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Über dieses Buch

45 years after the discovery of transition metals and organometallics as cocatalysts for the polymerization of olefins and for organic synthesis, these compounds have not lost their fascination. The birthday of Karl Ziegler, the great pioneer in this metalorganic catalysis, is now 100 years ago. Polyolefins and polydienes produced by Ziegler-Natta catalysis are the most important plastics and elastomers. New impulses for the polymerization of olefins have been brought about by highly active metallocenes and other single site catalysts. Just by changing the ligands of the organometallic compounds, the structure of the polymers produced can be tailored in a wide manner. In invited lectures and posters, relevant aspects of the metalorganic catalysts for synthesis and polymerization are discussed in this book. This includes mechanism and kinetics, stereochemistry, material properties, and industrial applications.

Inhaltsverzeichnis

Frontmatter

Hetrogeneous Ziegler-Natta Catalysis

Frontmatter

Polyethylene: Polymer with Future

Polyethylenes play a very important role today, because these polymers have a lot of advantages in comparison to other materials. They are produced using easily accessible, reasonable raw materials, they are environmentally harmless, and they can be recycled or energetically exploited after loss of performance. However, the most important aspect is, that they can be tailored in an excellent way using well established modern, energy saving, and non-polluting technologies of large scale.To make these products and to run these processes appropriate catalysts mostly together with cocatalysts are required. The catalyst or the catalyst/cocatalyst system plays the key role for catalytic polymerization of olefins. Now, a broad spectrum of high mileage catalyst systems is available and some new ones are under development. New catalyst systems open prospectives for future progress. The catalyst system and the polymerization process are forming the polymerization technology and both parts must be well-balanced to reach a high level of effectiveness.Besides the polymerization technology, the correlations between polymer structure and polymer properties must be known to tailor products. Based on these three legs: catalyst or catalyst system, process, polymer properties/polymer structure relations, polyethylenes with new and so far unknown properties can be designed and brought to the market. With these polymers consumers needs can be better met saving material and energy for processing, transportation and finally, waste management.

L. L. Böhm, J. Berthold, H.-F. Enderle, M. Fleissner

Polypropylene: 44 Years Young! The Challenge for the 21st Century

Polypropylene is one of the most versatile and successful materials in the market because of the ever-increasing spectrum of polymer composition and properties which have originated from continuing breakthroughs in catalyst and process technology. Industrial polypropylene production is based on Ziegler-Natta supported catalysts. The success of MgCl2-supported catalysts is also due to the development of spherical catalysts with controlled particle size and porosity, used in bulk liquid monomer and gas-phase processes for production of a broad range of homo- and copolymers and multiphase polymer alloys via “Reactor Granule” technology. The most recent development is the discovery of MgCl2/TiCl4/diether catalysts which can give PP yields twice as high as those obtained with previous catalysts. The achievement of a better control of the polymer structure has resulted in an increased capability to tailor the products according to the performance requirements, both in the conversion technologies and in the application life cycle, as well as to extend their application to new market areas.

P. Galli, G. Cecchin, J. C. Chadwick, D. Del Duca, G. Vecellio

Characterization of PP prepared with the latest metallocene and MgCl2-supported TiCl4 catalyst systems

A novel metallocene, rac-Me2Si[2-n-Pr-4-(9-Phenanthryl)-Ind]2ZrCl2, was synthesized and employed for propylene polymerization in conjunction with Ph3CB(C6F5)4 as a cocatalyst. The resulting polypropylene (m-PP) shows 99.6 % of mmmm by 13C NMR and 162.8 °C of melting temperature (Tm) by DSC. In addition, m-PP was compared with the polypropylene (Ti-PP) produced by our latest MgCl2-supported TiCl4 catalyst system, which shows 99.0 % of mmmm and 165.7 °C of Tm, by TREF analysis. TREF indicated that m-PP has narrower stereo-regularity distribution than Ti-PP and Tm of the fraction eluted from m-PP at the highest temperature is 163.6 °C, while that from Ti-PP reaches to 167.3 °C. The individualities of both catalyst systems are discussed.

Norio Kashiwa, Shin-ichi Kojoh, Jun-ichi Imuta, Toshiyuki Tsutsui

An Absolute Test of Rival Theories for MWDs in Heterogeneous Polymerization-MWDs during Quasi-Living Polymerization

Many rival theories proposed for the origin of the broad MWDs of polymers produced with heterogeneous catalysts still persist. As an absolute test for them, the importance of the transitional behavior of MWDs during the quasi-living stage of polymerization is emphasized. Based upon the different mechanisms, all the rival theories have been constructed so as to explain the broad MWDs at the stationary state. Therefore, all competing rate processes are balanced in the stationary state, and any specification of the kinetic mechanism can not be tested by the stationary MWDs. However, for the transitional MWD from the living stage to the stationaiy state, all the rival theories predict respective behavior in response to their different mechanisms. The observed transitional MWDs show that MWDs in the living stages are always broad and then mostly narrow or remain unchanged for which all the rival theories are invalid. To understand this situation, a new theory of non-uniform sites not only with propagation but also slightly with transfer rate is proposed. The non-uniformity that conforms to a popular kinetic model gives a unified explanation about the abnormal decay kinetics recognized in many systems as well as that of the supported Ziegler catalyst.

Tominaga Keii, Teruo Matsuzawa

Olefin Polymerization with Novel Type of Ziegler Catalysts

A series of dichlorobis(β-diketonato)titanium complexes were synthesized and the corresponding MgCl2 -supported catalysts were prepared by impregnation method. Those complexes combined with MAO or alkylaluminums hardly showed the activity for propene polymerization. Whereas, the MgCl2-supported catalysts displayed high activity even using alkylaluminums as cocatalyst. The catalyst isospecificity was drastically increased by adding a suitable Lewis base as an external donor. Isotactic polypropene (PP) with Tm over 169 °C could be thus obtained under appropriate polymerization conditionsOn the other hand, copolymerization of ethene and propene over them gave poly(ethene-co-propene) with a fairly high molecular weight and a narrow chemical composition in high yieldThis paper summarizes the characteristics of the MgCl2-supported catalysts for propene polymerization and ethene–propene copolymerization.

Kazuo Soga, Eiichi Kaji, Toshiya Uozumi

Kinetics and Mechanism of Ethylene Polymerization and Copolymerization Reactions with Heterogeneous Titanium-Based Ziegler-Natta Catalysts

A detailed kinetic analysis of ethylene homopolymerization reactions and its copolymerization reactions with 1-hexene with a supported Ti-based Ziegler-Natta catalyst shows a number of kinetic features which are interpreted as a manifestation of multi-site catalysis. The catalyst contains several types of active centers which differ in stability and formation rates, the molecular weights of polymer molecules they produce and in their response to the presence of an α-olefin. Several kinetic effects in ethylene polymerization reactions require an introduction of a special kinetic mechanism which postulates an unusually low reactivity of the growing polymer chain containing one ethylene unit, the Ti-C2H5group. This peculiarity of the Ti-C2H5group, which is probably caused by its β-agostic stabilization, predicts two features of ethylene polymerization reactions which have not been described in the literature yet: (a) formation of deuterated ethylenes in ethylene homopolymerization reactions in the presence of deuterium, and (b) an apparently increased reactivity of α-olefins in chain initiation reactions involving the Ti-H bond. Both effects were confirmed experi-mentally.

Yury V. Kissin, Robert I. Mink, Thomas E. Nowlin, Anita J. Brandolini

New insight into propene polymerization promoted by heterogeneous Ziegler-Natta catalysts

The configurational analysis of polypropylenes made with coordination catalysts has received a tremendous impulse by the recent application of high-field 13C NMR techniques. In particular, unprecedented determinations of stereosequence distribution at heptad/nonad level have made more realistic and sophisticated models of chain propagation applicable for the first time in a statistically significant manner. In this presentation, the most recent applications to «high-yield» MgCl2-supported Ziegler-Natta catalysts are illustrated

Vincenzo Busico, Roberta Cipullo, Guglielmo Monaco, Giovanni Talarico, Michele Vacatello, John C. Chadwick, Anna Laura Segre, Olof Sudmeijer

Energy Distribution of Active Sites in Heterogeneous Ziegler-Natta Catalysts. Method of Study of Active Site Non-Uniformity

The new method of investigation of active site non-uniformity was developed. The method is based on mass-spectrometric study of temperature programmed desorption (TPD) products from the catalyst surface at initial stages of olefin polymerization (up to 10 – 15 monomer units in chain). The method allows to obtain the information concerning the energy non-uniformity of active sites in terms of a distribution of active sites over activation energy of active Mt-C bond thermal destruction. By the method, the initial stages of ethylene and deuteroethylene polymerization with Ti-supported catalysts of different structure were studied. It is shown that the view of energy distribution of active sites depends on catalyst structure. The values of activation energy of thermal destruction of Ti-C bonds in differing active sites were estimated and energy spectra of active sites for catalysts were obtained.

L. A. Novokshonova, N. Yu Kovaleva, Yu A. Gavrilov, V. G. Krasheninnikov, T. A. Ladygin, I. O. Leipunskii, A. M. Zhigach, M. L. Kuskov

Ziegler-Natta and Metallocene Polymerisation of Olefins with Heterogeneous Catalysts

The reactions of AlMe3 or Al(iBu)3 (TIBA) with the clay mineral montmorillonite form surface fixed aluminoxanes. By further addition of metallocenes — Cp2ZrCl2 or Et(Ind)2ZrCl2 — heterogeneous metallocene complexes are produced. The activities of these catalysts in ethylene or propylene polymerisation are as high as the activities known of similar homogeneous catalyst systems with MAO as cocatalyst. The reaction of AlMe3 with montmorillonite and the further addition of TiCl4 or VC14 yields very active heterogeneous Ziegler-Natta catalysts. Both types produce high molecular weighted polyethylenes.

Karin Weiss, Sandra Botzenhardt, Monika Hofmann

Homogeneous Catalysis, Synthesis and Polymerization

Frontmatter

Formation, structure and mechanism of oligomeric methylaluminoxanes (MAO)

Evidence for hexa-methyl-tetra-aluminoxane as a main product of MAO is demonstrated. Stability and measured molecular weights in benzene, trimethylaluminum, dioxane and tetrahydrofurane are explained by self-association. A new band reactor is described to produce MAO in a small temperature range. NMR-spectra during preparation and after the completion of the reaction allow to understand the mechanism of formation. A compound [Al,(CH2)3]n insoluble in hydrocarbons is prepared.

Hansjörg Sinn, Ingrid Schimmel, Mathias Ott, Norbert von Thienen, Annette Harder, Wiebke Hagendorf, Bernd Heitmann, Erhard Haupt

The Activation of Metal-Fluorine Bonds in Compounds of Group 4 by Aluminum Alkyls

In recent years we have developed the facile preparation of group 47#x2013;6 and main-group fluorides from the corresponding chlorides using Me3SnF as a fluorinating reagent. Reactions of group 4 organometallic fluorides with alkyls of group 13 elements, especially those of aluminum, are of particular interest with regard to the mechanism of homogeneous catalysis for the polymerization of olefins. The formation of adducts of group 4 metallocene halides with AlMe3 is assumed to be the first step of activation of a polymerization catalyst when AlMe3 containing methylaluminoxane (MAO) is used. The following methylation of the metallocene centers is markedly facilitated by this electrophilic support. In order to understand the catalytic activity of those compounds, it is neccessary to examine whether a selective coordination of the fluorine atoms and an exchange for alkyl and amino groups, respectively, is possible using aluminum compounds.

Helge Wessel, Axel Herzog, Peihua Yu, Herbert W. Roesky

A DFT quantum-chemical study of the structures and reactive sites of polymethylalumoxane

DFT quantum-chemical calculations have been performed to elucidate the geometrical and electronic structure of methylalumoxanes (-Al(Me)0-)n with different size (n=6,8,12). The three-dimensional oxo-bridged (cage) structures of methylalumoxane (MAO) have been analyzed.It has been found that the cage structure consisting of three layers of [-Al(CH)30-]4 units is the most stable for MAO with n=12. Trimethylaluminium reacts with MAO by cleavage of a Al-O dative bond and the formation of acidic tricoordinated Al-atoms and basic dicoordinated O-atoms in the MAO molecule. Two molecules of AlMe3 are associated with these sites. The total heat of the TMA interaction with MAO depends on the n value and the MAO structure. The reactive sites of MAO are proposed based on the obtained data.

Ivan I. Zakharov, Vladimir A. Zakharov, Georgii M. Zhidomirov

In situ FTIR spectroscopy shows no evidence of reaction between MAO and TMA

In situ infrared spectra of TMA depleted commercial MAO with increasing additions of TMA have been recorded at 25 °C in toluene solution. The spectra of the mixtures are the sums of the spectra of TMA depleted MAO (CH3/A1 ratio 1.5) and of TMA. There is no evidence of any reaction between these compounds; the basic MAO entity seems to be completely uninfluenced by additions of TMA at this temperature.

Jan L. Eilertsen, Erling Rytter, Martin Ystenes

Alumoxanes alternative to MAO: Synthesis and characterization

A new alumoxane alternative to MAO was synthesised, characterized and used as cocatalyst for metallocene based polymerizations. It is based on Al(2,4,4-trimethylpentyl)3 (TIOA). Alumoxanes were prepared by reacting TIOA and H2O with different molar ratios. 1H NMR spectra of these products are characterized by the presence of broad bands and of resolved multiplets. Their relative amount in the region between 1.9 and 2.5 ppm was identified as the “finger-print” of the polymerization activity.

T. Dall’Occo, M. Galimberti, I. Camurati, M. Destro, O. Fusco, D. Brita

Expanding the Scope of Metallocene Catalysis: Beyond Indenyl and Fluorenyl Derivatives

Group 4 metallocenes with bridged and substituted Ind and Cp/Flu ligands have produced high-molecular-weight isotactic (I-PP), syndiotactic (S-PP), atactic (A-PP) and hemi-isotactic (HIT-PP) (Scheme 1) polypropylenes.i

John A. Ewen, Robert L. Jones, Michael J. Elder

New C1-Symmetric Metallocenes for the Polymerization of Olefins

For the polymerization of propene in solution three new C1-symmetric metallocenes, (I) (Me2C(PhCp)(Flu)]ZrCl2, (II) [Me2C(cHCp)- (Flu)]ZrCl2, and (III) [PhMe3PenFlu)]ZrCl2, were compared. The zirconocene (III) is more stereorigid than (I) and (II) and, therefore, has special properties. At a polymerization temperature of 30 °C, (I) in combination with MAO exhibits the highest activity of 7500 kg PP/(mol Zrh*cp), which is about 5 times higher than the unsubstituted [Me2C(Cp)(Flu)]ZrCl2 catalyst. At 60 °C however, compound (III) is much more active than the others due to the higher thermal stability. A strong dependence of the activity on the propene concentration is observed with all catalysts. The high molecular weight of the polypropene produced by (III) is of particular interest; it is two to four times higher than that of polymers synthesized with the other C1-symmetric zirconocenes. All three catalysts produce polymers with a hemiisotactic microstructure. (III) affords a polymer with more isotactic blocks while polymer produced by (I) has more syndiotactic blocks.

Walter Kaminsky, Ralf Werner

New Catalyst Concepts for the Polymerization of Ethylene with Metallocenes

Diphenylmethylidene(cyclopentadienyl)(2-dimethylamino-fluorenyl)zirconium dichloride (Ph2C(Cp)(2-Me2NFlu)ZrCl2) catalyst activated with dimethylanilinium tetrakis(pentafluorophenyl)borate (Me2PhNH·B(C6F5)4)/triisobutylaluminum (i-Bu3Al) or methylaluminoxane (MAO) produced a high molecular weight polyethylene with a high activity at high temperatures. The molecular weight of the polyethylene was significantly decreased with an increase in the concentration of the aluminum compounds, followed by the formation of vinyl end groups. This phenomenon was not observed for the Ph2C(Cp)(Flu)ZrCl2 based catalysts.

A. Akimoto, A. Yano

Synthesis of Novel Complex with Bridged Bis(indenyl) Ligand and its Polymerization Behavior of Propylene

Novel ansa-zirconocenes characterized by a bis(indenyl) ansa ligand bridged between 4 and 4’ positions were synthesized. The behavior of these complexes as polymerization catalysts in the presence of methylalumoxane and properties of the polymers thus obtained were studied. Isotactic polypropylene was obtained by using C2-symmetrical zirconocene. Especially, rac-Me2Si[4,4’-(3-methyl-1-phenylindenyl)2]ZrCl2 produced polypropylene with high tacticity, and a small amount of 3,1-type regiodefect. By the polymerization test with above complex at various propylene pressures, the depression of melting point of polymer was observed with decrease of monomer pressure, which seemed to be due to the lowering of isotacticity mainly. And by the plot of 1/PNversus 1/[propylene], we got a relatively large value of kTO/kP, and it is suggested that β-H transfer to propylene was not suppressed by substituent at 3 position effectively. Changing substituent at 3 position from methyl group to ethyl group resulted in increasing of molecular weight of polymer.

Taku Kato, Hideshi Uchino, Naoshi Iwama, Kaori Imaeda, Masami Kashimoto, Yasuko Osano, Toshihiko Sugano

Linked Amido—Cyclopentadienyl Complexes of Group 3 and 4 Metals: The First “Post-Metallocenes”

Linked amido—cyclopentadienyl ligands were introduced by Bercaw and Shapiro in the late eighties with the catalysts of the type Sc(η5:η1-C5Me4SiMe2NtBu)X (X = H, alkyl) [1]. These electronically more unsaturated and sterically more accessible analogs of ansa-scandocene complexes were found to be capable of catalyzing the living oligomerization of the α-olefins propylene, 1-butene, and 1-pentene. In these complexes the steric constraint [2] of Brintzinger-type ansa-metallocenes is alleviated by the replacement of one cyclopentadienyl ligand by an amido ligand NR’ (Scheme 1). In order to explore sterically demanding derivatives of this dianionic ligand (C5R4ZNR’)2-, iron and titanium complexes were synthesized shortly thereafter [3].

Jun Okuda

Late Transition Metal Catalysts for Olefin Polymerization

The polymerization behavior of [(2-tertBuPh)2AND]NiBr2 and [(2,6-isoPr2Ph)2AND]NiBr2 activated by methylaluminoxane (MAO) and diethylaluminium chloride (DEAC) are investigated using central composite experimental designs to model response surfaces for catalytic activity and polymer properties. Beside the catalyst and experimental conditions the catalytic performance is influenced by the choice of the cocatalyst. DEAC activation yields lower catalytic activity and polymers featuring a lower molecular weight but increased branching than MAO activation.

Oliver Pyrlik, Mattis Gosmann, Michael Arndt-Rosenau

Homogeneous Catalysis, Mechanism of Polymerization

Frontmatter

Chain growth in zirconocene-catalyzed olefin polymerization - DFT studies on possible reaction paths and the influence of a second olefin ligand

To clarify the nature of the reaction barriers which limit the rate of propene insertion into the Zr-C bond of an alkyl zirconocene cation, the energy surface available to a species [(C5H5)2Zr-ethyl(propene)]+ has been explored as a function of the orientation of the ethyl C(α)-C(β) bond and of the distance between the ethyl-C(α) and the propene-C(2) atoms. The two-dimensional energy surface thus obtained shows three local minima each containing a distinct intermediate: (i) The “starting” geometry I1 arises by coordination of propene to the β-agostic resting state I0 and has the ethyl group still bound to the Zr center by a β-agostic bond, (ii) a “freed” species I2 has a widely rotatable ethyl group and an energy close to that of geometry I1, but is separated from it by a transition state T1 with an activation barrier of 20-25 kJ/mol and (iii) the γ-agostic insertion product I3, with an energy of ca. -30 kJ/mol, which is reached via an α-agostic transition state T2, with an activation energy of 25-30 kJ/mol. Especially for catalyst systems with sterically burdened zirconocene and alkyl moieties, the olefin insertion step I2→[T2]→I3 will be rate-limiting for polymer-chain growth. We have further explored the effects of a second propene in the vicinity of the cation [(C5H5)2Zr-ethyl (propene)]+ on the course of polymer-chain growth. Whereas little interaction is found for the corresponding states I1P and I2P, a weak but significant binding of the external olefin arises in the transition state T2P. Approach to the insertion product I3P, finally, is associated with a steep descent in energy, which signifies attraction of the external olefin toward the metal. As the final state I3P has the olefin already in place for the next insertion, chain growth can now proceed with increased efficieny through an alternative catalytic cycle involving only intermediates I2P and I3P. A kinetic analysis of polymer formation rates based on the operation of both catalytic cycles leads to an estimate of kinetic and equilibrium constants compatible with the observed olefin concentration exponents of 1.4-1.8 in the polymer fomation rate law. Other experimental observations are discussed in relation to these alternative reaction paths in zirconocene-catalyzed α-olefin polymerization.

Marc-Heinrich Prosenc, Frank Schaper, Hans-Herbert Brintzinger

Syndiotactic and Isotactic Specific Metailocene Catalysts with Hapto-flexible Cyclopentadienyl-Fluorenyl Ligand

The unbridged metallocenes can generally be classified as stereo-chemically non-rigid molecules. The fast rotation of the aromatic rings about their bond axis to the transition metal attributes a very high fluxionallity to these molecules. Non-rigid character can be considered for bridged metallocenes if one extends the notion of fluxionallity of the ring(s) to their capability of rapidly and reversibly changing their bonding order (hapticity) to the transition metal. The hapto-tropic behavior of metallocenes with substituted and unsubstituted cyclopentadienyl ring(s) is known as common occurrence in transition metal organometallic chemistry and homogeneous catalysis [1]. The hapto-flexible aromatic ligands bound to the transition metal can facilitate the ligand exchange reaction by lowering “temporarily” the hapticity in the transition state and permitting the increase of the formal co-ordination number without breaking the canonic electronic rules [2]. In this article we have reviewed the basic ideas of stereoselectivity in the light of recent metallocene structure discoveries revealing the presence of haptotropy. The quasi five fold increase of the molecular weight of the syndiotactic polypropylene produced with diphenylmethylidene-μ-(cyclopentadienyl-fluorenyl)ZrCl2/MAO catalyst system with respect to the molecular weight of the syndiotactic polymer produced with the parent isopropylidene-μ-(cyclopentadienyl-fluorenyl)ZrCl2 is brought in direct relation to the difference in hapticity of these molecules in solution and in their cationic forms as active species. The experimental proof for this assumption is given unequivocally through facile hydrogenation of the fluorenyl’s six-member rings in the former and complete inertness of the benzenic rings of the latter to the hydrogenation. In an extension of the same idea haptotropy is also proposed to be responsible for the formation of short blocks of syndiotactic sequences in predominantly isotactic chains formed with the zirconocene isopropylidene-μ-(3-trimethylsilylcyclopentadienyl-fluorenyl)zirconium dichloride. It is further demonstrated that a change in the size and nature of the catalyst’s substituents could increase the probability of occurrence of the haptotropic behavior. The possibility of haptotropy being involved in occasional isospecific/syndiospecific site transformation via a reversible η5↔η3↔η1 mechanism is discussed. The argument is reinforced by introduction of a new syndiotactic specific monocyclic η5, η1 metallocene structure exhibiting similar symmetry properties.

Abbas Razavi, Vincenzo Bellia, Yves De Brauwer, Kai Hortmann, Marine Lambrecht, Olivier Miserque, Liliane Peters, Stéphane Van Belle

Current Vitality of Ziegler’s Monumental Discovery of Zirconium Catalysis in Olefin Polymerization: Metallocene and Nonmetallocene Catalysts via Reductive Dimerization

Although the avalanche of technical advances unleashed by Ziegler’s discovery of the low-pressure polymerization of ethylene is most often associated with the use of titanium procatalysts, it is well to recall that the key initial experiment leading to the formation of polyethylene was achieved in 1953 with zirconium(IV) acetylacetonate.1 Titanium salts maintained their superiority in the heterogeneous Ziegler-Natta catalysts used for olefin polymerization during the next two decades. With the reawakening of interest in homogeneous, single-site metallocene polymerization catalysts in the late 1970s, the zirconocene(IV) derivatives have regained a marked ascendancy, because they undergo deactivating reduction much less readily than titanocene(IV) derivatives.The synthesis of such metallocenes of titanium, zirconium and hafnium generally requires the interaction of the Group 4 MCl4 with the appropriately substituted cyclopentadienyl salt. In the present work we show how a great variety of bridge-substituted ansa-metallocenes can be prepared by the reductive dimerization of a suitable fulvene by the preformed Group 4 MCl2:2If R and R′ are methyl, the tetramethylethylene-bridged ansa-metallocene can readily be obtained. If R = H and R′ = alkyl or aryl, varying proportions of racemic and meso isomers can be obtained and separated into individual isomers.This reductive coupling can also be applied to imines and even carbonyl derivatives and thus can lead to nonmetallocene catalyst systems as exemplified by the reductive coupling of benzalaniline:All the foregoing metallocene and nonmetallocene procatalysts, when combined with MAO, are efficient polymerization catalysts for ethylene. The possible stereoselectivity of the racemic isomers for the polymerization of propylene is under investigation.

John J. Eisch, Xian Shi, Fredrick A. Owuor

Kinetic Features of Living Polymerization of Propene with the [t-BuNSiMe2Flu]TiMe2/B(C6F5)3 Catalyst

Propene polymerization was conducted by [η1:η3-tert-butyl(dimethylfluorenylsilyl)amido]dimethyltitanium combined with B(C6F5)3 as a cocatalyst. Living polymerization proceeded at -50 °C in the presence of suitable amounts of B(C6F5)3 and AlOct3. Addition of AlOct3 and excess B(C6F5)3 drastically increased the polymer yield and molecular weight with a small increase in the number of polymer chains. The results indicated that these Lewis based enhanced the propagation rate although chain transfer reaction was slightly induced. The time-conversion curve showed that the polymerization rate depended on almost second order of propene concentration

Takeshi Shiono, Hideaki Hagihara, Satoru Yoshida, Tomiki Ikeda

Quantitative Structure-Activity Relationships for Unbridged Zirconocene Catalysts During Ethene Polymerization

Polymerization of ethene catalyzed by alkyl-substituted dicyclopentadienyl zirconium dichlorides [(R-Cp)2ZrCl2] was performed with methylaluminoxane as cocatalyst in toluene at T=50°C and PEthene=2 bar. A kinetic model which includes activation of the dichloride, propagation of the polymer chain, and (non-permanent) deactivation of the active site was used to extract rate constants from the time-dependent polymerization activity curves. A calibration set of nine catalysts (R=H; Me; l,2Me2; l,3Me2; lMe2Et;n-Pr; n-Bu; Me4; Me5) was used to establish quantitative structure-property relationships, both for the average polymerization activity over one hour and the propagation rate constant derived with the kinetic model. Structural parameters were obtained from low-energy conformations of γ-agostic (R-Cp)2ZrC4H9+ cations, assumed to be reasonable representations of the active site. Geometries were optimized within the PM3(tm) semiempirical model, and electronic descriptors were computed via density-functional energy calculations on the PM3(tm) geometries. A principal-component analysis (PCA) followed by partial least-squares (PLS) regression indicates that the catalyst with R=1Me2Et is an “outlier”. Better linear models were found for the propagation rate constant than for the average polymerization activity. Several steric and electronic parameters have significant regression coefficients, indicating that the propagation rate is a complex function of molecular structure. Quantitative predictions were made for the propagation rate constant of catalysts that were not members of the calibration set: R=Et, n-Pen, t-Bu, and i-Pr, and Ind2ZrCl2.

J. A. Støvneng, A. Stokvold, K. Thorshaug, E. Rytter

Coexistence of Two Active Species in the Polymerization of 1-Hexene Catalyzed With Zirconocene / MAO Catalysts

The polymerization behaviour of 1-hexene with catalyst systems consisting of different zirconocene dichlorides and MAO as the cocatalyst has been studied as a function of the polymerization temperature. The shape of the GPC curves obtained and the „Arrhenius plot” of the temperature dependence of the number average molecular weight suggest the coexistence of two different active species. A model mechanism for the treatment of the polymerization kinetics was developed, and some thermodynamical parameters of the polymerization reaction were calculated.

Holger Frauenrath, Helmut Keul, Hartwig Höcker

In-depth Investigation of Unsaturated Chain-end Groups: a Tool for Understanding Hydrogen Activation Mechanism in Zirconocene Catalysed Propene Polymerization

Detailed NMR analysis of the microstructure of polypropenes prepared using a range of methylaluminoxane-activated zirconocene catalysts, with and without hydrogen present, have shown that chain transfer to hydrogen by the hindered metal polymeryls which result from secondary monomer insertion cannot be the only mechanism for the well known hydrogen activation effect. It is proposed that another mechanism which may give rise to the activation is that hydrogen should renew catalytic sites which have reacted with unsaturated chain terminal groups in the polymerization mixture to form inert species (such as metal allylics or other sterically hindered sites). Propene was polymerized in solution at partial pressures from 0.4 to 1.1 bar and temperatures ranging from 30°C to 100°C, using a range of three methylaluminoxane-activated zirconocene catalysts. It was found that of the several types of unsaturated terminal group observed using NMR spectroscopy, only vinylidene, 2-butenyl and 4-butenyl are actually formed during polymerization reactions conducted at less than 60°C. Preliminary investigations have shown that the activity of the zirconocene based catalysts is lessened on addition of low molecular weight olefins as models for unsaturated chain-end groups.

Maria Carmela Sacchi, Fabrizio Forlini, Incoronata Tritto, Paolo Locatelli, Andrew Carvill

Supported Metallocene Catalysts

Frontmatter

Supported Metallocene Catalysts for Propene Polymerization

A series of silica supported ethylenebisindenylzirconium dichloride catalysts have been prepared using a number of different experimental procedures and using different types of silica also pretreated under differing conditions. The kinetic and activity behaviour of these catalysts when used with methylaluminoxane (MAO) cocatalyst have been investigated for the polymerization of propene at various MAO concentrations. The activities of these supported catalysts were shown to be affected significantly by their methods of preparation and by the thermal treatment of the silica supports. Higher catalyst activities were obtained by first pretreating dehydrated silica with MAO and then reacting the product either with the metallocene or with a precontacted mixture of the metallocene and MAO. The use of a lower dehydration temperature, 260 °C rather than 460 °C, increased the activity of the supported catalyst systems. The catalyst activities also initially increased with increase in the concentration of external MAO. The order of treatment used for the supported catalyst preparation affected the shapes of the rate-time profiles which were obtained. MAO pretreated silica catalysts were shown by SEM studies to yield polymer of good morphology and evidence for silica fragmentation was also obtained. Leaching experiments were performed using selected MAO pretreated catalysts and showed the significance of leaching processes in these polymerization systems. These results are discussed in terms of a pore restricted model for the polymerization process.

Peter J. T. Tait, Ratna Ediati

Influence of the particle size of silica support on the kinetics and the resulting polymer properties at the polypropylene polymerization with heterogeneous metallocene catalysts; Part I: experimental studies and kinetic analysis

The main focus of this study is the polypropylene polymerization with silica supported metallocene catalysts and especially the investigation of the influence of particle diameter on polymerization activity as well as the changing product properties in dependence on pellet size. The metallocene used was rac-Me2Si[IndR2]2ZrCl2 which was supported on a Grace silica/MAO system of four different particle sizes (10 μm, 35 μm, 50 μm, 80 μm). The propene-polymerizations were carried out in a toluene slurry at 40°C. It was observed that the highest activity is obtained with the smallest catalyst particles and the least activity results from the largest pellets. Also the molecular weights (Mw) strongly depend on the diameter of the support. The Mw of polypropylene produced by an 80 μm catalyst system is smaller by about 50% compared to polypropylene obtained with a 10 μm catalyst system. Furthermore, the polymer growth and the polymer properties were investigated in dependence on time by SEM-images, microtome sections, 13C-NMRs and DSC measurements.

Christian Przybyla, Joachim Zechlin, Bernd Steinmetz, Bernd Tesche, Gerhard Fink

Influence of the Particle Size of Silica Support on the Kinetics and the Resulting Polymer Properties at the Polypropylene Polymerization with Heterogeneous Metallocene Catalysts; Part II: Development of a Model as Well as a Mathematical Simulation

In heterogeneous olefin polymerization, the influence of monomer mass transport in the growing particle and the fragmentation of the support have been comprehensively modeled for conventional Ziegler catalyst but the simulation of the polymerization process of silica supported metallocene catalyst was calculated only by few authors. The expansion and modification of the existing ‘particle growth model’ for the catalytic system SiO2/MAO/rac-Me2Si[IndR2]2ZrCl2 of Bonini et al. is presented. Especially the influence of the catalyst particle size on the kinetics and the fragmentation behaviour was modeled. It was observed experimentally that the maximum polymerization rate as well as the polymer properties depend on the average particle size of the catalyst pellet. In our calculations we were able to demonstrate that the propagation rate and the chain transfer rate alter relative to the varying pellet radius due to the different gradients of [MAO]/[metallocene]-ratios from the particle surface to the granule center.

Christian Przybyla, Bruno Weimann, Gerhard Fink

Supported Metallocene Catalysts in Olefin Polymerization: Toward High Performances

In order to get a supported metallocene type catalyst, different methods have been used to link the group IV metal to the surface. The simplest procedure starts with a metal chloride (titanium or zirconium tetrachloride) supported on magnesium chloride or silica. This solid precursors are modified by a chemical treatment in order to replace in one step one of the chlorines by a cyclopentadienyl or a modified cyclopentadienyl ligand. The results are very different when titanium or zirconium are considered: the titanium catalyst is not different from a conventional Ziegler-Natta catalyst. On the contrary, the zirconium catalyst is similar to a metallocene system, producing polyethylene homo and copolymers with narrow molecular weight distribution which can not be fractionated by solvents. Another approach consists of the metal to the surface using a silicium bridging 2 indenyl ligands. In both cases the zirconium catalysts seem to be very close to the definition of a single site system. High activities have been observed in ethylene polymerization but in it was never possible to produce any isotactic polypropylene.

R. Spitz, N. Verdel, V. Pasquet, J. Dupuy, J. P. Broyer, T. Saudemont

Zeolite Supported Metallocene Catalysts: Effect of Support Structure and Surface Groups on the Polymerization Process

The preparation and catalytic properties in monoalkene polymerization with various metallocene complexes of group IV transition metals (Ti, Zr, Hf) supported on HY zeolites and mesoporous silica MCM-41 are reported. These systems, as indicated by results obtained in a few laboratories and in the authors’ laboratory, polymerize monoalkenes with significant productivity, which is lower than in homogeneous phase, but in general give polymer with higher molecular weight. Selectivity effects, catalyst leaching, role of support surface and pore size are discussed in case of ethylene and propylene polymerization, as well as of ethylene copolymerization with different α-olefins.

F. Ciardelli, A. Altomare, M. Michelotti, G. Arribas, S. Bronco

Preparation of Novel Supported Metallocene and their Olefin Polymerization Capabilities

Cp2ZrCl2 confined inside the supercage of NaY zeolite (NaY/MAO/Cp2ZrCl2) provides shape-selective copolymerization in which comonomer reactivity ratio depends on the shape and size of comonomer. In ethylene/propylene copolymerization over NaY/MAO/Cp2ZrCl2, a comonomer enhancement effect on the polymerization rate was observed, whereas in ethylene/1-hexene copolymerization comonomer enhancement effect was not observed. Comonomer depression effect was observed in ethylene/1-octene copolymerization. In ethylene/isobutylene copolymerization, isobutylene did not influence the polymerization rate. Copolymerization rate was also the same as the ethylene homopolymerization rate, indicating that isobutylene could not diffuse into the pores of the NaY zeolite during copolymerization because the kinetic diameter of isobutylene is larger than the pore diameter of NaY preadsorbed with methyl-aluminoxane (MAO). The comonomer content in the copolymer chain prepared with NaY/MAO/Cp2ZrCl2 was less by about one-half than that in the copolymer chain prepared with Cp2ZrCl2. Melting endotherm measured with DSC after successive annealing of copolymer shows that copolymers prepared with NaY/MAO/Cp2ZrCl2 show a narrower comonomer distribution than that prepared with Cp2ZrCl2.Me2SiCp2ZrCl2 and (MeCp)2ZrCl2 catalysts were synthesized in NaY supercage by ship-in-bottle synthesis method, and used for ethylene homopolymerization.The activity of (MeCp)2ZrCl2/NaY/MAO system was larger than that of Me2SiCp2ZrCl2/NaY/MAO system. However, the absolute magnitude of the catalytic activity was small because LiCl salt formed during metallation was not removed completely and might act as a poison. Because of the difficulty in separating unreacted compounds and inactive or less active by-products from the supercage of NaY, the polymerization activity per Zr atom must be quite low.

Young Soo Ko, Tae Seok Seo, Dae Sik Hong, Seong Ihl Woo

Development of Supported Single-Site Catalysts and Produced Polyethylene

Following the development of conventional multi-site Ziegler-Natta catalysts during the 60–80s, large academic and industrial efforts are been devoted to the design and synthesis of well defined new family of single-site olefin polymerization catalysts, with the group 4 metallocene class of compounds receiving the most attention. Recently, there is also a growing interest in the late transition metal catalysts based on nickel, palladium, iron and cobalt compounds.The new generation of single-site catalysts can really impact the polyolefin industry if they can be used as dropped into large capacity production plants and produced resins that can be processed in the existing equipment without major modifications. Both requirements should be achieved at a favorable cost/performance balance respect to conventional polyolefin technologies. The main objectives of the present contribution is to address two of the most important issues the single-site catalysts technology is currently facing, namely, development of methods for supporting the new single-site catalysts suitable for dropping into slurry and gas-phase processes and the development of polyethylene with better properties and good processability. Firstly, after describing existing procedures for the preparation of supported metallocene catalysts, the method developed by Repsol is then followed. Repsol proprietary technology is based on functionalized metallocene that can react with appropriate carriers producing supports catalysts exhibiting: high activities (while retaining the essential characteristics of their homogeneous analogs), high stability, no reactor fouling or sheeting, good morphology (polymers replicate the catalyst morphology) and bulk densities of the resulting polymers. This method is also very suitable for the design of well defined multi-site catalysts that produce tailor-made bimodal or multimodal resins (either polymer molecular weight and/or chemical composition distributions) with controlled polymer architectures and showing good processability.Finally, the advantages and disadvantages of supporting nickel α-diimine and iron pyridine bis-imine catalysts will be discussed together with the produced polyethylene.

A. Muñoz-Escalona, L. Méndez, J. Sancho, P. Lafuente, B. Peña, W. Michiels, G. Hidalgo, M. F. Martínez-Nuñez

Ethylene Polymerization with the Heterogeneous Single Site CpIndZrCl2 Catalyst

For ethylene polymerization, the supported metallocene catalyst was prepared by anchoring CpIndZrCl2 on silica with a hexamethyl-trisiloxane or pentamethylene spacer. The anchoring procedures exert a strong influence on the catalyst activity since the different anchoring methods lead to the formation of different structures of active sites. By the new anchoring route, it is possible to prepare a „heterogeneous single site” catalyst which has only one catalyst structure on silica surface. The „heterogeneous single site” catalyst exhibits a higher catalyst activity than other supported catalysts. In addition, the activity of the „heterogeneous single site” catalyst was comparable to that of the unsupported homogeneous zirconocene at polymerization temperature of 70°C.

Dong-Ho Lee, Seok Kyun Noh

The Impact of the Cocatalyst on the Polymerisation Behaviour of Supported Metallocenes

Recently a new supported metallocene catalyst system for the propylene polymerisation has been developed. For the activation of the catalyst common aluminium alkyls are necessary. The use of the cocatalysts has a great impact on the whole polymerisation behaviour. The aluminium alkyls effect the activation, the deactivation and the kinetic profile as well as the polymer properties of the resulting polypropylene.The formation of a new kind of soluble MAO free metallocene catalyst as a result of the complex extraction from the catalyst particles by the cocatalyst has been assumed.

E. Ernst, J. Reußner, P. Denifl

Heterogenised MAO-free Metallocene Catalysts

The treatment of dehydroxylated silica with B(C6F5)3 in the presence of dimethylaniline results in borato-modified silica of the approximate composition [HNMe2Ph][(SiO2)50B(C6F5)3] which on addition of metallocene dimethyls in the presence or absence of AlMe3 give catalysts for the polymerisation of ethylene. Nanoparticulate silica gives materials of composition [HNMe2Ph][(SiO2)35B(C6F5)3] and allows higher catalyst loading. Ion exchange of the ammonium salts with [CPh3] [B(C6F5)4] affords stable [CPh3][(SiO2)50B(C6F5)3]; the resulting catalyst give polymers of increased molecular weight. Trityl salts of siloxyborates as homogeneous models for silica-supported catalysts show that the stability of the anion towards one-electron processes, and hence its ability to generate stable catalysts, is crucially dependent on steric factors; e.g. the salts [CPh3][(C6F5)3BOSiR3] are stable and give active catalysts if R3 = Ph3 or ButPh2 but not if R = Me or Pri.

Simon J. Lancaster, Sean M. O’Hara, Manfred Bochmann

A New Supported Zirconocene Catalyst for Ethylene Polymerization

Metallocene catalysts enable the structure of polymers to be tailored in a way which has not been reached before. However, they are more active than the conventional Ziegler — Natta catalysts only as homogeneous metalocene systems, a fact that has essentially restricted their use to industrial processes producing polymers in solution. Modern polymerization processes are solvent free slurry (with liquid monomer) or gas phase processes. To use metallocene catalysts in these modern processes, it is necessary to convert them to heterogeneous catalysts [1, 2]. However, problems have appeared chiefly concerning the activity of the supported catalysts, because heterogeneous metallocene catalysts are much less active than supported Ziegler—Natta catalysts [3,4]. Most solid systems that have been reported cause a dramatic decrease in the activity when compared with the corresponding metallocenes in the solution. Generally, developing of heterogeneous catalyst, with the metallocene as active component supported on the surface of a solid carrier, is the point of extreme interest of resent years.

Wioletta Ochedzan-Siodlak, Maria Nowakowska, Marek Wasielewski

Polystyrene and Copolymers

Frontmatter

Syndiospecific Polymerization of Styrene

Syndiotactic polystyrene, namely XAREC® is being developed by Idemitsu Petrochemical Co., Ltd. as a major new polymer family. XAREC® is a new crystalline engineering thermoplastic with a crystalline melting point of 270 °C. Because of its crystalline nature, XAREC® has a high heat resistance, an excellent chemical resistance and a water/steam resistance. XAREC® also has the dip soldering resistance. Potential applications for XAREC® include surface-mount electronic devices and electrical connectors. In this paper, some mechanistic models for polymerization and stereo-regulation as well as the factors which affect the activity and stereospecificity of the catalysts are discussed. The effects of substitutions on Cp ligand of half titanocene complexes were examined. The bulky substitution groups reduce the activity. Also, borate compounds as activator and effects of hydrogen are discussed.

K. Yokota, T. Inoue, S. Naganuma, H. Shozaki, N. Tomotsu, M. Kuramoto, N. Ishihara

Monocyclopentadienyl Titanium Catalyst

Monocyclopentadienyl titanium complexes are active catalysts for syndiotactic polymerization of styrene. The activity is severely suppressed when the Cp ligand has a substituent with a Lewis basic heteroatom. The active species is a titanium cation generated by the usual cocatalyst. Electron paramagnetic resonance and polymerization studies of a series of monocyclopentadienyl titanium precursors with different propensity for reduction showed that both the tetravalent and trivalent Ti+ species are active, with the former having the greater activity than the latter. Very stable catalysts have been found as a result. In contrast, monocyclopentadienyl titanium complexes are poor for ethylene or propylene polymerization; but the activity is greatly improved with a coordinative substituent on the Cp ligand.

James C. W. Chien, Marvin D. Rausch

The effects of the bridge structure and the ligand system of zirconocene catalysts on the copolymerization of styrene and ethylene

The catalytic properties of zirconocene / MAO systems in the copolymerization of styrene and ethylene strongly depend on the structure of the zirconocene. An isopropylidene bridge leads to a relatively small bite angle and copolymers with a high styrene content. Fused ring substituents of cyclopentadienyl group such as indenyl or benzindenyl show remarkable effects on the styrene content, the catalytic yield and the molecular weights of the copolymers produced. Among the zirconocene complexes tested, rac-isopropylidenebis(45-benzindeny) zirconiumdichloride exhibits the best catalytic performance in the copolymerization. The zirconocene formed a novel styrene-ethylene random copolymer with isotactic stereoregularity and head to tail styrene-styrene structures. The C2 symmetry of the zirconocene is considered to be responsible for both the isotacticity and the formation of head to tail sequences.

Toru Arai, Toshiaki Ohtsu, Shigeru Suzuki

Branched Polyethenes Prepared via Olefin Copolymerization and Migratory Insertion

Branched polyethenes with variable alkyl side chains were prepared via three routes: (1) metallocene-catalyzed copolymerization of ethene with propene, 1-octene, 1-eicosene, (2) simultaneous ethene polymerization and copolymerization of in-situ formed 1-alkenes resulting from ethene oligomerization, using a blend of Ni- and Ti-based catalysts (“hybrid catalysts”), and (3) Ni- and Pd-catalyzed ethene homopolymerization with branching occurring due to migratory insertion. The resulting families of materials included high density, low and ultralow density semierystalline polyethenes as well as highly flexible and elastomeric polyethenes. The degree of branching (DB), as measured by the number of branched C/1000 C, was correlated with comonomer incorporation, catalyst structure, polymerization conditions, polyethene melting temperature and melting enthalpy. Polyethenes prepared by ethene/1-olefin copolymerization were compared with branched ethene homopolymers. Linear low density polyethenes with DB<50, produced with Ni-catalysts, resembled poly(ethene-co-propene). Highly branched polyethene elastomers were applied as toughening agents and blend components of isotactic polypropene in order to improve polypropene’s impact resistance.

Johannes Heinemann, Philipp Walter, Dietmar Mäder, Rupert Schnell, Jürgen Suhm, Rolf Mülhaupt

Metallocene Catalyzed Alternating Copolymerization of Olefins

C1-symmetric metallocenes enable the production of alternating copolymers as well as that of blocky ones. A new model of copolymerization has been developed and applied to ethene/norbornene, ethene/propene and ethene/octene copolymerization. It is shown that the mechanism of polymerization depends on the catalysts structure, the monomer structure, and the temperature of polymerization.

Inken Beulich, Franck Freidanck, Anne-Meike Schauwienold, Ulrich Weingarten, Michael Arndt-Rosenau, Walter Kaminsky

Copolymer Microstructures of Ethylene Norbornene Copolymers Prepared with Homogeneous Metallocene Based Catalysts

Series of ethylene-norbornene copolymers were synthesized in the presence of zirconocenes with different symmetries and ligand patterns and at different norbornene/ethylene ratios. Copolymers were characterized by 13C NMR spectroscopy; Inadequate NMR sequences were used also. The comparison of 13C NMR spectra of copolymers prepared with different norbornene content and the correlation between 13C NMR chemical shifts and conformational structures of the chain on the basis of molecular mechanics calculations were performed. Preliminary assignments were revised and new comonomer sequences such as ENNE which contain meso and racemo NN dyads were assigned.

Incoronata Tritto, Laura Boggioni, Maria Carmela Sacchi, Paolo Locatelli, Dino R. Ferro, Augusto Provasoli

Studies on Properties of Metallocene Catalysed Copolymers of Ethylene and Linear, Non-conjugated Dienes

The effect of diene addition on the structure of ethylene copolymer was studied. The dienes used were 1,5-hexadiene (HD), 1,7-octadiene (OD), and 7-methyl-l,6-octadiene (MOD).Polymerizations were conducted in n-heptane in the presence of the metallocene catalyst cyclopentadienyl zirconium dichloride (Cp2ZrCl2) with methylaluminoxane (MAO) as a cocatalyst. The structure of the copolymer was determined by NMR-techniques. The 1,5-hexadiene comonomer was predominantly incorporated as a 5 member ring structure into the polyethylene backbone. OD and MOD formed branches in the polyethylene chain. The ethylene/HD copolymers were analysed using dynamic rheometry to study the effect of ring structures on the rheological properties of the product. The ring structures stiffen the chain, which was manifested as increasing viscosity and shear sensitivity of the melt. At low hexadiene ring content, the effect of the ring structure was masked by the long chain branching already present in the ethylene homopolymer.

P. Pietikäinen, A. Malmberg, B. Löfgren, J. Seppälä

Ethylene/α-Olefin Copolymerization with Dimethylsilyl-bis(2-methyl-4-phenyl-indenyl) zirconium dichloride and Methylaluminoxane: Influences on Polymerization Activity and Molecular Weight

The copolymerizations of ethylene with 1-hexene and of ethylene with 1-octene have been investigated using rac-Me2Si [2-Me-4-Ph-Ind]2 ZrCl2 and methylaluminoxane as cocatalyst. This metallocene catalyst readily incorporates α-olefin, and at the same time the polymerization activities remain relatively high. Interestingly no comonomer effect can be observed with this catalyst in contrast to other metallocene catalysts, e. g. Cp2ZrCl2 or Me2Si-[Ind]2ZrCl2. Also the mode of addition of catalyst components influences the polymerization rate. The separate addition of the metallocene from the MAO is accompanied by longer induction periods, whereas the combined addition induces copolymerization almost instantaneously. The activities obtained with 1-octene are slightly lower than those obtained with 1-hexene. The molecular weight drops with increasing α-olefin concentration, however it is relatively high compared to copolymers produced with other metallocene catalysts. With a highly racemic mixture of the title catalyst unprecedented activities were obtained of 1,170,000 kg polyethylene/(mol Zr x h x [mon]) at 40 °C, and 477,000 kg ethylene/1-hexene copolymer/(mol Zr x h x [mon]) at 45 °C and a monomer ratio of unity in the reaction.

Massoud Miri, David Hetzer, Adam Miles, Mark Pecak, Brent Riscili

Functional Polyolefins and Polydienes

Frontmatter

The Role of the Cyclopentadienyl Ligand in Catalysts for 1,3-Diene Polymerization

CpTiCl3-MAO is active for the polymerization of various types of 1,3-dienes. Polymers with a 1,2, a cis-1,4 or a mixed cis/1,2 structure are obtained depending on the type of monomer and the polymerization temperature. An interpretation of the factors that determine chemoselectivity and stereospecificity is presented. CpVCl2-MAO gives predominantly cis polymers from various dienes. The systems Cp2TiCl-MAO and Cp2VCl-MAO are also active catalysts; hypotheses are presented on the nature of the active species in these systems.

Lido Porri, Giovanni Ricci, Antonino Giarrusso

Catalytic Reaction Mechanisms and Structure-Reactivity Relationships in the Stereospecific Butadiene Polymerization

Starting with the reaction model of the allylnickel complex catalyzed butadiene polymerization, some essential mechanistic aspects and details, which have been elucidated by DFT quantum chemical calculations are reported. In comparison the present state of the knowledge about the allyllanthanide complex catalyzed butadiene polymerization is outlined. Besides neutral tris(allyl) lanthanide complexes as first one-component lanthanide catalysts for the trans-1,4 polymerization, also bis(allyl) and mono(allyl)lanthanide halides as well as cationic bis(allyl)lanthanide complexes of the general type [Ln(η3-C3H5)2L4] B(C6F5)4 (Ln: La, Nd; L: THF, dioxane) have been synthesized. Allylneodymium halides combined with MAO result in highly active complex catalysts for the cis-1,4-polymerization of butadiene, while cationic bis(allyl)neodymium complexes catalyze the cis-1,4 polymerization without any cocatalyst. Polymerization degree and polydispersity of the polybutadienes allow important conclusions concerning the catalytic reaction mechanism which give further support to the suggested reaction model for the allylanthanide complex catalyzed butadiene polymerization.

R. Taube

Styrene and Conjugated Dienes Polymerization with Half Sandwich Titanocene Catalysts

The Cp’TiX3 - MAO catalytic system (Cp’ =η5-C5H5, η5-C5Me5; X= halide, alkyl, alkoxy; MAO = methylalumoxane) promotes polymerization of ethylene, α-olefins, styrene and conjugated diolefins.Polymerization of styrene and conjugated diolefins is stereospecific and the results, for this last class of monomers, dramatically depend on the structure of the monomer.This presentation mainly reports some results of polymerizations performed with isotopically labelled reagents suggesting some hypothesis on the polymerization mechanism and the organometallic active species.

Adolfo Zambelli, Alfonso Grassi, Pasquale Longo

Half-Vanadocene Catalyst for Butadiene Polymerization

CpVCl3 in combination with either MAO or (C6H5)3CB(C6F5)4/TEA was found a remarkably active catalyst system in butadiene polymerization relative to catalyst systems formed from a titanium analogue, Cp2VCl2 and Cp2VCl. For the CpVCl3/(C6H5)3CB(C6F5)4/TEA system, the dependencies of conversion on time, B/V mole ratio, an amount of TEA, and the dependency of molecular weight of polybutadiene on time have been examined. The catalyst system gives polymers with very high molecular weights and narrow polydispersities. The molecular weight and the conversion decrease with an increase in a feed of hydrogen gas as a chain transfer agent. The polymers consist of high 1,4-cis units and nearly 10% of 1,2-vinyl units. The sequence distribution of 1,4 and 1,2 units was found random by 13C-NMR analysis.

S. Ikai, M. Suzuki, N. Tsujimoto, Y. Iwamoto, S. Yuasa, J. Yamashita, M. Murakami, Y. Kai, T. Yano

Chemical Functionalization of Polypropylene with a V-based Living Polymerization Catalyst

The V(acac)3 (acac = acetylacetonato)/AlEt2Cl catalyst was modified by reacting with α,ω -unconjugated diene compound, and the resulting catalyst was applied to the polymerization of propylene. The polymer produced showed a bimodal molar mass distribution, where the higher molecular weight (Mn(h)) was approximately twice of the lower molecular weight (Mn(l)). From a detailed analysis of the polymer quenched with CO, the Mn(h) fraction was confirmed to have a telechelic structure. Such a telechelic polymer might be produced by the dinuclear vanadium species formed between V(acac)3 and an α,ω-unconjugated diene compound.

Masahide Murata, Yoshifumi Fukui, Kazuo Soga

Copolymerization of Ethylene/ω-Hydroxy α-Olefins

Two different homogenous catalyst systems, a C2 symmetric ansa-zirconocene (1) and a α-Diimine Ni complexes (2) activated by methylaluminoxane were used in copolymerization of ethylene /α-olefins with OH functional groups.The α-olefins with OH functional group used as co-monomer in the polymerisation reactions were 5- Hexen-l-ol (3) and 10-Undecen-1-ol (4).Catalyst (1) shows low activities when monomer (3) is used. Only with very small concentrations of monomer the activities are comparable to those obtained in the absence of the polar monomer (3). The activities obtained with catalyst (2) are higher, even when high concentrations of monomer (3) and (4) are used. 1H and 13C NMR spectra, used to characterise the polymers, show the presence of carbons linked to OH groups. So, these catalysts systems allow us to obtain functionalised copolymers by direct polymerisation of ethylene/hydroxy-α-olefins.

Maria M. Marques, Sandra G. Correia, J. Ascenso, Alberto R. Dias, Mathew Blais, Marvin D. Rausch, James C. W. Chien

Stereospecific Polymerization of Methacrylates with Dimethylsilylene-bridged Zirconocene Catalysts

Polymerization of methyl methacrylate (MMA) was conducted with a series of dimethylsilylene-bridged zirconocene complexes (rac-Me2ilnd2ZrMe2, 1; Me2SiCpIndZrMe2, 2; Me2SiCpFluZrMe2, 3: Cp, cyclopentadienyl; Ind, indenyl; Flu, fluorenyl) to investigate the effects of the cyclopentadienyl ligand. Thezirconocene complexes were activated by [Ph3C][B(C6F5)4] or [PhMe2NH][B(C6F5)4]in the presence of diethylzinc. It was found that 1 and 2 gave polymers but 3 did not at 0°C. The dependence of polymer yieldand molecular weight on polymerization time indicated that some chain transfer reaction occurred in both systems. 13C NMR analysis revealed that C1symmetric 2 as well as C2-symmetric 1 gave isotactic rich polymer (mmmm = 84–87%) by enantiomorphic-site controlled mechanism. Polymerization of allyl methacrylate (ALMA) was also conducted with Cp2ZrMe2 and 1. These catalysts selectively polymerized the methacryl group to give syndiotactic-rich and isotactic polymers, respectively with pendant allyl group.

Nobuya Saegusa, Tetsuya Saito, Takeshi Shiono, Tomiki Ikeda, Hai Deng, Kazuo Soga

Development of Catalytic Systems Based on Lanthanoïd Complexes for Olefin Polymerization

The use of the alkylation technique of Cp*2LnCl2Li(OEt2)2 complexes for the synthesis of lanthanocene active species which are useful for olefin polymerization, is described. Both butyl lithium and butyl-ethyl magnesium (BEM) are shown to be suitable as alkylating reagents for ethylenepolymerization. Using BEM in excess allows the synthesis of higher dialkylmagnesium compounds via a chain transfer reaction between magnesium and lanthanoide atoms following the insertion reaction of the monomer into the Ln-alkyl bond. For methyl methacrylate polymerization, using a butyl lithium/Ln ratio of 2 gives the best results, leading to the production of syndiotactic (>80%) PMMA with low molecular weight distributions (<2), in high yields and molecular weights (up to 2*105).

Karel Bujadoux, Thomas Chenal, Christine Fouga, Xavier Olonde, Jean-François Pelletier, André Mortreux

Polymer Characterization and Processes

Frontmatter

Initial 2,1-Insertions in Metallocene Polymerizations of Polypropylene

2,1-insertions during propylene polymerizations with a metallocene catalyst produce regio defects within the polypropylene chain and n-butyl end groups after chain transfer with hydrogen of a terminal 2,1-inserted propylene unit. In this study, initial 2,1-insertions, which produce 2,3-dimethylbutyl end groups, are reported for the first time. The structural proof was obtained with model compounds, a NMR DEPT experiment and gc-mass spectrometry of propylene oligomers. The mole percent of initial 2,1-insertions ranges from 25 to 40%. From 13C NMR, a conservation of end group concentrations is established through the observation that the sum of n-propyl + 2,3-dimethylbutyl initial groups is equal to the sum of the n-butyl + iso-butyl final groups. Number average molecular weights calculated from the end group concentrations are in excellent agreement with number average molecular weights from GPC. A linear relationship is observed when the total 2,1-insertions per molecule are plotted versus the degree of polymerizat.

J. C. Randall, C. J. Ruff, J. C. Vizzini, A. N. Speca, T. J. Burkhardt

Olefin Polymerization with DuPont’s Versipol™ Catalyst System

In collaboration with the University of North Carolina, DuPont is developing a new catalyst technology for olefin polymerization. Versipol™ catalyst technology is based upon the late transition metals. The steps in DuPont’s commercialization effort are outlined.

Steven D. Ittel

Features of Cyclopentadienyl Metal Catalysts for Ethylene Copoly-Merization in Gas and Liquid Phase

Catalysis in gas phase reactions for the production of olefin polymers is well known in the polyolefin industry [1]. Developments in the UNIPOL® process for polyethylene, EPR/EPDM, and polypropylene continue to demonstrate the broad versatility of the process. The emergence of metallocene catalysis in many laboratories around the world has added yet another significant catalytic tool for manipulating and controlling the molecular framework of polyolefms. Selection of the appropriate metallocene catalyst, with control of ligand environment at the active site, continues to provide the basis of improved process operations and unique product opportunities.

Frederick J. Karol, Sun-Chueh Kao, Eric P. Wasserman, Zhengtian Yu

How to Avoid Gas-Liquid Mass Transfer Limitations during Polymerization of Olefins

Propene was polymerized using a modern Ziegler-Natta catalyst dispersed in decane. The stirring rate was changed during polymerization, and the observed monomer feed rates were analyzed using a steady state and a dynamic mass balance to obtain mass transfer coefficients. A theoretically founded mass transfer model for a semi batch stirred laboratory reactor was developed. It is shown how the model can be used to secure minimal transport limitations in kinetic experiments during polymerization of olefins. It is found that introducing baffles and sparging considerably decrease the transport resistance at high stirring rates.

Pal Kittilsen, Rune Tøgersen, Erling Rytter, Hallvard Svendsen

Ternary Metallocene Based Catalysts in High Temperature, High Pressure Polymerization

High pressure copolymerizations of ethene and 1-hexene were performed by use of a ternary catalyst system based on Me2Si[Ind]2ZrCl2, A1(iBU)3 and [PhNHMe2][B(C6F5)4]. The productivity depends strongly on the molar ratio of [Al]/[Zr] used. With small amounts of 1-hexene in the feed a rate enhancement of the ethene polymerization rate was observed. Incorporation of 1-hexene in the polymer was studied as well as the influence of 1-hexene on polymer density.

G. Luft, A. Rau, A. Dyroff, C. Götz, S. Schmitz, T. Wieczorek, R. Klimesch, A. Gonioukh

Advances in the Use of Stopped-flow Techniques for Olefin Polymerization

The stopped-flow method, by which a reaction can be conducted within an extremely short period (ca. 0.1 s), has been extensively applied to various kinds of investigations of olefin polymerization using Ziegler catalysts. The most important studies using this method are related to kinetic investigations of the polymerization. This method seems to be most suitable for the kinetic study of olefin polymerization with Ziegler catalysts, because the quasi-living polymerization stage can be attained, in which the states of the active sites are constant without a time-dependent change, and the chain-transfer reaction can be essentially negligible. For this reason, it is possible to clarify the effects of hydrogen and the co-catalyst, which are significant and indispensable factors that must be taken into account during the olefin polymerization, and for the polymerization behavior in the initial stage. Attention is also focused on the study of the active sites on the catalysts using the stopped-flow method. This can be done because the nature of the active sites just after their formation can be directly reflected in the polymer obtained during the initial polymerization stage. The method has been employed to produce a novel olefin block copolymer by taking advantage of the polymerization within an extremely short period, where the polymerization time is considered to be shorter than the lifetime of the growing polymer chain. In this article, we outline the various investigations related to the stopped-flow method for the polymerization of olefins with Ziegler catalysts.

Minoru Terano, Mikio Yamahiro, Hideharu Mori

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