Supported Metallocene Complexes for Ethylene and Propylene

1224

Ind. Eng. Chem. Res. 1997, 36, 1224-1237

Supported Metallocene Complexes for Ethylene and Propylene Polymerizations: Preparation and Activity Maria R. Ribeiro,*,† Alain Deffieux,‡,§ and Manuel F. Portela† Grupo de Estudos de Cata´ lise Heteroge´ nea, I.S.T., Technical University of Lisbon, Av. Rovisco Pais, 1096 Lisboa Codex, Portugal, and Laboratoire de Chimie des Polyme` res Organiques, UMR ENSCPB-CNRS, Avenue Pey Berland, B.P. 108 33402, Talence, Cedex, France

Important research is currently underway to develop supported metallocene-based catalysts that could be widely used in the polyolefin industry. Recent developments concerning these systems are reviewed. The main preparation methods for metallocene immobilization on various supports are first systematized and described. Then, the nature and structure of active sites as well as their formation mechanism are analyzed. The performances for ethylene and propylene polymerizations of various supported metallocene systems are compared and discussed on the basis of the different catalyst preparations and of the operational polymerization conditions. Finally, the influence of metallocene heterogenization on the final polymer properties is examined. 1. Introduction Sinn and Kaminsky’s discovery of new catalytic systems based on the combination of metallocenes with alkylaluminoxane started a new era in polyolefins. Since that time, homogeneous catalysis of olefin polymerization based on group IV metallocenes has been the subject of intensive research, leading, in recent years, to the development of a broad series of new metallocene complexes. In comparison with conventional Ziegler-Natta systems, metallocene-based catalysts offer higher versatility and flexibility both for the synthesis and the control of the structures of polyolefins. For example, metallocenes can be tailored to produce polyolefins with special stereoregularity and a high degree of tacticity. Moreover, these homogeneous systems are able to polymerize several olefins with high activities into highmolecular-weight polymers and copolymers, characterized by a narrow molecular weight distribution (≈2) and homogeneous chemical composition. High-density polyethylene (HDPE), polypropylene with different stereostructures (atactic, isotactic, syndiotactic, hemiisotactic, etc.), and random copolymers of ethylene with R-olefins are among the most remarkable products obtained. The use of metallocene catalysts for the preparation of novel elastomers may also have high commercial impact. However, despite their numerous advantages, several technical problems still need to be solved before metallocene catalysts can be used widely in industry. Two of the main problems observed are (1) the difficulty in controlling polymer morphology with soluble homogeneous catalysts and, consequently, their inability to be used in slurry and gas-phase processes (moreover, significant reactor fouling takes place when using homogeneous systems) and (2) the very large amount of methylaluminoxane (MAO) needed to achieve maximum metallocene catalytic activity. One route developed to overcome this last problem involves the generation of cationic metallocene complexes with the aid of noncoordinating anions. However, this approach does not allow for any control of polymer morphology. Another possibility involves the * Fax: 351-1-8499242. E-mail: [email protected]. † Technical University of Lisbon. ‡ UMR ENSCPB-CNRS. § E-mail: [email protected]. S0888-5885(96)00475-7 CCC: $14.00

immobilization of metallocene compounds on a support, as already performed in Ziegler-Natta catalysis. In this case, the aim is to find a way to attach the metallocene to the support without losing the performances of the homogeneous complex (high catalytic activity, stereochemical control, ability to produce copolymers with statistical comonomer distribution, etc.) while improving the morphological characteristics of the polymers and the metallocene activation step in order to meet the requirements for industrial applications. The development of supported metallocenes will, in particular, enable their use in gas- and slurry-phase processes and prevent reactor-fouling problems. Formation of uniform polymer particles with narrow size distribution and high bulk density can be expected as for Ziegler-Natta-supported catalysts. A large number of scientific articles and several reviews dealing with metallocenes for the catalysis of olefin polymerization have been published in recent years (Gupta et al., 1994; Sinclair and Wilson, 1994; Mohring and Coville, 1994; Kaminsky, 1994; Reddy and Sivaram, 1995; Soares and Hamielec, 1995; Huang and Rempel, 1995). However, they are mostly focused on homogeneous systems, and despite the importance of supported metallocenes for industrial olefin polymerization processes, no comprehensive review is available on this subject. The scope of this review is restricted to the analysis of the methodologies involved in the preparation of metallocene-supported catalytic systems and the study of the nature of the corresponding active sites involved in ethylene and propylene polymerizations. The influence of metallocene heterogenization on catalytic performances and on the final polymer properties is also examined. 2. Main Routes to Supported Metallocenes One of the earlier attempts to heterogenize a soluble metallocene catalyst is due to Slotfeldt-Ellingsen and co-workers (1980). Bis(cyclopentadienyl)titanium dichloride, Cp2TiCl2, was supported on silica gel and used to polymerize ethylene with AlEtnCl3-n as the cocatalyst. In the last few years, a large number of studies have been devoted to the transformation of soluble metallocene complexes into heterogeneous catalysts by supporting them on inorganic or organic carriers. The nature of the support and the technique used for supporting the metallocene have a crucial influence © 1997 American Chemical Society

Ind. Eng. Chem. Res., Vol. 36, No. 4, 1997 1225 Table 1. Preparation Conditions for Supported Metallocenes (Methods 1 and 2)a metallocene

support

calcination of support

modification of support

method of prepn

prepn cond

obsd

CpTiCl3

SiO2

800 °C, 3 h

1

100 °C, 3 h

CpTiCl3

Al2O3

200 °C, 6 h

1

100 °C, 3 h

Et[IndH4]2ZrCl2

400 °C, 6 h

1a

rt, 10 min

400 °C, 6 h

1a

rt, 10 min

Cp2ZrCl2

MgCl2, Al2O3, or SiO2 Al2O3, MgCl2, MgF2, CaF2, etc. SiO2

1a and 2

rt, 30 min

washed with excess toluene

Et[Ind]2ZrCl2

SiO2

500 °C, 3 h

1b

70 °C, 16 h

extracn in refluxing toluene for 2 days

Et[Ind]2ZrCl2

SiO2

500 °C, 3 h

1b

70 °C, 20 h

Et[Ind]2ZrCl2 or Cp2ZrCl2 Et[Ind]2ZrCl2 or Cp2ZrCl2 Et[IndH4]2ZrCl2

SiO2

650 °C, 5 h

1b

70 °C, 16 h

2

30 °C, 1/2 h

repeated washing with toluene repeated washing with toluene washed toluene

i-Pr(Flu)(Cp)ZrCl2 or Cp2ZrCl2

400 °C, 6 h

Cl2SiMe2 (7-h reflux with toluene), NaHCO3, and/or MAO

1/

SiO2

650 °C, 5 h

MAO, 30 °C,

SiO2

400 °C, 6 h

MAO, rt, 30 min

2

rt, 30 min

washed toluene

Et[Ind]2ZrCl2

SiO2

350 °C, 18 h

MAO, 50 °C, 4 h

2

T ) (?), overnight

washed toluene

rac-MeSi[Ind]2ZrCl2

SiO2

MAO

2

50 °C, 2 h

washed toluene

Cp2MeCl2

SiO2

AlEt3 or C2H5MgCl, 50 °C, 1 h

2

40 °C, 30 min

washed toluene

2

h

washed with excess toluene washed with excess toluene washed with excess toluene washed with excess toluene

ref Soga et al. (1991) Soga et al. (1994c) Kaminaka and Soga (1991) Soga and Kaminaka (1993) Soga et al. (1993) Kaminsky and Renner (1993) Chen et al. (1995) Sacchi et al. (1995) Sacchi et al. (1995) Soga and Kaminaka (1992) Soga and Kaminaka (1993) Chien and He (1991)

200 °C, 4 h

a

600 °C, 10 h

Bonini et al. (1995) Ihm et al. (1994)

R ) alkyl, Me ) methyl, i-Pr ) isopropyl, Cp ) cyclopentadienyl, Ind ) indenyl, Flu ) fluorenyl, rt ) room temperature.

on the resulting catalytic behavior. Inorganic oxides, finely divided polymers, or other high-surface-area materials have been used as supports. The main inorganic supports used are silica, alumina, and magnesium compounds. Nevertheless, less common materials such as cyclodextrin (Lee and Yoon, 1994, 1995), polystyrene (Nishida et al., 1995; Grubbs et al., 1973), polysiloxane derivatives (Soga et al., 1995b), and zeolites (Ismayel et al., 1993; Arribas et al., 1994; Ciardelli et al., 1994; Woo et al., 1995) have also been investigated. Surface modification of the support can also be applied to improve the catalysts’ performances. This may include reactions of the support with organometallic compounds (such as magnesium or aluminum alkyls) or other compounds (SiCl4, SiMe2Cl2, etc.), as well as thermal treatments. The main preparatory routes reported in the literature for metallocene immobilization on these supports can be classified according to three main methodologies, as follows: Method 1. The first method involves direct impregnation of metallocene on the support (modified by previous treatment or not). This can be done either (a) with mild impregnation conditions or (b) at high temperatures and long impregnation times (refined route). Method 2. The second method involves immobilization of MAO on the support followed by reaction with the metallocene compound. A modified version of this method involves the replacement of MAO by an aluminum alkyl. Method 3. The third method involves immobilization of aryl ligands on the support followed by addition of a metal salt such as zirconium halide; recently, titanium and neodymium halides have also been used to form the attached metallocene. Method 1 involves physical mixing of metallocene and support, and it was one of the first preparatory routes used. In this method, the dry support is reacted first

with the metallocene compound in a solvent such as toluene. The solid part is then recovered by filtration and washed with a hydrocarbon. The mixing temperature and the contact time are important parameters since they influence both the catalytic performances and the final properties of the polymer, as will be further discussed. Kaminaka and Soga (1991) and Soga and Kaminaka (1993) used this impregnation method, at very mild conditions (room temperature and impregnation time ) 10 min), to prepare and compare the performances of different supported systems. Later on, Kaminsky and Renner (1993) used a refined route (method 1b) for the preparation of silica-supported ansa-metallocene catalysts. This method involves direct reaction of metallocene with SiO2 at high temperature (T ) 70 °C) and for a long period of time (t ) 16 h). The traces of the remaining highly active homogeneous catalyst were carefully extracted from the solid catalyst, to prevent the formation of low-melting and low-molecular-weight polypropylene. The supported metallocene catalysts prepared by method 1 are listed in Table 1. The main supports used are Al2O3, SiO2, or MgCl2. In several cases, the carrier was modified by the addition of Cl2Si(CH3)2 before impregnation by a metallocene derivative (Et[IndH4]2ZrCl2, i-Pr(Flu)(Cp)ZrCl2, or Cp2ZrCl2). The second and third methods have been mostly used for the preparation of silica-supported metallocenes. Silica is one of the most frequently used carriers, since it leads to good morphological features for polymer particles. In method 2, silica is first pretreated with a small amount of MAO under mild conditions (room temperature, t ) 30 min). After filtration and washing with toluene, the MAO-modified SiO2 support is then mixed with the metallocene and treated as described in method

1226 Ind. Eng. Chem. Res., Vol. 36, No. 4, 1997

Figure 1. Modification of silica surface by addition of different compounds. Reprinted with permission from Soga et al. (1995b). Copyright 1995 Huthig & Wepf.

1. The supported zirconocenes obtained in this way can be activated by MAO (Kaminsky and Renner, 1993; Chien and He, 1991; Chen et al., 1995) or by common alkylaluminum (Soga and Kaminaka, 1992, 1993; Soga, 1994a,b). Recently, Ihm et al. (1994), used a slightly modified procedure in order to support Cp2MtCl2 (Mt ) Ti, Zr, Hf) on silica. They replaced MAO by Al(C2H5)3 and by (C2H5)MgCl during SiO2 pretreatment. Ciardelli et al. (1994) also prepared supported Cp2MtCl2 catalysts (Mt ) Ti or Zr) using SiO2 modified with MeLi and zeolite HY treated with AlMe3 or Me3SiCl as carriers. Chang (1991, 1992, 1993) patented the direct synthesis of supported aluminoxanes, in slurry- and gas-phase reactors, especially for the production of HDPE and LLDPE. Instead of contacting the support with aluminoxane, the latter was generated in situ by reacting an alkylaluminum (TMA or a mixture of trialkylaluminums) directly with water adsorbed on the material support, generally silica gel. The aluminoxane-coated support was then contacted with a metallocene solution to form the final catalytic system. The order and rate of addition of silica gel and trialkylaluminum are important: slow addition of silica gel to a solution of trialkylaluminum is necessary in order to obtain high catalytic activity. Recently, Lee et al. (1995) applied the method developed by Chang to synthesize Cp2ZrCl2 silica-supported catalysts. Hydrated silica was prepared by two procedures. In the first one, SiO2 was fully hydrated in

deionized water, filtered, and fluidized in a column under nitrogen gas flow, yielding silica with 45 wt % water. In the second method, SiO2 was fluidized with wet nitrogen. Silica with 16 wt % water was obtained. The catalyst support was then prepared by contacting the hydrated silica (HSiO2) with a solution of TMA in toluene. The supported catalyst was finally synthesized by addition of the metallocene to the support in toluene suspension. Examples of supported metallocene systems prepared by method 2 are also given in Table 1. It is likely that immobilization of metallocenes on the surface of inorganic carriers, according to the procedures described above, proceeds through ionic interactions between the metallocene and some peculiar surface sites of the support or of the anchored MAO. A new preparation method in which metallocene is more tightly attached to the support has been developed by Soga and co-workers (Soga, 1994b, 1995; Soga et al., 1994a,b, 1995a; Jin et al., 1995), method 3. Method 3 deals with the synthesis of catalysts where metallocene ligands are chemically bonded to the support (mainly modified SiO2). It involves four steps: Step 1 is the modification of the silica surface by addition of compounds such as SiCl4, C2H2Br4, SOCl2, or MeSiCl2. Typical conditions are reaction in toluene at reflux for 48 h. Depending on the additive, the structures in Figure 1 may be obtained. Step 2 is the reaction of modified SiO2 with the lithium salt of the aryl derivatives to be immobilized (indenyllithium, cyclopentadienyllithium, fluorenyllithium, etc.). This step is generally achieved in THF at relatively low temperatures. Step 3 is the treatment of the resulting aryl-grafted silica gel with a solution of butyllithium in hexane (at room temperature) to form new aryllithium derivatives. Step 4 is the reaction of the latter system with zirconium, titanium (Soga et al., 1995a), or neodymium (Jin et al., 1995) halides to yields supported metallocenes. After each modification step, the silica is filtered and washed with large quantities of THF and finally evaporated to dryness under vacuum. These supported metallocenes can be used with either MAO or a common trialkylaluminum as the cocatalyst. A typical catalyst preparation according to this procedure, as well as the structure of the species formed, is summarized in Figure 2.

Figure 2. Preparation of supported metallocene through ligands attachment on SiO2 surface. Reprinted with permission from Soga (1994b). Copyright 1994 Huthig & Wepf.

Ind. Eng. Chem. Res., Vol. 36, No. 4, 1997 1227 Chart 1. Surface Species on Various Inorganic Supports (Reprinted with Permission from Finch et al. (1990). Copyright 1990 American Chemical Society)

Figure 3. Synthetic scheme of (IndMeSiO)nZrCl2. Reprinted with permission from Soga (1995). Copyright 1995 Huthig & Wepf.

This route was recently adapted by Nishida et al. (1995) to the preparation of polystyrene-supported metallocenes. The main preparative steps are identical, except that lithiated polystyrene is used as the starting material. A similar approach has been utilized by Soga et al. (1995b) to prepare polysiloxane-supported metallocene catalysts. It involves the three following steps: (a) synthesis of organosilanes with aryl substituents; (b) condensation between equivalent amounts of water and the above compounds to form polysiloxane precursors; and (c) metallocene anchoring on the precursors using an identical procedure to the one previously described. The corresponding synthetic pathway is summarized in Figure 3. In addition to the above procedures, it is worth mentioning the immobilization of titanocene on MgCl2 (Satyanarayana and Sivaram, 1993; Marathe et al., 1994; Sarma et al., 1994) using THF-soluble MgCl2‚2THF and Cp2TiCl2 complexes. The solid catalyst is obtained by coprecipitation of the two complexes in hexane. Finally, Janiak et al. (1993) have described the use of “polymeric MAO”, with a high surface area, as the support for metallocene catalysts. Polymeric MAO was produced as a three-dimensional lattice by reaction of MAO and 1,10-dodecanediol or 1,6-dodecanediol. Preliminary results show that zirconocene dichloride presents a higher activity when supported on “polymeric MAO” than on SiO2. 3. Nature of the Active Sites and Mechanism of Formation It is well-established that the adsorption of organometallic molecules on inorganic surfaces can drastically alter their reactivities and catalytic activities. Unfortunately, the structure and the chemistry of the resulting adsorbates are generally unknown. One major difficulty is that very few analytical probes can provide insight into the molecular level of such adsorbates. In addition, the possibility of forming various types of active sites of different structure and reactivity on solid surfaces must be taken into account. Nevertheless, many efforts have been made to elucidate the nature of the interactions between metallocenes and the supports and their effects on catalyst performance. The main information gathered on the matter is presented in this section. In earlier studies, Marks and co-workers, (He et al., 1985; Hedden and Marks, 1988; Finch et al., 1990), using an integrated chemical/spectroscopic approach, proposed a quite detailed picture of surface organometallic adsorbates. The adsorption of a series of organoactinides, Cp′AnR2 (Cp′ ) η5-(CH3)5C5; An ) Th, U; R ) alkyl), used as model adsorbates, was investigated on a range of supports (Al2O3, MgCl2, SiO2-Al2O3,

SiO2-MgO, MgO); the reactivities of the organoactinides toward olefins were studied as well. The 13C CPMAS NMR spectroscopic analysis of the surfaces suggests a relationship between the surface/adsorbate microstructure and the observed catalytic activity. Basically, three different CPMAS spectroscopic patterns are observed in the case of supported Cp′AnR2 complexes. For supports with strong Lewis acid character [dehydroxylated alumina (DA), MgCl2, dehydroxylated silica alumina (DSA)], a transfer of alkyl groups from the organoactinide to an acceptor site on the surface is observed (Chart 1; A), yielding a “cation-like” Th+-R species. Authors reported that the Cp′2Th+R species are highly reactive toward olefin hydrogenation and polymerization. The second type of CPMAS pattern corresponds to hydroxylated supports (partially dehydroxylated alumina (PDA), partially dehydroxylated silica (PDS), and MgO). No evidence for alkyl transfer to the surface is found. A “µ-oxo-like” structure is suggested for these adsorbates (Chart 1; B and C). The third type is observed for dehydroxylated supports of weak Lewis acid character possessing relatively weak metal-oxygen bonds on their surface [dehydroxylated silica (DS), dehydroxylated SiO2/MgO (DSM)]. Both a µ-oxo-like resonance and a surface transfer of alkyl are observed, suggesting a structure of type D (Chart 1). Significant catalytic activities are observed in systems exhibiting cation-like character (Cp′2Th+CH3), while activity is negligible in systems exhibiting only µ-oxolike (Cp′2Th(CH3)O) spectral features. Soga and co-workers have examined several supported metallocene systems prepared by direct impregnation of the support. Al2O3- and MgCl2-supported zirconocene (Et[IndH4]2ZrCl2, i-Pr(Flu)(Cp)ZrCl2, or Cp2ZrCl2) catalysts activated by alkylaluminum promote propylene polymerization with a fairly good activity, whereas zirconocenes supported on SiO2, combined with AlR3 cocatalyst, are almost inactive (Kaminaka and Soga, 1991, 1992; Soga and Kaminaka, 1992). These results are explained by the differences in support acidity: carriers exhibiting strong Lewis acidity lead to active catalysts. Taking into consideration the previous work of Marks, showing alkylation of MgCl2 by trialkylaluminum with the formation of a stable anion, the pathway presented in Scheme 1 for catalyst activation was proposed (Soga and Kaminaka, 1993). A similar mechanism has also been suggested by Satyanarayana and Sivaram (1993) for the formation of active sites in the case of Cp2TiCl2 supported on MgCl2.

1228 Ind. Eng. Chem. Res., Vol. 36, No. 4, 1997 Scheme 1. Profile of Catalyst Activation on MgCl2 or Al2O3 Supports (Reprinted with Permission from Soga and Kaminaka (1993). Copyright 1993, Huthig & Wepf)

Scheme 3. Formation Mechanism of Zirconocenium Species for MAO-Mediated Catalysts (Reprinted with Permission from Chen et al. (1995). Copyright 1995 John Wiley & Sons, Inc.)

Scheme 2. Formation Mechanism of (SiO-‚Zr+) Species (Reprinted with Permission from Chen et al. (1995). Copyright 1995 John Wiley & Sons, Inc.)

Although directly impregnated silica-supported systems are inactive in olefin polymerization when AlR3 is the cocatalyst, the use of MAO yields active polymerization catalysts (Soga et al., 1991; Kaminsky and Renner, 1993; Kaminsky, 1995a; Chen et al., 1995; Sacchi et al., 1995). By analogy with homogeneous metallocene/MAO systems, Kaminsky and Renner (1993), Chien and He (1991), and Chen et al. (1995) have suggested the formation, on silica supported catalysts, of ionic species of the type (SiO-‚Zr+); see Scheme 2. However, considering this mechanism, it is not clear why directly impregnated silica catalysts behave differently when combined with MAO and with AlR3 (Soga et al., 1991; Kaminaka and Soga, 1991, 1992). It can be speculated that the formation and the stabilization of Zr+ cations are more difficult in the case of supports with weak Lewis acid character. Consequently, cationic species can only be formed if the cocatalyst is acidic enough to remove the alkyl ligand. Recently, Chen et al. (1995) reported the preparation of SiO2/metallocene catalytic systems that can be activated with alkylaluminum. These catalysts were obtained by using the refined method 1. For MAO-mediated silica systems, in which silica is first treated with MAO before contact with the metallocene, Soga and Nakatani (1990) and Soga and Kaminaka (1992) proposed the following reaction path be-

Si O

Si OH + MAO

Si O

MAO + CH4

(1)

MAO + Cp2ZrX2

Si O (MAO)δ–(Cp2ZrX2)δ+

(2)

where X = CH3 or Cl

tween the MAO, the metallocene, and the hydroxyl groups of silica: MAO bonds chemically to the SiO2 surface by reacting with hydroxyl groups (eq 1); in the second stage, the metallocene reacts with MAO fixed on SiO2 to form the supported metallocene (eq 2). The latter can then be activated either by alkylaluminum or by MAO.

A more detailed picture has been proposed by Chien and He (1991) and Chen et al. (1995); see Scheme 3. These authors assume that metallocene ionic species are trapped and stabilized by multicoordinating “crown” aluminoxane complexes. Since the silica surface is essentially covered by MAO, it is postulated that the cationic zirconocene species floats over the solid surface, much like in solution. This results in a close similarity between this type of supported system and the homogeneous metallocene. These interpretations are, however, very simplified pictures. Several types of surface groups likely exist on the carrier surface, leading to several types of active sites, differing in electronic and steric connections to the support. In that respect, chemical and thermal treatment of the support may have a drastic influence on the nature of the carrier surface groups and, therefore, on the type of species formed upon contact with the metallocene. Using infrared spectroscopy, Ihm et al. (1994) observed the presence of different types of surface groups on commercial silica: single hydroxyl, hydrogen-bonded hydroxyl, paired hydroxyls, and adsorbed water. After thermal treatment (600 °C under nitrogen atmosphere), only single-hydroxyl groups remain. Thus, with appropriate treatment, it is possible to control the proportion of each type of hydroxyl group on the surface. Collins et al. (1992) have studied well-characterized carriers presenting different proportions of surface hydroxyl groups: hydroxylated, partially dehydroxylated, and fully dehydroxylated SiO2 and Al2O3 (100% OH-S, PDS, and DS and 100% OH-A, PDA, and DA). With silica supports, very low activities are observed for 100% OH-S or PDS. It was postulated that metallocene compounds react with surface hydroxyls of silica during the adsorption step, yielding inactive species and free ligands, Scheme 4. High catalytic activities observed with AlMe3-treated silica support this assumption. Pretreatment of silica by compounds such as SiCl2(CH3)2 (Soga et al., 1993) or MeLi (Ciardelli et al., 1994) was thus used to prevent the deactivation of zirconocene by reaction with silanol functionalities. At the present time, the interpretations presented by the different groups are often restricted to the analysis

Ind. Eng. Chem. Res., Vol. 36, No. 4, 1997 1229 Scheme 4. Reaction of Metallocene Compound with Surface Hydroxyl Groups (Reprinted with Permission from Soga et al. (1995a). Copyright 1995 Huthig & Wepf)

of their own results. A more general and profound interpretation would necessarily involve rationalization of the experimental data available. 4. Effect of Metallocene Heterogenization on Polymerization Activity and on Polymer Characteristics Metallocene/aluminoxane catalytic systems are effective for homo- and copolymerization of various vinyl monomers. However, up to now, major attention has been paid to the homopolymerizations of ethylene and propylene. 4.1. Ethylene Polymerization. Most PE grades used commercially have MW’s of 20 000 to 300 000, and depending upon the applications, the MWD can be either narrow, medium, or broad. To be applicable to large-volume PE production, metallocenes must yield polymers of similar MW’s and MWD’s. As a result of the drastic MW decrease with polymerization temperature, soluble metallocene systems are not suited for solution and high-pressure processes. In addition, to be used in slurry- or gas-phase processes, metallocenes should be supported on a solid carrier to provide adequate control of polymer morphology (Sinclair and Wilson, 1994). Published literature (see Table 2) shows the efforts already made to find a good way to support metallocenes and get high-catalytic-activity and highmolecular-weight polymers. This table also includes, when available, the performances of the corresponding homogeneous metallocenes. As can be seen, both nonstereorigid- and stereorigidsupported metallocenes have been used for ethylene polymerization. It should be noted that the aluminoxane/metallocene ratios used for supported metallocene systems are significantly lower (generally in the 50400 range) than those necessary in the case of homogeneous metallocenes. The need for a smaller amount of MAO in supported metallocene catalysts has been attributed to metallocene immobilization, which prevents deactivation by bimolecular processes, a very important deactivation route in the case of homogeneous metallocenes. The catalytic activities of supported systems are, however, usually lower than those observed for soluble ones. Besides, supported metallocenes lead in general to PE of broader MWD (2-5) than the corresponding homogeneous systems (1-2). The MW broadening likely results from the interactions between the metallocene and the support, which leads to the formation of active sites differing in electronic and steric character.

Kaminsky and Renner (1993) were among the first researchers, in the published literature, to produce PE of extremely high molecular weight (1 × 106 g/mol) with supported metallocenes. In similar conditions, the corresponding homogeneous systems only yield to molecular weights of about 2 × 105 g/mol. They immobilized Et[Ind]2ZrCl2 directly on silica using method 1b (see previous paragraphs) and activated the supported zirconocene with MAO. It was suggested that zirconocene immobilization on silica prevents deactivation by bimolecular processes and thus increases molecular weights. Silica is the most commonly used support for ethylene polymerization. Modification of the SiO2 surface has important effects both on polymerization activity and on polymer properties. Soga et al. (1993) prepared a silica gel modified with Cl2Si(CH3)2/NaHCO3 to support Cp2ZrCl2 using preparation methods 1a and 2. They observed that the polymerization activity increases remarkably (2-3 times) with the modified SiO2 and is strongly dependent on the nature of the alkylaluminum (AlEt2Cl < AlEt3 < Al(i-Bu)3 < AlMe3). The maximum activity is obtained when MAO is fixed to the modified silica gel (5550 kg of PE/(mol of Zr‚h)). Nevertheless, MAO-free catalysts composed of modified SiO2, Cp2ZrCl2, and Al(CH3)3 can also be activated by common trialkylaluminums (3490 kg of PE/(mol of Zr‚h)). It may be postulated, therefore, that MAO is not necessarily required for catalyst activation. Ihm et al. (1994) immobilized the metallocene compounds Cp2ZrCl2, Cp2TiCl2, and Cp2HfCl2 on modified SiO2 pretreated with small amounts of MAO, AlEt3, or (C2H5)MgCl. Ethylene polymerization was then carried out with these supported catalysts using MAO or a common alkylaluminum as cocatalysts. Among the various supported catalysts examined, Cp2ZrCl2 supported on SiO2 modified by MAO shows the highest activity, whereas titanocene-based systems show the lowest. This latter result was attributed to the bimolecular deactivation of titanocene by aluminum compounds. Likely, in relation to this, bimodal MWD’s are observed for titanocene supported on SiO2/MAO or on SiO2/AlEt3 but not for SiO2/(C2H5)MgCl. It was speculated that the interaction of titanocene and aluminum species (MAO and AlEt3) affects the molecular weight distribution. A comparison of ethylene polymerization performed on Cp2ZrCl2 supported on silica (refined method 1) and on silica pretreated with MAO (method 2) was reported recently by Sacchi et al. (1995). The modified SiO2/ MAO-supported systems exhibit rather high activities, although still lower than homogeneous systems. However, the polyethylene molecular weight obtained with these systems remains low and nearly identical to those produced by homogeneous metallocenes. On the contrary, directly impregnated SiO2-supported systems present low activity but yield to polymers with higher molecular weights. Similar behavior was observed by Chen et al. (1995) when comparing the performances in olefin polymerization (ethylene and propylene) of stereorigid metallocenes, supported directly on SiO2 or on MAO-modified SiO2. Recently, Lee et al. (1995) reacted a partially hydrated silica (HSiO2) with trimethylaluminum (TMA) to produce aluminoxanes in situ. The resulting HSiO2/TMA/ Cp2ZrCl2 systems are effective for ethylene polymerization even when a common alkylaluminum is used as

1230 Ind. Eng. Chem. Res., Vol. 36, No. 4, 1997 Table 2. Polymerization of Ethylene Using Supported Metallocene Catalystsg

metallocene Cp2ZrCl2 Cp2ZrCl2 Cp2ZrCl2 Cp2ZrCl2 Cp2ZrCl2 Cp2ZrCl2 Cp2ZrCl2 Cp2ZrCl2 Cp2ZrCl2 Et(Ind)2ZrCl2 Et(Ind)2ZrCl2 Cp2ZrCl2 Cp2ZrCl2 Cp2ZrCl2 Cp2HfCl2 Cp2HfCl2 Cp2HfCl2 Cp2TiCl2 Cp2TiCl2 Cp2TiCl2 Cp2TiCl2 Cp2TiCl2 Cp2TiCl2 Cp2TiCl2 Cp2TiCl2 Cp2ZrCl2 Cp2ZrCl2 Cp2ZrCl2 Cp2ZrCl2 Cp2ZrMe2 Cp2ZrMe2 Cp2ZrCl2 Cp2ZrCl2 Cp2TiCl2 Cp2TiCl2 Et(Ind)2ZrCl2

support SiO2/MAO SiO2/Cl2Si(CH3)2/MAO SiO2/Cl2Si(CH3)2/MAO SiO2/Cl2Si(CH3) none none SiO2/MAO SiO2 SiO2/MAO SiO2/MAO SiO2 none SiO2/MAO SiO2/MAO none SiO2/MAO SiO2/MAO none SiO2/MAO SiO2/MAO none none MgCl2 MgCl2 MgCl2 none HY HY HY-AlMe3 HY**-AlMe3 HY**-AlMe3 none NaY-MAO none NaY-MAO SiO2

[men]2Sil[ind]2ZrCl2 none [men]2Sil[ind]2ZrCl2 [men]2Sil[ind]2ZrCl2 [men]2Sil[ind]2ZrCl2 [men]2Sil[ind]2ZrCl2 Et(Ind)2ZrCl2 Cp2ZrCl2 Cp2ZrCl2 Cp2ZrCl2 Cp2ZrCl2 Cp2ZrCl2 Cp2ZrCl2 Cp2ZrCl2 Cp2ZrCl2 Cp2ZrCl2 (CH3)2Si(Ind)2ZrCl2 (Ind)2ZrCl2 (Flu)2ZrCl2 MeSi(Ind)2ZrCl2 Si(Ind)2NdMe Si(Ind)2NdMe Si(Ind)2NdMe MeSi(Ind)NdMe2 Cp2ZrCl2 Cp2ZrCl2 Cp2ZrCl2 Cp2ZrCl2 Cp2ZrCl2 (MeCp)2ZrCl2 (n-BuCp)2ZrCl2 Ind2ZrCl2

none SiO2/MAO SiO2 SiO2 SiO2 SiO2 none R-CD R-CD R-CD/PMAO R-CD/PMAO R-CD/TMA SiO2/PMAO SiO2/TMA SiO2 none (MeSiO)n (MeSiO)n PSLi SiO2 SiO2 SiO2 SiO2 SiO2/TMA SiO2/MMAO H(16)SiO2/TMA H(45)SiO2/TMA H(16)SiO2/TEA H(16)SiO2/TMA H(16)SiO2/TMA H(16)SiO2/TMA

cocatalyst Al(i-Bu)3 Al(i-Bu)3 AlMe3 AlMe3 MAO MAO MAO MAO Al(i-Bu)3 MAO MAO MAO MAO Al(i-Bu)3 MAO MAO Al(i-Bu)3 MAO MAO Al(i-Bu)3 MAO Al(i-Bu)3 MAO MAO Al(i-Bu)3 MAO AlEt3 MAO MAO AlMe3 MAO MAO MAO MAO MAO noned

solv toluene, 40 °C, 1 h toluene, 40 °C, 1 h toluene, 40 °C, 1 h toluene, 40 °C, 1 h toluene, 50 °C, 1 h toluene, 50 °C, 1 h toluene, 50 °C, 1 h toluene, 50 °C, 1 h toluene, 50 °C, 1 h toluene, 50 °C, 1 h toluene, 50 °C, 1 h toluene, 60 °C, 1/2 h toluene, 60 °C, 1/2 h toluene, 60 °C, 1/2 h toluene, 60 °C, 1/2 h toluene, 60 °C, 1/2 h toluene, 60 °C, 1/2 h toluene, 60 °C, 1/2 h toluene, 60 °C, 1/2 h toluene, 60 °C, 1/2 h xylene, 40 °C, 1 h xylene, 40 °C, 1 h xylene, 40 °C, 1 h xylene, 40 °C, 1 h xylene, 40 °C, 1 h toluene, 25 °C toluene, 25 °C toluene, 25 °C toluene, 25 °C toluene, 25 °C toluene, 25 °C toluene, 50 °C, 2 h toluene, 70 °C, 1 h toluene, 50 °C, 12 h toluene, 50 °C, 1 h toluene, 50 °C, 1 h

MAO

Al/Mt

200 500 200 200 200 130 500 500

1 000 50 50 500 50 1 500 12 1 500 1 500 100 3 000 17 500 560 17 500 840 39d

heptane, 25 °C, 2 500 15 min Al(i-Bu)3/PB 30s 400 heptane, 25 °C Al(i-Bu)3/PB 2 min 400 50 Al(i-Bu)3/PB 1 h Al(i-Bu)3 1 h toluene, 50 °C 50 TIBA 1h 50 TIBA 1h 50 PMAO toluene, 40 °C, 2 h 10 000 TMA toluene, 40 °C, 2 h 1 000 MMAO toluene, 40 °C, 2 h 1 000 TMA toluene, 40 °C, 2 h 1 000 MMAO toluene, 40 °C, 2 h 1 000 TMA toluene, 40 °C, 2 h 1 000 TMA toluene, 40 °C, 2 h 1 000 MMAO toluene, 40 °C, 2 h 1 000 TMA toluene, 40 °C, 2 h 1 000 MAO toluene, 40 °C, 1 h 4 000 MAO toluene, 40 °C, 1 h 10 000 MAO toluene, 40 °C, 1 h 10 000 MAO toluene, 75 °C, 0.3 h Al(i-Bu)3 toluene, 40 °C, 6 h 300 MAO toluene, 40 °C, 6 h 300 BuMgEt toluene, 40 °C, 6 h 49 BuLi toluene, 40 °C, 6 h 46 TMA 70 °C, 1 h TMA 70 °C, 1 h TMA 70 °C, 1 h TMA 70 °C, 1 h TMA 70 °C, 1 h TMA 70 °C, 1 h TMA 70 °C, 1 h TMA 70 °C, 1 h

}

}

activity, kg PE/ (mol Mt‚h) 10-3Mw 1 550 3 750 5 550 3 490 2 095 660 172 11 420 329 143 682 515 212 479 136 152 424 121 121 77 0 74 141 2.2 372.5 3 195 2 800 30 591 12 500 3 426 347 77 121

263a 266a 269a 439a 190a 177 >500 52b 49b 103b 56b 52b 108b 73b 50b,c 54b,c

mp, °C

136 134 133 131 139

78

60b 84b 307b 1 090e

133.4 139.8 134.4 137.2 137

20.5f 3 060f 57.2f 0.27f 0.07f 0.83f 0.15f 9 213 55 775 848 958 647 885 867 tr 19 300 2 228 4 507 3 192 7.72 4.05 91.3 3.3 38 709 895 581 11 1 007 2 400 400

58e 161e 1030e 1560e 1090e 1240e 30 105 237 160

68 428 29 2 940 1 460 99 57

131 135 135 135 135 135 129.2 129.1 128.5 132.9 136 135.8 131.7 130.5 138.4 138.4 139.2 136.4 136 134.9

194 258

134 133 138

46b 48b 142b

134 132 131

ref Soga et al. (1993) Soga et al. (1993) Soga et al. (1993) Soga et al. (1993) Sacchi et al.(1995) Sacchi et al. (1995) Sacchi et al. (1995) Sacchi et al. (1995) Sacchi et al. (1995) Sacchi et al. (1995) Sacchi et al. (1995) Ihm et al. (1994) Ihm et al. (1994) Ihm et al. (1994) Ihm et al. (1994) Ihm et al. (1994) Ihm et al. (1994) Ihm et al. (1994) Ihm et al. (1994) Ihm et al. (1994) Sarma et al. (1994) Sarma et al. (1994) Sarma et al. (1994) Sarma et al. (1994) Sarma et al. (1994) Ciardelli et al. (1994) Ciardelli et al. (1994) Ciardelli et al. (1994) Ciardelli et al. (1994) Ciardelli et al. (1994) Woo et al. (1995) Woo et al. (1995) Woo et al. (1995) Woo et al. (1995) Kaminsky and Renner (1993) Chen et al. (1995) Chen et al. (1995) Chen et al. (1995) Chen et al. (1995) Chen et al. (1995) Chen et al. (1995) Chen et al. (1995) Lee and Yoon (1995) Lee and Yoon (1995) Lee and Yoon (1995) Lee and Yoon (1995) Lee and Yoon (1995) Lee and Yoon (1995) Lee and Yoon (1995) Lee and Yoon (1995) Lee and Yoon (1995) Soga et al. (1995b) Soga et al. (1995b) Soga et al. (1995b) Nishida et al. (1995) Jin et al. (1995) Jin et al. (1995) Jin et al. (1995) Jin et al. (1995) Lee et al. (1995) Lee et al. (1995) Lee et al. (1995) Lee et al. (1995) Lee et al. (1995) Lee et al. (1995) Lee et al. (1995) Lee et al. (1995)

a Determined by SEC. b M . c Bimodal MWD. d Immobilization of the metallocene on the support followed by treatment with MAO, n used without adding new MAO. e Viscosimetric molecular weight. f In g of PE/(mol of Zr‚[C2H4]‚h) × (10-6). g R ) alkyl, Me ) methyl, i-Pr ) isopropyl, i-Bu ) isobutyl, Cp ) cyclopentadienyl, Ind ) indenyl, Flu ) fluorenyl, [men]2Sil[ind]2ZrCl2 ) (1′(S),2′(R),5′(S)dimenthoxy]silylene-bis[η5-1(R,R)-(+)-indenyl]dichlorozirconium, Al(i-Bu)3/PB ) Al(i-Bu)3/Ph3CB(C6F5)4, R-CD ) R-cyclodextrin PMAO ) methylaluminoxane commercial grade from Tosoh-Akzo (Al 7.56 wt %), MMAO ) methylaluminoxane commercial grade from Akzo (Al 12.5 wt %), (MeSiO)n ) polysiloxane, PsLi ) lithiated polystyrene, H(16)SiO2/TMA ) hydrated silica (16 wt % of water) treated with trimethylaluminum, H(45)SiO2/TMA ) hydrated silica (45 wt % of water) treated with trimethylaluminum, HY ) zeolite HY, HY** ) exhaustive dealumination with acetylacetone/ethanol, NaY ) zeolite NaY.

Ind. Eng. Chem. Res., Vol. 36, No. 4, 1997 1231

the cocatalyst. The catalytic activity was found to depend on the H2O content of silica, on the H2O/TMA ratio, and on the nature of the metallocene and of the cocatalyst. These catalytic systems have been compared to MAO/SiO2- and TMA/SiO2-supported systems. TMAtreated silica shows very low polymerization activity, while MMAO (modified MAO) treated silica gives high productivity. In the case of HSiO2-supported catalysts, those obtained from H(16)SiO2 (16 wt % water) exhibit higher activity than H(45)SiO2 (45 wt % water) supported ones. The difference was explained by a fast and uncontrolled reaction between TMA and water in the case of H(45)SiO2. The effect of cyclopentadienyl (Cp) substituent in supported zirconocenes was also investigated. Catalysts with monoalkyl-substituted Cp (n-BuCp, MeCp) show higher activities than those with cyclopentadienyl or indenyl ligands. It was suggested that the alkyl-Cp substituents increase the metal electron density, thus favoring ethylene coordination (Lee et al., 1995; Ewen, 1986). Determination of the pore volume and the surface area of the H(16)SiO2-TMA catalyst precursor suggests that TMA reacts in the pores with water so that the pores are filled with the produced MAO. This reaction might cause cracks in the pores and even break them apart. Besides, CPMAS 13C NMR data suggest that the aluminum compounds formed on the H(16)SiO2-TMA surface are relatively similar to those observed in SiO2/MAO systems. Nevertheless, the precise structure of the aluminoxane formed in situ still remains of considerable controversy. The efficiencies in the ethylene polymerization of other catalyst carriers such as MgCl2, zeolites, polysiloxanes, polystyrene, and cyclodextrin have also been examined. Satyanarayana and Sivaram (1993) have prepared MgCl2-supported Cp2TiCl2 catalysts exhibiting significant activity for ethylene polymerization after activation by Al(i-Bu)3. Those supported catalysts show steadystate kinetics with no loss of activity up to 1 h, when operating at low Al/Ti ratios (1500

4.7

128

Et[IndH4]ZrCl2

SiO2/MAO

Al(iPr)3

450

14.7

137

i-Pr(Flu)(Cp)ZrCl2

none

MAO

758

39.3

123

77 (rrrr%)

i-Pr(Flu)(Cp)ZrCl2

Al2O3

AlMe3

toluene, 121 40 °C, 1 h toluene, 610 40 °C, 1 h toluene, 121 40 °C, 1 h toluene, 610 40 °C, 1 h toluene, 61 40 °C, 1 h toluene, 365 40 °C, 1 h toluene, 3250 40 °C, 1 h 18 h 110

9.3

4.6

138

86 (rrrr%)

i-Pr(Flu)(Cp)ZrCl2

MgCl2

AlMe3

18 h

480

8.4

10.7

134

81 (rrrr%)

i-Pr(Flu)(Cp)ZrCl2

MgF2

AlMe3

18 h

240

3.4

i-Pr(Flu)(Cp)ZrCl2

SiO2/MAO

Al(i-Pr)3

1h

270

141

45.2

133

83 (rrrr%)

Et(Ind)2ZrCl2

none

MAO

20b

122

Et(Ind)2ZrCl2

SiO2

MAO

11

520b

159

94.6c

Et(Ind)2ZrCl2

SiO2

nonea

9.6

800b

160

93.5c

Et[Ind]2ZrCl2

none

MAO

1450

18

142

89.9

Soga and Kaminaka (1993) Soga and Kaminaka (1993) Soga and Kaminaka (1993) Soga and Kaminaka (1993) Soga and Kaminaka (1993) Soga and Kaminaka (1993) Soga and Kaminaka (1993) Soga and Kaminaka (1992, 1993) Soga and Kaminaka (1992, 1993) Soga and Kaminaka (1992, 1993) Soga and Kaminaka (1992, 1993) Soga and Kaminaka (1992, 1993) Soga and Kaminaka (1992, 1993) Soga and Kaminaka (1993) Soga and Kaminaka (1993) Soga and Kaminaka (1993) Soga and Kaminaka 1993) Soga and Kaminaka (1993) Kaminsky and Renner (1993) Kaminsky and Renner (1993) Kaminsky and Renner (1993) Collins et al. (1992)

Et[Ind]2ZrCl2

PDA-AlMe3 MAO

185

19.5

143

89.7

Collins et al. (1992)

Et[Ind]2ZrCl2

PDA

MAO

Et[Ind]2ZrCl2

DA

MAO

Et[Ind]2ZrCl2

100% OHA

MAO

Et[Ind]2ZrCl2

PDS-AlMe3 MAO

Et[IndH4]ZrCl2

none

Et[IndH4]ZrCl2

PDS-AlMe3 MAO

Et[IndH4]ZrCl2

DS

MAO

Et[IndH4]ZrCl2

PDS

MAO

Et[IndH4]ZrCl2

100% OH-S

MAO

Et(Ind)2ZrCl2

none

MAO

Et(Ind)2ZrCl2

SiO2/MAO

MAO

Et(Ind)2ZrCl2

SiO2/MAO

Al(i-Bu)3

Et(Ind)2ZrCl2

SiO2

MAO

(Ind)2ZrCl2

none

MAO

(Ind)2ZrCl2

SiO2/MAO

MAO

(Ind)2ZrCl2

SiO2

MAO

Cp2ZrCl2

SiO2

MAO

rac-(CH3)2Si(Cp-n-Rn)2ZrCl2 none

MAO

rac-(CH3)2Si(Cp-n-Rn)2ZrCl2 SiO2/MAO

Al(i-Bu)3

MAO

71

ref

toluene, 3000 2070 40°C, 1 h 18 h 225-677 9-14

toluene, 150 50 °C, 2 h toluene, 37a 50 °C, 2 h toluene, 30 °C, 1.5 h toluene, 30 °C, 1.5 h toluene, 30 °C, 1.5 h toluene, 30 °C, 1.5 h toluene, 30 °C, 1.5 h toluene, 30 °C, 1.5 h toluene, 30 °C, 1.5 h toluene, 30 °C, 1.5 h toluene, 30 °C, 1.5 h toluene, 30 °C, 1.5 h toluene, 30 °C, 1.5 h toluene, 300 50 °C, 1 h toluene, 300 50 °C, 1 h toluene, 110 50 °C, 1 h toluene, 300 50 °C, 1 h toluene, 300 50 °C, 1 h toluene, 300 50 °C, 1 h toluene, 300 50 °C, 1 h toluene, 300 50 °C, 1 h toluene, 3000 30 °C, 2 h toluene, 312 30 °C, 2 h

111

[mmmm] or [rrrr], %

1.7-3.2 131-137 90

90

85

135


15


nil


689

19.0

143

89.0


1800

6.0

136

90.4


330

6.8

139

91.8


36


10


nil


221

9.1d

85c

Sacchi et al. (1995)

131

11.3d

85c


33

16.5d

85c


6

166d

71c


154

wax

18c


95

wax

20c


4

215d

71c


tr


7500

93.5d

156

95.2

600

190.1d

156.1

95.5

Soga and Kaminaka (1994b) Soga and Kaminaka (1994)

Ind. Eng. Chem. Res., Vol. 36, No. 4, 1997 1233 Table 3 (Continued)

metallocene

support

cocatalyst

polym cond

activity, kg PP/ [mmmm] Al/Mt (mol Mt‚h) 10-3Mn mp, °C or [rrrr], %

ref

Me2C[(Cp)(Flu)]ZrCl2 SiO2

MAO

Cp2ZrCl2

none

MAO

Cp2ZrCl2

Al2O3

AlMe3

heptane, 25 °C, 20 min 2500 heptane, 25 °C, 8 min 200 58.2e heptane, 25 °C, 15 min 40 1.1e toluene, 5900 50 °C toluene, 180 50 °C toluene, 1000 132 40 °C, 1 h toluene, 40 °C, 18 h 2.6

Cp2ZrCl2

MgCl2

AlMe3

toluene, 40 °C, 18 h

9.6

Cp2ZrCl2

MgF2

AlMe3


0.8

Cp2ZrCl2

SiO2/MAO Al(i-Bu)3


99

1.8

CpTiCl3

none

MAO

0.6-2.4

n.d

n.d.

atactic

CpTiCl3

SiO2

MAO

10

4

n.d.

atactic

Soga et al. (1994c)

CpTiCl3

MgCl2

MAO

134

n.d.

atactic

Soga et al. (1994c)

CpTiCl3

MgCl2

TIBA

244

n.d.

atactic

Soga et al. (1994c)

CpTiCl3

Al2O3

MAO

CpTiCl3

Al2O3

TIBA

toluene, 40 °C, 2 h toluene, 40 °C, 2 h toluene, 40 °C, 2 h toluene, 40 °C, 2 h toluene, 40 °C, 2 h toluene, 40 °C, 2 h

Chen et al. (1995) Chen et al. (1995) Chen et al. (1995) Kaminsky and Renner (1993) Kaminsky and Renner (1993) Kaminaka and Soga (1992) Soga and Kaminaka (1993) Soga and Kaminaka (1993) Soga and Kaminaka (1993) Soga and Kaminaka (1993) Soga et al. (1994c)

[men]2Sil[Ind]2ZrCl2 [men]2Sil[Ind]2ZrCl2 [men]2Sil[Ind]2ZrCl2 Me2C[(Cp)(Flu)]ZrCl2

none none SiO2/MAO none

MAO Al(i-Bu)3/PB Al(i-Bu)3/PB MAO

2.1e

177d 211d 47

150 151 131

6

350

158

90

0.33f

atactic

0.39f

atactic

0.37f

atactic atactic atactic

11

20

n.d.

atactic

Soga et al. (1994c)

4.9

32

n.d.

atactic

Soga et al. (1994c)

a Immobilization of metallocene on the support followed by treatment with MAO, used without adding new MAO. b Viscosimetric molecular weight. c [mm] triads. d Mw. e In g of PE/(mol of Zr‚[C2H4]‚h) × 10-6. f Estimated from 13C NMR spectroscopy. g R ) alkyl, Me ) methyl, i-Pr ) isopropyl, i-Bu ) isobutyl Cp ) cyclopentadienyl, Ind ) indenyl, Flu ) fluorenyl, Al(i-Bu)3/PB ) Al(i-Bu)3/Ph3CB(C6F5)4, rac-(CH3)2Si(Cp-n-Rn)2ZrCl2 ) rac-(CH3)2Si(2,4-(CH3)2C5H3)(3′,5′-(CH3)2C5H3)ZrCl2, 100% OH-S and PDS, DS ) hydroxylated, partially dehydroxylated and dehydroxylated SiO2, 100% OH-A, PDA, and DA ) hydroxylated, partially dehydroxylated and dehydroxylated Al2O3.

% crystallinity, Xc ) 70%). The properties of the polypropylenes obtained with homogeneous chiral ansametallocenes differ significantly in several aspects, making them unsuitable for industrial applications. They generally present low and broad Tm and appreciable Xc ≈ 60% (Huang and Rempel, 1995). The low melting temperature observed (20-30 °C lower than conventional isotactic PP) results both from a low degree of isotacticity (ranging from 70 to 95%) and imperfect regiospecificity. Almost all the polypropylenes produced with homogeneous metallocenes show, in addition to the normal 1-2 addition, some misinsertions yielding to the formation of 1-3 or 2-1 linkages (Hungenberg et al., 1994). Besides, soluble metallocenes produce isotactic polypropylenes with much narrower MWD’s (1.8-2.2) than heterogeneous Ziegler-Natta catalysts (5-8). The main attempts to polymerize propylene with supported metallocene systems in order to improve the properties of polypropylene are listed in Table 3. Kaminaka and Soga (1991, 1992) and Soga and Kaminaka (1992, 1993) were the first to systematically screen the capacities of several kinds of heterogenized zirconocene catalysts for propylene polymerization. Kaminsky-Sinn-type catalysts of different stereospecificity, Et[IndH4]2ZrCl2, i-Pr(Flu)(Cp)ZrCl2, and Cp2ZrCl2, were supported on Al2O3, SiO2, MgCl2, MgF2, CaF2, and AlF3 by impregnation method 1a. Common aluminum alkyls were used in place of MAO as cocatalysts. When Al2O3, MgCl2, MgF2, CaF2, and AlF3 are used as carriers, the resulting supported metallocene catalysts can be easily activated by common trialkylaluminums, whereas SiO2-supported catalysts did not show any activity for propylene polymerization in these conditions.

Isotactic polypropylene is obtained when Et[IndH4]2ZrCl2 is supported either on Al2O3 or on MgCl2. These systems, activated by AlR3 (R ) Me or Et), show activities up to 20% of that of the homogeneous Et[IndH4]2ZrCl2/MAO catalyst. Polymerization activities increase markedly at first with the Al/Zr mole ratio; then a gradual activity decrease is observed with a further increase of Al/Zr proportion. Al2O3-Et[IndH4]2ZrCl2/AlR3 systems yield narrow MWD’s (2), whereas the analogous MgCl2-supported metallocene gave broader MWD’s (4-5). The polypropylene produced with these supported metallocenes shows higher melting points (130-140 °C) than those observed with the corresponding conventional Kaminsky-Sinn catalysts (Soga and Kaminaka, 1993). i-Pr(Flu)(Cp)ZrCl2 and Cp2ZrCl2 supported on Al2O3 or MgCl2 activated with AlR3 gave respectively highly syndiotatic PP and atactic PP (Kaminaka and Soga, 1992). The polymers produced with the syndiospecific heterogeneous systems show higher Tm (134-138 °C) and higher [rrrr] pentad fractions (81-86%) than those produced with the homogeneous system (Tm ) 123 °C and [rrrr] pentad fraction 77%). Attempts to support these metallocene on SiO2 yielded inactive systems. However, highly active SiO2-supported metallocenes can be obtained, even using common alkylaluminums as cocatalysts, provided that silica is pretreated with a small amount of MAO (MAO-mediated systems, method 2). Soga and Kaminaka (1992, 1993) have shown that Et[IndH4]2ZrCl2-(SiO2/MAO) associated with AlR3 as cocatalyst induces the isotactic polymerization of propylene. Catalytic activity is dependent upon the cocatalyst used and markedly increases in the order AlEt3 < AlMe3 < Al(i-Bu)3. By changing the sequence of


addition of MAO and zirconocene on silica (i.e., SiO2 is first treated by zirconocene and then by MAO), the resulting supported catalyst associated with alkylaluminum shows hardly any polymerization activity. It was shown that in these conditions, the majority of the zirconium compound, physically adsorbed on the SiO2 surface, was removed from the support by MAO, into the liquid toluene phase. Soga and Kaminaka (1994b) have shown that it is possible to improve to a great extent the stability of the catalysts and the morphology of polymer particles by using supported metallocenes. They prepared a MAOmodified silica to support rac-(CH3)2Si(2,4-(CH3)2C5H3)(3’,5’-(CH3)2C5H3)ZrCl2 (A) and compared this system with the corresponding homogeneous metallocene in propylene polymerization. The use of a support markedly improves the molecular weight and the bulk density of isotactic PP. In addition, the size distribution of polymer particles can be easily controlled by conventional methods applied to Ziegler-Natta catalysts (prepolymerization). The lifetime of the metallocene-active species formed on the SiO2 surface is also significantly enhanced. Isotactic polypropylene was obtained in relatively high productivity by Collins et al. (1992), using partially hydroxylated SiO2 and Al2O3 pretreated with TMA as support for Et[Ind]2ZrCl2 and Et[IndH4]2ZrCl2. The activities over such systems activated by MAO remain lower than those obtained with the corresponding homogeneous catalysts, but the Al/Zr ratio necessary for activation is significantly lower. Besides, polymer properties such as stereoregularity, MWD, and degree of crystallinity are not much affected. The authors have noticed that the metallocene compounds are partially decomposed during the supporting process, especially when AlMe3-free SiO2 is used as the carrier (see Scheme 4). Supported catalysts for propylene polymerization were also prepared with monocyclopentadienyltitanium derivatives (RCp)TiCl3 (R ) H, CH3) attached on silica (Park et al., 1992; Soga et al., 1994c). In the presence of a mixture of trialkylaluminum and Ph3C+B(C6F5)4-, high-molecular-weight (Mn ≈ 106, at 40 °C) atactic PP with frequent chemical inversions (head-head and tailtail) is obtained. Random copolymers of ethylene and propylene with structures very similar to that obtained with homogeneous vanadium catalysts may also be prepared with these supported titanocene systems. The above-mentioned catalysts present several interesting advantages but are not very efficient for stereoregularity improvement. This is reflected by the low PP melting temperature (135-145 °C) observed in comparison to the values obtained with conventional supported Ziegler-Natta systems (≈160 °C). Kaminsky and Renner (1993) succeeded in preparing highly isotactic PP with Mw ) (6-8) × 105, [mm] ) 9396%, and Tm ) 160-161 °C using a SiO2-supported Et[Ind]2ZrCl2 prepared according to refined method 1. Catalyst activity is, however, noticeably low, although it increases when arising the temperature from 0 to 75 °C. The molecular weights and the melting temperatures of PP also increase with the temperature in contrast to homogeneous catalysts. Improvement of PP properties by supporting metallocene in this way is explained by the direct interaction between the support and the metallocene (see Scheme 2): immobilization of the zirconocene on silica prevents deactivation by bi-

molecular processes and favors regio- and stereospecificity (Kaminsky and Renner, 1993; Kaminsky, 1995a). Other highly isospecific supported metallocenes were prepared using refined method 1 (Chen et al., 1995; Sacchi et al., 1995). Sacchi et al. produced a prevailing isospecific polymer ([mm] ) 71% and Mw ) 2 × 105) using the aspecific [Ind]2ZrCl2 supported on SiO2, while the homogeneous zirconocene or the zirconocene supported on MAO-modified silica only gave atactic oligomers. This fact suggests that isospecific centers can be formed by anchoring metallocenes to silica, independently of their initial stereochemical structure. This is in agreement with data reported by Kaminsky (1995a), for a SiO2-supported syndiospecific metallocene, Me2C[(Cp)Flu)]ZrCl2. By using the refined method 1, to support this metallocene compound, this syndiospecific working catalyst is changed into an isospecific one (PP isotactic pentads ≈ 90%). The exact structure of the metallocene after adsorption on the silica surface is still unclear. Based on the analysis of the chemical composition of the supported metallocene system, Sacchi and co-workers (1995) proposed that Zr-Cl bonds are involved in the reaction between the metallocene and SiO2. Another approach to obtain highly isospecific catalysts for propylene polymerization was developed by Soga and co-workers (Soga, 1994a,b, 1995; Soga et al., 1994a,b, 1995a,b). It consists of the synthesis of a series of metallocenes with aromatic ligands chemically bound to the solid surface (preparation method 3). These catalytic systems lead to great improvements (see Table 4) of PP isotacticities and molecular weights when compared to analogous homogeneous systems. The proposed structures of some rigidly immobilized metallocenes are presented in Chart 2. Soga et al. (1994b) have compared the isospecificities of catalysts prepared by different routes and concluded that preparative route 3 is the best for improving both molecular weights and isotacticities of PP. However, it must be taken into consideration that the immobilization of ligands on SiO2, followed by the addition of zirconium halide, may lead to catalysts containing a mixture of meso and racemic metallocene isomers, able to produce respectively atactic and isotactic PP. Therefore, polypropylenes obtained with these systems were fractioned, and the results presented in Table 4 concern only the isotactic fractions. In some cases, isotactic PPs produced with these supported catalysts display two melting temperatures, suggesting that two kinds of isospecific active sites are present. Soga (1994b) proposed that the zirconocene supported on SiO2 calcined at the lowest temperatures (200 and 400 °C) are more rigidly immobilized on the SiO2 surface, thus yielding isotactic PP with higher stereoregularity, whereas the zirconocene supported on SiO2 calcined at 900 °C, due to a lesser amount of dual silanol groups, is more loosely fixed on the SiO2 surface (Chart 3). These two metallocene species, A and B, might be responsible for the production of PPs with a higher and lower melting temperature, respectively. Very interesting results were found with Cl2Zr(Ind)2Si-SiO2 and Cl2Zr(Ind)2Et-SiO2 catalysts prepared using method 3. These systems show a very similar isospecific character for propylene polymerization, whereas analogous homogeneous metallocenes present increasing stereoregulating order: Et[Ind]2ZrCl2 < Me2Si[Ind]2ZrCl2. In addition, PP obtained with the Cl2Zr(Flu)(Cp)Si-SiO2 catalyst prepared by route 3 show highly isotactic triad content and single Tm. The

Ind. Eng. Chem. Res., Vol. 36, No. 4, 1997 1235 Table 4. Polymerization of Propylene Using Rigidly Immobilized Zirconocenesa

metallocene

support

cocatalyst

polym cond

Me2Si(Ind)2ZrCl2 Si(Ind)2ZrCl2f Si (Ind)2 ZrCl2f Si (Ind)2 ZrCl2f Et[IndH4]2ZrCl2 Et(Ind)2ZrCl2f Et(Ind)2ZrCl2f Et(Ind)2ZrCl2f i-Pr(Flu)(Cp)ZrCl2 (Flu)(Cp)SiZrCl2 (Flu)2SiZrCl2f

none SiO2 SiO2 SiO2 none SiO2 SiO2 SiO2 none SiO2 SiO2 SiO2 SiO2 SiO2 PS PS PS Alk (MeSiO)n (MeSiO)n

MAO MAOb MAOc Al(i-Bu)3 MAO MAO Al(i-Bu)3 AlEt3 MAO MAO MAO Al(i-Bu)3 MAO Al(i-Bu)3 MAO MAO MAO MAO MAO

toluene, 40 °C, 1 h 20 h 20 h 20 h toluene, 40 °C, h 20 h 20 h 20 h toluene, 40 °C, 1 h 20 h 20 h 20 h 20 h 20 h toluene, 40 °C, 6 h toluene, 40 °C, 6 h toluene, 40 °C, 6 h toluene, 40 °C, 24 h toluene, 40 °C, 24 h

(MeCp)2Si ZrCl2 Si(Ind)2ZrCl2f MeSi(Ind)2ZrCl2f MeSi(Ind)2ZrCl2f (Ind)2ZrCl2 (Flu)2ZrCl2

activity, mp, °C II,a [mmmm] kg PP/ (mol Mt‚h) 10-3Mw Tm1 Tm2 % or [rrrr], % 74 0.3 0.27 0.2 2070 0.47d 0.40d 0.21d 758 0.26 0.51d 0.45d 0.38d 0.60d 497 150 72 2395/24 85/24

30 340 720 3

142 157 153 154 111 150

485 39 270 330

153 123 160 160 164

270 23 27 27 38 105

160 139 138 137 145 154

32 83.3 163 68 159 68 94 158 80 98 71 160 46 93 158 55 97.1 161 68 77 (rrrr%) 95 93 40 96 54 60 91

94.4 86.7

ref Soga (1994b); Soga et al. (1994b) Soga (1994b); Soga et al. (1994b) Soga (1994b); Soga et al. (1994b) Soga (1994b); Soga et al. (1994b) Soga (1994b); Soga et al. (1994b) Soga (1994b); Soga et al. (1994b) Soga (1994b); Soga et al. (1994b) Soga (1994b); Soga et al. (1994b) Soga et al. (1994b) Soga et al. (1994b) Soga et al. (1994b) Soga et al. (1994b) Soga et al. (1994b) Soga et al. (1994b) Nishida et al. (1995) Nishida et al. (1995) Nishida et al. (1995) Soga et al. (1995b) Soga et al. (1995b)

a Heptane insoluble part. b 10 mmol. c 1 mmol. d Yield (in g) obtained with 200 mg of catalyst, over 20 h; the content of Zr on the supported catalyst is not referred. e R ) alkyl, Me ) methyl, i-Pr ) isopropyl, i-Bu ) isobutyl, Cp ) cyclopentadienyl, Ind ) indenyl, Flu ) fluorenyl, (MeSiO)n ) polysiloxane, PS ) polystyrene. PSAlk ) alkylated polystyrene. f Corresponding structures represented on Chart 2.

Chart 2. Proposed Structures for Rigidly Immobilized Zirconocenesa (Reprinted with permission from Soga et al. (1995a,b) and Soga (1995). Copyright 1995 Huthig & Wepf)

a A, Si(Ind) ZrCl -SiO ; B, Et(Ind) ZrCl -SiO ; C, Si(Flu) ZrCl 2 2 2 2 2 2 2 2 SiO2; D, Si(Ind)2ZrCl2-PS; E, MeSi(Ind)2ZrCl2-PS; F, MeSi(Ind)2ZrCl2-PSAlk; PS, polystyrene; PSAlk, polystyrene alkylated.

soluble heptane fraction (75%) is also isotactic PP (and not syndiotactic) but with less stereoregularity. Based on these observations (Table 4), Soga and co-workers have proposed that the formation of isospecific species might involve the SiO2 surface, as for isospecific sites in conventional supported Ziegler-Natta catalysts. However, the structure of the isospecific active species, as well as the number of ligands attached to zirconium, still remains unclear. More recently, Soga et al. (1995a),

Chart 3. Models of Singly and Doubly Bound Metallocene Species (Reprinted with Permission from Soga et al. (1995a). Copyright 1995 Huthig & Wepf)

used a different type of bridge, a Sn bridge, to connect metallocene ligands to the silica surface. Isotactic PPs obtained with the tin-bridged catalyst display a single Tm at 162 °C. It is speculated that the higher reactivity of SnCl4 toward the surface hydroxyl groups is responsible for the formation of more uniform active species on SiO2. Supported titanocenes yielding highly isotactic PPs with considerably high MW’s, but exhibiting low activities are also described. Organic materials have also been used as supports. Nishida et al. (1995) have prepared rigidly immobilized zirconocenes on polystyrene support using a slightly modified preparation route 3. Preliminary results show that considerably high activities in propylene polymerization can be obtained at high temperatures. In addition, PP produced between 40 and 70 °C with a catalyst presenting a more rigid structure did not show any difference in MW and in Tm. Using polysiloxanesupported metallocene catalysts, Soga et al. (1995b) obtained isotactic PP with a melting point and a [mmmm] value that lie between those produced with the corresponding homogeneous catalyst and the SiO2supported catalyst. The total activities are remarkably improved when compared with those of corresponding SiO2-supported catalysts. 5. General Trends in Supported Metallocene Catalysts Among the polymerization features which distinguish supported metallocene from their homogeneous counterparts, the following are worth noting: (a) the smaller Al/Zr ratios required to obtain the maximum activity


with supported systems (aluminoxane/metallocene ratios can be usually reduced from several thousands to the range 50-400); (b) the possibility to activate some supported metallocene systems by common alkylaluminums (trimethylaluminum, triethylaluminum, and triisobutylaluminum) in the absence of any MAO; (c) a more limited dependence of polymerization activity on MAO or Al/transition-metal ratios. This can be related to a much slower catalyst deactivation by bimolecular processes due to the immobilization of active sites on the surface support. Supported metallocene systems are, however, generally less active polymerization catalysts than homogeneous ones, probably because of the much less efficient formation of active sites from the initial metallocene compound. A comparison of the relative performances of supported metallocene catalysts must be made with particular care since the support (nature and treatment), the preparation method, the preparation conditions, and the operational polymerization conditions may drastically affect the catalytic behavior. However, in the particular case of SiO2-supported systems, the most extensively studied support, the following trends in catalyst activity and isospecificity are observed: for activity: method 2 . refined method 1 g method 3; for stereospecificity, method 2 < refined method 1 e method 3. Indeed, MAO-mediated systems (obtained by method 2) present rather high polymerization activities but lead to polymers presenting only slightly improved properties (Tm, isotacticity, and MW). These supported catalysts have also been described as being rather sensitive to the nature of cocatalysts, to the Al/Zr ratio, and to other experimental conditions, therefore resembling homogeneous metallocene catalysts (Soga and Kaminaka, 1993; Chen et al., 1995; Sacchi et al., 1995). It was suggested by Sacchi et al. (1995) that the same metallocene cationlike active species (Cp2MtMe+‚MAO-) is formed either with MAO in solution or when the latter is anchored to the silica surface; as the bonding is mediated by MAO, no significant influence of the support on the active species is observed (Kaminsky and Renner, 1993; Chen et al., 1995). The refined impregnation method leads to systems which are much more efficient for the synthesis of PP with characteristics similar to those observed with traditional Ziegler-Natta catalysts. It is proposed that the direct interaction between the support and the metallocene may affect the metallocene structure and form a more stabilized and rigid species on the support surface (Kaminsky and Renner, 1993; Kaminsky, 1995a,b). However, these catalysts present very low polymerization activity. This may be attributed to a low concentration of active species, due to deactivation during the long and high-temperature impregnation procedure), as well as to a low rate constant of propagation (Chen et al., 1995). Rigidly immobilized metallocenes seem to be a promising alternative for the synthesis of highly stereospecific catalysts. However, several aspects still need to be improved: catalyst synthesis is quite complex and may result in mixtures of meso and racemic active site isomers, with consequent formation of isotactic and atactic polymer fractions; the polymerization activities are still very low; different isospecific sites may also be formed. At the end of this review concerning the present status of olefin polymerization catalyzed by supported

metallocene, it is clear that although important progress has already been made, much needs to be done to gain a better understanding of the elementary reactions as well as the different types of interactions involved between metallocene and the various supports. This knowledge will ensure better control of the active site structure and of operating polymerization mechanisms both in direct relationship with the characteristics and the properties of the resulting polyolefins. Many technological difficulties still have to be overcome, in particular regarding isotactic PP, before metallocene-supported-based technologies become available for widespread industrial use. Nevertheless, we believe that the rapid progress in the field of supported metallocenes will soon allow the use of these heterogeneous catalysts in slurry- and gasphase processes for the production of common PE and PP grades and of new types of polyolefins with tailormade properties. The impact and importance of supported catalysts in the polyolefin industry will continue to grow rapidly in the coming years. Literature Cited Arribas, G.; Conti, G.; Altomare, A.; Ciardelli, F. Zeolite. Supported metallocene complexes for polymerization of monoalkenes. Proc. Int. Symp. Synth., Struct. Ind. Aspects Stereospec. Polym., STEPOL 94 1994, 210. Bonini, F.; Fraaje, V.; Fink, G. Propylene polymerization through supported metallocene /MAO catalyst: Kinetic analysis and modelling. J Polym. Sci. A: Polym. Chem. 1995, 33, 2393. Chang, M. Olefin polymerization catalysts from tryalkylaluminum mixture silica gel and a metallocene. U.S. Patent 5,006,500, 1991. Chang, M. Preparing metallocene-aluminoxane/silica gel polymerization catalysts. U.S. Patent 5,086,025, 1992. Chang, M. Supported catalysts for R-olefin polymerization. U.S. Patent 5,238,893, 1993. Chen, Y.-X.; Rausch, M. D.; Chien, J. C. Heptane soluble homogeneous zirconocene catalyst: Synthesis of a single diastereomer, polymerization catalysis, and effects of silica supports. J. Polym. Sci. A: Polym. Chem. 1995, 33, 2093. Chien, J. C.; He, D. Olefin copolymerization with metallocene catalysts. III. Supported metallocene/methylaluminoxane catalyst for olefin copolymerization. J. Polym. Sci.: Part A: Polym. Chem. 1991, 29, 1603. Ciardelli, F.; Altomare, A.; Arribas, G.; Conti, G.; Masi, F.; Menconi, F. In Catalyst design for Tailor-Made polyolefins; Soga, K., Terano, M., Eds.; Elsevier: Kanazawa, 1994; p 257. Collins, S.; Kelly, W. M.; Holden, D. A. Polymerization of polypropylene using supported chiral, ansa-metallocene catalysts: Production of polypropylene with narrow molecular weight distribution. Macromolecules 1992, 25, 1780. Ewen, J. A. Catalytic polymerization of olefins; Keii, T., Soga, K., Eds.; Kodansha: Tokyo, 1986; p 271. Finch, W. C.; Gillespie, R. D.; Hedden, D.; Marks, T. J. Organometallic Molecule-inorganic surface coordination and catalytic chemistry. In situ CPMAS NMR delineation of organoactinide adsorbate structure, dynamics and reactivity. J. Am. Chem. Soc. 1990, 112, 622. Grubbs, R. H.; Gibbons, C.; Kroll, L. C.; Bonds, W. D., Jr.; Brubaker, C. H., Jr. Activation of homogeneous catalysts by polymer attachement. J. Am. Chem. Soc. 1973, 95, 2373. Gupta, V. K.; Satish, S.; Bhardwaj, I. S. Metallocene complexes of group 4 elements in the polymerization of monoolefins. Rev. Macromol. Chem. Phys. 1994, 3, 439. He, M.-Y.; Xiong, G.; Toscano, P. J.; Burwell, R. L., Jr.; Marks, T. J. Supported organoactinides. Surface chemistry and catalytic properties of alumina-bound (Cyclopentadienyl)- and (Pentamethyl cyclopentadienyl)thorium and -uranium hydrocarbyls and hydrides. J. Am. Chem. Soc. 1985, 107, 641. Hedden, D.; Marks, T. J. [(CH3)5C5]2Th(CH3)2 surface chemistry and catalysis. Direct NMR Spectroscopic observation of surface alkylation and ethylene insertion/polymerization on MgCl2. J. Am. Chem. Soc. 1988, 110, 1647.

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Soares, J. B. P.; Hamielec, A. E. Metallocene/Alumoxane Catalysts for olefin polymerization. A review. Polym. React. Eng. 1995, 3, 131. Soga, K. Homogeneous and heterogeneous metallocene catalysts activated by ordinary alkylaluminium compounds. Proc. Int. Symp. Synth., Struct. Ind. Aspects Stereospec. Polym., STEPOL 94 1994a, 69. Soga, K. In Catalyst design for Tailor-Made polyolefins; Soga, K., Terano, M., Eds.; Elsevier-Kodansha: Tokyo, 1994b; p 307. Soga, K. Highly isoespecific, immobilized zirconocene catalysts supported on chemically modified SiO2. Makromol. Symp. 1995, 89, 249. Soga, K.; Kaminaka, M. Polymerization of propene with the heterogeneous catalyst system Et[IndH4]2ZrCl2/MAO/SiO2 combined with trialkylaluminium. Makromol. Chem. Rapid Commun. 1992, 13, 221. Soga, K.; Kaminaka, M. Polymerization of propene with zirconocene-containing supported catalysts activated by common trialkylaluminiums. Makromol. Chem. 1993, 194, 1745. Soga, K.; Kaminaka, M. Copolymerization of olefins with SiO2-, Al2O3-, and MgCl2-supported catalysts activated by trialkylaluminiums. Macromol. Chem. Phys. 1994a, 195, 1369. Soga, K.; Kaminaka, M. Polymerization of propene wit a rac(CH3)2Si(2,4-(CH3)2C5H3)(3′,5′-(CH3)2C5H3)ZrCl2/MAO/SiO2-Al(iC4H9)3 catalyst system. Macromol. Rapid Commun. 1994b, 15, 593. Soga, K.; Nakatani, H. Syndiotactic polymerization of styrene with supported Kaminsky-Sinn catalysts. Macromolecules 1990, 23, 957. Soga, K.; Park, J. R.; Shiono, T. Copolymerization of ethylene and propylene with a CpTiCl3/SiO2-MAO catalyst system. Polym. Commun. 1991, 32, 310. Soga, K.; Shiono, T.; Kim, H. J. Activation of SiO2-supported zirconocene catalysts by common trialkylaluminiums. Makromol. Chem. 1993, 194, 3499. Soga, K.; Kim, H. J.; Shiono, T. Highly isoespecific SiO2-supported zirconocene catalyst activated by ordinary alkylaluminiums. Macromol. Rapid Commun. 1994a, 15, 139. Soga, K.; Kim, H. J.; Shiono, T. Polymerization of propene with highly isoespecific SiO2-supported zirconocene catalysts activated with common alkylaluminiums. Macromol. Chem. Phys. 1994b, 195, 3347. Soga, K.; Uozomi, T.; Saito, M.; Shiono, T. Structure of polypropylene and poly(ethylene-co-propene) produced with an aluminasupported CpTiCl3/common alkylaluminium catalyst system. Macromol. Chem. Phys. 1994c, 195, 1503. Soga, K.; Arai, T.; Nozawa, H.; Uozomi, T. Recent development in heterogeneous metallocene catalysts. Macromol. Symp. 1995a, 97, 53. Soga, K.; Arai, T.; Hoang, B. T.; Uozomi, T. Olefin polymerization with metallocene catalysts supported on polysiloxane derivatives. Macromol. Rapid Commun. 1995b, 16, 905. Woo, S. I.; Koo, Y. S.; Han, T. K. Polymerization of ethylene over metallocenes confined inside the supercage of a NaY zeolite. Macromol. Rapid Commun. 1995, 16, 489. Xie, T.; McAuley, K. B.; Hsu, J. C.; Bacon, D. W. Gas phase ethylene polymerization: Production processes, polymer properties, and reactor modeling. Ind. Eng. Chem. Res. 1994, 33, 449.

Received for review August 1, 1996 Revised manuscript received November 13, 1996 Accepted November 14, 1996X IE960475S

X Abstract published in Advance ACS Abstracts, February 15, 1997.

Supported Metallocene Complexes for Ethylene and Propylene

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