Studies in Surface Science and Catalysis 89 CATALYST DESIGN FOR TAILOR-MADE POLYOLEFINS Proceedings of the Internationa...
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Studies in Surface Science and Catalysis 89 CATALYST DESIGN FOR TAILOR-MADE POLYOLEFINS Proceedings of the International Symposium on Catalyst Design for Tailor-made Polyolefins, Kanazawa, March 10-12, 1994
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Studies in Surface Science and Catalysis Advisory Editors : B . Delmon and J. T. Yates Vol .89
CATALYST DESIGN FOR TAILOR- MADE POLY0LEFlNS PROCEEDINGS OF THE INTERNATIONAL SYMPOSIUM ON CATALYST D ESIG N FOR TAI LOR-M A DE POLY0LEFINS , KANAZAWA, MARCH 10-12, 1994 Edited by Kazuo Soga
Japan Advanced Institute of Science and Technology, Hokuriku
Minoru Terano
Japan Advanced Institute of Science and Technology, Hokuriku
KODANSHA Tokyo
1994
ELSEVIER Amsterdam - London - New York - Tokyo
Copublished by KODANSHA LTD., Tokyo and ELSEVIER SCIENCE B.V., Amsterdam exclusive sales rights Japan KODANSHA LTD. 12-21, Otowa 2-chome, Bunkyo-ku, Tokyo 112, Japan
for the rest of the world ELSEVIER SCIENCE B.V. 25 Sara Burgerhartstraat, P.O. Box 211, 1000 AE Amsterdam, The Netherlands
ISBN 0-444-98656- 1 ISBN 4-06-2071 86-X (Japan)
Copyright @ 1994 by Kodansha Ltd.
All rights reserved No part of this book may be reproduced in any form, by photostat, microfilm, retrieval system, or any other means, without the written permission of Kodansha Ltd.(except in the case of brief quotation for criticism or review) PRINTED IN JAPAN
List of Contributors Numbers in parentheses refer to the pages on which contributors’ paper begin.
Abe, M. (327) Osaka Research Laboratory, Mitsui Toatsu Chemicals, Inc., Takaishi, Osaka 592, Japan Akino, Y. (1 19) Research Laboratory of Resources Utilization, Tokyo Institute of Technology, Midori-ku, Yokohama 227, Japan Akiyama, M. (327) Central Research Institute, Mitsui Toatsu Chemicals, Inc., Sakae-ku, Yokohama 247, Japan Albizzati, E. (139) Himont “G. Natta” Research Center, P. le G. Donegani, 12 44100 Ferrara, Italy Altomare, A. (257) Department of Chemistry and Industrial Chemistry, University of Pisa, via Risorgimento 35, 56126 Pisa, Italy Arndt, M. (179) University of Hamburg, Edmund-Siemers-Allee 1, Germany Arribas, G. (257) Escuela de Quimica, Facultad de Ciencias, Universidad Central de Venezuela, Caracas, Venezuela Asanuma, T. (327) Osaka Research Laboratory, Mitsui Toatsu Chemicals, Inc., Takaishi, Osaka 592, Japan Bacon, D. W. (81) Chemical Engineering Department, Queen’s University, Kingston, Ontario, K7L 3N6, Canada Beck, S. (193) Fakultat fiir Chemie, Universitat Konstanz, D-78434 Konstanz, Germany
vi
List of Contributors
Berry, I. G . (55) Department of Chemistry, UMIST, Manchester M60 IQD, U.K. Bohm, L. L. (351) Hoechst AG, 65926 Frankfurt(M), Germany Brintzinger, H. (193) Fakultat f i r Chemie, Universitat Konstanz, D-78434 Konstanz, Germany Bujadoux, K. (249) E.C.P. EniChem Polymeres France, Centre de recherche, 62670 Mazingarbe, France Burfield, D. R. (91) Chemistry Department, University of Malaya, 59100 Kuala Lumpur, Malaysia Busico, V. (21) Dipartimento di Chimica-Universita’ di Napoli via Mezzocannone, 4-1-80 134 Napoli, Italy Chu, K. J. (299) Department of Chemical Engineering, Korea Advanced Institute of Science and Technology, 373- 1 Kusong-dong, Y usong-gu, Taejon 305-701, Korea Ciardelli, F. (257) Department of Chemistry and Industrial Chemistry, University of Pisa, via Risorgimento 35, 56126 Pisa, Italy Cipullo, R. (21) Dipartimento di Chimica-Universita’ di Napoli via Mezzocannone, 4-1-80 134 Napoli, Italy Conti, G. (257) Department of Chemistry and Industrial Chemistry, University of Pisa, via Risorgimento 35, 56126 Pisa, Italy Corradini, P. (21) Dipartimento di Chimica-Universita’ di Napoli via Mezzocannone, 4-1-80134 Napili, Italy Dall’ Occo, T. (139) Himont “G. Natta” Research Center, P. le G. Donegani, 12 44100 Ferrara, Italy Dupuy, J. (109) CNRS-Laboratoire de Chimie et Procedes de Polymerisation LCPP BP 69390 Vernaison, France Dyachkovskii, F. S. (201) Institute of Chemical Physics Russian of Scienses, Chernogolovka, 142432, Moscow Region, Russia
List of Contributors vii
Eisch, J. J. (221) Department of Chemistry, State University of New York at Binghamton, Binghamton, NY 13902-6000, U.S.A. Enderle, H. F. (351) Hoechst AG, 65926 Frankfurt(M), Germany Ewen, J. A. (405) Catalyst Research Corporation, 1823 Barleton Way, Houston, TX 77058, U.S.A. Fleissner, M. (351) Hoechst AG, 65926 Frankfurt(M), Germany Galimberti, M. (139) Himont “G. Natta” Research Center, P. le G. Donegani, 12 44100 Ferrara, Italy Gan, S. N. (91) Chemistry Department, University of Malaya, 59 100 Kuala Lumpur, Malaysia Guyot, A. (43) CNRS-LCPP, BP 24-69390 Vernaison, France Han, T. K. (163) Department of Chemical Engineering, Korea Advanced Institute of Science and Technology, Y usong-gu, Daejon 305-701, Korea Hosoda, S. (365) Sumitomo Chemical Co., Chiba Research Laboratory, Sodegaura, Chiba 299-02, Japan Hsu, J. C. (81) Chemical Engineering Departoment, Queen’s University, Kingston, Ontario, K7L 3N6, Canada Hungenberg, K. D. (373) BASF AG, Plastics Laboratory, D-67056 Ludwigshafen, Germany Ihara, E. (237) Department of Applied Chemistry, Faculty of Engineering, Hiroshima University, Higasi-Hiroshima, Hirosima 724, Japan Ihm, S. K. (299) Department of Chemical Engineering, Korea Advanced Institute of Science and Technology, 373- I Kusong-dong, Yusong-gu, Taejon 305-701, Korea Imai, M. (1 71) Tonen Chemical Corporation, Tonen Corporate R&D Laboratory, Iruma-gun, Saitama 356, Japan
viii
List of Contributors
Inoue, N. (327) Central Research Institute, Mitsui Toatsu Chemicals, Inc., Sakae-ku, Yokohama 247, Japan Ishihara, N. (339) Central Research Laboratories, IDEMITSU KOSAN Co., Sodegaura, Chiba 299-02, Japan Jeong, Y. T. (153) Department of R&D, Korea Petrochemical Industrial Co., Ulsan 680-1 10, Korea Jordan, R. F. (271) Department of Chemistry, University of Iowa, Iowa 52242, U.S.A. Journaud, C. (43) CNRS-LCPP, BP 24-69390 Vernaison, France Kakugo, M. (129) Chiba Research Laboratory, Sumitomo Chemical Co., Sodegaura, Chiba 299-02, Japan Kaminsky, W. (1 79) University of Hamburg, Edmund-Siemers-Allee 1, Germany Kanazawa, S. (471) Tonen Chemical Corporation, Tonen Corporate R&D Laboratory, Iruma-gun, Saitama 356, Japan Kang, K. K. (153) Department of R&D, Korea Petrochemical Industrial Co., Ulsan 680- 1 10, Korea Kao, S. C. (389) Union Carbide Corporation, P.O. Box 670, Bound Brook, NJ 08805, U.S.A. Karol, F. J. (389) Union Carbide Corporation, P.O. Box 670, Bound Brook, NJ 08805, U.S.A. Kashiwa, N. (381) Polymers Laboratories, Mitsui Petrochemical Industries Ltd., Waki, Y amaguchi 740, Japan Keii, T. (1) Japan Advanced Institute of Science and Technology, Hokuriku, Nomi-gun, Ishikawa 923-12, Japan Kerth, J. (373) BASF AG, Plastics Laboratory, D-67056 Ludwigshafen, Germany Kimura, S. (327) Osaka Research Laboratory, Mitsui Toatsu Chemicals, Inc., Takaishi, Osaka 592, Japan
List of Contributors ix
KO, Y. S. (163) Department of Chemical Engineering, Korea Advanced Institute of Science and Technology, Y usong-gu, Daejon, 305-701, Korea Kohno, M. (327) Central Research Institute, Mitsui Toatsu Chemicals, Inc., Sakae-ku, Yokohama 247, Japan. Kojima, K. (365) Sumitomo Chemical Co., Chiba Research Laboratory, Sodegaura, Chiba 299-02, Japan Kuramoto, M. (339) Polymer Research Laboratory, IDEMITSU Petrochemical Co., Ichihara, Chiba 299-01, Japan Lancaster, G. M. (285) Polyolefins and Elastomers Research and Development Laboratories, The Dow Chemical Company, 2301 Brazosport Boulevard, B-1607, Freeport, T X 77541, U.S.A. Langhauser, F. (373) BASF AG, Plastics Laboratory, D-67056 Ludwigshafen, Germany Langlotz, J. (315) Institute of Inorganic Chemistry, Martin-Luther-University Halle-Wittenberg, Geusaer StraBe, D-062 17 Merseburg, Germany Leclerc, M. (193) Fakultat fur Chemie, Universitat Konstanz, D-78434 Konstanz, Germany Lee, D. H. ( 1 53) Department of Polymer Science, Kyungpook National University, Taegu 702-701, Korea Loi, P. S. T. (91) Chemistry Department, University of Malaya, 59 100 Kuala Lumpur, Malaysia Masi, P. (73)(257) EniChem, via Maritano 26, 20097 S.Donato Milanese, Italy Masson, P. (109) CNRS-Laboratoire de Chimie et P r o d d b de Polym&isation LCPP BP 69390 Vernaison, France Menconi, F. (73)(257) EniChem, via Maritano 26, 20097 S.Donato Milanese, Italy Morimoto, M. (237) Department of Applied Chemistry, Faculty of Engineering, Hiroshima University, Higashi-Hiroshima, Hiroshima 724, Japan
x
List of Contributors
Morini, G. (139) Himont “G. Natta” Research Center, P. le G. Donegani, 12 44100 Ferrara, Italy Mortreux, A. (249) Laboratoire de Catalyse hCiCrog6ne et homogene, URA C N R S 402, USTL, ENSCL, BP 108, 59652 Villeneuve d’Ascq Cedex, France Muller, P. (373) BASF AG, Plastics Laboratory, D-67056 Ludwigshafen, Germany Murata, M. (171) Tonen Chemical Corporation, Tonen Corporate R&D Laboratory, Iruma-gun, Saitama 356, Japan Nakano, A. (171) Tonen Chemical Corporation, Tonen Corporate R&D Laboratory, Iruma-gun, Saitama 356, Japan NG, S. C. (91) Chemistry Department, University of Malaya, 59100 Kuala Lumpur, Malaysia Nodono, M. (237) Department of Applied Chemistry, Faculty of Engineering, Hiroshima University, Higashi-Hiroshima, Hiroshima 724, Japan Olonde, X. (249) E.C.P. EniChem PolymZres France, Centre de recherche, 62670 Mazingarbe, France Patin, M. (109) CNRS-Laboratoire de Chimie et ProcCd6 d e Polym&-isation L C P P BP 69390 Vernaison, France Pellecchia, C. (209) Dipartimento di Fisica, Universitii di Salerno, 1-8408 1 Baronissi(SA), Italy Pelletier, J. F. (249) Laboratoire de Catalyse hEt6roghe et h o m o g h e , URA C N R S 402, USTL, ENSCL, BP 108, 59652 Villeneuve d’Ascq Cedex, France Petit, F. (249) Laboratoire de Catalyse hEtCrog&ne et h o m o g h e , URA C N R S 402, USTL, ENSCL, BP 108, 59652 Villeneuve d’Ascq Cedex, France Pombrik, S. I. (221) Department of Chemistry, State University of New Y ork at Binghamton, Binghamton, N Y 13902-6000, U.S.A. Robert, P. (109) CNRS-Laboratoire de Chimie et Procgdb d e Polymerisation L C P P BP 69390 Vernaison, France
List of Contributors xi
Rbll, W. (193) Fakultat f i r Chemie, Universitat Konstanz, D-78434 Konstanz, Germany Shariati, A. (81) Chemical Engineering Department, Queen’s University, Kingston, Ontario, K7L 3N6, Canada Shigematsu, Y. (365) Sumitomo Chemical Co., Chiba Research Laboratoy, Sodegaura, Chiba 299-02, Japan Shiomura, T. (327) Central Research Institute, Mitsui Toatsu Chemicals, Inc., Sakae-ku, Yokohama 247, Japan Shiono, T. ( 1 19) Research Laboratory of Resources Utilization, Tokyo Institute of Technology, Midori-ku, Yokohama 227, Japan Soga, K . ( 1 19)(307) Japan Advanced Institute of Science and Technology, Hokuriku, Nomi-gun, lshikawa 923-12, Japan Solli, K. A. (35) Borealis AS, N-3960 Stathelle, Norway Spitz, R. (43)(109) CNRS-Laboratoire de Chimie et Procedb de PolymCrisation LCPP BP 69390 Vernaison, France Stehling, U. (193) Fakultat fur Chemie, Universitat Konstanz, D-78434 Konstanz, Germany Stevens, J. C. (277) Polyolefins and Elastomers Research and Development Laboratories, The Dow Chemical Company, 2301 Brazosport Boulevard, B-1607, Freeport, TX 77541, U.S.A. Sugimoto, R. (327) Osaka Research Laboratory, Mitsui Toatsu Chemicals, Inc., Takaishi, Osaka 592, Japan Sun, L. (81) Chemical Engineering Department, Queen’s University, Kingston, Ontario K7L 3N6, Canada Swogger, K. W. (285) Polyolefins and Elastomers Research and Development Laboratories, The Dow Chemical Company, 230 1 Brazosport Boulevard, B- 1607, Freeport, TX 77541, U.S.A.
xii
List of Contributors
Tait, P. J. T. ( 5 5 ) Department of Chemistry, UMIST, Manchester M60 IQD, U.K. Taube, R. (315) Institute of Inorganic Chemistry, Martin-Luther-University Halle-Wittenberg, Geusaer StraBe, D-062 17 Merseburg, Germany Terano, M. (101) School of Materials Science, Japan Advanced Institute of Science and Technology, Hokuriku, Nomi-gun, Ishikawa 923- 12, Japan Tjaden, E. B. (271) Department of Chemistry, University of Iowa, Iowa 52242, U.S.A. Uemura, A. (365) Sumitomo Chemical Co., Chiba Research Laboratory, Sodegaura, Chiba 299-02, Japan Vindstad, B. K. (35) Statoil R&D, N-7004 Trondheim, Norway Wache, S. (315) Institute of Inorganic Chemistry, Martin-Luther-University Halle-Wittenberg, Geusaer StraBe, D-062 17 Merseburg, Germany Wester, T. S. (35) Norwegian Institute of Technology, Department of Inorganic Chemistry, N-7034 Trondheim, Norway Woo, S . I . (163) Department of Chemical Engineering, Korea Advanced Institute of Science and Technology, Y usong-gu, Daejon 305-701, Korea Yamamoto, I . (365) Sumitomo Chemical Co., Chiba Research Laboratory, Sodegaura, Chiba 299-02, Japan Yamashita, M. (237) Department of Applied Chemistry, Faculty of Engineering, Hiroshima University, Higashi-Hiroshima, Hiroshima 724, Japan Yasuda, H. (237) Department of Applied Chemistry, Faculty of Engineering, Hiroshima University, Higashi-Hiroshima, Hiroshima 724, Japan Yim, J. H. (299) Department of Chemical Engineering, Korea Advanced Institute of Science and Technology, 373- 1 Kusong-dong, Y usong-gu, Taejon 305-701, Korea
List of Contributors xiii
Yokote, Y. (327) Central Research Institute, Mitsui Toatsu Chemicals, Inc., Sakae-ku, Yokohama 247, Japan Yoshioka, S. (237) Department of Applied Chemistry, Faculty of Engineering, Hiroshima University, Higashi-Hiroshima, Hiroshima 724, Japan Ystenes, M . (35) Norwegian Institute of Technology, Department of Inorganic Chemistry, N-7034 Trondheim, Norway Zambelli, A . (209) Dipartimento di Fisica, Universitg di Salerno, 1-8408 1 Baronissi(SA), Italy
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Contents
List of Contributors ................................................................................................ Preface ...............................................................................................................
1.
2.
3.
4.
5.
6.
7.
V
xix
Articulation of Kinetics of Quasi-Living Stages to those of Slurry Polymerization and an Unified Explanation-Propene Polymerization with MgCl,/EB/TiCl,-Al(C,H,),-(T. Keii)
1
Active Sites and Mechanisms of Stereospecificity in Heterogeneous Ziegler-Natta Catalysts (P. Corradini, V. Busico and R. Cipullo)
21
Dependence of Transient Comonomer Kinetics on Catalyst Design by Magnesium Chloride Supported Polymerization of Ethene and Propene (K.A. Solli, B.K. Vindstad, T.S. Wester and M. Ystenes)
35
A New Mechanism for Hydrogen Activation in Propene Polymerization Catalysts (A. Guyot, R. Spitz and C. Journaud)
43
Rate Enhancement Effects in the Prepolymerization and Copolymerization of Ethylene and a-Olefins (P.J.T. Tait and I. G. Berry)
55
Characterization of Active Sites in Ti/Hf/MgC12 Catalysts by Chiral Reagents (F. Masi and F. Menconi)
73
A New Polymer-Supported Catalysts for Olefin Polymerization (L. Sun, A. Shariati, J.C. Hsu and D.W. Bacon)
81
xvi
Contents
Active Center Determination in Ziegler-Natta Polymerization : an Innovative Dual-Labeling Approach (S.N. Gan, P.S.T: Loi, S.C. N G and D.R. Burfield)
91
Recent Tendency of Research Targets for Industrial Polypropylene Catalysts (M. Terano)
101
10. The Control of Molecular Weight Distributions in Ziegler-Natta Catalysis (R. Spitz, M. Patin, P. Robert, P. Masson and J. DuPuY)
I09
8.
9.
1 1. Synthesis and Application of Terminally Magnesium Bromide-
Functionalized Isotactic Poly (Propene) (T. Shiono, Y. Akino and K. Soga)
119
12. Wide Range Control of Microtacticity in Propylene Polymerization with Heterogeneous Catalyst Systems (M. Kakugo)
129
13. New Heterogeneous Catalysts for Polyolefins (E. Albizzati, T. Dall’Occo, M. Galimberti and G. Morini)
139
14. Change of Internal Donor for Mg(OEt),-Supported TiCI, Catalyst (D.H. Lee, Y.T. Jeong and K.K. Kang)
153
15. Temperature Programmed Decomposition of MgCI,/TH F/ TiC1, Bimetallic Complex Catalyst and its Effect on the Homoand Copolymerization of Ethylene (Y.S. KO, T.K. Han and S.I. Woo)
I63
16. Characterization of Mg/Ti Type Catalysts Prepared from Different Mg Components (M. Murata, A. Nakano, S. Kanazawa and M. Imai)
171
17. Mechanism of the First Steps of the Isotactic Polymerization with Metallocene Catalysts (W. Kaminsky and M. Arndt)
179
18. Reaction Mechanisms in Metallocene-Catalyzed Olefin Polymerization (H. Brintzinger, S. Beck, M. Leclerc, U. Stehling and W.
Roll)
193
19. Role of Ions in Coordination Polymerization of Olefins (F.S. Dyachkovskii)
20 I
20. Copolymerization of Hydrocarbon Monomers in the Presence of CpTiCI, - M A 0 : Some Information on the Reaction Mechanism from Kinetic Data and Model Compounds (A. Zambelli and C. Pellecchia)
209
Contents xvii
21. The Role of Ion-Pair Equilibria on the Activity and Stereoregularity of Soluble Metallocene Ziegler-Natta Catalysts (J.J. Eisch and S.I. Pombrik)
22 1
22. High Molecular Weight Monodisperse Polymers Synthesized by Rare Earth Metal Complexes (H. Yasuda, E. Ihara, S. Yoshioka, M. Nodono, M. Morimoto and M. Yamashita)
237
23. Lanthanocene Based Catalysts for Olefin Polymerization : Scope and Present Limitations (J.F. Pelletier, A. Mortreux, F. Petit, X. Olonde and K. Bujadoux)
249
24. Effect of Ligand and Inorganic Support on Polymerization Performances of Ti and Zr Catalyst (F. Ciardelli, A. Altomare, G. Arribas, G. Conti, F. Masi and F. Menconi)
257
25. Design of Non-Metallocene Single-Site Olefin Polymerization Catalysts (E.B. Tjaden and R.F. Jordan)
27 1
26. InsiteTM Catalyst Structure/Activity Relationships for Olefin Polymerization (J.C. Stevens)
277
27. Novel Molecular Structure Opens Up New Applications for Insite@ Based Polymers (K.W. Swogger and G.M. Lancaster)
285
28. Molecular Weight Distribution Control with Supported Metallocene Catalysts (S.K. Ihm, K.J. Chu and J.H. Yim)
299
29. Highly Isospecific Heterogeneous Metallocene Catalysts Acivated by Ordinary Alkylaluminums (K. Soga)
307
30. Mol Mass Regulation in the Ally1 Nickel Complex Catalyzed 1, 4-cis Polymerization of Butadiene (R. Taube, S. Wache and J. Langlotz)
315
3 1. Syndiotactic Polypropylene (T. Shiomura, M. Kohno, N. Inoue, Y. Yokote, M. Akiyama, T. Asanuma, R. Sugimoto, S. Kimura and M. Abe)
327
32. Syntheses and Properties of Syndiotactic Polystyrene (N. Ishihara, and M. Kuramoto)
339
33. The Industrial Synthesis of Bimodal Polyethylene Grades with Improved Properties (L.L. Biihm, H.F. Enderle and M. Fleissner)
35 1
xviii
Contents
34. Structure and Properties of Ethylene/ a-Olefin Copolymers Polymerized with Homogeneous and Heterogeneous Catalysts (S. Hosoda, A. Uemura, Y. Shigematsu, I. Yamamoto and K. Kojima)
365
35. Progress in Gas Phase Polymerization of Propylene with Supported TiCI, and Metallocene Catalysts (K.D. Hungenberg, J. Kerth, F. Langhauser and P. Miiller)
373
36. Feature of Metallocene-Catalyzed Polyolefins (N. Kashiwa)
38 1
37. Ligand Effects at Transition Metal Centers for Olefin Polymerization (F.J. Karol and S.C. Kao)
389
38. Propylene Polymerizations with Metallocene/Teal/Trityl Tetrakis (Pentafluorophenyl) Aluminate Mixtures (J.A. Ewen)
405
The International Symposium on Catalyst Design for Tailor-made Polyolefins was held at the Ishikawa High-tech Conference Center in Kanazawa, March 10-12, 1994 in memory of the establishment of the Japan Advanced Institute of Science and Technology (JAIST, Hokuriku) through the efforts of President Dr. Tominaga Keii. The symposium had over 200 attendants including 90 foreign scientists from 13 nations. At this meeting various trends in the following were noted. HETEROGENEOUS CATALYSTS Polymerization kinetics and mechanism Unsolved problems Catalyst preparation METALLOCENE CATALYSTS Polymerization mechanism Modeling and modification Applications NEW TRENDS IN T H E POLYOLEFIN INDUSTRY This volume is a collection of 22 invited and 16 contributed papers, which were subjected to scientific review. Unfortunately, the 36 poster papers presented at the symposium have not been included because of limited space. We believe that these proceedings are an excellent guide to the recent developments in both heterogeneous Ziegler-Natta and homogeneous Kaminsky-Sinn catalysts. Large grants from JAIST and the Ministry of Culture and Education, Japan are deeply appreciated. This symposium could not have been held without such invaluable financial support. The editors thank the authors for the superior quality of their presentations as well as for contributing to this volume. Thanks are also extended to Mr. Ippei Ohta of Kodansha Scientific for his invaluable assistance in the editing of this volume. June 1994
Kazuo Soga Minoru Terano
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I
1. Articulation of Kinetics of Quasi-Living Stages to those of Slurry Polymerization and an Unified Explanation-Propene Polymerization with MgCl,/EB/TiCl,-Al(C,H,),-
Tominaga Keii Japan Advanced Institute of Science and Technolagy, Hokuriku. Tatsunokuchi, Ishikawa 923-12, Japan
INTRODUCTION
For this twenty years the author has been possessed by some curious kinetic behavior of the propene polymerization with a MgC12/EB/TiC1-A1(C2H5)3 catalyst. As described in the previous papers(ll2), the observed kinetic behavior of the polymerization in
a slurry system were so complex that the
usual kinetic analysis could not be applied. Since we supposed that the kinetic behavior suffered from the rapid rate decay of the polymerization, we attempted to develop some
new method that applicable for observing kinetic behavior of
the polymerization free from any rate decay or those, at least, with a negligibly small rate decay.
A stopped flow reactor developed with Terano et
a1.(3) was useful to carry out the polymerization for a short time, such as 0.03-1s at room temperature, where the polymerizations were those of quasipolymerization with constant rates. stages of the polymerizations, we
From the results of the quasi-living could determine precise values of rate
constants of propagation and transfer reaction as well as concentrations of polymerization centers, as communicated before(3)' ( 4 ) t ( 5 ) . observation gives
In addition, the
us some important key to understand our kinetic data of the
slurry polymerization together with those reported by Giannini(6) and Hsu et a1.(7), on the basis of an unified kinetic model, the description of which is the purpose of
this reporting.
First, the problems remain unsolved in the slurry polymerization are summarized. Then, they are discussed in the light of of new data obtained by the stopped flow method. The whole data
articulated are reviewed ahd explained
2 T. Keii unifiedly on the basis of an unified theory of non-uniform active centers.
OBSERVED
KINETICS
OF
SLURRY
POLYMERIZATION;
UWSOLMD
PROBLEMS
The observed kinetic results of the slurry polymerizations carried out under the conditions: temperature (1-65OC), monomer concentration [MI ( 0 . 2 2 0.48mol/dm3), triethy
aluminum
concentration
[A]
(1-100 mmol/dm3)
and
polymerization time t (5s-3h), are summarized in comparison with the results and Hsu et al. ( 7 ) as follows.
reported by Giannini(6) Rat.
docay
, the rate decay is a third
As described in the report
order with respect to rate itself at the beginning stages of the polymerization (0-lh) and order.
it slows down to a second order and then approaches to a first
In the range of
temperature, 1-6S0C,
a
second
approximately could be applied for the time course during
order
decay
0.5-3h at 4loC, as
Re-examining the experimental data, we found that the constant kd is a function of [A] as that
kd'kd'
fAlz61.4 e-17'6 kJ'RTIAl
The rate equation reported by
%,
1[MI = el/(i
S ' ,
0.005> 1, changes
The latter gives that from
c ( N*,
P
to 2 as t increases from
accepted conclusion for
t > l/ktr , which is widely
homogeneous polymerizations.
Here, the author shows that the time-invariant MWD can be explained by means of the averaging procedure with the use of T(k/k) in the case of y = 2 . Averaged value with the use of
Z ( N*,,
+
+
Zn( N*,, h2(N*n
Nn
+
which give that
Nn Nn
= C*,
)
1 +
= C*o ( 1
) )
(
=
xw/K
C*,
= 2
T(k/k) = exp(-k/k) are
ktrt
)
+ ktrt + kP [MI t
(2(kp[Mlt)2/( 1 +
)
(49)
ktrt))
independent of t. This is an explanation of the
time-invariant nature of the polydispersity during quasi-living stages. The observed
time-invariant nature of
the shape o f
GPC-curve of prod,Jced
polymers,i.e. W(1ogM) against logM, during quasi-living stages can also be explained on the same basis, as that
I . Kinetics of Propene Polymerization and Unified Explanation
17
This result shows that GPC-curve shifts with time by log(t/l+ ktrt) but its shape remain unchanged during the quasi-living stages. Thus, the time invariant property of MWD can be explained on the basis of "Intrinsic Fluctuation" theory. However, the theory can not explain any i.e.
broadening of MWD,
-Mw/En
though its values in this propene catalyst
are
small
3-5. ( 2 )
> 2 , in the heterogeneous polymerizations,
polymerization The
broadening
with of
MWD
MgC12-supported in
heterogeneous
polymerizations, however, has been interested by many workers. As well-known, there are the three
rival theories; diffusion control ( 2 2 ) , chain length
control(23) and non-uniform surface(2) . The mathematical procedures involved in respective theories have been so devised that they lead some averaged values of the ratio of kp[Ml and ktr.
So far i t
concerns stationary MWD, only
established criterion to judge the theories is the effect of hydrogen on MWD. It has been proposed by Roe(24) who proved that hydrogen does not affect on MWD only in the case of non-uniform surface. The present author prefers the view of non-uniform surface, mainly on the experimental confirmation of
no effect of
hydrogen on MWDs in many heterogeneous Ziegler-Natta polymerization systems. The behavior of MWD during quasi-living stages is a new one of criteria for judging the rival theories. It will be shown that the time-invariant broad MWD during quasi-living stages is a decisive evidence of the non-uniform surface theory articulated with the above "Intrinsic Fluctuation" theory.
Non-uniform
Surface: The broadening of MWD can be explained on the
basis of a surface heterogeneity that the catalyst surface is not of a single crystal
but
of
polycrystal.
Assuming
that
a
component
surface
i
is
characterized by k p , (i) and its number of active sites is denoted by C*,, (i), and both ktr
and kd are common for all surfaces, the averages of R Q , t and
C * t , Eq.(40) and Eq.(38), over the whole surface
can be represented by
18
T. Keii
(52)
In the case of quasi-living stages, where f (kdt) i
Eqs.(49) and ( 5 0 ) . remain unchanged excepting that kp
by and O
40
tI?.?/(rnl")
F i g u r e 1 . T h e ch an g e i n p o l y m e r r a d i o a c t i v i t y w i t h l 4 C O
contact t i m e . SDPM per m i n u t e .
specific disintegration
These findings are essentially the same as numerous earlier studies8s11-16) and must now be regarded as characteristic of the interaction of CO with these systems. The scheme that most adequately fits the published data is similar to the earlier conclusions of Bukatov et a l l ' , namely that
8. Active Center Determination in Ziegler-Natta Polymerization 97
the initia
fast reaction corresponds to site labeling and that the
subsequent slow incorporation is due to side reactions such as chain transfer w th co-catalyst (equation 7 ) followed by reinitiation of chain growth and subsequent retagging. This is consistent with model studies’) , would explain the enhancement in the presence of monomer15) and with increased metal alkyl con~entration’~), and would be expected to give rise to the observed low molecular weight impurities11
.
Quenching Experiments In the quenching experiments, excess CH30T was added after the initial polymerization. All the metal-polymer bonds become tagged with tritium. Ti-PI A1-P’ t CH30T 4 Ti-OCH3, Al-OCH3 + T-P t T-P’ (8) Dual-labeling ExDeriments In the dual-labeling experiments, during the initial polymerization, exchange reactions with AIR3 would have generated some A1-P. The monomer gas was cut off (in the case of propylene and ethylene) and the radiotagging procedure was carried out. 15 minutes after the addition of 14C0, all the active sites would have presumably been tagged to form Ti-l4CO--P. Unpon subsequent quenching with CH30T, the resulting polymer sample would contain radioactivities due to both the incorporated 14C and T iaotopes. Comparison of Single Labeling and Dual Labeling ExDeriments The results obtained from single labeling and dual labeling experiments between polymerizations carried out under similar conditions are compared (Table 1). As expected, the amounts of incorporated 14C0 tags were similar in both the dual-labeling and single labeling experiments since insertion could occur only at the Ti-P bond. On the other hand the amounts of incorporated tritium in dual labeling experiments were much lower than those of single labeling experiments. These are most readily explained as follows.
98
S.N.Gan. P.S.T. Loi. S.C. NG and D.R. Burfield
In the single labeling experiments, all the metal-polymer bonds, MPB, become tagged with tritium (reaction 8). While in the case of dual labeling, only the base metal polymer bond would become tagged with tritium as represented in the following scheme. A1-P
t
Ti-14CO-P
CHQOT
+ Al-OCH3 + Ti-H t
t CH30T
*
Table 1 : Comparison of C
(9)
T-P
t
(active center concentration) and
** C (non-active metal-polymer
bond concentration) ~~~~
No.
Labeling Monomer mode type
(10)
CH30-14CO-P
T
= c**
14c
= C
*
~
[ MPB I /mmol/mol Ti
The sums of the 14C0 tags and the incorporated tritium from the dual labeling experiments agreed quite well with the total metal polymer bonds determined by single labeling quenching experiments. Use of Dual Labeling Techniaue to Demonstrate Transfer Reactions The transfer reactions, such as ( 3 ) and (7), can be demonstrated by dual labeling technique (Table 2) in the same runs, instead of
duplicate runs with single labeling technique. While Ti-P concentration remained low, the total A1-P bonds increased with reaction time as the polymer chains were constantly being transferred from the titanium sites to the aluminum sites.
8. Active Center Determination in Ziegler-Natta Polymerization 99
Polymerization t ime/min.
14C0 tag = [Ti-PI
T incorporated [Al-P]
[ MPB I
nmol/mol Ti
_-______________-____------------------------------------------60 120
0.33 0.41
180
0.44
0.94 2.08 2.20
1.27 2.49 2.64
[TiC13.AA]= 25 m M ; [A1Et2C1]= 95 m M ; monomer=propylene; 30'C CONCLUSION It is concluded that quantitative 14C0 tagging of active site requires short contact times and high 14C0 concentrations to minimize interfering side reactions. Under optimum conditions, I4CO and CH30T dual labeling approach can lead to a mixture of single radioactive isotope labeled polymer chains, with 14C tagging the active metalpolymer bonds, while the incorporated tritium corresponds to the amount of base metal-polymer bonds. REFERENCES 1. D.H.Ballard, "Coordination Polymerization", J.C.W. Chien, Ed., Academic Press, London, 1975, p.223. 2. J.Mejzlik, L.Lesna, and J.Kratochvila, Adv.Polym. Sci. 81, 84 (1987) A.D.Caunt, S.Davies, P.J.T.Tait, in "Transition Metal Catalyzed Polymerizations, Ziegler-Natta and Metathesis Polymerizations", R.P.Quirk,Ed.,Cambridge University Press,Canbridge, 1988, p.105 4. D.R.Burfield, P.J.T.Tait, Polymer l3, 315 (1972) 5. C.F.Feldman, E.Perry, J.Polywer Sci., 46, 217 (1960) 6. J.Mejzlik, M.Lesna, Makromol. Chem. 178, 261 (1977) 7. Y.Doi, M.Murata, K.Soga, Makromol.Chem.Rap.Comm.5,811(1984) 8. J.Mejzlik, M.Lesna, J.MaJor, Makromol. Chem. 184, 1975 (1983) 9. M.Kakugo, H.Sadatoshi, K.Wakamatsu, H.Yoshioka, Polymer Preprints (Japan) 28 650 (1979) 3.
100 S.N.Gan, P.S.T. Loi. S.C. NG and D.R. Burfield
10.
T.Shiono, M.Ohgizawa, K.Soga, Makromol. Chem.
11.
G.D.Bukatov,
V.A.Zakharov,
194, 2075
Yu.I.Ermakov, Makromol. Chem.
(1993)
179,
2097 (1978)
12.
J.C.W.Chien
and C.I.Kuo, J. Polym. Sci., Polym. Chem, Ed.
a,
731 (1985) 13.
V.Warzelhan, T.T.Burger, D.T.Stain,
Makromol. Chem.
183, 489
( 1982)
14.
P.J.T.Tait,
in "Transition-metal Catalyzed Polymerization-
Alkenes and Dienes", Part 1, R.P.Quirk,
Ed., Harwood Academic,
New York,1983, p. 115ff. 15. 16.
A.D.Caunt, Brit. Polym. J., 22 (1981) P.J.T.Tait,
B.L.Booth,
Cornmun. 9 393 (1988)
M.O.Jejelowo,
Makromol. Chern. Rapid.
101
9. Recent Tendency of Research Targets for Industrial Polypropylene Catalysts
M. TERANO
School of Materials Science, Japan Advanced Institute of Science and Technology, Asahidai 15, Tatsunokuchi, Ishikawa 923- 12, Japan
ABSTRACT Recent tendency of research targets for industrial propylene polymerization catalysts was investigated with academical papers and industrial patents. Research for Ti-based Ziegler-Natta catalysts is still very active in the industrial and the academical fields. However, tendency of the research targets was found to have changed gradually from 1990 to 1993, that is, from basic catalyst features to advanced polymer properties.
INTRODUCTION After a discovery of metallocene catalyst1), most of the research efforts seem to shift to this type of catalysts. In the field of polyethylene (PE), metallocene catalyst is already commercially used to produce a new special grade of polymer, but for polypropylene (PP) the catalyst is applied only for pilot scale production of syndiotactic PP. For isotactic PP, it is not too much to say that the present industrial production completely depends on the Ti-based heterogeneous catalysts. Many patents of MgC12-supported catalysts have been proposed continuously from the reading PP manufacturers in the Even in a basic field,
102 M. Terano
academical papers on Ziegler-Natta type catalysts are still actively published by many scientists.5-7) From the situation mentioned above, Ti-based Ziegler-Natta catalysts are regarded as the industrial PP catalyst in this paper.
WORLD POLYOLEFIN CAPACITY World PE and PP forecast capacities reported by Payn8) are shown in Table 1.
Table 1. Total 1995 Forecast Capacity * HDPE LLD/HD LLDPE LDPE North America Western Europe Japan Pacific Rim China Middle East Eastern Europe Latin America Other Regions Grand Total
* 10
3,588 4,207 1,118 2,037 285 262 840 658 408
6,373 1,433 533 2,012 281 260 190 0 365
1,111 510 210 846 430 50 370 160
3,914 5,467 1,369 1,899 717 779 1,738 2,018 53
13,403
11,447
3,687
17,954
0
PP
TOTAL
5,651 6,989 2,902 3,936 5 10 1,400 971 1,727 593
20,637 18,606 6,132 10,730 1,793 3,131 3,789 4,773 1,579
24,679
71,170
mtlyr
He also mentioned in the paper about the current world wide polyolefin capacity commitments by metallocene catalysts from various companies, which were 650,000 mt/y for PE and 295,000-320,000 mt/y for PP. They are only a few percent of existing capacity. World polyolefin industries still have to depend on the Ziegler-Natta type heterogeneous catalysts almost completely. In the near future, the situation will not be so largely different. From such a view point, it is discussed in the following that what type of catalyst property is now trying to develop or improve for industrial PP production.
9. Recent Tendency of Polyolefin Research Targets
103
PAPERS AND PATENTSUSED IN THIS STUDY To know about the recent tendency of research targets for industrial PP catalysts, academical papers and industrial patents were studied independently. Papers published from 1990 to 1993 concerning industrial PP catalysts were selected from 10 journals listed in Table 2.
Table2. List of Journal
Die Makromoleculare Chemie Die Makromoleculare Chemie ,Macromolecular Symposia Die Makromoleculare Chemie ,Rapid Communications European Polymer Journal Journal of the American Chemical Society Journal of Applied Polymer Science Journal of Polymer Science Macromolecules Polymer Polymer Bulletin
Patents were limited to the application for Japan and to the term from January 1, 1990 to December 31, 1993 to be investigated by using a computer patent search system with an international patent class; CO8F4/00 (polymerization catalyst). The amount obtained was found to be 1863. Then, the patents directly related to the subject of this paper were selected manually, then used in the following analysis. The quantity was 455.
104 M. Terano
TENDENCY OF RESEARCH TARGETS FOR INDUSTRIAL CATALYSTS Table 3 shows the amounts of paper and patent for each year.
Table3. Paper and patent Tic13 cat. paper patent
Year ~
Supported cat. Paper patent
~~
1990
1
18
9
89
1991
0
21
15
105
1992
3
11
17
121
1993
4
4
20
86
Numbers of supported catalysts are much larger than those of Tic13 catalysts, which reflects the recent industrial importance of the supported catalyst. Amount of patents of Tic13 catalysts becomes quite small in 1993. Although it is said that the Tic13 catalysts have lost the importance in the polyolefin fields, the research of the catalysts is not stopped but continued both in an academical and an industrial fields. Nevertheless, it is no doubt that the MgC12-supported catalysts are most important as an industrial catalyst. Therefore, industrial patents of the catalysts were analyzed to find the tendency of recent research targets. As shown in Table 4, the patents were divided into 6 targets and others. Zucchini9) and Karol'O) have mentioned about the main properties which are required for an industrial polyolefin catalyst. The targets in Table 4 are similar to the properties written in their papers.
9. Recent Tendency o f Polyolefin Research Targets
Table 4. Number of Patent for Each Target Target 1990 1991
1992
1993
Activity
12
15
25
9
Stereospecificity
16
27
26
11
Morphology
18
16
16
16
Polymer Property
9
10
11
10
Copolymerization
8
9
17
13
121
86
~
Total
89
105
105
~~
Activity and stereospecificity are the most basic requirements but the amounts of patents are decreased in '93. Patents concerning morphology and polymer property are proposed on the constant level from '90 to '93. Numbers of copolymerization and molecular weight (distribution) are increasing. Thus, the tendency of research targets changed gradually from '90 to '93 reflecting the difference of industrial requirements for the catalyst. For instance, recently wider molecular weight distribution of the PP is regarded as one of the most important targets for MgC12-supported catalysts because metallocene catalysts can not produce the polymer with that feature. Following 2 Japanese laid open They employed different patents are the typical examples for the target. approaches but obtained similar wonderful results. Ueki et. a1.I l ) claimed to use special type of Si compounds as an external donor. While, Asanuma et.
106 M. Terano
external donor
Si(0Me)2
$O\Si(OMe)2
d
d
G
O \ t-Bu /Si(oMe)2
0-0,
i-Pr F
o M e ) l
S. Ueki, N. Aoki, K. Imanishi, Japanese Laid Open Patent, 5-331234
preparation method MgC12 : 300g, C S H ~ ( C O Z C ~:H 7.5~ )ml ~ Tic14 :60 ml, C~tTiClz: 7g
-
)
ground,40h
aA
( A : log, toluene : 60 ml ) 114"c, 30min.
washing with heptane solid catalyst component
T. Asanuma, K. Morita, S. Kimura, Japanese Laid Open Patent, 4-222804
9. Recent Tendency of Polyolefin Research Targets
a1.12) used a solid catalyst component prepared with 2 Ti compounds. values of Mwfin obtained were 7.5 and 7.9, respectively.
107
The
CONCLUSION The research targets for industrial PP catalysts have been changing from basic catalyst features such as activity or stereospecificity to advanced polymer properties like wider molecular weight distribution, which reflects the difference of industrial requirements for the catalysts. Academical papers as well as industrial patents of MgC12-supported catalysts are still actively proposed and published by many scientists to satisfy the requirements. Therefore, this type of catalysts may have the industrial life for another several decades by improving their property and polymerization technology.
ACKNOWLEDGEMENT The author is grateful to Mr. K. Ishii, Mr. K. Tashino, Mr. K. Ohnishi and Dr. H. Mori for their contribution to this work.
REFERENCES 1. H. Sim, W. Kaminsky, H. J. Vollmer, and R. Woldt, Angew. Chem., Int. Ed. Engl., l9, 390 (1980). 2. Y. Uehara, and F. Shimizu, Japanese Laid Open Patent, 5-97922 (1993). 3. T. Fujita, Japanese Laid Open Patent, 5-93013 (1993).
4. T. Matsumoto, K. Shinozaki, and M. Kioka, Japanese Laid Open Patent, 5- 170843 (1993). 5. M. Terano, M. Saito, and T. Kataoka, Makromol. Chem., Rapid Commun., 13, 103 (1992). 6. Y. V. Kissin, T. E. Nowlin, and R. I. Mink, Macromolecules, 26, 2151 (1 993). 7. I. Kim, H. K. Choi, T. K. Han, and S . I. Woo, J. Polym. Sci., Part A: Polym. Chem., 30, 2263 (1 992).
108
M. Terano
8. C. F. Payn, Proceeding of Metcon'93, 1993, p.5 I . 9. U. Zucchini, Makromol. Chern., Macromol. Symp., 66,25 (1993). 10. A. Guyot, L. Bohrn, T. Sasaki, U. Zucchini, F. Karol, and I. Hattori, Makromol. Chem., Macromol. Symp., 66, 31 1 (1993). 11. S. Ueki, N. Aoki, and K. Imanishi, Japanese Laid Open Patent, 5-331234 (1993). 12. T. Asanuma, K. Morita, and S. Kimura, Japanese Laid Open Patent, 4-222804 (1992).
I09
10. The Control of Molecular Weight Distributions in Ziegler-Natta Catalysis
R. SPITZ , M. PATIN, P. ROBERT, P. MASSON and J. D U P W CNRS - Laboratoire de Chimie et Procedes de Polymerisation LCPP BP 69390 Vernaison France ABSTRACT According to the fact that very narrow molecular weight distributions (MWD) are easily produced with metallocene catalysts, the actual problems related to MWD are all concerned with wide distributions. Metallocene mixtures are able to produce bimodal distribution, requiring extreme differences in sensitivity to transfer reactions, but the expected properties will not be the same than those of wide peak distributions. The classical heterogenous systems produce sometimes broad to very broad distributions and this result is associated to a cluster structure of the transition metal. This cluster structure often forbids to mix 2 species to get the sum of 2 polymers. Examples combining titanium and vanadium chloride are presented. The effect of heat and monomer diffusion on MWD is generally not important. INTRODUCTION Classical heterogeneous Ziegler-Natta catalysts never produce polyolehs with narrow molecular weight distributions (MWD), that means close to the value expected for a polymerization with associated transfer reactions (Mw/Mn)) 2). On the contrary homogeneous catalysts are well known to often produce polymers with the expected narrow distribution. This property is one of the most important as it defines the ability of the polymer to be processed and also some of the final properties of the polymer. The presence of a medium to broad distribution has favored the development of this family of polymers due to an easier processing but developments in 2 main directions are necessary: very narrow and very broad MWD. From a hdamental point of view it would be interesting to understand what are the main phenomena associated to the control of the molecular weight distribution. The discussion of these phenomena was clearly introduced 10 years ago in a review made by Zucchini and Cecchin I ) . 2 main theories have been discussed and remain for a part open: the diffusion theory and the chemical theory. According to the diffusion theory, the barrier to the transfer of monomer or heat results in distributions of polymerization conditions in a growing polymer particle and thus in distributions of chain lengths. The MWD is then the envelop of these distributions. The more important the diffusion barrier, the broader the expected MWD will be. According to the chemical theory the heterogeneous catalysts have 2 or more different active species producing in the same polymerization conditions 2 or more different mean molecular polymers. The MWD is then associated to the number of families and to the differences between these families.
110 R. Spitz. M. Patin. P. Robert. P. Masaon and J. Dupuy
In fact none of these explanations are really satisfjhg : the MWD generally resist to any attempt to make a direct change in the conditions associated to one or to the other explanation. Considering catalysts based on the same particles size, porosities and particle size distributions one would expect that the MWD will be very different ifthese catalysts have very high or very low activities (change of the activity may occur by slight modifications of the catalyst composition, for instance a moderatelyhigh thermal treatment) but this is not the case: MWD are generally almost independent on the level of activity even on ranges covering 3 or 4 orders of magnitude, as well in gas phase as in suspension polymerization. For this reason, the development of a particular family of supported heterogeneous catalysts for propene polymerization (using diakylphtalates and silanes as Lewis bases) has restricted to a unique particular value the MWD of theses polymers. Broader distributions are only observed with Solvay type non supported systems 2 , which, for this reason, remain present on the market. Very wide MWD are obtained by 2 or more stages of polymerization. As the MWD is controlled by the presence of different families of active centers according to the chemical explanation it should be expected that the addition of different chemical species would led to a broadening of the distribution. But attempts to load different families of active centers on the same camer are not often successll and Ziegler catalysts used to produce polymers processed by extrusion blowing are generally not able to produce these polymers in one polymerization step. Contemporary problems related to the control of the MWD can be summarized as follows: i) evaluation and interpretation of the contribution of difksion effects highlighted by the modem theories, ii) possibility of broad controlled distributions with metallocene catalysts, iii) interpretation of the broad MWD observed with heterogeneous systems based on metal chlorides. EXPERIMENTAL Magnesium-titanium catalysts: i) milling: magnesium chloride is milled (6h) and contacted with titanium tetrachloride in large excess at 80 "C for 1 hour, washed with heptane and dried under vacuum. ii) magnesium chloride (30 g) is milled for 6 hours, then comilled with 1.5 ml of titanium tetrachloride. Magnesium-vanadium chloride catalvsts: magnesium chloride is comilled with S i c 4 ( 5 % by weight) and then contacted at room temperature with V C 4 in solution in heptane. Quantitative adsorption of the vanadium compound occurs within seconds. The catalyst is dried under vacuum and recovered as a powder containing all the vanadium and less than 0.5 % Si. Polymerization: The standard conditions of slurry polymerization are: total pressure 8 bars, variable hydrogen pressure, akylaluminium: triisobutylaluminium (TiBA) or trihexylaluminium : 3 mM, temperature: 80 "C. Duration 1 hour RESULTS AND DISCUSSION Diffusion control of the polvmerization. The idea that olefin polymerization could be controlled by d f i s i o n is an old idea which became more popular with the development of high mileage catalysts. The decreasing shape of many kinetic curves seemed to be related to the increase of the size of the polymer particle (the diffusion length) and suggested that the larger the polymer grows,
10. Control of M M D in Ziegler-Natta Catalysis
III
the thicker the difision barrier is. This idea was demonstrated to be false both on theoretical bases 3 .4 ) and on experimental bases ’). The time decreasing kinetics are related to chemical deactivation of the catalysts and a correct diffusion theory leads to a a s i o n bamer decreasing with polymerization time proportionally to the particle radius (r): the transfer properties increase proportionally to the external surface area (r2) and decrease proportionally to the particle size (r). A complete description of these phenomena are to be found in the papers of Ray and ~ o l l . ~ ’As ~ , a~ consequence ). of it, 2 main behaviors are expected, corresponding to 2 different kinetic shapes in the 2 main polymerization processes (gas phase and slurry). In gas phase, the polymerization rate reaches a maximum before 1 min. polymerization time and then decreases continuously. The diffusion barrier decreases continuously and becomes neghgible after a few minutes. The production of polymer during the time Corresponding to a strong diffusion barrier is small. Ifwe perform an integration of the polymer production during 1 hour polymerization the contribution of the difision barrier to the MWD is negligible. Fig. 1 presents the typical computed behavior of 1 catalyst particle (30 p diameter, 4000 g polymer per g catalyst in 1 hour) during polymerization using the same set of parameter than Ray and CON.@ MWD is calculated using a variation of the MW with temperature which was measured experimentally in gas phase polymerization. According to the theory the logarithm of the temperature vanes almost linearly with the logarithm of the particle size, but the variation of the molecular weight is small and the variation of MWD is negligible. The same holds in a larger range of sizes and activities, limited to the conditions avoiding the melting of the polymer particle, 2
1
0’
P
-B
-I
0
-1 1.25
1.75
2.25
2.75
log(d1
figure 1 variation of Mn and M w M vs. particle diameter d during a gas phase polymerization (activity: 4000 g polymer per g catalyst per hour). deltaT is the Merence in temperature between the particle surface and the polymerization medium in K.
I I 2 R. SpitL. M. Patin, P. Robert, P. Masson and J. Dupuy
7
6
LD
-
~~
70000 g l g l h
5 4
..
3
--
2
-.
20000 g l g l h
.-
0. 0
6000glglh
200
400
600
800
1000
1200
1400
1600
diameter (crrn)
Figure 2. Melt-index (190 "C, 5 Kg) as a function of polymer particle size for different activities in slurry polymerization. The situation in suspension polymerization is rather different. The polymerization rate increases generally during 10 min. or more . The diffusion bamer is enhanced during at least a part of this time and polymer production out of steady-state is not negligible. One could thus expect a sensitivity of polymer properties to the polymerization rate and kinetic shape and also, of course, to the particle size and shape. This can be checked by the study of the molecular weight or viscosity as a function of particle size, simply by grading the polymer particles after polymerization. The trend which are expected are: molecular weight strongly decreasing with increasing particle sue; molecular weight strongly decreasing with increasing catalytic activity. Experimental studies are not really convincing. We have used a family of catalysts with the same particle properties but with activities ranging from the activity computed by Ray and coll. to 20 times larger values that means approaching lo5 g polymedg catalyst / h. The melt-index ( E viscosity-') of the polymer is presented as a function of the particle size on the fig. 2. The melt-index increases with increasing particle size but not with the catalyst activity as expected with a diffusion control. For each of these catalysts the differences in molecular weights remain small and the MWD do not change. The differences between the catalysts may be associated to different diffusion effects during the preparation of the catalysts themselves. In order to interpret this results we have to turn back to theory. We have written a computer model of growth of a polymer particle which is rather simple but leads to the same quantitative values than the model of the literature when the same parameter are used '). On the basis of such a model, activities in the range of 50000 g per g per h are almost impossible to get as the polymerization is them restricted to the shell of the polymer particle, the monomer concentration in the core being almost equal to zero. This supposes that the activity in the shell is almost infinite. This discrepancy between theory and experiment is due to a particular choice of the diffUsion parameter set. The values used in the literature correspond to a reaction which is l l l y controlled by diffusion I. The kinetic shape showing a polymerization rate increasing with reaction time corresponds to the decrease of the diffusion bamer with the particle growth. Assuming that the kinetics are controlled by chemistry, we have to use monomer diffusion parameters in medium and in the particle pores which correspond to the upper range of the possible values. The model is then in better agreement with experiment and diffusion plays a minor role except perhaps for the most active catalysts which
10. Control of M M D in
Ziegler-Natta Catalysis
113
are above the values currently used in industry. In other words: the fact that very high activities are observed implies that normal activities cannot be controlled by diffusion. Fig. 3 shows a simulation of an ethylene polymerization at a rate of 25 000 glgm . The maximum of concentration gradient becomes important for large catalyst particles but the effect on molecular weight is limited and the variation in MWD (not presented) is less than 1%. 2
450 400 350
1.75
300 250
1.5
200
8
150 100 50
i
-*-
t
Mn
0 1 0
5
10
15
20
25
30
1.25
-3 0
C1 35
particla radius (pm)
figure 3. Minimum value of the monomer concentration on the surface of the growing polymer particle and in the centre and minimum value of the Mn during polymerization as a h c t i o n of the catalyst particle size. Catalyst activity 25000 g per g per hour in ethylene slurry polymerization. Ethylene pressure 6 bars, ethylene concentration 0.43 M Another argument can be found in the literature concerning metallocene catalysts. Kaminsky et aL9) present a detailed study of polymerizations using a large M y of different metallocene catalysts in ethylene and propene polymerization. In most cases the polymerization medium is heterogeneous, the polymers being insoluble in the diluent. With activities ranging fiom 1 to 100 in relative scales, the MWD remain close to 2. M s i o n effects in a very heterogeneous medium are thus not able to contribute to large changes of the distribution. This is confirmed by the fact that supported metallocene catalysts, which are heterogeneous, are able to produce narrow MWD polymers lo). Chemical interpretation of the MWD The chemical interpretation of the MWD supposes that the distribution is associated to a distribution of chemical species. Each of these species produces a statistical distribution of chain lengths which correspond to the Schulz-Flory most probable distribution . It is often assumed that the presence of 2 or 3 families of active centers is able to explain all the distributions of MW observed experimentally. This is not the case. Any particular distribution curve can be decomposed in a little number of components but this does not mean at all that the number is really small. According to the fact that the MWD are rather stable versus changes in the polymerization conditions (activity, temperature, transfer agents) and that the distributions are seldom bi or polymodal it seems reasonable to assurne that the distribution of MWD is continuous and thus so is also the distribution of active centers. What could explain a continuous distribution of active centers with a continuous distribution of properties? The active centers are both not very different but always different. This could be due to small changes in the environment on the surface of the catalyst. But, as the catalysts are generally supported on small crystallized particles, this does not explain the fact that a great number of
114
R . Spitr, M . I’atin, P. Robert. P. Masson and J . Dupuy
different species are really present, and that the same order of magnitude can be observed with supported as well as not supported species. We suggest another explanation: the active species belong to clusters of the salt of the transition metal: this clusters correspond to the crystallites with the non-supported systems or cover a part of the surface of the supported species. The active centers are on the edges of these clusters, the inner part being inert toward polymerization. This idea explains different features of the systems: a continuous distribution of properties, related to the shapes and sizes of the cluster. AU the active centers have then a different environment. Of course, this does not exclude the idea that the active specie belong to 2 or more families, having for instance a different number of C1 vacancies as it is mentioned in the literature” ). The hypothesis of a relation between the clustered structure of the active center and the distribution affords a new insight on the properties. Lf a new component is added to a clustered structure the behavior of the system will depend on the interaction between the species. The new specie can be of the same nature (only changing the cluster sizes and distribution) or may lead to new chemical species ifthe component are Werent. The only case avoiding any interaction is when the different components are separated onto the catalyst support, giving rise to the situation described by B o b and coll.12’.We will examine the other situations on examples. The simplest case corresponds to one chemical specie associated to one support, for instance a catalyst obtained by milling magnesium chloride and interacting it in different manner with titanium tetrachloride in the absence of any other chemical treatment. The distribution of the titanium clusters will be supposed to depend on the distribution of the chlorine vacancies on the surface of the support. The catalysts obtained by milling of magnesium chloride followed by adsorption of titanium tetrachloride have a MWD which is different of that got by comilling the two component. During the comilling, transient defects on the carrier surface are able to react with titanium, producing a new clustered state. This leads to MWD which are dependent on the way that the 2 components have been contacted more than to the Ti content. The comilled solids, which contain structures which are not present on the catalyst prepared by contacting, have the broadest MWD. Table 1. Ethylene polymerization using two catalysts with the same component (magnesium chloride, titanium tetrachloride ) with the same activity (2000 g polymer per g catalyst per hour) but a different clustering of Ti. Details are given in the experimental part.
comilline.
I milling+ impregnation
surface area 42 I48
Ti (w YO) 1.8
10.5
MFR= Izl/Is 19.7
I 14.3
Catalvsts with 2 components. Case of the metallocenes: The presence of metallocene catalysts producing polymers with very different molecular weight and constant distribution opens the possibility of the production of polymer mixtures with bimodal distributions. The fig. 4 presents the variation of the polydispersity of a mixture of the same mass of 2 polymers, each of them having the same polydispersity index 2, as a h c t i o n of the ratio of the molecular weights of these 2 polymers. The broadening of the distribution is got when the 2 polymers are in equal proportion. It is to be noticed that the difference in molecular weight between
10. Control of M M D in Ziegler-Natta Catalysis
I15
these polymers must be large in order to reproduce the common polydispersities measured with heterogeneous catalysts, and must reach values close to 20 in order to get very broad distributions. 12
figure 4. Polydispersity index (Mw/Mn) as a h c t i o n of the ratio k of the molecular weights of 2 polymers mixed in equal proportion with polydispersity 2. Pmkhrrs = 0.5 (2+k+l/k) Metallocene systems associating Zr and Hf compounds are able to present such differences and bimodal mixtures of this type have been described ). The difference in molten viscosity between the 2 fractions of such polymers will be more larger than 1000 times which may lead to problems during extrusion. Catalvsts with 2 components. Heterogeneous systems: the simplest way to prepare controlled broad MWD should be the association of two different catalytic species with Merent sensitivities to the transfer. It is rather easy to find such species using different transition metals: compared to titanium chloride, vanadium chloride generally produces low molecular weight polymers although zirconium and hafhium lead to ultra high molecular weights. All these compounds are able to polymerize although in the same conditions, but the differences of sensitivity to transfer, the differences in activity and the temperature effect induce some complications in the choice of the polymerization conditions. Catalysts associating such species are documented in the literature, and positive results concerning MWD are reported which the 2 heavier metals associated to titanium 14). Vanadium could be a very interesting choice as supported vanadium catalysts are known to produce polymers with broad distributions and possibly low molecular weights due to an outstanding response to transfer by hydrogen Is ) but its possible uses are restricted due to the low activity and the unwanted properties of V residues. In a preceding paper16’ we have described the preparation of such MgClz / VCl, supported catalysts and their activation. On the basis of this results it seemed promizing to prepare titanium-vanadium supported catalysts in order to have at the same time a high activity and the control of a wide range of MWD. The MWD of the polymers is very broad (up to Mw/Mn =18). Numerous catalysts associating these 2 metals are described in the literature I’ , I 8 ) . Such catalysts are reported for narrow MWD 19) as well as for broad MWD ’ O ) .
R . Spitz, M. Patin. P. Robert. P. Masson and J. Dupuy
I16
Considering the polydispersities measured with vanadium (Pa=18) and titanium (Pb=7) supported separately on the same type of magnesium chloride carrier it is easy to compute the values of the expected polydispersities of mixtures of polymers prepared with these two catalysts. Mixtures are defmed by the ratio k =Mwa/Mwb, and x being the relative fraction of polymer produced by the V catalyst, the polydispersity of the mixture is: P= (I/x).(x+k (I-x)).(x.k.Pb+(I-x).Pa). Broad to very broad distributions are expected in a large range of compositions. Of course the best results are expected with a major contribution of the V catalyst but polydispersities above 15 are possible even when the titanium catalyst produces the 2/3 of the polymer as it can be observed on fig. 5 . The molecular weights of the 2 polymers must be of course v e v different . Such a condition can be hlfilled with a large difference in sensitivitv vs. transfer bv hvdrogen 30
25
--
w
n
15
// /
/
10
0
0.2
0.4
0.6
0.8
1
proportion of polymer 2
figure 5 Polydispersity of a mixture of a polymer with polydispersity index P=7 with a polymer with polydispersity index P= 18 as a function of the proportion by weight and as a fimction of the ratio k= Mwll Mw2 (polymer 1 is for titanium and 2 for vanadium). Catalysts are prepared by successive contacting of magnesium chloride with excess titanium tetrachloride followed by vanadium tetrachloride. In the second step the catalyst looses a part of the Ti fixed in the first step (table 2). Table 2: catalyst modified by vanadium tetrachloride, catalysts slurry polymerization 1 hour 80 "C Catalyst
T
TVI Tv2 TV3
10. Control of M M D i n Ziegler-Natta Catalysis
I17
The activity decreases but the MWD remains unchanged or becomes slightly narrower. The presence of V-type active centers is revealed by a slight increase of the heptane soluble polymer which is typical for the vanadium catalysts. This is observed only for the sample containing more V and associated to a slight broadening of the MWD. All the catalysts are far beyond what is expected . Similar catalysts can be prepared in an opposite manner. Catalysts are first prepared by supporting VCL, on magnesium chloride, then treated with titanium tetrachloride. In that case the MWD, starting from the value corresponding to the vanadium catalysts becomes narrower and the activity increases to rather high levels (table 3). The molecular weights are increased and the heptane soluble fraction which is 2 % with vanadium alone is reduced to 0.5 %.
Table 3: vanadium-titanium catalysts (2 and 1.8 % vanadium respectively). Catalyst
Ti W%
VI"' VlTl v2 V2T I
---1.0
--1.2
productivity g/g/h 1700 4200 300 3000
15
m= I*,/Is
I 0.7 2.5 0.5
23.7 17.3 22.8 14.2
H2 bars 1.3 3.0 1.5 2.5
These behaviors can be interpreted as follows: the MWD associated to the Ti or V catalysts are related to the cluster state of these compounds. If V is added to a titanium catalyst, V binds to titanium (vanadium does not bind easily to magnesium chloride) and a part of the Ti is extracted by the solvent. This results in a slight change in the cluster state of the titanium and in the presence of a small fraction of active centers producing low molecular weight polymer. Starting with the V catalyst, the cluster state of the vanadium is not too modified by the addition of titanium, but titanium is able to add to the surface of magnesium chloride. The presence of a typical broad distribution associated to the V centers is masked by the large increase in activity due t o the titanium, but remains nevertheless present and explains the rather large distributions observed. CONCLUSION The molecular weight distributions of polyolefins are controlled by the chemical composition of the catalysts. The diffusion of monomer and heat transfer generally produce only minor effects, which become noticeable with large particles andor high activities. The chemical effects are related to the presence o f 2 or more types of active centers, each of them producing a narrow molecular weight distribution. The mixtures of 2 types of active center produces narrow (P= 3-4)or bimodal distributions if the ratio of the molecular weights produced respectively becomes large. Broad MWD requires a large number of different active species which can be explained by the presence of clusters, which allow slight differences between all the active centers o f a catalyst. The formation of these clusters make it difficult to associate different species as the catalysts contain then intermediate mixed species which do not produce the expected polymers. This explains that the preparation of
118
R. SpitL. M. Patin, P. Robert, P. Masson and J . Dupuy
catalysts producing broad molecular weight distributions in a large range of polymerization conditions and in different processes remains a difficult problem. Acknowledgments This work was supported by Elf-Atochem. REFERENCES 1 Zucchini and Cecchin , Adv. Polym. Sci , 3 , 1 0 1 , (1993) 2 A. Bernard and P. Fiasse in (( Catalytic O l e h Polymerization )) T. Keii and K Soga ed Kodansha Tokyo p. 405, (1990) 3 S. Floyd, K. Y.Choi, T. W. Taylor, W. H. Ray, J. Appl. Polym. Sci., 2_L ,223 1, (1986) 4 RA. Hutchinson, C. M. Chen, W. H. Ray, J. Appl. Polym. Sci. 44, 1389, (1992) 5 R Spitz, J-L Lacombe, M. Primet and A. Guyot in (( Transition Metal Catalyzed Polymerizations )) R P . Quirk ed., MMI Symposium Series 4, p 389 Harwood (1983) 6 S. Floyd, G.E. Mann,W. H.Ray (( Catalytic Polymerization of O l e h s )) T. Keii, K.Soga ed. Kodansha-Elsevier Amsterdam p. 339 (1986) 7 R Spitz, J. Terle, J. Dupuy in (( Recents progres en g h i e des procedes )) 27, 19, (1993) 8 V.B. Skomorokhov, V.A. Zakharov and V. A. Kirillov Polymer Science 35, 881, (1993) 9 W Kaminsky, R Engehausen, K. Zoumis, W Spaleck and J. Rohrmann, Makromol. Chem. 193, 1643, (1992) 10 S. Collins, W. Mark Kelly and D. A. Collins, Macromolecules 25, 1780, (1992) 1 1 K Soga,T. Shiono, Polym. Bull., 8 ,261, (1982) 12 L. L. Bohm , J. Berthold, R Franke, W. Strobel and U. Wolfmeier in (( Studies in Surface Science and Catalysis )) 25 , T. Keii, KSoga ed. Elsevier Amsterdam p 29, (1986) 13 A. Ahlers and W. Kaminsky, Makromol. Chem. Rapid Commun. 9,457, (1988) 14 (F. Masi, S. Malquari, F. Menconi, C. Ferrero, A. Moali and R InverniZzi in (( Studies In Surface Science and Catalysis 6 (( Catalytic Olefin Polymerization )) T. Keii, KSoga ed. Elsevier Amsterdam, p355 (1989) 15 F. J. Karol, K. J. Kann and B. W. Wagner in (( O l e h Polymerization ) ) , W. Kaminsky and H. Sinn ed. Springer Berlin p. 149 (1988) 16 R Spitz, V. Pasquet, A.Guyot in ((40 years Ziegler catalysis )) Makromol. Chem, Symp. in press. 17 EP 22,658 and EP 57,589 to BP Chemicals (1981) Chem. Abs. 94: 175 856, Chem. Abs. 98:4 896 18 EP 32 734 to Montedison S.p.A.( 1981), Chem. Abs. %:170104 19 DE 3028479 to Asahi Chemical Industry (1981), Chem. Abs. 93:s 056 20 DE 3635028, (1988), Chem. Abs. 1 0 9 : 5 5 449 and DE 3,242,150 to BASF A. G., (1984), Chem. Abs. M : 9 1 656
I I9
11. Synthesis and Application of Terminally Magnesium Bromide-Functionalized Isotactic Poly (Propene)
Takeshi Shiono, Yoshi-hide Akino and Kazuo Soga* Research Laboratory of Resources Utilization, Tokyo Institute of Technology, 4259 Nagatuta, Midori-ku, Yokohama 227, Japan *Japan Advanced Institute of Science and Technology, Hokuriku 15 Asahidai, Tatsynokuchi, Ishikawa 923-12, Japan ABSTRACT Isotactic poly(propene) (PP) having a terminal vinylidene group was prepared with the ethylenebis(4,5,6,7-tetrahydro-lindeny1)zirconium dichloride-methylaluminoxane catalyst system. The polymer produced was treated with borane-dimethylsulfide in toluene, followed by reacting with pentane-lI5-di(magnesium bromide) to obtain magnesium bromide(MgBr1-terminated isotactic PP. The polymer was brought into contact with iodine to give isotactic PP having an iodine group at the chain end in about a Polymerization of methyl methacrylate was then 85 % yield. conducted using the MgBr-terminated PP as an initiator to synthesize isotactic PP-block-poly(methy1 methacrylate) copolymer. INTRODUCTION Terminally functionalized polymers are useful as precursors of block and graft copolymers. The Zn-, Al- and B-terminated isotactic poly(propene)s (PPs) were synthesized by a chain-transfer reaction with metalalkyls’) or by hydrometalation of the terminal vinylidene group formed via a B -hydrogen abstraction.2) These metal-polymer bonds were utilized for the functionalization of chain ends as well as for the synthesis of block-copolymers. In this paper, the magnesium bromide(MgBr)-terminated isotactic PP was synthesized and applied for the synthesis of the isotactic PP-block-poly(methy1 methacrylate) (PMMA) copolymer.
120 T. Shiono. Y . Akino and K . Soga
EXPERIMENTAL Materials. Propene (Mitsubishi Petrochemical Co.) was purified by passing through columns of CaC12, P2O5 and molecular sieve 3 A . rac-Ethylenebis(tetrahydroindeny1)zirconium dichloride (Et[H4IndI2ZrCl2) was prepared according to the literature. 3 , Methylalminoxane (Tosoh Akzo Chemicals Co. ) and borane-dimethylsulfide complex (Aldrich Chemical Co.) were used without further purification. Research grade benzene and toluene commercially obtained were dried over calcium hydride under refluxing for 24 h and distilled on molecular sieve 4A. Methyl methacrylate (MMA, extra pure grade) was dried over calcium hydride and distilled before use. Iodine was purified by sublimation and used as a 0.5 M solution in toluene. Argon (99.9995%) was used without further purification. Pentane-I,S-di(magnesium bromide) in tetrahydrofuran (0.6 MI was synthesized from magnesium turnings (for Grignard reagent, Wako Chemical Co. ) and 1,5dried over molecular dibromopentane (Aldrich Chemicals C o . , sieves 4A). Preparation of isotactic PP. Propene polymerization was conducted with a 200-mL glass reactor equipped with a magnetic stirrer. Toluene (100 mL) and methylalminoxane (1.8 mmol) were added into the reactor under an argon atmosphere, and then propene was introduced at 30 OC until the solvent was saturated with propene. Polymerization was started by adding 4 mL of toluene solution containing 0.01 mmol of Et[H4IndI2ZrCl2 and terminated by the addition of a dilute. solution of hydrochloric acid in ethanol. The precipitated polymer was filtered, washed with plenty of ethanol and dried under vacuum at 60 O C for 8 h. The polymer produced was extracted with boiling acetone to obtain approximately 90 wt% of boiling-acetone insoluble fraction, which was confirmed to have the structure ( I ) from 13C NMR and 'H NMR as reported previously.2bt4)
c c C C I 1 I I c=c-c-c-(c-c)n-c-c-c-c-c(I) The polymer was characterized as follows; melting point = 114 'C, isotactic triad = 0.82, number average molecular weight(Fln) determined by chain end analysis = 5,300, Rn by GPC =
I I . Synthesis of Terminally Functionalized Iso-PP
121
2,200 (polydispersity = 2.0). Such a discrepancy of An may result from the limitation of GPC in a low molecular weight range. The vinylidene content in the polymer estimated by assuming An as 5,300 was 0.19 mmol/g-polymer. Synthesis of MgBr-terminated PP. The terminal C=C bonds of the polymer was hydroborated by borane-dimethylsulfide complex. In a 50-mL Schlenk tube equipped with a magnetic stirrer, ca. 1 g of PP, 10 mL of toluene and 0.086 mmol of borane-dimethylsulfide complex were added under an argon atmosphere, and the mixture was heated at 70 - 80 OC for 2 h. Then 0.173 mmol of pentane-I ,5di(magnesium bromide) in tetrahydrofuran solution was added, and the mixture was continued stirring at 70 - 80 OC for 2 h to obtain the MgBr-terminated PP6). Synthesis of PP-block-PMMA copolymer. Polymerization of MMA with the MgBr-terminated PP was conducted at -78, 0 and 45 OC. In MMA (9.4 mmol) was case of the polymerization at 0 or 45 ' C , added into the reactor containing ca. 1 g of the MgBr-terminated PP in 10 mL of toluene at the polymerization temperature. Whereas, in case of the polymerization at -78 OC, MMA was added at 0 OC and the mixture was quickly cooled down to -78 OC using a dry ice-ethanol bath. Polymerization was quenched by pouring the polymerization mixture into ethanol containing hydrochloric acid. The precipitate was collected and dried under vacuum at 60 OC for 6 h. The polymer obtained was extracted with boiling acetone, and the acetone-insoluble fraction was supplied for analyses. Analytical procedures. H spectra of samples were recorded on a EX-90 or a JEOL FX-100 spectrometer operated at 89.45 or 99.45 MHz in the pulse Fourier Transform (FT) mode. 13C NMR spectra were recorded on a JEOL GX-500 spectrometer operated at 125.65 MHz in the pulse FT mode. In 'H NMR measurements, the pulse angle was 45 and 100 - 500 scans were accumulated in 9 s of pulse reputation. In I3C NMR measurements, broad band decoupling was used to remove I3C-'H couplings. The pulse angle was 45 and 6000 - 9000 scans were accumulated in 9 s of pulse reputation. The spectra were obtained at 60 or 80 OC in CDC13 or C ~ solution D ~ (2 wt % for I H NMR and 1 5 wt % for 1 3 NMR ~ in a 5mm 0.d. tube), using CHC13 (7.24 ppm for 'H NMR and 77.0 ppm for I3c NMR, respectively) or C6H6 (7.15 ppm for I H NMR and 128.0 ppm for 3~ NMR, respectively) as an internal reference O ,
O ,
.
122 T.Shiono. Y . Akino and K . S o p
The gel permeation chromatograms (GPC) of polymers were recorded on Sensyu SSC-7100 equipped with a Shodex GPC UT-806L column at 1 4 5 OC using o-dichlorobenzene as solvent. The molecular weights of polymers were determined by the universal calibration technique. Differential scanning calorimetry (DSC) measurements were made with a Seiko DSC-220. Polymer samples (ca. 3 mg) were encapsulated in aluminum pans. Samples were pretreated at 200 O C for 5 min, chilled with liquid nitrogen, and scanned at 1 0 OC/min. RESULTS AND DISCUSSION Synthesis of MgBr-terminated PP. We have already reported that chlorine-, bromine and iodine terminated isotactic PPs were obtained in high yields(>80%) by or Al-terminated2c) polyhalogenolysis of the Zn-terminated' mer. However, such halogen-terminated isotactic PPs cannot be f,
used as precursors of Grignard reagents due to poor solubility in polar solvents. Therefore, in this paper, the MgBr-terminated isotactic PP was prepared by transmetalation of the B-terminated PP. It is reported that trialkylborane is quantitatively converted to the corresponding Grignard reagent by the reaction with pentane-1,5-di(magnesium bromide) in benzene or toluene according to the following scheme.6) The formation of a relatively stable bicyclic borate might probably cause to shift the equilibrium to the right. R3B
+
2 BrMg(CH2)5MgBr + 3 RMgBr
+
qn [ ( H C) B (CH )
2
3
w 2 5
]+MgBr-
The MgBr-terminated isotactic PP synthesized according to the procedure described in the experimental section was subjected to iodolysis. The iodolysis was conducted by adding the toluene solution of iodine to the MgBr-terminated PP in toluene at 60 O C until the color of iodine did not disappear. Figure 1 shows the 'H spectra of the polymers before and after iodolysis. In the spectrum of the polymer after iodolysis, the resonance of vinylidene proton completely disappeared and a new resonance assignable to methylene protons connected to iodine appeared at around 2.9 ppm. Using the resonances of main chain protons as an internal
I I . Synthesis of Terminally Functionalized Iso-PP
123
standard, the conversion of vinylidene to iodine was estimated to be approximately 85%.
PPM l ' ' ' ' ' ' ' ' ' / ' ' ' ' ' ' ' ' ' 1 ' ' ' ' ' ' ' ' ' 1 ' ' ' ' i ' ' ' ' I ' ' ' ' ' ' ' ' ' ~
5
4
3
2
1
0
Figure 1 90-MHz 'H NMR spectra of isotactic PP. (a):original, (b):after iodolysis Figure 2 shows the I3C NMR spectra of the polymers after hydrolysis and iodolysis, where several weak resonances can be observed in addition to the strong resonances of main chain carbons. All the resonances except for those of the tetramethylene sequence in main chain (marked by * ) are assignable to the carbons of 2-methylpentyl, 2-methylpropyl and 3-iodo-2-methylpropyl end groups, which correspond to the initiation end, and the hydrometalated ends after subjecting to hydrolysis and iodolysis, respectively. The intensities of the 2-methylpropyl end group drastically decreased by iodolysis. Some of the resonances of the 3-iodo-2-methylpropyl group were split into doublet due to the presence of four diastereomers (two pairs of enanthiomers), which are derived from the highly isotactic structure of chain end and non-enanthioselectivity in the hydrometalation process of vinylidene group as reported previously. 3 , For reference, the iodine-terminated isotactic PP was pre-
124 T. Shiono, Y . Akino and K . Soga
k
I,.
Pl
xl n
i2 il-it
PPH 1
"
"
l
50
Figure 2
"
4:
"
1
"
~
40
'
1
'
'
35
"
1
~
30
~
'
"
'
~
~
~
25
1
20
'
'
~
'
15
125-MHz 1 3 C N M R spectra of isotactic PP.
(a):after hydrolysis, (b):after iodolysis
1
~
~
'
I I . Synthesis of Terminally Functionalized Iso-PP
125
pared from the B-terminated polymer by reacting with sodium iodide and chloramine-T7) in the mixture of toluene, methanol and water. The conversion was, however, found to be very low due to poor solubility of the polymer. MMA polymerization by MgBr-terminated PP. Polymerization of MMA was then conducted at -78, 0 and 4 5 O C using approximately 1 g of the MgBr-terminated polymer as an initiator. The polymers produced were extracted with boiling acetone to remove the homo-PMMA. The results are summarized in Table 1.
f"3 -fCH2-fk
c=o I
OCH 2 h
6 h
12 h
24 h
48 h
Figure 3 100-MHz 'H NMR spectra of isotactic PP-block-PMMA obtained at -78 ' C with different polymerization time (2-48 h). The 'H NMR spectra of the acetone-insoluble polymers obtained at -78 O C were illustrated in Figure 3. In addition to the strong resonances of PP, the resonance of methoxy protons can be observed at around 3 . 5 ppm, the intensity of which gradually in-
Table 1
Results of M M A polymerization by MgBr-terminated isotactic PP
Run no.
Polymn. conditions Temp["C]
Time[h]
Yield[ g ] Whole
-
-
-
1
-78
2
1.28
2
-78
6
3
-78
4
-78
5
Insol.a
Properties of acetone-insoluble fraction mol-MMA/mol-Pb
Tg[ "Cl Tm[ "Cl
H [ J/g] Anxl O - 3 c
0
-1 5 . 7
114
54.3
2.2
0.98
0.02
-15.2
113
54.3
2.4
1.14
0.86
0.04
-12.2
113
53.1
2.8
12
1.18
1.04
0.08
-11.0
113
52.3
3.0
24
1.20
1.03
0.09
-10.7
113
50.3
3.0
-78
48
1.43
1.20
0.12
-10.0
110
49.8
2.9
6
0
1
1.27
1.10
0.06
-1 1 . 2
111
50.2
2.6
original PP
7
0
2
1.47
1 .14
0.08
-10.1
113
48.4
2.5
8
0
6
1.22
0.97
0.10
-10.0
114
52.1
2.9
9
0
12
1.24
1.07
0.10
-10.2
113
51 . 3
2.9
10
45
0.25
1.02
0.93
0.03
-1 3 . 2
114
56.6
-
11
45
1
1.03
0.92
0.03
-13.7
111
56.4
-
aweight fraction of boiling acetone-insoluble fraction. bcomonomer ratio determined by ' H NMR spectra. 'determined
by GPC.
I I . Synthesis of Terminally Functionalized Iso-PP
127
creased with an increase in the polymerization time. The methoxy protons could be observed also in the polymers obtained at 0 and 45 'C. The ratios of monomer units (MMAIpropene) in the copolymers were estimated from the relative intensities of the methoxy and hydrocarbon protons (see Table 1). The results are shown in When the MMA polymerization was conducted at - 7 8 or Table 1. 0 'C, the content of MMA in the copolymer increased with prolonging the polymerization time. The number average molecular weight of the resulting polymer also increased with an increase in the polymerization time to reach a constant value, indicating formation of the block copolymer. The thermal properties of the isotactic PP-block-PMMA copolymer were briefly investigated by DSC, the results of which are The copolymer essentially shows the melting shown in Table 1. point(Tm) and glass transition temperature(Tg) of isotactic PP, although Tg slightly increased with an increase in the PMMA content. In conclusion, the MgBr-terminated isotactic PP was synthesized via hydroboration of the vinylidene-terminated polymer followed by transformation of B-C bonds with pentane-I ,5di(magnesium bromide). The MqBr-terminated polymer was found to initiate the polymerization of MMA at low temperatures to produce the isotactic PP-block-PMMA copolymer. ACKNOWLEDGEMENT The authors thank Dr. Toshiya Uozumi (JAIST Hokuriku, Japan) for the GPC measurements. REFERENCES 1. For example, (a)Y.Doi, K.Soga, M.Murata, and Y.Ono, Makromol. Chem., Rapid Commun., 4, 789 (1983);(b)D.R.Burfield, Polymer 25, 1817 (1984);(c)G.Redina, and E.Albizzati, Eur. Pat. Appl., 350059(1989) (d)T.Shiono, K.Yoshida, and K.Soga, Makromol. Chem., Rapid Commun., 1 1 , 169 (1990) ;(e)T.Shiono, H.Kurosawa, and K.Soga, Makromol. Chem., 193, 2751 (1992); (f)H.Kurosawa, Dr. Thesis, Tokyo Institute of Technology (1994) 2. (a)R.Mulhaupt,T.Duschek, and B.Rieger, Makromol. Chem., Macromol. Symp., 48/49, 317 (199l);(b)T.Shiono, and K.Soga,
128 T. Shiono. Y . Akino and K . Soga
3.
4. 5. 6. 7.
Macromolecules, 25, 3356 (1992);(c)T.ShionoI and K.Soqa, Makromol. Chem., Rapid Commun., 13, 371 (1992);(d)T.ShionoI H.Kurosawa, O.Ishida, and K.Soga, Macromolecules, 26, 2085 (1993) F.R.W.P.Wild, M.Wasiucionek, G.Huttner, and H.H.Brintzinger, J. Orqanometal. Chem., 288, 63 (1985);T.Tsutsuir A.Mizuno, and N.Kashiwa, Polymer, 30, 428 (1989) A.Grassi, A.Zambelli, L.Resconi, E.Albizzati, and R.Mozzocchi, Macromolecules, 2 l , 617 (1988) L.M.Brown, R.A,Brown, H.R.Crissman, M.Opperman, and R.M.Adams, J. Orq. Chem., 36, 2388 (1971) K.Kondo, and S.Murahashi, Chem. Lett., 1237 (1979) G.W.Kabalka, and E.E.Gooch, J. Org. Chem., 4 6 , 2582 (1981)
I29
12. Wide Range Control of Microtacticity in Propylene Polymerization with Heterogeneous Catalyst Systems
Masahiro Kakugo Chiba Research Laboratory, Sumitomo Chemical Co. Ltd., 2- I Kitasode, Sodegaura, Chiba, Japan 299-02
ABSTRACT Heterogeneous highly isospecific Ti-Mg catalyst system was shown by a combination of temperature-programmed column fractionation (TPCF) and NMR analysis of the polymer obtained to give polypropylene (PP) which mainly composed of two types of isotactic polymers differing in microtacticity and molecular weight.
This finding agrees with that found previously in 6-TiC13-
AIEt2CI system, showing that the control of the microtacticities and the molecular weights of both isotactic polymers as predominant components will enable us to design the catalyst giving various molecular structures, i.e., microtacticity and molecular weight distribution.
On the basis of this
concept, new catalyst systems have been developed to improve the properties of PP.
INTRODUCTION It is known that heterogeneous Ziegler-Natta catalysts comprise some types of active centers.
The kind and the nature of the active centers will be memorized in the structure of PP produced. The detailed structural analysis of polymer, therefore, gives valuable information about active centers.
Previously, along this idea we studied the detailed structure of PP prepared with 6-
TiC13-AlEtzCI system by a combination of TPCF and NMR analysis.
As a result, the molecular
structure of PP would be explained basically in terms of the presence of three types of active centers.
On the basis of this result, we proposed a model for the active centers 1-3).
GTiC13-
AIEt2CI system, that is, consists of three types of the active centers (Scheme I ) , i.e., ( I ) the highly isospecific active center having four firmly bound C1 ions, an alkyl group, and a CI vacancy, (2) the
130 M . Kakugo
Scheme 1.
Model of the active centers on &Tic13
9
-B
Structure of active center change
Stereospecificity
highly isospecific
low isospecific
' P1
IP,
Stereoregularity of polypropylene
syndiospecific
Stereoblock
SP
nonstereospecific
AP
(SB)
low isospecific center consisting of at least a loosely bound CI ion, and alkyl group, and n CI vacancy, and (3) the nonstereospecific active center consisting of two firmly bound CI ions, a CI
ion, an alkyl group, and two CI vacancies.
In addition, we considered that the low isospecific
active center will become syndiospecific one by configurational change of the CI ion, the alkyl group, and the vacancy during polymerization.
The presence of these active centers results i n the
forination of polymers with different stereoregularities, i.e., highly isotactic (IPl), low isotnctic (IP2), low isotactic-syndiotactic stereoblock (SB), syndiotactic (SP), and atactic (AP).
We
analyzed similarly PPs prepared with Ti-Mg catalyst system and have found that the kind and the nature of the active centers present in Mg-Ti catalyst system are essentially similar to those in the 6 TiC13-AIEt2CI system4). On the basis of this finding , we have designed Ti-Mg catalyst systems with a variety of the stereospecificities and molecular weight distributions.
EXPERIMENTAL Polymerization
Polymerization was carried out in a 3-L autoclave i n liquid propylene or n-
heptane. Solvent extraction
The sample was completely dissolved in boiling xylene and the solution
was cooled gradually to 20°C.
The precipitated polynier was separated by filtration.
polymer soluble in xylene at 20°C was recovered from the filtrate by evaporation.
The
12. Control of Microtacticity in Propylene Polymerization
Fractionation
I3 I
Temperature-programmed column fractionation (TPCF) method1) and cross
fractionation chromatography (CFC) by using a Yuka Denshi CFC-T-150A instrument were applied to the fractionation of polymer obtained. Analysises
I3C N M R spectrum was obtained on a JEOL EX-270 pulsed Fourier transform
NMR spectrometer in o-dichlorobenzene at 135OC.
of polymers in o-dichlorobenzene.
Sample was prepared as 5-50mg/ml solution
The pulse interval was IOs, the acquisition time was 4.2s. the
pulse angle was 4.5".and the number of transients accumulated was 3000-10000.
was determined from the area of the resonance peaks of the methyl region.
Pentad tacticity
The molecular weight
distribution of the samples was determined by a Waters Associates type 150C GPC instrument in 0dichlorobenzene at 145°C.
The melting temperature of the samples was measured on a Perkin
Elmer Type-2 differential scanning calorimeter (DSC).
The sample was premelted in DSC at
22OOC for 5 min. and cooled from 150 to 40°C at a rate of S0C/min.
Thermogram was recorded
by raising from 40 to 170°C at a rate of 5"C/min.
RESULTS AND DISCUSSION 1. Microtacticity distribution of polypropylene p r e p a r e d with Ti-Mg catalyst
system Table I shows the molecular weights and the isotactic pentad fractions of PPs prepared with the Ti-Mg catalyst system and the &Tic13 catalyst system.
Both polymers possessed similar
molecular weight and the polymer obtained with the Ti-Mg catalyst system was 0.98 in mmmm fraction, higher isotactic than that with the &Tic13 catalyst system, 0.96.
In order to know the difference of the microtacticity in detail, we fractionated these polymers by TPCF technique and compared the microtacticity distributions of the polymers.
Figure 1 shows
the cumulative fractionation curves of the polymers in which the elution temperature corresponds to the microtacticity of polymer, that is, the higher isotactic polymer elutes at the higher temperature. Table 1.
Sample list for fractionation
Catalyst system
Mw
mmmm fraction
&Tic13 catalyst
249000
0.96
Ti-Mg Catalyst
22.5000
0.98
132 M. Kakugo
100
80
60 40
20
- SB -
0
20
//
I
I
I
1
I
I
40
60
80
100
120
140
Elution temperature ( " C ) Figure 1.
Cumulative fractionation curves of polypropylenes prepared with &Tic13 catalyst
system and Ti-Mg catalyst system.
The fractionation data indicate that the Ti-Mg catalyst system formed less proportion of AP, SP and
SB compared with the &-Tic13catalyst system.
Figure 2 indicates the differential fractionation
curves of the isotactic parts of the PPs obtained from the data shown in Figure 1 , which clearly shows that both the Ti-Mg catalyst system and the &Tic13 catalyst system give similarly two types of isotactic polymers (IPI and IP2), but the proportion of IPI to IP2 in the Ti-Mg catalyst system is higher than that in &Tic13 catalyst system. higher than that in the &Tic13 catalyst system.
In addition, the rnicrotacticity of IPI is rcmarkably The Ti-Mg catalyst system gave mainly isotactic
polymers, 75% of IP1 and 20'70 of IP2, and a small amount (5%) of low stereoregular polymers,
i t . , AP, SP, and SB. This means that in the Ti-Mg catalyst. system a control of the proportion and microtacticities of IPI and IP2 with keeping the generation of the low stereoregular polymer low will lead to the development of the catalysts in giving a wide variety of PPs.
12. Control o f Microtacticity in Propylene Polymerization
IP,
&TiCI,
1 '
I:
Ti-Mg
0.90
0.95
1.oo
lsotactic pentad fraction Figure 2.
Microtacticity distribution curves of isotactic parts of polypropylenes prepared with
&Tic13 catalyst system and Ti-Mg catalyst system: (-)
observed curves; (- --) calculated curve
(&Tic13 catalyst system: [mmmm]=0.958,Mn=84000 and [mmmm]=o.975, Mn=3 1500, Ti-Mg catalyst system: [rmiriirn]=0.960,Mn=33600 and [mmmm]=0.988, Mn=l68000).
133
134
M. Kakugo
2. Control of the microtacticity of isotactic part The polymerization results with several Ti-Mg catalyst systems, A-D are shown i n Table 2. Although the proportions of atactic polymer are kept at lower level than 2%, the microtacticities of the whole polymers are different from each other, suggesting that these polymers have different microtacticity distributions of the isotactic parts.
Figure 3 shows the relationship between the
generation of atactic polymer and the microtacticity of the whole polymers prepared with catalyst systems A-D (solid line) and conventional catalyst system (dotted line).
In the case of
conventional catalyst system, the change of microtacticity was accompanied usually by a relatively large change of AP generation.
This means that there is a limitation of structural control by using
conventional catalyst system because of the deterioration of the properties of PP caused by AP. On the contrary, in the present Ti-Mg catalyst systems, the microtacticity could be controlled ranging from 0.92 to 0.99 with maintaining the proportions of AP at a low level. The polymers prepared with catalyst systems A-D were fractionated by CFC technique. Figure 4 shows the differential fractionation curves of the isotactic parts of these polymers.
This
figure indicates that the relative portion of the IPI to the IP;! changes slightly among these polymers. However the microtacticities of IP1 and IP2 change significantly, i.e., the whole polymer with higher microtacticity consists of the higher microtacticities of both IP1 and IP2.
Table 2.
fi)
Results of propylene polynierization with various Ti-Mg catalyst systems") Catalyst
Activity
system
(g-PPIniol-Ti h )
A
4000
I .7
3.6
0.92
B
20000
1.1
3.7
0.96
C
45000
0.7
3.8
0.98
D
52000
0.6
4.2
0.99
E
59000
1 .o
6.4
0.98
APD) MwlMn (~1%)
mnitiim
fraction
Polymerization was carried out in a 3-L autoclave in liquid propylene at 80°C in I h.
0)Fraction soluble in xylene at 20°C.
12. Control of Microtacticity in Propylene Polymerization
I 0
'
Conventional \\
catalyst system
\ \ \ \
0 I 0.90;
Figure 3.
'
'
'
' 5 AP (wt%)
'
'
'
10
Relationship between isotactic pentad fraction of whole polymer and proportion of
atactic polymer.
90 100 110 El u l i o n I emper at u r e Figure 4. A-D.
120
130
"C
Differential fractionation curves of polypropylenes prepared with catalyst systems
135
136
M. Kakugo
3. Control of Molecular Weight Distribution
As shown in Table 2 , the polymer prepared with catalyst system E has the same niicrotacticity and almost same proportion of A P as that prepared with catalyst system C, but its molecular weight distribution is remarkably broader.
Table 3.
The average molecular weight of
the IPl and the IP2 in catalyst systems C and E Catalyst system
Mw
IPI
IP2
C
399000 86000
E
415000 71000
101
102
103
104
Chain length Figure 5.
105
1 o6
(A)
Molecular weight distributions of the IP1 and the IP2 of polypropylenes prepared
with catalyst systems C and E.
12. Control of Microtacticity in Propylene Polymerization
137
In order to understand the difference in molecular weight distribution in more detail, the polymers were fractionated by CFC technique.
The molecular weight distributions of IPI and IP2 were
obtained from the summation of molecular weight distributions of the fractions eluted in the temperature regions of IP1 and IP2, respectively.
The calculated molecular weight distributions
are shown in Figure 5 and the average molecular weight of the 1P1 and the IP2 are described in Table 3.
The relative portion of the IP1 to the IP2 is largely different from each other.
In catalyst
system E giving a broader molecular weight distribution the IP2 is higher relatively than that in catalyst system A .
Additionally, a difference between the average molecular weights of the IPI
and the 1P2 is larger than that in catalyst system E.
These differences enable us understand the
reason of the wide molecular weight distribution of PP obtained with catalyst system E.
4. Properties of polypropylenes prepared with catalyst systems A-E
Figure 6 shows the relationship between the microtacticity of the whole polymer and the flexural modulus.
The flexural modulus increases with increasing the microtacticity of the whole polymer.
The molecular weight distribution of polymer also affects the flexural modulus; the broader is
0.90
0.95
lsotactic pentad fraction Figure 6.
Relationship between isotactic pentad fraction and flexural modulus.
1.oo
138
M. Kakugo
E
D
-r B
*/O’ C
A
0.95 lsotactic pentad fraction
0.90
Figure 7.
1
1 .oo
Relationship between isotactic pentad fraction and melting temperature
Figure 7 shows the relationship between the rnicrotacticity and the melting temperature of polymer, indicating that the melting temperature depends primarily on the isotactic pentad fraction, not on niolecular weight distribution. CONCLUSION
We have developed a new catalyst technology using Ti-Mg catalyst system for controlling both rnicrotacticity and molecular weight distribution of isotactic polypropylene.
The properties o f
isotactic polypropylene can be controlled by these catalyst systems in a wide range. ACKNOWLEDGEMENT
The author wishes to express his gratitude to Suinitomo Chemical Co. Ltd. for permission to publish this work.
The author acknowledges helpful discussions with Messrs. H. Sadatoshi, K.
Mizunuina, S . Kishiro, and T. Ebara. It EITE R EN C ES 1. M. Kakugo, T. Miyatake, Y. Naito, and K. Mizunumn, Mncromolecules, 21, 714 (1988)
2 . M. Kakugo, T. Miyatake. Y. Naito, and K. Mizunuma, Mnkrorrzol. Chenr., 190, 505 (1989) 3. M . Kakugo, T. Miyatake, and K. Mizunuma, Macrorirolecufes,24, 1469 (1991) 4. T. Miyatake. K . Mizunuma, in. Kakugo, Stud. in Sui$ Sci. Catal., 56(Cat(71. Olejin Polyrrr.), IS5 ( I 989)
139
13. New Heterogeneous Catalysts for Polyolefins
E. Albizzati, T. Dall'Occo, M. Galimberti, G. Morini Himont "G. Natta" Research Center, P.le G. Donegani, 12 44100 Ferrara (Italy)
ABSTRACT
The key factor that allowed the outstanding development of polyolefins has been the Ziegler-Natta catalysis that played and is still playing an innovative role in this field. More andmore sophisticated new catalysts have made possible advanced polymerizationtechnologies, improvedproductgrades and a broader range of applications, through a better understanding of the relationships among the catalyst architecture, the micro and macrostructure of the polymer and its properties. Aiming to widen the "property envelope" of polypropylene we have to improve the followig aspects: i) polymer architecture control ii) polymer microstructure control iii) modification of the surface properties i iii) modification of the rheological properties. The guidelines that we have followed, by using heterogeneous MgC1, based catalysts, to overcome these problems are reported. INTRODUCTION
The expansion of polyolefins into the worldwide plastic market in the last thirty years has been exceptional. The polyolefins world market share was around 20% of the total thermoplastics market in the 60's while it is reaching almost 60% in the 90's with an average growth rate of 7-8% per year. The key factor that allowed the realization of this outstanding development has been Ziegler-Natta catalysis that had played and is still playing an innovative role in this field.
140 E. A l h i i i a t i . T. Dall'Occo. M. Galirnberii a n d G. Morini
More and more sophisticated new catalysts have made possible advanced polymerization technologies, improved product grades and a broader range of applications. Besides, the research effort was aimed at modifying some particular properties of polyolefins in order to widen their application fields. We believe that the expansion of the Inpropertyenvelopel' of polyolefins has been made possible through the following steps: The continuous development of high yield MgC1, based catalysts. The polymer architecture control, in terms of morphology and porosity. The polymer structure control in order to: i) obtain high crystallinity (isotactic index of PP higher than 99%); ii) regulate MW and MWD; iii) distribute randomly one or more comonomers; iiii) obtain new polymers, by using metallocene based catalytic systems. Modification of the surface properties (e.g.compatibility with other polymers, fillers and fibres) by introducing in the backbone polar groups or unsaturation suitable for crosslinking and other chemical reactions. Modification of the reological properties by introducing long chain branching by postreatment of the polymer or copolymerization with diolefins. In this paper the guidelines that we have followed to achieve these development steps are reported.
1)
HIGH YIELD M N l z BASED CATALYSTS We have recently discovered [l] new MgC1, based catalysts
f o r PP production containing a new family of internal donor belonging to the class of 1,3-diethers. These catalysts are able to give with high yield highly stereospecific PP in the absence of any external donor (fig.1).
13. New Heterogeneous Catalysts for Polyolefins
141
Fig.1 : General formula of 1J Diethers
widely accepted mechanism of stereoregulation by Lewis bases, first proposed by Corradini [2], is based on the competition of the Lewis base with TiC1, for selective coordination to unsaturated magnesium atoms on the different later?l faces of MgC1,. According to this model, dimeric titanium species, responsible for the synthesis of isotactic polymer, should be present on the (100) face, whereas the Lewis base should saturate the vacancies of tetracoordinate Mg atoms present on (110) face, thus avoiding the placement of TiC1, and the consequent formation on this plane of non stereospecific sites. As a consequence of this model, we believe that one of the most important feature of a bifunctional electron donor in propylene polymerization is the distance between the coordinating atoms, that must be suitable for chelating on tetracoordinate magnesium atoms located on (110) face of MgC1,. The results obtained with the catalyst system containing phthalates and silanes, both bifunctional bases, respectively as internal and external donors strongly support the above model. Through molecular calculation and conformational analysis it was possible to identify some diethers, in particular 1,3diethers, that have this right distance. These compounds, tested as internal donors in propylene polymerization give outstanding results in term of activity and stereospecificity. A
142
E. Albizrati. T. Dall’Occo. M. Cialimberti and G. Moririi
In table 1 are reported the performances of catalysts containing different diethers as internal donors. In general it is possible to observe that when the maximun probability value of the oxygen-oxygen distance, determined according to Conformation Statistical Distribution methodology [ 3 ] , is near to 3 Angstroms the catalyst performance is very good, whereas when the distance value is spread out in a wide range the performance is very poor.
Tab. 1: 1,3-DIETHERSBASED MgCl SUPPORTED CATALYSTS
DONOR
0-0 Distance
MILEAGE
A
KgPP/gCat
CI
2.9 - 4.7
4.0
CI
3.9 - 7.2
30.0
XI
2.7 - 4.0
35.0
74.9
Polymeridion conditions’ 4 I reactor,propylene 1.2 Kg. hyckogen 1.7 NI.
[TEAL] 2 5 rnrnoVI. 70’C. 2 hrs
13. New Heterogeneous Catalysts for Polyolefins
2)
143
POLYMER ARCHITECTURE CONTROL
The polymer architecture control allows t h e synthesis of new materials with improved properties like HETEROPHASIC OLEFIN COPOLYMERS and POLYOLEFIN ALLOYS with non-olefinic polymers which HIMONT has called HIVALLOY TECHNOLOQY:
-
HETEROPHASIC COPOLYMERS
Heterophasic polypropylene copolymers [ 4 ] are tough, high impact materials where polypropylene is the continuous phase and an elastomeric phase (usually an ethylene-propylene rubber) is uniformly dispersed within the matrix. Before the discovery and commercial exploitation of the high yield MgC1, based catalysts, such heterophasic copolymers, with high rubber content, were essentially made by melt blending of the preformed polymers in an extruder. There were, however, significant limitations on the properties of polymers that could be blended in this way. For istance, a too great difference in the melt viscosities of the various components of the blend prevents from the formation of domains of appropriate size of low modulus EPR particles. An optimum size is necessary to deconcentrate stress during impact which, according to classic rubber toughening theory, acts to initiate delocalized energy absorption and reduce catastrophic brittle failure. In figure 2 is reported a cross section of a such heterophasic polypropylene copolymer where EPR rubber particles can clearly be seen uniformly dispersed in the polypropylene matrix. To make the optimum heterophasic polymer structures directly in the polymerization reactor it is important to tailor the catalyst not only for the production of the ideal polymeric chemical structure but also for the location of the various polymeric phases. The rubbery phase must be homogeneously dispersed and its size controlled in order to achieve the best stiffness-impact balance. The catalyst must be capable of producing a homopolymeric phase with high isotacticity and then to copolymerize the desired elastomeric material with a high degree of randomness uniformly dispersed within the matrix.
144
E. AlhizLati, T. 1)all'Occo. M. Calirnherti and G. Morini
FIG.2
Cross section of heterophasic copolymer with an high rubber content (2000 x).
One of the most important concept developed from Himont/Montecatini's 40 years of commitment to research in Ziegler-Natta catalysis is the "Reactor Granule Technology" [5] where a controlled polymerization process takes place in each polymer granule according to diffusion and kinetic phenomena, related to the structure of the selected catalyst. It produces a growing, spherical granule that provides a porous reaction bed within which other monomers can be introduced and polymerized to form a polyolefin alloy. Figure 3 is a photograph of this Reactor Granule illustrat.ing the porous nature of the resin particle during the production of a polypropylene heterophasic alloy. This technology allows high rubber-containing blends and alloys to be made directly in the reactor and is not limited to a two components heterophasic system, indeed a third or even more phases can also be introduced. Figure 4 is a photograph of a reactor made PP/EPR heterophasic copolymer in which polyethylene has been incorporated to improve stress whitening on impact of a molded part.
13. New Heterogeneous Catalysts for Polyolefins
FIG. 3
FIG. 4
Reactor Granule (35 x)
.
Cross section of three-phase copolymer PP/EPR/PE after removal of rubber (20.000 x).
145
146 E. Albirrati, T. Dall’Occo, M . Galiniherti and G. Morini
-
HIVALLOY
The Reactor Granule Technology makes possible an exciting new technical frontier, allowing the incorporation and polymerization of non olefinic monomers in a polyolefin matrix. The porous polyolefin granule gives a very high specific surface area and a very high reactivity substrate suitable for easy reaction with non olefinic monomers at level greater than 50% wt. via free radical graft copolymerization. Himont calls this emerging technology Hivalloy [6] and the combining of non olefinic monomers with an olefinic substrate makes possible a family ofmaterials not commercially achievable previously. These resins are expected to bridge the performance gap between advanced polyolefin resins and engineering plastics, and are therefore, truly “Specialty Polyolefinsll. A first target of the Hivalloy family of products will be those applications currently served by ABS. Possessing both olefinic and non olefinic characteristics, Hivalloy products are designed to combine the most desirable properties of PP, such as processability, chemical resistence and low density, with many of desirable features of engineering resins which cannot be achieved with currently available polyolefins, such as improvements in the material’s stiffness/ impact balance, improved mar and scratch resistance, reduced molding cycle time and improved creep resistance. Because of their olefinic base, Hivalloy polymers readily accept minerals and reinforcing agents, providing added flexibility and control over properties further expanding the PP property envelope into the specialty area. In conclusion the basic requirements for a high yield catalyst suitable for Reactor Granule Technology are as follow: 1) High surface area. 2) High porosity. 3) High enough mechanical strength to withstand mechanical Processing, but low enough to allow the forces developed by the growing polymer to break down the catalyst into the microscopic particles that remain entrapped and dispersed in the expanding polymer particles.
13. New Heterogeneous Catalysts for Polyolefins 147 4)
5) 6)
Homogeneous distribution of active sites. Free access of the monomers to the innermost regions of the catalyst. Maintenance of above characteristics with a range of different monomers.
3)
POLYMER STRUCTURE CONTROL
-
HOMOGENEOUS CATALYSIS
Metallocene based catalysts [7,8,9] constitute a new class of extremely active Ziegler/Natta polymerization catalysts, which are able to produce all known polyolefins and are unique in producing a large series of new polymers such as highly stereoregular syndiotactic polypropylene, syndiotactic polystyrene, syndiotactic poly-4-methyl-l-penteneI perfectly random LLDPE and EPR/EPDM rubbers. In our laboratories we have recently discovered [lo] some new catalytic systems able to produce EPR and EPDM rubbers with a controlled microstructure in terms of random distribution of comonomers and microtacticity of the short propylene sequences. The elastomeric properties are particularly outstanding: the raw copolymer behaves as a cured elastomer (tab.2). We believe that the most relevant drawback related to the use of metallocene based catalyst systems is the difficulty in controlling the morphology of the polymer. For this reason we have focused our research activity towards the supportation of metallocenes, aiming at using this catalyst in gas-phase processes. In table 3 the most promising results [ll] that we have obtained are reported: it is worthwhile to point out that the properties of the polymers obtained employing the supported catalyst are very similar to those of the polymers obtained with the unsupported ones.
148
E. Albizzati. T. Dall'Occo, M. Galimberti and G. Morini
TAB. 2
-
MAIN FEATURES OF NEW EPR RUBBERS FROM METALLOCENES
VERY HIGH POLYMERIZATION ACTIVITY Ashes Content: Zr = 0.5
-
2 ppm, CI = 0.3 - 1.5 ppm, A1 < 400 ppm
NARROW DISTRIBUTION OF MOLECULAR MASSES AND CHEMICAL COMPOSITION MwIMn = 2 - 3 Ethylene content of a fraction = +I- 5 % of the ethylene content of the taw copolymer
VERY LOW CRISTALLINITY ethylene I propylene copolymers amorphous in the composition range: 40 - 75 % as ethylene molar content
NEW PHYSICAL - MECHANICAL BEHAVIOUR: OUTSTANDING ELASTICITY Tension Set (200%.23°C. 1')
< 10 (ethylene I propylene copolymer, 70% by moles of ethylene, 3 as I.V.)
ITH SUPPOIUED METAWx)CENE CATACYSTS POLYMER CATALYST
ACTMTY o(-Olefin
Tm
A M I.V.
Mw/Mn
BUM
NOTE
MNSrrY
LLDPE#
EPR*
#
KglgZrlh
wt.%
"C
J/g
dug
elmi
A-Unsupported A-Supported
800 220
15.6 15.6
95 101
77
0.92 2.5 1.4 3.8
0.20 0.44
Fine Light Powder SpherelGranule
6-Unsupported 6-Supported
460 190
11.6 11.7
99
05
91
79
1.3 1.1
2.9 3.6
0.15 0.44
Fine Light Powder SpherelGranule
C-Unsupported C-Supported
1300 1160
38 44
36 2.5 4.4 amorphous 3.4
3.0 2.0
.___ .___
Little Fouling No Fouling
Propane slurry polymerization process at 50°C. Propene slurry polymerization process at 50°C.
57
13. New Heterogeneous Catalysts for Polyolefins
4)
149
INTRODUCTION OF POLAR GROUPS AND UNSATURATIONS
In our laboratories we have developed a new synthetic route [12] to obtain polyolefins containing polar groups linked to the main backbone; so far this route presents only a scientific interest, however it is very important to prepare model compounds in order to evaluate the surface properties of these new materials in terms of compatibility with other polymers, fillers and fibers. The synthetic procedure consists of a copolymerization of propylene (and/or ethylene) with 4-iodo-lbutene in the presence of a vanadium based catalyst followed by a substitution reaction of iodine with different polar groups or a dehydrohalogenation reaction to obtain a pendant vinyl group (fig.5).
REACI'ION PATHWAY
Y - 0 2 = 100
-
100 100
x - 0
Polymerization
-
(x
+
(y
(x
+ 3 + 2)
y)
[CH~-CH~]-~-[-CH~-CH-(R)]-~-[-CH~-CH-(CHZ-CH~~]-~
X- I
K+ I lB-crown-6
[CH~-CH~]-X-[-CH~-CH-(R)]-~-[-CHZ-CH-(CH=CHZ)]-~
[CH~-CH~]-~-[-CH~-CH-(R)]-~-[-CH~-CH-(CH~-CH~-X)
X =
OR [Ow,OCOR, CH(COOR)2 [CHzCOOH], -N-PHTALIMIDE R =
Fb5
-
ALKYL, ARYL GROUP
ETHYLENE PROPENE COPOLYMERS CONTAININ0 #IuR QROUPS PREPAMTION OF MODEL COMPOUNDS
150 E. Albizzati, T. Dall’Occo, M. Galimberti and G. Morini
-
CROSS-LINKABLE PP
By using MgC1, based high yield catalysts it is possible to carry out the copolymerization between propylene and 1,3 butadiene [ 131 to obtain a random copolymer; the insertion of butadiene can be controlled by either the polymerization conditions or the catalytic system. Thus a copolymer with 5-10% of butadiene can be produced with prevailing 1,2 or 1,4 trans enchainment obtaining, in the first case, a saturated polymer with a pendant vinyl group and in the second an unsaturation in the polymer chain. Such unsaturate polymers are very reactive towards the radical grafting of polar monomers such as methylmethacrylate, styrene, butadiene, acrylonitrile or the crosslinking reaction necessary for a thermoplastic elastomer. 5)
MODIFICATION OF RHEOLOGICAL PROPERTIES
Aiming to improve the melt viscosity of PP it is possible to submit the polymer to treatment under specific conditions in order to introduce long chain branching. Such a modified polymer is useful for applications in which a high melt strenght is required as in foams, melt thermoforming and blow molding processes. Similar results are obtained via copolymerization of propylene and alfa-omega diolefins with MgC1, high yield supported catalysts.
13. New Heterogeneous Catalysts for Polyolefins
15 1
PEFERENCEB
[l] E.Albizzati, P.C.BarbB, L.Noristi, R.Scordamaglia, L.Barino, U.Giannini, G.Morini, U.S.Patent 4,971,937(1990) to Himont andP.C.BarbB,L.Noristi, R.Scordamaglia, L.Barino, E.Albizzati, U.Giannini, G.Morini, U.S.Patent 4,978,648(1990) to Himont and G.Agnes, G.Borsotti, G.Schimperna, E.Barbassa, U.S.Patent 5,095,153(1992) to Himont
.
[2] P.Corradini, V.Barone, R.Fusco and G.Guerra-Gazz.Chim.Ita1. 113,601 (1983) [3] R.Scordamaglia, L.Barino in J.K.Seyde1 Ed.QSAR Strategies in the Design of Bioactive Compounds, VCH, Weinheim, 1984, p.299 and R.Scordamaglia, L.Barino, Poster presented at "40 YEARS ZIEGLER CATALYSTS1', Freiburg, Sept. 1-3, 1993. [4] P.Galli, T.Simonazzi and D.Del Duca Acta Polimerica 39(1988) ,81. [5] P.Galli, J.C.Haylock Proceeding of SPE Meeting, Houston 2,24,1991. [6] P.Galli, A.De Nicola - Proceeding of "Strategies for Engineering Thermoplasticsll, Brussels 6,29,1992. Adv. Organomet. Chem. 18,99(1980). [7] H.Sinn, W.Kaminsky [8] J.A.Ewen J. Am. Chem. SOC. 106,6355(1984). Makromol. Chem. [9] A.Zambelli, C.Pellecchia and L.Oliva Macromol. Symp.48/49,297(1991). [lo] M.Galimberti, L.Resconi, E.Martini, F.Guglielmi and E.Albizzati Ital.Pat.App1. MI92A000666 to Montecatini Tecnologie. [ll] E.Albizzati, T.Dall'Occo, L.Resconi, F.Piemontesi, Ital.Pat.App1. MI93A001467. [12] M.Galimberti, U.Giannini, R.Mazzocchi, E.Albizzati and U.Zucchini, E.P.A.489,284 to Himont Inc. and M.Galimberti, U.Giannini, E.Albizzati, S.Caldari and L.Abis submitted to J.Mol.Cat. [13] G.Cecchin, F.Guglielmi and F.Zerega U.S.Patent 4,602,077 to Himont Inc.
.
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I53
14. Change of Internal Donor for Mg(OEt),-Supported TiCI, Catalyst
DONG-HO LEE1, YOUNG-TAE JEONG2 and KAP-KU KANG2 1. Department of Polymer Science, Kyungpook National University, Taegu 702-701, Korea 2. Department of R & D, Korea Petrochemical Industrial Co., Ulsan 680-1 10, Korea ABSTRACT During the in-situ preparation of Mg(OEt)2/di-n-butylphthalate(DNBP)/TiC4 catalyst, some amount of DNBP converted into its derivatives such as diethylphthalate(DEP) >> ethyl-nbutylphthalate(EBP). With binary DNBPDEP internal donor, DNBP and DEP contents in catalyst could be controlled, and it was found that catalyst activity depends on relative amounts of DNBP and DEP rather than total diester content. With addition of Ti(OBu)4, DEP formation was suppressed and molecular weight distribution of polypropylene became wider. INTRODUCTION For high-efficient catalysts of propylene polymerization, it was found that MgCI2 is a suitable support and the preparation and characterization of MgC12-supported T i c 4 catalyst were studied intensively. ,2) In addition, magnesium alkoxides were reported as efficient support.3) Recently, Mg(OEt)2-supported Tic14 catalysts were prepared by not only physical milling method4) but also chemical reaction and the chemical composition and During the in-situ polymerization behaviours of those catalysts were studied in detail. preparation of Mg(OEt)2-supported Tic14 catalysts, diisobutylphthalate added as internal donor (ID) changes into its derivatives78 and this conversion of ID depends on preparation condition^.^) In this article, Mg(OEt)2/di-n-butylphthalate(DNBP)/TiCl4 catalyst was prepared by chemical reaction method, and the chemical composition as well as propylene polymerization behaviours of catalyst were studied in detail. Especially the changes of DNBP and effects of IDScomposition on catalyst activity and isospecificitywere examined. EXPERIMENTAL Reagents. Propylene(po1ymerization grade, 99.5% purity, Korea Petrochemical Ind. Co., Korea) was dried by passing through two columns of preactivated molecular sieve 4A. Triethylaluminum(TEA, Tosoh Akzo Corp., Japan), TiClq(Toho Titanium Co., Japan), di-nbutylphthalate(DNBP, Aldrich Chemical Co., U.S.A.) and cyclohexylmethyldimethoxysilane (CMDMS, Shin Etsu Co., Japan) were used without hrther purifications. n-Hexane(Tokyo
* Dedicated to Lee's mother deceased on February 28, 1994.
154
D.H. Lee, Y.T. Jeong and K.K. K a n g
Kasei Co., Japan) and n-decane(Aldrich Chemical Co., U.S.A.) were dried over preactivated molecular sieve 4A for 24 h and contained 8)and the reaction of ester with Ti(OEt),Cl4-, which is produced from Mg(OEt)2 and TiC14.9)
14. Internal Donor for Mg(OEt),-Supported TICI, Catalyst
155
With the above backgrounds, direct reaction of di-n-butylphthalate(DNBP) and Mg(OEt)2 in the absence of Tic14 was carried out at 90, 100 and 115OC, and reaction products of diester were analyzed with GC as shown in Table 1.
Table 1. Reaction Products of DNBP and Mg(OEt)2 Reaction Temp(OC) Diester(mo1efraction)
-.-
100
90 DNBP EBP
DEP
115
DNBP EBP
DEP .
Reaction
0
Time(min)
10 20 30 40
1.00 0.93 0.79
0.00 0.00 0.07 0.00
60
0.60
0.19 0.02 0.34 0.06
90
0.20
0.50
0.30
1.00 0.93 0.86 0.68 0.38 0.12
0.00 0.07 0.14 0.29 0.47 0.47
DNBP EBP
DEP
~
~
0.00
1.00
0.00
0.74
0.22 0.04
0.35 0.00
0.34 0.34
0.00
0.00 0.00 0.04
0.15 0.41
0.31 0.66
-
-
a); mole ratio of DNBP/Mg(OEt)2 = 0.16
As shown in Table 1, DNBP converted into its derivatives such as ethyl-nbutylphthalate(EBP) and diethylphthalate(DEP), and DNBP portion decreased with increasing reaction temperature and time. In addition, the produced amount of EBP was larger than that of DEP in every conditions. With the above results, it was considered that transesterification reaction between DNBP and Mg(OEt)2 occurs even in the absence of Tic14 and DEP produces via EBP stepwisely. This transesterification of DNBP wth Mg(OEt)2 was sensitive to reaction temperature and time. Mg(OEtl2/DNBP/TiClq - catalvst The chemical composition and polymerization behaviours such as activity and isospecificity
of Mg(OEt)2/DNBP/TiCIq catalysts prepared at different temperature were examined and the results are given in Table 2 and 3. As expected, conversion of DNBP into EBP and DEP was also possible during the in-situ preparation of Mg(OEt)2/DNBP/TiClq catalyst. However, DNBP was still remained even at 12OOC, 2 h while DNBP disappeared completely even at 1150 C, 1 h for the reaction with Mg(0Et)z in the absence of TiClq.(Table 1) In addition, DEP was main product for catalyst preparation while EBP was produced mainly for the reaction of DNBP with Mg(OEt)2 only.
156 D.H. Lee, Y.T. Jeong and K.K. Kang
Table 2. Chemical Composition of Mg(OEt)2/DNBP/TiClq Catalysts Obtained with Reaction for 2 h at Different Temperature ~
_
_
_
Catalysts
Reaction
No.
Temperature(°C)
Ti(wt%)
DNBPa)
EBPa)
DEPa)
Total Diestera)
90
3.1
34 1
28
72
44 1
100
3.0
266
44
135
445
110
2.6
144
302
2.3
126 57
32
120
24
144
225
a): concentration, xi03 nunoYgatalyst b); mole ratio of DNBP/Mg(OEt)2 = 0.16
Although the reason of these different results is not clear at the present time, the mutual interactions between components such as complex formation of various diester(DNBP, EBP, DEP) and TiC14, chlorination of diester and formation of Ti(OEt),&x, etc. could exist. With increasing reaction temperature, DNBP amount as well as total amount of diesters decreased while DEP increased, and the titanium content decreased slightly.
Table 3. Activity and Isospecificity of Reaction for 2 h at Different Temperature Catalysts No.
1 2 3 4
Activity a) 1.1(wt%) without H2 27.9 27.2 27.0 27.8
99.0 98.6 98.5 98.4
Mg(OEt)2/DNBP/TiClq Catalysts Obtained with
Activity a) 1.1(wt%) with H2b) 63.4 64.0 63.0 61.1
98.5 98.4 98.3 98.3
a); catalytic activity, kg-PP/g-Ti.h.atm b); hydrogen pressure, 0.18 k@m2
As shown in Table 3, the catalyst activity and isotactic index(I.1) of polypropylene(PP) had less dependence on diester content in the prepared catalyst.
14. Internal Donor for Mg(OEt),-Supported TiCI, Catalyst
157
For Mg(OEt)2/diisobutylphthalate@IBP)/TiC~catalyst, Chadwick et d.9) reported that catalyst activity decreased and fraction of xylene-soluble PP increased with decreasing total diester content in the catalyst. To check the effects of total amount and composition of diesters on chemical composition and polymerization behaviours of catalysts, various catalysts were prepared by adding different mole ratio of DNBPDEP as binary ID and the experimental results are given in Table 4.
Table 4. Chemical Composition and Polymerization Behaviours of Catalysts Prepared with Binary DNBP/DEP Internal Donor at 9OOC, 2h Catalysts DNBP/DEP DNBPa) EBPa) DEPa) Total Diestera) Ti No. (Mole Ratio) (wt %)
Activityb)
5
1 .OO/O.OO
336
27
44
407
2.9
62.7
98.9
6
0.7W0.25
332
27
141
500
2.9
58.8
98.5
7
0.67/0.33
214
24
195
433
2.7
59.7
98.5
8
0.50/0.50
111
13
305
429
2.4
58.3
98.6
9
0.33/067
111
14
366
491
2.4
56.7
98.4
10 11
0.2W0.75 0.00/1.00
109
11
443 485
563
2.3
55.7
98.3
485
2.3
46.1
97.8
-
1.1 (wt %)
a): concentration, x103 mmot/gzatalyst
b): catalytic acfivky, kg-PP/g-Ti,h.atm,hydrogen pressure, 0.18 kg/cm2 c); mobratio of DNSP/Mg(OEt)2 = 0.16
It was expected that DEP formation from DNBP is suppressed with DEP addition if transesterification of DNBP to DEP was equilibrium reaction. However, as shown in Table 3, DEP content increased steadily while DNBP content decreased continuously with increasing amount of added DEP. EBP formation could be neglected compared to DEP. The total content of ID was in range of 0.40-0.55 mmoYg-catalyst with less correlation to added mole ratio of DNBPDEP. Titanium content of catalyst decreased slightly with increasing DEP amount. The catalyst activity showed strong dependence on mole ratios of DEP or DNBP rather than total amount of ID; i.e. catalyst activity decreased with increasing amount of DEP or decreasing amount of DNBP. The heptane-insolubleportion of PP was almost constant irrespective to ID amount and composition.
158 D.H. Lee, Y.T. Jeong and K.K. K a n g
Those above results are contradictory to those of Chadwick.9) The reason is not clear, but it might be due to differences in experimental conditions such as catalyst preparation procedure, catalyst washing medium and external donor, etc. M~~OE~7fl>NsPrriCl~rri~OBu!4 - catalyst From the above experiments, it has been found that DEP is formed by transesterification of DNBP even with the presence of DEP during the in-situ preparation of catalyst and DEP amount should be diminished for high catalyst activity. To suppress the formation of DEP, various amount of Ti(OBu)4 was added with ID in the procedure of catalyst preparation . The effect of Ti(OBu)4 addition on catalyst composition was examined as shown in Table 5 .
Table 5 . Effects of Ti(OBu)4 Addition on Catalyst Composition Catalyst Ti(OBu)4/ Ti
No.
Mg(OEt)2
DNBPa) EBPa) DEPa) Total
DNBP
DEP
Butoxy
Diestera) Fraction Fraction (wt%)
(wt%)
(mole ratio) 386
28
23
437
2.8
332
57
46
435
2.8
259
71
42
372
2.9
250
92
31
373
2.8
156
128
34
3.0
120
80
14
150
94
16
260
2.4
317
124
13
1.5
309
89
0
12
0.0
3.0
13
0.2
14
0.4
15
0.6
16
1.o
17
1.5
18
2.0
2.7
19
3.O
20
4.0
0.05
0.23
0.76
0.10
0.58
0.70
0.11
0.77
0.67
0.08
0.78
318
0.49
0.11
1.04
214
0,56
0.07
1.01
0.58
0.06
0.88
454
0.70
0.03
0.94
398
0.78
0.00
0.90
0.88
a): concentration, x103 mmol/g-catalyst
b); catalyst preparation ;90 OC, 2h
With addition of Ti(0Bu)q in catalyst preparation, DNBP content as well as DEP content decreased while EBP amount increased with much contribution. In this case, minor component was DEP(mo1e fraction; ca. 0. l), which indicated that Ti(OBu)4 has some contribution in transesterification to suppress DEP formation. Total amount of diester and DNBP mole fiaction decreased with increasing Ti(OBu)4 amount for Ti(OBu)4 < 2.0 mole. The butoxy
14. Internal Donor for Mg(OEt),-Supported TiCI, Catalyst
I59
group came from TiCl,(OBu)q_, and its content in the catalyst increased with amount of Ti(0Bu)q. Titanium content was remained almost constant. The effects of Ti(0Bu)q addition on catalyst activity, isospecificity and molecular weight of PP were examined as shown in Table 6.
Table 6. Effects of Ti(0Bu)q Addition on Catalyst Behaviours for Propylene Polymerization Catalyst
Activiv)
I.I(Wt%)
Mw/Mn
Mw/Mn
with H2b)
10-3 mi H2
10-3 H2 b)
6851113
218153.4
Activip)
I.I(Wt%)
No.
without H2 12
27.7
99.3
63.3
98.8
13
21.4
98.4
61.6
98.2
14
17.9
98.0
59.5
98.4
15
14.8
98.2
53.1
98.3
16
13.4
98.6
44.6
98.7
17
12.3
98.7
36.3
98.5
18
10.0
96.8
32.2
98.4
19
7.1
97.0
20.4
97.3
540178.2
191138.7
20
6.7
96.0
16.3
97.1
587180.0
187137.3
216153.0 6301103 22615 1.5 642199.5
206145.0 209142.5
a): catalytic activity, kg-PP/g-Ti.h,atm
b): hydrogen pressure, 0.18 k&m2
The catalyst activity decreased continuously with increasing Ti(0Bu)q amount while 1.1 was constant for Ti(0Bu)q < 2.0 mole. For Ti(0Bu)q > 2.0 mole, activity decreased drastically and 1.1 also decreased slightly due to the large amount of alkoxy titanium active site which has less activity and less stereoregularity.10) To remove the alkoxy titanium species, the catalysts were retreated with Tic14 and catalyst composition as well as polymerization behaviours were examined as shown in Table 7. By retreatment of the catalysts with TiClq, titanium and butoxy contents as well as amount of DNBP decreased while catalyst activity increased with unchanged 1.1. The weight-average molecular weight(Mw) and number-average molecular weight(Md decreased simutaneously with addition of Ti(0Bu)q as shown in Table 6. The polydispersity index(P1, M@n) was measured for various amount of Ti(OBu)4 and the results were plotted in Fig. 1.
160 D.H.
Lee, Y.T. Jeong and K.K. Kang
Table 7. Effect of TiClq Retreatment
Catalyst Ti(wt%) No. 14 16 18 20
Activitya) no H2
Activitya) DNBPC) EBPC) H2b)
DEPC)
(AY@)
(AY@)
(A)/@)
(A)/@)
(A)/@)
(AY@)
2.812.5 2.812.4 2.712.3 1.511.3
17.9127.7 13.4125.0 11.1127.4 5.718.4
59.5170.6 44.6172.9 34.U40.1 16.3130.0
45140 23115 1861173 5671231
65/68 3551335 1251200 290/200 62/61 I 100150 I
Butoxy (wt%)
- - -
(A)/@) 0.7510.64 1.0410.67 1.0310.36 0.7810.50
(A); without Tic14 retrcatmnt (B); with Tic14 (60ml)retreatment
a); catalytic activity, kg-PP/g-Ti.hatm b): hydrogen pressure, 0.18 kg/cm2 c); concentration, x103 mmougatalyst
4.5 4.0
+
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Ti(OBu)q/Mg(OEt)2 (Mole Ratio) Fig. 1 Change of polydispersity index(Mw/M,J of PP with amount of Ti(0Bu)q in absence(0) and presence(@) of hydrogen
As shown in Fig. 1, PI increased 0.9-1.2 more due to larger contribution of low molecular weight portion with amount of Ti(0Bu)q. However, molecular weight distribution became narrower in the presence of hydrogen as shown in the previous paper.11)
14. Internal Donor for Mg(OEt),-Supported TiCI, Catalyst
161
REERENCES 1) P.C. Barbe, C. Cecchin and L. Noristi, Adv. Polym. Sci., 8,1 (1987) 2) T.Keii and K. Sogqeds.), "CatalyticOlefin Polymerization",Kodmha, Tokyo, 1990 3) US.Patent 4,548,951(1985)(Shell Oil Co.) 4) Y.-T. Jeong and D.-H. Lee,Makromol. Chem., 191,1487 (1990) 5 ) Y.-T. Jeong, D.-H. Lee and K. Soga, Makromol. Chem., Rapid Commun., 12,s (1991) 6 ) Y.-T. Jeong, D.-H. Lee, T. Shiono and K. Soga, Makromol. Chem., 192,1727 (1991) 7 ) D.-H. Lee,Y.-T. Jeong and K. Soga, Znd Eng. Chem. Res., 31,2642 (1 992) 8) D.-H. Lee, Y.-T. Jeong, K. Soga and T. Shiono, J. Appl. P o h . Sci., 47,1449 (1993) 9)J.C. Chadwick, A.Miedema, B.J. Ruisch and 0. Sudmeijer, Makromol. Chem., 193, 1463 (1992) 10)T. Garrof,E.Iiskola and P. Sormunen, in "TrmitionMetals and Organometallics(IS Cutulystsfor Olefin Polymerization",W . Kaminsky and H. Sinn(eds.), p. 200, Springer-Verlag,Berlin, 1988 11) D.-H. Lee and Y.-T. Jeong, Eur. Polym. J., 29,883 (1993)
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I63
15. Temperature Programmed Decomposition of MgCl,/THF/TiCl, Bimetallic Complex Catalyst and its Effect on the Homo- and Copolymerization of Ethylene
Y. S. KO, T. K. HAN and S. I. WOO Department of Chemical Engineering, Korea Advanced Institute of Science and Technology, Yusong-gu, Daejon, 305-70 1, Korea ABSTRACT A MgC12/THF/TiC14 bimetallic complex catalyst was prepared by reacting magnesium chloride with titanium tetrachloride in tetrahydrohran(TH3). During the temperature programmed decomposition(TPD) of the bimetallic complex, THF and 1,4 dichlorobutane were identified by Mass spectroscopy(MS). TI-F decoordinated from Ti species reacted with adjacent CI, resulting in the formation of 1, 4-dichlorobutane. When the MgC12/THF/TiC14 bimetallic catalyst (Mg/Ti=5.2) was heated below 108 OC, the catalytic activity of polymerization increased, while it decreased above 140 OC. In ethylene-1-hexene copolymerization, the lowest catalytic activity was obtained at the molar ratio of hexene to ethylene in monomer feed(CH/CE), 1.14 or 2.22. The comonomer distribution of copolymer prepared with thermally pretreated catalyst was more homogeneous than that of copolymer prepared without thermal treatment. INTRODUCTION The MgC12/THF/TiC14 bimetallic complex catalyst was reported that it had high activity in ethylene polymerization with aluminum alkyl cocatalyst.’) 2) 3) Sobota have concluded that the three different complexes( [Mg(THF)6][TiCI5(THF)], [(THF)4Mg(p-C1)2TiC14], [Mg2(pC1)3(THF)3][TiCI~(THF)] ) were synthesized from the reaction between TiC14(THF)2 and MgC12(THF)2.4) These complexes can be decomposed by thermal energy and the structures of active sites can be also changed due to the decoordination of weakly coordinated THF from the complexes. This may affect the catalytic activity of bimetallic complex. The coordination site and strength of THF to MgC12 and Tic14 will determine its polymerization behavior in ethylene polymerization. Therefore, the temperature programmed decomposition(TPD) study was performed to obtain some informations on the structures of bimetallic catalyst. Comonomer effects of or-olefin on kinetics in ethylene copolymerization and properties of copolymer were reported by many authors due to their industrial importance.’) 6 ) 7 ) In ethylene copolymerization using MgCl2/THF/TiC14 catalyst it was reported that the addition of 1-hexene decreased the rate of ethylene consumption compared to homopolymerization.*) Thermal pretreatment of bimetallic catalyst can influence the kinetics of copolymerization, comonomer
164 Y.S.
KO,T.K.Han and S.I. W O O
distribution and the properties of copolymer significantly. In the present study, the temperature programmed decomposition of MgC12/THF/TiC14 bimetallic complexes of various Mg/Ti molar ratios was performed. The effect of the thermal pretreatment of the bimetallic complex catalyst prepared under various condition(temperature and time) on the ethylene and ethylene- 1-hexene polymerization was investigated. EXPERIMENTS The MgC12/THF/TiC14 bimetallic complex catalyst was prepared by the precipitation method. The reactivity ratio of monomers in ethylene-1-hexene copolymerization was determined after 30 min of polymerization. The detailed procedures for the preparation of catalyst and the polymerization were provided elsewhere.2)3)The TPD and MS experiments were conducted for the analysis of the evolved gas during heat treatment of the samples. The evolved gases were analyzed by MS. The detailed procedures have been given el~ewhere.~) Polyethylene and ethylene- 1-hexene copolymers were fractionated with boiling heptane for 6 hrs in a Soxhlet extraction apparatus. Copolymer composition was measured by the IR method using the calibration curve based on A138dA1368 absorbance ratio as reported by Nowlin et al.l0) Melting points and heats of fusion of polymers were measured by DSC. Two DSC procedures have been used as follows. Method A is that first scan temperature was raised at 20 Wmin and second scan temperature was raised at 5 W m i n from 50 OC to 150 OC. Crystalhities of polymer were calculated by the equation, x(%) = 100 x AH,/293 where AHf is the heat of fusion measured by DSC. Method B is that polymer samples were melted at 160 OC at inert atmosphere for 3 hrs. Then the sample was successively annealed at 125, 113, 97, 87, 78, 69, 5 5 , and 35 OC for 12 hrs at each step. RESULTS AND DISCUSSION Figure 1-(A) shows the TPD spectra of bimetallic catalysts of various Mg/Ti molar ratios monitored by TCD detector. When Mg/Ti was 5.2,the catalyst was decomposed at 108, 140 and 242 OC and only THF was observed at 80 OC. THF and 1,4-dichlorob~tane,however, were observed at 210 OC by MS. As MgiTi ratio decreased, TPD spectra became similar to that of TiClq(THF)2(Mg/Ti = 0). When MgiTi ratio increased, TPD spectra became similar to that of MgC12(THF)2. Figure 1-(B) shows temperature-programmed mass-spectra of THF(mass to charge ratio; 42) and 1,Cdichlorobutane (mass to charge ratio; 55). 1,4-dichlorobutane was not be produced in the spectrum of MgC12(THF)2 and only a small amount of 1,4-dichlorobutane was detected in the TPD spectra of the bimetallic complex of high Mg/Ti molar ratio. It may be concluded that some of THF coordinated from Ti by thermal treatment reacted with adjacent CI to form 1,4-dichlorobutane. Figure 2 shows the polymerization rate profiles polymerized with the thermally-pretreated bimetallic catalyst. Thermal treatments at 80 OC and 108 O C enhanced the activity in ethylene polymerization. Above 140 OC, however, the polymerization activity was decreased. These results could be explained by the fact that new active sites were formed by decoordination of THF during thermal treatment at 80 and 108 OC. However, titanium active sites were unstable above 140 OC.
15. Temperature Programmed
Decomposition of MgCI,/THF/TiCI,
0
100
200
300
100
200
165
300
T e m p e r m ~ u r a .OC 0
ZOO
100
300
T e m p e r a t u r a , ‘C
(A) (B) Figure 1. TPD spectrum (A) and mass spectra (B) for THF(-) and 1,4-dichlorobutane(---)of MgC12/THF/TiC14 catalysts. (a) Mg/Ti=O, (b) Mg/Ti=l.O, (c) Mg/Ti=2.1, (d) Mflk5.2, (e) Mg/Ti = 16.5, (0 Mg/Ti = w. m
I m e , rnin
Figure 2. Ethylene polymerization rate profiles after thermal treatment of bimetallic catalyst(Mg/Ti = 5.2). Thermal treatment condition: (a) none, (b) 80 OC, Smin, (c) 108 OC, 5 min, (d) 140 OC, 5 f i n ; Polymerization condition: Pethylene = 3 atm; T= 70 OC and [AI]/[Ti] =128. From these results, we can propose the plausible change in the structure of the MgC12/THF/TiC14 bimetallic complex as shown in Figure 3. When Mg/Ti is 5.2 the catalyst is a mixture of [MgC12(pL-Cl)3(THF)6]+[TiCI5(THF)]and MgC12(THF)2, which was reported by Sobota et al.4)
166 Y.S. KO, T.K. Han and S.I. Woo
> >
140
c
HWnn
0 I
TI
/
I I I I
\
CI
CI
CI-C-C-C-C-CI I l l 1
Wlr
* THF
w w nn
IIV)
Figure 3. Plausible change in the structure of bimetallic catalyst (MgITi treatment.
=
5.2) during thermal
Ethylene and 1-hexene were copolymerized at 70 OC for 30 min with the catalyst (Mg/Ti = 5.2) thermally pretreated at various temperatures. The activity in polymerization and properties of polymers are summarized in Table I. The hexedethylene (CH/C,) molar ratio was changed id the range of 1.14 - 5.42. As shown in Figure 4(A), ethylene consumption rate (activity) for TT-0 increased, which was explained by the fact that the physical disintegration of decreased as CH/C~ catalyst particle did not happen rapidly by I-hexene during the polymerization with catalyst of high Mg/Ti ratio and that propagation rate of 1-hexene is smaller than ethylene.*) The different trends in changes of activity at various 1-hexene concentrations were observed with TT-1, 2, 3 and 4 as shown in Figure 4(B) and Table I. In the case of TT-1, the activity decreased in the range of CH/CE molar ratio between 0 and 1.14. The activity increased when C H / C is ~ higher than is higher than 1.14. The similar trend for TT-2 and TT-3 was observed. When the catalyst was heated at 108 OC for 60 min, the ethylene consumption rate in copolymerization increased when C,/C, was above 2.22. These results also demonstrate that the new copolymerization active site was formed after the decoordination of THF by heating. Table I shows that the comonomer content of copolymer polymerized by TT-0 was slightly higher than that of TT-I, 2, 3, 4’s. The crystalhities of the copolymers obtained by TT-1, 2, 3, 4
15. Temperature Programmed
167
Decomposition of MgCI,/THF/TiCI,
were higher than that of the copolymers obtained by TT-0 despite of the similar comonomer content. This can be explained by the fact that comonomer distribution of the copolymer became more homogeneous after heat treatment. Each melting peak in Figure 5 is representative of a distinct family of macromolecules (or blocks) with different short chain branching. l )
,
300
I
h
L c
I
I
I
I
-F .c I
200
M
'r
-2
-E
150
h 0
h
I
0
a
100
I M Y
M
x
2
4
I
L
250
.F.
h,
600 I
v
v
a
50
E0
0
I0
0
20
30
0
I
I
I
I
I
5
10
15
20
25
30
TIME(M1N)
TIME(MIN)
Figure 4. Ethylene consumption rate in copolymerization; (A) catalyst not thermally treated, (B) heated at 108 OC for 60min; Copolymerization condition : P=3atm, T=70 OC,[AI]/[Ti]=128.
=
CJC,
0.00
c,/c,=0.00
7--
3 0.5 W/g
0.5 W/g
30
60
90 120 Temperature( 'C)
150
30
60
I20 0 Temperature( C)
150
(A) (B) Figure 5 . DSC thermograms of ethylene-1-hexene copolymers after annealing; (A) not thermally pretreated; (B) heated at 108 OC for 60min.
168
Y.S. KO, T.K. Han and S.I. Woo
Table I. Effect of 1 -Hexene on the Polymerization of Ethylene Copo1ymerization.a Catalyst
CHICE Tm molar (OC) ratio
xc (%)
R ,b C6 in 3tmin Copolym. (mol %)
in feed
0.00
TT-0
TT- 1
TT-2
TT-3
1.14 2.22 3.57 5.42 0.00 1.14 2.22 3.57 5.42 0.00 1.14 2.22 3.57 5.42 0.00 1.14 2.22 3.57 5.42 0.00 1.14 2.22 3.57 5.42
136.0 125.4 123.4 121.8 122.8 134.2 124.3 123.8 123.8 121.7 134.4 126.5 124.4 122.7 122.6 135.9 126.9 125.0 122.8 123.5 135.3 128.1 124.9 122.5 121.5
52.1 126.9 32.3 104.9 30.3 105.7 28.8 82.6 18.1 31.9 55.2 147.1 39.5 129.2 34.1 138.7 33.8 150.0 24.3 174.0 57.4 142.0 42.2 126.0 36.8 156.7 35.3 162.1 27.7 164.2 58.8 179.4 37.5 131.3 33.2 132.7 32.9 157.9 20.3 178.1 54.1 198.4 45.0 174.9 39.6 103.0 33.5 163.2 29.6 206.7
Reactivity ratio by F-RC
Reactivity ratio by M-~d
0.0
‘1 52.6 ‘2 -0.13
1.8 2.6 3.1 4.0 0.0 1.7 2.4 2.8 4.0 0.0 1.7 2.4 3.3 3.5 0.0 1.7 2.4 2.6 3.9 0.0 1.5 1.9 2.4 3.0
‘1 55.1 ‘2 -0.14
67.1 -0.085
77.0 -0.072
‘1
55.3 r2 -0.13 ‘1 56.3 ‘2 -0.12
64.5 -0.098
79.2 -0.072
‘1 52.9 87.0 ‘2 -0.13 -0.090 a AyTi=l28, T = 70 OC, t = 30min, P = 3atm. Catalyst; TT-0 : no thermal treatment, TT-I: 80 OC, 5 min, TT-2: 80 OC, 60 min, TT-3: 108 OC, 5 min, TT-4: 108 OC, 60 min. Activity = kg-polymer(g-Ti hr)-l Calculated by Finemann-Ross equation. Calculated by Mayo-Lewis equation.
TT-4
The reactivity ratio in Table I can be calculated from the copolymer composition by FinemannRoss and Mayo-Lewis equation. Bohm suggested that ‘1 can be evaluated by simplification for low comonomer content. Iz) In our present study, full equation approaches were used because simplification did not work reliably. The Finemann-Ross ( 1 ) and Mayo-Lewis (2) equations are given as follows. d [ H ] I d [ E ] = [ H ] I [r,E[HI ] I [El + 1 ---_( 1 ) [HI / [ E l+ rz
F ( f - 1 ) - F2 - -r, -r, ---- (2)
f
f
15. Temperature Programmed Decomposition of MgCI,/THF/TiCI,
169
where d[Hl/d[E] ( f ) and [HI@] ( F ) are hexendethylene molar ratio in the copolymer and initial molar ratio in feed, respectively. The two procedures gave somewhat different rl and r2 values and negative values of r2. Floyd explained that a physically meaningless negative value of r2 can be taken as an indication of heterogeneity of polymer.'3) CONCLUSIONS TJ3F and l,4-dichlorobutane were produced during the thermal treatment of the MgC12/THF/TiC14 bimetallic catalyst. Some THF coordinated to Ti was decomposed by thermal treatment and reacted with adjacent C1 of Tick, to form 1,4-dichlorobutane. The decoordination of THF resulted in the formation of new active sites. The thermally pretreated catalyst showed the higher activity than the catalyst not heated in ethylene polymerization. In ethylene-1-hexene copolymerization, the catalytic activity of thermally pretreated catalyst increased at high CH/CE molar ratio due to the new active sites. The copolymer polymerized by thermally pretreated catalyst showed a comonomer distribution more homogeneous than that obtained by the not thermally pretreated. REFERENCES 1. Han,J. D., Kim, I., and Woo, S. I., Polymer(Korea),13,147(1989). and Woo,S. I., "Catalytic Olefin 2. Kim, I., Chung, M. C., Choi, H.K., Kim, J. H., Polymerization", Soga, K. Eds., Kondansha Ltd., Tokyo, 1990, p323. 3. Kim, I. and Woo, S. I., Polym. Bull., =,239(1989). 4. Sobota, P., Utko, J., and Jana, Z., J. Organomet. Chem., U19(1986). 5. Kissin, Y. V. and Beach, D. L., J. polym. Sci. Polym. Chem Ed., =,333(1984) 6. Chien, J. C. W. and No&, T., J. Polym. Sci. Polym. Chem. Ed., 227(1993) 7. Jaber, I. A,, Ray, W. H., J. Appl. Polym. Sci., 1709(1993). 8. Kim, I., Kim, J. H., Choi, H.K., Chung, M. C., and Woo, S. I., J. Appl. polym. Sci., 48, 72 1(1993). 9. Choi, H.K., Chung, D. W., Han,T. K. and Woo, S. I., Macromolecules,-6 2 452(1993). 10. Nowlin, T. E., Kissin, Y. V., Wagner, K. P., J. Polym. Sci. Polym. Chem. Ed., 26, 755(1988). 4337(1992). 11. Addison, E., Ribeiro, M., Deffieux, A., Fontanille, M., Polymer, 12. BBhm, L. L., J. Appl. Polym. Sci., 29,279(1984). 13. Floyd, S., J. Appl. Polym. Sci., 3,2559(1987).
a,
a
This Page Intentionally Left Blank
171
16. Characterization of Mg/Ti Type Catalysts Prepared from Different Mg Components
M. Murata ,A. Nakano ,S. Kanazawa and M. Imai Tonen Chemical Corporation Tonen Corporate R & D Laboratory 1- 3 - 1 Nishitsurugaoka , Ohi - machi , Iruma - gun Saitama 356, Japan
Summary M f l i catalysts for propylene polymerization were prepared from several Mg compounds such as MgC1, , MgClJ2-ethylhexylalcohol solution Mg(OEt), or Mg(0Et)Cl. Catalyst structure regarding Ti atom location in the solid was examined by elemental analyses, X R D and XPS. Ti atoms in the catalysts prepared with MgC1, and MgCld2-ethylhexylalcohol solution were locally concentrated on MgC1, surface. In contrast with this , it was suggested that Ti atoms in the catalysts from non - MgCl, components of Mg(OEt), o r Mg(0Et)Cl were highly dispersed in the particle. It was also confirmed that propylene polymerization behavior such as initiation and rate decay was influenced by the catalyst structure. These results strongly indicate that the properties of active site are changed by the kind of Mg component used for catalyst preparation. Introduction It is well known that Mg/Ti type catalysts have excellent polymerization performances for olefin polymerization”. And many different preparation methods have been reported so far. However, most of the research effort in this area has been focused on the discussions of the roles of Mg component or donors”. On the other hand, there are very few studies aiming the understand of a relationship between catalyst preparation process and polymerization behavior. Terano et. al. reported that the propagation rate constants(kp) were changed by catalyst preparation
172 M. Murata, A. Nakano, S. Kanazawa and M. lmai
procedure3’. Although this result indicates that the properties of active site are controlled by catalyst synthetic procedure , the origin to vary the characteristics of sites are still not clear. In this study , the transformation of catalyst structure , which will be induced by the kind of Mg component used as starting material , will be discussed. Experimental Catalyst preparations 10 catalysts prepared by various Mg compounds and procedures combinations were used in this study : Cat - 1 : 10.5g of MgC1, and 1.4g of TiC1, were placed in a 0.31 stainless steel vibration mill pot with 650g of 12mm# balls and ground for 8h at room temperature. Cat - 2 : cat - 1 preparation procedure was repeated with 10.5g of MgC1, and 0.15g of TiC1,. After milling, solid part was washed with n-hexane. Cat - 3 : 10.5g of MgCl, and 0.02ml of di-ethyl phthalate@EBP) were co-ground by same condition as cat - 1 preparation. Solid part was treated with lOOml of TiCl, of 110°C for 2hrs. The obtained product was further washed with n - hexane. Cat - 4 : In place of DEBP , di-n-buthyl phthalate(DNBP) was used in Cat - 3 preparation. solution was prepared by the Cat - 5 : MgC1~2-ethylhexylalcohol(2-EHA) reaction of log of MgC1, and 48.7ml of 2-EHA in n-dodecane at 130°C for 2h. This solution was introduced dropwise to 25Oml of TiC1, cooled at -20°C. The solution was heated up to 120°C for 4h and treated at the temperature for 2h. The solid product was further washed with n-hexane. Cat - 6 : 2.428 of DNBP was dissolved in MgCld2-EHA solution prepared by the same procedure as the case of Cat - 5 . After the conduction of same TiCl, treatment for Cat - 5 , the solid was treated again with 250ml of TiC1, at 120°C for 2h. The obtained solid was further washed with n-hexane. Cat - 7 : 1.75mol/l of n-ButhylMgCl was prepared in di-n-butyl ether from Mg and n-Butylchloride. HC(OEt), was added to the Grignard solution
16. Characterization of Mg/Ti Type Catalysts
173
(HC(OEt)JMg=lmol/mol) at room temperature and gradually heated up to 80°C and maintained at the temperature for 4h. The precipitated solid was washed with n-hexane. log of the solid was treated with 2.2.2-trichloro ethanol(TCE) (TCE/Mg=0.3ml/ml) to obtain Mg component. After washing with n-hexane and toluene, Mg component was treated with lOOml of TiC1, at 90°C for 2h. The obtained product was further washed with n-hexane. Cat - 8 : log of Mg(OEt), and 0.02ml of DNBP was co-ground under the same condition as the case of Cat - 1 preparation. Twice TiCl, treatments at 120°C for 2h each were conducted and the product was washed with n-hexane. Cat - 9 : Mg component was prepared with n-ButylMgCl and Si(OEt),. The solid obtained( log) was treated with DNBP(0.02mol) and Tic&(100ml) at 120°C for 2h. After remove out the solution, solid part was trearted with 1OOml of TiC1, at 120°C for 2h. The product was further washed with n-hexane. Cat - 10 : Mg component was prepared by the same procedure as the case of Cat- 7. And DNBPniCl, treatment was conducted with C a t - 9 preparation method. Characterizations of Catalysts Crystallographic evaluation of catalyst solid was conducted by X-ray diffraction. (XRD) Ti and Mg contents were determined by normal elemental analyses. Ti/Mg molar ratio of catalyst particle surface was measured by X-ray photoelection spectroscopy.(XPS , Kratos Exam 800) It was observed that peak intensities of Ti and Mg were decreased with increasing of X-Ray exposing time. Thus, the amount of the element originally exsisted on the surface was determined by extraporation of the intensity-time curve to time zero. Propylene Polymerization Slurry polymerizations in n-heptane were conducted with various catalyst prepared at 48°C under atmospheric propylene pressure with 4Omml of AlEt, cocatalyst. Initiation rate and polymerization rate decay were investigated from time-rate profile.
174 M. Murata, A. Nakano, S. Kanazawa a n d M. lmai
Results and Discussions Figure 1 illustrates XRD patterns of 4 different catalysts. Each figure shows a) Cat - 1 ,b) Cat - 6 ,c) Cat - 7 and d) Cat - 10 ,respectively. a) (prepared from MgCl,) and b) (prepared from MgCld2-EHA) indicated the typical MgC1, crystal structure with the peaks at 15" ,30° to 35" and 50' . c) (prepared from Mg(0Et)Cl without donor) and d) (prepared from Mg(0Et)Cl with donor) have new peak at around 10' to 13" which was not observed in a) or b). It could be confirmed that all the catalysts from non-MgCl, (Cat - 7 to Cat - 10) had this new peak although catalysts from MgC1, (Cat - 1 to Cat - 6) did not have. These results clearly indicate that new crystal face of long lattice distance, which does not have in the catalyst from MgCl, , is appeared in the solid from non-MgC1,. In another word ,catalysts from non-MgCl, component probably have different crystallographic structure from so-called MgC1,. It might be Ti- Mg cocrystal like structure since the appearance of the new XRD peak is independent of existence or absence of internal donor. In order to investigate Ti atoms situation in the catalyst particle, Ti/Mg ratios of both whole (average) and surface of particle were examined. In table 1 , Ti/Mg ratio of whole catalyst solid and that of surface determined by XPS are summarized. In Cat - 1 to Cat - 4 which were prepared by milling of MgCl,, it could be seen that Ti/Mg ratio of surface was higher than that of whole , This result suggests that Ti atoms are locally concentrated on the solid. Cat - 5 and Cat - 6 prepared from MgCld2-EHA solution had higher Ti/Mg ratio of whole than that of surface ,indicating that this type of catalyst contained Ti atoms located in the particle where the species would be silent by XPS measurement. Cat - 7 to Cat - 10 from non-MgC1, components also had higher Ti/Mg value of whole than that of surface , showing similar phenomenon to the cases of MgCldZEHA. However, the major difference between MgCld2-EHA and non-MgC1, type catalysts was their crystallographic structure of whole particle as shown by XRD evaluation. Based on these results , catalyst particle structures are proposed as shown in Figure 2. In Milling type catalysts of Cat - 1 to Cat - 4 , T i atoms is deposited on MgC1,. In MgClJ2-EHA type (Cat - 5 and
16. Characterization of Mg/Ti Type Catalysts
175
Cat - 6) , small size of particles having MgC1, milling type structure are agglomerated since the particle should have MgCI, crystal structure and some Ti atoms should be exist in the solid. This structure can also be understood from the process of catalyst preparation , that is , fine MgC1, powder might be formed at the early stage of the reaction of MgCld2-EHA solution with excess TiCl, , where the very rapid reaction of 2-EHA and TiC1, may take place and fine particle of MgC1, may be precipitated as the result. In non-MgC1, type catalysts (Cat - 7 to Cat - l o ) , Ti atoms are dispersed in the particle and formation of "Ti/Mg cocrystal" like structure might be speculated. As shown here , it can be concluded that fundamental structures of catalyst are devided to two category. One is that Ti atoms dispersed on MgC1, and the other is that Ti is dispersed in the particle. These drastic change in the structure might be attribated to the Mg component which is used as the starting material for catalyst preparation. Figure 3 shown the time-rate curves of propylene polymerization with different catalyst combined with AlEt,. Here ,three catalysts prepared from different Mg compounds of MgCl,(Cat - 4) , MgC142-EHA(Cat - 6) and Mg(OEt)Cl(Cat - 10) are compared. And all catalysts contain same internal donor of DNBP. Both Cat - 4 and Cat - 6 showed rapid initiation and decay type profile. It is considered that this similarity is from equivalent catalyst structure discussed previously. In compare with this , Cat - 10 showed relatively slow initiation , suggesting slow initiation of Ti atoms located in the catalyst particle. Bottom three figures in Figure 3 shows the reciprocal rate-time curves. In all cases , linear relationships were observed for rate decay polymerizations. These indicated that 2nd order rate decay was took place. From the slope of the line decay constant (kd) values were determined and plotted against Ti/Mg ratio measured by XPS. Figure 4 shows the results. kd values were increased with increasing surface Ti/Mg ratio. This results clearly indicate that kd is controlled by the concentration of surface Ti atoms. However, the correlation of MgC1, type was different from non-MgC1, type. At the same Ti/Mg ratio of surface, non-MgCl,
176 M. Murata, A. Nakano, S. Kanazawa and M. Imai
catalyst has much lower kd value in compare with MgCl, type one. In addition to this it could be expected that active sites in the particle of non-MgCI, type catalyst which is hard to form from MgC1, might be very stable during the course of polymerization. Conclusions Several catalysts were prepared from MgCI, and non-MgCI, from some organo-Mg compounds. In the catalysts with MgCl, as the Mg source, it could be confirmed that Ti atoms were mainly located on MgC&. In contrast with this, non-MgC1, type catalysts from organo-Mg components had the structure that Ti atoms were dispersed in the particle. Changing of initiation rate and decay constant with different catalysts could be understood by consideration of the differences in catalyst structures.
car-I
ca1.4
cat.-7
cat.-10
I5 20 25 30 35 40 45 50 20 (dcgnc)
Figure 1
15 20 25 30 35 40 45 50 28 ( d e w 4
XRDresults
16. Characterization of Mg/Ti Type Catalysts
Table I
Cornparson of Ti/Mg ratios of whole catalyst and surface Elemental Analysis (whole) Ti ( ~ 1 % ) Mg ( w ~ % ) TWg
Catalyst
XPS (surface) TMg (moYmol)
(moUmd)
cat.-l cat.-2 cat.-3
MgClz MgClZ MgC12
3.2 0.3 2.5
22.3 25.4 16.7
0.072
0.10f0.01
0.006
0.012f0.02 0.22f0.03
0.076
4.3 14.5 0.15 0.16 f 0.02 cat.-4 MgClz ................................................................................................................... cat.-5
MgClZ / 2-EHA 10.0 0.34 0.24 f 0.04 14.8 cat.-6 MgClz I 2-EHA 0.11 *0.02 0.14 ................................................................................................................... 2.3 10.9 cat.-7 Mg(0Et)CI 4.5 19.2 0.18 0.16f0.01 cat.-8 Mg(0Et)Z cat.-9 n-BuMgCI ISi(OEt)4 cat.-10 Mg(0Et)CI
Figure 3
1.7 3.9 1.7
17.3 17.7 17.3
0.050
0.038f0.008
0.11
0.060f 0.01 0.030 f0.002
0.050
h p y l e n e Polymerization Rates with Different CaUbWs
177
178 M. Murata, A. Nakano, S. Kanazawa and M. Imai
50
t
Ti/Mg (surface) (mol/mol)
Figure 4 Correlation between Ti/Mg ratio of Catalyst Surface and 2nd Order Rate Decay Constant
references 1) P. C. Barbe , G . Cecchin and L. Noristi , Adr. Polym. Sci. , 81,l(1987). 2) K.Soga ,T. Shiono and Y. Doi , Makromol. chem. ,189, 1531(1988). 3) M.Terano ,T. Kataoka and T. Keii , Catalytic Olefin Polymerization T. Keii ,K.Soga(Eds.) ,Kodansha Tokyo ,1990 P55. 'I
I'
I79
17. Mechanism of the First Steps of the Isotactic Polymerization with Metallocene Catalysts
W. Kaminsky, M. Arndt University of Hamburg
1. Introduction
Since the beginning of the polymerization of propene to isotactic polymers with Ziegler-Natta catalysts it was an open question, what the stereospecifity controls. Because the prochiral olefins like propene or l-butene have no chirality, Natta proposed that the insertion of the monomers take place in a chiral structure1I2). There are two possibilities for this: First, the monomer forms at leaat after the second insertion step into a titanium hydride or titanium alkyl group a chiral carbon. This chirality can influence the next and the following insertion steps (chain end control)=. Ti
-
CH2
-
y 3 CH 1
-
CH2
-
CH2
- CH3
Second, the active center is chiral independent of the polymer chain (enantiomorphic side control). The enantiomorphic site control could be given at the surface of heterogeneous catalysts, forming si- or re-faces4). The si-enantioface is preferred because of the stereo hinderance of the methyl groups. What is mainly important for the stereo control? A lot of scientists prefer the enantiomorphic site control to be the main background for this; others find the chain end control most important. All experiments to add chiral donors to heterogeneous or supported catalysts to find an excess of an optically active oligomer, were not very successful5)
.
The situation changed when chiral metallocenes together with methylaluminoxane as catalysts were used6). It was clear now that a chiral active center is very important to give isotactic poly-
180 W.Karninsky and M. Arndt
mers. But still there were some experiments which show that also metallocenes (biscyclopentadienyltitaniumdiphenyl)can catalyze parts of isotactic polypropylenes'
.
2. Chain End Control To find out how big is the influence of the chain end control on the stereospecifity of polypropylenes catalyzed with metallocenes, titanocenes and zirconocenes with a chiral alkylligand were synthesized. 2-Methyl-butyl was used because of its chirality center in a j3-position to the transition metal. The bis(cyc1opentadieny1)titanium- or zirconium bis(2-methylbutyl compounds (1 and 2) were prepared by reaction of the biscyclopentadienyl metal dichlorids with lithium-2-methylbutyl.
cp\ CP
CH3 CHZ-CH-CHZ-CH~
/ Ti 7H3 'CHZ-CH-CHZ-CH~
'
or
These compounds were used as catalysts for the propene polymerization*) If the mechanism is right , so that these metallocenes react with MA0 forming a cationic spezies by transferring an alkyl group, one 2-methylbutyl group remains at the transition metal. The polymerization was carried out by different temperatures, a metallocene concentration of mol/l in 150 ml toluene, a propene concentration of 1,7 mol/l and a molar Al/Zr ratio of 5 x lo4' At temperatures below -20 OC only two or three polymer chains were formed by every active centre. Table 1 shows the 13C-NMR measured pentads of the resulting polypropylenes.
.
All polymers are soluble in toluene and show an atactic behavior. This means that the chain end control is not very strong, but
17. Mechanism of the First Steps of lsotactic Polymerization
TABLE 1
181
.
13C-NMR Measured Pentades of Polypropylenes Catalyst: Bis(cyclopentadieny1)zirconium bis(2-methylbutyl)
Pentade
30
OC
7
-20
OC
OC
-60
OC
-35
OC
(Ti)
0.052
0.085
0.106
0.140
0.430
0.124
0.173
0.182
0.202
0.224
0.076
0.085
0.075
0.072
0.030
0.100
0.108
0.102
0.120
0.047
0.245
0.248
0.255
0.242
0.188
0.157
0.139
0.132
0.107
0.040
0.036
0.031
0.022
0.016
0.011
0.113
0.069
0.055
0.041
0.012
0.091
0.060
0.062
0.052
0.012
there are some effects. The chain end control increases with decreasing temperature. It is much stronger by the titanium than by the zirconium compound. The pentads contain isolated r dyads which are characteristic for a chain end control. In this model it must be independent for the pentads, which alkylated metallocene compound is used, if the model of the cationic active center for the metallocene catalysts is right. The picture becomes clearer if the isotacticity, the different sequence lengths are calculated by the method of Randallg) (see Tab. 2).
Isotacticity I = [(mm) + 0,5 Isotactic sequence lenght niso = 1 : [(rr) + Syndiotactic sequence length nr = [(rr) + 0,s msequence length nm [(mm) + 0 , 5
-
(M)] x 100 0,s (M)] (mr)] : [0,5(mr)l ( = ) I : [O15(mr)l
182 W. Kaminsky and M. Arndt
TABLE 2
13C-NMR Measured Isotacticities and Iso, S y n and Racemic Sequence Length of Polypropylenes
30
OC
7
OC
-20
OC
-60
"C
-35
OC
50.38
56.15
57.34
60.28
75.33
"is0
2.02
2.28
2.36
2.53
4.09
"rn
1.50
1.69
1.74
1.88
3.17
1.48
1.32
1.29
1.23
1.13
1.1. /%
"r
(Ti)
It is interesting to note that the titanocene shows polypropylenes with a higher isotacticity at 35 O C than the zirconocene at 60 O C . The reason for it could be the shorter bond length between the carbon atom and titanium in relation to zirconium.
-
-
The result is that even starting with chiral alkyl groups on the metallocenes by very low polymerization temperatures it is impossible to prepare highly isotactic polymers.
3. Enantiomorphic Site Control Highly isotactic polypropylenes can be obtained using chiral zirconocenes and MAO. This indicates the high influence of the enantiomorphic site control. To measure the influence of chiral active centres optically active metallocenes were prepared. Two methods to separate the racemic mixture of ethylene(bistetrahydroindeny1)zirconium dichloride or dimethylsilyl(bistetrahydroindeny1)zirconium dichloride into the enantiomers are given. 1. reaction with S-binaphthol 2. reaction with o-acetyl-R-mandelate Among these reactions, diastereomers are formed which could be obtained in pure forms. In the first case the S-zirconocene forms a
17. Mechanism of the First Steps of Isotactic Polymerization
183
complex with the S-binaphthol which crystallizes while the other diastereomer remains in the solution. The o-acetyl-R-mandelacic reacts only with the S-zirconocenes. This complex could be separated from the remaining compounds (see Fig. 1).
n
n = 6-20
FIG. 1
Structural Formula of (S)-[l,l'-ethylenebis(4,5,6,7-tetrahydro-l-indenyl)]zirconiumbis(O-acetyl-(R)-mandelate) and Methylalumoxane
The oligomerization starts when an olefin undergoes insertion into a transition metal hydrogen or methyl bond formed by methylation with methylalumoxane (Scheme 1). There are mainly 1,2 and very few 2.1 insertions. Subsequent insertions lead to chain growth. Chain termination takes place by j3-hydrogen transfer to the transition metal atom or to a complex bound olefin, resulting in formation of the hydrid or alkyl transition metal compound in addition to the oligomer. The former, in furn, allows new insertion steps to occur. The formed dimers do not contain a chiral carbon atom. Optical activity is first observed in trimers and higher oligomers")
.
184 W. Kaminsky and M. Arndt
-&
R
c-; SCHEME 1
R
P
B
0,08
0947
0,05
09x9
R
Dherization of Propene (P) and 1-Butene (B). The Amount of Different Isomers is Measured by Gaschromato9raPhY
4. Propene Oligomerization
The average molecular weights of the produced oligopropenes can be controlled by adjustment of reaction temperature and monomer concentration. Ethylenebis(tetrahydroindenyl)zirconi~di(O-acetyl(R)-mandelate) was used as transition metal compound. To obtain sufficient amounts of product with a propene feed rate ‘of 2,5 to 20 ml/min the reaction time had to be extended to between 15 and 24 hours. The reaction temperature was varied in the range from 20 to 60 O C . Depending on reaction time yields ranged from 18 to 24 g of oligopropenes. For reaction temperatures of 30 OC and above the products are oily liquids whereas oligomerization at 20 OC yielded waxy products. The reaction temperature has a great effect on the average degree of oligomerization”
.
17. Mechanism of the First Steps of lsotactic Polymerization
185
The products contain oligopropenes of various degrees of oligomerization. By means of gas chromatography branched alkenes from dimers up to nonamers could be detected. Figure 2 shows the capillary gaschromatogram of a mixture of oligomers produced at 50 O C . In the various oligopropene fractions a number of by-products (isomers) are formed next to the main component. Table 3 gives the amounts of olefins differing in degree of oligomerization. The table not only shows a shift of distribution maxima with temperature but also makes it clear that the oligomerization can be conducted in a way that mainly trimers through heptamers are formed. Provided that the number of active centers be independent of temperature the amounts of lower oligomers should grow with increasing temperature. Up to a reaction temperature of 60 OC this is the case. when the oligomerization is carried out at 70 O C , however, the sume of dimers to nonamers decreases indicating a slight decrease in the number of active centers. TABLE 3
Massdistribution of Propene Oligomers at Different Temperatures
T [ O C )
30 40 50 60 70
Gew. -%
Di
Tri
Tet
Pen
Hex
Hep
OCt
Non
EDi-Non
0,l 1,3 214 4,O 315
210
311 619 1115
415
413 814 11,3 12,l 1415
4,l 113 9,4 9,4 1115
4,2 6,9 5,8 6,l 610
4,l 5,2 2,8 2,9 215
26,4 49,5 64,3 85,s 8218
512 819 14,4 1115
18,8 17,l
0,3 1212 17,2 16,2
5. Isomers
The propene oligomers synthesized with the (S)-En(IndHq)2Zr(C10H804)2/MAO catalyst predominantly consist of 1-alkenes as they are formed by lI2-insertion and isomeric by-products. In order to record all isomers of an individual degree of oligomerization, the products were analytically separated by gas chromatography over a 50 m capillary column.
186
W. Kaminsky and M. Arndt
Independent of reaction temperature and monomer concentration, the capillary gas chromatogram of the dimersfeatures one main peak corresponding to 2-methyl-1-pentene and several other peaks of lower intensity. The fraction of propene trimers, by contrast, is made up of a mixture of several isomers (Fig. 2).
Tri
Tri,
,
Tri,
Tri,
A
c
I
I
FIG. 2
d
10 12 t [min] Capillary-Gaschromatographic Separation of Propene Trimers Synthesized by 50 O C
The composition varies with reaction temperature and monomer concentration (Tab. 4). TABLE 4 Distribution of Isomers in the Trimer Fraction of the
Propene Oligomerization as a Function of Temperature and Propene Flow Rate mol/l Catalyst: (S)-En(IndH4)2Zr(CloH804)2 5 x MA0 4,2 x 10- mol a1 units/l Reaction time: 24 h; propene pressure: 2,2 bar T [OC]
Propene [ml/min]
30 40 50 50 50
10 10 215 5 10
50 50 60 70
15
20 10 10
Concentration w t . - % : Tril Tri2 Tri3 99,3 96,s 85,4 87,3 88,2 89,2 91,8 80,2 71,l
-
-
113 519
0,4 519 3,3 1,9 1,3
515
417 417 413 713 10,2
1,2
4,3 6,9
Tri4
-
Tri5
111 1,l 0,9
or7 or9 210 211 212 212 212
1,s
st2
2,3
615
-
-
XTri2-5 017
218 14,9 12,o 917 812 817 18,3 25,9
17. Mechanism of the First Steps of Isotactic Polymerization
187
At 30 O C and 10 ml/min of propene feed 99 % of the trimer fraction consists of 2,4-dimethyl-l-heptene (Tril) which is formed by 1,2insertions. A marked decrease in the relative concentration of this main component is observed at higher oligomerization temperaures as well as lower monomer feed rates. Simultaneously, other isomers that are formed by double bond migration, 2,1-, and 1,3insertion gain significance. Scheme 2 assigns structures to the individual isomers.
Tril
2,4-Dimethyl-l-heptene
Tri2
2,4-Dimethyl-2-heptene
Tri3
2,6-Dimethyl-l-heptene
Tri4
2,4,5-Trimethyl-l-hexene
+
2,4,6-Trimethyl-l-heptene SCHEME 2
Isomers of Trimeric Oligopropene
The trimer Tri2 stems from Tril via double bond migration. This reaction becomes increasingly important at higher temperatures. Tri3 is formed through an initial 2,l-insertion followed by a 1,3insertion which, in turn, results from rearrangement of another 2,l-insertion after the first one. This order of events becomes plausible when one considers that a regular 1,2-enchainment is sterically hindered after a 2,l-insertion thus favoring another 2,l-insertion. It is this steric hindrance between two adjacent methyl groups in a 2,1-1,2-sequence that is responsible for the relatively low concentration of Tri4
188
W.Kaminsky and M. Arndt
which contains an initial 2,l-enchaiment followed by two insertions with lI2-orientation. Finally, Trig is formed as Tril by three consecutive 1,2-insertions. This time, however, the initial propene unit is inserted into a Zr-methyl bond as it is formed in a reaction of the zirconocene with methylaluminoxane as opposed to a Zr-hydrogen bond resulting from the common j3-hydride transfer. The isomers Trill Tri2, and Tri5 were positively identified by NMR- and mass spectrometry. The propene tetramer contains two asymmetric carbon atoms. Therefore the synthesis with chiral metallocenes leads to the formation of diastereomers. The optical activity of the chiral oligopropenes was determined at various wavelengths. Polarimetric measurements were not only conducted with product mixtures from oligomerizations at various monomer concentrations and reaction temperatures but also with individual fractions of dimers, trimers, and tetramers. To this end the product mixtures were fractionated by distillation over a split tube column (Table 5). TABLE 5
Specific Optical Rotation [a]25 of the Trimers, Tetramers and Mixed Oligomers at Different Wavelengths and Different Reaction Temperatures and Propane Flow Rates
40 40 40 40 50 50 60 60 70 70
589 546 436 365 589 365 589
365 589 365
+ 1,7 + + + + +
2,o 3,7 6,5 0,9 3,O + 0,4 + 1,5
+
0,08
+
0114
+ 3,5 + 4,3 + 7,3 + 11,8 + 2,8 + 8,7 + 2,2 + 6,6 + 1,8 + 5,6
+ + + + + + + + + +
3,O 3,5 5,8
9,2 2,6 7,6 2,2 6,8 1,9 5,6
17. Mechanism of the First Steps of lsotactic Polymerization
189
The propen oligomers starting with the trimers are dextro rotatory. As expected, the achiral dimer does not show any optical activity. The trimer, 2,4-demethyl-l-heptenef which was produced catalyst ~ O ~ ) ~ bears / M A O S-confiwith the ( S ) - E ~ ( I ~ ~ H ~ ) ~ Z ~ ( C ~ O H guration, since a specific optical rotation [ a ] of~ -6.1 ~ ~ was determined for the R-enantiomer' )
.
With increasing reaction temperatures the specific optical rotation of all oligomers decays. This proves that the stereoselectivity of the organometallic catalyst decreases at higher temperatures. The optical activity of the tetramers is higher than that of the trimers. This increase is caused not only by the additional chiral carbon but also by an increase in stereoselectivity due to the longer alkyl chain attached to the active center. This difference is particularly significant at elevated temperatures. While the specific optical rotation of the trimer is lowered by a factor of 20 in the temperature interval1 from 40 to 70 OC, it is only reduced by one half for the tetramer. The extent of stereoselectivity in the chiral synthesis can be checked by determining the enantiomeric excess of the optically active alkenes in the products. Since no literature data was available for the optical rotation of the enantiomerically pure alkenes, their optical purity was determined through gaschromatographic resolution of enantiomers by means of an optically active column. Thermostable substituted Cyclodextrines are best suited as asymmetric phases"). The trimer, 2 ,4-dimethyl-l-hepteneI was resolved into its enantiomers by capillary gaschromatography with an octakis-(6-0-methyl-2,3-d-O-pentyl)-y-cyclodextrine phase. At low temperatures (20 "C) the formation of the first chiral center proceeds with a high selectivity of 97,6 % leading to an enantiomeric excess of 95,3 %.At higher temperatures the ee-value decreases to 23,8 % at 50 OC and 2,5 % at 70 OC. As expected, the
190
W. Karninsky and M. Arndt
ee-value of the trimer produced with the racemic catalyst is 0 (Fig. 3 ) .
-----J
i
10 12 20
95,3
FIG. 3
10 30 73,4
Cminl T ["c]
10
10
10
lo
t
40
50
60
51,3
23,8
10,9
70 2,s
ee
[%I
Asymmetric Oligomerization of Propane. Gaschromatographic Separation of 2,4-Dimethyl-2-heptene(Trimer) Using Octakis(6-o-methyl-2,3-di-O-pentyl)cyclodextrine
It is evident that at high oligomerization temperatures the isotacticity is low. At the same temperature it is higher for the tetramers. It could be calculated how high is a hypothetic eevalue from isotactic polypropylene by using the mm triads (see Scheme 3 , next page).
The results are given in Tab. 6. TABLE 6
Comparison of Measured and Calculated ee-Values of Propene Oligomers and Polymers Temperature ( ' C )
Tetramers
Polymers
50
7314 51, 3 23,8
38,l
95,s 92,8 90,o 87,s
70
2f5
510
20 30 40
Trimers 95,3
mmmm (0,972) (0,958) (0,939) (0,918) 68,O (0,802)
17. Mechanism of the First Steps of lsotactic Polymerization
191
m
2
K \ \
.
1
K
ka
A-B ee= A+B
1
ee=(2kr2-1)
SCHEME 3
1
jk,2 =-(ee+l)
2
Calculation of the ee-Value from the Isotacticity of Polypropylenes
By an oligomerization temperature of 50 O C , the trimers show an ee-value of 23,8, the tetramers of 38,1, and the polymers of 8 7 , 5 . This shows the great influence of the growing chain on the stereospecifity. In conclusion, to come to a high isotacticity, a chiral metallocene is needed. The first insertion steps show a low stereospecifity which increases with the growing polymer chain.
192 W. Kaminsky and M. Arndt
6. References
1. G. Natta, Angew. Chem. l2, 393 (1956) 2. G. Natta, P. Pino, G. Mazzanti, R. Lanzo, Chem.Ind. 39, 1032 ( 1957 ) 3. V. Venditto, G. Guerra, P. Corradini, R. FUSCO, Polymer 3 l , 530 (1990)
4. L. Cavallo, G. Guerra, L. Olive, M. Vacatello, P. Corradini, Polym.Commun. 30, 16 (1989) 5. P. Pino, P. Cioni, J. Wei, J.Am.Chem.Soc. 109, 6189 (1987) 6. W. Kaminsky, K. Kiilper, H.H. Brintzinger, F.R.W.P. Wild, Angew.Chem. 97, 507 (1985); Angew.Chem.Int.Ed.Eng1. 24, 507 (1985) 7. J.A. Ewen, J.Am.Chem.Soc. 106, 6355 (1984) 8. 0. Rabe, Dissertation Hamburg 1993 9. J.C. Randall, Polymer Sequence Determination, Academic Press, New York 1977 10. W. Kaminsky, A. Ahlers, 0. Rabe, W. K h i g , in: Organic Synthesis via Organometallics, D. Enders, H.J. Gais, W. Keim (eds.), Vieweg, Braunschweig 1993, p. 151 11. W. Kaminsky, A. Ahlers, N. Mtjller-Lindenhof, Angew.Chemie 101, 1304 (1989); Angew.Chem.Int.Ed.Eng1. 28, 1216 (1989) 12. D.E. Dorman, M. Jantelat, J.D. Roberts, J.Organomet.Chem. 36, 2757 (1971)
193
18. Reaction Mechanisms in Metallocene-Catalyzed Olefin Polymerization
H. BRINTZINGER,
S. BECK, M. LECLERC, U. STEHLING and W. ROLL
Fakultat fur Chemie, Universitat Konstanz, 0-78434 Konstanz, Germany
ABSTRACT
1. Studies by 'H NMR on equilibria between contact ion pairs such as Cp2ZrCH3d+...H3C-B(C6F5)3d-and binuclear alkyl zirconocene cations of the type (Cp,ZrCH,),b
- CH,)
+
lead to the conclusion that these binuclear species must
generally be considered as participants in all homogeneous Ziegler-Natta systems.
2. Different polypropene chain lengths, which are obtained from cis- and trans1D - propene with the catalyst en(thind)2ZrC12/MA0,show that exchange of a-H with
a-D atoms affect the rate of chain growth by a large kinetic isotope effect; this supports the notion that an a-agostic interaction facilitates the olefin insertion step. 3. A strong increase in polymer chain lengths, which is caused by the presence of amethyl groups in ansa-zirconocene catalysts, is shown, by the effects of propene pressure on ,M ,
to be due to the suppression of the otherwise predominant direct
I3 - H-transfer to a coordinated olefin molecule by these a-substituents. INTRODUCTION Open questions with regard to the mechanisms of metallocene-catalyzed olefin polymerizations concern the equilbria which lead to catalyst activation and deactivation, the factors which control the rate and stereoselectivity of the olefin insertion step, and the mechanisms of chain termination. Some recent studies related to these questions are reported here.
EXPERIMENTAL
I . Solutions of B(c~F,),
' 1 and of CP~Z~(CH,)~ in
C,D,
(10 - 40 mM) were
combined in various proportions under extreme exclusion of humidity (flamed glassware, glovebox techniques) and their 'H NMR spectra measured at room temperature on a Bruker AC 250 MHz spectrometer.
194 H . Brintzinger, S. Beck. M. Leclerc, U. Stehling and W. Roll
2. Cis- and trans-a-deuterated propene were prepared by lithiation o f cis- and trans-chlorpropene, respectively, and subsequent cleavage with D20. The samples thus obtained were purified by repeated distillation from dry MAO. Polymerizations were conducted at 5OoC with en(thir~d)~ZrCI,/MAOin toluene ([Zrl =
M, Al:Zr
= 1200:l 1 at 1 bar. The molecular weights of the polymer products were determined
from their 13C NMR spectra, run at 13OOC in CD ,C , ,I
by the ratio of n-propyl end-
group and methyl side-chain signals at 14.3 and 20.0-21.8 ppm, respectively. 3. Polymerizations were conducted with MAO-activated Me2Si(benzind)2ZrC12and Me,Si(2-Me-ben~ind)~ZrCI,([Zrl = 1.25
M, A1:Zr = 15800:1, T,
= 5OoC), at
propene pressures between 1 and 7 bar. The molecular weights of the polymer products were determined by GPC (BASF AG, Dept. ZKP).
RESULTS
1. Binuclear Cations in Metallocene-Based Zlegler-Natta Catalysts. Indications for the occurrence of binuclear cations of the type (Cp2ZrCH3),@CH3)
+
have been
reported in several instances.'-4 In the 'H-NMR spectra of reaction systems containing B(C6F5), and an excess of Cp2Zr(CH3), in C&6, we observe at room temperature t w o distinct species of this kind. Based on the chemical shifts and the relative intensities of each of their signal sets, both o f these species are undoubtedly ion pairs of composition (Cp2ZrCH3)2@-CH3)+ H&-B(C&),-;
since one of them becomes more
prominent on dilution at the expense of the other, we assign the former t o a solventseparated and the latter t o an associated ion pair consisting of a binuclear cation and a methyl borate anion (Figure 1). For the reaction described by equation 1, we determine an equilibrium constant K, and H,C-B(C6F,),-
= 1.O
f 0.2; this indicates that Cp2Zr(CH3),
+.
are equally strong Lewis bases toward the cation CpzZrCH3
Even in the presence o f excess Lewis-acid activator A, binuclear cations could be present in amounts comparable t o the contact-ion pair CP~Z~CH,~+.-H,C-Ab-,
if
excess A is capable of efficiently complexing the anion H3C - A - according t o eq. 2: 2 Cp2ZrCH,d+-H3C -Ab-
+ (Cp,ZrCH,),(p
- CH,)
+
f A-H,C
-A -
(2)
18. Mechanisms of Metallocene-Catalyzed Olefin Polymerization
6+5.4
6+0.3
6-o*1
= 6+5.6
195
6+5.7
1.020.2
6-0.1
0 + H,C-B(C,F,), (6+1.3, separated)
=
0.520.1 mM"
0 H3C-B(C6F5)3
(&+lo, associated)
(c.f. Li+ H$-B(C6F,),-
6+0.85)
Figure 1. Equilibria between contact ion pairs, excess dimethyl zirconocene and alternative binuclear zirconocene cations, with 'H NMR shift values. If binuclear cations do not contribute to chain growth, as indicated by a recent study,
4,
but still allow chain termination to occur, their presence might explain the
shortening of chain fengths associated with elevated zirconocene concentration^.^) 2. The Olefin Insertion Step. In previous studies, we have observed stereokinetic
isotope effects 61 for the hydro-oligomerization of cis- and trans-1D-1-hexene by Cp2ZrC12/MA0and en(thind),ZrCI2/MAO;') based Ziegler-Natta catalysts
these and related studies on scandocene-
support the notion that an agostic interaction of an
u - H atom of the migrating polymer chain with the metal center facilitates the olefin insertion step, as proposed by Rooney, Green and B r o ~ k h a r t . ~ ~ ' ~ )
196 H . Brintzinger, S. Beck, M. Leclerc, U . Stehling and W. Roll
We have now studied the polymerization of cis- and trans- 1D-propene with en(thind)2ZrCI/MA0, and find that the mean chain length obtained with the trans isomer, PN(trans) = 128, is about 2.8 times larger than that obtained with the cis isomer PN(cis) = 45. This indicates that the olefin insertion step is favored by a large isotope effect (k,/k,
= 2.8) when an a-H atom, rather than an a-D atom, is placed in
the agostic bridging position, as it is to be expected from consecutive insertion reactions of trans- and cis- 1D-propene, respectively (Figure 2). These results provide experimental support for recent theoretical studies on the course of the olefin insertion step in cationic metallocene catalysts.l1-l3'
0-HT
\ DHC=CMeR'
cis-1D-propene:
kD PN = 45
kD
0-HT
\ DHC=CMeR'
Figure 2. Reaction schemes for consecutive insertions of trans-1D-propen (top), which place an a-H atom in the agostic bridging position, and of cis-1D-propene, which place an a-D atom in this position.
3. Chain Termination Mechanisms. Previous metallocene-based polymerization catalysts have given much shorter polymer chain lengths than classical heterogeneous catalysts; recently however, polymers with molecular weights of several hundred thousands have become available by use of ansa-zirconocenecatalysts with a-methyl s u b ~ t i t u e n t s . ' ~ ~In' ~studies ) on the effect of propene pressure on the polymer
18. Mechanisms of Metallocene-Catalyzed Olefin Polymerization
197
molecular weights, we find the molecular weight of polypropene obained with (CH3I2Si-bridgedbis(indeny1) and bis(bedndenyl1complexes to dependent very liitle on propene concentration (Table 1). This indicatesthat the dominant chain termination process is R-H transfer to a coordinated olefin molecule, in accord with previous evidence from studies on the end-groupdistribution in ethene-propenecopolymers. Catalyst
L
IIMAO
Benzlnd
1
0.31
29 800
88
IIMAO
Benzlnd
2
0.66
35 100
88
IIMAO
Benzlnd
3
1.02
38 600
88
IIMAO
Benzlnd
7
2.43
39600
90
IIIMAO
2-MeBenzlnd
1
0.31
80500
92
IIIMAO
2-MeBenzlnd
2
0.66
137 100
92
IIIMAO
2-MeBenzlnd
3
1.02
182 200
93
II/MAO
2-MeBenzlnd
5
1.72
247 700
93
plbar
c(C3H6)
M ,
% mmmm
Table 1. Effect of propene pressure on the molecular weight of polypropene obtained with MAO-activatedMe2Si(benzindI2ZrCl2(I,top) and Me2Si(2-Me-benzind)2ZrC12(11, bottom). T, 5OOC; [Zrl 1.25*10-6mol/L; [AIl:[Zrl 15 800. With o-methyl substituted ansa-zirconocenesas catalysts, however, the molecular weight of polypropene shows a strong increase with propene pressure (Table 11, in accord with expectations for a chain termination by R-H transfer to the metal center. From a plot of PN-' versus c(C3H6)-' (Figure 31, we determine that both types of catalysts have almost identical rate constants for R-H transfer to the metal (kTM), whereas the rate constant for R-H transfer to olefin (kTo) is about ten times smaller for the complex with a-methyl substituents. These substituents thus appear to interfere with the transition state for R-H transfer to a coordinated olefin (Figure 41, which appears to be sterically rather demanding, as indicated by a relatively large lateral extension angle of more than 180". 'I
198 H. Brintzinger, S. Beck, M. Leclerc, U. Stehling and W. Roll
2.50
2.00
1.50
a \ 0
z
0
1.00
0.50
0.00
0.50
1.00 1
/
1.50 c(C,H,)
2.00
2.50
3.00
3.50
[Vmoll
Figure 3. Plot of PN-' vs. c ( C ~ H , ) - ~for Me2Si(benzind)2ZrC12(I, top) and
Me2Si(2-Me-benzind)2ZrC12(11, bottom). PN-' = c(C,H,)-~ *(kTM/kp) k,,/k,
+ kTo/kp gives
as the slope and kTo/k, as the abscissa intercept of each graph.
Figure 4. Model of the reaction complex for 13-H transfer to a coordinated olefin; (I-
methyl groups (shaded) interfere with the formation of this reaction complex.
18. Mechanisms of Metallocene-Catalyzed Olefin Polymerization
199
ACKNOWLEDGEMENTS Financial support of this work by the VW Foundation and BMFT is gratefully acknowledged.
REFERENCES 1.
X.Yang, C.L.Stern and T.J.Marks, Angew. Chem., Int. Ed. Engl. JQ4,1406 (19911, Organometallics N, 840 (1991).
2.
G.G.Hlatky and H.W.Turner, quoted in ref. 4.
3.
M.Bochmann and S.J.Lancaster, J. Organomet. Chem.,
a, C1 (1992);
M.Bochmann, results reported a t symposium "40 Years Ziegler-Natta Catalysts", Freiburg (1993).
14,91 (1993).
4.
N.Herfert and G.Fink, Makroml. Chem. Rapid Commun.,
5.
W.Kaminsky, M.Miri, H.Sinn and R.Woldt, Makromol. Chem. Rapid Commun.
4, 41 7 (1983); W.Kaminsky, K.Kulper and SNiedoba, Makromol. Chem. Macromol. Symp.
3,377 (1986); W.Kaminsky, A.Bark
and R-Steiger, J. Mol.
Catal., 74, 109 (1992). 6.
L.Clawson, J.Soto, S.L. Buchwald, M.L.Steigerwald and R.H.Grubbs, J. Am. Chem. SOC.,1pz, 3377 (1985).
7.
H.Krauledat and H.H.Brintzinger, Angew. Chem., Int. Ed. Engl.,
B,1412
(1990); M.Leclerc and H.H. Brintzinger, in preparation. 8.
W.E.Piers and J.E. Bercaw, J. Am. Chem. SOC., 1 1 2 , 9 4 0 6 (1990); D.W.Cotter and J.E.Bercaw, J. Organomet. Chem. 417, C1 (19911.
9.
D.T.Laverty and J.J.Rooney, J. Chem. SOC., Faraday Trans. L9, 869 (1983).
10.
M.Brookhart and M.L.H.Green, J. Organomet. Chem.,
m, 395
M.Brookhart, M.L.H.Green and L.Wong, Prog. Inorg. Chem.,
(1983);
X,1 (1986).
11.
M.Prosenc, C.Janiak and H.H. Brintzinger, Organometallics, 11,4036 (1992).
12.
H.Kawamura-Kuribayashi, N.Koga and K.Morokuma, J. Am. Chem. SOC., 114 8687 (1992).
n,432 (1994).
13.
T.K.Woo, L.Fan and T.Ziegler, Organometalllics
14.
WSpaleck, M.Antberg, J.Rohrmann, A.Winter, B-Bachmann, P.Kiprof, J.Behm and W.A.Herrmann, Angew. Chem. Int. Ed. Engl.,
a,1347
(1992);
J.Rohrmann, V.Dolle, A.Winter and F.Kuber, Eur. Pat. Appl. 921 20287.5 (1991 1.
200
15.
H . Brintzinger, S . Beck, M. Leclerc, U . Stehling and W. Roll
E.Karl, W.RtiII, H.H.Brintzinger, B.Rieger and U-Stehling, Eur. Pat. Appl. 92108888.6 ( 1991 1.
m, 428 (1989).
16.
T.Tsutsui, A.Mizuno and N-Kashiwa, Polymer,
17.
P.Burger, K.Hortmann and H.H.Brintzinger, Makromol. Chem., Macromol. Symp., 66, 127 (1993).
20 I
19. Role of Ions in Coordination Polymerization of Olefins
F. S.Dyachkovskii Institute of Chemical Physics Russian Academy of Sciences, Chemogolovka, 142432, Moscow Region, Russia. ABSTRACT Studying of homogeneous csystem Cp2TiC12AlR2Cl it was shown that ions as Cp2TiRf play important role in the formation of active centers. More over by means of electroddysis the composition of ionic active centers have been determiaed for difFerent catalyhc systems. Using mass-spectrum technique the interaction of Cp2TiCH3' ions with ethylene in gas-phase was shown. Quantum-chemical investigation of Ti-C bond leads us to conclusion that deficiency of electron density on the titanium atom result m the deformation of Ti-C bond energy curve and decreasing of activation energq of insertion reaction of olefin mto Ti-C bond The ionic nature of active centers in Zr-cene catalytic systems will be discussed. INTRODUCTION It is well known that free ions are very reactive to unsaturated compound. In the gasphase ions react at very collision with saturated and unsaturated hydrocarbons. In solution the reactivity of ions is decreased due to sohation. But in the non polar solventa the reactivity of ions could be very lugh and even at low concentration their role might be important. Cationic and anionic polymerization processe% m hychcarbon s o h t are well studied, Depending on stabilization of gegenim and nature of solvent a free ions or ion-@ are formed. But role of ions in coordination polymerization of olefins needs more dew investigation. RESULTS AND DISCUSSION In the last years ions structure of active centers m homogeneous catalytic systems based on Ti and Zr is discussed in the litenrture very much. It is believed that active centers of Zr-cene catalyhc systems with MA0 have an ionic nature. In present paper the mechanism of homogeneous coordination p o l y m d o n , the reactivity of Ti€ bond, kinetic of macromolecule formation dependingof polarity of the catalytic complex will be discussed.
202
F.S. Dyachkovskii
Investigation of kinetic and mechanism of olefin polymerization in the presence of complex Cj~TiC12.AlR2Cl(A) showed, that not complex A itself, but particles in equilibrium with the complex are catalyhc active [l]. The rate of ethylene polymerization in the presence of complex A was very much depend on the small amount of impurities in the s o h t and was proportional to the square root of A concentration. It indicated that complex is dissociate for two particles. It was suggested that there are positive ions containing Ti in equilibrium with the complex A, the former bemg in fact ache m polyme&ation. Cp2TiC12 + AlR2Cl= Cp2TiRCl.AlRC13 Cp2TiRCl.AlRCl3 = Cp2TiR+ t AlRCl3Cp2TiR+ + ethylene = polymerization In agreement with this assumption the rate of the reaction of complex A with olefins was found to be proportional conductivity of the solvent and therefore was strongly depended on the nature of the solvent. For instance, it was considerably higher for benzene than for than for benzene. heptane, and for ch-le It was shown that there had been a CoIIVersion of the Ti-CH3 group into a Ti-C3H7 during the reaction of active complex with ethylene: Cp2TiCH3Cl.AlCH3C12 + C2H4 = Cp271'iC3H$L41CH3C12 The kinetic curves of hies reaction in Werend s o h t s is demonstrated on fig. 1.
t, min
Fig. 1. Kinetic cu~ve8for complex Ti-C3H7 formation and decomposition in heptane (l), benzene (2) and chlorobenzme (3).
19. Role of Ions in Coordination Olefin Polymerization
203
The direct proof of the positive charge of catalytically active ions containing titanium was achieved in a study of electroddysis of solution of the complex A [2]. Dichloroethane was used as solvent After complex Cp2TiCH3ClAlCH3C12 was subjected to electrodialysis, the number of ions containing titanium and passing to the cathode chamber was approximately 0.5 of all the ions moving through the membrane to another sides. Hence the majority of positive ions in the solution of complex A WM certain to contain a titanium atom. Titanium was not detected in the anode chamber after electroddym. In electroddysis of the complex Cp2Ti14CH3ClA114CH3C12 (€3) the titanium atoms were found to enter the cathode chamber together with the 14CH3 labeled g r o q ~and in quantities approximating the quantity of titanium. It may be concluded from the results that the catalytically active complex A dissociates on ions in solution according to the scheme Cp2TiCH3ClAlCH3C12 = Cp2TiCH3+ + AlCH3Cl3The study of ionic composition of the Ti% +Al(CH3)2Cl catalyst system in dichloroethane showed that only positive ions contain the titanium atom m this case. It is connected with the dissociation of complex CH3TiC12.AlCH3C13, on ions. The electroddysis method in the Ti(OR)4+AlR3 catalyst system confirmed the existence of the (ROhTi+, (C~HS)A~(OR~T~+ C ~[(C2H+4l(ORh]2Ti+ H~, and complex ions, depending on the AVTi ratio in the initial cataipt system. To make clear the role of ions in polymerization, the solution of the side chambers was enriched with the monomer. It the electroddysia of complexes A and B ethylene polymerization was observed only in the cathode chamber. The quantity of the polymer increased simultaneously with the increase in Cp2TiCH3+ ion mcentration m the cathode chamber. When complex B contained the14CHg labeled groups, the polyethylene obtained was radioactive. This shows that the polymer chain f d o n proceeds by the inmiion of ethylene molecules into Ti€ bond right in the ion Cp2TiCH3' We started to mvestigate the electroconductivity of Cp2ZrC12.AlR2Cl solubion m CH2Cl2. It was shown that conductivity of the complex solution at least 10 h e s higher than additive conductivity of its components. The total conductivity of complex sohtion L is m a good correlationwith the equation A-A m - k C1'2, where C is the concentrationof Zr complex. The fonnation of h e ions frm the complex CpzTiCH3Cl AlCH3C12 m gas-phase by mass-spectrum technique has been studied. For this purpose complex Cp2TiC12 ALMe2C1 was placed into the chamber of maas-spectrometer. The ions formation was detected. If ethylene
-
204
F.S. Dyachkovskii
Ions Calculated 1
~pt+i~12 fC2H4
2
cp2i'icl
3
CmTi
4
+
+
tC2H4 +C$4
CpTiCl K2H4
5
Cp2kH3 +C2H4
I
247.964 275.994 212.995 241.026 178.026 206.058 147.956 175.987 193.037 221.068
Mass Found
A
247.967
0.003
212.999 240.992 178.032 206.098 147.958 176.014 193.040 221.057
0.004 0.034 0.006 0.04
0.002 0.027 0.003 0.011
--
-
* This results were obtained together with Dr.Ueno in Kyoto University. From the figures we can draw the conclusion that different positive ions are formed including [Cp2TiCH3]+ during evaporation and ionivlhion of complex A. There is a good correlation between calculated mass and observed one. In the presence of ethylene no mass change in ion Cp2TiCl2+ was observed. On contrary, mass of ions as Cp2TiCI+, Cp2Ti+, CpTiC1' and CmTiCH3? was increased by the mass of ethylene molecular. The best correlation between calculated and observed mass was found for reaction of Cp2TiCH3+ ion with ethylene what confirmed the reaction Cp2TiCH3+ + C2H4 -> Cp2TiC+17t. It should be noted that last four ions 2-5 have the free coordination site, but Cp2TiC12' in tetrahedron structure has hot.results showed that ions [Cp2TiRIS type interact with ethylene in gas-phase and h e coordination site is important for that interaction. The discovery of Zr-cene/MAO catalysts in early 1980's generated renewed interest in our proposal that C n = + ions are active species m soluble c a m system. The ion structure of active centers [ C m MRLltX' type was shown due to extensive studies by Eischp], Jordar1(4], Boc-51, Zambelli[6], Marks[7] et.al. A key feature of these type of active centers is the vacant coordination site. The organic group R of t h cation ~ is incorporated into polymer chain. Cations exist m equilibriumof contact and sohrent-separated ion pairs.
19. Role o f Ions in Coordination Olefin Polymerization
205
Studylng of Zr-cene/MAO catalyst Fink[l] showed that with increasing dielectric constant of the solvent mixture the propylene polymerization rate increases linearly, but the stereospesiiity of the catalyst decrease strongly. Hence, the .sterecmpea&y of this catalyst system is connected with the existence of a polarized Zr-cT-AI complex or a tight contact ion pair with a stereo regulaung role of counter ion. So, ionic nature of active Bite can be extensivety modified, allowing tuning of steric, chirality and electronic properties. Unfortunately one important point was not discussed in literaape much. That is the influence of poSitiVe charge on the reactivity of M-carbon bond. That quesfion waa examined in 19-10]. The catalytic activity would obviously be conditioned by the reactivity of metal-carbon bond coupled with the existence of coordination site. The high transition metal carbon bond reactivity is caused by its liability and easy deformation. The behavior of potential M-C bond curve of transition metals can be compared with of main group of metas. Potential curves of Ti-C bond in CH3TiCl3 and AI-C bond in AlCH3C12 calculated with Hartree-Fock method are given in fig.2 [9].
-
-960.
-1340
e.SV
cv
@I
-962.
-1341
-964. -1344
-966-1346
-968-1348
!a
-970,
25
3.0
35
4.0
45
-
,
.
, . , -
5.0
.
-
.
-
.
-
.
.
5
F w 2. h t i a t i o n energy for T i c and AI-C bonds. Comparison of potential curves shorn that a more -cant deformation occurs m the Ti-C bond at the same energy of bond excitation. It is umnected with the appearance of "triplet instability" that occurs well before in transition metal derivatives. The pair of electrons, which forms the M-C bond, is localized in d-, p and s-orbitals at the equih'brium distance. Partial unpairing of electrons between Ti and C atoms occurs at a r e h t k b d hctsase of distance and unpaired electron is futhl localized in d-A0 of titanium. By the following streching of the bond the spin density in these orbitals increase up to the complete transition of the electron in the Ti@) fragment formed. The low dif€usionof d-A0 of Ti in mmpatkn to s- and p A O is ofgreat importance. Bond stretchmg c a d a rapid decrease of d-A0 overlapping with carbon
206
F S. Dyachkovskii
orbitals and thus the appearance of "triplet instability" (the rearrangement of valence state toTi(m) &agment) already at a relatively small degree of bond stretchmg. The main group metal (aluminum, for example) does not change practically its valence configuration on bond stretchmg for quite long distance.So, the transition metal is able to easily rearrange its electron structure which leads to the high reactivity of the M-C bond, compare with the main group with anti metal bond. The energy transition into the lower triplet electron-excitedstate AE,,t, bondmg properties relative to the M-C- bond, was used as the relative parameter for the M-C bond reactivity [9,10]. The small value of AE,t indicates the decrease of energetic barrim of reaction m wordination metal sphere and decrease of total energy of the M-C bond. AE,t was quantitatively calculated and thus the influence of various factors (structure, polarization and charge) on the reactivity of M-C bond considered. Calculated AE,t for different configuration and polarity of catalyst complexes are given in Table 2.
Table 2 Characteristics of T i w ) derivatives. Compound
Transition energy (eV) E , t
2.6 2.7 2.2 2.3 1.8
1.4 1.7 2.5 1.9
2.7 1.9
We can see that appearance a positive charge near the titanium atom sharply increase the ability of the transition metal for rearrangement of electron structure, thereby decreasing Es4 So, the positive chasged ions IL,MR]+type and polar complex L M R .X-] could exhibit lugh activity m polymerizatiOn reaction due to a slower increase of potential energy curve of M-C
'
19. Role of Ions in Coordination Olefin Polymerization
207
bond and to a decrease of the activation barrier in the insertion and analogous reaction proceedmg through cyclic transition state. The other possible way for the appearance of charge, as you can see Erom the table, can be "protonization" of complexes. The calculation show, that interaction of a proton with chlorine complexes of titanium leads, almost in all caw, to a decrease of A Es -t . In the presence of strong proton acceptors in the M-complexes the equilikum quantity of protonated structures may be considerable. In these cases the favourable deformaton of M-C bond energy can be occur. Takmg the role of complex "protonation"into account, the mechanism of activation of titanium complex fixed on MgO, alumoxanes, ahnnosilicates was explain [1I]. The estimation of the energy n&,t of protom& iimw of surface complexes shows that they can be considered as the active centers of catalysts on supports. It should be noted that recently [12] ethylene insertion into the Ti-C bond in positively charged ion CH3TiCL3+ was curry out. These calculation showed that metal in transition state remenge its electron structure very much,actually change its d e n t state. This changes leads to a decrease of activation energy of insertion reaction h11-14 to 4 kcaVmole. So, it is confirm the main idea of our model [9, lo]. The role of ions in the kinetic of macrmolecule formation is essential. The propagatitm rate on the ions and on the complexes should be different and it means that M-polymerbond couldbeinactiveorinactivefom: "p + X * "p.X active form "p + Lm --t"p+l + Km -* nptl+k inactiveform
+x Jr -x
+x -x
"pX
"p+P
-
+xit -x
wl+k+.X
So, there is a time when potymer chain grows ('gr) and when it is "sleeping" (hi). The ratio
@b+bl could be very small, dependmg on the condition and catalyBt system The calculation shows that Mw and MWD are vcry Sensitjve to that ratio [13,14]. Hence, the equilibrium between active and inactive form (ions, ion-pair, neutral complex) should be taken into account at the consideration of kinetic of polynerization processes, calculation of the active centers concentration and rate of propagation. In conclusion we can generalize the role of ions m coordination polymerization as following: 1. Ion gives a fiee coordination site on the metal. 2. Positive charge on the metal makes favourable deformation of M C bond. 3. By the nature of solvent possible to change the stereo regularity of active site. 4. Acceptors and donors of electrons change the reaciivity of M-C bond. 5 . Ions equilibrium allowed to regulate M, and MWD of polymer.
208 F.S. Dyachkovskii
REFERENCES 1. F.S.Dychkovsku, A.K.Shilova, and A.E.Shilov, J. Polym. Sci., Part .C, No 16,pp.23332339 (1967). 2. F.S.Dyachkovsku, E.A.Cingoryan, and O.N.Babkina, International J. of Chem. Kinetics, Vol. 13,603-613 (1981). 3. J.J.Eisch, A.M.Piotrowski, S.K. Brownstein, E.J. Gabe, F.L.L,ee, J. Am. Chem. SOC., 107, 7219, (1985). 4. R.F.Jordan, P.K.Bradley, R.E. Lapointe, and D.F.Taylor, New J. Chem., 14. 505511,(1990). 5. M.Bochmann, L.M. Wilson, R.L.Short, Organmetallics, 6, 2556, (1 987). 6. CPellecchb, A.Grassi and A.Zambelli, J. of Molec. Catal ., 82, 57-65 (1993). 7. G. Jeske, H. Lauke, KMammam, P.N.Sweptson, H.Schumann, T.J.Marks., J. Am. Chem Soc., 107,8091 (1985). 8. G.Fink and N.Herfert, International Symp. on Advances in olefin, cycloolek and dioleh polymerization. Lyon, France, Apd , 1992, p.15. 9. V.E.Lvovsky, E.A.Fushman, and F.S.Dyachkmk& J. Molec. Catal., 10, 43-56 (1981) 10. V.E.LVOV&Y, E.A.Fuehman and F.S.Dyachk~~d&, Zh.FiZ. khim., 56, NO.8, 18641878 (1982). 11. V.E.Lvovsky, A.A.Ba& and S.S.Ivanchev,Symposium on Catalysis, Novosibirsk, USSR, 183, (1982). 12. K.Morokuma, Chtm. rev., 91, 823 (1991). 13. E.A.Grigoryan, F.S.Dyachkmk~i, and A.E.Shilov, Kinetics and Mechanism of PoIyreaction, Budapest, Hungary, 11,239-241 (1969). 14. B.I,.Erusalimclkii, S.Cr.Lybezkiiin "Process of ionic polymerization" Chemishy, Leningrad, 1974, pp 33-34.
209
20. Copolymerization of Hydrocarbon Monomers in the Presence of CpTiC1, - M A 0 : Some Information on the Reaction Mechanism from Kinetic Data and Model Compounds
ADOLFO ZAMF3ELLI and m
Diparthento d i Fisica, (SA),
Z
F
m
U n i v e r s i t d di S a l e r n o ,
I-84081
Baronissi
Italy
ABSTRACT The title half-metallocene catalyst is active in the polymerization of olefins, styrenes, and conjugated dienes. An insight into the polymerization mechanism emerges from kinetic data concerning homo- and copolymerization of some of the above monomers, as well as from the structure of some novel cationic zirconium complexes. INTRODUCTION Monocyclopentadienyl titanium derivatives, such as CpTiX3 and CpTiX2 (Cp = V5-C5H5, X = C1 o r hydrocarbyl), after reaction with methylalumoxane (MAO), afford very efficient and versatile homogeneous catalysts that promote polymerization of ethylene and a-olefins,l) polymerization of styrene and substituted styrenes to highly syndiotactic polymers,*) stereospecific polymerization of 1,3-dienes to either c i s - 1 , 4 or 1 , 2 syndiotactic polymers, depending on the particular monomer and the reaction conditions.3, In this paper we will discuss some kinetic data obtained in our laboratory concerning the homopolymerization and the binary copolymerization of some of the above mentioned monomers in the presence of the catalytic system CpTiC13-MAO. Some unexpected results concerning the relative reactivities of different monomers in homo- and copolymerization will be tentatively explained by taking into account the wide spectrum of possible coordination modes and strengths of both the monomers and the growing chain ends.
210
A. Zambelli and C. Pellecchia
The p e r f o r m a n c e s of T i - b a s e d
homogeneous c a t a l y s t s w i l l be
a l s o compared t o t h o s e of s i m i l a r c a t a l y s t s based o n Z r , a n d d i s c u s s e d c o n s i d e r i n g t h e s t r u c t u r e a n d t h e r e a c t i v i t y of some c a t i o n i c organozirconium complexes s y n t h e s i z e d i n o u r l a b o r a t o r y . RESULTS AND DISCUSSION on a n d c The
o
w in
reported
data
o ofn stvrenes.
~
Table
concerning
1,
the
of s t y r e n e , pm e t h y l s t y r e n e , a n d p - c h l o r o s t y r e n e , show t h a t s u b s t i t u t i o n of t h e aromatic r i n g of t h e monomer w i t h a n e l e c t r o n - r e l e a s i n g CH3 g r o u p homopolymerizations
in
comparable
conditions
t o a n i n c r e a s e of t h e p o l y m e r i z a t i o n r a t e , w h i l e a n electron-withdrawing C 1 s u b s t i t u e n t produces t h e opposite effect. leads
Table 1.
R e l a t i v e r e a c t i v i t i e s i n homopolymerization o f s t y r e n e
and s u b s t i t u t e d styrenesa) Monomer
Time i n h
Yield i n g
Relative reactivities
styrene p-Me - s t y r e n e
0.1 0.1
0.57
1
0.75
1.3
p-C1-styrene
18
0.09
0.001
a)
P o l y m e r i z a t i o n c o n d i t i o n s : t o l u e n e , 10 mL; CpTiClg, 3 p o l ; MAO,
3 mmol; monomer, 35 mmol,;
temperature, 20 "C. Data f r o m Ref. 2c.
The r e a c t i v i t y r a t i o s f o u n d f o r b i n a r y c o p o l y m e r i z a t i o n s of s t y r e n e w i t h p-methylstyrene and w i t h p - c h l o r o s t y r e n e ,
reported i n
Table 2, a n d d e f i n e d a c c o r d i n g t o t h e scheme o f L e w i s a n d Mayo:
C*-M1
...
C*-M1..
.
+
+
Mi M2
kll
k12
C*-(M1)2
...
C*-M2(M1).
..
rl
=
kll k12
(where C*-Mi i s a c a t a l y t i c complex bound t o a g r o w i n g c h a i n e n d i n g w i t h monomer i ) show t h a t t h e r e a c t i v i t y of t h e monomers toward a n y g r o w i n g c h a i n e n d is p - m e t h y l s t y r e n e
> styrene > p-chlorostyrene.
20. Copolymerization with CpTiC1,-MA0 Catalyst 21 I
The same order for the reactivity of these monomers had been found by Natta et a1.4) in the presence of isotactic-specific catalysts, and was interpreted by assuming that the rate determining step is an electrophilic attack of the monomer by an electron-deficient active species. Table 2. Reactivity ratios for binary copolymerizations of styrene with substituted styrenes2=) Comonomer (Mp) p-Me-styrene p-C1-styrene
rl
r2
rl'r2
0.49 20
1.5 0.37
0.74 7.4
It is currently believed that the syndiotactic-specific active species are group 4 metal cationic complexes (see below) and this very fact provides a simple rationale for the observed values of the reactivity ratios. S t y r e n e and c o n i w a L & d The CpTiC13-MAO catalyst also promotes cis-1,4 polymerization
of 1,3-butadiene and isoprene, and 1,2 syndiotactic polymerization of 4-methyl-l,3-pentadiene . 3 ) Porri et a1 . 5 ) have recently found an unusual behaviour in the polymerization of (Z)-1,3-pentadiene with the same catalyst: a prevailingly isotactic cis-1,4-poly(l,3pentadiene) is obtained at room temperature, while a syndiotactic 1,2-polymer is obtained at -28 OC. Moreover, the polymerization rate seems to be higher at low temperature. A comparison of the homopolymerization rates of some conjugated dienes and styrene, in comparable reaction conditions, is displayed in Table 3.6) One can see that the reactivity in homopolymerization increases in the order isoprene 0 (see butadiene
copolymerization,
Table 5)
.
Table 5. Effect of t h e addition of butadiene c o p o l y m e r i z a t i o n s a t c o n s t a n t c o n c e n t r a t i o n o f styrenes) Styrene
butadiene
productivity
(mol/l)
(mol/l)
(g/mmol T i - h )
3.32
0
117
3.22 3.26
0.10 0.21
14.4
3.21
0.39
17.1
in
15.3
a)Polymerization conditions: toluene, 6.5 mL; C p T I C 1 3 , 5 M o l ; MAO, 4.5 mmol; temperature, 18 "C; time, 90 min. Data from Ref. 6b. Assuming t h a t t h e c o n c e n t r a t i o n of t h e a c t i v e species d e r i v i n g from a f i x e d amount o f CpTiC13 a n d MA0 i s n o t a f f e c t e d by t h e p r e s e n c e o f d i f f e r e n t monomers, one c o u l d c o n c l u d e t h a t t h e low homopolymerization r a t e o f i s o p r e n e i n comparison w i t h s t y r e n e i s o n l y d u e t o t h e lower r e a c t i v i t y o f t h e growing c h a i n s e n d i n g with an isoprene u n i t , while t h e higher r e a c t i v i t y of isoprene i n c o p o l y m e r i z a t i o n c o u l d be d u e t o a f a v o u r a b l e c o m p e t i t i o n w i t h s t y r e n e i n t h e c o o r d i n a t i o n s t e p . The k i n e t i c d a t a c o n c e r n i n g homo- a n d c o p o l y m e r i z a t i o n o f b u t a d i e n e s u g g e s t t h a t t h e growing c h a i n s e n d i n g w i t h a b u t a d i e n e u n i t a r e less r e a c t i v e t h a n t h o s e e n d i n g w i t h a s t y r e n e u n i t , a n d more r e a c t i v e t h a n t h o s e e n d i n g with a isoprene u n i t . I t i s widely accepted7) t h a t c a t a l y t i c polymerization of c o n j u g a t e d d i e n e s i n v o l v e s q3 c o o r d i n a t i o n o f t h e growing c h a i n end t o t h e c a t a l y t i c s i t e s
(see F i g u r e 1). F o r s y n d i o s p e c i f i c p o l y m e r i z a t i o n of s t y r e n e ( w h i c h p r o c e e d s t h r o u g h s e c o n d a r y w e proposed an analogous c o o r d i n a t i o n i n s e r t i o n o f t h e monomer) o f t h e growing c h a i n e n d , i n v o l v i n g t h e a r o m a t i c r i n g . 2 c ) T h i s h y p o t h e s i s i s now s u p p o r t e d by t h e s t r u c t u r e o f some c a t i o n i c
214 A. Zambelli and C. Pellecchia
zirconium benzyl complexes, showing very strong qn coordinations (see below).
CH2 \\
/
CH
I
I
I
CH2
CH2
I
CH2 I I
I I
I I
Figure 1. Schematic representation of the propagating species resulting from the insertion of butadiene (A), isoprene (B), 4methylpentadiene (C), and styrene (D) In A-C the growing chain ends are 113 coordinated, while in D involvement of the aromatic ring can lead t o different q n coordinations (see below). Of q 1 could be course, equilibria o f the type, e. g., q 3
.
-
involved in the polymerization.
An q 4 monomer
coordination
has
been
postulated
as
a
preliminary step in the polymerization of butadiene and isoprene.7) This could account for the favourable competition of these monomers with styrene in copolymerization. The particularly large reactivity of 4-methyl-1,3-pentadiene is probably due to the higher nucleophilicity of this monomer and possibly, as suggested by P ~ r r i , ~ ,to ~ )an q2 coordination to the catalytic complexes, followed by rapid insertion. The products of the reactivity ratios for styrene-butadiene, styrene-isoprene, and butadiene-isoprene copolymerizations are somewhat larger than 1. This deviation from the perfectly random comonomer sequence distribution could originate from the fact that the electrophilicity of Ti of the catalytic species (see Figure 1) is affected by the mode of coordination of the last unit of the growing chain end, and, in turn, could influence the coordination of the next monomer unit. In fact, the selectivity in attacking nucleophiles of different strength should increase while the strength of the electrophile decreases; consequently, a perfectly
20. Copolymerization with CpTiC1,-MA0 Catalyst 2 I5
random comonomer distribution (r1.r~= 1) cannot be expected when the last unit of the growing chain strongly influences the electrophilicity of the active species. It is worth mentioning that CpTiC13-MAO promotes a substantially block copolymerization of styrene and ethylene . g ) This finding could be accounted for in the framework of the above mechanism. U D 4- C
The active species involved in the CpTiC13-MA0
catalytic
system, as well as in closely related systems based on Ti and Zr compounds not carrying q5 ligands, such as TiBz4, ZrBz4, Ti(OR)4 (Bz = benzyl),lO) were suggested to be cationic complexes analogous to those involved in metallocene-based catalysts,11) on the basis of several indirect evidences .2c) The ionic structure was denied by Chien et al. on the basis of electrodialysis experiments .12) However, strong support to the former hypothesis came from the finding that catalysts performing similarly to the MAO-based systems can be obtained from monocyclopentadienyl or Cp-free hydrocarbyls, according to one of the following reactions:I3)
R=Me; n = l M
=
Ti, Zr
Cp' R
=
Bz; n
=
=
C5H5
(=
Cp) or C5Me5
(=
Cp*)
0, 1
In particular, Cp*TiR3 with B (CgF5)3 affords an extremely active catalyst for syndiotactic-specific polymerization of styrene, rivalling with C P T I C ~ ~ - M A O . ~ ~ ) Although the formation of [Cp*TiR2]+ cationic complexes has been clearly detected by NMR,15) clean isolation and full characterization of these species have not yet been accomplished, due to concurrent decomposition, possibly leading to Ti(II1) species . 1 6 )
216 A. Zarnbelli and C. Pellecchia
On t h e c o n t r a r y , w e s u c c e e d e d i n i s o l a t i n g several a n a l o g o u s Z r c o m p l e x e s , some o f which h a v e b e e n s t r u c t u r a l l y c h a r a c t e r i z e d . The X-ray c r y s t a l s t r u c t u r e s of [ ~ r ~ z 3 ][ B+ Z B ( C ~ F ~ ) ~(] 1- 1 ~ 1 7
[CpZrBz21t [BZB(C6F5)3]- ( 2 ) ,I8 a n d [Cp*ZrBz2]+ [BzB(C6F5)3]- (3)19) are r e p o r t e d i n F i g u r e s 2 and 3 .
Figure
X-ray
2.
( l e f t ) and
Of
crystal
s t r u c t u r e s of
[ZrBz3]+[BzB ( C g F g ) 3 ] - 1 [CpZrBz~l+[BzB(CgFg)3]-2 ( r i g h t ) . 1 7 t r 8 )
Compounds 1-3 are c a t a l y t i c a l l y a c t i v e i n t h e p o l y m e r i z a t i o n e t h y l e n e a t 2 5 O C a n d 1 atm, w h i l e t h e y are n o t a c t i v e i n s y n d i o s p e c i f i c p o l y m e r i z a t i o n o f s t y r e n e . R e a c t i o n of 1 a n d 3 with propene and h i g h e r a - o l e f i n s i n m i l d c o n d i t i o n s affords of
s i n g l e i n s e r t i o n a d d u c t s , 2 0 ) o n e of which,
[Cp*Zr (CH2CHMeCH2Ph)B z l +
[BZB(C6F5)31- ( 4 ) , h a s b e e n s t r u c t u r a l l y c h a r a c t e r i z e d (see F i g u r e 2 ) .19)
The most i n t e r e s t i n g f e a t u r e i n t h e c o n t e x t o f t h e p r e s e n t d i s c u s s i o n i s t h e v a r i e t y o f c o o r d i n a t i o n modes of t h e b e n z y l ligands,
r e l i e v i n g t h e e l e c t r o n i c u n s a t u r a t i o n of Z r . I t i s w o r t h
recalling that styrene
of a metal-benzyl
i n t h e syndiotactic s p e c i f i c polymerization
the polyinsertion
growing c h a i n e n d . Compounds 1 a n d 2
i s 2,1,
are
leading t o
zwitterionic,
owing
to
the
q6
c o o r d i n a t i o n of t h e b e n z y l l i g a n d of t h e b o r a t e a n i o n . I n 2 t h e t w o Zr-bound b e n z y l s a r e s i m p l y q1 ( Z r r e a c h e s a 1 6 - e l e c t r o n c o n f i g u r a t i o n ) , w h i l e i n 1 o n e o f t h e b e n z y l s i s q2 a n d t h e o t h e r
t w o a r e q1 surprisingly,
(Zr
reaches
a
14-electron
configuration).
3 has a completely d i f f e r e n t s t r u c t u r e ,
Quite
with no
20. Copolymerization with CpTiC1,-MA0 Catalyst
c a t ion-anion
217
b o n d i n g i n t e r a c t i o n : Z r h a s o n e q3-benz y l a n d o n e
unprecedented
q7-benzyl
configuration. Finally,
ligand,
reaching
a
18-electron
i n 4 Z r i s bound t o o n e fll-benzyl,
while
t h e -CH2CHMeCH2Ph g r o u p b e h a v e s a s a c h e l a t i n g f11:q6 l i g a n d ; t h i s unusual back-biting
arene coordination,
due
Z r r e a c h e s a 16-
electron configuration.
F i g u r e 3 . X-ray c r y s t a l s t r u c t u r e s of [Cp*ZrBz21t 3 ( l e f t ) and o f
[Cp*Zr (CH2CHMeCH2Ph)B z I t 4 ( r i g h t ), d e r i v i n g from propene s i n g l e i n s e r t i o n i n t o t h e former. The [BzB(CgF5)3]- anions, which are not i n t h e coordination sphere of Z r , are CONCLUSIONS The complexes d e s c r i b e d above show t h e s t r o n g t e n d e n c y o f t h e coordinatively unsaturated Z r cations t o r e l i e v e t h e i r electrond e f i c i e n c y a l s o t h r o u g h u n u s u a l bonding i n t e r a c t i o n s . A s i m i l a r behaviour
i s r e a s o n a b l y e x p e c t e d f o r T i a n d it i s
a l s o e x p e c t e d t h a t i n s o l u t i o n d i f f e r e n t complexes a r e o b t a i n e d d e p e n d i n g on t h e c o m p e t i t i o n f o r c o o r d i n a t i o n o f t h e p a r t i c u l a r ligands,
i . e . t h e c o u n t e r i o n , t h e s o l v e n t , t h e monomer and, when
t h e complexes a r e c a t a l y t i c a l l y a c t i v e , t h e growing c h a i n e n d .
seems l i k e l y t h a t , i n t h e p r e s e n c e o f s u c h d i f f e r e n t monomers a s s t y r e n e , c o n j u g a t e d d i e n e s o r o l e f i n s , a c t i v e species of d i f f e r e n t s t r u c t u r e might b e formed, and t h a t t h e y i n t e r c o n v e r t t o e a c h o t h e r d u r i n g c o p o l y m e r i z a t i o n , a l s o as a c o n s e q u e n c e o f t h e i n s e r t i o n of d i f f e r e n t monomers. The p o s s i b i l i t y o f o b t a i n i n g s y n d i o t a c t i c p o l y s t y r e n e from many d i f f e r e n t c a t a l y t i c c o m b i n a t i o n s (CpTiC13-MA0, CpTiC12-MAOI Cp*TiR3-B (C6F5) 3, C p * T i R 3 - [ H N R 3 1 + [B (C6F5) 4 ] - , TiBz4-MAO, T i ( O R ) 4It
218
A. Zambelli and C. Pellecchia
MAO, Ti (acac)3-MAO (acac = acetylacetonate) , ZrBz4-MA0, Zr(acac)2C12-MAO) suggests that in any case the syndiotactic specificity arises from steric interactions between the last unit of the growing chain end and the monomer to be incorporated next, in the presence of a rather crowded and stereorigid ligand environment. This hypothesis is also supported by the experimentally observed polymer microstructure, which is in agreement with the first order Markovian statistical model of syndiospecific propagation.lo=) The reasons of the higher activity of the catalysts based on Ti compounds in comparison with catalysts based on Zr compounds in promoting styrene polymerization are not clearly established. The possibility of obtaining active catalysts using Ti (111) compounds could suggest that the active species are formed after reduction of the group 4 metal, which is easier for Ti(1V) than for Zr(1V). Another difference between the two metals is the softer Lewisacidity of Zr in comparison with Ti, which is confirmed also by the formation of strong Zr-arene Ic-bonding interactions in the above mentioned cationic complexes: on this basis, one could hypothesize different reactivities of the metal-polystyryl bonds for Zr and Ti. REFERENCES AND NOTES 1. K.Soga, J.R.Park, and T.Shiono, P o l y m . Commun., 2, 310 (1991). 2. (a) N. Ishihara, M.Kuramoto, and M.Uoi, Macromolecules, 2, 3356 (1988); (b) A.Zambelli, C.Pellecchia, and L,Oliva, ibid., 22, 2129 (1989); (c) A.Zambelli, C.Pellecchia, L.Oliva, P.Longo, and A.Grassi, Makromol. Chem., 104 (1991).
u,
3. (a) L.Oliva, P .Longo, A.Grassi, P .Ammendola, and C .Pellecchia, Makromol. Chem., Rapid Commun., JJ, 519 (1990); (b) G.Ricci, S.Italia, A.Giarrusso, and L.Porri, J. Organomet. Chem.,
m,
67 (1993).
4. G.Natta, and F.Danusso, Chim. Ind. (Milan),
a,445
(1958).
5. L.Porri, private communication: G.Ricci, S.Italia, and L.Porri, Macromolecules, in press. 6. (a) C.Pellecchia, A.Proto, and A.Zarnbelli, Macromolecules, E, 4450 (1992); (b) A.Zambelli, A.Proto, P.Longo, and P.Oliva, Makromol Chem., submitted
.
.
20. Copolymerization with CpTiC1,-MA0 Catalyst 219
7. See e.g. : L.Porri, A.Giarrusso, and G.Ricci, M a k r o m o l . Chem., Macromol. Symp., 48/49, 239 (1991). 8. C.Pellecchia, P.Longo, A.Grassi, P.Ammendola, and A.Zambelli, M a k r o m o l . Chem., R a p i d Commun., B, 277 (1987). 9. P.Longo, A.Grassi, and L.Oliva, Makromol. Chem.,
u, 2387
(1990). 10. (a) A.Grassi, C.Pellecchia, P.Longo, and A.Zambelli, G a z z . Chi m. Ital., U , 65 (1987); (b) A.Zambelli, P.Longo,
C.Pellecchia, and A.Grassi, M a c r o m o l e c u l e s , a,2035 (1987); (c) A.Zambelli, P.Ammendola, and A.Proto, i b i d . , 2,2126 (1989). 11. For recent reviews of the matter, see, e . 9.: (a) A.Zambelli,
C.Pellecchia, and L.Oliva, M a k r o m o l . Chem., M a c r o m o l . S y m p . , 48/49, 297 (1991) ; (b) R.F.Jordan, Adv. O r g a n o m e t . Chem., z, 325 (1991). 12. J.C.W. Chien, Z.Salajka, and S.Dong, M a c r o m o l e c u l e s ,
25, 3199
(1992). 13. (a) R.E.Campbel1, Eur. P a t . Appl. EP 421,659 to Dow Chemical
Co. (1991); (b) C.Pellecchia, A.Proto, P.Longo, and A. Zambelli, M a k r o m o l . Chem., R a p i d Commun., U , 663 (1991); (c) idem, i b i d . , 277 (1992).
u,
14. C.Pellecchia, P .Longo, A.Proto, and A.Zambelli, M a k r o m o l . Chem., R a p i d Commun., 265 (1992).
u,
15. D.J.Gillis, M.-J.Tudoret, and M.C.Baird, J. Am. Chem. SO C. 2543 (1993). 16. NMR monitoring of the reaction between Cp*TiBzj and B(C6F5)3
m,
at low temperatures showed the formation of [Cp*TiBz2]+ [BZB(C6F5)3]-, which evolved over a short period of time. ESR experiments at room temperature showed the rapid formation of Ti(II1) species. Unpublished results from our laboratory. 17. C.Pellecchia, A.Grassi, and A.Immirzi, J. Am. Chem. S O C . , m, 1160 (1993). 18. C .Pellecchia, A. Immirzi, A.Grassi, and A. Zambelli, O r g a n o m e t a l l i c s , U , 4473 (1993). 19. Unpublished results from our laboratory. 20. (a) C.Pellecchia, A.Grassi, and A.Zambelli, J. Chem. SO C. , Chem. Commun., 947 (1993); (b) C.Pellecchia, A.Grassi, and A.Zambelli, O r g a n o m e t a l l i c s , 298 (1994).
u,
This Page Intentionally Left Blank
22 I
21. The Role of Ion-Pair Equilibria on the Activity and Stereoregularity of Soluble Metallocene Ziegler-Natta Catalysts
JOHN J. EISCH and SONYA I. POMBRIK Department of Chemistry, State University of New York at Binghamton, Binghamton, New York 13902-6000 U.S.A. STEFAN GifRTZGEN, RAINER RIEGER and WOLFRAM UZICK Witco GmbH, D-59192 Bergkamen, Germany, a subsidiary of Witco Corporation, 520 Madison Avenue, New York, New York 10022, U.S.A. ABSTRACT By means of temperature-dependentmultinuclear NMR studies, electrical conductivity measurements and polymerization activity assessments, the nature of the resulting complexes formed between metallocene alkyls or metallocene dihalides and Group 13 Lewis acids was investigated comprehensively. The influences of solvent polarity, concentration, temperature and the strength and proportion of the Lewis acid upon the structure of the metallocene-Lewis acid complexes furnish cogent evidence for the existence of an equilibrium between contact ion pairs (CIP)and solvent-separated ion-pairs (SSIP). Three systems were considered in this study: 1) Cp2TiQ + AlC13; 2) bisb-butylcyclopentadieny1)zirconiumdimethyl + (C6F~)3B;and 3) bisb-butylcyclopentadieny1)zirconium dichloride + MAO. More polar media and higher dilution have been shown to favor the solvent-separatedion-pair isomer over the contact ion-pair isomer. In pj-basic solvents, such as arenes, evidence indicates that a 1:l:l complex of the metallocene, the Lewis acid and the arene is formed reversibly (solvated cation-anion pair, SCAP). Polymerization activities toward ethylene or propylene, as measured in these studies or reported in the literature, support the conclusion that the solvent-separated ion pairs are the most active catalyst sites but are less stereoselective in syndiotactic polymerization. In a related study, the MqAl-content of MA0 could be reduced to zero by toluene-evaporationsat 25OC. The MqAl-free MAO, upon admixture with (CD,),AI, rapidly displayed an 'H N M R signal revealing the regeneration of "free" Me,Al. This observation is consistent with the rapid methyl group exchange between the terminal Me2A1 groups of MA0 chains, MqAl-(-OAIMe-)-,Me, and the added (CD3),A1 and supports the suggestion that these terminal Me2Al groups are the most reactive structural unit of MAO,
222
J.J. Eisch and S.I. Pornbrik
either toward external Me3A1or toward metallocene dialkyls or dihalides. In this view such terminal M q A l groups are responsible for the heightened cocatalytic activity of MA0 in Ziegler-Natta catalysts. This view conforms with the heuristic Steiger-Kaminsky hypothesis. INTRODUCTION Ziegler-Natta catalysts based on transition metal salts and aluminum akyl cocatalysts have been valued as effective polymerization catalysts for unsaturated hydrocarbons, such as olefins and 1,3-dienes. for over 40 years'). However, the active sites of these possibly multi-site catalysts have never been completely identified because of the complexity of the surface reactions occurring in these heterogeneous systems2). After the initial discoveries of Ziegle?) and Natta4) a second breakthrough in polyolefin catalysis was initiated by Ewen5), by Kaminski and Sinn6) and by Brintzinger'), who were successful in polymerizing olefins stereospecifically by means of bridged cyclopentadienyl transition metal complexes, or stereorigid metallocenes, that had been activated by partially hydrolyzed aluminum alkyls known as aluminoxanes, (-RAl-O-)n. In the intervening decade these stereorigid homogeneous catalysts have attracted much interest in industrial and academic laboratories because of their high activity and their potential for producing polymers with novel and highly specific properties*). Over and beyond their commercial importance, these catalyst systems confront researchers with the question of their molecular mode of action. In attempting to answer this question, we and others have found that such homogeneous catalyst systems lighten the task somewhat by permitting kinetic and spectral measurements to be made in solution. Our report is intended to contribute to an understanding of this molecular mode of action and thereby to supplement the independent studies of various groups, including our own, who have marshaled evidence that ion pairs are involved9) and that some type of ionic intermediate is clearly either the active catalyst site or an essential precursor of such a site.lO) In order to probe the ionic character of such a catalytic site, we chose to examine three combinations of a metallocene and a Group 13 Lewis acid 1) titanocene dichloride (4) and AlCl, (5)9b); 2) bis(Il-butylcyclopentadienyl)zirconium dimethyl (la) and tris(pentafluoropheny1)borane (2); and 3) bis(pbutylcyclopentadieny1)zirconiumdichloride (1b) and poly(methy1aluminoxane) (MAO, 3). The techniques employed were multinuclear NMR spectroscopy and measurements of electrical conductivity and polymerization activity. The last two systems represent active catalysts for the polymerization of ethylene or propylene and hence their molecular modes of action have great practical relevance for Ziegler-Natta industrial polymerization technology. The first system, CpZTiCl2 AlCl,, is not an olefin polymerization catalyst -, but it is closely related to the Natta-Breslow homogeneous catalysts, Cp2TiC12-R,A1,,. Accordingly, the formation of ionic intermediates can be studied in the (4 + 5) system without the disturbing influence of transalkylation (equation 1):
21. Role of Ion-pair on Activity and Stereoregularity
223
In addition, some studies were carried out to learn how "free"MqAl is bonded in MA0 and how readily methyl groups undergo exchange between MA0 and "free" Me3Al. Such information is important in defining the cocatalytic action of MA0 in Ziegler-Natta catalysis. RESULTS The Svstern, TitanoceneDichloride (4) and Aluminum Chloride (51. To obtain a better understanding of how titanocene dihalides and aluminum halides interact and yet avoid group-exchange equilibria (e.g., equation l), the system, cp2TiC12-AlC13was examined by variable-temperature, multinuclear NMR spectroscopy and with variations in concentration and solvent polarity. Presented in Figure 1 are the 'H N M R spectra of 1:l mixtures of Cp2TiC12 and AlCl, in methylene chloride at two concentrationsand at five temperatures between +27 and -30 OC. In both cases, the singlet near 6.80-6.81 pprn at 27 OC resolves into two singlets at 6.90 and 6.77 pprn at -30 OC. The resolution into these two signals upon cooling and the coalescenceinto the one signal upon warming are fully reversible. It is furthermore noteworthy that, of the two, the high-field signal becomes dominant upon dilution (Figure la). Similar observations were made when the I3C N M R spectra of 1: 1
I
mol% Metallocen
Electric conductivity of the system la/2 at 0 OC in toluene solution. Figure 1. Absolute concentration of la: 0 - 149 mm0v1.
224 J.J. Eisch and S.1. Pombrik
mixtures of CpZTiCl2 and AlC13 in CH2C12at two concentrations were examined. The singlet near 123 ppm at 25 OC resolved into two singlets, in a reversible fashion, near 123.3 and 122.6 ppm at -30 O C . Again the high field singlet at -30 OC had significantly higher intensity in more dilute solution. These results demonstrate the existence of two different types of cyclopentadienyltitium compounds that are in ready equilibrium with each other. The variable temperature nAl N M R spectrum of the Cp2TiCl2-A1Cl3 system at 0.1 M in CH2C!12displayed a broad, dominant peak at 104.5 ppm at 25 OC (wlR= 356 Hz) with a minor shoulder peak at 99 ppm. Cooling the sample successively to -20°, -40°, and then -70 OC caused this peak to broaden and then to narrow selectively on its high-field side ( W I R - 563,666, and 300 Hz,respectively). At the same time a new, unresolved peak of comparable area began to emerge in the 98-100 ppm region (win = 356 Hz). Limited solubility of the components and high viscosity at -70 OC prevented better peak resolution. Nevertheless, these "Al N M R results support the presence of at least two different aluminum-containingcomponents, each of which is tetracoordinate. The effect of solvent polarity on the ratio of the two cyclopentadienyltitanium componentspresent in the Cp2TiC12-AIC13system was proved by recording the 'H spectrum in CHzC12containing 0,20, or 33% of CC1, (v/v). As is evident from Figure 2, the singlet
I Figure 2.
1
I,
Y
'H-NMR spectrum of metallocene l a in toluene-d8 at room temperature.
observed at 25 OC (column a) shifts from 6.75 to 6.82 ppm as the solvent contains more CCI, and thereby becomes less polar. In keeping with this, the ratio of the two peaks observed at -30 OC (row b) changes to favor the component at lower field (peak near 6.9 ppm). Since this component is favored by a medium of lower polarity, it must be less polar than the component absorbing near 6.7 ppm. An analogous change in the ratio of these two components was exhibited when the CH,CI, solution was diluted with toluene; integration
21. Role o f Ion-pair on Activity and
Stereoregularity 225
of the two peaks at -30 OC permits the determination of equilibrium constants: high field peak = 120 in pure CH2Q and 0.37 in a 5:l (v/v) mixture of low-field peak CH2C12-toluene. Keq Of
Metallocenes
Lewis Acids
The System, Bish-butvlcvclouentadienyl) Dimethyl (la) and Trisbentafluoropheny1)borane (2). Even at temperatures below -90O C immediate reaction takes place between l a and 2 in toluene solution upon addition of an excess metallocene la to 2, resulting in a two-phase system. A yellow color spontaneously occurs at the phase-contact boundary. Upon warming to ambient temperature the increasing methane evolution indicates the onset of extensive decomposition. Upon cooling below the the freezing point of toluene-d8 (-1 10 "C), a red color develops, which disappears upon warming to ambient temperature and reappears on recooling. This readily reversible thermochromic effect could also be observed with other metallocenes, as for example 1,l'ethylene-bis(indeny1)zirconium dimethyl. Guided by earlier studies of Natta-Breslow catalysts"), we performed electrical conductivity measurements on mixtures of la and 2 in toluene solution in order to obtain evidence for the presence of ions. The results are give in Figure 3. A maximum total conductance of 20.7 pS was measured at 165 mole % of la and was shown to be reproducible. Such increasing conductance is clear evidence for ion-pair formation. Upon increasing the excess of l a to more than 165 mole % we observed a separation of phases. According to the electric conductance figures obtained after phase separation (see Table I), the ionic products are obviously concentrated in the lower layer.
226 J.J. Eisch and S.I. Pombrik
su
h
293 K 258 K
I
248 K 238 K
208 K I
'
6
:
4
'
6'2
'
6'0
'
5'8
'
5'6
'
5'4
5'2
5'0
'
4'8
Expansion of cp proton absorption area in temperature dependent 'H-NMR Figure 3. spectra of equimolax mixtures of la and 2 in tolueneas (a) - (0. The top line shows the signals of pure l a for comparison.
Table 1. Electric conductivity data of separated layers at 0 OC. Maximum concentration of la: 320 mmolefi. Electric Conductivity [ pS ] Excess l a [mole %]
Upper layer Lower layer
186 2.2
110
196 1.1 240
207
0.7 270
Multinuclear N M R Measurements. In the 'H-NMR spectrum of la the signals at 5.70 to 5.90 ppm can be assigned to the Cp-ring protons and the signals at 2.60, 1.50 to 1.70 and 1.10 ppm to the protons of the pbutyl group. The singlet at 0.02 ppm is caused by the protons of the two equivalent methyl groups attached to zirconium. The temperature-dependence of the 'H NMR spectrum of an equirnolar mixture of l a and 2 (cf. Figure 4) shows that the dimethylzirconium grouping no longer is evident while two new signals appear between 0 and 1 ppm, in addition to a signal at 0.4 pprn representing a small amount of methane.
21. Role of Ion-pair on Activity and Stereoregularity
227
zr.0 = 21 upper layer
B.0 = 1:l
a 0 = 2 : 1 lowerlayer
20=12
I\
a 0 = 0:1
Temperature dependent 'H-NMR spectra of equimolar mixtures of l a and 2 Figure 4: in toluene-d8. The top line shows the signals of pure la for comparison. The new signal at 0.5 ppm can be assigned to one methyl group attached to a zirconium cation;the new signal at 0.3 ppm would accord with one methyl group attached to boron. Significant line-broadening of all signals can be observed upon decreasing the temperature. The Cp-ring-proton signals are resolved to form additional multiplets, indicating new components with non-equivalent Cp-rings. The observed appearance of new Cp-proton absorptions upon cooling was found to be completely reversible and is in good agreement with our previous NMR investigations on the system, Cp2TiC12 and Alc13'~). By means of solvent polarity variation the high-field Cp proton signal, @f. infra) which appears upon cooling. can be assigned to that arising from solvent-separated ion pairs. This is also supported by our results illustrated in Figure 4. Furthermore, ion-pair formation is supported by the "B-NMR spectra at different molar ratios of l a and 2. The absorption of covalent boron in 2 appears at 60 ppm. Upon reaction with l a a new signal appears at -14 ppm, which can be assigned to an anionic boron component. The System, Bis(n-butvlcvcloDentadienvlhirconiumdichloride i l b ) and Poly(methy1aluminoxane) (3) Electrical Conductivity Measurements. In contrast with the reaction of l a and 2, no phase separation could be observed upon addition of metallocene l b to a poly(methy1aluminoxane) (3) solution in toluene. However, color changes from colorless to yellow could also be observed. Electric conductivity studies were performed at O°C and at this temperature we found only very slight methane evolution and were able to achieve a good reproducibility in our measurements. A steady, almost linear increase in total conductance was observed by increasing the amount of lb. These results give evidence for
228 J.J. Eisch and S.I. Pombrik
the formation of ion pairs upon reaction of metallocene l b with methylaluminoxane 3 in toluene solution. The electric conductance obtained was of the same magnitude as that observed by the addition of metallocene la to 2: after 140 mole % of l b had been added to 3, the resulting conductance was 17 pS. Mulfinuclear N M R Measurements. The temperature-dependent 'H N M R spectra obtained from a mixture of l b and 3 gave results comparable with those obtained from equimolar mixture of la and 2 M. Figure 4). Besides the signals arising from unreacted l b and 3 (broad high field signal), smaller signals of about 20% comparable intensity could be observed (partly overlapping), These smaller signals show the same shift dependency by variation of the temperature as it was found in the la 2-system. An additional new signal was found at 0.5 ppm indicative of a methyl group. This shift is nearly the same as the shift observed for the cationic Zr-CH3 group in the l a 2-system. hemration of Polv(methv1aluminoxane)Not Containing "Free" Trimethylaluminurn. A toluene solution of poly(methy1aluminoxane (MAO) in toluene (10% by weight from Schering GmbH) displays a broad unresolved 'H NMR signal between +0.50 and -0.75 ppm. This broad signal is surmounted at -0.30 ppm by a sharp singlet arising from so-called "free" trimethylaluminum (TMA) even though the TMA is undoubtedly complexed with oxygen in a OA12-unit. Although the TMA can be diminished by heating MAO, the MA0 undergoes irreversible structural alterations by such thermal treatment. In order to remove the "free" TMA without the risk of such structural change, we have attempted to remove the TMA from MA0 by co-evaporation with toluene at 25OC. By evaporating the original toluene in vacuo and by replenishing the toluene and re-evaporating three more times, the original TMA-signal at -0.30 ppm (estimated at 30% of the methyl groups) had completely disappeared. When such "TMA-free" MA0 was redissolved in toluene, treated with (CD3)3Al (98% minimum deuteriation) and the 'H NMR spectrum remeasured, a strong, sharp signal assignable to "free" TMA was clearly evident. From this facile generation of "free" TMA, it can be concluded that certain MeAl units in the MAO, probably the terminal Me2Al unit, can readily exchange with TMA. Catalvst Productivity Numbers for the Homogeneous Catalysis of Ethylene Polymerization. Measuring and interpreting the kinetics of ethylene polymerization, even under initially homogeneous conditions, are difficult to perform in a reproducible and reliable manner. In order to obtain some convenient, useful measure of the catalyst activity of the Cp2TiMeC1-Me,AlC13-, system, therefore, batch polymerizations were conducted under standardized experimental conditions with individual variations in solvent, temperature, concentration, ratio of the Ti:Al components, and the nature of the Lewis acid aluminum cocatalyst. In order to produce an easily measurable amount of polyethylene, the polymerization runs were conducted for a standard 25-min period, during which time the initially homogeneous catalyst system turned heterogeneous. Such heterogeneity was shown not to be a controlling factor in altering the ranking of productivity numbers as the solvent
-
-
21. Role of Ion-pair o n Activity and Stereoregularity 229
polarity or catalyst concentration was changed by the following experiments. Polymerization runs of short duration (100 s), during which time the catalyst system remained homogeneous (little or no precipitation), gave essentially the same results: increasing the polarity of the solvent and decreasing the catalyst concentration increased the PN values. Table II.
Variations in the Productivity Number (PN) for the Homogeneous, Catalytic Polymerization of Ethylene by Cp2Ti(Me)C1
Me,A1Cl3-, with Reaction
Conditions * ’
run no.
solvent
temp
concn,
ratio
OC
mmolL’
Ti:A
Lewis acid
PN
1
CH,CI,
25
1.o
1:1
MeAICI,
140
2
CH,CI,
25
1.o
1:2
MeAICI,
163
3
CH,CI,
25
1.o
1:8
MeAICI,
140
4
CHZCI2
25
0.26
1:8
MeAICI,
440
5
CH,CI,
25
1.o
1:16
MeAICI,
94
6
CH,CI,
25
1.o
1:8
Me3AI
20
7
CH2CI2
25
1.o
1:8
Me2AICI
137
8
CH2CI2
25
1.o
1:8
AICI,
112
9
toluene
25
1.o
1:8
MeAICI,
49
10
toluene
25
0.26
1:8
MeAICI,
197
11
mesitylene
25
1.o
1:8
MeAICI,
11
12
toluene
70
1.o
1:8
MeAICI,
75
13
toluene
50
1.o
1:8
MeAICI,
69
14
toluene
25
1.o
1:8
MeAICI,
49
15
toluene
0
1.o
1:8
MeAICI,
10
16
toluene
-10
1.o
1:8
MeAICI,
c1
a
Productivity number (PN) is defined as grams of polyethylene per gram of Cp,TiMeCI per atm of monomer per hour and was found in six repeated runs to be reproducible to within f5%.
On the basis of six runs under identical conditions, average productivity numbers were determined as grams of polyethylene per gram of methyltitanocene chloride per atmosphere of ethylene per hour, which values were reproducible to within 3 3 % (Table 11). The catalyst system in solution before polymerization was generally golden colored,
230 J.J. Eisch and S.I. Pornbrik
consistent with the persistence of titanocene(IV). Only with Me3A1as a cocatalyst (run 6) did a deep blue color develop after 5 min of admixing; this indicated alkylative reduction to titanocene0. Catalyst Productivitv Numbers as a Function of the Concentration of the Polv(methvla1uminoxane)(MAO). In contrast with the increase in PN upon dilution of the catalyst concentration, as noted with the CpzTi(Me)C1-MeAlCl2 system, diluting the concentration of the Cp2TiC12-MA0 catalyst had no significant effect on the PN for the polymerization of ethylene. Thus, the following PN (conc. mmoVL) were observed: 212 (OSO), 241 (1.0) and 212 (2.0). DISCUSSION Interaction of Titanocene Dichloride (4) and Aluminum Chloride (5). From the foregoing variable-temperature,multinuclear NMR data, it is evident that the interaction of A1C13 (5) with Cp2Ti(Me)C1(6a), with Cp2Ti(CH2-SiMe3)C1 (6b). and even with Cp2TiC1, leads to the generation of some positive charge at titanium and the formation of the partly or wholly free AlCL-ion. Whether these effects find their explanation in either a contact-ion-pairstructure (6) or a solvent-separatedion pair (7) or both remains to be decided (equation 2).
66a R = M e 6b R = CH,SiMe, 6c R = C I
As to the positive charge on titanium, several data supports such a view: (1) the CH, group in 6a and the CH2 group in 6b are shifted downfield in the 'H spectrum by 1-2 ppm over their positions in the starting titanocenes, analogous to the downfield shifts seen in protons adjacent to carbenium ion centers: (2) the Cp protons in 6a 6c also occur 0.2-0.3 ppm downfield from their positions in the starting titanocenes; (3) in the known crystal structure of Cp2Ti(C1) A1MeC12, the bridging chloro ligand has a Ti-Cl separation of 0.23A. greater than that of the unbridged Ti-Cl bond. Either the presence of 6 or 7 in solution or a rapid equilibration between them at 25 OC would account for these observations. That at least a significantproportion of such 1:l complex with AlC13 exists, below -2OoC, as 7 is indicated by the presence of a relatively sharp, dominant "Al peak at 103 ppm. This peak corresponds exactly to the value reported for the free A1C14- ion. Upon warming, this signal broadens toward the low-field side and yields a maximum at 25OC between 104 and 105 ppm. From the 27Alspectra of similar complexes, this broadening is consistent with the equilibration depicted in equation 2. For example, the crystal structure
-
21. Role of Ion-pair on Activity and Stereoregularity 231
Ph(MeC=C(SiMq)Ti+Cppz- A1C14- shows the presence of individual ions, and displays its 27Alpeak as a sharp singlet at 103.6 ppm (CH2C12). Since the equilibrium of equation 2 was most likely operative in interconverting the bridged structures, 6, into their solvent separated counterparts, 7, we chose to study this equilibrium for the case where R = Cl. In this situation, no competing reaction could occur whereby any akyl group on titanium could be transferred to aluminum. Cooling in either CH2C12or toluene to below -20 "Cgave two well-resolved signals for the Cp-ring protons or carbons. Neither signal occurred where the signals of any uncomplexed Cp2TiC12would have occurred, if the low-temperature NMR spectra arose from the "freezing out" of the extensive dissociation of 17c into its components. The only reasonable interpretation, then, of the low-temperature N M R results is that the equilibration between 6 (contact IP) and 7 (solvent-separated IP) (equation 2) has been "frozen out". That such systems contain ions is evident from the pioneering work of Dyachkovskii and co-workers on the electrical conductivity, electrodialysis, and polymerization of ethylene observed in halocarbons.")* 12) It remained to be learned whether such spectra at -30 OC responded to changes in concentration and in solvent polarity, as would be expected of CIP-SSIP equilibria. In accordance with Ostwald's dilution law, the two-particle, solvent-separatedion pairs (SSIP) should be favored at lower concentrations over one-particle, contact ion pairs (CIP), and that is what is observed. Furthermore, SSIP should be preferred over CIP as the medium becomes more polar, and again this is observed. From these observations, the high-field signal in the 'H and 13CN M R spectra at -30 OC can be assigned to the solvent-separated ion pair and the low-field signal to the contact ion pair. Productivity Numbers of the Cp,Ti(Me)C1-Me,AIClq, Svstem for the Polymerization of Ethylene as a Function of Experimental Conditions. The observed changes in PN (Table II) with variation in the experimental conditions for polymerization (more polar solvent, lower concentration, relative insensitivity to temperature increase above a threshold temperature, and relative insensitivity to the Lewis acid strength of Me,AlC13-,,) can best be reconciled with the conclusion that the solvent-separated ion pair Cp2Ti+Me11 A1Me,C14-, is the most active polymerization initiator in polar, nondonor solvents such as CH2C12 If the contact ion pair Cp2(Me)Ti C1 Me,AlC13-, were the active site, then the PN should have shown an increase at higher concentrations and in polar solvents. The relative insensitivity of PN to the Me,AlC13, species used as the Lewis acid with Cp2TiMeC1is consistent with the interpretation that even the weakest acid, Me2AlC1, used in a 1:l ratio (run 1). is sufficient to produce the SSIP (equation 3) in significant
Cp2TiMeCI
+
MefiICI
A 7
Cp2Ti+ Me AIMe2C12-
(3)
proportions. Used in a 1:2 ratio (run 2), MeAlC12 could shift the equilibrium of equation 3 to the right by the law of mass action. On the other hand, the deleterious effect on PN of a
232 J.J. Eisch and S.I. Pombrik
-
Ph(MeC=C(SMe3)Ti+Ch A l Q - shows the presence of individual ions, and displays its 27Alpeak as a sharp singlet at 103.6 ppm (CHZC12). Since the equilibrium of equation 2 was most likely operative in interconverting the bridged structures, 6, into their solvent separated counterparts, 7, we chose to study this equilibrium for the case where R = C1. In this situation, no competing reaction could occur whereby any alkyl group on titanium could be transferred to aluminum. Cooling in either CH2C12or toluene to below -20OC gave two well-resolved signals for the Cp-ring protons or carbons. Neither signal occurred where the signals of any uncomplexed Cp2TiC12would have occurred, if the low-temperatureNh4R spectra arose from the "freezing out" of the extensive dissociation of 17c into its components. The only reasonable interpretation, then, of the low-temperatureNMR results is that the equilibrationbetween 6 (contact IP) and 7 (solvent-separatedIP) (equation 2) has been "frozen out". That such systems contain ions is evident from the pioneering work of Dyachkovskii and co-workers on the electrical conductivity, electrodialysis, and polymerization of ethylene observed in halocarbons."). 12) It remained to be learned whether such spectra at -30 OC responded to changes in concentration and in solvent polarity, as would be expected of CIP-SSIP equilibria. In accordance with Ostwald's dilution law, the two-particle, solvent-separatedion pairs (SSIP)should be favored at lower concentrations over one-particle,contact ion pairs (CIP), and that is what is observed. Furthermore, SSIP should be preferred over CIP as the medium becomes more polar, and again this is observed. From these observations,the high-field signal in the 'H and 13CNMR spectra at -30 OC can be assigned to the solvent-separatedion pair and the low-field signal to the contact ion pair. Productivitv Numbers of the Cu7Ti(Me)Cl-Me,A1C1?-m Svstem for the Polvmerization of Ethvlene as a Function of Experimental Conditions. The observed changes in PN (Table II) with variation in the experimental conditions for polymerization (more polar solvent, lower concentration,relative insensitivity to temperature increase above a threshold temperature, and relative insensitivity to the Lewis acid strength of Me,A1Cl3.,) can best be reconciled with the conclusion that the solvent-separatedion pair Cp2TitMe 11 A1Me,Cl4-, is the most active polymerization initiator in polar, nondonor solvents such as CH2ClP If the contact ion pair Cp2(Me)Ti C1 MenA1C13, were the active site, then polar solvents. the PN should have shown an increase at higher concentrationsand in The relative insensitivity of PN to the Me,AlC13-, species used as the Lewis acid with Cp2TiMeClis consistent with the interpretation that even the weakest acid, MqAlCl, used in a 1:1 ratio (run 1). is sufficient to produce the SSIP (equation 3) in significant
Cp,TiMeCI
+
MefiICI
7
Cp2Ti+Me AIMe2C12-
(3)
proportions. Used in a 1:2 ratio (run 2), MeA1C12 could shift the equilibrium of equation 3 to the right by the law of mass action. On the other hand, the deleterious effect on PN of a
21. Role of lon-pair on Activity and Stereoregularity 233
large ratio of Lewis acid to Cp2TiMeCl (1:l -,16:1, PN of 140 494, runs 1 and 5 ) can be attributed to a transmethylation that destroys the crucial Ti-Me bond of Cp2TiMeCl. In a similar vein, the negative effect of MqAl (run 6) is readily ascribed to the destruction of Cp2TiMeC1by reduction to T i m . From the lower PN displayed by Cp2TiMeC1-MeAlQ2 as one passes from CH2C12 (140. run 3) to toluene (49,run 9) to mesitylene (11, run 11). it is clear that the solvated cation-anion pair 8 is the dominant ion pair present as an q'-complex in aromatics (equation 4) and that such a SCAP must be the least active polymerization site. The relative
reactivity of these ion pairs in polymerization can therefore be ordered as SSIP >> CIP > SCAP. Nature of the Poly(methv1aluminoxanae) (MA01Used in These Studies. The observation that MAO, which has been separated from any "free" TMA, readily exchanges methyl groups with externally added (CD3)3k1suggests that there are Me-A1 units that can undergo bridging and thus facile exchange with external TMA. We propose that the chain terminus units of MAO, namely the dimethylalumino groups, are the most likely sites for such exchange. Furthermore, such MqA1 units should also be the most reactive methylating sites for transition metal halides. Finally, the chloro- or dichloroalumino sites resulting from such methylation should be both sterically and electronically the strong Lewis acid sites that can foster metallocenium ion formation (equation 5). This proposal is based upon the
1CP2MCI2
Me2AI-MAo)
Cp2MMe2
C'2A1-MA0)
Cp2M+-Me
+
' cI..cI/'
Me,?Af '\Af CI
Me
8
L
(5)
4 % (0-AlMe j-
Me
findings and hypotheses of Steiger and Kaminsky. The fact that MA0 with Cp2TiC12yields a high PN (>200) that is relatively insensitive to dilution of the catalyst supports the conclusion that MA0 initially produces such a large proportion of solvent-separatedion pairs that dilution no longer promotes the dissociation of any significant proportion of contact ion pairs. The Polymerization Catalyst Systems. Bis(n-butylcycloDentadienylhirconium Dimethyl (la) with =)?B (2) and Bis(n-butylcvclomntadieny1hirconium Dichloride (lb) with MA0 (3). The main problem in observing ionic species under conditions typical for industrial polymerization processes is the low polarity of the reactants and the solvent. With weakly coordinating solvents like toluene and the complex anions possibly fonned from the typical methylaluminoxanecocatalyst, the stabilization opportunities for metallocenium
234 J.J. Eisch and S.I. Pombrik
cations are very limited. This, of come, limits the shelf-life of such ion complexes significantly so that we were not able to isolate any complexes from toluene up to now, whereas the solvatecomplexes with THF or acetonitrile are reported as isolated crystals and have been characterized by means of x-ray crystallography?) Unfortunately, these solvated complexes are inactive in polymerization. The present studies of the polymerization catalyst systems, l a with 2 and l b with 3, nicely complement the foregoing investigations of the Cp2TiCl2-A1Cl3 system. Although the temperature-dependentmultinuclear studies of the latter system have furnished the first evidence for the existence of equilibria among contact (CIP),solvent-separated (SSIP) and solvated-cation(SCAP) ion pairs, it remained to be established that such ion pairs were actually present into industriallyimportant Ziegler-Natta catalysts. Our present results with the l a 2 and l b 3 systems accomplish exactly this desired goal. The significant increase in electric conductivity upon reaction of the metallocenes l a or l b with either boron activator 2 or methylaluminoxane 3, respectively, clearly supports the formation of solvent-separatedion pairs and the existence of an equilibrium with contact ion-pairs. The 'H-NMR- and "B-NMR results provide further evidence for ion-pair formation in the l a 2 system. The molecular steps of activation by methylaluminoxaneare believed to be more complex. Some ideas concerning this mechanism of activation by MA0 have already been published and are considered here. The role of MA0 in these catalyst system will surely be the subject of further research. However, it can be stated that ion-pair formation can indeed be observed in olefin polymerization catalyst systems under conditions close to those employed in commercial-scalepolymerization. Imulications of Ion-Pair Formation for StereoregularPolvmerization. Although there is little doubt that solvent-separatedion pairs are the most active catalyst sites for the polymerization of ethylene and of propylene by soluble metallocene-Lewisacid combinations,the further tantalizing question remains: what is the role of such ion pairs in the stereoregulationof a-olefin polymerization? A partial answer to this question may be contained in a most recent, pertinent study by Herfert and Fink.13) These researchers investigated the syndioselectivepolymerization of propylene with the isopropylidene(fluoreny1)cyclopentadienyliirconium dichloride-MA0 catalyst system in CH2C12-toluenemixtures and found that as the polarity of the solvent increased, the rate of polymerization increased but the syndiotacticindex decreased. This suggests that solvent-separatedion pairs are more active sites but they are less syndioselective than contact ion pairs. Additional research on the influence of ion pairs on both syndiotactic and isotactic polymerization indices is needed, in order to settle this important issue.
-
-
-
REFERENCES 1. J. Boor, Jr.: "Ziegler Natta Catalysts and Polymerizations", Academic Press, New York, 1979, p. 670.
21. Role of Ion-pair on Activity and Stereoregularity 235
2. 3. 4. 5.
6. 7. 8. 9a. b. C.
d. 10a.
b. C.
d.
e.
f.
J.C.W. Chien, "Coordination Polymerization", Academic Press, New York (1975). K. Ziegler, Angew. Chem., 76,545(1964). G. Natta, Makromol. Chem.,l6,213 (1955). J.A. Ewen, J. Am. Chem. Soc.,106.6355(1984). W. Kaminsky, CLB Chemie f. Labor und Betrieb, 38,398,(1987). H.H. Brintzingner, et al., J. Organomet. Chem., 2&63 (1985). Cat. SOC.of Japan, 33,536,(1991). J.J. Eisch, A.H. Piotrowski, S.K. Brownstein, E.J. Gabe, F.J. Lee, J. Am. Chem. SOC.,
107,7219(1985). J.J. Eisch, S.I.Pombrik, G.X. Zheng, Organometallics,l2,3856 (1993). P.G. Gassmann, M.P. Callstrom, J. Am. Chem. Soc.,lO9,7875(1987). R.P. Jordan, L.S. Bajgur, R. Willett, B. Scott, J. Am. Chem. S O C . , ~7410 , (1986). M. Bochmann, S.J. Lancaster, Organometallics, 2,633 (1993). J.C.W. Chien, A.D. Rausch, W.M. Tsai, Appl. Organomet. Chem., z (1993). G.G. Hlatky, H.W. Turner,R.R. Eckmann, J. Am. Chem. S O C . , ~2728 , (1989) T.J. Marks,X. Yang, C.L. Stem, J. Am. Chem. S O C . , ~3623 , (1991). R. Jordan, D.J. Crowther, M.C. Baenzinger, A. Verme, Organometallics, 2.2574 (1990). e.g. Y.W. Aelyunas, N.C. Beanzinger, P.K. Bradley, R.F. Jordan, Organometallics,
12.
13, 148 (1994). F.S.Dyachkovskii, in 'Toordination Polymerization" (Ed. J.C.W. Chien). Academic Press, New York, 1975,p. 199. The electric conductivity of a pure toluene solution of l a under these conditions was
13.
determined to be d o 0 5 pS. N. Herfert and G. Fink, Makromol. Chem., 193,773(1992).
11.
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237
22. High Molecular Weight Monodisperse Polymers Synthesized by Rare Earth Metal Complexes
H. YASUDA", E. IHARA, S . YOSHIOKA, M. NODONO, M. MORIMOTO, and M. YAMASHITA Department of Applied Chemistry, Faculty of Engineering, Hiroshima University, Higashi-Hiroshima 724, Japan
ABSTRACT High molecular weight polyethylene ( M n > 300,000, M,/Mn = 1.6) was obtained by using bulky Sm(I1) or Sm(II1) species such as Me2Si(2-SiMe34-tBu-CgH2)2Sm(THF) and Me2Si[2(3),4-(SiMe3)2-CgH212SmCH(SiMe3)2 as initiator. These complexes also conduct the polymerization of 1-pentene and 1hexene to give isotactic polymers of M n > 20,000 with Mw/Mn = 1.6. By contrast the polar monomers such as methyl methacrylate and alkyl acrylates also proceeded the living polymerization by using Ln(C5Me5)2R (R = H, Me) to give high molecular weight polymers ( M n > 450,000) with extremely low polydispersity (Mw/Mn < 1.05). INTRODUCTION Classical Ziegler-Natta catalyst positions as the 1st generation catalyst for polymerizations of ethylene or propylene. The 2nd genaration catalyst lies in MgC12 and/or donor supported Ziegler-Natta catalyst, which exhibits 100 times higher catalytic activity as compared with the 1st generation catalyst. These two are heterogeneous systems composed of two or three metal components. More recently, Kaminsky and Ewen catalyst systems, Z1€p2Cl/(AlMe-0-)~ and Me2C(flurorenyl)CpHfC12/(A1Me-O-)nYwere found as the 3rd generation catalyst for polymerization of ethylene or propylene. These systems are homogeneous, but the clarification of the polymerization mechanism has failed because of the complex structure of (AlMe-O-)n. Homogeneous organolanthanide complexes such as LaH-(C5Me5)2 belongs to the 4th generation catalyst exhibiting high initiating property for the polymerizations. We have synthesized new series of bulky organo-rare earth(I1) and -(III) complexes as excellent catalyst for polymerization of ethylene and 1olefins. On the other hand, we have first found that organolanthanides such as LnR(C5Meg)2 (Ln = Y, Yb, Sm, Lu; R = H, Me) exhibits excellent catalytic activity for the polymerization of polar monomers such as alkyl methacrylates and alkyl acrylates. These initiators conducted the living polymerization of these monomers
238 H. Yasuda, E. Ihara, S. Yoshioka. M. Nodono, M. Morimoto and M.Yamashita
to afford high molecular weight polymers (Mn > 450,000) with extremely narrow molecular weight distribution (Mw/Mn ~ 1 . 0 5 ) .By taking advantage of the living polymereization properties for both methyl methacrylate(MMA) and alkyl acrylates such as butyl acrylate(BuA), a MMA/BuA/MMA tri-block copolymer-ization was realized by the addition of these monomers in this order. Various lactones could be polymerized in a living fashion.
EXPERIMENTAL All the operations were performed under argon General Consideration. by using standard Schlenk techniques. Ethylene was used without further purification. 1-Pentene and 1-hexene (Aldrich Chem) were dried over CaH2 and distilled before use. Methyl methacrylate and alkyl acrylates were dried over CaH2 for more than 4 days and the distillate was further dried over activated molecular sieves 3A for 5 days. 1H and 13C NMR spectra were recorded on a JEOL GX-500 or a JEOL GX-270 spectrometer. Gel permeation chromatographic analyses were run on a Tosoh Model SC-8010 using columns TSK gel G1000, (32500, G4000 and (37000 in chloroform at 25°C for poly(MMA) and poly(alky1 acrylate) and run on a Waters 150C with Shodex column (AT8OM) using 1,2,4-trichlorobenzene as eluent at 130°C for polyethylene. The molecular weight of these polymers were determined with the calibration curve obtained using standard polystyrene. Preparation of Bulky Sm(ZZ) Complex. To a solution of CgHgNa (420 ml of a 2.38 M solution, 1.0 mol) was added dropwise 2-bromo-2-methylpropane (181 ml, 1.5 mol). After being stirred for 24 h, the reaction mixture was poured into cold water. The organic product was then extracted with hexane and was distilled under reduced pressure (54°C 35mmHg). Resulting tBuCgH5 (49.6 g, 380 mmol) was added dropwise to a suspension of NaH (14.4 g, 380 mmol) in 250 ml of THF at 0°C. Stirring was continued further for 18 h at room temperature. After the removal of solvent, 300 ml of hexane was added to the residue. To the hexane suspension was added dimethyldichlorosilane (23.1 ml, 190 mmol) and the mixture was stirred for 18 h. After quenching the product with cold water, the resulted product was extracted with hexane and distilled to give Me2Si(3-tBu-CgH3)2 (165"C, 0.1 mmHg). Subsequently n-BuLi (97.2 mmol, 60.8 ml of 1.56 M solution in hexane) was added to a THF solution (200 ml) of Me2Si(3-tBu-CgH4)2. After being stirred for 6 h, trimethylchlorosilane (14.7 ml, 116.6 mmol) was added to the solution and stiriring was continued for 12 h. The mixture was quenched with aq. sodium carbonate and the organic layer was distilled to give Me2Si(2-SiMe3-4-tBuC5H3) (190 - 200"C, 0.1 mmHg). Yield, 26%. To a solution of Me2Si(2-SiMe3-4tBu-CgH3)2 (3.01 g, 6.77 mmol) in 60 ml THF was added 8.2 ml of 1.66 M nBuLi/hexane solution(l3.5 mmol) at 0°C. In order to exchange Li metal with K metal, a THF solution (20 ml) of tBuOK(1.52 g, 13.6 mmol) was added to a THF
22. High M.W. Monodisperse Polymers 239
solution of Me2Si(2-SiMe3-4-tBu-C5H2)2Li2. The mixture was refluxed for 12 h to afford potassium derivative. Resulted THF solution of Me2Si(2-SiMe3-4-tBuCgH2)2-K2 (6.77 mmol) was added to a THF solution (80 ml) of SmI2 (6.8 mmol). The mixture was refluxed for 12 h and THF soluble part was evaporated to dryness. The product was recrystallized from THF/hexane to give Me2Si(2-SiMe3-4-tBuC5H2)2Sm(THF)2. To a solution of CgHgNa (1.2 Preparation of BuZky Sm(ZZZ) Complex. mol) in 300 ml of THF was dropwise added SiMe3C1 (1.2 mol, 152.3 ml) at 0°C. The reaction was carried out for 2 days and then the product was quenched with water. Distillation of haxane soluble part (48 mmHg/59"C) gave 52 ml of Me3SiC5H5 in 45% yield (52 ml). Then to the suspension of NaH (0.47 mol, 18.8 g) in 170 ml of THF was added 52 ml of Me3SiCgHg. After stirring the mixture overnight, the resuting solution was centrifuged to remove the excess NaH. To the mother liquor, Me3SiC1 (0.47 mol, 60 ml) was added at 0°C and the mixture was stirred there for 1 day. After quenching with water, desired (Me3Si)zC5H4 (0.2 mol, 50 ml) was obtained from the hexane soluble fraction (66"C/6 mmHg). The colorless (Me3Si)2C5H4 (48 ml) was then added to NaH (18.8 g, 0.47 mol) in THF (130 ml) at 0°C and stirred there overnight. Me2SiC12(0.1 mol, 14 ml) was added dropwise to the resulting solution and stirred at 60°C for 60 h. Thus Me2Si[(SiMe3)2CgH2]2 was obtained in 52% yield by distillation using Kugelrohr. The resulted ligand (1 ml) was lithiated with BuLi (3.8 mmol, 2.4 ml in hexane) by stirring overnight in THF (10 ml). Then the resulted lithium salt was added to the anhydrous SmC13 (1.6 mmol, 0.42 g) suspended in THF (15 ml) and the mixture was refluxed for 8 h. After evaporation of the mixture to dryness, ether (30 ml) was added to the residue. The ether soluble part was evaporated to dryness and hexane was added. From hexane soluble part, Me2Si[2,4-(Me3Si)2C5H2]2SmC12Li(THF)2 (racemo) was obtained as orange crystals. From hexane [2,3-(Me3Si)2CgH2]SmC12Li(THF)2 (C1 insoluble part, Me2Si[2,4-(Me3Si)2-C5H2] symmetry) was obtained as yellow crystals. Respective products (0.23 g, 0.29 mmol) were treated with LiCH(SiMe3)2 (0.29 mmol) for 24 h and the corresponding alkylsamarium (111) were obtained in 20-30% yield. Other rare earth metal compounds(II1) are prepared in essentially the same method as described previously. Polymerizations of Ethylene and Alkyl Acrylates. Ethylene was bubbled at 1 atmospheric pressure at 25°C to the toluene solution included the catalyst for a fixed time and the resulted polyethylene was quenched with water and then dried. Alkyl methacrylates and alkyl acrylates were polymerized with the catalyst for a fixed time by the addition of alkyl(Meth)acrylsates to the catalyst solution in toluene.
240 H. Yasuda, E. Ihara, S. Yoshioka, M. Nodono, M. Morimoto and M.Yamashita
RESULTS AND DISCUSSION I . Polymerization of Ethylene with Organolanthanide(ZZ) and - ( Z l Z ) Species. 1-21 Ethylene polymerization using the conventional rare earth metal(I1) complexes such as Sm(C5Meg)2(THF)2 proceeds to afford the polymer of Mn = 20,000 with relatively low polydispersity. However, when the molecular weight of resulted polyethylene exceeds Mn = 25,000, the polydispersity increased significantly to Mw/Mn > 2.2. The present polymerization should occur in the following equation by changing the Sm(I1) species to Sm(II1).
Table. 1 The Mode of Polymerization with Sm(C5Me5)2(THF)2 Cocn, mM 1.o 1.o 1.o
Time/min Activity(Kg/ mol h) 10-3 Mn
0.5 1 3
5 10 430 410
1.80 2.28 2.46
Mw/Mn 1.25 1.32 2.28
In order to improve this disadvantage, we have designed new type of Sm(I1) complexes with bulky ligand. The preparation was carried out in the following scheme. The resulted Sm(I1) (racemo) complex was active for polymerization of ethylene and provided the polymer of Mn = 330,000 with low polydispersity (Mw/Mn = 1.6). In the similar manner, meso-type Sm(I1) was synthesized by the following scheme. However, meso-type complex produced the high molecular weight polyethylene with rather broad polydipersity.
22. High M.W. Monodisperse Polymers 241
On the other hand, rare earth metal (111) species such as La(C5Me5)2H is known to exhibit good activity for polymerization of ethylene and conducted the polymerization to give Mn = 670,000 with rather low polydispersity (Mw/Mn = 1.8), while Ln-(C5Me5)2CH(SiMe3)2 is completely inert towards ethylene. The Ln(CgMe5)2H is however thermally unstable and was not isolated as yet. Therefore, we have synthesized thermally stable organolanthanides in the following scheme. Hexane Insoluble
'SiMej
Me3SI Li' ,,@MeQ/JiMe3
THF
0 Me3Si
Me
Me,SI
+
L1'
SrnC1,Me&,,
L
Hexane soluble
I@SIMe3
9
0
D
Mezs&;i>Ll: Meas1
V I The resulted alkylorganolanthanide(II1) complex was revealed by single X-ray analysis to be C1-symmetry (one set of SiMe3 groups locate in meso-like position). The precursor of racemi-type complex was also analyzed by X-ray studies as illustrated below. The Cp'-Sm-Cp' dihedral angle is 117", about 15" smaller than that of the non-bridged Sm(CgMeg)2Me. ,.S iMe3 S ' S iMe3 I \ .SiMe3
n CH2=CH2 c
242 H. Yasuda, E. Ihara, S. Yoshioka, M. Nodono, M. Morirnoto and M.Yarnashita
Fig. 1, Molecular structure of Me2Si-
Fig. 2, Molecular structure of Me2Si-
[2(3),4-(SiMe3)2-C5H2]2SmCH(SiMe3)2 [2,4-(SiMe3)2-CgH2]2SmCH(SiMe3)2 (C1 symmetry)
(racemo)
The results of ethylene polymerizations by using these complexes are summarized in Table 2. Table 2. Characterization of Polyethylene Obtained by Bulky Sm(1I) and Sm(II1) Complexes. Initiator
10-3 Mn MwIMn
Activity (kg/mol h)
Me2Si(2-SiMe34-tBu-C~H2)2Sm(THF)2 (racemo) 356 1.60 139 Me2Si[2(3),4-(SiMe3)2-C5H2]2LaCH(SiMe3)2 498 1.88 80 Me2Si[2(3),4-(SiMe3)2-CgH2]2SmCH(SiMe3)2 (C1) 41 3 2.19 33 Me2Si[2(3),4-(SiMe3)2-C~H2]2YCH(SiMe3)2 (C1) 331 1.65 188 Me2Si[2,4-(SiMe3)2-C5H2]2SmCH(SiMe3)2 (racemo) no polymerization Me2Si[2,4-(SiMe3)2-C5H2]2YCH(SiMe3)2 (racemo) no polymerization 590 1.81 [(C5Me5WaHI 2 2 . Polymerizations of 1 -0lefins with Sm(II) and Ln(IIZ) Complexes. Me2Si(CgHq)(N-tBu)YH and Me2Si(2-SiMe3-4-tBu-C5H2)2YH are known to exhibt high catalytic activity for polymerization of 1-olefins such as propylene, 1pentene and 1-hexene. We have found that bulky Sm(I1) such as MezSi(2-SiMe3-4tBu-CgH2)2Sm(THF)2 (racemo) exhibits good intiating property for polymer-
22. High M.W. Monodisperse Polymers 243
ization of 1-pentene and 1-hexene. Especially noteworthy is the formation of highly isotactic poly( 1-olefin) by this catalyst. Isotacticity exceeds over 97%. In Figure 1, 13C NMR spectrum of the resulted poly(1-pentene) is shown. The C3 signal appeared as singlet peak to indicate the formation of isotactic polymer. On the other hand, Me2Si[2,4-(SiMe3)2-C5H2][3,4-(SiMe3)2-CgH2]YCH(SiMe3)2 (C1 symmetry) also exhibits good catalytic activity. However, this initiator provides atactic poly( 1-pentene) or poly( 1-hexene) (Table 3). Table 3. Characterization of Poly(1-olefin) Prepared by Bulky Sm(I1) and Y(II1) Complexes. Monomer 1-pentene
1-hexene
Initiator
1 0 - 3 ~Mw/Mn ~
Me2Si(2-SiMe3-4-tBu-CgH2)2Sm(THF)2 13 Me2Si[2(3),4-(SiMe3)2-CgH2]2YCH(SiMe3)2 16 Me2Si(2-SiMe3-4-tBu-C5H2)2YH 20 Me2Si(2-SiMe3-4-tBu-CgH2)2Sm(THF)2 19 Me2Si[2(3),4-(SiMe3)2-C5H2]2YCH(SiMe3)2 64 Me2Si(2-SiMe3-4-tBu-CgH2)2YH 24
1.63 1.42 1.99 1.58 1.20 1.75
3. Living Polymerization of Methyl Methacrylate3-5 1 Polymerization of methyl methacrylate with organolanthanide(II1) complexes were performed with SmH(C5Me5)2, LnMe(CgMeg)2(THF) (Ln = Y, Yb, Sm) or Ln(CgMe5)2Me2AlMe2 (Ln = Sm, Yb, Lu). As a typical example of polymerization, SmH(C5Meg)2 initiated polymerization is summarized in Table 4.
(6 38.0.mmmm)
1 I
,
m PPM
40
30
20
10
Fig. 3 13C NMR spectrum of poly(1-pentene)
244
H. Yasuda, E. Ihara, S . Yoshioka, M. Nodono, M. Morimoto and M.Yamashita
These reactions involve the following marked features. 1) The polydispersity of resulting polymers are unusually low and reach Mw/Mn=l.O3. 2) Polymerization proceeds very rapidly and is complete in a short period with high initiator efficiency. 3) The polymerizations gave high molecular weight poly(MMA) especially when the concentration of the complex was lower than 0.2 mol%. 4)The polymerization proceeds at wide range of reaction temperature starting from +40 to -95°C. 5) Highly syndiotactic polymerizations occur at lower temperature. Table 4. Characterization of Poly(MMA) Synthesized by SmH(CsMe5)2 ~~
~
Polymerization MMA/initiator Temp. ("C) charged, mol/mol
40 25 0 0 -78 -95
500 500 1500 3000 500 lo00
10-3 Mn
55 57 215 563 82 187
Mw/Mn
1.03 1.02 1.03 1.04 1.04 1.04
IT
conversion %,(reacn. h)
77.3 79.9 82.6 82.3 93.1 95.3
99(1) 99(1) 93m 98(3) 97(17) 82(60)
rr; syndiotacticity These results indicate that the present polymerizations proceed in a living fashion. In fact, the Mn of polymers increased linearly in proportion to the conversion irrespective of the initiator concentration, while M w/Mn remains intact during the polymerization. Consequently, we can readily estimate that the present polymerization occurs in a living fashion. To get further insight into the initiation mechanism, we have demonstrated the stoichiometric reaction at 0°C between SmH(CjMe5)2 and MMA. As a result the 1:2 adduct was obtained as single crystals (mp 132°C). This adduct is active for polymerization of MMA and produced the polymer of Mn = 110,000 (Mw/Mn = 1.03) when 100 equivalents of MMA was added. Deuterolysis of the adduct gave DCMe(C02Me)CH2C(Me)2CO2Me to indicate the formation of Sm-enolete or Sma-carbon bond. To verify the exact structure of SmH(MMA)2(CsMe5)2, single crystal X-ray analysis was performed. The adduct has an eight-membeed ring structure. The enolate group bears a cis configuration and binds with another MMA molecule which coordinates to the metal with its ester group.
22. High M.W. Monodisperse Polymers 245
n
v Fig. 4 X-ray analysis of SmH(MMA)2(C5Me5)2 These results indicate that, in the initiation step, the hydride should attack the CH2 group of MMA to generate a transient Sm-O-C(OCH3)=C(CH3)2 species, and then the incoming MMA molecule may participate in a 1P-addition to afford the eight memberted ring intermediate. Then in the propagation step another MMA molecule may attack the growing end, liberating the coordinated ester group. Syndiotactic polymerization should occur by repeating these reactions, where the coordination site changes alternatively. 4. Living Polymerization of Alkyl Acrylates Living polymerizations of methyl-, ethyl-, and butyl acrylate have not been achieved since their acidic a-H easily takes place nucleophilic addition reaction. However, living polymerizations proceed by the unique function of organolanthanide complexes such as SmMe(CgMe5)2(THF) and YMe(C5Me5)2(THF). The results are shown in Table 5. In these cases, living polymerization gave atactic polymers.
Table 5. Polymerization of Alkyl Acrylate with SmMe(CgMeg)2(THF) Monomer
10-3 Mn
Mw/Mn ~
Methyl acrylate Ethyl acrylate Butyl acrylate
55 65 88
Conversion/% ~~~
1.04 1.04 1.04
99 94 99
246 H. Yasuda, E. Ihara, S . Yoshioka, M. Nodono, M. Morimoto and M.Yamashita
The rate of polymerization of alkyl acrylates increases in the order Bu > Et > Me, by sharp contrast to the order Me > Et > Bu observed in the cases of alkyl methacrylates. Table 6. Properties of Tri-block Copolymers System
Tensil Tensile Elongation Compression % % modulas(MPa) strength(MPa)
Poly(MMA/BuA/MMA) (2551 :24) (8 :72: 20) Poly(MMA/EtA/EtMA) (26:48: 26) Poly(MMA)
46 0.8 119 610
22 0.7
81 163
100 58
22 80
276 21
62 100
BuA , n-butyl acrylate; EtA, ethyl acrylate; EtMA, ethyl methacrylate
-, ~ C - C H ~ ~ C - C H ~ ~ ~ C - C H ~ ~ ~ MMA H+
poly(MMA-BuA-MMA)
Me
H
Me
C02Me I C02Me
fl
,2
C02Me
/, t
i
\
poly(MMA)
I 1
i
j
!
20.0
30.0
Time (min)
Fig. 5 GPC profilesof mono-, di- and triblock copolymers
22. High M.W. Monodisperse Polymers 247
As a result, poly(MMA/BuA/MMA) tri-block copolymer in the ratio of 8:72:20 and poly(MMA/EtA/EtMA) in the ratio of 26:48:26 showed the big elongation and small compression to indicate that these polymers exhibt rubber-like elastic property. The GPC profile of the mono-, di and tri-block polymers are shown below.
5. Living Polymerization of Lactones. As an extention of the presen work, we have examined the polymerization of lactones such as P-propiolactone (PL), E-valerolactone (VL) and E-caprolactone (CL) and foud that these systems proceeds the living polymerization. The resuls are shown in Table 7.
The addition of one equivalent lactone to YOMe(C5H5)2 resulted in the formation of 1:l adduct, which gave upon hydrolysis the original lactone, while lactone polymerization starts by the addition of two equivalent of lactone and one equivalent capric acid was obtained by hydrolysis. This result clearly indicates that 0-acyl bond cleavage occur in the propagation step. The M n increases in proportion to the conversion, while molecular weight distribution remains intact.
5
1.00 I
0
I
25
50
75
100
Conversion (O/o)
Figure 6. M n and M / M n vs. conversion for polymerization of caprolactone with YOMe(CgRg)2
248 H. Yasuda. E. Ihara, S . Yoshioka, M. Nodono, M. Morimoto and M.Yamashita
Table 7. Living Polymerization of Lactones. Initiator [YOMe(C5H5)212 SmMe(CgMeg)2(THF) [YOMe(C5H5)212 SmMe(CgMeg)(THF)
Monomer PL VL CL CL CL
10-3 Mn
60 75 130 39 33
M w/Mn
1.13 1.07 1.06 1.04 1.03
Conversion/% 78 80 95 52 87
References 1) H. Yasuda and H. Tamai, frog. folym. Sci., 18, 1097 (1993). 2) H. Yasuda and E. Ihara, J. Synrh. Org. Chem. Jpn., 51, 931 (1993). 3) H. Yasuda, H. Yamamoto, K. Yokota, S . Miyake, and A. Nakamura, J. Am. Chem. SOC.,114,4908 (1992). 4) H. Yasuda, TH. Yamamoto, Y. Takemoto, M. Yamashita, K. Yokota, A. Nakamura, S. Miyake, Y. Kai, and N. Kanehisa, Macromolecules, 26, 7134 (1993). 5 ) H. Yasuda, H. Yamamoto, Y. Takemoto, M. Yamashita, K. Yokota, S . Miyake, and A. Nakamura, Makromol. Chem. Macromol. Symps. 67, 187 (1993). 6) H. Yasuda, M. Furo, H. Yamamoto, A. Nakamura, S . Miyake, and N. Kibino, Macromolecules, 25,5115 (1992).
249
23. Lanthanocene Based Catalysts for Olefin Polymerization : Scope and Present Limitations
J. F. PELLETIER, A. MORTREUX, F. PETIT Laboratoire de Catalyse hCi4rogPne el homoghe, URA CNRS 402, USTL, ENSCL. BP 108.59652 Villeneuve d h c q Cedex (France)
X. OLONDE AND K. BUJADOUX E.C.P. EniChem Polymeres France, Cenire de recherche. 62670 Mazingark (France)
ABSTRACT The ethylene polymerization has been studied over pentamethylcyclopentadienyl based neodynium and samarium catalysts under various conditions,ranging from low temperature - low pressure (1 atm - 20°C) to those used in a high temperature - high pressure pilot plant (180°C - 1200 b). The catalyst remains stable, but attempts at copolymerization with 1-butene have failed, even in the presence of an ylide as modifier. A comparison with the more conventional Cp2ZrCI2 - MA0 catalyst shows that these lanthanocene catalysts, although more reactive, are not able to copolymerize ethylene with a-olefins under industrial conditions.
INTRODUCTION Olefin insertion into metal carbon bonds and p hydrogen elimination are fundamental reactions occuring in Ziegler-Natta catalysis. The characterization of the active sites is however complicated by their multicomponent composition. Several years ago, tremendous advances in lanthanides and group 3 element chemistry provided well defined alkyl metal complexes which served as excellent models for mechanistic studies. Watson [ 11, Marks [2], Bercaw [3] and Teuben [4] synthesized hydrides and alkyls lanthanocenes, scandocene and yttrocene, which are highly active in polymerization but are also extremely sensitive towards impurities like oxygen and moisture. In general, to be used in industrial processes, Ziegler-Natta catalysts contain a slight excess of cocatalyst (alkyl reagent) as scavenger. We have recently reported the possibility to produce polymerization catalysts by direct alkylation between Cp*2NdC12Li(OEt2)2 1 and common alkylating reagents [ 5 ] . Their behaviour at high temperature was also examined. In this paper, we wish to report some data obtained on other lanthanocene based catalysts and discuss about their behaviour in copolymerizations with olefins.
250 J.F. Pelletier, A . Mortreux, F. Petit, X. Olonde and K . Bujadoux
EXPERIMENTAL All reactions were done with dry solvents under nitrogen. The complexes Cp2*LnC12Li(OEt)2 [6], Cp2*NdCH(SiMe3)2 [2], [Cp2YC1]2 [7] and the ylide [81 were synthesized as previously described in the litterature. AtmosPheric DRSSUE te StS. A double envelope 1 liter flask is dried at 12OOC and purged three times with nitrogen. The flask is then decontaminated from moisture by 500 ml of a 10-2M butylethylmagnesium (BEM) solution in Isopar L (high boiling point saturated hydrocarbons fraction) for 1 hour at 80°C. After evacuation, 500 ml of dry Isopar L are introduced, and saturated with ethylene at 80°C. The catalyst, previously obtained from reaction of the precursor with BEM for 1 hour at ambient temperature in toluene, is then added and the ethylene consumption followed with flowmeters. At the end of the reaction, 10 ml of ethanol are introduced. The polymer is precipitated with a large quantity of ethanol or isopropanol, filtered on a sintered glass, washed with n-heptane and dried in an oven at 80°C for 48 hours.
High temperature-low pressure tests The autoclave (1 liter capacity) is monitored with an external heating allowing to reach 250°C. A constant ethylene pressure of 6 bar is applied and the ethylene flowrate can be varied from 100 to 3000 l/h. A mechanic stirrer rotating at speeds up to 1500 rpm is used. Rotameters allow an accurate measurement of the ethylene consumption vs. time (1 min reaction). Before the reaction, the autoclave is decontaminated with an Isopar L solution of BEM at 16OOC for 45 min. After evacuation, 600 ml of dry Isopar are introduced and saturated with ethylene. The catalyst (10 ml of a 10-2M solution) is injected rapidly via a sas with a nitrogen overpressure of 8 bar. High temperature - high pressure te StS This apparatus has been initially developed by Cdf Chimie [9] and consists of a pilot plant where the operating conditions are very close to the industrial ones. The reaction conditions can be adjusted from 160 to 280°C with a pressure range 600-2000 bar under dynamic conditions. At these high pressures, the reaction medium is homogeneous under supercritical conditions. The temperature of this adiabatic reactor is adjusted and regulated by the catalyst solution flowrate. The average residence time is 40 sec, which allows conversions from 10 to 20%and needs a recycling of the unreacted monomers.
23. Lanthanocene Based Catalysts for Olefin Polymerization 25 I
RESULTS AND DISCUSSION Generalization of ethylene homoDolynerization on lanthanocene based catalvsts At it can be seen in table 1, the catalytic systems consisting of 1 or 2 and BuMgEt
polymerize ethylene with high activity at 80°C. The kinetic and the molecular weights depend on the Mg/Nd ratio and on the polymerization temperature. The initial activity decreases with an increase of Mg/Nd ratio, an induction period being even observed for a Mg/Nd ratio of 20. At low temperature (0°C) the catalytic system is only slightly active and requires a low magnesium content : a Mg/Nd ratio of 10 is sufficient to prevent any polymerization. The polydispersities are much broader than those obtained at higher temperature and the GPC curves show a bimodal distribution. Nevertheless, at 80°C a narrow distribution is controlled by the fast PH elimination chain transfer. Table 1. Temperature effect on ethylene polymerizationa
Catalysts
-
-
1530
7200
4.1
660
2880
1220
2.5
Polymerization Mg/Ln Yield temperature ("C) ratio dmmo1.h.b
Cp*2SmC12Li(OEt2)22
Ob
10
Cp82SmC12Li(OEt2)22
Ob
I
Mw
-
Mw&
0
0.34
Cp*2NdC12Li(OEt2)2 1
80
Cp*2NdC12Li(OEt2)2 1
80
20
230
1800
2920
1.6
Cp*2SmC12Li(OEt2)2 2
80
10
660
1830
2200
1.2
2.5
a Catalysts and BuMgEt were mixed at 20°C for 1 h. Polymerizaiion conditions: P C ~ =H1 bar; ~ [Ln] = 0.4 mmol/l; solvent = Isopar L (500 rn11.b solvent = lolucne (100 m ~ )
As previously shown in our first paper [ 5 ] the amount of cocatalyst is a crucial factor determining the activity of the catalyst. This economical and convenient method for the preparation of the polymerization catalysts has been extended to other lanthanides and yttrium. In table 2 are reported the results obtained at high temperature with several complexes activated by butylethylmagnesium. The yield for the yttrium catalyst is lower than those obtained with neodymium and samarium, a result which can be correlated with the ionic radius [ 2 ] .Only the ytterbium catalyst gave very low activities. This may be related to its reduction into YbII species.
252 J.F. Pelletier, A. Mortreux, F. Petit, X. Olonde and K. Bujadoux
At 160°C. in contrast to the results obtained at low temperature, the effect of the M@d ratio is much less pronounced. All polymers have about the same molecular weight - (k loo0 and Mw/Mn = 1.5). A Mg/Nd ratio of 50 is needed to observe a drop of the initial rate constant (kp). This effect could be explained by the fact that the excess of BuMgEt could react with the fourteen electron active species, via the formation of 3 centers, 2 electrons bridge, leading to a bulky adduct in which the orbital required for olefin complexation is occupied. This interaction must be broken by thermal activation in order to give back the active species as depicted in the following equilibrium (eqn 1)
-
Table 2. Ethylene polymerization : comparison between several catalytic systemsa
M a n ratio
Yield g/mmo~.mn.mo~ 1-1 of C2H4
kP mol/l.s
Cam1ysts
Polymerization temperature ("C)
Cp*2NdC12Li(OEt2)2 1
160
3
1600
1 100
Cp*2SmC12Li(OEt2)22
160
3
1600
1100
Cp*2YC12Li(OEt2)24
160
3
1100
1070
Cp*2YbC12Li(OEt2)25
I60
3
0
0
Cp*2YbC12Li(OEt2)2 5
I20
3
190
150
Cpf2NdCI2Li(OEt2)2 1
160
50
920
700
Cp*2NdCH(SiMe3)2 3
160
0
1160
620
Cp*2NdCH(SiMe3)2 3
160
3
1870
1880
aThe alkylation by BuMgEt was carried out at 20°C for 1 h; polymerization conditions: P ( c ~ H ~=)6 bar; [Ln] = 0,2 mmol/l; solvent = Isopar L (600ml).
23. Lanthanocene Based Catalysts for Olefin Polymerization 253
The bulky, well defined complex Cp*2NdCH(SiMe3)2 3, which does not polymerize ethylene at low temperature and atmospheric pressure [2], is a good catalyst at high temperature (160OC) but has a particular behaviour: the initial rate constant with 3 is about the same as with the catalytic system based on 1 and 50 equivalents of BuMgEt. Indeed the kinetic polymerization curve (fig. 1) shows that the ethylene consumption increases to reach a maximum and decreases, indicating that the first ethylene insertion step is very slow. AS already shown by Bercaw et al. [3], this is probably due to the bulkiness of the alkyl ligand -CH(SiMe3)2 or to the non bonding interaction between the lanthanide and SiMe3 [2]. 4 -
catalysts kp 1 + 3eqBEM 1100
+ 50 eq BEM
I
4 3 without BEM
5
10
15
20
25
30
35
40
45
50
55
700 620
60
Time (s)
Figure 1. Polymerization kinetics at 160OC - 6 bar for catalysts 1 and 3. It can be noticed (table 2) that the highest initial rate constant is achieved when complex 3 is mixed with 3 equivalents of BuMgEt. To explain this and also the fact that, at low temperature (8O0C), the molecular weight decreases at high M o d ratio,as it has already been shown in our previous report [ 5 ] , an alkyl transfer reaction occuring between the neodymium and the magnesium compounds can again be involved (eqn 2). Cp*2Nd CH(SiMe3)?+ MgR2
20°C ------=
"Cp*ZNdR" + RMgCH(SiMe&
(2)
3 The reactivity of 3 towards alkylmagnesium and alkylaluminium has been followed by lH NMR in C6D6. The spectrum obtained with BuMgEt is very complex, but the signal corresponding to the -CH(SiMe3)2 group is shifted from -16 ppm to -0.3 ppm. A similar behaviour is observed with (AIMe3)2 (eqn 3). The reaction appears to be much faster and the complex Cp*zNd(pMe),AIMe2 6 (characterized by microanalytical data) cnstallizes from the solution.
254
J.F. Pelletier, A. Mortreux, F. Petit, X. OIonde and K. Bujadoux
Me.
20°C
c ~ * ~ N d c H ( S i M+e (AlMe,), ~)~
/ \AlMe2 + Me2A1CH(SiMe3)2 Cp*2Nd \ /
(3)
Me
6
However, complex 6 does not polymerize ethylene even at low temperature and under ethylene pressure (70 bar) in contrast with the homologous yttrium complex 141.
mod ifier W
Effect of an
t
. .
s at coDolvmemion with I - b u m
The use of these systems for ethylene- 1-butene copolymerization has already shown that no copolymerization occured in a pilot plant under industrial conditions (1200 bar - 20OOC) [ 5 ] .With the aim to find a catalytic system suitable for copolymerization, attempts have been made to modify the lanthanocene complex by a ligand exchange with the ylide Ph3P=CH-C(O)Ph. Table 3 compares the results observed without and in the presence of 1 equivalent of this ligand at 160OC. Table 3. Comparison of activities of binary systems Cp2*LnC12Li(OEt2)2 + BEM and ternary systems with the ylide Ph3P=CH-C(O)Ph for ethylene homopo1ymerization.a
Ln
kP mol. 1-1 s-1
Nd Sm Ndb Smb a Polymerization conditions : PC,H,
Yield g/mmol.min.mol.l-]of C2H4
1100 1100 3 380 4 900
1500 1600 4 150 5 200 = 6 b [Ln] = 0,1 mM ; M g L n = 3 ; To= 160°C ; 1 min reaction. b
Addition of 1 eq of the ylide for 1 hour at 20°C bcfore the addition of Bu Mg Et.
Due to this enhancement of activity, this new catalytic system has been also tested at high temperature and pressure for ethylene- 1 -butene copolymerization. The results have been compared with the yttrocene and ziconocene catalysts (Cp2YC1)2 and Cp2ZrC12 where only cyclopentadienyle groups are present (table 4).
23. Lanthanocene Based Catalysts for Olefin Polymerization
255
Table 4. High temperature - high pressure ethylene- 1-butene copolymerization testsa. Catalyst
cocatalyst
yield
(ratio)
kdrnrnol
-Mn
Mnmn
Density
vinyF vinyiidenec intemaF
1.8 0.961 0.5 22.6 C~*NdC12Li(OEt2)2~ BEM (3) 23 700 2.3 >0.960 0.4 (CP2YC1)2b BEM (3) 14 7 100 cp2zrc12 M A 0 (100) 8 16 800 3.2 0.9395 0.37 apolymerization conditions: Pressure = 1200 bar; temperature = 180°C; but-I-ene 40% ; b lcq PPh3=CHC(O)Phadded before alkylation. double bonds per loo0 carbons.
-
0
0.05
0.03
0.78
0.05
0.17
Although the neodymium catalyst is more reactive, no copolymerization was observed. The less sterically crowded (Cp2YC1)2 isoelectronic system did not give any copolymerization as well. The infrared polymer analysis shows the presence of vinylic double bonds which are produced by the classical PH elimination process after ethylene insertion. However, vinylidene (CH2=CHR) and internal (-CH=CH-) double bonds are present for the yttrium and zirconium systems, indicating that the comonomer insertion step is possible in these two cases. As compared with zirconium, the density of the polymer produced with yttrium is much higher and the molecular weight lower : I-butene acts as an efficient transfer reagent by PH elimination after primary and secondary insertions as described in scheme 1. Surprisingly, the yttrium catalyst induces more secondary than primary insertions which are usually found with Ziegler Natta type catalyst.
[Nd+Fl
CII3-CH2-CtFCH-CH2-@
INSERTION RUTTKANSFER
Primary insertion
CHrCHl CH.$ Ctl*
Scheme 1. Chain transfer reactions in ethylenebut-1-ene copolymerization
256
J.F. Pelletier, A . M o r t r e u x , F. Petit, X. O l o n d e a n d K. B u j a d o u x
CONCLUSION At least in high temperature-high pressure conditions, these bis Cp* lanthanocene and bis Cp yttrocene based catalysts are not suitable for ethylene - a olefin copolymerization, although their productivity for ethylene homopolymerization is tremendously high considering the yield obtained per overall (catalyst + cocatalyst). To achieve this goal, further work should be done in this area, perhaps via ligand modification(s), to provide catalytic systems which could substitute the zirconocene catalysts in a useful way, that is to reduce the amount of cocatalyst generally required in this fascinating chemistry.
References 1.
P.L. Watson and G.W. Parshall. Acc. Chem. Res., 18. 5 1 (1985).
2.
G. Jeske. H. Lauke, H. Mauermann, P.N. Swcpston, H. Schumann and T.J. Marks, J . Am. Chem.
SOC.,107, 8091 (1985). 3
B.J. Burger, M.E. Thompson, W.P. Cotter and J.E. Bcrcaw, J . Am. Chem. SOC.,112, 1566 (1990).
4
K.H. Den Haan, Y. Wiclstra, J.J.W. Eshuis and J.H. Tcubcn, J . Orgnnomcr. Chcm., 323, 181 (1987).
5.
X . Olonde. K. Bujadoux, A. Mortreux and F. Petit, J . Mol. Caial., 8 2 , 7 5 (1993).
6.
T. don Tilley and R.A. Andersen. Inorg. Chem., 20,3267 (1981)
7.
W.J. Ewans. J.H. Meadows, A.L. Wayda, W.E. Hynter and J.L. Atwood, J. Am. Chem. SOC.. 104,2008 (1982)
8.
F. Ramirez and J. Dershowitz, J. Org. Chem., 22.43 (1957)
9.
J.P. Machon, "Transition Mctal Catalyzed polymerizations Zicglcr-Natta and Metathesis Polymerization", Cambridge University Prcss, R.P. Quirk Ed., Cambridge, 1988. p. 344.
257
24. Effect of Ligand and Inorganic Support on Polymerization Performances of Ti and Zr Catalyst
F. CIARDELLI, A. ALTOMARE, G. ARRIBAS*, G. CONTI Department of Chemistry and Industrial Chemistry, University of Pisa, via Risorgimento 35, 56126 Pisa, Italy. *Escuela de Quimica, Facultad de Ciencias, Universidad Central de Venezuela, Caracas, Venezuela F. MAS1 AND F. MENCONI EniChem, 20097 S.Donato Milanese, Italy
ABSTRACT In the present work the activity was discussed of various soluble complexes of Ti and Zr with phenolate, carboxylate, unsubstituted and variously substituted cyclopentadienyl ligands in ethylene and 1-olefins homo- and copolymerization after activation with aluminum alkyls or MAO. Some of these complexes were also used for preparing catalysts supported on inorganic materials such as silica or zeolites after modification of surface functionality. The discussion of the results takes into accounts steric and electronic effects of ligands and support which allow to modulate catalyst performances INTRODUCTION The chemical mechanism by which metallocene complexes of IV group transition metals can catalyze with great efficiency monoalkenes polymerization is now generally accepted as based on the formation of stable cationic complexes.1 In these last the transition metal bears in addition to a o-alkyl group, a positive charge
258
F. Ciardelli, A . Altomare. G . Arribas. G . Conti, F. Masi a n d F. Menconi
having transferred one electron to a ligand which becomes part of complex anion assisted by a cocatalyst such as alumoxane2-4 or another more conventional Lewis acid.5 Both electron transfer and reactivity of the cation are dependent on the transition metal environment provided by ligands and cocatalysts. Even if many outstanding contributions appeared already in the chemical literature putting lights on these aspects, several points remain still to be clarified. These last refer in particular to the role of aluminum alkyls and alumoxane as well as to the possibility of heterogeneizing the above systems without detracting their properties. In this broad context one objective of this work is to contribute additional evidence on the role of the ligands in combination with cocatalyst in determining productivity of ethylene polymerization. On the other side these aspects are also used in order to develop supported cataly~t6~7 with comparable or improved characteristics in respect to their homogeneous precursors to be used in slurry and gas-phase processes. EXPERIMENTAL Materials. All reactions were carried out under argon atmosphere. Solvents were dried over calcium chloride and then freshly distilled under argon from sodium-potassium benzophenone ketyl. Trimethylaluminum, diethylaluminuni chloride, triethylaluminum, triisobutylaluminum and M A 0 (4.5 M in toluene) (Witco), titanium alkoxides, titanocene dichloride, zirconocene dichloride (Aldrich) were used as received. Titanocene and zirconocene dimethyl derivatives were synthesized by literature methods.8 [Pyrocatecholate(2)]titanium(IV) dichloride, cyclopentadienylpyrocatecholatetitanium(1V) chloride, bisnonanoatetitanium(1V) dichloride, pentamethylcyclopentadienyltitanium(1V) trichloride were prepared by methods described earlier.9 1H and 13C-NMR spectra were recorded by using a Varian Gemini 200 spectrometer. Bis~entamethvlcvclopentadienvlzirconium(IV) dichloride. 3 g (12.35 mmol) of ZrC14 freshly sublimed and 4.3 g of Cp*K were added at -80°C in 100 ml of dry toluene. This mixture was warmed to 2 5 T , then refluxed for three days. Solvent was removed under reduced pressure and the solid yellow-green residue was taken up in 200 ml of chloroform. Petroleum ether (150 ml, 90-100°C) was added and the solvent slowly removed by rotary evaporation. The residual solution
(50 ml) was cooled, and the product was filtered off and washed with cold
24. Effect of Ligand and Support on Polymerization Performances 259
petroleum ether, yield 4 g ( 75%) of pale yellow crystals. Anal. calcd. for C20H30C12Zr: C, 55.56; H, 6.94; C1, 16.40. Found: CS5.20; H, 6.83; C1, 16.95. 1HNMR (CDC13): 6 = 1.98 ppm (s); 13C-NMR(CDC13):6 = 11.95 and 123.52 ppm. Bis-tetraDhenvlcvcloDentadienvlzirconium ( I W dichloride. See ref. 10 Silica treatment. Croxfield-type silica (surface area 300 m2/g; [OH] = 2-10-3 moles/g) was heated for six hours at 300°C under vacuum (0.05 mm). 0.8 ml of a 1.6 M solution of LiMe in diethyl ether were added SiO7-LiMe. dropwise at -78°C to a suspension of 3.04 g silica in freshly distilled THF over a period of 1 hour. The temperature was allowed to rise at 20°C and then the silica was washed with THF, the solvent was evacuated and the solid was finally dried under vacuum for three hours. 45.7 ml of a solution 0.15 M of MgC12 in THF were added SiO7-MgCI7. dropwise under magnetic stirring at room temperature to 30.6 g of silica in 60 ml of dry THF. The solvent was evacuated and the solid was dried under vacuum (0.05 mm) at 75°C. Method 1 /N2TiC12-Si02-MgC12): 2 Preparation of supported catalvsts. ml of a solution 0.26 M in n-heptane of bisnonaoatetitanium(1V) dichloride (N2TiC12) were added to a suspension of 5.2 g of Si02-MgC12 at the room temperature under magnetic stirring. The reaction mixture was stirred over a period 1 hour; then the solid product was washed with n-heptane. Method 2 (Cp2TiC12-Si02-LiMe): 3.1 ml of a 0.098 M THF solution of Cp2TiC12 were added to a suspension of 4.0 g Si02-LiMe in dry THF at room temperature under magnetic stirring. The solid catalyst was washed with THF and then with methanol. The solvents were removed under vacuum (0.05 mm). Method 3 (Cp2ZrC12-HY**AlMe3): 0.92 ml of a 0.05 M solution of Cp2ZrC12 were added to a slurry of 2.5 g HY**-AlMe3 in toluene under magnetic stirring at the room temperature. The reaction mixture was stirred for three days and then washed with toluene. A HY type zeolite with Si/AI ratio of 7.25 was heated Zeolite treatment. at 300°C under vacuum (0.05 mm) over a period of six hours. 100 ml of a 38 70 Exhaustive dealumination of the zeolite (HY **). solution of acetylacetone in methanol were added to 12.4 g of HY zeolite. The suspension was refluxed under magnetic stirring for 12 hours, then the solid product was filtered . This treatment was repeated three times, then the solid was calcinated at 600°C under a stream of dry air for six hours.
260
F. Ciardelli, A. Altomare, G . Arribas, G. Conti. F. Mas; and F. Menconi
HY **-AIMeJA
1 ml of 2.0 M solution of AlMe3 in toluene was added to a
toluene slurry of 1.5g of dealuminated zeolite and the reaction mixture was kept under magnetic stirring for three days at room temperature; the solid was washed with toluene until AlMe3 elimination. HY**-Nia-AlMeT. 2.5 ml of a 0.04 N solution of nickel (11) nitrate were added under magnetic stirring to a slurry of 2.142 g HY** in water. The solid product was filtered, heated at 300°C for 20 hours and then suspended in 30 ml of freshly distilled toluene. 1 ml of 2.0 M solution of AlMe3 was added at room temperature to the resulting suspension and the reaction mixture was stirred for 4 hours and then washed with dry toluene. HY **-MeSiC1. 20 ml of distilled Me3SiC1 were added to 3 g of HY** and the mixture was refluxed overnight. The excess Me3SiC1 was eliminated under vacuum (0.05 mm). Polvmerization experiments. Ethylene polymerization experiments were carried out by introducing the cocatalyst solution in toluene and the catalytic slurry in the same solvent into the reaction vessel under argon atmosphere. After 10 minutes ageing ethylene was introduced and its partial pressure kept at 1 bar during polymerization time. RESULTS AND DISCUSSION Soluble catalvsts. A possible correlation between ligands of the original transition metal complex and cocatalyst was initially investigated by examining the productivity per g atom of transition metal (SA) or per g atom of transition metal and g atom aluminum @A*), obtained for different Ti or Zr complexes with aluminum alkyls or MAO, respectively.9 The maximum values obtained and the corresponding conditions are reported in Table 1. In the case of titanium, when Cp is not present AlEt3 and M A 0 give SA of the same order of magnitude, but higher Al/Ti ratios are necessary for the latter. In any case the A l n i ratio for optimum productivity is much lower than for CpzTiX2 which however provides much larger activity per Ti atom (SA). Even if the presence of Cp ligandl 1 substantially activate the complex versus MAO, SA* remains usually lower than with AIEt3. Cp*TiC13 has an unusual behaviour and is always more active with AIMe3 rather than MAO. This is substantially in agreement with an excessive Ti reduction with the massive M A 0 necessary.
24. Effect of Ligand and Support on Polymerization Performances
261
Table 1 Polymerization of ethylene by soluble titanium complexes activated with different aluminum derivative@ RUIl
H1
H2 H3 H4 H5 H6 H7 H8 H9 H10 H11 H12 H13 H14 H15 HI6 HI7 H18
Catalyst Ti(n-OBu)4 g Ti(n-OBu)4 g Ti(2-EH)4 l1 Ti(2-EH)4 l1 PcTiC12 PcTiC12 CpPcTiCl j CpPcTiCl J N2TiC12 N2TiC12 Cp*TiC13 I Cp*TiC13 I Cp2TiCl2 Cp2TiC12 cp2zrc12 cp2zrc12 Cp*2ZrC12 O (Cp$4)2ZrC12 P
Cocatalyst AIEt2CI MA0 AIEt2CI MA0 AIEt3 MA0 AlEt3 MA0 AlEt3 MA0 AIMe3 MA0 AIEt2C1 MA0 AlEt3 MA0 MA0 MA0
[AlI/[Mtl 6.0 200.0 5.O 30.0 1.5 100.0 9.0 100.0 4.0 100.0 8.0 200.0 2.5 3000.0 4.0 1500.0 1500.0 3000.0
S.A.b
S.A.*C
0.1 0.7 0.9 0.8 5.7 7.2 0.4 33.4 5.8 16.7 7.2 1.1 3.7 300.0 -
0.01 3 0.004 0.180 0.027 3.800 0.072 0.040 0.330 1.450 0.167 0.900 0.005 1.480 0.100
372.5d 185.6e 80.4f
0.248 0.124 0.010
-
a Optimum productivity at Pethylene = 1 bar, T = 25 "C. b Kg PE/g atom Mt-h. Kg PE/g atom Mt-g
atom Al-h. Mn*10-' = 0.35, Mw-10-5= 0.78; e q = 7.5 in decaline at 135OC; fMII.10-5 = 0.04,
Mw. lo-' = 0.17. g Tetrakis-(n-butanolate)titanium(IV).hTetrakis(2-ethylhexanolate)titaniurn(IV). [Pyrocatecholate(2)] titanium (IV) dichloride. 1 Cyclopentadienylpyrocatecholatetitanium(IV) chloride. Bisnonanoatetitanium(1V) dichloride. 1 Pentamethylcyclopentadienyltitanium(1V) trichloride. Biscyclopentadienyltitanium(1V) dichloride. '1 Biscyclopentadienylzirconium(1V) dichloride. 0 Bispentamethylcyclopentadienylzirconium (IV) dichloride. P Bistetraphenylcyclopentadienylzirconium (IV) dichloride.
The characterization of the catalytic systems and their kinetic behaviour as well as polymer features suggest that the polymerization mechanism is substantially the same for all examined transition metal complexes in the presence of either aluminum alkyls or alumoxane. The formation of active species should consist of
262
F. C'iardelli, A . Altomare. G. Arribas. G . Conti, F. Masi a n d F. Menconi
alkylation of titanium by replacement of chlorine atoms with alkyl groups and consequent formation of unsaturated active species.*2 When Cp ligands are not present, AIR3 and M A 0 give more or less the same productivity, and a lower amount of the former is requested. Such behaviour can be tentatively interpreted by considering that AIR3 is the actual cocatalyst and therefore a consistent amount of M A 0 is necessary to attain the optimal AlR3/Ti ratio. When the Cp ligand is present,l3) M A 0 becomes more effective in giving high productivity at rather high MAO/Ti ratios, thus suggesting that, at least at that concentration level, a different activation mechanism can be operative. The different polymerization rates and activities observed when changing catalyst can arise from different propagation rate constants (k,) and/or active sites concentration ([C*]). These differences are a result of the effect of ligands on the reaction between titanium complexes and cocatalyst, which determines [C* I and steric and electronic effects on the Ti-C bond, which in turn affect the k, value. In the case of MAO, stabilization and activation of cationic species is probably also effective. Considering the higher interest and potentiality of metallocene complexes we examined only Zr-derivatives of this type. Cyclopentadienyl and pentamethylcyclopentadienyl Zr derivatives did not show activity to high molecular weight polyethylene with aluminum alkyls as cocatalyst (Table 1). In the presence of M A 0 the use of substituted Cp-ligands (Table l), providing different electronic and steric properties, has a substantial effect on both productivity and molecular weight. Thus while with bispentamethylcyclopentadienylzirconium dichloride high molecular weight polyethylene was obtained with good productivity, even if SA is about 50% less than with Cp2ZrC12, bistetraphenylcyclopentadienylzircon~unidichlorideg gave only C6-C30 oligomers with interesting productivity. The formation of short chains cannot be merely attributed to the rather large amount of M A 0 used, as concentration of this last has not a remarkable effect on molecular weight at the polymerization temperature used.14 Pre 1im ina ry experiments with supported cat a1y st s Supported catalvsts. were performed by using the metal complexes described in the previous section and silica, which had been treated as described in the experimental. Table 2 reports the best productivity obtained and the related conditions adopted.
24. Effect of Ligand and Support on Polymerization Performances
263
Bisnonanoatetitanium dichloride (N2TiC12) on silica (run S 1) or silica/MgC12 (run S2) shows more or less the same productivity as in solution (run H9) after activation with aluminum alkyls. Table 2. Polymerization of ethylene with various titanium and zirconium catalysts supported on silicaa Run
SI s2 s3 s4 s5 S6 s7 S8 s9 s10 s11
Catalyst N2TiC12/Si02 N2TiCIdSi02/MgC12 N2TiC12/Si02/MgC12 N2TiC12/Si02/MgC12 Ti(2-EH)4/Si02 PcTiCIdS i 0 2 Cp2ZrC12/Si02 Cp2TiCIdSi02 Cp2TiC12/SiOfliMe Cp2TiC12/Si02/LiMe Cp2TiC12/Si02/LiMe
Cocatalyst AIEt2CI AIEt2CI MA0 MA0 AIEt2CI AIEt2C1 AIEt3 AIEt2C1 AIEt2CI MA0 MA0
[All/[Mt]
30 35 I50 760 30 24 10 25 30 I00 1000
S.A.b 3.4 6.7 6.9 24.2 2.4 5.5
S.A.*C
0.113 0.191 0.005 0.03 1 0.079 0.229 -
15.0d 33.0e 13.4 41.3
0.145 1.100 0.134 0.04 1
aSilica Croxfield : 300 in*& ; [OH] 2.10-3 moles/g. bKg PE/g atom Mt-h. CKg PE/g atom Mt-g atom Al-h. dMv-lO-5 = 5.92. eMv-10-5 = 16.2.
The same complex on Si02/MgC12 needs a larger amount of M A 0 (runs S3 and S4) to display the same productivity as in the solution (run H10). In the case of Cp2TiC12 some important differences can be observed thus suggesting that the Cp ligand still plays a certain role. With AIEt2CI as cocatalyst, this last complex when supported on silica (run S8) or LiMe pretreated silica (run S9) results more productive than in the solution. However with MA0 the Si02LiMe supported species show (runs S10 and S1 1) comparable activity as with AlEt2CI and much lower than in solution (run H14). It seems therefore reasonable that during supportation some of the Cp ligands are removed15 despite the treatment with LiMe should have converted silanol groups into -SiOLi groups. Cp2ZrCl2 on silica does not give polyethylene with AIEt3, similarly to what happens in solution (runs S7 and H15, respectively). Soga et al. did however report that good yield can be obtained with Cp2ZrC12 supported on Si02 pretreated with C12SiMe2 and activated with trialkylaluminum.16
264
F. Ciardelli, A . Altomare, G . Arribas, G . Conti, F. Masi and F. Menconi
On the basis of these results showing the possibility of analyzing different effects in supported metallocene complexes as well as the importance of the functionalization of the support surface induced us to use HY-zeolite as a support. This crystalline and better defined material appeared more promising in the attempt to produce supported metallocene catalysts displaying similar performances as in solution. When directly supported on merely thermally treated HY -zeolite, Cp2ZrC12 displays (Table 3) rather modest activity with aluminum trialkyls (runs Z1 and Z3), which is substantially improved by using MA0 (run Z8), even if remaining below the value obtained in solution under similar conditions (Table 1, run H16). As this result could be in some way connected to a modification of Zr-complex due to reaction with the silanol functionalities, the zeolite was treated with AlMe3.15 The catalyst prepared with this last support provided improved activity (one order of magnitude) with AlMe3 and excellent activity with M A 0 giving productivity comparable to that expected for the analogous complex in solution (run Z15). Also good activity was obtained in the ethylene/propene copolymerization, with about 20% mol of a-olefin in the copolymer (run 216). In an analogous experiment in toluene solution CpzZrC12 with MA0 (AI/Zr = 1500) gave SA = 2,200 kg/mol Zrohebar with 20% mol propene in the final product. These results suggested the possibility of achieving supportation of metallocene species on zeolite supports. In order to investigate these aspects in better detail Cp2ZrMe2 and more thoroughly purified HY-zeolite were used. Indeed, even the dealuminated zeolite contains both Si-OH groups and extraframework aluminum. The first ones can be simply removed by treatment with trimethylaluminum which occurs with methane evolution and conversion of all -OH groups into Si-O-A1 oxane species.17
lSi-OH 0
+ Al(CH3)3-
-1Si-O-Al(CH3)2 0
+
CH4
The effectiveness of this treatment is clearly shown by the fact that productivity increases of one order of magnitude for the zeolite supported Cp2ZrC12 when activated with trialkylaluminum cocatalyst (Table 3, runs 21-23). Extraframework aluminum can be removed by exhaustive extraction at 50°C with a solution of acetylacetone in ethanol.18 After this treatment the 27Al-NMR (MAS) spectrum shows (Fig lb) a single resonance at 57.45 ppm of the tetrahedral
24. Effect of Ligand and Support on Polymerization Performances
265
Al,19 whereas resonances at 0 and 30-50 ppm of the extraframework A1 (Fig. la) are completely lacking.20 However silanol groups are still present and treatment with CpzZrMe:! is accompanied by CH4 evolution associated with the Zr-carbon bond cleavage. After extraction with acetylacetone, the zeolite was then pretreated with 2M solution of AlMe3 in toluene and successively washed with dry toluene until the test for aluminum was negative; the resulting support shows in the 27AlNMR (MAS) spectrum three resonances at 60.4, 33.1 and 2.2 ppm (Fig. 2a), suggesting that two different species of aluminum, associated with absorbed AlMe3 and the reaction product of AlMe3 with silanol groups, are now present. The addition of CpzZrMez to the modified zeolite does not produce any CH4 evolution, and the 27AI-NMR (MAS) spectrum shows the same resonances as before the zirconocene addition, the relative intensities resulting only moderately changed (Fig. 2b). Moreover, in the 29Si-NMR (MAS) spectrum only the resonance of the Si(OA1) species at -107 ppm can be observed,*1 indicating that no change occurred for Si after addition of the zirconocene to the zeolite pretreated with AlMe3. All these indications suggest that no chemical reaction occurred during complexation and the zirconocene in the support has maintained its original structure. Polymerization experiments carried out with this modified zeolite (HY**) are reported in table 4.
Figure 1. 27Al-NMR (MAS) spectra Figure 2. 27AI-NMR (MAS) spectra of a) untreated and b) acetylacetone of HY zeolite treated with a) AlMe3 and extracted HY zeolite (see text). b) AIMe3 + Cp2ZrMe2 (see text).
266
F. Ciardelli. A . Altomare. G. Arribas. G. Conti, F. Masi and F. Menconi
Table 3. Polymerization of ethylene with zeolite supported Cp2ZrCl2 activated with different aluminum alkyl derivatives.a Run
Cocatalyst
[AI]/[Mt]
Surface treatment
S.A.b
z1
10 50 12
-
22 23
AIMe3 AIMe3 AIEt3
HY -AIMe3
3 37 3
0.28 0.73 0.28
28 Z 15d-e Z I 6d7f
MA0 MA0 MA0
1500 1500 1500
HY -Al Me3 HY-AlMe3
195 2800 2280
0.13 1.87 1.52
-
S.A.*C
Table 4. Polymerization of ethylene with zeolite supported Cp2ZrMe2 activated with different aluminum a k y l derivatives.a Run
Cocatalyst
24 z5 Z6
AIMe3 AIMe3 AlMe3
z9 z10 z11 212
MA0 MA0 MA0 MA0
[AI]/[Mt]
Surface treatmentb
S.A.C
100 100 100
HY**-AIMe3 HY**-Me3SiC1 HY **-Ni+2-AIMe3
30
0.30
-
-
-
-
1500 3000 1500 1500
HY**-AIMe3 HY**-AIMe3 HY **-Me3SiC1 HY**-Ni+Z-AIMe3
181
0.12 0.20 0.10 0.2s
59 1 150 382
S.A.*d
aPetI1ylene = 1 bar, T = 25 "C. bHY** = exhaustive dealurnination with acetylacetone/etlianol. CKg PE/g atom Zr-h. dKg PE/g atom Zr-g atom A1.h.
When supported on HY **,Cp2ZrMe2 with MA0 as cocatalyst gave comparable activity as in solution and needed comparable amounts of M A 0 (run ZlO), as expected by a fixation on the zeolite surface and inside the channels22 of unmodified species.13 Replacement of AlMe3 with Me3SiC1 for HY ** pretreatment gave a support without free silanol groups and extraframework aluminum. With this last support no activity was detected for Cp2ZrMe2 in the presence of AlMe3
24. Effect of Ligand and Support on Polymerization Performances
267
cocatalyst (run ZS), whereas with M A 0 analogous productivity was achieved as with the HY**-AIMe3 support (run Z1 l), indicating that addition of alumoxane is necessary for producing active species. Interchange with N i ( N 0 3 ) 2 brought to the fixation of Ni++ species on the zeolite surface.23
+
Ni(NO,),
-
1 -Si I\
0 0 Ni
I f
+
2HN0,
2
Again Cp2ZrMe2 on this modified support has no activity with AIMe3 (run Z 6 ) , while excellent activity was observed with M A 0 (run 212). Preliminary experiments with Cp2TiMe2 supported on HY** and activated with M A 0 (Al/Ti = 2,000) gave polyethylene with SA = 600 kg/mol Tiehebar. Kinetic analysis indicated that some interesting differences existed between soluble and zeolite-supported species in the case of Cp2ZrMe2 on HY**-AIMe3. Variation of polymerization rate with time indicated that the soluble system is initially more active than the supported one, but shows a typical decay profile of polymerization rate (Rp) vs. time.24 By contrast R, of the zeolite supported system remains almost constant in the first 60 minutes and already after 20 minutes is higher than for the soluble catalyst (Figure 3). Then the comparable productivity of the zeolite supported catalysts with respect to the corresponding systems in solution, despite the lower initial activity, is a consequence of the better stability of the active sites in the former systems. These preliminary results show that the use of properly treated zeolite supports allows to obtain heterogeneized zirconocene species showing appreciable activity with constant R, thus indicating that entrapment in the zeolite channels prevents deactivation reactions and allows to modulate catalytic activity by molecular modification of the support without preventing activation by MAO. While the diameter of channels of the zeolite HY used in this study is high enough to accommodate the cyclopentadienylzirconium complexes, they may exert a certain
268
F. Ciardelli. A . Altomare. G . Arribas, G. Conti. F. Masi and F. Menconi
shape selection towards different molecular species present in the M A 0 mixture. This last effect could be responsible for the substantial stability of active sites number as indicated by the time dependence of the polymerization rate.
.
WI
**..
c1
2.0 -
'b..,
1.5-
o
Cp2ZrMe2-HY**-AlMe3/MA0
-0.1
0
10
20
30
40
50
60
Time (min) Figure 3
Variation with time of ethylene polymerization rate (Rp) in the
presence of homogeneous and supported catalysts (at 25OC, PetIlylene = 1 bar).
ACKNOWLEDGEMENT Partial support by MURST-Rome (60%) is gratefully acknowledged. G.C. thanks SNS-EN1 for PhD fellowship REFERENCES 1 M.Bochmann, S.J.Lancaster, Oryanometulfics, 12, 633 (1993) 2 C.Sishts, R.M.Hathorn, T.B.Marks, J.Am.Chem.Soc.,114, 11 12 (1992) 3 J.A.Ewen, H.J.Elder, Makromol.Ckem.,MacromolSymp., 66, 17.9 (1993) 4 D.J.Crowther, R.F.Jordan, Makromol.Chem.,MacromoI.Symp.,66, 121 (1 993) 5 J.C.W.Chien, W.Song, M.D.Rausch, Macr,omolecules, 26, 3239 ( 1993) 6 K.Soga, M.Kaminaka, Makromol.Ckeni. , Rapid Commun., 13, 221 (1992) 7 W.Kaminsky, F.Renner, Makromol.Chem. ,Rapid Commuii., 14,239 (1993)
24. Effect of Ligand and Support on Polymerization Performances
8 9 10 11 12 13 14
15 16 17 18 19 20 21 22 23 24
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E.Samue1, M.D.Rausch, J.Am.Chem.Soc., 95,6263 (1973) G.Conti, G.Arribas, A.Altomare, F.Ciardelli, J.Mo1.Cat. (1994) in press. G.Conti et al, in preparation K.Soga, J.R.Park, T.Shiono, Polymer Commun., 32,310 (1991) P.Pino, U.Giannini, L.Porri, in “Encyclopedia of Polymer Science and Engineering”, ~01.8,Wiley Interscience, New York, 1984, p.148 J.C.W.Chien, D.He, J.Polym.Sci.,Part A , 29, 1603 (1191) L.Resc0ni.F. P i e mo n t e s i , G .Francis c o n o , L .A b i s , T.Fiorani, J.Am.Chem.Soc., 114, 1025 (1992) S.Collins, W.M.Kelly, D.A.Holden, Macromolecules ,25, 1780 (1992) K.Soga, H.J.Kim, T.Shiono, Makromol.Cltem., Rapid Commun., 14, 765 (1 993) G.A.Nesterov, V.A.Zakharov, G.Fink, W.Fenz1, J.Mol.Catal., 69, 129 (1991) F.Ciardelli, A.Altomare, G.Conti, G.Arribas, B.Mendez, A.Ismaye1, Makroniol .Cliem. ,Macromol. Symp., in press G.Engelhardt, D.Miche1, “High resolution Solid-state NMR of silicates and zeolites”, Wiley, New York, 1987 J. Klinowski, Ciieni. Rev., 91, 1459 (1991) J. Klinowski, Inorg. Chem., 22,63 (1983) G.A.Ozin, C.Gil, Ciiem. Rev., 89, 1749 (1989) R.I.Soltanov, E.A.Paukshtis, E.N.Yurchenko, B.A.Dadashev, S.E.Mamedov, B.A.Gasymov, Kinet. Karal., 25 (3), 618 (1984) D.Fisher, S.Jungling, R.Miilhaupt, Makroniol. Chem., Macromol. Symp., 66, 191 (1993)
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27 I
25. Design of Non-Metallocene Single-Site Olefin Polymerization Catalysts
Erik B. Tjaden and Richard F. Jordan.
Department of Chemistry, University of Iowa, Iowa City, Iowa, USA 52242
Absffact: Cationic group 4 metal alkyl complexes containing teuaaza macrocycle or tetradentate Schiff base ligands, e.g. (Meg-taa)Zr(R)+,(Meq-taen)Zr(R)+,and (FSacen)Zr(R)+,are prepared by protonolysis of suitable neuual diakyl precursors. These complexes display electrophilic behavior, but are less active for ethylene polymerization than CpzZr(R)+cations. INTRODUCTION Cationic group 4 metallocene akyl complexes Cp2M(R)+ (M= Zr,Hf) have been extensively exploited as olefin polymerization catalysts. Fundamental organometallic studies of these and related group 3 and f-element metallocene systems have provided a working rationale for the high activity and selectivity of these systems.' The key steric and electronic properties of Cp2M(R)+ species which are important for catalytic activity are: (i) the do metal elecaon configuration, (ii) the highly unsaturated metal center, and (iii) the availability of vacant coordination sites cis to alkyl ligand. A current challenge is to exploit the general insights gained from studies of CpzM(R)+ systems to develop new classes of single site catalysts with improved and/or complementary properties. Our approach to this problem is to design new types of cationic early transition metal alkyl complexes which are structurally and electronically similar to Cp2M(R)+ species, but which are based on non-metalloceneancillary ligands. RESULTS AND DISCUSSION In a previous study, we investigated the synthesis and chemistry of (N4-macrocycle)M(R)+ complexes (1,2; M = Zr,Hf) incorporating Meg-taa or Meq-taen ligands in place of Cp2 iigands.2 The pockets of these macrocycle ligands are too small to accommodate the large ZrIV and H e V ions, so the metal lies above the N4 plane and additional ligands/substrates are forced to coordinate cis to the alkyl ligand (3). Cationic (N4-macrocycle)M(R)+ species coordinate a variety of ligandshbstrates, exhibit non-classical metal-akyl bonding modes (i.e., agostic interactions) characteristic of electrophilic metal systems, and undergo C-H activation and akyne insertion
277
E.B. Tjaden and R.F. Jordan
reactions. These species also polymerize ethylene in the absence of cocatalysts, but activities are far lower than for Cp2M(R)+catalysts.
The most likely reason for the lower activities of (N4-macrocycle)M(R)+catalysts 1 and 2 is that strong electron donation from the macrocycle ligand results in reduced metal electrophilicity and less effective olefin coordination and activation. To circumvent this problem we are exploring systems containing tetradentate N2022- Schiff base ligands which are expected to be weaker donors due to the higher elecmnegativity of oxygen vs. nitrogen. Floriani has prepared a series of (acen)MXZ halide complexes, some of which adopt cis-MX2 structures.3 However, it has proved rather difficult to convert these precursors to alkyl derivatives. We have developed more direct routes to (acen)MRz and (acen)M(R)+complexes and investigated the reactivity of these systems. The tetradentate ligands Fg-aCen (4a) and &-acen (4b) are readily prepared via condensation reactions (eq l).4 Neutral dialkyl complexes (%-acen)ZrR'Z (5a-5c) are obtained directly via alkane elimination reactions of ZrR'4 compounds and (&-acen)H2 (eq 2). A single crystal X-ray analysis of (Fg-acen)Zr(CH~CMe-& (5a. Figure 1) revealed a mgonal prismatic geometry. The C-Zr-C angle (1300) is larger than in (Nq-macrocycle)MR2or Cp2MR2 complexes (85 - 950).
(R6-acen)y
4a, R I F 4b,R=H
25. Design o f Non-Metallocene Single-Site Catalysts 273
Protonolysis5 of 5a with the ammonium reagent [HNMe2Ph][B(C6F5)41 yields (Fgacen)Zr(CHzCMe3)(NMe2Ph)+ (6a) as the NMe2Ph adduct (eq 3). The fact that 6a retains coordinated amine indicates that this species is more electrophilic than (N4-macrocycle)M(R)+or Cp2M(R)+ species, which generally do not coordinate NMezPh.
5a
A single crystal X-ray analysis (Figure 1) established that 6a is structurally similar to Sa, although the Fg-acen ligand adopts a more planar conformation and the NMezPh-Zr-CH2CMe3 angle is large ( 1700).6
FZS
\
@Cl3
Figure 1. Structures of (Fg-acen)Zr(CH~CMe3)2(5a) and (Fg-acen)Zr(CH~CMe3)(NMezPh)+ (6a). The B(C&5)4- anion of 6a is not shown. Complex 6a undergoes ligand exchange reactions (PMe3, RCN) and inserts polar substrates (CO. ketones), but exhibits only low ethylene polymerization activity. We initially hypothesized that this results from tight amine binding which inhibits coordination of the olefin. In the presence of 2 equiv Al(iBu)g, added to scavenge the amine, in siru-generated 6a is a moderately active catalyst
274
E.B. Tjaden and R.F. Jordan
(eq 4). Under the same conditions, the non-fluorinated catalyst derived from 5c is much less active (eq 4). These results prompted us to explore the synthesis of fluorinated buse-free cations via protonolysis reactions using bulkier ammonium reagents. The reaction of 5a with [HNMePh2][B(C6F5)4] affords the base-free cation (F6acen)Zr(CH2CMe3)+(78) which can be isolated as an analytically pure solid (eq 3). The bulky, weakly basic amine NMePh2 does not coordinate to Zr. Surprisingly 7a is a poor ethylene polymerization catalyst (eq 5). This indicates that the role of Al(iBu)3in eq 4 is more complex than originally thought. Complex 7a can be activated for polymerization with I equiv Al(iBu)3 (eq 5); however, additional Al(iBu)3 does not increase activity. Thus the active species in eq 4 and 5 is formed by reaction of 7a and 1 equiv Al(iBu)3. 1) [ H N M ~ z P ~ I [ B ( G F ~ ) ~ I /R
( R6-acen)Zr,
R'
2)2 equiv AI~BU), 3) 3 atm ethylene
*
toluenekhlorobenzene 30 min, 50 OC
-.
-
...
(4)
-
5a, R = F; R' = CHpCMe 14,000 (g)(mol)-'(atrn)-'(hour)-' 5b, R = F; R' CHzPh 18,000 800 Sc, R = H; R' = CHzCMe3
iz -
No Activity
0 (F6-X811)Zr-C (C6Fd4' 78
H,CMe,
-.
1 AI(bu),
benzene, 45 OC
._
10,000 (g)(mol)-'(atm)-'(hour)"
At present, the mechanism by which Al(iBu)3 activates 7a for ethylene insertiordpolymerization is unknown. The low reactivity of 7a in the absence of AlR3 may result from non-optimum orientation of the coordinated olefin and the neopentyl ligand in the putative (F6acen)Zr(CH2CMe3)(ethylene)+ intermediate. If this intermediate is structurally similar to 6a, with the coordinated olefin replacing the amine, the olefin-Zr-alkyl angle would be too large (ca. 1700) for facile migratory insertion. The Al(iBu)g cocatalyst may bind the alkoxide oxygens of 7a, forcing the neopentyl ligand and the vacant coordination site into a more cis-like arrangement. It is also possible that 7a is inherently unreactive due to the steric bulk of the neopentyl ligand, which is expected to disfavor olefin insertion. The reaction of 7a with Al(iBu)3 may generate a Zr-H
25. Design of Non-Metallocene Single-Site Catalysts 275
species which is more reactive. Control experiments with Cp2Zr(R)+catalysts indicate that the role of Al(iBu)3 in eq 4 and 5 is not simply to scavenge impurities from the reactor. Experiments designed to elucidate the role of A1 cocatalysts in this system are in progress. SUMMARY
Cationic, group 4 metal (N4-macrocycle)M(R)+ and (Rg-acen)M(R)+ complexes can be prepared using synthetic routes developed for Cp2M(R)+ species. These non-metallocene systems exhibit electrophilic behavior, but are less active than Cp2M(R)+ species for olefin polymerization. Efforts to modify the ancillary ligands to increase polymerization activities are in progress. REFERENCES
2
ti
Jordan, R. F. Adv. Organomet. Chem. 1991,32, 325. Uhrhammer, R.; Black, D. G.; Gardner, T. G.; Olsen. I. D.; Jordan, R. F. J . Am. Chem. SOC. 1993,115, 8493. (a) Corazza, F.; Solari, E.; Floriani, C.; Chiesi-Villa, A.; Guastini. C. J . Chem. Soc., Dalton Trans. 1990, 1335. (b) Solari, E.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. J . Chem. SOC., Dalton Trans. 1992, 367. Liu, H. Y.; Scharbert, B.; Holm, R. H. J . Am. Chem. SOC. 1991,113, 9529. Hlatky, G.; Turner, H. W.; Eckman, R. R. J . Am. Chem. SOC. 1989.11 I , 2728. The X-ray structure of 6a was determined by Prof. Jeff Petersen at West Virginia University.
This Page Intentionally Left Blank
277
26. InsiteTM Catalysts Polymerization
Structure/Activity
Relationships
for Olefin
-
Polyolefins and Elastomers Research and Development Laboratories, The Dow Chemical Company, 2301 Brazosport Boulevard, Freeport, TX 77541 ABSTRACT
The Dow Chemical Company has developed a new family of polyolefins using Constrained Geometry Catalyst Technology (CGCT). The technology is being commercialized under the tradename INSITEm. These INSITE"' technology polymers are characterized by a narrow molecular weight and comonomer distribution. In general, a narrow molecular weight and comonomer distribution would be expected to improve physical properties at the expense of processability. The unique molecular structure of INSITEm technology polymers delivers increased physical properties without sacrificing processability. The improved processability is believed to be the result of significant amounts of long-chain branching. The structure/activity relationships of the family of Constrained Geometry catalysts which give rise to these unique polymers will be discussed. INTRODUCTION There have been numerous interesting developments in the polyolefins industry in recent years. One of the most exciting areas has centered around the development of homogeneous single-site catalysts. These single-sitecatalysts produce ethylene alpha-olefin copolymers with properties that are different when compared with traditional LLDPE and ULDPE polymers. The Dow Chemical Company has developed a new family of polyolefins using Constrained Geometry Catalyst Technology (CGCI'). The technology is being commercialized under the tradename INSITEm. INSITEm technology polymers are characterized by a narrow molecular weight and comonomer distribution. In general, a narrow molecular weight and comonomer distribution would be expected to improve physical properties at the expense of processability. The unique molecular structure of INSITE"' technology polymers delivers increased physical properties without sacrificing processability. The improved processability is believed to be the result of significant amounts of long chain branching. This paper will address the structure / activity relationships of the family of Constrained Geometry catalysts which gives rise to these unique polymers. EXPERIMENTAL The Constrained-Geometry complex syntheses and olefin polymerization conditions were as previously described'. Cyclic voltammetry was conducted in an argon filled drybox in a standard H cell comprising two electrode wells separated by a fine glass frit, platinum working and counter electrodes, and a silver reference electrode. The solvent was 1,2-difluorobenzenecontaining tetra-nbutylammonium tetrakis-pentafluorophenylborate supporting electrolyte.
278
J.C. Stevens
SINGLE-SITE CATALYSTS Metallocene catalysts based on bis-cyclopentadienyl complexes activated with M A 0 have been known for some time. The Kaminsky catalyst is a bis-cyclopentadienyl zirconium catalyst. This complex, when activated with MAO, can produce single-site olefin polymers with high efficiency at low temperatures. Unfortunately, in a high temperature low pressure solution process this catalyst system produces low molecular weight polymers. Additionally, a large amount of the expensive aluminoxane cocatalyst is required for optimum efficiency. C G n CATALYSTS
We have recently discovered a family of new Constrained Geometry Catalysts that allows Dow to produce unique polyolefin polymers in a low pressure solution process. The key catalyst features are shown in Structure 1. The catalysts are monocyclopentadienyl Group 4 complexes with a covalently attached donor ligand. The donor ligand stabilizes the metal electronically, while the short bridging group pulls the donor ligand away from its "normal" position. This has the effect of sterically opening up one side of the complex.
R
I
M = Ti, Zr, Hf Structure 1. General structure of Constrained Geometry Catalyst.
It is possible to synthesize a large number of derivatives of this basic structure and study the structure activity relationships in a rational manner. This paper will address the effect of changing the substituents on the cyclopentadienyl ring, the bridging (R2) group. the coordinating group, and the R3 group.
In general, the open nature of the catalytic site in the Constrained Geometry catalysts does not allow for much steric control of the polymerization reaction, and homopoly a-olefins are generally atactic to slightly syndiotactic. The degree of tacticity obtained under commercially useful conditions is so low that the catalysts should be considered to be atactic. The open nature of the active site allows the copolymerization of a wide variety of olefins with ethylene. Normal a-olefins such as propylene, butene, hexene, and octene are readily incorporated in large amounts. In addition, non-traditional olefins such as styrene can be incorporated. Styrene / ethylene copolymers containing significant amounts of styrene and having a high molecular weight have not been available in the past, as conventional polyolefin catalysts will not copolymerize ethylene with styrene to any appreciable extent. The catalyst activity, when activated with between 50 and 1,OOO equivalents of MA0 is excellent. Catalyst efficiencies between 150,000 and 750,000 g of polymer per gram of metal are obtained, depending on the reactor temperature, specific catalyst, MA0 level and other process variables.
26. INSITETMCatalyst Structure/Activity Relationships
279
(a) Figure 1. X-Ray Crystal smcture of [(tetramethyl-q5-cyclopentadienyl)(N-tbutylamido)dimethylsilyl] titanium dichloride. (a) Front view; (b) side view. The X-ray crystal structure of a titanium tetramethylcyclopentadienyl Constrained Geometry complex bridged with a single dimethylsilaneis shown in Figure 1. In general, the bond distances are unremarkable and are consistent with other known titanium (IV) cyclopentadienyl complexes. The titanium is unsymmemcally bound to the Cp ring, due to the covalent attachment of the amide through the bridging group. Several interesting features can be seen from the side view of this molecule, shown in Figure lb. In this view, it can be seen that the silicon bridging atom has been pulled out of the plane of the Cp ring and that there is a considerable amount of strain in the pseudo-4-membered ring formed by the Cp-Si-N-Ti. The silicon atom of the bridge is pulled out of the plane of the Cp ring by 0.87 A. In addition, the nitrogen atom of the amide ligand has been pulled down from a "normal" position due to the covalent attachment to the Cp ring. The angle f m e d by the Cp centroid, the metal. and the amido nitrogen is 107.6". Comparable Cp-M-N angles for non-constrained complexes are in the range of 115 - 120 O.2 The crystal structure of the analogous zirconium derivative is shown in Figure 2. Again, the bond distances are normal for a zirconium (IV)complex, and are 0.10 - 0.15 A longer than the titanium derivative, consistent with the larger covalent radius of zirconium. The side view of the same molecule (Figure 2b) a ain shows that a large amount of ring strain is evident. The silicon atom of the bridge is pulled 0.84 out of the plane of the cyclopentadienering, and the Cp-ZrN angle is 102.0 '. These titanium and zirconium complexes have a sterically open active center as a result of covalently attaching the amide ligand to the Cp ring. Selected bond distances for these and several other constrained geometry complexes are shown in Table 1.
x
M Ti
Zr Ti Ti
R2 -(SiMe2)-(SiMez)-(SiMe2)2-(CH2)2-
1.909 2.056 1.913 1.909
2.256 2.397 2.277 2.309
2.329 2.455 2.318 2.345
2.329 2.463 2.406 2.345
2.436 2.539 2.429 2.391
2.436 2.540 2.494 2.391
2.262 2.405 2.283 2.282
2.262 2.414 2.291 2.282
Table 1. Selected crystallographic bond distances (in A) for constrained geomeuy complexes.
280 J.C. Stevens
Figure 2. X-Ray Crystal structure of [(tetramethyl-q5-cyclopentadienyl)(N-tbutylamido)dimethylsilyl] zirconium dichloride. (a) Front view; (b) side view. Another constrained geometry catalyst with a slightly longer ethylene bridging p u p is shown in Figure 3. For this complex, the Ti - N bond length is identical to the silane-bridged species. However, the longer bridge allows the titanium to occupy a position more nearly centered over the Cp ring. The side view of this molecule (Figure 3a) shows that the longer bridge is less strained than the short single silyl bridge. The Cp-Ti-N angle is still quite acute in this catalyst, at 107.9 O. The bridge length can be increased further by the use of a disilyl group, as shown in Figure 3b. For this complex, the Cp-Ti-N angle is 120 O , and the active site is much less open than the shorterbridged complexes.
(a)
(b)
Figure 3. X-Ray Crystal structures of (a) [(tetramethyl-q5-cyclopentadienyl)(N-t-
butylamido)ethanediyl]titanium dichloride; and (b) [(tetramethyl-q~-cyclopentadienyl)(N-tbutylamido)teaamethyIdisilyl] titanium dichloride.
26. lNSITETMCatalyst Structure/Activity
Relationships 28 I
Polymerization Results The Constrained Geometry catalysts are effective LLDPE catalysts in high temperature solution polymerizations. Table 2 shows the results for the titanium complex bridged with a single dimethylsilane group. As can be seen, the catalyst is effective at temperatures as high as 160 OC. giving a useful melt index product even in the presence of hydrogen as a molecular weight control. The data shows that as the temperature of the polymerization is increased, the melt index of the polymer increases. At the same time, the density of the polymer increases, indicating that less octene is incorporated at higher temperatures. The second set of runs at 140 O C show that hydrogen is an effective molecular weight control with this catalyst.
Temperature 9J 110
130 140 160
octene
AH2
mL
kPa
150 150 150 150
345 345 345 345
AI:Ti
250 250 500 500
yield R
Mw
density
I2
98 147 128 90
161,000 136,000 66,500 53.000
0.9140 0.9197 0.9174 0.9317
0.15 0.15 3.34 10.66
182 0.9063 1.72 0 500 7.91 690 500 157 57,500 0.9075 All runs with 20 pmoles of [(C5Me4)SiMe2N(t-Bu)]TiC12,2OOO,d solvent, 450 psig ethylene, 10 140
140
300 300
minutes reaction time. Table 2. Ethylene / Octene Copolymer Production using Constrained Geometry Catalysts Table 3 shows that ultra-low density elastomers can easily be produced with constrained geometry catalysts. Fractional melt index elastomeric ethylenebtene resins with densities between 0.87 and 0.85g/mL can be obtained with high efficiencies. The open nature of the active site allows efficient actene incorporation at relatively low actene concentrations. The 0.855 density polymer is over 53 weight percent octene, as determined by l3C NMR. The last two runs runs show that the catalyst responds well to hydrogen, allowing excellent control of melt index over a wide range.
Temperature
[octene]
AH2
80 100 100 100
1.59 1.59 1.85 1.85
172 172 0 345
yield
density
I2
67.0 0.8672 co.10 70.0 0.8700 co.10 110.0 0.8570 0.66 131.9 0.8552 7.48 All runs with 10 p o l e s of [(C5Me4)SiMe2N(t-Bu)]TiCl2,1200 mL solvent. 450 psig ethylene, 10 minutes reaction time. Table 3. Ethylene / Octene Elastomer Production using Constrained Geometry Catalysts
282 J.C. Stevens
The effect of substitution on the cyclopentadiene ring is shown in Table 4. As the groups on the Cp ring are modified to make the ligand more electron withdrawing, there is a marked decrease in efficiency and melt index, as well as an increase in density. The electron density at the metal center for these complexes can be examined by looking at the electrochemical reduction potential for the complexes, or the Jc-H for the dimethyl derivatives. This data indicates that high efficiencies and high comonomer incorporation is correlated with increased electron density at the metal center.
Efficiency npolylgTi C5(CH3)4 150.000 C5H4 59,000 indenyl 31,000
Cp
density dmL 0.8850 0.9070 0.9179
I2
JC-H~
Hz 10.1 2.92 0.92
118.5 119.5 120.4
~ ~ / r b &/p
V -1.49
-1.28
L Y:
.. ,,a
,di
.II
\cl
All runs with 10 pmoles of catalyst. MAO, looomL solvent, 200 mL octene, 450 psig ethylene, 130 "C, 10 minutes run time. a) C-H coupling constant for respective Ti methyl complexes. b) Ti 314 couple, vs. SCE in 1,2-difluorobenzene. Table 4. Catalysis using various Cp derivatives The same effect is observed as the substituent on the nitrogen atom is varied. Table 5 shows that substitutingprogressively more electron-withdrawinggroups on the amido nitrogen leads to decreased efficiency, comonomer incorporation, and melt index.
R
t-Bu Cd5 4-F-CgHq
Efficiency R poly / n Ti 150,000 27,000 15,000
density dmL 0.8850 0.9087 0.9400
I2 10.1 6.37 2.90
GSi+
8, .q 4i
/
R
All runs with 10 pmoles of catalyst, MAO,lOOOmL solvent, 200 mL octene, 450 psig ethylene, 130 OC,10 minutes run time. Table 5. Catalysis using various Amido derivatives The nature of the bridge has a large effect on the activity of the constrained geometry catalyst. Table 6 shows the effect of substituting different bridging groups. As the bridge length is increased from a single dimethylsilyl to a disilyl bridge, the efficiency decreases five fold, while the amount of comonomer incorporated into the polymer decreases, a shown by the increase in the polymer density. The titanium catalysts with an acute Q-M-N angle have the highest efficiency and greatest amount of octene incorporation. This effect can be explained by the more crowded nature of the active site with the longer bridges, as was shown with the crystal structure shown earlier. The crystal structure of the intermediate length ethylene bridged complex showed it to be slightly more crowded than the single silyl bridged complex, and the density of the product reflects this fact. The all-hydrocarbon ethylene
26. lNSITETMCatalyst Structure/Activity Relationships
283
bridge imparts a favorable combination of steric and electronic factors, as shown by the high efficiency and low melt index.
oa
R2 (Si(CH3)2h Si(CH3h
Efficiency
density
g poly / g Ti
dmL 0.9441
23,000 150,000 560,000
120.5 107.6 107.9
(cH2)2
0.8850
0.9190
I2
6.14 10.13 0.21
a) Cp centroid - Ti - N angle. All runs with 10 pmoles of catalyst, MAO, looomL solvent, 200 mL octene, 450 psig ethylene, 130
"C. 10 minutes run time. Table 6. Catalysis using various bridged derivatives It can be seen in Table 7 that the substitution of zirconium for titanium has a dramatic effect. In each case, the zirconium analog has a lower efficiency, and gives a higher density and melt index product.
CP
R2
M Ti
C5(CH3)4 CS(CH314
si(CH3)2 si(CH3)2
indenyl indenyl
Si(CH3)2 Si(CH3)2
zr
CS(CH3)4 CS(CH314
(CH2h
zr
zr Ti Ti
I2
Efficiency
density
g poly / g Ti
dmL 0.8850 0.9571 0.9179
10.13 >250 0.92
3 1,000 30,500
0.9427
9.34
560,000 33.000
0.9190 0.9610
150,000 110,000
R21Cq
jpq
)I,
0.21 >250
All runs with 10 pmoles of catalyst, MAO, looomL solvent, 200 mL octene, 450 psig ethylene, 130 OC, 10 minutes run time. Table 7. Catalysis Results Comparing Ti and Zr Constrained Geometry Complexes. CONCLUSIONS Constrained Geometry catalysts allow the production of a unique family of olefinic polymers. The proper selection of the metal, bridging group, and other substituents allows the control of product properties in a high temperature process. With the proper selection of catalyst variables. products ranging from high molecular weight elastomers to high density polyethylene can be produced. ACKNOWLEDGMENTS The author would like to acknowledge David R. Wilson, Peter N. Nickias, and Robert Mussel1 of The Dow Chemical Company. In particular, the author would like to acknowledge the work of Phil R. Rudolf of The Dow Chemical Company for the solution of the X-ray crystal structures.
284 J.C. Stevens
REFERENCES 1. James C. Stevens, Francis J. Timmers. David R. Wilson, Gregory F. Schmidt. Peter N. Nickias, Robert K. Rosen, George W. Knight, Shih-yaw Lai. European Patent Application 416.815 A2. Aug. 30, 1990.
2. N. W. Alcock, G. E. Toogood, M. G. H. Wallbridge, Acta. Cryst. (1984). C40.598-600.
285
27. Novel Molecular Structure Opens Up New Applications for Insite@ Based Polymers
Director of Research and Development and G. M. Lancaster, Manager of
,Development
Polyolefins & Elastomers R&D, The Dow Chemical Company 2301 Brazospotl Blvd, 8-1607, Freeport, Texas USA 77541
Abstract The Dow Chemical Company has developed a new class of olefin copolymers utiliiing a single site catalyst with constrained geometry and trademarked INSITEQP Technology. The technology can deliver a wide range of new and innovative polymers ranging from polyolefin plastomers (POP, 20 wt.% octene comonomer) to high
performance polyolefins and polyethylenes. This paper will focus on two major advantages of this new technology which have created new polymer design capabiiities/rules for application and product development: 1) INSITEQPTechnology provides tor independent control of processability, and 2) INSITEQDTechnology provides an unprecedented control of molecular architecture. The use of these new design Capabilities will also be explored in three distinctively different development programs. The use of these new polymer design capabilities coupled with processlproductmodeling capabilities greatly reduces the application and product development time. Int roductlon The Dow Chemical Company has developed a new class of olefin copolymers based on a single site catalyst with constrained geometry and trademarked INSITEQPTechno1ogy.l The technology can deliver new and innovative polymers ranging from polyoiefin plastomers (POP, 20 wt.% octene comonomer) to high
performancepolyolefins and polyethylenes. These materials have superior physical properties due to their narrow molecular weight, and comonomer distributions. In June 1993, Dow announced the startup of a 125 million pound plant to produce POP and POE polymers utilking INSITEQPTechnology. Dow's INSITE@ Technology polymers (ITPs) offer improved physical and mechanical propertieswhen used in elastomer, plastomer and polyethyleneapplications as well as enhanced mall processabiiity. The improved physical and mechanical properties result from the narrow molecular weight and short chain branching distributions of the new polymers compared to conventional
286
K . W . Swogger and G.M. Lancaster
polymers. The enhanced melt processability results from insertion of long chain branches in the polymer b a ~ k b o n e ,the ~ * subject ~ of a recently allowed patent.4 In a major effort to rapidly commercializethese new polymers, a significant R&D program has been on-going linking customer application performance requirements to product design, material science, structure property relationship, and process capability. Dow can establish this direct linkage because of the differences of ITP polymers from conventional polyoletins. An example of the material science - product design linkage is being presented separately by Steve Chum, et.
This paper will
focus on two major advantages of this new technology which have created new polymer design capabilities/rules for application and product development: 1) INSITE@Technology polymers (ITPs) have independent control of processability, and 2) INSITE@Technology provides an unprecedented control of molecular architecture. Aspects of these two concepts and the resulting design capabilitieslrules will be discussed and three application developments shown as examples. Coupling the new design rules with process/product modeling capabilities greatly reduces the development cycle time for successful applications. New Rules for Polymer Deslgn The ability of INSITE@ Technology’s single site catalyst with constrained geometry to polymerize higher levels of alpha olefins with ethylene as well as novel alpha olefins offers new and decidedly different processing capabilities and physicaVmechanica1properties to the industry. POPS and POE’s provide unique properties across a wide range of densities and melt indices. The control of processability independent of MWD is a major design rule change. Because they do not have LCB, conventional copolymers made from Ziegler-Natta catalysts and metalloceneor single site catalysts (SSC) homogeneous copolymers require the MWD (via process changes or via blending) to be broadened or the incorporation of a processing aid in order to improve processability. ITPs are unique in their ability to have enhanced processability without broadening of the MWD and sacrificing performance prope~iies.~~’ The presence and control of long chain branching (LCB) in INSITE@Technology polymers offers good processability in addition to the narrow molecular weight distribution. In LLDPE no long chain branching (LCB) exists and 110112 is used as a measure of the processability or flowability of a polymer and can indicate the polydispersity or molecular weight distribution (Mw/Mn) of the LLDPE polymers (Figure 1). In LDPE where high levels of LCB exist, melt tension is used to characterize the melt elasticity of the polymer (Figure 2). The conventional rheological parameters do not adequately describe the unique relationship between the ITP structure, processing, and performance properties because of the presence of LCB (Figure 3 and Figure 4). In addition to melt index and density that can be used with ITP to characterize the flow and
27. INSITE@ Based Polymers 287 physical properties of the polymer, a new parameter has been proposed to better and more completely describe the LCB effects of ITP. This additional parameter is called the Dow Rheology Index or DR18 The Dow Rheological Index (DRI) is a processing performance index which characterizes the long chain branching effect of ITP's (Figure 5) independent of melt Index. DRI is defined as the extent that the rheology of ITP deviates from the rheology of the conventional homogeneous polyolefins that do not have LCB. DRI is defined by the following normalizedequation: DRI = (3.65E6 TO =
Characteristic Relaxation Time
qo
=
T O ~ O -1)
/lo;
Zero Shear Viscoslty
The parametersTO and qo are determined by a nonlinear regression of the experimental data numerically filied to the generalized Cross equation. The index ranges from 0 (for all SSC polymers which do not have LCB) to 30. Combined with MI, the DRI can be used to determine many existing measures of processability. DRI can be used to
calculate the flowability of ITP polymers (i.e., the ease of pumping the polymer through an extruder or the speed which an injection mold can be filled). Figure 6 shows the relationship between the high shear viscosity and DRI. The DRI can also be used to determine the melt elasticity of ITP polymers (i.e., the melt tension, bubble stability, Neck in, Draw resonance, hot green strength, etc.). Figure 7
shows the relationshipof melt tension and DRI. The type of LCBs contained in ITP is different from LDPE in three distinct ways (Figure 8): 1) ITP contains longer and fewer LCB's than high pressure LDPE, 2) ITPs can be designed with a controlled level of LCB along the polymer backbone5 and 3) unlike LCB in LDPE, ITPs LCBs are essentially linear and unbranched. The mechanical and physical properties of ITPs (POP and POE) with various DRls (level of LCB) are shown in Table 1. The relatively b w number and high chain length does not impact the physical or mechanical properties of ITPs but does increase the processability as noted via the increasing DRI. The design rules traditionally used to design a new product for a Ziegler-Natta catalyzed LLDPE are shown in Table 2. The new design rules for ITPs are shown in Table 3. Note that with conventional Ziegler Natta catalyzed LLDPE many of the parameters used to control or design the polymer are coupled and are affected strongly by the production conditions and catalysts. This forces the polymer designer, scientist or englneer to make tradeoffs or compromises. By contrast, INSITEQP Technology breaks these existing rules. Polymer design parameters (density, MW, MWD-2. and
288
K . W . Swogger and G.M. Lancaster
LCB) using INSITE@Technology can be controlled independently. This change enables the polymer designer, scientist, or engineer to design polymers without the current compromises.
As discussed in earlier papers, Dow's INSITEB Technology and process allows the control of molecular architecture to a new level. Dow can design polymers to meet Performance requirements because of our kinetic understanding of reactor operation and the knowledge of structure/property relationships of these new polymers.8 Combining this control of kinetics and structure with the long chain branching gives Dow unique design capabilities.2 By using models we can design a molecule based on structurelproperty relationships, determine plant conditions to make the polymer and know what the polymer is after it is made. Appllcatlon & Product Development This type of control allows us to do product design quite differently than in the past. We are asking our customers for Performance requirements rather than product characteristics (Table 4) for both existing and new applications. This is especially true for the POEs, where ethylene-octene copolymers have not been available until now, and for POP'S, where the new design rules have created new performance opportunities. Polymer specifications for existing applications must be thoroughly reviewed. Usually the specifications are based on the old rules of polymer design and the compromises of performance and processability are often built in. Thus, the polymer designer must go back to performance requirements in order to fully exploit the new relationships that are being established. The INSITE@Technology application and development program links (via predictive modeling and scientific understanding) the Performance requirements of the customers' application with the material science, the processing / fabrication science relationships and the polymer microstructure I property relationships in order to design the polymer. Then utilizing the kinetic process / product model the process conditions to make the designed polymer are defined and the product is produced. In order to fully understandthis process let's examine three applications. Sealant Application (Blown Fllm) The performance requirements for a sealant application are shown in Table 5. This application requires a Nylon barrier layer and will be produced on blown coextrusion equipment. In addition to the performance requirements there are a few additional polymer design rules that should be examined. The linear, ethylene octene structure of POPS brings toughness for extra product protection and /or gauge reduction, plus thermal stability and compatibillty with other polyolefins for co-extrusion. The narrow MWD and comonomer distributions produce lower extractables, excellent optics, and lower heat sealing temperature8 to provide packages with improved organoleptic pedormance, enhanced package appeal, and faster packaging speeds. The LCB content enhances the
27. INSITE@ Based Polymers
289
processability (i.e., improves both the melt elasticity and pumping efficiency) of the resin and eliminates melt fracture (Figure 9) from occurring at high line film extrusion line production rates.7 Utilizing the new polymer design rules (MW, comonomer content, LCB, MW=2 and comonomer type) of ITPs, a polymer can be designed which has significantly improved extrusion, sealing performance, optics, and toughness. Typical sealant materials considered for this application are shown in Table 6. Compared to the competitive materials, the plastomers exhibit improved heat seal strength over a wide temperature range (Figure 10). Plastomer 1 sealed at temperatures similar to the EVA and ionomer, while Plastomer 2 sealed at temperatures 5 to 10°C below the competitive polymers. Ultimate seal strengths were a minimum of 30% greater for the plastorners compared to the competitive polymers. Initiation temperatures for the EVA and Plastomer 1 were similar (approximately 95°C). The lowest initiationtemperature was noted for Plastomer 2 at approximately82"C, slightly lower than that of the ionomer. Ultimate hot tack strengths of the plastomers were 60% higher than the ionomer. The EVA copolymer exhibited poor ultimate hot tack strength. (Figure 11). In summary, plastomers offer outstanding heat seal and hot tack strengths at low sealing temperatures, resulting in faster packaging line speeds and reduced leaker rates. When this is combined with the excellent processability, toughness, puncture resistance and optics, these polymers change the rules for applications requiring high performancesealant materials. Face Mask (Injectlon Moldlng) The performance requirements for the face mask application are shown in Table 7. The main performance requirements for this application is processability and the elimination of plasticizers or processing aids. The injection molding pressures of three ITP polymers and one homogeneous polymer are shown in Table 8. The trial shows the importance of DRI since broad changes in density and MI complicates the use of I10112 flow relationships for polymer characterization. The excellent optics and physical properties of ITP allow for injection molded parts to have optical and physical properties as good as or better than 1-PVC molded parts since no plasticizer is used. Figure 12 shows the effect density or % comonomer has on the stress strain properties of a molded plaque. The excellent processability of ITP's allow parts to be Injection molded on existing molds with excellent optics and flexability and thereby the rules for material selection for injection molded articles have been changed. Wlre & Cable (Banbury Compounded & Cable Extruslon) The key performance requirements for a flexible wire and cable insulation are shown in Table 9. In addition to the performance requirements the application must meet or exceed the current
290 K . W . Swogger and G.M. Lancaster specification (UL1281 Class 45). One of the key performance requirements is the polymers ability to accept high levels of filler and modifiers. A typical formulation is shown in Table 10. The POE family of polymers (>20 wl 'YO octene) have excellent filler and modifier acceptance. Utilizing the new polymer design rules (MW, comonomer content, LCB and comonomer type) and the unique features (the improved physical properties resulting from the narrow MWD) of ITPs, moderate molecular weight iTPs can provide the cross link efficiency, and mechanical properties comparable to very high MW EPDM rubbers (Table 11). From the data one can see that even though the starting Mooney viscosity is much lower than the EPDM's, the ITP based formulations exhibit excellent crosslinkability and filler and oil acceptance. In fact, the ability to have a lower MW and thus, a lower viscosity allows a high level of filler and oil loading to be achieved during the compounding stage. This greatly enhances the compounding efficiency. The LCB of the ITP achieves the required melt strength and results in the elimination of melt fracture during wire line processing. In addition, the narrow MWD and octene comonomer allow a high level of oil to be incorporated without any observation of "bleeding" or phase separation that is the general rule for medium MW EPDM rubbers. The meeting and exceeding of the performance requirements by these polymers combined with its excellent compounding efficiency change the rules for materials used for flexible wire and cable insulation.
Summary Because of Dow's ability to control molecular architecture, once performance requirements are understood it is relatively easy and fast for Dow to either deliver the polymer to the customer or tell him that it can not be done. This has a tremendous benefit to both our customers and Dow. Our customers see quicker response, less trial and error, less cost, very consistent products, and more ability to get the performance they require. Dow sees less cost and resources utilized, quicker development, more satisfied customers, and a wider range of application markets. Focused market development continues in North America and Europe, in conjunction with a wide range of customers under secrecy agreements. The target markets for POP'S and POE's include packaging, automotive, wire and cable, medical, and consumer and industrial goods. The INSITE@Technology application and product development process has been designed to take advantage of the new set of polymer design rules which are being built around the following: 1) ITP's have independent control of processability, and 2) INSITEQPTechnology provides an unprecedented control of molecular architecture. Wide scale commercial product availability into specific markets will be announced during 1993. 63 INSITE is a Trademark of The Dow Chemical Company
Paper Presented at SPO '93 Conference, USA. Used with permission of Schotland Business Research, Inc.
27. INSITEQ Based Polymers 291
Bibliography Trademark Announcement, December 1992. Swogger, K.W., and C.I. Kao, Proceedingsof SPE PolyolefinsVII International Conferecence, Feb. 1993, ANTEC 1993. Swogger, K.W., 'The Material Properties of Polymers Made from ConstrainedGeometry Catalyst", Proceedings of the Sec. Int'l Bus. Forum on Specialty Polyolefins, SPO '92, p. 155165, Sept., 1992
Story, B.A., and G.W. Knight, "The New Family of Polyolefinsfrom INSITE@Technology", Proceedings of Metcon '93 Worldwide Metallocene Conference, p. 112-123, May, 1993 Chum, P.S., Third InternationalBusiness Forum on Specialty Polyolefins, SPO Conference, Sept. 1993. Mergenhagen. L.K., and N.F. Whiteman, "Polyolefin Plastomers'As Sealants In Packaging
-
Applications", 1993 TAPPI Polymers, Laminations and Coatings Conference, Sept. 1993. Edmondson, M.S., and S. E. Pirtle, "CGCT: New Rules for Ethylene Alpha-Olefin Interpolymers
- Processing-Structure- Property Relationshipsin Blown Films', SPE Antec '93 Conference Proceedings Technical Papers Volume XXXIX, p. 63 - 65, May 1993 Lai, S, and G. W. Knight, "Dow Constrained Geometry Catalyst Technology (CGCT): New Rules
-
for Ethylene Alpha-Olefins Interpolymers Controlled Rheology Polyolefins", SPE Antec '93 Conference Proceedings Technical Papers Volume XXXIX, p. 1188-1192, May 1993 Knight, G.W., and S. Lai, "Constrained Geometry Catalyst Technology: New Rules for Ethylene
--
Alpha-Olefin lnterpolymers Unique Structure and Property Relationships" Proceedingsof the SPE Polyolefin Vlll International Conference, p.226-241, Feb. 1993
292 K . W . Swogger and G.M. Lancaster
PROPERTY Toughness Modulus Fbwability (Il~dlp) Melt Strength Melt Index
MAJOR PARAMETERS MW,MWD, Density Density (0.912 to 0.960)
MINOR PARAMETERS
Mw
Mw,MWD Mw MW of HI3 Frartinn
MANY OF THESE PARAMETERS ARE COUPLED 8 AFFECTED STRONGLY BY CATALYSTS
PROPERTY Toughness Modulus
MAJOR PARAMETERS Density (SCB) Average Density (0.86510 0.958) LCB, SCB LCB
Fbwability (Ildlp) Mek Strength Mek Index
w
MINOR PARAMETERS
Mw w
w LCB
DENSITY, LCB AND MW CAN BE CONTROLLED INDEPENDENTLY
E 4
-
TYPlCAl -R F F P FOR RESINS IN THF SO'S Customers Will Need To Know Performance Requirements Such As:
*
Stiffness Bubble Stability Impactfroughness Processability Abuse Resistance Dimensional Stability Taste and Odor
* *
-
Sealability Optics Printability Handling (Conversion) Tear Resistance Weatherability FDA
27. INSITE" Based Polymers 293
LE 5
-
PFRFORMANCF REQUlREMENTS FOR SEALANT APPLICATION
Fabrication Process: Breakthrough: Applicable Regulatons:
Blown Film Coextrusion High Hot T a d and Wide Heat Seal Range FDA Direct Food Contact
4: POLYMER TYPE . POP1 POP 2 ULDPE EVA
COMONOMER 9.0 wt % C8 12.0 wt % C8 9.0 wt % C8 9.0 wt % VA 1
Innnrnar
POP ULDPE EVA
7 Fabrication Process: Breakthrough: Applicable Regulatons:
- PFRF-
/Ns hn\
--
MELT INDEX (dglmln) 1.0MI 1.0MI 1.0 MI 2.0 MI 1
MI
N I
Polyolefin Plastomer Ultra Low Density Polyethylene Ethylene Vinyl Acetate
R F Q J J J T S FOR FACF-
Injection Molding (Sprue) Improve Processabiliy, Elimination of Platicirer. Non-PVC 51OK FDA ApprovaWAverage 9-12 Months
v Msterlal M Density DRI I10/12 Ini. Pressure
DRI 4.5 3.1 NA NA
PERFORMANCF INJFCTIOY
Sample 1
Sample 2
Sample 3
Sample 4
10.87 0.872 0.53
10.26 0.903
10.00 0.880 0.00
7.1
10.82 0.887 0.35 7.8
7.1
5.8
1017
in73
1143
1 A35
0.30
294 K.W. Swogger and G.M. Lancaster
Fabrication Process:
Banbury Internal Mixing / Wire Line Extrusion With Steam Continuous Vulcanization INSITE@Technology Polymers Can Provide Cross Link Efficiency, Wire Line Extrusion And Mechanical Properties Comparable To High Mw EPDM UL 1581 Class 45 (90 and l05OC EPR)
Breakthrough: Applicable Specifications: Feature
Teat Method
I Wire Smoothness 8
I Lower Cvcle Times 8 Lower I Pass SDark Test on Wire I
I
I
Unmet Nerdllmprovement
Mln. Requlrement
? Drop Temperature o Scorch. Cures Within CV Tube > 700 psi > 250%
Wire Line Extension Tensile Elongation Heat Age T&E Retention At 121°C/10d 50% of Original Value and 135'ffd
I
f Higher
ASTM D-638 ASTM 0-638
Lower A 0 Levels Required
ASTM 0-573 8 0-638
Untreated Clay Paraffinic Oil Peroxide Coagent Antioxidant
2.5 1.6
Vinvl Silana
Base Polymer Liinimum Torque Maximum Torque T90 Mooney @ 250°F (ML) Minimum Torque Maximum Torque Delta 3 Crosslinked 4OO0F Tensile Strength (psi) Tensile Q 100% Strain (psi) Elongation Shore A Hardness
I Sag At Strainer Extruder
I Good Melt Strength
INSITE@ Technology
Vlatelon@ 7000 EDPM
Royalone@ 539 EPDM
4 12 6.7
11.5 6.3
14.5 35 6.4
16.5 27 6
47.5 60 6.5
58 73 5
1113 752 218 73
1197
1139 706 214 67
37
837
170 74
27. INSITE" Based Polymers 295
FIGURE 1 FLOW CHARACTERISTICS MWDvs 110/12 nwan 11
10 8
6
Heterogeneous
7
ITP
6
5
Homogemr
4
"":"":'":"":"'':"":"":"":'"'I
1 4
6
6
7
D
0
l
0
1
1
1
2
1
3
iron.
FIGURE 2 FLOW CHARACTERISTICS MWD vs Melt Tens MwMn Hetorogeneoll. ITP
1.6$ 1
. . . .
: 1.6
.
.
.
.
:
. 2
.
.
.
:
-
. . 25
.
:
.
.
.
.
4
3.1
3
Molt Tonrlon (Orom)
FIGURE 3 110A2 RATIO vs LCB 0.85 1.15 Melt Index AND 0.87 0.935 Density ITP
-
-
14.
I, 13-
-=
11-
I
I I10-
:i
7
n
# - .
*
I
- . - . - . - . - ' -
296
K.W. Swogger and G.M. Lancasier
FIGURE 4 MELT TENSION RATIO vs LCB 0.85 1.15 Meit Index AND 0.87 0.935Denslv ITP
-
-
Moll Tonsla. am.
FIGURE 5 DRI ve PREDICTED LCWlooOOC 0.5-30MI& .870 0.920 Density ITP POLYMERS
-
-
DRI 20
10 : 5 2 -
I
0
1
0.5
1.5
2
PRED. LCB/1OOOOC
35,000
-
30.000
-
25.000
-
20,000
-
16.000
10,000 6,000
-
1 0.5 MI
L
-
lo0 >loo 95 >I00 >lo0 >lo0 88 89 Transmittance x 91 88 75 66 90 82 74 82 84 Haze x 32 13 27 41 5 13 25 88 57
SPP(MI= 10)
Remarks
tlPP(hm:MI=4). t*lPP(random:MI=1.5). NB : do not break
336 T. Shiomura
Figure 6 Timc for crystallization
Figure 7 Calenderfd sheet and cast shee! from SPP
7 1 : .
i ,
1
0
..__I
..
I i i
.
20
TABLE 7
.
s
--4
~
.. ..
..
$0 60 i c (C)
100
80
Figure 8 Injection molded articles from SPP a) stewed caps. b) s y r i n g e barrels. c ) tumblers
Comparison of
injection molding conditions Machine: JSW JlOOE-C5 SPP-A IPP (MI=21) (MI-10) Temperature Cylinder C 190/210 190/210 Nozzle C 210 210 Mold C 30 30 Pressure Injection % Boost X
70 40
50 30
Cycle time Inj. /Boost sec Cooling sec
5 30
3 8
WeiRht
B
7.4
7.3
3 1. Syntheses and Properties of Syndiotactic Polypropylene 337
Literature
1) J.A.Ewen, L.Jones, A.Razavi and J.D.Ferrara, J. Am. Chem. SOC., 110 , 6255 ( 1 9 8 8 ) ; J.A.Ewen, M.Elder, L.Jones, L.Haspeslagh, J.Atwood,S.Bott and K.Robinson, Makromol. Chem. Makromol. Symp. ~
48/49
,
253 (1991)
2 ) (a) Y.Chatani, H.Maruyama, K.Noguchi, T.Asanuma and T.Shiomura, J.
Polym. Sci., Part C, Polym. Letters,B, 393 (19gO);
Y.Chatani.
H.Maruyama, T.Asanuma and T.Shiomura, ibid., Part B, Polym. Phys., 29,
1649 (1991);
T.Asanuma, S.Nakanishi, T.Shiomura and T.Kanaya,
Sen-i Gakkaishi.49, 260 (1993);
T.Asanuma, T.Shiomura, Y.Hirase,
T.Matsuyama, H.Yamaoka, A.Tsuchida, M.Ohoka and M.Yamamoto, Polym. B u l l . , z , 79 ( 1 9 9 2 ) ;
T.Asanuma, Y.Nishimori, M.Ito, N.Uchikawa
and T.Shiomura, ibid.,B, 567 ( 1 9 9 1 ) ;
T.Asanuma, Y.Nishimori,
M.Ito, and T.Shiomura, Makromol. Chem., Rapid Commun.,g,
315
(1993)
(b) E.Shamshoum and D.Rauscher,"MetCon
(lgg3)"',
173- (1993);
' 9 3 (Houston), May 26-28
E.Shamshoum. S.Kim, L.Sun, R.Paiz, M.Goins
and D.Barto1, "SPO '93 (Houston), Sept. 21-23 (1993)", A.Razavi, D.Vereecke, L.Peters, D.V.Hessche,
205 (1993);
K.Den Dauw,
L.Nafphiotis and Y.de Froimont, ibid., 105 (1985); H.N.Cheng and J.A.Ewen, Makromol. Chem.
190,1931
(1989);
J.A.Ewen, M.J.Elder,
R.L.Jones, S.Curtis and H.N.Cheng,"Catalytic Olefin Polymerization", Kodansha(Toky0)-Elsevier,
439
(T.Keii and K.Soga, Eds.),
(1990)
R 30, 319 M.Antberg, V.Dolle, S.Haftka, J.Rohrmann, W.Spaleck,
(c) S.Haftka and K,KOnnecke, J. Macromol. Sci.-Phys., (1991);
A.Winter and H.J.Zimmermann, 48/49,
Makromol. Chem. Makromol. Symp.,
333 ( 1 9 9 1 )
(d) G.Balbontin, D.Dainelli, M.Galimberti and G.Paganetto, Makromol. C h e m . , m , 693 ( 1 9 9 2 ) ; P.Sozzani, M.Galimberti and G.Balbontin, Makromol. Chem., Rapid Commun.,&, 305 (1992); P.Sozzani, R.Simonutti and M.Galimberti, M a c r o m o l e c u l e s , x , 5782 (1993) ( e ) G.R.Hawley, T.G.Hil1,
P.P.Chu,
R.L.Geerts,
S.J.Palacka1
H.G.Alt;' " S P d - ' P 3 (Houston), Sept. 21-23 (1993)'",
91 (1993)
3)
Chemical Week, May 18, 7 ( 1 9 9 3 )
4)
Mitsui Toatsu Chemicals, Inc., Jpn. Appl. No. 04-138.960
and
338 T. Shiomura
5)
Mitsui Toatsu Chemicals, Inc., Jpn. Appl. No. 03-713,419;
05-074,
229; 6)
Mitsui Toatsu Chemicals, Inc., W092/01723
7 ) Fina Technology, Inc., Jpn. Kokai 03-179.005;
03-179,006
8 ) Mitsui Toatsu Chemicals, Inc., Jpn. Kokai 04-02-8,703 cf. Idemitsu Kosan Co. Jpn. Kokai 60-217.209; Mitsui Petrochemical Ind. Jpn. Kokai 6 3 4 9 , 5 0 5 9 ) Mitsui Toatsu Chemicals, Inc., EP 414,202 cf. EP 466,926.; EP 419,677; EP 414,047; EP 428,972; EP 4 5 1 , 7 4 3 cf. Jpn. Appl. No. 05-274,072; 05-274,073; 05-271,694; 05-270.136;
lo)
05-274,074; 05-271.693; 05-266.875; 05-262,429; 05-275.440 P.Prentice, Polymer, 22, 250 ( 1 9 8 1 ) ; F.Altendorfer and
A.Wolfsberger, Kunststoffe, cf.R.D.Leaversuch,
80, 691
(1990)
Modern Plast. Int., Aug. 1 6 ( 1 9 9 1 ) ; J.Ogando,
Plast. Technol., Feb. 110 ( 1 9 9 3 ) 11) Mitsui Toatsu Chemicals, Inc., Jpn. Kokai 05-162.158 1 2 ) Mitsui Toatsii Chemicals, Inc., EP 431,475; Jpn. Kokai 03-250,030
339
32. Syntheses and Properties of Syndiotactic Polystyrene
F.ISHMARA*. AND M. KURAMOTO** * Central Research Laboratories, IDEMITSU KOSAN Co.,Ltd., 1280 Kami-izumi Sodegaura, Chiba 299-02, Japan **Polymer Research Laboratory, IDEMITSU Petrochemical Co., Ltd., Anesaki-Kaigan, Ichihara, Chiba, 299-01, Japan
ABSTRACT Homogeneous titanium compound and methylaluminoxane(MAO) system is an effective catalyst for syndiospecificpolymerization of styrene. A comparison of the stereoregularities of the polypropylene and the polystyrene formed by various metallocene catalysts is studied. (CgH6)2C(rl-CgHq)(rl-C9H6)TiC12 / M A 0 system give homogeneous catalyst, for the polymerization of propylene giving isotactic rich polypropylene and of styrene to give syndiotactic polystyrene. Heterogeneous titanium compound containing halogen makes a mixture of isotactic and syndiotacticcomponents.The amount of syndiotacticpolystyrene obtained is dependent on the molar ratio of A1 to Ti. The result of ESR measurement suggests that Ti 3+ species are important as a highly active site for producing syndiotactic polystyrene (SPS). Syndiotactic polystyrene (SPS) is a new crystalline engineering thermoplastic. With a melting point of 270 "C and its crystalline nature, SPS has high heat resistance, excellent chemical resistance, water/ steam resistance. The rate of crystallization is very fast in comparison with isotactic polystyrene (IPS),thus, SPS can be used in a number of forming operations, including injection molding, extrusion and thermoforming.
INTRODUCTION The control of stereoregulaxity is practically important both in the development of new polymers or tailor-made polymers and in the control of polymer properties. When a vinyl monomer (CH2=CHR) is polymerized, the three types of polymers can be obtained ; Atactic, Isotactic and Syndiotactic. When there is a random arrangement of R groups, the structure's
340 N. lshihara and M. Kurarnoto
called atactic. When all the R groups lie uniformly on the same side, the structure's called isotactic. And finally if the R groups occupy positions alternatively above and below the backbone plane, the structure's called syndiotactic. tensivethe Since research discovery concerning of Ziegler-Nana the stereospecific catalyst, poex-
4 1
?A
lymerization of olefins has been carried out. In most cases, isotactic polymers are obtained and syndiotacticpolymers are rare. However, we have I succeeded in synthesis highly syndiotactic poly146.0 146.0 styrene in 1985 in Central Research Laboratories C b m k d ShUl (ppm) of IDEMITSU KOSAN Co., Ltd.1)-2) The 13Cn, 1 m e 7 a w w ~ l p c h d k p m ~Wc I ~ NMR spectra of three types of polystyrenes are ~~~1~~~~~~~~~~~~~~~~~ .given in Fig. 1. Atactic polystyrene is one of the most common plastics in the world. However, the softening point of this polymer's not so high. So, the use of this plastics at high temperature's restricted. Isotactic polystyrene which was discovered by Natta in 1955 is a polymer with a high melting point, 24OOC (degree centigrade). It should be a plastic with high heat resistance. Therefore, many companies tried to industrialize this polymer. However, the crystallization rate of this type of polystyrene is too slow for practical use. Thus this polystyrene has not been industrialized yet. On the other hand, our syndiotactic polystyrene has a high melting point, 270OC. It is higher than that of isotactic polystyrene. Furthermore the crystallization rate of this polymer is so fast that this polystyrene could be industrialized as a plastic with high heat resistance (Table 1). 1
Table 1 The propertles of three types of polystyrenes
Atactlc PS
lsotactlc PS 1955 G. Natta
Syndlotactlc PS 1985
N. lshlhara l IDEMITSU KOSAN C0.LTD.1
Amorphous Crystallization Rate Tg W)
Tm("C)
100
-
Crystalline Slow 99
240
Crystalline Fast 100 270
32. Syntheses and Properties of Syndiotactic Polystyrene
341
RESULTS AND DISCUSSION bperties of SPS Fig. 1 shows the 1 3 C - M spectra of the expanded phenyl C1 carbon of three types of polystyrenes, isotactic,atactic and syndiotactic. In polystyrene the resonance of methylene and phenyl C1 carbon of polymer reflects the conformations of polymer. In particular phenyl C1 carbon provide the best guide to determine stereoregularity of polystyrene. The spectrum of atactic polystyrene shows five main peaks corresponding to its various configurational sequences. The spectrum of isotactic polystyrene shows a sharp singlet at lower magnetic fields corresponding to mmmm pentad configuration. In contrast, the spectrum of syndiotacticpolymer displays a sharp singlet at higher magnetic fields corresponding to rm pentad configuration. The syndiotacticity was more than 99%. Fig. 2 shows you the IH-NMR spectra of the methine and methylene proton signals of the three types of polystyrenes. It was reported that the methylene proton signal of the atactic polystyrene was only a broad resonance and the two methylene protons in isotactic polystyrene were nonequivalent. In agreement with this observation, the spectrum shown here had eight peaks due to the signals of two nonequivalent methylene protons. However, as shown here, the methylene proton signal of the syndiotactic polymer shows only a hiplet. This suggests that two methylene protons of this polymer are equivalent and that the structure’s pure syndiotactic. A well-defined X-ray diffraction pattern of this polymer is quite different from that of isotactic polystyrene. The identity period measured from the fiber spectrum of this structure is about 5.1 A. The result indicates that the crystalline form of SPS has a trans planar conformation like this. Recently, from further investigation it has been suggested that there existed not only a zig-zag planar structure with annealing, but also a helical structm upon crystallization from dilute solution (Fig. 3).DSC and IR observation indicate that a solid-solidphase transition from the p to a form occurs at 190 “C.a-form of SPS is more stable than the pfonn 3). The rate of crystallization of SPS is several orders of magnitude higher than isotactic polystyrene (Fig. 4). Maximum crystallization rate. occurs near 160 “C.The crystallinity of SPS,as well as its hydmarbon nature yields excellent resistance toward moisture, steam and various chemicals. Typical properties for these products are shown in this Table 2. A wide range of products have been formulated with SPS,including glass reinforced resins and I
342 N . lshihara and M. Kuramoto
M. Kobayashi. T. Nakaoki, N. Ishihara; Macromolecules, 22,4377 (1989)
Flg. 3 Schernatlc representationof molecular structures of a-SPS and &SPS.
0.8 h
-E
T
C
0.6
Y
i! 5
-1
1
0.4
0.2
0 0
100
200
300
CrystalllzatlonTemperature ( "C) Fig. 4 Crystalllzatlon rate wlth temperature for SPS
32. Syntheses and Properties of Syndiotactic Polystyrene 343
Table 2 Summary of Physical Propertiesfor SPS Products
Property
Neat Resin
SPS 1WGlasa
30%Glass
Filled
Fllled
I
PET
30%Glass ! Fllkd
SpecHlc Gravlty
1.01
1.09
1.26
I I
1.55
Tenslle strength ( MPa )
35.3
71.6
118
I
152
Tenslle Elongatlon (%)
20
3.1
Flexural Strength ( MPa )
63.7
115
185
Flexural Modulus ( MPa )
2550
4000
9020
lzod Impact ( KJhn2 )
10.0
8.8
2.5
10.8
DTUL 1.82 MPa ( O C )
95
130
251
0.45 MPa ( OC )
110
262
269
2.6
2.8
2.9
Dlelectric const [ 1MHz ] Dlelectrlc loss tangent [ 1MHz I
I
I I I
: I I
I I I
I
I I I
;
2.5 196 9810 8 245 250 3.5
I
< 0.001
< 0.001
indenyl > fluorenyl L 9-methylfluorenyl. This decrease in hydrogen response is probably related to the decreased electron density at the chromium center in the ligand series above. The CrOdSiO2 catalyst has very little, or any, response to hydrogen as a chain transfer agent. As a result of the high hydrogen response with the chromocene catalyst, a highly saturated polyethylene is produced. Polyethylenes produced with the CrOslSi02 catalyst usually have one double bond per molecule, indicating a different chain transfer process from the chromocene catalyst.19 Thermal aging of the chromocene catalyst led to removal of the cyclopentadienyl ligand and loss of the high hydrogen response of the catalyst.18 Polyethylenes produced with the chromocene catalyst are considered relatively narrow in molecular weight distribution. Addition to the catalyst of ethers,no ammonia,21 or siloxanes22 prior to the polymerization led to modified catalysts which produced polymers with a more narrow molecular weight distribution. Certain chromium-containing catalysts provide examples of unsaturated metal centers generated by ligand abstraction.14 A homogeneous ethylene polymerization catalyst, chromium(1ll) 2-ethylhexanoate and hydrolyzed triisobutylaluminum (PIBAO) can produce small quantities of 1-hexene as well as polyethylene. Addition of dimethoxyethane to the catalyst solution led to a significant Increase in 1-hexene selectivity to 74%.23 The principal byproduct was polyethylene, although small amounts of butenes and octenes were also produced. The modified catalyst had a rate of 1.2 mol/mol Crosec for 1-hexene generation (eq 5).
37. Ligand Effects at Transition Metal Centers
393
One view of the origin of the unsaturated chromium centers relates to the conversion of chelating carboxylate ligands surrounding the chromium center to oxide ligands.14 The net effect of such an interaction In the presence of PIBAO is to convert the chromium center into three-coordinate structures (eq 6) which satisfy the requirements of the proposed mechanism of 1-hexene formation.
The rate of 1-hexene formation was dependent on the square of ethylene pressure. Addition of dienes at very low levels resulted in the inhibition of l-hexene formation. These observations can be understood if two ethylene molecules are coordinated with the active chromium site in the activated complex involved in the rate-determining step.
alalysk. Bimetallic complexes containing magnesium, titanium, and electron-donor molecules when combined with aluminum alkyls show high catalytic activity in ethylene polymerization.24-27 The ligand exchange reaction between MgC12(THF)2 and TiC14(THF)2 in tetrahydrofuran yields a yellow crystalline salt [ M Q ~ C I ~ ( T H F ) ~ ] + ~ ~ C I ~The ( T Hcrystal F ) ] - . structure of this salt has been defined in our laboratories and by another group.28 The presence of MgC12 in titanium-based catalysts serves to increase the number of active centers for polymerization. The THF acts as a solvent for the reactants and participates in complex formation rendering the complex stable and permitting the exchange reaction to occur. Removal of THF from
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the complex by organoaluminum compounds provides a route for introducing coordinative unsaturation at the titanium center. Generation of 1-butene from ethylene with high selectivity is well-known technology.29-30 One titanium catalyst is based on directly synthesized titanium(lV) alkoxides and alkylaluminum cocatalysts (eq 7). C2H4
R,AI + Ti(OR)4
R,AI
+ TiCI4
C2H4
high Selectivity to 1-butene
(7)
PE
Because of the fixed alkoxide and chloride ligand environments at the two titanium centers, it was possible to simultaneously dimerize ethylene to 1-butene and copolymerize (eq 8) the resultant 1-butene with ethylene.31-33 The catalyst systems are compatible with each other and operate under the same reaction conditions of temperature, monomer pressure, and solvent. Recent investigations with certain polypropylene catalysts illustrate how ligand abstraction from titanium-based catalysts can lead to polymerization centers with two vacant sites.34 The catalyst was prepared using TiCI3*3Pyridine/MgCln in the presence of A12(C2H5)3C13. The catalyst combined with (C2H5)aAI selectively gave atactic polypropylene.
a,,
01, C2H5#,0 +E
-
L