Living copolymerization of ethylene with norbornene catalyzed by bis(pyrrolide-imine) titanium complexes with MAO

Article abstract of DOI:10.1021/ja048357g

Bis(pyrrolide-imine) Ti complexes in conjunction with methylalumoxane (MAO) were found to work as efficient catalysts for the copolymerization of ethylene and norbornene to afford unique copolymers via an addition-type polymerization mechanism. The catalysts exhibited very high norbornene incorporation, superior to that obtained with Me₂Si(Me₄Cp)(N-tert-Bu)TiCl ₂ (CGC). The sterically open and highly electrophilic nature of the catalysts is probably responsible for the excellent norbornene incorporation. The catalysts displayed a marked tendency to produce alternating copolymers, which have stereoirregular structures despite the C₂ symmetric nature of the catalysts. The norbornene/ethylene molar ratio in the polymerization medium had a profound influence on the molecular weight distribution of the resulting copolymer. At norbornene/ethylene ratios larger than ca. 1, the catalysts mediated room-temperature living copolymerization of ethylene and norbornene to form high molecular weight monodisperse copolymers (M_n > 500 000, M_w/M_n < 1.20). ¹³C NMR spectroscopic analysis of a copolymer, produced under conditions that gave low molecular weight, demonstrated that the copolymerization is initiated by norbornene insertion and that the catalyst mostly exists as a norbornene-last-inserted species under living conditions. Polymerization behavior coupled with DFT calculations suggested that the highly controlled living polymerization stems from the fact that the catalysts possess high affinity and high incorporation ability for norbornene as well as the characteristics of a living ethylene polymerization though under limited conditions (M_n 225 000, M_w/M_n 1.15, 10-s polymerization, 25 °C). With the catalyst, unique block copolymers [i.e., poly(ethylene-co-norbornene)₁-b-poly(ethylene-co-norbornene) ₂, PE-b-poly(ethylene-co-norbornene)] were successfully synthesized from ethylene and norbornene. Transmission electron microscopy (TEM) indicated that the PE-b-poly(ethylene-co-norbornene) possesses high potential as a new material consisting of crystalline and amorphous segments which are chemically linked.

Full text of DOI:10.1021/ja048357g

Published on Web 09/01/2004
Living Copolymerization of Ethylene with Norbornene
Catalyzed by Bis(Pyrrolide-Imine) Titanium Complexes
with MAO
Yasunori Yoshida,† Jun-ichi Mohri,† Sei-ichi Ishii,† Makoto Mitani,† Junji Saito,†
Shigekazu Matsui,† Haruyuki Makio,† Takashi Nakano,† Hidetsugu Tanaka,†
Mitsuhiko Onda,‡ Yukari Yamamoto,§ Akira Mizuno,§ and Terunori Fujita*,†
Contribution from the R & D Center, Mitsui Chemicals, Inc., 580-32 Nagaura, Sodegaura,
Chiba, 299-0265, Japan; Mitsui Chemical Analysis & Consulting SerVice, Inc., 580-32 Nagaura,
Sodegaura, Chiba 299-0265, Japan; and Mitsui Chemical Analysis & Consulting SerVice, Inc.,
6-1-2 Waki, Waki-Cho, Kuga-Gun, Yamaguchi 740-0061, Japan
Received March 23, 2004; E-mail: Terunori.Fujita@mitsui-chem.co.jp
Abstract: Bis(pyrrolide-imine) Ti complexes in conjunction with methylalumoxane (MAO) were found to
work as efficient catalysts for the copolymerization of ethylene and norbornene to afford unique copolymers
via an addition-type polymerization mechanism. The catalysts exhibited very high norbornene incorporation,
superior to that obtained with Me2Si(Me4Cp)(N-tert-Bu)TiCl2 (CGC). The sterically open and highly
electrophilic nature of the catalysts is probably responsible for the excellent norbornene incorporation. The
catalysts displayed a marked tendency to produce alternating copolymers, which have stereoirregular
structures despite the C2 symmetric nature of the catalysts. The norbornene/ethylene molar ratio in the
polymerization medium had a profound influence on the molecular weight distribution of the resulting
copolymer. At norbornene/ethylene ratios larger than ca. 1, the catalysts mediated room-temperature living
copolymerization of ethylene and norbornene to form high molecular weight monodisperse copolymers
(Mn > 500 000, Mw/Mn < 1.20). 13C NMR spectroscopic analysis of a copolymer, produced under conditions
that gave low molecular weight, demonstrated that the copolymerization is initiated by norbornene insertion
and that the catalyst mostly exists as a norbornene-last-inserted species under living conditions.
Polymerization behavior coupled with DFT calculations suggested that the highly controlled living
polymerization stems from the fact that the catalysts possess high affinity and high incorporation ability for
norbornene as well as the characteristics of a living ethylene polymerization though under limited conditions
(Mn 225 000, Mw/Mn 1.15, 10-s polymerization, 25 °C). With the catalyst, unique block copolymers [i.e.,
poly(ethylene-co-norbornene)1-b-poly(ethylene-co-norbornene)2, PE-b-poly(ethylene-co-norbornene)] were
successfully synthesized from ethylene and norbornene. Transmission electron microscopy (TEM) indicated
that the PE-b-poly(ethylene-co-norbornene) possesses high potential as a new material consisting of
crystalline and amorphous segments which are chemically linked.
merization of ethylene, propylene, 1-hexene, or other olefins.2-5
These catalysts have enabled us to prepare a wide array of
Introduction
Making polymers with precise control over molecular weight,
composition and architecture of the polymer (precisely con-
trolled polymers) has been a long-standing challenge in the field
of polymer chemistry. Living olefin polymerization is one of
the most useful tools for the synthesis of precisely controlled
polymers such as monodisperse polymers, terminally function-
alized polymers, and block copolymers. These polymers are
expected to display unique material properties that have not been
achieved by conventional polymers.
Recent advances in the rational design and synthesis of well-
defined transition metal complex catalysts for olefin polymer-
ization1 have resulted in the discovery and development of
quite a few efficient and selective catalysts for the living poly-
living-polymerization-based polymers, which include high
molecular weight monodisperse polyethylenes (PEs), highly
syndiotactic polypropylenes (sPPs), highly isotactic poly(1-
hexene)s (iPHs), and a variety of block copolymers from
ethylene and R-olefins [PE-b-poly(ethylene-co-propylene), sPP-
b-poly(ethylene-co-propylene), iPP-b-PE, PE-b-poly(ethylene-
co-1-octadecene)].6,7
(1) For recent reviews, see: (a) Brintzinger, H. H.; Fischer, D.; Mu¨lhaupt, R.;
Rieger, B.; Waymouth, R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143-
1170. (b) McKnight, A. L.; Waymouth, R. M. Chem. ReV. 1998, 98, 2587-
2598. (c) Britovsek, G. J. P.; Gibson, V. C.; Wass, D. F. Angew. Chem.,
Int. Ed. 1999, 38, 428-447. (d) Ittel, S. D.; Johnson, L. K.; Brookhart, M.
Chem. ReV. 2000, 100, 1169-1203. (e) Gibson, V. C.; Spitzmesser, S. K.
Chem. ReV. 2003, 103, 283-315. (f) Suzuki, Y.; Terao, H.; Fujita, T. Bull.
Chem. Soc. Jpn. 2003, 76, 1493-1517.
† Mitsui Chemicals, Inc..
(2) For a recent review, see: Coates, G. W.; Hustad, P. D.; Reinartz, S. Angew.
Chem., Int. Ed. 2002, 41, 2236-2257. For living olefin polymerization
with phenoxy-based catalysts, see ref 1f.
‡ Mitsui Chemical Analysis & Consulting Service, Inc., Chiba.
§ Mitsui Chemical Analysis & Consulting Service, Inc., Yamaguchi.
9
10.1021/ja048357g CCC: $27.50 © 2004 American Chemical Society
J. AM. CHEM. SOC. 2004, 126, 12023-12032
12023

A R T I C L E S
Yoshida et al.
Compared with ethylene and/or common R-olefin (co)-
polymerizations, ethylene (E)/norbornene (NB) copolymeriza-
tions have been investigated less despite the importance of the
resultant copolymers in various fields due to their remarkable
material properties (e.g., high thermal stability, high transpar-
ency, high refractive indices).8-11 Therefore, there are only a
few examples of catalysts that copolymerize E and NB in a
(quasi) living fashion.12 Such catalysts are rac-Et(Ind)2ZrCl2/
methylalumoxane (MAO) and Me2Si(Me4Cp)(N-tert-Bu)TiCl2/
MAO as reported by Tritto and co-workers.12b-d In addition,
there exists only one recent report, and that is by Li et al. on
the synthesis of E- and NB-based block copolymers using bis-
(â-enaminoketonato) Ti complexes,12e which should display
distinctive properties and thus may have expanded utility. Hence,
the development of catalysts for living copolymerization of E
and NB is a comparatively uncharted field though the develop-
ment would have an impact on catalyst chemistry and polymer
chemistry.
(3) (a) Yasuda, H.; Furo, M.; Yamamoto, H.; Nakamura, A.; Miyake, S.;
Kibino, N. Macromolecules 1992, 25, 5115-5116. (b) Mashima, K.;
Fujikawa, S.; Tanaka, Y.; Urata, H.; Oshiki, T.; Tanaka, E.; Nakamura, A.
Organometallics 1995, 14, 2633-2640. (c) Gottfried, A. C.; Brookhart,
M. Macromolecules 2001, 34, 1140-1142. (d) Matsugi, T.; Matsui, S.;
Kojoh, S.; Takagi, Y.; Inoue, Y.; Nakano, T.; Fujita, T.; Kashiwa, N.
Macromolecules 2002, 35, 4880-4887. (e) Mitani, M.; Mohri, J.; Yoshida,
Y.; Saito, J.; Ishii, S.; Tsuru, K.; Matsui, S.; Furuyama, R.; Nakano, T.;
Tanaka, H.; Kojoh, S.; Matsugi, T.; Kashiwa, N.; Fujita, T. J. Am. Chem.
Soc. 2002, 124, 3327-3336. (f) Bambirra, S.; van Leusen, D.; Meetsma,
A.; Hessenn, B.; Teuben, J. H. Chem. Commun. 2003, 522-523. (g)
Reinartz, S.; Mason, A. F.; Lobkovsky, E. B.; Coates, G. W. Organome-
tallics 2003, 22, 2542-2544.
(4) (a) Killian, C. M.; Tempel, D. J.; Johnson, L. K.; Brookhart, M. J. Am.
Chem. Soc. 1996, 118, 11664-11665. (b) Saito, J.; Mitani, M.; Mohri, J.;
Ishii, S.; Yoshida, Y.; Matsugi, T.; Kojoh, S.; Kashiwa, N.; Fujita, T. Chem.
Lett. 2001, 576-577. (c) Tian, J.; Hustad, P. D.; Coates, G. W. J. Am.
Chem. Soc. 2001, 123, 5134-5135. (d) Mitani, M.; Furuyama, R.; Mohri,
J.; Saito, J.; Ishii, S.; Terao, H.; Nakano, T.; Fujita, T. J. Am. Chem. Soc.
2003, 125, 4293-4305. (e) Hasan, T.; Ioku, A.; Nishii, K.; Shiono, T.;
Ikeda, T. Macromolecules 2001, 34, 3142-3145. (f) Hagimoto, H.; Shiono,
T.; Ikeda, T. Macromol. Chem. Phys. 2004, 205, 363-369.
In our study, we have performed research into the ligand-
oriented design of catalysts in order to acquire high-performance
olefin polymerization catalysts.3d,e,4b,d,6b,13-15 As a consequence,
we have developed bis(pyrrolide-imine) Ti complexes (named
PI Catalysts)16,17 that were discovered as a result of the
combination of electronically flexible nonsymmetric [N-, N]
chelate ligands and group 4 transition metals.18 PI Catalysts
combined with MAO display high ethylene polymerization
activities comparable to those seen with early metallocene
i
catalysts. In addition, PI Catalysts in conjunction with Bu3Al/
Ph3CB(C6F5)4 form ultrahigh molecular weight polyethylenes.
Moreover, we found that PI Catalysts with MAO can carry out
(5) (a) Scollard, J. D.; McConville, D. H. J. Am. Chem. Soc. 1996, 118, 10008-
10009. (b) Jeon, Y.-M.; Park, S. J.; Heo, J.; Kim, K. Organometallics 1998,
17, 3161-3163. (c) Tshuva, E. Y.; Goldberg, I.; Kol, M.; Goldschmidt, Z.
Chem. Commun. 2001, 2120-2121. (d) Schrock, R. R.; Adamchuk, J.;
Ruhland, K.; Lopez, L. P. H. Organometallics 2003, 22, 5079-5091. (e)
Keaton, R. J.; Jayaratne, K. C.; Henningsen, D. A.; Koterwas, L. A.; Sita,
L. R. J. Am. Chem. Soc. 2001, 123, 6197-6198. (f) Fujita, M.; Coates, G.
W. Macromolecules 2002, 35, 9640-9647. (g) Nomura, K.; Fudo, A. J.
Mol. Catal. A 2004, 209, 9-17.
(12) (a) Cherdron, H.; Brekner, M.-J.; Osan, F. Angew. Makromol. Chem. 1994,
223, 121-133. (b) Jansen, J. C.; Mendichi, R.; Locatelli, P.; Tritto, I.
Macromol. Rapid Commun. 2001, 22, 1394-1398. (c) Thorshug, K.;
Mendich, R.; Boggioni, L.; Tritto, I.; Trinkle, S.; Friedrich, C.; Mu¨lhaupt,
R. Macromolecules 2002, 35, 2903-2911. (d) Jansen, J. C.; Mendichi, R.;
Sacchi, M. C.; Tritto, I. Macromol. Chem. Phys. 2003, 204, 522-530. (e)
Li, X. F.; Dai, K.; Ye, W. P.; Pan, L.; Li, Y. S. Organometallics 2004, 23,
1223-1230.
(13) (a) Inoue, Y.; Nakano, T.; Tanaka, H.; Kashiwa, N.; Fujita, T. Chem. Lett.
2001, 1060-1061. (b) Suzuki, Y.; Kashiwa, N.; Fujita, T. Chem. Lett. 2002,
358-359. (c) Suzuki, Y.; Inoue, Y.; Tanaka, H.; Fujita, T. Macromol. Rapid
Commun. 2004, 25, 493-497.
(14) (a) Makio, H.; Kashiwa, N.; Fujita, T. AdV. Synth. Catal. 2002, 344, 477-
493. (b) Matsukawa, N.; Ishii, S.; Furuyama, R.; Saito, J.; Mitani, M.;
Makio, H.; Tanaka, H.; Fujita, T. e-Polymers 2003, no. 021 (http://www.e-
Polymers.org). (c) Mitani, M.; Nakano, T.; Fujita, T. Chem.sEur. J. 2003,
9, 2396-2403. (d) Nakayama, Y.; Mitani, M.; Bando, H.; Fujita, T. Yuki
Gosei Kagaku Kyokaishi 2003, 61, 1124-1137. (e) Nakayama, Y.; Bando,
H.; Sonobe, Y.; Fujita, T. Bull. Chem. Soc. Jpn. 2004, 77, 617-625. (f)
Mitani, M.; Saito, J.; Ishii, S.; Nakayama, Y.; Makio, H.; Matsukawa, N.;
Matsui, S.; Mohri, J.; Furuyama, R.; Terao, H.; Bando, H.; Tanaka, H.;
Fujita, T. The Chemical Record 2004, 4, 137-158.
(15) (a) Saito, J.; Mitani, M.; Matsui, S.; Kashiwa, N.; Fujita, T. Macromol.
Rapid Commun. 2000, 21, 1333-1336. (b) Matsui, S.; Mitani, M.; Saito,
J.; Tohi, Y.; Makio, H.; Matsukawa, N.; Takagi, Y.; Tsuru, K.; Nitabaru,
M.; Nakano, T.; Tanaka, H.; Kashiwa, N.; Fujita, T. J. Am. Chem. Soc.
2001, 123, 6847-6856. (c) Ishii, S.; Saito, J.; Mitani, M.; Mohri, J.;
Matsukawa, N.; Tohi, Y.; Matsui, S.; Kashiwa, N.; Fujita, T. J. Mol. Catal.
A 2002, 179, 11-16. (d) Ishii, S.; Saito, J.; Matsuura, S.; Suzuki, Y.;
Furuyama, R.; Mitani, M.; Nakano, T.; Kashiwa, N.; Fujita, T. Macromol.
Rapid Commun. 2002, 23, 693-697. (e) Furuyama, R.; Saito, J.; Ishii, S.;
Mitani, M.; Matsui, S.; Tohi, Y.; Makio, H.; Matsukawa, N.; Tanaka, H.;
Fujita, T. J. Mol. Catal. A 2003, 200, 31-42. (f) Tohi, Y.; Makio, H.;
Matsui, S.; Onda, M.; Fujita, T. Macromolecules 2003, 36, 523-525. (g)
Makio, H.; Tohi, Y.; Saito, J.; Onda, M.; Fujita, T. Macromol. Rapid
Commun. 2003, 24, 894-899. (h) Prasad, A. V.; Makio, H.; Saito, J.; Onda,
M.; Fujita, T. Chem. Lett. 2004, 33, 250-251. (i) Nakayama, Y.; Bando,
H.; Sonobe, Y.; Kaneko, H.; Kashiwa, N.; Fujita, T. J. Catal. 2003, 215,
171-175. (j) Nakayama, Y.; Bando, H.; Sonobe, Y.; Fujita, T. J. Mol.
Catal. A 2004, 213, 141-150. (k) Tohi, Y.; Nakano, T.; Makio, H.; Matsui,
S.; Fujita, T.; Yamaguchi, T. Macromol. Chem. Phys. 2004, 205, 1179-
1186.
(6) (a) Gottfried, A. C.; Brookhart, M. Macromolecules 2003, 36, 3085-3100.
(b) Kojoh, S.; Matsugi, T.; Saito, J.; Mitani, M.; Fujita, T.; Kashiwa, N.
Chem. Lett. 2001, 822-823. (c) Busico, V.; Cipullo, R.; Friederichs, N.;
Ronca, S.; Togrou, M. Macromolecules 2003, 36, 3806-3808.
(7) Recent advances in the rational design of catalysts for living olefin
polymerization have allowed the catalytic production of living-polymeri-
zation-based polymers, see: Mitani, M.; Mohri, J.; Furuyama, R.; Ishii,
S.; Fujita, T. Chem. Lett. 2003, 32, 238-239.
(8) For a recent review, see: Janiak, C.; Lassahn, P. G. Macromol. Rapid
Commun. 2001, 22, 479-492.
(9) (a) Kaminsky, W.; Bark, A.; Arndt, M. Makromol. Chem., Macromol. Symp.
1991, 47, 83-93. (b) Bergstro¨m, C. H.; Seppa¨la¨, J. V. J. Appl. Polym.
Sci., Part A: Polym. Chem. 1998, 36, 1633-1638. (c) Harrington, B. A.;
Crowther, D. J. J. Mol. Catal. A: Chemical 1998, 128, 79-84. (d)
McKnight, A. L.; Waymouth, R. M. Macromolecules 1999, 32, 2816-
2825. (e) Arndt-Rosenau, M.; Beulich, I. Macromolecules 1999, 32, 7335-
7343. (f) Huang, W. J.; Chang, F. C.; Chu, P. P. J. J. Appl. Polym. Sci.,
Part B: Polym. Phys. 2000, 38, 2554-2563. (g) Lee, B. Y.; Kim, Y. H.;
Won, Y. C.; Han, J. W.; Suh, W. H.; Lee, I. S.; Chung, Y. K.; Song, K. H.
Organometallics 2002, 21, 3481-3484. (h) Grassi, A.; Maffei, G.; Milione,
S.; Jordan, R. F. Macromol. Chem. Phys. 2001, 202, 1239-1245. (i) Abu-
Surrah, A. S.; Lappalainen, K.; Kettunen, M.; Repo, T.; Leskela¨, M.; Hodali,
H. A.; Rieger, B. Macromol. Chem. Phys. 2001, 202, 599-603. (j) Benedikt,
G. M.; Elce, E.; Goodall, B. L.; Kalamarides, H. A.; McIntosh, L. H., III;
Rhodes, L. F.; Selvy, K. T.; Andes, C.; Oyler, K.; Sen, A. Macromolecules
2002, 35, 8978-8988. (k) Kiesewetter, J.; Kaminsky, W. Chem.sEur. J.
2003, 9, 1750-1758.
(10) (a) Ruchatz, D.; Fink, G. Macromolecules 1998, 31, 4669-4673. (b)
Ruchatz, D.; Fink, G. Macromolecules 1998, 31, 4674-4680. (c) Ruchatz,
D.; Fink, G. Macromolecules 1998, 31, 4681-4683. (d) Ruchatz, D.; Fink,
G. Macromolecules 1998, 31, 4684-4686. (e) Wendt, R. A.; Mynott, R.;
Hauschild, K.; Ruchatz, D.; Fink, G. Macromol. Chem. Phys. 1999, 200,
1340-1350. (f) Wendt, R. A.; Fink, G. Macromol. Chem. Phys. 2001, 202,
3490-3501. (g) Wendt, R. A.; Mynott, R.; Fink, G. Macromol. Chem.
Phys. 2002, 203, 2531-2539. (h) Wendt, R. A.; Fink, G. J. Mol. Catal. A
2003, 203, 101-111. (i) Wendt, R. F.; Angermund, K.; Jensen, V.; Thiel,
W.; Fink, G. Macromol. Chem. Phys. 2004, 205, 308-318.
(11) (a) Provasoli, A.; Ferro, D. R.; Tritto, I.; Boggioni, L. Macromolecules
1999, 32, 6697-6706. (b) Tritto, I.; Boggioni, L.; Sacchi, M. C.; Locatelli,
P.; Ferro, D. R.; Provasoli, A. Macromol. Rapid Commun. 1999, 20, 279-
283. (c) Tritto, I.; Marestin, C.; Boggioni, L.; Zetta, L.; Provasoli, A.; Ferro,
D. R. Macromolecules 2000, 33, 8931-8944. (d) Tritto, I.; Marestin, C.;
Boggioni, L.; Sacchi, M. C.; Brintzinger, H. H.; Ferro, D. R. Macromol-
ecules 2001, 34, 5770-5777. (e) Tritto, I.; Boggioni, L.; Jansen, J. C.;
Thorshaug, K.; Sacchi, M. C.; Ferro, D. R. Macromolecules 2002, 35, 616-
623. (f) Boggioni, L.; Bertini, F.; Zannoni, G.; Tritto, I.; Carbone, P.;
Ragazzi, M.; Ferro, D. R. Macromolecules 2003, 36, 882-890. (g) Carbone,
P.; Ragazzi, M.; Tritto, I.; Boggioni, L.; Ferro, D. R. Macromolecules 2003,
36, 891-899.
(16) (a) Matsui, S.; Nitabaru, M.; Yoshida, Y.; Mitani, M.; Fujita, T. Europe
Patent, EP-1008595, 2000 (filing date, Dec. 11, 1998) (Chem. Abstr. 2000,
133, 43969). (b) Yoshida, Y.; Saito, J.; Mitani, M.; Fujita, T. Jp. Patent
application 2002-325098 (filing date, Nov. 8, 2002).
(17) (a) Yoshida, Y.; Matsui, S.; Takagi, Y.; Mitani, M.; Nitabaru, M.; Nakano,
T.; Tanaka, H.; Fujita, T. Chem. Lett. 2000, 1270-1271. (b) Yoshida, Y.;
Matsui, S.; Takagi, Y.; Mitani, M.; Nakano, T.; Tanaka, H.; Kashiwa, N.;
Fujita, T. Organometallics 2001, 20, 4793-4799. (c) Yoshida, Y.; Nakano,
T.; Tanaka, H.; Fujita, T. Isr. J. Chem. 2002, 42, 353-359. (d) Yoshida,
Y.; Saito, J.; Mitani, M.; Takagi, Y.; Matsui, S.; Ishii, S.; Nakano, T.;
Kashiwa, N.; Fujita, T. Chem. Commun. 2002, 1298-1299. (e) Matsui,
S.; Spaniol, T. P.; Takagi, Y.; Yoshida, Y.; Okuda, J. J. Chem. Soc., Dalton
Trans. 2002, 4529-4331. (f) Matsui, S.; Yoshida, Y.; Takagi, Y.; Spaniol,
T. P.; Okuda, J. J. Organomet. Chem. 2004, 689, 1155-1164.
9
12024 J. AM. CHEM. SOC. VOL. 126, NO. 38, 2004

Copolymerization of Ethylene with Norbornene
A R T I C L E S
Table 1. E/NB Copolymerization Resultsa
d
NB/E
yield
(mg)
Mn
103)
NB contente
(mol %)
d
entry
complex
NBb (g)
molar ratio
activityc
(×
Mw/Mn
1
2
3
4
5
1
1
1
10
1
1
10
0.34/1
3.4/1
0.34/1
0.34/1
3.4/1
356
206
591
0
4272
2472
7092
0
652
285
126
1.28
1.11
1.95
26.5
45.0
8.3
rac-Et(Ind)2ZrCl2
Me2Si(Me4Cp)(N-tert-Bu)TiCl2
Me2Si(Me4Cp)(N-tert-Bu)TiCl2
1280
15 360
858
4.66
31.2
a Conditions: 25 °C, 5 min, atmospheric pressure, E gas feed (50 L/h). Complex: 1 µmol, cocatalyst; MAO 1.25 mmol as Al (entries 1-4), iBu3Al 0.25
mmol, Ph3CB(C6F5)4 6 µmol (entry 5), toluene 250 mL. b Charged NB. c kg-polymer/mol-cat/h. d Determined by GPC, equipped with refractive index (RI)
detector, by using polystyrene calibration. e Determined by 13C NMR.
Scheme 1. Synthetic Procedure for Complexes 1-4
kg-polymer/mol-cat/h) for the polymerization, it produced higher
molecular weight polymer with higher NB content (Mn 652 000,
NB content 26.5 mol %) than rac-Et(Ind)2ZrCl2 with MAO (Mn
126 000, NB content 8.3 mol %). Under the conditions
employed, CGC/MAO exhibited practically no reactivity toward
the polymerization, and neither oligomeric nor polymeric
materials were isolated.20 Since CGC often shows higher cata-
lytic properties on activation with a borate cocatalyst than with
MAO,1b we also performed E/NB copolymerization with CGC/
iBu3Al/Ph3CB(C6F5)4. The CGC system produced copolymer
having a NB content of 31.2 mol % with very high productivity
(15 360 kg-polymer/mol-cat/h, entry 5). It is noteworthy that
complex 1 formed a copolymer with higher NB content (45.0
mol %, entry 2) than CGC (31.2 mol %) which is well-known
to display very high incorporation of sterically large monomers.
Considering that NB is a sterically encumbered monomer and
has higher nucleophilicity relative to common R-olefins, the high
NB incorporation observed may be associated with the high
electrophilicity and sterically open nature of the active site of
complex 1.17c DFT calculations21 suggest that the Ti center of
a cationic methyl species derived from complex 1 has higher
electrophilicity (Mulliken charge of the Ti center in atomic units
1.84) than that from CGC (Mulliken charge of the Ti center in
atomic units 1.69). The high electrophilicity may stem from
the relatively low HOMO energy of a pyrrolide-imine ligand
(e.g., pyrrolide-imine ligand of complex 1; HOMO -3.21 eV,
Cp ligand; HOMO -2.33 eV, calculated by PM3 method22).
It is significant to note that the copolymers arising from
complex 1/MAO possess very narrow molecular weight distri-
butions (Mw/Mn: entry 1, 1.28; entry 2, 1.11). These Mw/Mn
values suggested that the complex 1 catalyst system may have
the characteristics of a living E/NB copolymerization. While
rac-Et(Ind)2ZrCl2/MAO was not able to produce narrow mo-
lecular weight distribution copolymer (Mw/Mn 1.95) under the
conditions examined (NB/E molar ratio 0.34/1), Tritto et al.
living E/NB copolymerization at room temperature and produce
high molecular weight monodisperse alternating copolymers.
In this contribution, we describe the detailed E/NB copolym-
erization behavior of PI Catalysts and discuss the mechanism
of the living copolymerization. Additionally, we introduce the
preparation of E- and NB-based block copolymers with unique
architectures using PI Catalysts. The results discussed herein
would provide a new strategy for achieving highly controlled
living copolymerization of ethylene with strained cyclic olefins.
Results and Discussion
Synthesis of Bis(Pyrrolide-Imine) Ti Complexes. The
synthetic route used to prepare the titanium complexes utilized
in this work is depicted in Scheme 1. Complexes 1 and 2 were
synthesized and purified according to previously reported
procedures.17b Complexes 3 and 4 were prepared from TiCl4
and the lithium salts of the corresponding pyrrolide-imine
ligands using a similar method. The desired complexes were
obtained in moderate to good overall yields from pyrrole-2-
carboxaldehyde (1, 36%; 2, 51%; 3, 55%; 4, 41%).
Ethylene/Norbornene Copolymerization Promoted by the
Complexes 1-4/MAO Systems. Using MAO as a cocatalyst
E/NB copolymerizations with complex 1 and two metallocenes
[i.e., rac-Et(Ind)2ZrCl2 and Me2Si(Me4Cp)(N-tert-Bu)TiCl2
(CGC)], for comparison, were carried out at 25 °C under
atmospheric pressure. Polymer yields, polymerization activities,
Mn, Mw/Mn, and NB contents of the resulting polymers are
reported in Table 1.19 Although complex 1/MAO displayed
somewhat lower (but still respectable) activity (entry 1, 4272
(19) NB/E molar ratio in a polymerization medium was calculated based on
the literature data under the assumption that the toluene is saturated with
E during the course of the polymerization and that NB consumption is
negligible for the polymerization. See: Sernetz, F. G.; Mu¨lhaupt, R.;
Waymouth, R. M. Macromol. Chem. Phys. 1996, 197, 1071-1083.
(20) With CGC/MAO at 50 °C, Tritto et al. obtained an E-NB copolymer having
a narrow molecular weight distribution of 1.3 (Mn 100 000) with low
efficiency.12c Details of the polymerization conditions are not given.
(21) (a) te Velde, G.; Bickelhaupt, F. M.; van Gisbergen, S. J. A.; Fonseca
Guerra, C.; Baerends, E. J.; Snijders, J. G.; Ziegler, T. J. Comput. Chem.
2001, 22, 931-967. (b) Fonseca Guerra, C.; Snijders, J. G.; te Velde, G.;
Baerends, E. J. Theor. Chem. Acc. 1998, 99, 391-403. (c) ADF2003.01,
SCM, Theoretical Chemistry, Vrije Universiteit, Amsterdam, The Nether-
lands, http://www.scm.com. (d) Becke, A. D. Phys. ReV. A 1988, 38, 3098-
3100. (e) Lee, C.; Yang, W.; Parr, R. G. Phys. ReV. B 1988, 37, 785-789.
(f) Miehlich, B.; Savin, A.; Stoll, H.; Preuss, H. Chem. Phys. Lett. 1989,
175, 200-206. (g) Vanka, K.; Xu, Z.; Ziegler, T. Organometallics 2004,
23, 2900-2910. (h) Kim, E. G.; Klein, M. L. Organometallics 2004, 23,
3319-3326.
(18) Pyrrolide-imine ligated transition metal complexes have recently been
studied actively as precatalysts for olefin polymerization by other research
groups.: (a) Gibson, V. C.; Maddox, P. J.; Newton, C.; Redshaw, C.; Solan,
G. A.; White, A. J. P.; Williams, D. J. Chem. Commun. 1998, 1651-1652.
(b) Dawson, D. M.; Walker, D. A.; Pett, M. T.; Bochmann, M. J. Chem.
Soc., Dalton Trans. 2000, 459-466. (c) Tian, G.; Boone, H.; Novak, M.
Macromolecules 2001, 34, 7656-7663. (d) Gibson, V. C.; Newton, C.;
Redshaw, C.; Solan, G. A.; White, A. J. P.; Williams, D. J. J. Chem. Soc.,
Dalton Trans. 2002, 4017-4023. (e) Tsurugi, H.; Yamagata, T.; Tani, K.;
Mashima, K. Chem. Lett. 2003, 32, 756-757. (f) Bellabarba, R. M.; Gomes,
P. T.; Pascu, S. I. J. Chem. Soc., Dalton Trans. 2003, 4431-4436.
(22) PM3 calculations were carried out using Spartan ’02 program, Wavefunc-
tion, Inc., Irvine, CA. See: Stewart, J. J. P. J. J. Comput. Chem. 1989, 10,
209-220, 221-264.
9
J. AM. CHEM. SOC. VOL. 126, NO. 38, 2004 12025

A R T I C L E S
Yoshida et al.
Table 2. E/NB Copolymerization Results with Complexes
1-4/MAOa
d
e
NBb
(g)
time
yield
(mg)
Mn
Tg
C )
d
entry
complex
(min)
activityc
(
×
103)
Mw/Mn
(
°
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
1
1
1
1
2
2
2
3
3
3
3
4
4
4
4
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
1
3
5
10
5
10
20
1
3
5
10
1
3
54
143
206
455
45
96
176
38
110
186
359
56
166
273
531
3240
2860
2472
2730
540
576
528
2280
2200
2232
2154
3360
3320
3276
3186
74
1.07
1.11
1.11
1.16
1.08
1.10
1.15
1.08
1.10
1.14
1.24
1.09
1.14
1.18
1.23
116
118
118
120
126
130
132
120
120
120
121
124
124
124
126
179
285
521
72
127
229
61
177
239
417
81
237
344
600
5
10
Figure 2. GPC profile of the E-NB copolymer formed with complex
1/MAO: (a) 1 min, Mn 74 000, Mw/Mn 1.07; (b) 3 min, Mn 179 000, Mw/
Mn 1.11; (c) 5 min, Mn 285 000, Mw/Mn 1.11; (d) 10 min, Mn 521 000,
Mw/Mn 1.16.
a Conditions: 25 °C, atmospheric pressure, E gas feed (50 L/h).
Complex: 1 µmol, cocatalyst; MAO 1.25 mmol as Al, toluene 250 mL.
b Charged NB. c kg-polymer/mol-cat/h. d Determined by GPC, equipped
with refractive index (RI) detector, by using polystyrene calibration.
e Measured by DSC.
plexes 2-4 that possess different substituents on the imine-
nitrogens (R: 2, Ph; 3, 4-tert-butylcyclohexyl; 4, cyclooctyl)
were also investigated for their potential as E/NB copolymer-
ization catalysts (entries 5-15 in Table 2).23 These complexes
were found to form amorphous copolymers having very narrow
molecular weight distributions and high Tgs (2, Mw/Mn 1.08-
1.15, Tg 126-132 °C; 3, Mw/Mn 1.08-1.24, Tg 120-121 °C;
4, Mw/Mn 1.09-1.23; Tg 124-126 °C) with high efficiency (2,
540-576 kg-polymer/mol-cat/h; 3, 2154-2280 kg-polymer/
mol-cat/h; 4, 3186-3360 kg-polymer/mol-cat/h). The living
nature of the complexes 2-4/MAO systems was indicated by
the linear relationship between Mn and polymerization time as
well as by the narrow molecular weight distributions observed
(see the Supporting Information). Judging from the Tg values
of the resulting copolymers, we believe complexes 1-4 have a
similar ability to incorporate NB, which is substantially higher
than that of CGC under the given conditions.
Microstructure of the E-NB Copolymer Produced with
the Complex 1/MAO System. Figure 3 displays the 13C NMR
spectrum of the living copolymer formed with complex 1 (Mn
285 000, Mw/Mn 1.11, entry 2 in Table 1). Peak assignments
were performed based on a comparison of the observed chemical
shifts with the literature data.11c The spectrum indicated that
complex 1 in conjunction with MAO promoted an addition-
type polymerization of NB, which is exo-exo enchained as
indicated by the presence of the peak at 33.0 ppm derived from
the C7 of NB (exo-exo enchainment) and the absence of the
peaks in the region of 36-37 ppm attributed to the C7 of NB
with endo-endo or endo-exo enchainment.9j
Figure 1. Plots of Mn and Mw/Mn vs polymerization time with complex
1/MAO.
achieved a quasi-living copolymerization with this catalyst
system at a high NB/E molar ratio of 28.4/1 (Mn 133 000, Mw/
Mn 1.16, activity 920 kg-polymer/mol-cat/h).12b,d
In an attempt to confirm the living nature of the complex 1
catalyst system, Mn and Mw/Mn values were monitored as a
function of polymerization time (entries 1-4 in Table 2). For
each run, a similar glass transition temperature (Tg 116-120
°C), (Tg correlates with NB content),9j,10d and thus a similar
NB content copolymer was obtained, indicating that the po-
lymerization proceeded at practically the same NB/E molar ratio
under the conditions employed (calculated NB conversion <
5%). A plot of Mn and Mw/Mn values vs polymerization time is
shown in Figure 1. The Mn value increased proportionally with
polymerization time, and the narrow Mw/Mn value was retained
for each run (Mw/Mn 1.07-1.16), suggesting that the system is
indeed living. GPC peaks of the produced copolymers shifted
to the higher molecular weight region with an increase in
polymerization time while the unimodal shape was maintained
and no shoulder peak and/or no low molecular weight tail was
detected during the course of the polymerization (Figure 2).
These results clearly indicate that the complex 1 catalyst system
initiates highly controlled living E/NB copolymerization.
To obtain further information about the E/NB copolymeri-
zation behavior of bis(pyrrolide-imine) Ti complexes, com-
The peak at 47.8 ppm and the peaks in the region of 46.8-
47.4 ppm are assigned to C2 and C3 in the alternating isotactic
units and to C2 and C3 in the alternating syndiotactic units and
in the isolated units, respectively. The peaks in the region of
41.9-42.1 ppm are ascribed to C1 and C4 in the alternating
isotactic units, and those in the region of 41.4-41.7 ppm are
assignable to C1 and C4 in the alternating syndiotactic units
and in the isolated units. Additionally, the peak at 30.4 ppm is
attributed to C5, C6 and the carbons derived from successive E
enchainment. The peaks at 30.8 ppm and at 30.1 ppm are
(23) Complex 4 displayed a very high E polymerization activity of 33 200 kg-
PE/mol-cat/h, which exceeds those for early group 4 metallocenes (Cp2-
TiCl2; 16 700 kg-PE/mol-cat/h, Cp2ZrCl2; 20 000 kg-PE/mol-cat/h) under
identical conditions.
9
12026 J. AM. CHEM. SOC. VOL. 126, NO. 38, 2004

Copolymerization of Ethylene with Norbornene
A R T I C L E S
Table 3. E or NB Homopolymerization and E/NB
Copolymerization with Complex 1/MAOa
d
NBb
(g)
time
gas E/N2
yield
(mg)
Mn
d
entry
(min)
(L/h)/(L/h)
activityc
(
×
103)
Mw/Mn
1
2
3
0
0
0
5
2/100
50/0
50/0
11
132
94
225
429
2.10
1.15
1.38
1
/
87 (31 320)
195 (23 400)
6
0.5
4
10
20
0/50
0
0
5e
10 20 + 10 0/50+50/0 220
(440)
338
1.29
a Conditions: 25 °C, atmospheric pressure, complex 1: 1 µmol,
cocatalyst; MAO 1.25 mmol as Al, toluene 250 mL. b Charged NB. c kg-
polymer/mol-cat/h. d Determined by GPC, equipped with refractive
index (RI) detector, by using polystyrene calibration. e After the treatment
of 1/MAO and NB for 20 min, E gas was introduced into the resulting
mixture.
The catalyst system provided PE having an Mw/Mn of 2.10,
indicating that complex 1 with MAO does not initiate living E
polymerization under the given conditions. Interestingly, the
catalyst system was found to produce a high molecular weight
PE with a very narrow molecular weight distribution (Mn 225
000, Mw/Mn 1.15) in a short polymerization time of 10 s though
the molecular weight distribution was somewhat broadened for
30-s polymerization (Mn 429 000, Mw/Mn 1.38). These results
show that complex 1/MAO possesses some characteristics of a
living E polymerization and chain growth can occur without
significant chain transfer or termination for a short time
polymerization. The molecular weight and molecular weight
distribution that were attained suggest a very high ratio of the
rates of propagation to chain transfer for E polymerization with
the catalyst system.
Figure 3. 13C NMR spectrum for the living E-NB copolymer formed with
complex 1 (entry 2 in Table 1).
In contrast, complex 1/MAO was found to show practically
no reactivity toward NB homopolymerization, and neither
oligomeric nor polymeric materials were isolated (entry 4). This
result is consistent with the very high propensity of the catalyst
system to afford alternating copolymers.
assigned to the carbons derived from E in the alternating
isotactic units and those in the alternating syndiotactic units,
respectively.
The living copolymerization catalysis displayed by 1/MAO
is unique since the catalyst system initiates neither E nor NB
living polymerization under analogous conditions. Interestingly,
though treatment of the catalyst system (1/MAO) with NB at
25 °C for 20 min formed neither polymeric nor oligomeric
products, subsequent addition of E (50 L/h, 10 min) to the
resulting mixture produced a high molecular weight copolymer
having a narrow molecular weight distribution (Mn 338 000, Mw/
Mn 1.29, entry 5) with a reasonable polymer yield (220 mg).
This fact indicates that a catalytically active species is fairly
stable under the conditions where no insertion of monomers
occurs for 20 min.24
Effect of the Norbornene/Ethylene Ratio on the Copo-
lymerization. Table 4 contains the results obtained for the
copolymerization using 1/MAO as a function of the amount of
NB charged at 25 °C. As the charged NB increased (and thereby
NB/E molar ratio increased), both the catalytic activity and the
product molecular weight decreased. Although increasing the
charged NB raised the incorporation of NB in the copolymer,
the NB content in the copolymer reached a plateau value of ca.
50 mol %. Therefore, the decrease in the catalytic activity and
the product molecular weight may be due to the predominant
coordination of NB to an NB-last-inserted active species.
The relative peak intensities show that, though the copolymer
contains 45.0 mol % of NB, it predominantly consists of
alternating E-NB blocks [alternating sequence (-NB-E-NB-
E-NB-), 95.4%]. In addition, the copolymer contains some
isolated NB units present in PE sequence [isolated sequence
(-E-NB-(E)n-, n g 2, 3.7%] and only a small amount of
NB diads (0.9%). These results suggest that complex 1/MAO
displays a very high tendency to afford alternating E-NB
copolymers. Although NB can coordinate to a NB-last-inserted
species (which will be discussed later), steric congestion
associated with the insertion of NB to a Ti-norbornyl linkage
probably disfavors successive NB enchainment. The relative
peak intensities also reveal that the copolymer consists of about
48/52 of syndiotactic/isotactic units, indicating that the E-NB
copolymer adopts an -NB-E-NB-E-NB- sequence with
practically random tacticity. These facts suggest that an E-last-
inserted active species cannot distinguish between coordination
of NB with a bridging methylene group up or down though
precatalyst complex 1 possesses C2 symmetry. The sterically
open nature of the active site may be related to the low degree
of polymerization stereocontrol. The living copolymers stem-
ming from complexes 2-4/MAO possess virtually the same
microstructures as that obtained with complex 1/MAO.
Ethylene and Norbornene Homopolymerization with the
Complex 1/MAO System. Table 3 summarizes the results of
the homopolymerization of E and NB using complex 1/MAO.
(24) The NB coordination to the cationic active species might play a role in the
suppression of catalyst decay as a consequence of the steric protection to
active site and the reduction of electrophilicity of the Ti center.
9
J. AM. CHEM. SOC. VOL. 126, NO. 38, 2004 12027

A R T I C L E S
Yoshida et al.
Table 4. E/NB Copolymerization Results with Complex 1/MAOa
If the polymerization starts with E insertion into the Ti-
CH3 bond of an initial active species generated from complex
1 and MAO, the resulting copolymer possesses CH3-E-E-
(CH3 of n-pentyl group; ca. 14.1 ppm) and/or CH3-E-NB-
(CH3 of n-propyl group; ca. 14.8 ppm). However, no peaks
assignable to the methyl carbons of the chain-end structures
CH3-E-E- and CH3-E-NB-26 were detected in the NMR.
In addition, no peaks derived from the â-methylene carbons of
the chain-end structures of CH3-E-E- and CH3-E-NB- (ca.
20-23 ppm) were found in the NMR. Rather, the peak at 15.8
ppm is attributable to the methyl carbon of the chain-end
structure CH3-NB-.26 Additionally, the peaks at 40.6, 41.0,
and 45.0 ppm are assignable to C3, C4, and C2 originating from
the CH3-NB- chain end, respectively. Therefore, the polym-
erization is initiated by NB insertion, resulting in the formation
of the initiation chain-end structure CH3-NB-. This fact further
confirms the high incorporation capability of the catalyst system
for NB.
NB/E
molar
ratio
NB
d
NBb
(g)
yield
(mg)
Mn
103)
contente
d
entry
activityc
(×
Mw/Mn
(mol %)
1
2
3
4
5
0.5
1
5
10
20
0.17/1
0.34/1
1.7/1
3.4/1
6.8/1
2043
1343
684
455
217
12 258
8058
4104
2730
1302
1998f
1078
732
521
295
1.86f
1.46
1.18
1.16
1.16
22.2
37.5
44.5
46.5
6
0
0/1
18
108
377
2.47
0
a Conditions: 25 °C, 10 min, atmospheric pressure. Entries 1-5: E (50
L/h). Entry 6: ethylene (5 L/h)/nitrogen (50 L/h). Complex 1: 1 µmol,
cocatalyst; MAO 1.25 mmol as Al, toluene 250 mL. b Charged NB. c kg-
polymer/mol-cat/h. d Determined by GPC, equipped with refractive index
(RI) detector, by using polystyrene calibration. e Determined by 13C NMR.
f Soluble part in solvent under the measurement conditions.
Regarding the termination chain-end structures, the peaks at
29.1, 35.4, 36.8, and 38.6 ppm are assigned to C5, 7, 4, and 3
derived from the NB-E- chain end, respectively. The other
carbons derived from the NB-E- chain end (C1, C2 and C6)
are not assignable because of the overlap with the peaks
originating from the main chain NB units. On the other hand,
no peaks due to the E-E- (CH3 of n-butyl group; ca. 12.1
ppm) and the E-NB- (CH3 of ethyl group; ca. 12.0-14.0 ppm)
were found in the NMR. These facts show that the catalytically
active species mostly exists as a NB-last-inserted compound
during the course of the polymerization. These results suggest
that the NB insertion into the E-last-inserted species is much
faster than the E insertion into the NB-last-inserted species under
the conditions employed.
Origin of the Living Copolymerization. A plausible po-
lymerization mechanism for E/NB copolymerization with the
bis(pyrrolide-imine)Ti complex/MAO system is presented in
Scheme 2. The chain-end analysis suggests the initial formation
of Ti-NB-CH3 species (1). Considering that the catalyst system
favors the production of an alternating copolymer, after the
formation of (1), propagation predominantly occurs by the
insertion of E followed by NB one after the other according to
the sequence (A)-(B)-(C)-(D).
Figure 4. Plots of NB content and Mw/Mn vs NB/E molar ratio with
complex 1/MAO.
The most dramatic change observed is in the molecular weight
distribution of the resultant copolymer. The plots of the NB
content and Mw/Mn value of the resultant polymer vs NB/E
molar ratio in a polymerization medium are shown in Figure 4.
The NB/E molar ratio (and thus NB content of the resulting
copolymer) significantly affects the molecular weight distribu-
tion; i.e., the catalyst system formed very narrow molecular
weight distribution polymers under the conditions where the
NB/E molar ratio is larger than 1, whereas the smaller NB/E
molar ratio resulted in the production of broader molecular
weight distribution polymers. It seems that an NB content of
larger than ca. 30 mol % is a requirement for producing narrow
molecular weight distribution copolymers in the present system.
As Fink and co-workers described,10d an NB-last-inserted
species (2) is fairly stable toward chain transfers because of
the difficulty in â-H transfers, whereas an E-last-inserted species
(4) may undergo relatively fast chain transfer.27 Therefore, the
achievement of the highly controlled living copolymerization
is probably as a consequence of the stabilization of an E-last-
inserted species (4) toward chain transfers and its smooth
transformation to a chain-transfer-wise stable NB-last-inserted
species (2).
Chain-End Analysis of the Copolymer. Chain-end analysis
of a low molecular weight living copolymer using 13C NMR
spectroscopy was performed in order to obtain further informa-
tion about the copolymerization. Figure 5 shows the 13C NMR
spectrum of the low molecular weight copolymer stemming from
1/MAO (Mn 1800, Mw/Mn 1.16, NB content 50.8 mol %).25
When the fact that the living copolymer (entry 3 in Table 1)
contains a very small amount of NB-NB units is taken into
account, chain-end structures which should be considered for
the copolymer are CH3-E-E-, CH3-E-NB-, CH3-NB-
E- for the initiation chain ends and E-E-, E-NB-, NB-
E- for the termination chain ends (see the Supporting Infor-
mation).
Relative formation energies estimated by DFT calculations21
indicate that a NB-coordinated E-last-inserted species (5) [the
(26) Peak assignments were performed based on a comparison of the observed
chemical shifts with the literature data (exo-2-methylbicyclo[2.2.1]heptane,
exo-2-ethylbicyclo[2.2.1]heptane) (Lippmaa, E.; Pehk, T.; Belikova, N. A.;
Bobyleva, A. A.; Kalinichenko, N.; Ordubadi, M. D.; Plate´, A. F. Org.
Magn. Reson. 1976, 8, 74-78.) and with the chemical shifts of the
synthesized authentic sample of exo-2-n-propylbicyclo[2.2.1]heptane.
(27) E/NB copolymerization with 1/MAO at 90 °C for 1 min produced a
broadened molecular weight distribution copolymer (Mn 13 800, Mw/Mn
1.86) that possesses a vinyl end group (which is derived from a â-H transfer
from the last-inserted E unit). These facts probably indicate that an E-last-
inserted species undergoes fast chain transfer relative to an NB-last-inserted
species.
(25) Polymerization conditions: complex 1 (200 µmol), MAO (10 mmol),
E- and N2- saturated toluene (250 mL, E 50 L/h, N2 50 L/h), charged NB
(10 g), 0 °C, 5 s.
9
12028 J. AM. CHEM. SOC. VOL. 126, NO. 38, 2004

Copolymerization of Ethylene with Norbornene
A R T I C L E S
Figure 5. Chain-end analysis of the low molecular weight E-NB copolymer produced with complex 1/MAO.
Scheme 2. Plausible Mechanism for Living E/NB Copolymerization Promoted by Complex 1/MAO
calculated structure is displayed in Figure 6(A)] is more stable
than the corresponding E-coordinated species (7) by 8.33 kJ/
mol, indicative of dominant NB coordination to the Ti center
of the E-last-inserted species. The coordination of highly
nucleophilic and sterically encumbered NB to the E-last-inserted
active species ((5), coordination energy; -17.05 kJ/mol) would
reduce the electrophilicity of the active species and, in addition,
provides steric congestion in close proximity to the active site,
which probably mitigates chain transfers (e.g., â-hydrogen
transfer to a reacting monomer, chain transfer to alkyl Al
9
J. AM. CHEM. SOC. VOL. 126, NO. 38, 2004 12029

A R T I C L E S
Yoshida et al.
Figure 6. Calculated structures of an E-last-inserted species in the presence of NB ((5) in Scheme 2) and a NB-last-inserted species in the presence of E
((3) in Scheme 2).28 Hydrogen atoms are omitted for clarity.
species). The facile insertion of NB to the E-last-inserted species
was suggested by the fact that a growing polymer chain is
detected exclusively as an NB-last-inserted state when the living
copolymerization was quenched. The high NB affinity and the
fast NB insertion are thought to arise from the sterically open
and highly electrophilic nature of the active site.
Since the copolymers contain some isolated NB units present
in the successive E units, reaction pathway (4)-(7)-(9) is also
involved in the living copolymerization. As discussed, the
catalyst system has characteristics of a living E polymerization
though under limited conditions. The characteristics would allow
the successive E enchainment without significant chain transfer
with the E-NB copolymer exhibiting living character.
DFT calculations indicate that an E-coordinated species (3)
[the calculated structure is shown in Figure 6(B)] is more stable
Figure 7. GPC profile of the poly(E-co-NB)1-b-poly(E-co-NB)2 formed
than the NB-coordinated congener (6) by 5.70 kJ/mol, which
may result in the formation of the NB-E sequence. Although
the calculations suggest the preference of E coordination to an
NB-last-inserted species (coordination energy; -14.44 kJ/mol),
the coordination of NB to an NB-last-inserted propagating
species (coordination energy; -9.74 kJ/mol) does not seem to
be negligible considering the facts that increase in NB concen-
tration in a polymerization medium results in a decrease in
catalytic activity and that the copolymer contains NB-NB
blocks though only a small amount. The NB coordination to
the sterically hindered NB-last-inserted species presumably
stems from the inherently high electrophilic characters of the
active species.
with complex 1/MAO: (a) prepolymer, Mn 329 000, Mw/Mn 1.11; (b) diblock
copolymer, Mn 745 000, Mw/Mn 1.23.
Synthesis of Block Copolymers from Ethylene and Nor-
bornene. Given the established living nature of E and E/NB
(co)polymerizations with the bis(pyrrolide-imine) Ti complexes/
MAO systems, we decided to explore the creation of E- and
NB-based block copolymers, which consist of amorphous and
amorphous or crystalline and amorphous segments.
Poly(E-co-NB)1-b-poly(E-co-NB)2 in which each copolymer
segment contains a different NB content was prepared using
E/NB toluene solutions. Treatment of 1 (1 µmol)/MAO (1.25
mmol) with E-saturated toluene (250 mL, E 50 L/h) containing
NB (1 g) for 2 min with a continuous feed of E (50 L/h) resulted
in the formation of the first poly(E-co-NB)1 segment. Subse-
quent addition of NB (10 g) to the resulting mixture with the
continuous E feed (50 L/h) formed a well-defined high molec-
ular weight poly(E-co-NB)1-b-poly(E-co-NB)2. An overlay of
the unimodal GPC elution curves for the first poly(E-co-NB)1
(Mn 329 000, Mw/Mn 1.11, NB content 26.2 mol %) and the
final poly(E-co-NB)1-b-poly(E-co-NB)2 (Mn 745 000, Mw/Mn
1.23, NB content 34.3 mol %) suggests a shift toward the higher
molecular weight region due to the subsequent copolymerization
step without providing any peak in the low-molecular weight
region (Figure 7), demonstrating the creation of the target block
copolymer. It is noteworthy that the block copolymer displays
two sets of Tg’s, 50 °C derived from the first segment (NB
On the basis of the above discussions, we concluded that the
facile coordination of NB to the E-last-inserted species and its
fast insertion to the species as well as the living character of E
polymerization play key roles in the achievement of the highly
controlled living copolymerization.29
(28) The distances between the coordinated NB and the Ti centers ((A) 4.030
Å, (B) 4.480 Å) are relatively large probably due to steric congestion
stemming from the ultimately or penultimately inserted NB in the polymer
chains.
(29) The quasi-living E/NB copolymerizations achieved by rac-Et(Ind)2ZrCl2
or Me2Si(Me4Cp)(N-tert-Bu)TiCl2 with MAO are probably due to the
enhancement of NB coordination to an E-last-inserted active species and
the acceleration of NB insertion to the active species with the aid of a high
NB concentration and, at the same time, a large excess of NB to E in a
polymerization medium.
(30) We observed that PE (segment) was colored easily relative to poly(E-co-
NB) (segment).
9
12030 J. AM. CHEM. SOC. VOL. 126, NO. 38, 2004

Copolymerization of Ethylene with Norbornene
A R T I C L E S
Table 5. Synthesis of Various Block Copolymers Using Complex 1/MAOa
prepolymer
diblock copolymer
NB contentc
b
d
d
b
d
d
first block
Mn
103)
NB contentc
(mol %)
Tg
C )
Tm
C )
second block
component
Mn
103)
Tg
C )
Tm
C )
b
b
entry
component
(×
Mw/Mn
(
°
(
°
(
×
Mw/Mn
(mol %)
(
°
(
°
1
2
3
4
(E-co-NB)1
(E-co-NB)3
(E-co-NB)5
PE
329
406
223
119
1.11
1.28
1.38
1.34
26.2
19.5
7.6
52
20
(E-co-NB)2
(E-co-NB)4
(E-co-NB)6
(E-co-NB)7
745
783
424
414
1.23
1.32
1.66
1.56
34.3
30.1
27.4
31.5
50, 119
17, 123
116
88
134
88
e
e
a Conditions: 25 °C, atmospheric pressure, E gas feed (50 L/h). Complex 1: 1 µmol, cocatalyst; MAO 1.25 mmol as Al, toluene 250 mL. b Mn and
Mw/Mn values were determined by GPC, equipped with refractive index (RI) detector (entries 1 and 2) and FT-IR detector (entries 3 and 4), by using
polystyrene calibration. c Determined by 13C NMR. d Measured by DSC. e Indistinguishable due to the overlap of Tg and Tm.
content 26.2 mol %) and 119 °C from the second segment (NB
content 41.3 mol %, calculated from the polymer yields and
NB contents of the first segment and the final block copolymer).
Likewise, two additional block copolymers, poly(E-co-NB)3-
b-poly(E-co-NB)4 and poly(E-co-NB)5-b-poly(E-co-NB)6, were
synthesized using different E/NB molar ratio toluene solutions.
The poly(E-co-NB)3-b-poly(E-co-NB)4 block copolymer (the
first segment; Mn 406 000, Mw/Mn 1.28, NB content 19.5 mol
%, total; Mn 783 000, Mw/Mn 1.32, NB content 30.1 mol %)
exhibits Tg’s of 17 and 123 °C. Interestingly, the poly(E-co-
NB)5-b-poly(E-co-NB)6 block copolymer (the first segment; Mn
223 000, Mw/Mn 1.38, NB content 7.6 mol %, total; Mn 424 000,
Mw/Mn 1.66, NB content 27.4 mol %) displays both Tm (88 °C)
due to the first crystalline segment and Tg (116 °C) associated
with the second amorphous segment.
Moreover, a PE-b-poly(E-co-NB) diblock copolymer was also
synthesized from E and NB by sequential monomer addition.
Treatment of 1 (1 µmol)/MAO (1.25 mmol) with E- and N2-
saturated toluene (250 mL, E 50 L/h, N2 50 L/h) for 10 s with
Figure 8. TEM micrographs of (A) PE and poly(E-co-NB) blend polymer
a continuous feed of E (50 L/h) and N2 (50 L/h) (the first
(blend conditions: toluene, reflux temperature, 1 h) and (B) PE-b-poly(E-
co-NB).30
segment; Mn 119 000, Mw/Mn 1.34) and then addition of NB
(10 g) to the resulting mixture and the halt of the N2 feed
produced a well-defined high molecular weight PE-b-poly(E-
co-NB) block copolymer (Mn 414 000, Mw/Mn 1.56, NB content
31.5 mol %). A shift of GPC elution curves for the first PE
segment and the final PE-b-poly(E-co-NB) toward the high-
molecular-weight region suggests the formation of the block
copolymer (see the Supporting Information). DSC measurements
did not provide distinguishable Tg and Tm of the block copolymer
because of the overlap of these temperatures.
Conclusions
In summary, the catalytic properties of bis(pyrrolide-imine)
Ti complexes (PI Catalysts) for E/NB copolymerization have
been described. PI Catalysts combined with MAO exhibit
excellent NB incorporation, which exceeds that for Me2Si(Me4-
Cp)(N-tert-Bu)TiCl2 (CGC). The catalysts can mediate highly
controlled room-temperature living E/NB copolymerization with
a high propensity to form alternating copolymers. The catalyst
systems can produce high molecular weight copolymers (Mn >
500 000, Mw/Mn < 1.2) and a number of block copolymers from
E and NB [e.g., poly(E-co-NB)1-b-poly(E-co-NB)2, PE-b-poly-
(E-co-NB)]. The highly controlled living copolymerization
originates from the fact that the catalysts possess the high affinity
and high incorporation ability for NB as well as some
characteristics of a living E polymerization. The sterically open
and highly electrophilic nature of the active species is probably
responsible for the high affinity and high incorporation capability
for NB. The achievement of the highly controlled living
copolymerization by PI Catalysts with MAO may result in a
new strategy for the development of high-performance catalysts
for the living copolymerization of E and strained cyclic olefins.
The results introduced herein together with our previous
reports17 suggest that PI Catalysts can exhibit unique polym-
erization behavior and thus have offered opportunities for the
syntheses of distinctive polymers.
Further information about the PE-b-poly(E-co-NB) block
copolymer is given by transmission electron microscopy (TEM).
The TEM micrograph of the press-sheet made of the PE/poly-
(E-co-NB) blend polymer [Figure 8(A)] shows the grown
lamellar structures of PE and the amorphous poly(E-co-NB)
segment exists among the PE lamellar structures, while con-
versely that of the PE-b-poly(E-co-NB) [Figure 8(B)] displays
considerable homogeneous structures. These results further
confirm the formation of the desired block copolymer and, at
the same time, demonstrate the high potential of the block
copolymer as a new material composed of crystalline and
amorphous segments that are chemically linked.
As disclosed in our patent16b filed on November 8, 2002, these
are probably the first examples of the syntheses of E- and NB-
based block copolymers. These unique block copolymers may
be applied to a broad spectrum of applications that include
compatibilizers, elastomers, and composite materials.
9
J. AM. CHEM. SOC. VOL. 126, NO. 38, 2004 12031

A R T I C L E S
Yoshida et al.
Acknowledgment. We would like to thank Drs. M. Mullins
and A. Valentine for fruitful discussions and suggestions.
zation, polymer analysis data (NMR, DSC, GPC, GC-MS),
13C NMR data for 2-n-propylbicyclo[2.2.1]heptane, scheme for
possible chain-end structures for an E-NB copolymer. This
material is available free of charge via the Internet at
http://pubs.acs.org.
Supporting Information Available: Experimental section,
DFT calculation results, plots of Mn and Mw/Mn vs polymeri-
zation time with complexes 2-4/MAO for E/NB copolymeri-
JA048357G
9
12032 J. AM. CHEM. SOC. VOL. 126, NO. 38, 2004