Macromolecules 2005, 38, 6767-6769
Scandium-Catalyzed Copolymerization of Ethylene with Dicyclopentadiene and Terpolymerization of Ethylene, Dicyclopentadiene, and Styrene Xiaofang Li and Zhaomin Hou* Organometallic Chemistry Laboratory, RIKEN (The Institute of Physical and Chemical Research), Hirosawa 2-1, Wako, Saitama 351-0198, Japan, and PRESTO, Japan Science and Technology Agency (JST), Japan Received June 22, 2005
The development of homogeneous, single-site polymerization catalysts has played a critically important role in the creation of new polymer materials with controlled microstructures and desired properties. Cyclic olefin copolymers (COCs), produced by the copolymerization of ethylene or R-olefins with cyclic olefins, are one of the most important engineering plastics for thermally stressed and optical applications because of their many desirable properties such as thermal stability, good transparency, and chemical resistance.1-3 Since Kaminsky first described the copolymerization of ethylene with norbornene using zirconocene-based catalysts in 1991,1a extensive studies have been carried out in this area.1-3 Most of COCs reported so far are based on strained cyclic olefins such as norbornene and cyclopentene. In comparison with norbornene and cyclopentene, dicyclopentadiene (DCPD) is a very promising and attractive cyclic olefin monomer because it contains both a norbornene unit and a cyclopentene unit and is industrially available at a low price. If only one of the two C-C double bonds in DCPD selectively participates in the copolymerization with ethylene, further functionalization of the remaining C-C double bonds in the resulting copolymers would be possible to lead to formation of a broad range of new functionalized polymers with improved properties.3,4 Nevertheless, the copolymerization of ethylene with DCPD has been much less extensively studied, and the alternating copolymerization of ethylene with DCPD has not been reported previously in the literature.5 Cross-linking appeared to be a major problem often encountered in DCPD copolymerization,5a and therefore, the search for a catalyst system that is not only sufficiently active but can also distinguish a norbornene unit from a cyclopentene unit is critically important to achieve ethylene-DCPD copolymerization in a controlled fashion. On the other hand, incorporation of an aromatic monomer such as styrene into COCs is expected to afford further versatile materials for many industrial applications.6 However, little is known thus far about the opportunities in terpolymerization of ethylene, styrene, and a cyclic olefin,6 and no catalyst was shown to be truly effective for such terpolymerization. Very recently, we reported a novel cationic halfsandwich scandium catalyst system, which was generated in situ by treatment of a neutral half-sandwich bis(alkyl) complex such as (C5Me4SiMe3)Sc(CH2SiMe3)2(thf) with 1 equiv of [Ph3C][B(C6F5)4] in toluene.1k,7 This catalyst showed some unprecedented behaviors in polymerization, such as incorporation of syndiotactic * Corresponding author. E-mail:
[email protected].
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styrene-styrene sequences into styrene-ethylene copolymers7 and formation of novel poly(ethylene-altnorbornene)-b-polyethylene block copolymers.1k To explore new polymerization/copolymerization reactions and create new polymer materials which are difficult to achieve with conventional catalysts, we have now examined the copolymerization of ethylene, DCPD, and styrene by use of this new scandium-based catalyst. We report here the first alternating copolymerization of ethylene with DCPD and the first terpolymerization of ethylene, DCPD, and styrene by use of the scandium catalyst. Functionalization (epoxidation) of an alternating ethylene-DCPD copolymer is also demonstrated. Since the (C5Me4SiMe3)Sc(CH2SiMe3)2(thf)/[Ph3C][B(C6F5)4] catalyst system is known to be very active for the copolymerization of ethylene with norbornene,1k its activity toward cyclopentene was first examined to see whether the polymerization reaction of DCPD could take place regioselectively. Neither homopolymerization of cyclopentene nor copolymerization of cyclopentene with ethylene was observed under standard conditions. In contrast, the copolymerization of DCPD with ethylene took place very rapidly, although DCPD homopolymerization was very slow under similar conditions (Table 1). The DCPD content of the resulting copolymers increased as the DCPD monomer feed was raised under 1 atm of ethylene and reached as high as 45 mol % when 50 mmol of DCPD was used (Table 1, entries 3-8). The catalytic activity also increased as the DCPD monomer feed was increased in the range 20-40 mmol (Table 1, entries 3-7), but the use of more DCPD (50 mmol) led to decrease in activity (Table 1, entry 8). These results suggest that the ethylene-DCPD alternating copolymerization is more preferred than the homopolymerization of either monomer. Such a “comonomer effect” on the catalyst activity was also observed previously in the scandium-catalyzed ethylene-norbornene copolymerization.1k The copolymerization of ethylene with DCPD could be carried out over a wide range of temperatures (0-70 °C). The highest catalytic activity (3.1 × 106 g of copolymer/(mol of Sc‚h‚tm)) was achieved at 50 °C with a DCPD incorporation of ca. 44 mol % (Table 1, entry 12). 1H and 13C NMR analyses revealed that the resulting ethylene-DCPD copolymers contained cyclopentene units, suggesting that the copolymerization proceeded through enchainment of the norbornene ring, which is consistent with the fact that the present catalyst system is active for ethylene-norbornene copolymerization but inert toward cyclopentene. The copolymers all showed similar 13C NMR spectra and could be assigned to alternating ethylene-DCPD copolymers, in which continuous DCPD-DCPD units were negligible (Figure 1). These copolymers showed both meso and racemic sequences with the latter being slightly prevailing over the former (iso/syndio ≈ 4/6 in most cases), indicating that the alternating parts in the copolymers are atactic.1d,1h All of the copolymer products are amorphous with glass transition temperature (Tg) values in the range of 101-125 °C. Their GPC curves are all unimodal with relatively narrow molecular weight distributions (1.73-2.69), consistent with the predominance of a single homogeneous catalytic species and the good selectivity in the copolymerization.
10.1021/ma051323o CCC: $30.25 © 2005 American Chemical Society Published on Web 07/15/2005
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Communications to the Editor
Macromolecules, Vol. 38, No. 16, 2005
Table 1. Alternating Copolymerization of Ethylene with Dicyclopentadienea
entry
DCPD (mmol)
T (°C)
V (mL)
yield (g)
activityb
1 2g 3 4 5 6 7 8 9 10 11 12 13
0 40 20 25 30 35 40 50 40 40 40 40 40
25 25 25 25 25 25 25 25 25 25 0 50 70
40 5 40 40 40 40 40 40 20 60 40 40 40
1.48 0.08 3.67 4.50 4.86 5.05 5.20 4.69 5.16 4.41 4.46 5.36 3.58
0.8 2.1 2.6 2.8 2.9 3.0 2.7 2.9 2.5 2.5 3.1 2.0
DCPD conv (%)
DCPD contc (mol %)
Mnd (104)
Mw/Mnd
Tge (°C)
2 100 100 95 85 77 70 76 64 65 80 50
100 35.1 38.5 41.8 42.2 43.1 45.0 43.3 41.2 42.1 43.6 38.1
13.1 n.d. 19.9 22.6 21.3 23.9 21.7 20.4 10.9 20.9 27.9 16.9 10.7
2.55 n.d. 1.73 2.69 2.26 2.19 2.28 2.25 2.28 2.16 1.98 2.38 3.28
n.d.f n.d. 101 115 117 118 121 125 124 117 120 121 114
a Conditions: 21 µmol of Sc, 21 µmol of [Ph C][B(C F ) ], P b 6 3 6 5 4 ethylene ) 1 atm, t ) 5 min, unless otherwise noted. 10 g of copolymer/(mol of Sc‚h‚atm). c DCPD content, determined by 1H NMR. d Determined by GPC in CHCl3 at 40 °C against polystyrene standard. e Measured by DSC. f n.d. ) not determined. g Pethylene ) 0 atm, t ) 2 h.
Table 2. Terpolymerization of Ethylene, Dicyclopentadiene, and Styrenea
entry
Et (atm)
DCPD (mmol)
St (mmol)
1 2 3f 4 5 6 7 8 9 10
1 1 0 1 1 1 1 1 1 1
0 30 20 5 10 20 30 30 30 30
20 0 20 20 20 20 30 20 10 5
yield (g) 1.74 4.86 trace 2.13 2.25 0.83 0.96 1.18 1.94 3.22
activityb
composition (DCPD/St/Et, mol %)c
1.0 2.8
0/48.3/51.7 41.8/0/58.2
1.2 1.3 0.5 0.6 0.7 1.1 1.8
4.9/46.4/48.7 8.8/42.7/48.5 9.5/43.2/47.3 6.9/57.3/35.8 12.4/44.5/43.1 22.2/15.4/62.4 26.4/4.0/69.6
Mnd (104)
Mw/Mnd
Tge (°C)
28.2 21.3 n.d.g 50.9 46.5 47.6 51.1 42.6 42.0 38.1
1.52 2.26 n.d. 1.21 1.26 1.29 1.45 1.37 1.37 1.42
115 117 n.d. 44 53 66 79 78 86 94
a Conditions: 21 µmol of Sc, 21 µmol of [Ph C][B(C F ) ], V ) 40 mL (toluene), T ) 25 °C, t ) 5 min, unless otherwise noted. b 106 g 3 6 5 4 of copolymer/(mol of Sc‚h‚atm). c Determined by 1H NMR. d Determined by GPC in o-dichlorobenzene at 120 °C against polystyrene standard. e Measured by DSC. f V ) 10 mL (toluene), t ) 2 h. g n.d. ) not determined.
Figure 1. 13C NMR spectrum of poly(ethylene-alt-DCPD) (Table 1, entry 8).
Epoxidation of the ethylene-DCPD alternating copolymers could be easily achieved by use of m-chloroperbenzoic acid (mCPBA) as an oxidant,5c which quantitatively converted the olefinic groups into the epoxy groups (see Supporting Information for details). More remarkably, the (C5Me4SiMe3)Sc(CH2SiMe3)2(thf)/[Ph3C][B(C6F5)4] catalyst showed high activity also for the terpolymerization of ethylene, DCPD, and sty-
rene, although it was inactive for the DCPD-styrene two-component copolymerization (Table 2). By changing the DCPD/styrene feed ratio under 1 atm of ethylene, the corresponding poly(ethylene-co-DCPD-co-styrene) terpolymers with styrene contents of 4-57 mol % and DCPD contents of 5-26 mol % (Table 2) could be easily prepared. Solvent fractionation experiments revealed negligible quantities of homopolymer impurities in the resultant terpolymers.8 The GPC curves of the polymer products are all unimodal with narrow molecular weight distributions (1.21-1.45), demonstrating the clean formation of the terpolymers. 13C NMR analyses revealed that the terpolymers are random copolymers that contain isolated DCPD units, isolated styrene units, and syndiotactic styrene-styrene sequences,7 while no styrene-DCPD sequences were observed (Figure 2). These results are in agreement with what was observed for the ethylene-DCPD, styrene-DCPD, and ethylenestyrene7 two-component copolymerizations. The high and controllable incorporation of styrene in the present terpolymerizations is of particular noteworthy, which
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Communications to the Editor 6769
Figure 2. 13C NMR spectrum of poly(ethylene-co-DCPD-costyrene) (Table 2, entry 8).
is in striking contrast with what was observed for the only previously reported titanium catalyst for the terpolymerization of ethylene, styrene, and a cyclic olefin, in which the maximum incorporation of styrene was less than 3 mol %.6 In summary, by use of a cationic half-sandwich scandium catalyst, the alternating ethylene-DCPD copolymerization and the ethylene-DCPD-styrene terpolymerization have been achieved with excellent selectivity and activity for the first time, which afforded a new series of novel polymers that are difficult to be prepared with other catalyst systems. These results demonstrate that cationic half-sandwich rare earth metal alkyl complexes are of unprecedented novel potentials as a catalyst system for copolymerization and terpolymerization of cyclic (di)olefins.
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(4) (5)
Acknowledgment. This work was partly supported by a Grant-in-Aid for Scientific Research on Priority Areas (No. 14078224, “Reaction Control of Dynamic Complexes”) from the Ministry of Education, Culture, Sports, Science and Technology of Japan. (6)
Supporting Information Available: Experimental details, GPC curves, DSC curves, and NMR spectra of representative polymer products. This material is available free of charge via the Internet at http://pubs.acs.org.
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References and Notes
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(1) For examples of COCs based on norbornene, see: (a) Kaminsky, W.; Beulich, I.; Arndt-Rosenau, M. Macromol. Symp. 2001, 173, 211-225. (b) Ruchatz, D.; Fink, G.
Macromolecules 1998, 31, 4669-4673. (c) McKnight, A. L.; Waymouth, R. M. Macromolecules 1999, 32, 2816-2825. (e) Tritto, I.; Marestin, C.; Boggioni, L.; Sacchi, M. C.; Brintzinger, H.-H.; Fetto, D. R. Macromolecules 2001, 34, 57705777. (d) Altamura, P.; Grassi, A.; Macromolecules 2001, 34, 9197-9200. (f) Lee, B. Y.; Kim, Y. H.; Won, Y. C.; Han, J. W.; Suh, W. S.; Lee, I. S.; Chung, Y. K.; Song, K. H. Organometallics 2002, 21, 1500-1503. (g) Nomura, K.; Tsubota, M.; Fujiki, M. Macromolecules 2003, 36, 37973799. (h) Yoshida, Y.; Saito, J.; Mitani, M.; Takagi, Y.; Matsui, S.; Ishii, S.; Nakano, T. S.; Kashiwa, N.; Fujita, T. Chem. Commun. 2002, 1298-1299. (i) Benedikt, G. M.; Elce, E.; Goodall, B. L.; Kalamarides, H. A.; McIntosh, L. H.; Rhodes, L. F.; Selvy, K. T. Macromolecules 2002, 35, 89788988. (j) Li, X. F.; Dai, K.; Ye, W. P.; Pan, L.; Li, Y. S. Organometallics 2004, 23, 1223-1230. (k) Li, X.; Baldamus, J.; Hou, Z. Angew. Chem., Int. Ed. 2005, 44, 962-965. For examples of COCs based on cyclopentene and cyclohexene, see: (a) Natta, G.; Dallasta, G.; Donegani, G.; Mazzanti, G. Angew. Chem., Int. Ed. Engl. 1964, 3, 723-729. (b) Kaminsky, W.; Spiehl, R. Makromol. Chem., Macromol. Chem. Phys. 1989, 190, 515-526. (c) Jerschow, A.; Ernst, E.; Hermann, W.; Mu¨ller, N. Macromolecules 1995, 28, 7095-7099. (d) Naga, N.; Imanishi, Y. Macromol. Chem. Phys. 2002, 203, 159-165. (e) Fujita, M.; Coates, G. W. Macromolecules 2002, 35, 9640-9647. (f) Wang, W.; Fuiki, M.; Nomura, K. J. Am. Chem. Soc. 2005, 127, 4582-4583. For examples of COCs containing polar functional groups, see: (a) Younkin, T. R.; Connor, E. F.; Henderson, J. I.; Friedrich, S. K.; Grubbs, R. H.; Bansleben, D. A. Science 2000, 287, 460-462. (b) Diamanti, S. J.; Khanna, V.; Hotta, A.; Yamakawa, D.; Shimuzu, F.; Kramer, E. J.; Fredrickson, G. H.; Bazan, G. C. J. Am. Chem. Soc. 2004, 126, 1052810529. For a review on functionalization of C-C double bond, see: Lane, B. S.; Burgess, K. Chem. Rev. 2003, 103, 2457-2474. The maximum incorporation of DCPD in ethylene-DCPD copolymers reported previously for group 4 metal catalyst systems is ca. 10 mol %. See: (a) Naga, N. J. Polym. Sci., Part A: Polym. Chem. 2005, 43, 1285-1291. (b) Simanke, A. G.; Mauler, R. S.; Galland, G. B. J. Polym. Sci., Part A: Polym. Chem. 2002, 40, 471-485. (c) Suzuki, J.; Kino, Y.; Uozumi, T.; Sano, T.; Teranishi, T.; Jin, J.; Soga, K.; Shiono, T. J. Appl. Polym. Sci. 1999, 72, 103-108. For an attempt to incorporate styrene into an ethylenenorbornene copolymer (PS content ) 2 mol %), see: Sernetz, F.; Mu¨lhaupt, R. J. Polym. Sci., Part A: Polym. Chem. 1997, 35, 2549-2560. Luo, Y.; Baldamus, J.; Hou, Z. J. Am. Chem. Soc. 2004, 126, 13910-13911. The ethylene-DCPD-styrene terpolymers were soluble in CHCl3 at 50 °C, while homo-PE, homo-sPS, and homopolyDCPD were insoluble.
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