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Synthesis and characterization of oligomer from 1-decene catalyzed by supported Ziegler–Natta catalyst
EUROPEAN POLYMER JOURNAL
European Polymer Journal 41 (2005) 2909–2915
www.elsevier.com/locate/europolj
Synthesis and characterization of oligomer from 1-decene catalyzed by supported Ziegler–Natta catalyst Qigu Huang *, Liguo Chen, Li Ma, Zhifeng Fu, Wantai Yang The Key Laboratory of Beijing City on Preparation and Processing of Novel Polymer Materials, Beijing University of Chemical Technology, Beijing 100029, PR China Received 4 April 2005; received in revised form 25 May 2005; accepted 27 May 2005 Available online 27 July 2005
Abstract Oligomer of 1-decene was synthesized with Ziegler–Natta catalyst which consisted of TiCl4 and Et2AlCl, using MgCl2 as support. The effects of temperature, Al/Ti ratio, time, and concentration of the catalyst on polymerization behaviors were investigated. The results showed that the catalyst system was desirable for the oligomerization of 1-decene with good catalytic activity, 143.8 kg oligo/mol Ti h, under typical conditions. The oligomer obtained was characterized with GC–MASS, GC and 13C NMR methods. Those results indicated that the oligomer was of a mixture consisting of di-, tri-, tetra- and pentamer. The 13C NMR data also implied that chain propagation of the oligomer involved primarily head-to-tail 1,2-insertions, as well as head-to-head and tail-to-tail 2,1-insertions. 2005 Elsevier Ltd. All rights reserved. Keywords: Heterogeneous Ziegler–Natta catalyst; 1-Decene; Oligomerization; Regiostructure
1. Introduction Many efforts to improve upon the performance of natural mineral oil based lubricants by the synthesis of oligomers from linear superior alpha-olefins, for example 1-decene, have been the subject of important research and development in the petroleum industry for decades and have resulted in the relatively recent market introduction of a number of polyalpha-olefin (PAO) synthetic lubricants. Synthetic lubricant from 1-decene features stable viscosity over a wide range of temperature, chemical stability and low pour point, comparison to mineral oil. The synthetic lubricant exhibits lower
*
Corresponding author. E-mail address: [email protected] (Q. Huang).
friction and hence increases mechanical efficiency across the full spectrum of mechanical loads from worm gears to traction drives and does so over a wider range of operating conditions. It also features excellent compatibility with mineral oil and/or grease and non-toxic to human beings. Due to extensive investigations on the polymerization of propylene and vinyl monomers, the mechanism of the polymerization of alpha-olefins and the effect of that mechanism on polymer structure is reasonably well understood, providing a strong resource for targeting on potentially useful oligomerization methods and oligomer structures. Commercially useful synthetic lubricants have been prepared from 1-decene prompted by either cationic or Ziegler catalysts, etc. Oligomerization of 1-decene is usually performed in the presence of a Lewis Acid catalyst such as boron
0014-3057/$ - see front matter 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.eurpolymj.2005.05.040
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Q. Huang et al. / European Polymer Journal 41 (2005) 2909–2915
trifluoride [1] or aluminum chloride [2], coupling with higher conversion of greater than 90% to monomer. Novel high viscosity index (V.I.) lubricant comprising polyalpha-olefins has been synthesized with reduced chromium oligomerization catalyst on porous silica support [3]. This lubricant obtained has a branch ratio less than 0.19, not only comprises the product of an essentially regular head-to-tail polyalpha-olefin but also provides an oligomer with large pendant alkyl groups on the recurring polymeric unit. One characteristic of the molecular structure of 1alkene oligomers that has been found to correlate with improved lubricant properties in commercial synthetic lubricants is the ratio of methyl to methylene groups in the oligomer. The ratio is called the branch ratio and is calculated from infrared data. Herein branch means that methyl side groups are methyl groups which occupy positions other than the terminal positions of the first and last (i.e., alpha and omega) carbon atoms of the longest carbon chain. Herein this longest carbon chain is also referred to as the carbon backbone chain of the olefin [4]. Oligomers prepared from 1-decene by cationic polymerization have branch ratios of greater than 0.20. But those prepared by chromium or Ziegler catalyst have lower branch ratios. Whether by rearrangement or isomerization, it is clear that synthetic lubricant with branch ratio leads to the limits of achievable properties, particularly with respect to viscosity index and pour point obviously. Viscosity index was found to increase with lower branch ratio, inverse via pour point [5]. The treatment of boron trifluoride (BF3) remained in oligomers is difficult. In factory, a special equipment is required to handle it. Not only is BF3 harmful to the vessel and other equipment, but it can also result in lung and eye problems. Although in a view foregoing, reduced chromium compound is perfect for oligomerization of 1-alkene, it would become an oxidized compound when it is exposed to air. Oxidized chromium is very harmful to human beings and environment. And chromium compounds can be deposited in animal bodies, fruits and vegetables which are all important food to mankind. Fortunately, Ziegler–Natta catalyst can resolve those problems mentioned above. It can not only belong to friendly catalyst to human beings and environment, but also shows higher catalytic activity for oligomerization of 1-alkene as well, additionally, commercial attractions. Many studies have been done on the oligomerization of 1-alkene and vinyl monomers prompted by Ziegler– Natta catalysts. So far, homogeneous processes are predominated because of showing better catalytic activity for oligomerization of 1-alkene. But the work after polymerization is complicated. So, heterogeneous processing which would show higher catalytic activity for oligomerization of 1-alkene certainly has more attraction to
industry. Herein, we report an efficient heterogeneous processing for oligomerization of 1-decene catalyzed by Ziegler–Natta catalyst, using MgCl2 as support. The effects of the oligomerization conditions on the catalytic activity, as well as the structure of oligomer obtained, are investigated.
2. Experimental 2.1. Materials All procedures were carried out under nitrogen atmosphere in Schlenk flasks. Toluene and hexane were refluxed from metallic sodium under nitrogen for 12 h and distilled before use. Diethylaluminum chloride (AlEt2Cl) solution in n-heptane (400 g/l) was purchased from Aldrich; MgCl2 was calcinated under nitrogen flow at 200 C for 2 h, 400 C for 4 h prior to use; 1-decene was also purchased from Aldrich and was distilled and collected the fraction at 58–62 C under vacuum before use. The other chemicals were purchased commercially and used without further purification. 2.2. Preparation of TiCl4/MgCl2 supported catalyst Excess TiCl4 (5.0 ml) was dropped with a syringe in 30 min to the mixture of MgCl2 (5.0 g) suspended in 50 ml heptane under well-stirred condition at 0 C, then warmed to room temperature. The mixture was stirred overnight. After filtering, the residue was washed with heptane (30 ml · 5) and dried under vacuum. The supporting TiCl4/MgCl2 catalyst was obtained. The Ti content was determined by ICP–MS to be 3.22%. About 10 mg of the supporting catalyst was dissolved with HF and HNO3 acid completely. The solution was diluted with distilled water and used for ICP–MS analysis. 2.3. Polymerization All polymerizations were carried out in a 200 ml autoclave glass reactor equipped with a mechanical stirrer. After purging out all moisture and oxygen by a high-vacuum pump, the reactor was sealed under nitrogen atmosphere. Desired amounts of freshly prepared AlEt2Cl, supporting catalyst and toluene (20 ml) were introduced in this order, and the mixture was stirred for 15 min for preactivation. After that, 20 ml of 1-decene was added. Hydrogen was added as appropriate by syringe. The nitrogen pressure was maintained at 0.3 MPa throughout the course of the reaction. The polymerization was stopped after 1 h at a selected temperature, then terminated by the addition of acidified alcohol. After filtering, the residue was washed with alcohol. The filtrate was concentrated under common
Q. Huang et al. / European Polymer Journal 41 (2005) 2909–2915
pressure then heated to remove the monomer under vacuum. The fraction from 90 C to 160 C was collected under vacuum, which was of 1-decene oligomers consisting of di-, tri-, tetra- and pentamer. The residue after distillation comprised of polymer with higher polymerization degree was sticky like paraffine. The conversion and the catalytic activity of PAO (polyalpha olefin consisting of polymer and oligomer) were calculated by the weight of the fraction distilled and of the residue to monomerÕs weight, while the conversion and the catalytic activity of oligomer was calculated by the weight of fraction distilled to monomerÕs weight.
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(30 m · 0.25 mm, 0.25 lm film thickness) was used. Nitrogen was used as the carrier. The column temperature program was set from room temperature to 100 C at a rate 10 C/min, followed by an increase to 300 C at a rate of 30 C/min for 1 h. The injection port of the GC was set at 320 C. 13 C NMR spectra of oligomer samples were obtained on an INOVA500 MHz instrument. The conditions used for quantitative 13C NMR were 15 wt% sample in benzene-d6, at room temperature, 90 pulse angle, inversegated decoupling with a 3 s delay between pulses, 1000 scans, tetramethylsilane as internal reference.
2.4. Characterization Gas chromatography–mass spectrometry (GC–MS) was performed on HP-6890GC-5973MSD. A fusedsilica capillary column DB-5 MS (30 m · 0.25 mm, 0.25 lm film thickness) was used. Helium and methane were used as the carrier and the reagent gas, respectively, for negative-ion chemical ionization. The following oven temperature program was used: 2 min at 70 C, then an increase to 100 C at a rate 10 C/min, followed by an increase to 300 C at a rate of 30 C/min for 1 h. The injection port of the GC was set at 300 C. The energy of 70 eV was used for electron ionization. When solvent comes off the GC column and hits the MS detector, the concentration of the solvent can be so high that it is destructive to the instrument. To prevent this from happening, the detector is programmed to be turned off during the time the solvent hits the detector. The maximum molecular weight that can be detected by this GC–MS instrument is approximately 500 Da. Gas chromatography (GC) was recorded on AGILENT-6890. A fused-silica capillary column DB-5 MS
3. Results and discussion 3.1. Oligomerization behaviors The effect of temperature on 1-decene polymerization behaviors was investigated and the data was shown in Table 1. One can notice that the highest catalytic activity of 198.6 kg PAO/mol Ti h for PAO and 143.8 kg oligo/ mol Ti h for oligomer was obtained at 60 C, respectively. The catalytic activity of oligomer formation was increased with the increase in temperature, for instance, the catalytic activity of 75.3 kg oligo/mol Ti h was obtained at 40 C, the greatest catalytic activity 143.8 kg oligo/mol Ti h at 60 C. However, if the temperature was over 60 C, the catalytic activity was slightly decreased, 121.9 kg oligo/mol Ti h at 80 C. Warm heating is possible of benefits to chain propagation to obtain more oligomer and PAO. But higher temperature usually resulted in species deactivated in coordination polymerization [6]. The percentage of dimer was increased
Table 1 The effect of temperature on the polymerization of 1-decene promoted by TiCl4/MgCl2/Et2AlCl Run
T (C)
Al/Ti (mol/mol)
PAOa (g)
Oligomerb (g)
Activityc (kg PAO/mol Ti h)
Activityd (kg oligo/mol Ti h)
Oligomer analysis (%)e Di-
Tri-
Tetra-
Penta
1 2 3 4 5 6 7 8
40 50 60 70 80 60 60 60
40 40 40 40 40 20 30 50
10.1 12.6 14.5 14.1 13.2 11.9 13.6 12.6
5.5 7.7 10.5 9.5 8.9 8.53 9.40 9.32
138.3 172.6 198.6 193.1 180.8 163.0 186.3 172.6
75.3 105.4 143.8 130.1 121.9 116.8 128.8 127.7
9 14 18 25 28 16 19 25
28 36 45 43 44 26 48 40
32 39 31 29 25 35 29 29
31 11 6 3 3 23 4 6
Polymerization conditions: catalyst (Ti), 7.3 · 102 mmol; 1-decene: 20 ml (14.8 g); solvent, toluene, 20 ml; time: 1 h; Al (AlEt2Cl)/Ti, 40. a The total weight of products. b The oligomersÕ weight. c Total activity for PAO. d Activity for oligomer consisting of di-, tri-, tetra- and pentamer. e Determined by GC.
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with the increase in temperature, but the amount of pentamer was decreased (runs 1–5 in Table 1). It was possible that the chain transfer took place easily at higher temperature. The effects of Al (alkyl aluminum)/Ti ratio on polymerization behaviors of 1-decene are shown in Table 1 (runs 3, 6, 7 and 8). The supporting catalyst exhibited the highest catalytic activity, 148.3 kg oligo/mol Ti h for oligomer, 198.6 kg PAO/mol Ti h for PAO at Al/ Ti = 40 (mol/mol) (run 3 in Table 1). The catalytic activities, however, were decreased regardless of the increase or decrease in Al/Ti ratio (runs 6, 7 and 8 in Table 1), for example, the catalytic activities, 126.8 kg oligo/mol Ti h for oligomer and 186.3 kg PAO/mol Ti h for PAO were obtained at Al/Ti = 30, and 127.7 kg oligo/mol Ti h for oligomer and 172.6 kg PAO/mol Ti h for PAO were obtained at Al/Ti = 50. It was thought that Al/Ti ratio had obvious effect on active species. Too little amount of alkyl aluminum could not completely eliminate impurity not good for olefins polymerization in the reaction system. On the other hand, in the presence of alkyl aluminum, TiCl4 was alkylated and reduced to become Ti3+ which was confirmed as active species for olefins polymerization [6,7]. Excessive amount of alkyl aluminum would result in the formation of Ti2+ not good for alkylene polymerization. One can note that the catalytic activity of 1-decene oligomerization was increased with the Al/Ti ratio, shows the greatest value at Al/Ti = 40. But the catalytic activity was not decreased sharply when Al/Ti was over 40, even up to 50 (run 8 in Table 1). It was possible that chain transfer to hydrogen and/or b-hydrogen elimination were predominated as the pathway of chain transfer rather than to alkyl aluminum for 1-decene oligomerization. Maybe, 1-decene coupled with longer side chain curved around the active species and exhibited large bulk to keep from chain transfer to alkyl aluminum. The effects of Ti concentration on 1-decene polymerization were shown in Fig. 1. The catalytic activity of 1-decene oligomerization decreased obviously with the increase in Ti concentration (Fig. 1a). The catalytic activity of 210 kg PAO/mol Ti h was obtained at Ti being 2.6 · 105 mol, however, 175 kg PAO/mol Ti h was obtained when Ti concentration was up to 1.8 · 104 mol. But the catalytic activity of oligomerization of 1-decene was slightly increased with increase in Ti concentration (Fig. 1b). The catalytic activity of 105 kg oligo/mol Ti h was obtained at Ti being 2.6 · 105 mol, and it was increased to 153.1 kg oligo/mol Ti h when Ti concentration was up to 1.8 · 104 mol. The effect of polymerization time on catalytic activity is shown in Fig. 2. One can note that the catalytic activity of PAO was slightly decreased with increase of polymerization time. The catalytic activity of PAO was reduced from 207.3 kg PAO/mol Ti h in polymeri-
Fig. 1. The effect of Ti concentration on catalytic activity of 1decene polymerization catalyzed by TiCl4/MgCl2/Et2AlCl. Polymerization conditions: Al/Ti = 40; T = 60 C; 1-decene: 20 ml (14.8 g); solvent, toluene, 20 ml; time: 1 h. (a) The catalytic activity of PAO; (b) the catalytic activity of oligomer of 1-decene.
Fig. 2. The effect of polymerization time on catalytic activity of 1-decene polymerization catalyzed by TiCl4/MgCl2/Et2AlCl. Polymerization conditions: catalyst (Ti): 7.3 · 102 mmol; Al/ Ti = 40; T = 60 C; 1-decene: 20 ml (14.8 g); solvent, toluene, 20 ml. (a) The catalytic activity of PAO; (b) the catalytic activity of oligomer of 1-decene.
zation time 20 min to 198.6 kg PAO/mol Ti h in 60 min and to 165.2 kg PAO/mol Ti h in 150 min (Fig. 2a). But the catalytic activity of oligomer of 1-decene was obviously decreased with increase of polymerization time (Fig. 2b). It was reduced from 153.3 kg oligo/ mol Ti h in polymerization time 20 min to 72.8 kg oligo/ mol Ti h in 150 min.
Q. Huang et al. / European Polymer Journal 41 (2005) 2909–2915
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3.2. Characterization The GC–MS results of oligomer (run 3 in Table 1) are shown in Fig. 3. One can note that the oligomer was a mixture consisting of four fractions that the elution time were 17.5 min, 30.2 min, 33.4 min and 41.3 min, respectively. The MS analysis confirmed that the first fraction, elution time about 17.5 min was dimer because of M+ = 281 [M + H], the molecular weight was just as two times as that of 1-decene. The second fraction, M+ = 421 [M + H], was trimer. The tetramer and pentamerÕs M+ was not obtained because of the maximum molecular weight of the GC–MS instrument is 500 Da. By deduced, the third and the fourth fraction, elution time about 33.4 and 41.3 min, were tetra- and pentamer, respectively. By contrast, the elution time of 1-decene was 13.2 min. The percent of oligomers of 1-decene obtained was determined by GC instrument. One can note from Table 1 that the percent of dimer of the oligomer were increased with the increase in temperature (runs 1–5) and in Al/Ti ratio (runs 6, 7, 3 and 8). However, the percent of pentamer was decreased with the increase in temperature. The microstructures of oligomers obtained with catalyst TiCl4/MgCl2/Et2AlCl were analyzed by 13C NMR (Fig. 4). From Fig. 4, the 13C NMR results confirmed that the oligomer contained regioirregular structures and a
Fig. 4. The
13
Fig. 3. The GC–mass spectra of oligomer of 1-decene (run 3 in Table 1).
nonnegligible proportion of 1-decene units arranged in tail-to-tail and head-to-head sequences were observed. Any signals of the residue from cocatalyst and of double
C NMR spectra of oligomer of 1-decene (run 3 in Table 1).
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Q. Huang et al. / European Polymer Journal 41 (2005) 2909–2915 16
C
6
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9
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C C
C5
C6 C8
Scheme 1. (a) Dimers of oligomer from 1-decene. (b) Trimers of oligomer from 1-decene. (c) Tetramer of oligomer from 1-decene.
Q. Huang et al. / European Polymer Journal 41 (2005) 2909–2915
bond in oligomer were not observed from 13C NMR spectra. The result indicated that the chain transfer to hydrogen was predominated, while the chain transfer to cocatalyst and b-hydrogen elimination were negligible. The regiostructures and assignments of 13C NMR of di-, tri-, and tetramer of 1-decene are compiled in Scheme 1. The subscript numbers in Scheme 1 are referred to in Fig. 4. The calculation of theoretical chemical shifts was referenced with Grant and Paul [8] and previous works [6,9]. For dimers of 1-decene, three kinds of sequences, head-to-tail (bb), tail-to-tail (bc) and headto-head (cb), were possibly produced. Tertiary carbons Tax (bb) and Tab (cb) were identified by the presence of the resonances at d 33.32 and 45.25 ppm, labeled with the number 13 and 21 in Fig. 4 and Scheme 1a. For trimers, four sequences could be obtained (Scheme 1b). One of them, head-to-tail (bbb) sequence existed two kinds of tertiary carbons in backbone, Tbb and Tbx, assigned at d 30.96 and 36.15 ppm and labeled by 9 and 16 in Fig. 4 and Scheme 1b. Txx at d 38.10 ppm was attributed to the tertiary carbon of bbc; Tax and Tab at d 46.31 and 49.30 ppm to cbc; Tba, T 0ab and T 0bb at d 45.25, 46.31 and 30.96 ppm to cbc sequences, labeled by 17, 22, 23 and 9, respectively. Six kinds of sequences for tetramers could be obtained (Scheme 1c). Tertiary carbons Txb, Tbb and T 0bb at d 39.75, 33.32 and 30.95 ppm were attributed to bbbb sequence. Tbx at d 38.10 ppm to bbbc, Tax, Tab and Tbb at d 46.31, 49.30 and 30.95 ppm to bcbb, Tax at d 46.31 ppm to bcbc, Tba, Tab, Tbb and T 0bb at d 45.25, 46.31, 32.30 and 30.95 ppm to cbbb, Tba, Tab and Tbx at d 45.25, 46.31 and 30.95 ppm to cbbc sequences, respectively. Methyl and ethyl carbons are assigned in Fig. 4 and labeled in Scheme 1. The regiostructures of pentamer, however, are not listed in Scheme 1, because the same assignments as that of tetramers were revealed by calculation according to Grant method [8]. 4. Conclusion Supported catalyst TiCl4/MgCl2/Et2AlCl exhibited higher catalytic activity for 1-decene oligomerization. Polymerization conditions such as polymerization temperature, Al/Ti ratio, Ti concentration and time showed considerable effects on catalytic activity and component of oligomers. The catalytic activity of 143.8 kg oligo/mol Ti h for oligomer was obtained under the typical conditions of Al/Ti ratio 40, Ti concentration 7.3 · 102 mmol/l, temperature 60 C and time 1 h. 13C NMR results confirmed regiostructures of oligomers from 1decene catalyzed by TiCl4/MgCl2/Et2AlCl catalyst and chain transfer to hydrogen was predominated.
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Acknowledgement Financial support of this research from the Natural Science Fund of Beijing University of Chemical and Technology for young scientist is gratefully acknowledged (Grant No. QN0406). References [1] Morganson NE, Bercik PG. Oligomerizing 1-olefins with a heterogeneous catalyst. US 4 365 105, 1982. [2] Bobsein RL. Catalyst compositions. US 4 436 948, 1984. [3] (a) Wu MM. Process for manufacturing olefinic oligomers having lubricating properties. US 4 827 073, 1989; (b) Wu MM. High viscosity index synthetic lubricant compositions. US 4 827 064, 1989. [4] (a) Pelrine BP. Fixed bed process for high viscosity index lubricant. US 4 914 254, 1990; (b) Clarembeau M. Production of monoolefin oligomer. US 6 002 061, 1999; (c) Sarin R, Sabyasachi S, Rai MM, Ghosh S, Bhatnagar AK, Sivaram S, et al., Process for oligomerisation of alphaolefins. US 6 002 060, 1999. [5] (a) Huang Q, Chen W, Jing Z. Oligomerization of alphaolefin. CN 1 453 254A, 2003; (b) Huang Q, Chen L, Fu Z, Jing Z, Yang W. Decene-1 oligomerization catalyzed by Ziegler–Natta catalyst supported. Petrochem Technol 2004;33(10):928–32 (in Chinese). [6] (a) Huang Q, Wu Q, Zhu F, Lin S. Synthesis and characterization of high molecular weight atactic polybutene-1 with half-titaniocene/MAO catalyst system. J Polym Sci Part A: Polym Chem 2001;39:4068–73; (b) Huang Q, Wu Q, Zhu F, Lin S. The synthesis of high molecular weight polybutene-1 catalyzed by Cp*Ti (OBz)3/ MAO. Polym Int 2001;50:45–8; (c) Zhu F, Huang Q, Lin S. Synthesis of multi-stereoblock polybutene-1 using novel monocyclopentadienyltitanium and modified methylalumiunoxane catalyst. J Polym Sci Part A: Polym Chem 1999;37:4497–502. [7] Asanuma T, Nishimorl Y, Ito M, Uchlkawa N, Shlomura T. Preparation of syndiotactic polyolefins by using metallocene catalysts. Polym Bull 1991;25:567–71. [8] Grant HK, Paul GE. Carbon-13 magnetic resonance. II Chemical shift data fir the alkanes. J Am Chem Soc 1964; 86:2984–8. [9] (a) Huang Q, Wu Q, Zhu F, Lin S. The characterization of polybutene-1 catalyzed by metallocene catalyst. ACTA Polym Sin 2001;1:49–53 (in Chinese); (b) Huang Q, Wu Q, Zhu F, Lin S. The synthesis of polybutene-1 catalyzed with metallocene catalyst. ACTA Polym Sin 2000;4:489–92 (in Chinese); (c) Huang Q, Wu Q, Zhu F, Lin S. Synthesis and characterization of high molecular weight polybutene-1 catalyzed with metallocene complexes/MAO catalyst system. J Chin Chem Uni 2002;23(1):167–9 (in Chinese).
European Polymer Journal 41 (2005) 2909–2915
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Synthesis and characterization of oligomer from 1-decene catalyzed by supported Ziegler–Natta catalyst Qigu Huang *, Liguo Chen, Li Ma, Zhifeng Fu, Wantai Yang The Key Laboratory of Beijing City on Preparation and Processing of Novel Polymer Materials, Beijing University of Chemical Technology, Beijing 100029, PR China Received 4 April 2005; received in revised form 25 May 2005; accepted 27 May 2005 Available online 27 July 2005
Abstract Oligomer of 1-decene was synthesized with Ziegler–Natta catalyst which consisted of TiCl4 and Et2AlCl, using MgCl2 as support. The effects of temperature, Al/Ti ratio, time, and concentration of the catalyst on polymerization behaviors were investigated. The results showed that the catalyst system was desirable for the oligomerization of 1-decene with good catalytic activity, 143.8 kg oligo/mol Ti h, under typical conditions. The oligomer obtained was characterized with GC–MASS, GC and 13C NMR methods. Those results indicated that the oligomer was of a mixture consisting of di-, tri-, tetra- and pentamer. The 13C NMR data also implied that chain propagation of the oligomer involved primarily head-to-tail 1,2-insertions, as well as head-to-head and tail-to-tail 2,1-insertions. 2005 Elsevier Ltd. All rights reserved. Keywords: Heterogeneous Ziegler–Natta catalyst; 1-Decene; Oligomerization; Regiostructure
1. Introduction Many efforts to improve upon the performance of natural mineral oil based lubricants by the synthesis of oligomers from linear superior alpha-olefins, for example 1-decene, have been the subject of important research and development in the petroleum industry for decades and have resulted in the relatively recent market introduction of a number of polyalpha-olefin (PAO) synthetic lubricants. Synthetic lubricant from 1-decene features stable viscosity over a wide range of temperature, chemical stability and low pour point, comparison to mineral oil. The synthetic lubricant exhibits lower
*
Corresponding author. E-mail address: [email protected] (Q. Huang).
friction and hence increases mechanical efficiency across the full spectrum of mechanical loads from worm gears to traction drives and does so over a wider range of operating conditions. It also features excellent compatibility with mineral oil and/or grease and non-toxic to human beings. Due to extensive investigations on the polymerization of propylene and vinyl monomers, the mechanism of the polymerization of alpha-olefins and the effect of that mechanism on polymer structure is reasonably well understood, providing a strong resource for targeting on potentially useful oligomerization methods and oligomer structures. Commercially useful synthetic lubricants have been prepared from 1-decene prompted by either cationic or Ziegler catalysts, etc. Oligomerization of 1-decene is usually performed in the presence of a Lewis Acid catalyst such as boron
0014-3057/$ - see front matter 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.eurpolymj.2005.05.040
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Q. Huang et al. / European Polymer Journal 41 (2005) 2909–2915
trifluoride [1] or aluminum chloride [2], coupling with higher conversion of greater than 90% to monomer. Novel high viscosity index (V.I.) lubricant comprising polyalpha-olefins has been synthesized with reduced chromium oligomerization catalyst on porous silica support [3]. This lubricant obtained has a branch ratio less than 0.19, not only comprises the product of an essentially regular head-to-tail polyalpha-olefin but also provides an oligomer with large pendant alkyl groups on the recurring polymeric unit. One characteristic of the molecular structure of 1alkene oligomers that has been found to correlate with improved lubricant properties in commercial synthetic lubricants is the ratio of methyl to methylene groups in the oligomer. The ratio is called the branch ratio and is calculated from infrared data. Herein branch means that methyl side groups are methyl groups which occupy positions other than the terminal positions of the first and last (i.e., alpha and omega) carbon atoms of the longest carbon chain. Herein this longest carbon chain is also referred to as the carbon backbone chain of the olefin [4]. Oligomers prepared from 1-decene by cationic polymerization have branch ratios of greater than 0.20. But those prepared by chromium or Ziegler catalyst have lower branch ratios. Whether by rearrangement or isomerization, it is clear that synthetic lubricant with branch ratio leads to the limits of achievable properties, particularly with respect to viscosity index and pour point obviously. Viscosity index was found to increase with lower branch ratio, inverse via pour point [5]. The treatment of boron trifluoride (BF3) remained in oligomers is difficult. In factory, a special equipment is required to handle it. Not only is BF3 harmful to the vessel and other equipment, but it can also result in lung and eye problems. Although in a view foregoing, reduced chromium compound is perfect for oligomerization of 1-alkene, it would become an oxidized compound when it is exposed to air. Oxidized chromium is very harmful to human beings and environment. And chromium compounds can be deposited in animal bodies, fruits and vegetables which are all important food to mankind. Fortunately, Ziegler–Natta catalyst can resolve those problems mentioned above. It can not only belong to friendly catalyst to human beings and environment, but also shows higher catalytic activity for oligomerization of 1-alkene as well, additionally, commercial attractions. Many studies have been done on the oligomerization of 1-alkene and vinyl monomers prompted by Ziegler– Natta catalysts. So far, homogeneous processes are predominated because of showing better catalytic activity for oligomerization of 1-alkene. But the work after polymerization is complicated. So, heterogeneous processing which would show higher catalytic activity for oligomerization of 1-alkene certainly has more attraction to
industry. Herein, we report an efficient heterogeneous processing for oligomerization of 1-decene catalyzed by Ziegler–Natta catalyst, using MgCl2 as support. The effects of the oligomerization conditions on the catalytic activity, as well as the structure of oligomer obtained, are investigated.
2. Experimental 2.1. Materials All procedures were carried out under nitrogen atmosphere in Schlenk flasks. Toluene and hexane were refluxed from metallic sodium under nitrogen for 12 h and distilled before use. Diethylaluminum chloride (AlEt2Cl) solution in n-heptane (400 g/l) was purchased from Aldrich; MgCl2 was calcinated under nitrogen flow at 200 C for 2 h, 400 C for 4 h prior to use; 1-decene was also purchased from Aldrich and was distilled and collected the fraction at 58–62 C under vacuum before use. The other chemicals were purchased commercially and used without further purification. 2.2. Preparation of TiCl4/MgCl2 supported catalyst Excess TiCl4 (5.0 ml) was dropped with a syringe in 30 min to the mixture of MgCl2 (5.0 g) suspended in 50 ml heptane under well-stirred condition at 0 C, then warmed to room temperature. The mixture was stirred overnight. After filtering, the residue was washed with heptane (30 ml · 5) and dried under vacuum. The supporting TiCl4/MgCl2 catalyst was obtained. The Ti content was determined by ICP–MS to be 3.22%. About 10 mg of the supporting catalyst was dissolved with HF and HNO3 acid completely. The solution was diluted with distilled water and used for ICP–MS analysis. 2.3. Polymerization All polymerizations were carried out in a 200 ml autoclave glass reactor equipped with a mechanical stirrer. After purging out all moisture and oxygen by a high-vacuum pump, the reactor was sealed under nitrogen atmosphere. Desired amounts of freshly prepared AlEt2Cl, supporting catalyst and toluene (20 ml) were introduced in this order, and the mixture was stirred for 15 min for preactivation. After that, 20 ml of 1-decene was added. Hydrogen was added as appropriate by syringe. The nitrogen pressure was maintained at 0.3 MPa throughout the course of the reaction. The polymerization was stopped after 1 h at a selected temperature, then terminated by the addition of acidified alcohol. After filtering, the residue was washed with alcohol. The filtrate was concentrated under common
Q. Huang et al. / European Polymer Journal 41 (2005) 2909–2915
pressure then heated to remove the monomer under vacuum. The fraction from 90 C to 160 C was collected under vacuum, which was of 1-decene oligomers consisting of di-, tri-, tetra- and pentamer. The residue after distillation comprised of polymer with higher polymerization degree was sticky like paraffine. The conversion and the catalytic activity of PAO (polyalpha olefin consisting of polymer and oligomer) were calculated by the weight of the fraction distilled and of the residue to monomerÕs weight, while the conversion and the catalytic activity of oligomer was calculated by the weight of fraction distilled to monomerÕs weight.
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(30 m · 0.25 mm, 0.25 lm film thickness) was used. Nitrogen was used as the carrier. The column temperature program was set from room temperature to 100 C at a rate 10 C/min, followed by an increase to 300 C at a rate of 30 C/min for 1 h. The injection port of the GC was set at 320 C. 13 C NMR spectra of oligomer samples were obtained on an INOVA500 MHz instrument. The conditions used for quantitative 13C NMR were 15 wt% sample in benzene-d6, at room temperature, 90 pulse angle, inversegated decoupling with a 3 s delay between pulses, 1000 scans, tetramethylsilane as internal reference.
2.4. Characterization Gas chromatography–mass spectrometry (GC–MS) was performed on HP-6890GC-5973MSD. A fusedsilica capillary column DB-5 MS (30 m · 0.25 mm, 0.25 lm film thickness) was used. Helium and methane were used as the carrier and the reagent gas, respectively, for negative-ion chemical ionization. The following oven temperature program was used: 2 min at 70 C, then an increase to 100 C at a rate 10 C/min, followed by an increase to 300 C at a rate of 30 C/min for 1 h. The injection port of the GC was set at 300 C. The energy of 70 eV was used for electron ionization. When solvent comes off the GC column and hits the MS detector, the concentration of the solvent can be so high that it is destructive to the instrument. To prevent this from happening, the detector is programmed to be turned off during the time the solvent hits the detector. The maximum molecular weight that can be detected by this GC–MS instrument is approximately 500 Da. Gas chromatography (GC) was recorded on AGILENT-6890. A fused-silica capillary column DB-5 MS
3. Results and discussion 3.1. Oligomerization behaviors The effect of temperature on 1-decene polymerization behaviors was investigated and the data was shown in Table 1. One can notice that the highest catalytic activity of 198.6 kg PAO/mol Ti h for PAO and 143.8 kg oligo/ mol Ti h for oligomer was obtained at 60 C, respectively. The catalytic activity of oligomer formation was increased with the increase in temperature, for instance, the catalytic activity of 75.3 kg oligo/mol Ti h was obtained at 40 C, the greatest catalytic activity 143.8 kg oligo/mol Ti h at 60 C. However, if the temperature was over 60 C, the catalytic activity was slightly decreased, 121.9 kg oligo/mol Ti h at 80 C. Warm heating is possible of benefits to chain propagation to obtain more oligomer and PAO. But higher temperature usually resulted in species deactivated in coordination polymerization [6]. The percentage of dimer was increased
Table 1 The effect of temperature on the polymerization of 1-decene promoted by TiCl4/MgCl2/Et2AlCl Run
T (C)
Al/Ti (mol/mol)
PAOa (g)
Oligomerb (g)
Activityc (kg PAO/mol Ti h)
Activityd (kg oligo/mol Ti h)
Oligomer analysis (%)e Di-
Tri-
Tetra-
Penta
1 2 3 4 5 6 7 8
40 50 60 70 80 60 60 60
40 40 40 40 40 20 30 50
10.1 12.6 14.5 14.1 13.2 11.9 13.6 12.6
5.5 7.7 10.5 9.5 8.9 8.53 9.40 9.32
138.3 172.6 198.6 193.1 180.8 163.0 186.3 172.6
75.3 105.4 143.8 130.1 121.9 116.8 128.8 127.7
9 14 18 25 28 16 19 25
28 36 45 43 44 26 48 40
32 39 31 29 25 35 29 29
31 11 6 3 3 23 4 6
Polymerization conditions: catalyst (Ti), 7.3 · 102 mmol; 1-decene: 20 ml (14.8 g); solvent, toluene, 20 ml; time: 1 h; Al (AlEt2Cl)/Ti, 40. a The total weight of products. b The oligomersÕ weight. c Total activity for PAO. d Activity for oligomer consisting of di-, tri-, tetra- and pentamer. e Determined by GC.
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with the increase in temperature, but the amount of pentamer was decreased (runs 1–5 in Table 1). It was possible that the chain transfer took place easily at higher temperature. The effects of Al (alkyl aluminum)/Ti ratio on polymerization behaviors of 1-decene are shown in Table 1 (runs 3, 6, 7 and 8). The supporting catalyst exhibited the highest catalytic activity, 148.3 kg oligo/mol Ti h for oligomer, 198.6 kg PAO/mol Ti h for PAO at Al/ Ti = 40 (mol/mol) (run 3 in Table 1). The catalytic activities, however, were decreased regardless of the increase or decrease in Al/Ti ratio (runs 6, 7 and 8 in Table 1), for example, the catalytic activities, 126.8 kg oligo/mol Ti h for oligomer and 186.3 kg PAO/mol Ti h for PAO were obtained at Al/Ti = 30, and 127.7 kg oligo/mol Ti h for oligomer and 172.6 kg PAO/mol Ti h for PAO were obtained at Al/Ti = 50. It was thought that Al/Ti ratio had obvious effect on active species. Too little amount of alkyl aluminum could not completely eliminate impurity not good for olefins polymerization in the reaction system. On the other hand, in the presence of alkyl aluminum, TiCl4 was alkylated and reduced to become Ti3+ which was confirmed as active species for olefins polymerization [6,7]. Excessive amount of alkyl aluminum would result in the formation of Ti2+ not good for alkylene polymerization. One can note that the catalytic activity of 1-decene oligomerization was increased with the Al/Ti ratio, shows the greatest value at Al/Ti = 40. But the catalytic activity was not decreased sharply when Al/Ti was over 40, even up to 50 (run 8 in Table 1). It was possible that chain transfer to hydrogen and/or b-hydrogen elimination were predominated as the pathway of chain transfer rather than to alkyl aluminum for 1-decene oligomerization. Maybe, 1-decene coupled with longer side chain curved around the active species and exhibited large bulk to keep from chain transfer to alkyl aluminum. The effects of Ti concentration on 1-decene polymerization were shown in Fig. 1. The catalytic activity of 1-decene oligomerization decreased obviously with the increase in Ti concentration (Fig. 1a). The catalytic activity of 210 kg PAO/mol Ti h was obtained at Ti being 2.6 · 105 mol, however, 175 kg PAO/mol Ti h was obtained when Ti concentration was up to 1.8 · 104 mol. But the catalytic activity of oligomerization of 1-decene was slightly increased with increase in Ti concentration (Fig. 1b). The catalytic activity of 105 kg oligo/mol Ti h was obtained at Ti being 2.6 · 105 mol, and it was increased to 153.1 kg oligo/mol Ti h when Ti concentration was up to 1.8 · 104 mol. The effect of polymerization time on catalytic activity is shown in Fig. 2. One can note that the catalytic activity of PAO was slightly decreased with increase of polymerization time. The catalytic activity of PAO was reduced from 207.3 kg PAO/mol Ti h in polymeri-
Fig. 1. The effect of Ti concentration on catalytic activity of 1decene polymerization catalyzed by TiCl4/MgCl2/Et2AlCl. Polymerization conditions: Al/Ti = 40; T = 60 C; 1-decene: 20 ml (14.8 g); solvent, toluene, 20 ml; time: 1 h. (a) The catalytic activity of PAO; (b) the catalytic activity of oligomer of 1-decene.
Fig. 2. The effect of polymerization time on catalytic activity of 1-decene polymerization catalyzed by TiCl4/MgCl2/Et2AlCl. Polymerization conditions: catalyst (Ti): 7.3 · 102 mmol; Al/ Ti = 40; T = 60 C; 1-decene: 20 ml (14.8 g); solvent, toluene, 20 ml. (a) The catalytic activity of PAO; (b) the catalytic activity of oligomer of 1-decene.
zation time 20 min to 198.6 kg PAO/mol Ti h in 60 min and to 165.2 kg PAO/mol Ti h in 150 min (Fig. 2a). But the catalytic activity of oligomer of 1-decene was obviously decreased with increase of polymerization time (Fig. 2b). It was reduced from 153.3 kg oligo/ mol Ti h in polymerization time 20 min to 72.8 kg oligo/ mol Ti h in 150 min.
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3.2. Characterization The GC–MS results of oligomer (run 3 in Table 1) are shown in Fig. 3. One can note that the oligomer was a mixture consisting of four fractions that the elution time were 17.5 min, 30.2 min, 33.4 min and 41.3 min, respectively. The MS analysis confirmed that the first fraction, elution time about 17.5 min was dimer because of M+ = 281 [M + H], the molecular weight was just as two times as that of 1-decene. The second fraction, M+ = 421 [M + H], was trimer. The tetramer and pentamerÕs M+ was not obtained because of the maximum molecular weight of the GC–MS instrument is 500 Da. By deduced, the third and the fourth fraction, elution time about 33.4 and 41.3 min, were tetra- and pentamer, respectively. By contrast, the elution time of 1-decene was 13.2 min. The percent of oligomers of 1-decene obtained was determined by GC instrument. One can note from Table 1 that the percent of dimer of the oligomer were increased with the increase in temperature (runs 1–5) and in Al/Ti ratio (runs 6, 7, 3 and 8). However, the percent of pentamer was decreased with the increase in temperature. The microstructures of oligomers obtained with catalyst TiCl4/MgCl2/Et2AlCl were analyzed by 13C NMR (Fig. 4). From Fig. 4, the 13C NMR results confirmed that the oligomer contained regioirregular structures and a
Fig. 4. The
13
Fig. 3. The GC–mass spectra of oligomer of 1-decene (run 3 in Table 1).
nonnegligible proportion of 1-decene units arranged in tail-to-tail and head-to-head sequences were observed. Any signals of the residue from cocatalyst and of double
C NMR spectra of oligomer of 1-decene (run 3 in Table 1).
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Q. Huang et al. / European Polymer Journal 41 (2005) 2909–2915 16
C
6
13
C
C
C2
C8
C
C 14
C8
C6
C
C8
C
C6
C8
C8
C
C8
C
C8
C7
C8
C
C7
C
C8
C7
C7
C
C7
C
C7
C 10
C 10
C
C 10
C
C 10
C4
C4
C
C4
C
C4
C1
C1
C
C1
C
C1
15
C
16
C
C
20
(a)
9
C
C4
C
6
14
C
17
C
6
14
C
C
C8
C
C8
C 15
C 16
C8
C 14
C8
C6
C6
C8
C6
C6
C8
C8
C8
C8
C8
C8
//
//
//
8
22
C3
8
22
C 14
C 14
C 14
C 16
C8
C6
C6
C6
C5
C8
C8
C8
C8
C8
C8
//
//
//
//
//
//
C
C
C8
C11
C8
C
C C C18 C16 C13 C20
9C
2
C
9
C
23
11
C
(b)
14
C3
8
C
C3
14
C8
C 15
C 15
C
C 14
C8
C6
C6
C6
C8
C8
C6
C8
C8
C8
C8
C8
C8
C8
C8
C8
//
//
//
//
//
//
//
//
11
C C
C
C8 C8 //
11
8C C
22
22
8
C11 C8
C
C8
C 16
C8
C C11
C 11
C8
C5
C8
C8
C6
C8
C8
C8
C8
C8
C8
C8
C8
//
//
//
//
//
//
//
C
C 15 C C11 C 14 C6 C
20
9
C
C3
C 14
22 C C19 C 10
C 16
C 16
C6
C6
C5
C8
C8
//
//
C C
8
14
C
22
8
C8
21
23
C8
C18
C17 C C17 C14 C8 C 8
C C
C 17
C
//
// 21
C
C
8
2
21
C
C
15
8
C
C8
C
C 16
//
6
8
C
C8
6
8
C
C3
C
C
21
C 14
22 C C19 C 10
C9 C14 C14
C5
C6
C6
C5
C8
C8
C8
C8
C8
C8
C8
//
//
//
//
//
//
C11
C
9
C
C3
2
(c)
C C
C5
C6 C8
Scheme 1. (a) Dimers of oligomer from 1-decene. (b) Trimers of oligomer from 1-decene. (c) Tetramer of oligomer from 1-decene.
Q. Huang et al. / European Polymer Journal 41 (2005) 2909–2915
bond in oligomer were not observed from 13C NMR spectra. The result indicated that the chain transfer to hydrogen was predominated, while the chain transfer to cocatalyst and b-hydrogen elimination were negligible. The regiostructures and assignments of 13C NMR of di-, tri-, and tetramer of 1-decene are compiled in Scheme 1. The subscript numbers in Scheme 1 are referred to in Fig. 4. The calculation of theoretical chemical shifts was referenced with Grant and Paul [8] and previous works [6,9]. For dimers of 1-decene, three kinds of sequences, head-to-tail (bb), tail-to-tail (bc) and headto-head (cb), were possibly produced. Tertiary carbons Tax (bb) and Tab (cb) were identified by the presence of the resonances at d 33.32 and 45.25 ppm, labeled with the number 13 and 21 in Fig. 4 and Scheme 1a. For trimers, four sequences could be obtained (Scheme 1b). One of them, head-to-tail (bbb) sequence existed two kinds of tertiary carbons in backbone, Tbb and Tbx, assigned at d 30.96 and 36.15 ppm and labeled by 9 and 16 in Fig. 4 and Scheme 1b. Txx at d 38.10 ppm was attributed to the tertiary carbon of bbc; Tax and Tab at d 46.31 and 49.30 ppm to cbc; Tba, T 0ab and T 0bb at d 45.25, 46.31 and 30.96 ppm to cbc sequences, labeled by 17, 22, 23 and 9, respectively. Six kinds of sequences for tetramers could be obtained (Scheme 1c). Tertiary carbons Txb, Tbb and T 0bb at d 39.75, 33.32 and 30.95 ppm were attributed to bbbb sequence. Tbx at d 38.10 ppm to bbbc, Tax, Tab and Tbb at d 46.31, 49.30 and 30.95 ppm to bcbb, Tax at d 46.31 ppm to bcbc, Tba, Tab, Tbb and T 0bb at d 45.25, 46.31, 32.30 and 30.95 ppm to cbbb, Tba, Tab and Tbx at d 45.25, 46.31 and 30.95 ppm to cbbc sequences, respectively. Methyl and ethyl carbons are assigned in Fig. 4 and labeled in Scheme 1. The regiostructures of pentamer, however, are not listed in Scheme 1, because the same assignments as that of tetramers were revealed by calculation according to Grant method [8]. 4. Conclusion Supported catalyst TiCl4/MgCl2/Et2AlCl exhibited higher catalytic activity for 1-decene oligomerization. Polymerization conditions such as polymerization temperature, Al/Ti ratio, Ti concentration and time showed considerable effects on catalytic activity and component of oligomers. The catalytic activity of 143.8 kg oligo/mol Ti h for oligomer was obtained under the typical conditions of Al/Ti ratio 40, Ti concentration 7.3 · 102 mmol/l, temperature 60 C and time 1 h. 13C NMR results confirmed regiostructures of oligomers from 1decene catalyzed by TiCl4/MgCl2/Et2AlCl catalyst and chain transfer to hydrogen was predominated.
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Acknowledgement Financial support of this research from the Natural Science Fund of Beijing University of Chemical and Technology for young scientist is gratefully acknowledged (Grant No. QN0406). References [1] Morganson NE, Bercik PG. Oligomerizing 1-olefins with a heterogeneous catalyst. US 4 365 105, 1982. [2] Bobsein RL. Catalyst compositions. US 4 436 948, 1984. [3] (a) Wu MM. Process for manufacturing olefinic oligomers having lubricating properties. US 4 827 073, 1989; (b) Wu MM. High viscosity index synthetic lubricant compositions. US 4 827 064, 1989. [4] (a) Pelrine BP. Fixed bed process for high viscosity index lubricant. US 4 914 254, 1990; (b) Clarembeau M. Production of monoolefin oligomer. US 6 002 061, 1999; (c) Sarin R, Sabyasachi S, Rai MM, Ghosh S, Bhatnagar AK, Sivaram S, et al., Process for oligomerisation of alphaolefins. US 6 002 060, 1999. [5] (a) Huang Q, Chen W, Jing Z. Oligomerization of alphaolefin. CN 1 453 254A, 2003; (b) Huang Q, Chen L, Fu Z, Jing Z, Yang W. Decene-1 oligomerization catalyzed by Ziegler–Natta catalyst supported. Petrochem Technol 2004;33(10):928–32 (in Chinese). [6] (a) Huang Q, Wu Q, Zhu F, Lin S. Synthesis and characterization of high molecular weight atactic polybutene-1 with half-titaniocene/MAO catalyst system. J Polym Sci Part A: Polym Chem 2001;39:4068–73; (b) Huang Q, Wu Q, Zhu F, Lin S. The synthesis of high molecular weight polybutene-1 catalyzed by Cp*Ti (OBz)3/ MAO. Polym Int 2001;50:45–8; (c) Zhu F, Huang Q, Lin S. Synthesis of multi-stereoblock polybutene-1 using novel monocyclopentadienyltitanium and modified methylalumiunoxane catalyst. J Polym Sci Part A: Polym Chem 1999;37:4497–502. [7] Asanuma T, Nishimorl Y, Ito M, Uchlkawa N, Shlomura T. Preparation of syndiotactic polyolefins by using metallocene catalysts. Polym Bull 1991;25:567–71. [8] Grant HK, Paul GE. Carbon-13 magnetic resonance. II Chemical shift data fir the alkanes. J Am Chem Soc 1964; 86:2984–8. [9] (a) Huang Q, Wu Q, Zhu F, Lin S. The characterization of polybutene-1 catalyzed by metallocene catalyst. ACTA Polym Sin 2001;1:49–53 (in Chinese); (b) Huang Q, Wu Q, Zhu F, Lin S. The synthesis of polybutene-1 catalyzed with metallocene catalyst. ACTA Polym Sin 2000;4:489–92 (in Chinese); (c) Huang Q, Wu Q, Zhu F, Lin S. Synthesis and characterization of high molecular weight polybutene-1 catalyzed with metallocene complexes/MAO catalyst system. J Chin Chem Uni 2002;23(1):167–9 (in Chinese).