molecularmass distribution curves for PE prepared with complexes (a) 1, (b) 2, (c) 3, and (d) 4 at (1) 30 and (2) 70°C.
chains proceeds on active centers of two isomeric forms of the catalyst. Under the action of complex 4, containing the electronacceptor substituent OCH3 in the para posi tion of the phenoxy group, the bimodal PE forms at both 30 and 70°C. Note that, in both cases, low molecularmass fractions with Mp ~ 230 × 103 (78%) and ~140 × 103 (69%), respectively, predominate; highmolecularmass fractions have Mp ~ 1300 × 103 (22%) and ~930 × 103 (31%) (Fig. 5d). These data lead us to state that, in the case of catalyst 4, the growth of polymer chains proceeds with time on different active centers of two isomeric forms at both 30 and 70°С. With change in the structure and nature of substit uents in the para position of the phenoxy group and the temperature of the process, the ratio between iso meric active centers changes. This effect makes it pos sible to control the molecularmass distribution of the resulting PE. Hence, the fine tuning of the structure of the bis(phenoxyimine) catalyst causes a targeted vari ation in the molecularmass characteristics of PE. For all polymers prepared with the use of com plexes 1–4, the structural and thermal characteristics were examined (Table 3).
As evidenced by FTIR spectroscopy (Table 3), PEs synthesized with complexes 1–4 in the presence of polymethylaluminoxane as a cocatalyst are almost devoid of methyl groups. This finding indicates the uniformity of the polymer chain (the absence of sub stituted ethylene groups), and a very low content of vinyl groups suggests an insignificant contribution of βhydride abstraction events. The thermal study of the polymers (maximum temperature of melting Tm) showed that the PE samples have Tm = (137–145)°C close to that of common highly linear ethylene poly mers [10]. These conclusions are validated by enthal pies of melting ΔH that were used to estimate the degree of crystallinity of the polymer (α = 78–86%) (Table 3). Our studies demonstrated that electronacceptor substituents Br and Cl located in the para position of the phenoxy group decrease the thermal stability of bis(phenoxyimine) complexes of titanium and the molecular mass of the polymers. After introduction of a small electronacceptor substituent in the ortho position of the phenoxy group, the bis(phenoxyimine) complex of titanium fully loses activity. Complexes containing electrondonor substituents tertBu and OCH3 in the para position of the phenoxy group make it possible to implement the living polymerization of
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Table 3. Properties of PE samples prepared with bis(phenoxyimine) complexes 1–4 Content of groups*
Т, °С
Catalyst 1
2
3
4
Тm, °С
ΔН, J/g
α, %
0.04
142.5
247
84
0
0.04
140.4
238
81
70
0
0.04
140.4
244
84
80
0
0.04
138.5
252
86
30
0
0.05
139.3
245
84
50
0
0.05
139.0
244
83
70
0
0.06
141.2
243
83
80
0
0.06
139.7
234
80
30
0
0.04
140.0
253
86
50
0
0.04
138.0
235
80
70
0
0.05
137.0
253
86
80
0
0.04
139.0
243
83
30
0
0.09
140.1
229
78
50
0
0.10
140.0
228
78
70
0
0.12
139.2
231
79
80
0
0.11
139.7
222
76
CH3–
CH2=CH–
30
0
50
* Per 1000 carbon atoms.
ethylene in the temperature range 30–70°C, while the presence of acceptor substituents Br and Cl deterio rates the living mechanism of ethylene polymerization even at 30°C. It is shown that PE samples with differ ent molecularmass distributions can be synthesized, depending on the electronic properties of substituents in the para position of the phenoxy group and the con ditions of polymerization. REFERENCES 1. M. Mitani, J. Saito, S.J. Ishii, et al., Chem. Record. 4, 137 (2004). 2. R. Furuyama, J. Saito, S. Ishii, et al., J. Mol. Catal., A 200, 31 (2003). 3. J. Suzuki, H. Terao, and T. Fujita, Bull. Chem. Soc. Jpn. 76, 1493 (2003). 4. S. S. Ivanchev, Usp. Khim. 76, 669 (2007).
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5. G. J. Domski, J. M. Rose, G. W. Coates, et al., Prog. Polym. Sci. 32, 30 (2007). 6. M. Yu. Malinskaya, N. I. Ivancheva, I. I. Oleinik, et al., Zh. Prikl. Khim. (S.Peterburg) 80, 1479 (2007). 7. S. Matsui, M. Mitani, J. Saito, et al., J. Am. Chem. Soc. 123, 6847 (2001). 8. Y. Tohi, T. Nakano, H. Makio, et al., Macromol. Chem. Phys. 205, 1179 (2004). 9. M. Mitani, J. Mohri, Y. Yoshida, et al., J. Am. Chem. Soc. 124, 3327 (2002). 10. R. Chiang, J. Polym. Sci. 36, 91 (1959). 11. N. Matsukawa, S. Matsui, M. Mitani, et al., J. Mol. Catal., A 169, 99 (2001). 12. S. S. Ivanchev, V. K. Badaev, N. I. Ivancheva, and S. Ya. Khaikin, Dokl. Akad. Nauk 394, 639 (2005). 13. Y. Tohi, T. Nakano, H. Makio, et al., Macromol. Chem. Phys. 205, 1179 (2004).
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