ContentsI. Introduction 1347II. Source Materials 1348III. Supported Catalysts Activated by
Trialkylaluminums1348
IV. Supported Catalysts Activated by Alumoxanes 1349A. Supported Alumoxanes 1350B. Supported Metal Complexes 1350C. Supporting Metal Complex−MAO Solutions 1352D. Influence of Hydroxyl Groups 1352E. Prepolymerization of Supported Catalysts 1353
V. Alumoxane-Free Supported Single-Site Catalysts 1354VI. Supported Catalysts without Cocatalysts 1356VII. Chemically Tethered Metal Complexes 1356VIII. Chemically Tethered Activators 1361
A. Alumoxanes 1361B. Boron Activators 1362
IX. Supported Group 3 and Lanthanide Single-SiteCatalysts
1364
X. Supported Group 5 Single-Site Catalysts 1365XI. Supported Group 6 Single-Site Catalysts 1365XII. Supported Late-Transition Metal Single-Site
Catalysts1366
XIII. Other Support Materials 1366A. Magnesium Chloride 1366B. Zeolites 1366C. Clays 1367D. Polymers 1367E. Miscellaneous Supports 1368
XIV. Heterogeneous Single-Site Catalysts withoutCarriers
1369
XV. Supported Mixed Single-Site Catalyst 1369XVI. Comparison of Homogeneous and
Heterogeneous Catalysts1370
XVII. Other Process Considerations 1371XVIII. Summary 1371XIX. References 1371
I. Introduction
Breakthroughs in single-site catalysis have com-pletely transformed our view of alpha-olefin polym-erization catalysis. The conventional Ziegler-Nattacatalysts used in industrial production of polyolefins
are heterogeneous systems, referring not only to theinsolubility of the catalyst in the polymerizingmedium, but also to its multisited nature. The resultis catalysts which are difficult to study and under-stand that produce complex polymer mixtures withwidely varying molecular weights and microstruc-tures.
The first homogeneous polymerization catalyst,Cp2TiCl2-AlEt2Cl (Cp ) η5-C5H5), was reportedwithin a few years of Ziegler’s discovery of low-pressure metal-catalyzed alpha-olefin polymeriza-tion.1 Although they are useful for model studies andkinetics, these titanocene catalysts were of no com-mercial interest because of their low activity, pro-pensity to decompose to inactive species, and inabilityto polymerize higher alpha-olefins. The discovery thatpartially hydrolyzed aluminum alkyls,2 in particularmethylalumoxane (MAO),3 as cocatalysts vastly in-creased catalyst activity, especially of zirconocenecomplexes, revived interest in these systems. Com-mercial interest was heightened by the disclosurethat judicious substitution of the zirconocene frame-work could influence activity, polymer molecularweight, comonomer incorporation,4 and stereospeci-ficity in alpha-olefin polymerization.5 The discoveryof fluoroaryl-based activators such as [R3NH]-
* To whom correspondence should be addressed (telephone: (513)530-4004; fax: (513) 530-4206; E-mail: [email protected]).
Gregory Hlatky was born in 1956 near Philadelphia, PA. He received hisB.S. degree in 1978 from Rider University, studying chemistry and history,and his Ph.D. degree in 1983 from Yale University, where he workedunder Robert Crabtree. After postdoctoral research at the University ofCambridge with Sir Jack Lewis and Brian Johnson, he joined ExxonChemical Company in 1984 at the Baytown Polymers Center in Baytown,TX. In 1996 he moved to Lyondell Petrochemical Company, now part ofEquistar Chemicals, LP. His research interests are in inorganic andorganometallic complexes for homogeneous catalysis, intellectual propertyanalysis, and chemical information. Otherwise he helps his wife breed,raise, and show Borzoi (Russian Wolfhounds) under the kennel nameSoyara.
[B(C6F5)4],6 [Ph3C][B(C6F5)4],7 and B(C6F5)38 led to
comprehensively characterizable catalysts with com-mercially significant activities. The search for newpolymerization-stable ancillary ligands has spurredthe development of “non-metallocene” single-sitecatalysts,9 the polymers from which can have unusualstructures, such as the hyperbranched polyethylenehomopolymer produced from nickel diimine cata-lysts.10
Regardless of the virtues these new catalystspossess, they would remain mere playthings of thelaboratory if they could not be adapted to run incommercial polymerization processes. Single-site cata-lysts are almost all homogeneous, not only, as theirname suggests, having a uniform polymerizing spe-cies, but also soluble and active in non-nucleophilicorganic solvents such as toluene or aliphatic hydro-carbons.
Commercial polymerization processes using solublecatalysts are mostly those in which the lower-crystallinity polymers produced are soluble in thereaction diluent (e.g., elastomers and very low-density ethylene copolymers) or which operate attemperatures above the melting point of the polymer.In these solution processes, the reaction diluent isvolatilized and the polymer recovered for compound-ing and pelletization.
In slurry, bulk-monomer, or gas-phase processes,the polymer is usually of higher density or crystal-linity (e.g., high-density polyethylene, linear-low-density polyethylene, isotactic polypropylene) and isthus insoluble in the reactor diluent or fluidizing gasstream. The continuous operation of these processessuggests the use of morphologically uniform catalystparticles which can be fed into the reactor smoothlywithout clumping, which in turn implies fixing thesolution-soluble catalyst on an insoluble carrier.
A continuous and gradual expansion of the particle,especially in the early stages of polymerization,ensures a uniform expansion and avoids overheatingof the particle and melting of the polymer, whichcould result in the particles adhering to form sheetson the reactor walls and agitator, or large chunkswhich disturb fluidization or product discharge.Premature fragmentation of the polymer particleforms fines which can be carried into recycle lines.11
The catalyst should polymerize the monomer toproduce a polymer product of high bulk density whichmirrors the particle size distribution of the catalystdespite a 25- to 200-fold increase in volume.12
A tall order! Yet single-site catalysts have beensuccessfully supported using numerous methods onmany different types of carriers and have been usedin commercial plants to produce with high catalystactivities polymers with narrow particle size distri-butions and high bulk densities. This review exam-ines catalyst and cocatalyst families, methods ofheterogenization, and process considerations in he-tereogeneous single-site catalysts. Although this isthe first comprehensive survey of the subject, thereader’s attention is drawn to a number of shortreviews which have appeared recently.13
II. Source MaterialsThe literature to be reviewed was taken from
searches on a number of online databases, includingChemical Abstracts, Derwent World Patent Index,European Patents Online, and the full text U.S.Patent database.14 The author has endeavored toencompass all the literature at least to the end of1998.
Because of the widespread industrial interest thesecatalysts have engendered, the majority of the lit-erature to be cited is in the form of patents orpublished patent applications.15 When a publishedpatent application has been subsequently issued asa U.S. Patent, the U.S. Patent number will be cited.When an equivalent application appears to a pub-lished PCT International Application in Japanese,the English-language version will be cited. Japaneselaid-open applications (Kokai) will be addressed tothe extent that the abstract gives a clear picture ofthe unique aspect of the invention. Chemical Ab-stracts accession numbers will be provided for allcited patent literature.
Patents are not journal articles. They are legaldocuments which contain scientific information. Ap-plicants are obliged to set forth the best means ofpracticing the claimed invention. They are not obligedto lay out their reasoning; indeed, a sensible ap-plicant will avoid such theorizing. Instead of at-tempting to reconcile observations conflicting withthose in the literature, the patent literature delightsin presenting unanticipated and unexpected results,which are rarely explained. The author is aware thatsome of the disclosures in this review may be con-tradictory; whenever possible these will be reconciled,but there will be many cases in which, regrettably,there is not enough information provided to do so.
III. Supported Catalysts Activated byTrialkylaluminums
Since its discovery, the attractiveness of the Cp2-TiCl2-AlR2Cl catalyst lay in its solubility, unlike thecommercial heterogeneous Ziegler-Natta systems.This solubility facilitated kinetics and active sitecharacterization. The inherently low activity of thetitanocene catalyst vis a vis conventional Zieglercatalysts provided no impetus for adapting it forcontinuous commercial processes. Some researchindicated that the titanocene catalyst was not inhib-ited by adsorbants. Ethylene is polymerized in thepresence of carbon black, the activity roughlymirroring the surface area of the carbon black used.16
Cp2TiCl2 supported on 1,2-polybutadiene affords aheterogeneous metallocene which, when allowed toreact with Al(i-Bu)2Cl, forms a catalyst which poly-merizes ethylene at a rate of 240 g/g Ti‚h.17 Chienand Hsieh reacted Cp2ZrMe2 and CpTiMe3 onMg(OH)Cl to form supported complexes which, whenactivated by AlEt2Cl, polymerized propylene, albeitwith quite low activities.18
Silica-supported Cp2TiCl2-AlEtnCl3-n catalysts af-ford quite different polyethylene products dependingon the preparation procedure. When the alkylalumi-num is contacted with silica prior to reacting with
1348 Chemical Reviews, 2000, Vol. 100, No. 4 Hlatky
the titanocene, the polyethylene formed has a highermolecular weight and broader molecular weightdistribution (Mw/Mn) than that produced from thehomogeneous catalyst. Supporting Cp2TiCl2 on silicaand reacting with alkylaluminum gives polyethylenewith a bimodal distribution, one component of whichhas a molecular weight similar to that produced fromthe soluble catalyst. Apparently, desorption of activecatalyst from the support in the latter case is thereason for this observation.19
Even though they are largely overshadowed by themore widely used MAO and fluorinated borate anionactivators, single-site catalysts activated by simplealkylaluminums continue to be studied because of thelow cost, stability, and wide availability of the co-catalyst. Much of this research focuses on modifyingthe activator or support to improve catalyst activity,especially with respect to zirconocene catalysts.
Using MgCl2 as the support for a titanocene dichlo-ride catalyst affords a catalyst which, when activatedby AlEt2Cl, has a higher activity than the homoge-neous system, as well as a longer lifetime: thehomogeneous catalyst ceases polymerization after 10min, whereas the supported system remains activeafter an hour.20 Supporting a Cp2TiCl2-AlEtCl2catalyst on silica treated with butyl ethylmagnesiumgives a system with high activity (102 kg/g Ti) andbulk density (0.32 g/cm3),21 whereas the same catalyston Mg(OEt)2 has inferior performance (6.9 kg/g Tiand 0.23 g/cm3).22
In some cases a greater range of alkylaluminumscan be used. Al(i-Bu)3 is not a useful cocatalyst forCp2TiCl2 but functions more effectively when thetitanocene is supported on MgCl2, with a catalystactivity of 142 kg/g Ti and polymer bulk density of0.37 g/cm3.23 Although AlMe3 fails to activate silica-supported Cp2ZrCl2, a combination of AlMe3, Bu2Mg,and CCl4 at an aluminum-metal ratio of 500-1000gives an active catalyst.24
Soga and co-workers have studied extensivelysupported zirconocenes activated by simple alkyl-aluminum compounds. In solution, alkylaluminumsare ineffective activators for zirconocenes, but whensupported on alumina or MgCl2 activity improvesdramatically in propylene polymerizations, though itis still less than the homogeneous MAO-activatedvariant (Table 1).25 Trialkylaluminums work well, butchlorine-containing compounds such as AlEt2Cl andAlEtCl2 suppress activity completely. Silica, the mostcommonly used support for heterogenized single-sitecatalysts, is a poor choice as a carrier when trialkyl-aluminums are to be used as cocatalysts; only bypretreating the silica with a small amount of MAOdoes activity improve. In ethylene copolymerizationswith propene or 1-hexene, mixtures of homopoly-ethylene and copolymer were formed from the Et-(H4-Ind)2ZrCl2-MgCl2-Al(i-Bu)3 (Et(H4-Ind)2 )1,2-ethylenebis(tetrahydroindenyl), but copolymerwas the only product when AlMe3 was the cocatalyst.The composition of the polymers resembled that fromhomogeneous systems, but molecular weights werehigher.26
In olefin polymerization, CpTiCl3 with MAO is arelatively poor catalyst and with Al(i-Bu)3 virtually
inactive, but it functions far better when supportedon silica, alumina, or MgCl2.27 The catalyst activityincreases in propylene polymerization when higheralkylaluminums such as Al(n-C10H21)3 are used ascocatalysts.27a The polypropylene produced is atactic,but isotactic polymer is formed when an externaldonor such as ethylbenzoate is added.28 A similarpattern is observed when bis(diketonato) metal di-halides are supported on MgCl2.29 The titanium-based catalysts are far more active than the zirco-nium analogues: (acac)2TiCl2-MgCl2-Al(i-Bu)3 (acac) acetylacetone) has an activity of 310 kg/mol M‚hvs 1.1 kg/mol M‚h for (acac)2ZrCl2-MgCl2-Al(i-Bu)3.Adding ethylbezoate or silane donors improves thepercentage of hepane insolubles from 25% to as highas 94%, but at the cost of most of the catalyst activity.
IV. Supported Catalysts Activated by AlumoxanesSingle-site catalysts activated by alumoxane, in
particular MAO, and supported on inorganic oxidesform the vast majority of heterogeneous single-sitecatalysts for olefin polymerization. Silica predomi-nates among support materials. Silicas with a widerange of particle sizes, surface areas, and porevolumes have been used. Most commonly, these havehad a particle size of about 50-100 µm, but single-site catalysts were supported on silica with anaverage particle size as low as 0.012 µm; improve-ments in film properties were claimed.30 Numeroustechniques have been disclosed for supporting andfinishing the catalyst in order to optimize catalystactivity, particle morphology, and particle bulk den-sity without seriously affecting polymer properties.
As a lagniappe, the ratio of alumoxane to metal canbe reduced considerably. It has been suggested thatlarge excesses of MAO (aluminum-to-metal ratios of1000-10 000) are needed in homogeneous polymer-izations with metallocene catalysts in order to pre-vent bimolecular deactivation processes (Scheme 1).
Table 1. Propylene Polymerization with SupportedZirconocene Catalysts Activated by SimpleAlkylaluminums
Catalyst for Olefin Polymerization Chemical Reviews, 2000, Vol. 100, No. 4 1349
Immobilizing the polymerizing centers on a carrieritself suppresses any interaction of polymerizingsites. Accordingly, the ratio of aluminum to metalcomponent can be reduced to a far lower and moreeconomical level of 50-300.31
Examination of the literature suggests there arethree basic methods of supporting alumoxane-acti-vated single-site catalysts: (1) supporting the alu-moxane, then reacting with the metal complex; (2)supporting the metallocene, then reacting with themetal complex; and (3) contacting the alumoxane andmetal complex in solution before supporting.
A. Supported AlumoxanesSupporting the alumoxane first, followed by reac-
tion with the metal complex, was among the earliestmethods used for preparing heterogeneous single-sitecatalysts. Welborn32 and Takahashi33 reacted silicawith a toluene solution of MAO and decanted thesolution to isolate the MAO-containing solids. Thesewere reacted with Cp′2ZrX2 (Cp ) substituted orunsubstituted cyclopentadienyl; X ) Cl, Me) to formthe finished catalyst, which was used in stirred-bedgas-phase ethylene polymerizations and copolymer-izations. Dilute solutions of MAO (<5 wt % Al) gaveinferior catalyst performance. Precipitating the MAOonto the silica by adding n-decane to the silica-MAOslurry in toluene is reported to narrow particle sizedistribution as well as improve activity.34
The metallocene is added to the supported MAOas a solution in toluene or aliphatic hydrocarbon.Subsequently subjecting the mixture to microwaveshas been claimed to fix the metal component on thesupport and reduce reactor fouling (adhesion ofpolymer to reactor surfaces).35 The metallocene canalso be dry-blended with the support, avoiding solu-bilization of the finished catalyst.36
A number of mono(cyclopentadienyl) complexes ofthe group 4 metals were supported by reaction withMAO on silica. The “constrained-geometry” trivalenttitanium complexes Et(Cp′)(NMe2)TiCl2 were com-bined with MAO supported on silica to form catalystsused in slurry or gas-phase ethylene copolymeriza-tions.37 Cosupporting the mono(cyclopentadienyl)titanium amine complexes with bis(cyclopentadienyl)zirconium complexes on MAO-silica gave polymerswith broad molecular weight distributions. CpZrCl3was contacted with MAO on silica to prepare acatalyst for gas-phase ethylene polymerization.38 Theinventors obtained the best results when an Al/Zrratio of 200 was used, and no further scavengerneeded to be added to the polymerization environ-ment.
Among the techniques used for fixing the alumox-ane to the support surface are heating the MAOsolution to 50-85 °C prior to supporting; this isclaimed to remove gels deemed deleterious to catalystperformance.39 Heating the toluene slurry of MAO
and silica at superatmospheric pressures (closedvessel) evenly distributes the aluminum through thesilica particles.40 Heating the dry MAO-silica mate-rial fixes the alumoxane to the surface more thor-oughly; whereas toluene washes a third to a half ofthe supported aluminum from a support heated to125 °C, scarcely any is lost when the support isheated to 200 °C.41 A catalyst formed when thesesupports are reacted with Me2Si(C5Me4)(N-t-Bu)-TiMe2 exhibits higher activities and superior bulkdensities with the latter formulation.
An alternative method of generating alumoxanesin situ hydrolyzes alkylaluminums with water in thepresence of the support, either in a hydrocarbonsuspension,42 in a spray dryer,43 or with the reactivecomponents in the gas phase.44 A toluene solution ofthe metallocene is added to the mobile powder to formthe finished catalyst. The elemental distribution ofaluminum on a silica-supported MAO from the gas-phase process shows that all of the MAO is locatedon the particle surface with no aluminum present inthe pores of the particle. The supported MAO wasreacted with (n-BuCp)2ZrCl2 and polymer growth inethylene polymerization was examined by electronmicroscopy. No particle fragmentation occurred andpolymer formed irregularly on the surface.45 Alumox-anes are also generated when solutions of trialkyl-aluminums are reacted with boric acid supported onsilica. Reaction with metallocene dichlorides gener-ates a catalyst, which can be generated and used insitu or isolated as a solid.46
The supported MAO may be chemically modifiedwhen supported. MAO supported on silica or aluminawas taken up in tetrahydrofuran (THF) and reactedwith a cross-linking agent such as bisphenol A (4,4′-isopropylidenediphenol).47 A one-step method reactsthe MAO and modifier simultaneously in the supportstep.48 The modified MAO support, reacted with Et-(Ind)2ZrCl2, polymerizes propylene to spherical poly-mer particles while the unmodified support formscoarse agglomerates. Pentafluorophenol has alsobeen used to modify the supported alumoxane, prob-ably converting it to (-Al(O)(OC6F5)-)n.49
B. Supported Metal ComplexesSupporting the metal complex on the carrier first,
then reacting with alumoxane, is more common forcomplexes chemically tethered to the carrier (SectionVII) and rarer for CpnMX3-n complexes. As inorganicoxides, especially silica, have been overwhelminglyused as supports for single-site catalysts, residualhydroxyl groups on the surface can react with themetal complex, sometimes in a deleterious manner(Section IV-D). Blitz and co-workers studied theadsorption of Cp2MCl2 complexes on bare silica, silicaheated to 600 °C-heated silica, and silica treated withthe dehydroxylating agent hexamethyldisilazine(HMDS).50 The order of reactivity is Cp2HfCl2 > Cp2-ZrCl2 > Cp2TiCl2. Metallocenes react with silicasurfaces to form dSi-O-MClCp′2 groups, which areconverted to catalytic species on reaction with MAO(Scheme 2).
While examining the dependence of calcinationtemperature on metallocene loading, dos Santos and
Scheme 1
1350 Chemical Reviews, 2000, Vol. 100, No. 4 Hlatky
co-workers noted that while silica treated undervacuum at room-temperature adsorbed the most (n-BuCp)2ZrCl2, the catalyst activity was quite low.51
They attributed this to the formation of the unreac-tive chloride-free zirconium species 1. Supports with
higher surface area adsorb more metallocene.52 Astudy on the effect of calcination temperature, graft-ing times and temperatures, and solvent effects ongrafting (n-BuCp)2ZrCl2 on Grace 948 silica shows agreat deal of scatter through the data, but theauthors suggest that intermediate grafting times onsilica dried at 450 °C with nonpolar solvents gave thebest activity in ethylene polymerization and narrow-est molecular weight distribution.53 At equal surfaceareas and zirconium loadings, an Et(Ind)2ZrCl2 cata-lyst (Et(Ind)2 ) 1,2-ethylenebis(indenyl)) on non-porous Aerosil is twice as active as than the samemetallocene on porous Crossfield silica.54 This wasattributed to easier access to cocatalyst and monomerin the nonporous carrier.
Kaminsky reacted Et(Ind)2ZrCl2 with silica (heatedat 100 °C in vacuo) and exhaustively extracted thetoluene with toluene before contacting the supportwith 35-200 equivalents of MAO. Polymerization ofpropylene at 50 °C with this catalyst afforded iso-tactic polypropylene with melting points of 157-161°C and molecular weights of 500,000-800,000 Da farhigher than the 122 °C melting point and molecularweight of 20,000 Da observed with the homogeneouscatalyst. Adsorbing the MAO on silica first, thenreacting with metallocene afforded a catalyst whichproduced i-PP resembling that from the homogeneouscatalyst.55 This difference was attributed to a closerinteraction of the cationic center with the silica whenthe metallocene is supported first, and a more“homogeneous” behavior when the MAO was sup-ported first.
A later study by Sacchi and co-workers usingessentially the same method and polymerizationconditions employed by Kaminsky found the i-PPproduced from the supported and homogeneous cata-lysts to be quite similar.56 Although the unbridged
metallocene (Ind)2ZrCl2 produces atactic PP in solu-tion, when supported on silica and subsequentlyreacted with MAO, it afforded a moderately isotacticpolymer with broad molecular weight distribution(12.6); the authors attributed this to the decomposi-tion of the metallocene framework and conversion ofthe metal complex to a stereospecific form.
CpTiCl3 supported on silica calcined at 800 °C wascontacted with MAO and used to copolymerize eth-ylene and propylene. The characteristics of thecopolymer (composition, comonomer reactivity ratios,differential scanning calorimetry profiles) closelyresemble those of a copolymer formed from a com-mercially used VOCl3-Al2Et3Cl3 catalyst.57 In thepolymerization of styrene, however, the same catalystdoes not produce exclusively the syndiotactic polymerof the homogeneous catalyst.58 The fraction of 2-bu-tanone soluble material increases with increasingconcentration of the titanium component on thesupport. Two titanium species were detected in theelectron spin resonance (ESR) spectrum, one of whichcorresponded to a soluble Ti(III) catalyst. Indeed, astrong ESR signal is observed in the soluble compo-nent after the supported CpTiCl3 is allowed to reactwith MAO in toluene.
Using the silsequioxane complex (c-C5H9)7Si8O12-OH, a model system for (1,3-SiMe3-C5H3)TiCl3 (2)
supported on silica was synthesized and tested inethylene polymerization.59 With MAO (X ) Cl) orB(C6F5)3 (X ) CH2Ph), active catalysts of the type [(c-C5H9)7Si8O12O)Cp′TiR]+ are formed. However, anactive catalyst is also formed from MAO (1,3-(SiMe3)-C5H3)TiCl((c-C5H9)7Si8O12O)2, suggesting that theSi-O-Ti unit in CpTiCl3 on silica may not bepolymerization stable with respect to MAO; there isno reaction with B(C6F5)3.
To remove reactive surface hydroxyl groups, thesupport may first be treated with compounds suchas simple alkylaluminums. Silica treated with alkyl-aluminums serves to fix metallocene complexesbearing polar substituents such as Et(2-(t-BuMe2-SiO)Ind)2ZrCl2
60 and bis(2-tetrahydrofuranylmethyl-Cp)2ZrCl2.61 Reacting the metallocene with a trialkyl-aluminum before supporting is reported to lead tocatalysts of higher activity than when metallocenedichlorides are supported alone.62 The metalloceneis usually added to the silica as a solution in toluene,but a solvent-free vapor deposition method has alsobeen disclosed to support mono- and bis(cyclopenta-dienyl) complexes on calcined silica or alumina.63 The
Scheme 2
Catalyst for Olefin Polymerization Chemical Reviews, 2000, Vol. 100, No. 4 1351
amount of metallocene supported is dependent on thecalcination temperature of the support: 6.5 wt %zirconium is deposited on silica calcined at 300 °C,whereas only 1.1% is found on silica calcined at 900°C.
One means of preparing a heterogeneous “metal-locene” catalyst is to assemble the components on thesupport. A silica-MgCl2 supported “titanocene” cata-lyst is formed when Cp2Mg is contacted with silica,reacted with TiCl4, and treated with gaseous HCl.Activation is by MAO or alkylaluminums.64 Compari-son of the gel permeation chromatograph (GPC)traces of a conventional Ziegler-Natta catalyst anda catalyst modified by Cp2Mg shows a narrowermolecular weight distribution for the latter catalyst.MCl4 (M ) Ti, Zr) supported on silica or alumina andreacted with Cp′-SiMe3 (Cp′ ) Cp, Ind, 1/2 Et(Ind)2)forms a heterogeneous “metallocene” catalyst whichcan be activated by MAO, alkylaluminums, or boratesalts to polymerize ethylene.65 No GPC data werereported, however, and it is difficult to say whetherthis functions as a single-site catalyst or as a modifiedZiegler-Natta system, but in a similar process usingCp′Li (Cp′ ) Cp, Ind) on ZrCl4 on silica, the molecularweight distributions were quite narrow (Mw/Mn )2.5-3), suggesting single-site behavior.66 When TiCl4was used, much broader distributions (4.8) wereobserved, though still less than unmodified TiCl4on silica (7.8).67 Similarly, adding Cp′-SiMe3
68 orCp′-Li69 reagents to conventional commercial Zie-gler-Natta catalysts gave polymers with distribu-tions no narrower than the unmodified catalyst.Supported titanium halides, it seems, are more proneto the formation of secondary active species.
C. Supporting Metal Complex−MAO SolutionsThe third most common method of supporting
single-site catalysts is to combine the metal compo-nent and alumoxane in a solvent, then add thesolution to the support material. There are severaladvantages to this method. The process maximizesthe number of active centers by activating the metalcomponent in solution, instead of carrying out theprocess with one or the other component in animmobilized state. Highly active catalysts can beproduced even at low Al/Zr ratios. Techniques havealso been developed to reduce the amount of solventused, thereby speeding the catalyst preparationprocess and avoiding large amounts of solvent byprod-ucts.
In this method, the metal component and MAO arecombined in a solvent, usually toluene. Metallocenesof low solubility dissolve in MAO solutions andimpurities can be removed by filtration.70 Allowinga toluene solution of Me2Si(2-Me-4-PhInd)2ZrCl2-MAO to stand for 18 h before adding to the silicasupport is claimed to improve the activity in pro-pylene polymerizations (193 kg of PP/g of metallocene‚h) over catalysts in which the solution was added tothe carrier immediately (103 kg of PP/g metallocene‚h).71
The solution is then added to the support; a methodof vacuum impregnation has been described whereinthe catalyst solution is added to the support held
under low pressure in order to improve penetrationinto the pores of the support.72 In the final step, theslurry is dried in a vacuum, by a nitrogen purge orby spray drying,73 to form the finished product as afree-flowing solid. It has been suggested that thepresence of gels in MAO is a cause of poor particlemorphology in catalysts supported by this method.The use of filtered MAO solutions dramaticallyimproves the particle size distribution of the finalpolymer product.74
A very useful refinement of this supporting tech-nique is the “incipient wetness” method, in which thepore volume of the support is measured and a volumeof catalyst solution is added which only just fills thepores of the support.75 The volume of the catalystsolution can exceed the pore volume of the supportas long as the ratio of aluminum to metal is low(<300) and the catalyst-support mixture does notform a slurry, but remains dry or has the consistencyof a paste.76
There are two perceived advantages to thismethod: the catalyst occupies the pores of the sup-port and less of the surfacesleading to improvedparticle morphologysand a greatly reduced volumeof liquid solvent need be used, thus decreasingpreparation time and lowering effluents and disposalcosts. Equipment has been described which is suit-able for preparing 25-50 kg of supported catalyst byincipient impregnation.77
D. Influence of Hydroxyl GroupsSilica, the most commonly used support for het-
erogeneous single-site catalysts, contains Si-OHgroups of varying structures and concentrationsdepending on the dehydration temperature. TheseSi-OH groups may be geminal (undehydrated silica),hydrogen bonded (dehydrated at temperatures up to600 °C), or isolated (dehydrated above 600 °C) (3A-3C). As described above, these can react with metal
dichloride complexes to form Si-O-M functionalitieswhich can be converted to active catalysts when acocatalyst is added. In some cases, though, thesehydroxyl groups can have a deleterious effect on thecatalyst. For example, Et(Ind)2ZrCl2 contacted withhydroxylated silica or alumina then reacted withMAO has no activity in propylene polymerization, aneffect which is attributed to decomposition of thecatalyst (Scheme 3).78 The diastereomeric zirconocene(1′S, 2′R, 5′S-menthoxy)2Si((R, R)-(+)-Ind)2ZrCl2supported on silica and activated by MAO had pooractivity in ethylene polymerization and was inactivein propylene polymerization.79 Rather more dramati-cally, Me2Si(Cp)(Flu)ZrCl2 (Flu ) η5-C13H8), which asa homogeneous catalyst produces syndiotactic polypro-pylene, forms isotactic polypropylene (Tm ) 158 °C,
1352 Chemical Reviews, 2000, Vol. 100, No. 4 Hlatky
mmmm ) 90%) when supported on silica and acti-vated with MAO.80
These surface hydroxyl groups can be removed bytreatment with a variety of agents. An IR spectro-scopic study of the action of AlMe3 and AlMe3-richand -lean MAO on 400 °C dried silica showed thatthe silanol groups reacted preferentially with AlMe3and less rapidly with the alumoxane oligomer.81 Theaforementioned Et(Ind)2ZrCl2-SiO2 (Al2O3)-MAOcombination78 polymerizes propylene with much im-proved activity when partially dehydroxylated silicaor alumina is first treated with AlMe3; AlMe2Cl hasalso been used as the passivating agent.82 Theactivity of a Me2Si(2-Me-4-PhInd)2ZrCl2-MAO cata-lyst increases from 67 to 242 kg/g of metallocene‚hand the melting point increases from 156 to 160 °Cwhen the silica is treated with AlMe3 before support-ing the catalyst.83
Similar beneficial effects of AlMe3 treatment wereobserved for (i-PrCp)2ZrCl2-MAO84 and MePhSi(C5-Me4)(N-t-Bu)TiCl2-MAO85 catalysts. Failure to treatsilica with AlMe2Cl before supporting a Cp2ZrCl2-MAO catalyst results in product with a much lowerbulk density (0.15 vs 0.36 g/cm3).86 Other surfacepassivating agents used include Me2(n-octyl)SiCl87
and (c-C6H11)2Si(OMe)2.88 The reaction of hexa-methyldisilazine with was found to cap the isolatedSi-OH groups (5) leaving the hydrogen bondedsilanols unreacted; virtually all silanols are elimi-nated from silica dried at 600 °C and treated withHMDS.50
Surprisingly, other disclosures indicate that thepresence of surface hydroxyl groups is beneficial,possibly by fixing an increased amount of aluminumto the carrier. Such apparently contradictory resultsmay depend on the type of metal complex used orthe procedure employed for supporting the catalyst.An (n-BuCp)2ZrCl2-MAO catalyst supported on silicafree of adsorbed water (<0.1 wt %) but with surfacehydroxyl groups (2.7 wt %) copolymerizes ethyleneand 1-butene to a morphologically uniform productwith fewer fines (0.8 wt %) than a similar catalystsupported on silica dried at a higher temperature.89
MAO was allowed to react with silica containing 1-5wt % water; metallocenes were then contacted withthese supported activators. Ethylene-butene copoly-mers from these catalysts showed higher melt tensionthan those from catalysts on more rigorously dehy-drated supports.90
At Al/Zr ) 200, a variety of metallocene-MAOcatalysts were supported on silicas dried at varioustemperatures (Table 2).91 Supports dried at lowertemperatures afforded catalysts of higher activities;pretreating the support with AlMe3 also diminishedactivity.92 Analysis of the distribution of aluminumand silicon indicates a very even distribution ofcocatalyst on the support, with no more catalyst onthe outer surface than within the pores.93
High surface area sol-gel aluminas with largeconcentrations of hydroxyl groups (0.5 mmol/mmolsupport) were prepared by calcining a bohemiteprecursor, heating to 600 °C, and passing water-ladenhelium over the solid at 300 °C. Allowed to react withMAO, these supports can carry more aluminum thanconventional silica supports.94 Heterogeneous met-allocene catalysts based on these supports have muchhigher activity than the silica supports examined(Table 3), but the morphology of the product appearsto be poor.
Surface functionalities can be modified in order toinfluence catalyst performance. Silica modified byMe2SiCl2, reacted with MAO, then with Cp2ZrCl2 hasa higher catalyst activity than the same catalyst onunmodified silica.95 Silica can also be modified by(MeO)3Si(CH2)3X agents (X ) SH, OMe) before sup-porting ansa metallocenes for propylene polymeriza-tion.96 When X ) Cl, the catalyst performace suffersconsiderably.
E. Prepolymerization of Supported CatalystsThe vigorous activity of the catalyst in the early
stages of polymerization can cause uncontrolledfracturing of the catalyst particle. The particle sizedistribution of the polymer formed suffers accord-ingly. Very small particles (fines) do not fall back intothe fluidizing bed and are all too easily caught inrecycle lines. Large chunks can be formed from
Scheme 3 Table 2. Polymerization Performance of MetalloceneCatalysts Based on Support DehydrationTemperature
Catalyst for Olefin Polymerization Chemical Reviews, 2000, Vol. 100, No. 4 1353
polymer particles melting and fusing together. Theseare too heavy to be fluidized and fall to the distributorplate. Further adhesion of polymer to the walls of thereactor interferes with heat transfer, and the bulkdensity of the product is reduced as well. Microstruc-turally, the temperature spike in the initial phase ofpolymer growth could lead to broadening of molecularweight and composition distributions or lowering ofthe polymer melting point in propylene polymeriza-tions. With the long residence times used in mostcontinuous-slurry, bulk-monomer, or gas-phase pro-cesses, a rapid decrease in catalyst productivity isan undesirable consequence of reaching the diffusionlimit too quickly.
To moderate the initial burst of activity in asupported catalyst, the catalyst is prepolymerized byadding monomer at ambient or subambient temper-atures and low pressures. This coats the catalystparticle with 1-50 g of polymer per gram of catalyst.The diffusion barrier to monomer reacting with thecatalyst can lead to smoother polymerization profilesand improved particle morphology. Ethylene-pro-pylene copolymers prepared in bulk propylene slurryfrom a silica-supported Me2Si(Ind)2ZrCl2-MAO cata-lyst form individual spherical particles without reac-tor fouling, even at relatively high propylene com-positions (ca. 50%),97 and a silica-supported Me2Si(2-MeInd)2ZrCl2-MAO catalyst similarly prepolymerizedwith ethylene has high activity to produce polymerin a bulk propylene slurry process with high bulkdensity (0.36 g/cm3).98
Investigators at Mitsui have synthesized prepoly-merized catalysts by isolating dry metallocene-MAOon silica, slurrying in n-decane, and prepolymerizingwith ethylene in the presence of Al(i-Bu)3,99 Al(i-Bu)2H,100 or Al(i-Bu)2(OMe).101 They found that leav-ing out the aluminum reagent in the prepolymeriza-tion step led to a polymer of lower molecular weightwhen the catalyst was used in the polymerization andcopolymerization of ethylene. Failing to remove allthe toluene from the catalyst before prepolymeriza-tion in a slurry process can cause the catalyst toagglomerate in the prepolymerization step,102 al-though the prepolymerization can be carried out ina vapor phase process, which moistens the catalystwith a volume of an aliphatic solvent approximatelyequal to the pore volume of the supported catalyst.103
Insufficient drying of the prepolymerized catalyst (>2wt % volatiles) can also lead to poor flowability ofthe solids and problems feeding the catalyst into agas-phase polymerization process.104
Although prepolymerization using supported Cp2-ZrCl2-MAO proceeds without incident, prepolymer-izing supported catalysts of metallocenes affordingpolymer of higher molecular weight (e.g. (1,3-Me-BuCp)2ZrCl2, rac-Me2Si(2-Me-4,5-BenzoInd)2ZrCl2)can result in severe fouling. Addition of hydrogen toreduce the molecular weight of the prepolymer avoidsthis problem.105
As an alternative to prepolymerizing with a gas-eous monomer such as ethylene, Brant added hydro-carbon-soluble poly(4-methyl)styrene or low molec-ular weight waxes to the supported catalyst to fillthe pores of the support.106 Using a pore-filling
technique to add (n-BuCp)2ZrCl2 in 1-hexene, 1-octene,or styrene to MAO on silica at low temperatures, thenwarming to ambient temperatures fills the pores ofa silica support with polymer.107 Melting paraffin waxwith a Me2Si(2-Me-4,5-BenzoInd)ZrCl2-MAO cata-lyst on silica and pouring the mixture into pentaneproduces a solid which not only polymerizes pro-pylene with high activity, but also is essentially air-stable.108
V. Alumoxane-Free Supported Single-SiteCatalysts
Supporting single-site catalysts activated by non-aluminum agentssprincipally borate anions such as[B(C6F5)4]- or B(C6F5)3sis far more problematic thansupporting those activated by alumoxane-based ana-logues. These systems are highly prone to deactiva-tion by adventitious impurities. Even silica treatedat 800 °C has sufficient surface hydroxyl groups torender a [Cp2ZrMe][B(C6F5)4] catalyst inactive (Scheme4).
Treatment of the support material with alkylalu-minums passivates the support surface to make itcompatible with Cp′2MMe2-[Ct][B(C6F5)4].109 Thealkylaluminum-treated support itself is not an effec-tive cocatalyst. The supported catalysts can be usedin slurry, bulk-monomer, or gas-phase processes.110
Similarly pretreated alumina, MgCl2, and cross-linked polystyrene are also suitable support materialsfor these ionic catalysts. Partially or fully hydroxy-lated supports can also be capped by deprotonatingthe Si-OH groups with butyllithium or butylethyl-magnesium followed by reaction with BrC6F5;111 orby reacting silica with NH4F112 or chlorodimethyloc-tylsilane.113 Surprisingly, nonfluorinated borate ac-tivators, ordinarily not compatible in solution withmost metallocenes, can be used when the catalyst issupported. Cp2ZrMe2 and [n-Bu3NH][B(p-tolyl)4] de-compose to inactive materials in solution, but whensupported on silica the combination forms an activecatalyst, though no productivity data were pro-vided.114
“Constrained-geometry” titanium dialkyls such asMe2Si(C5Me4)(N-t-Bu)TiMe2 form active catalystswhen reacted with alkylaluminum-treated silica con-taining [HNMe2Ph][B(C6F5)4]115 or B(C6F5)3.116 Sepa-rate addition of alkylaluminum-treated silica withoutmetallocene to the supported ionic catalyst has beenclaimed to improve catalyst activity, probably byscavenging of reactor impurities.117 Diene complexessuch as Me2Si(C5Me4)(N-t-Bu)Ti(η4-C5H8), convertedto zwitterionic complexes when contacted withB(C6F5)3 (Scheme 5), may also be adsorbed on pre-treated silica to form an active supported catalyst.118
The use of functionalized dienes such as 1-phenyl-4-(4-N,N′-dimethylaminophenyl)-1,3-butadiene wasreported to give a modest improvement in catalystactivity; the inventors imply that the amino groupaffords improved adsorption of the metal complex tothe support.119
Scheme 4
1354 Chemical Reviews, 2000, Vol. 100, No. 4 Hlatky
The Me2Si(C5Me4)(N-t-Bu)TiMe2-B(C6F5)3 catalystsupported on polyethylene or silica was used in thefluidized-bed gas-phase polymerization of ethyleneand interpolymerization of ethylene and 1-olefinsand/or dienes; the densities of the copolymers can beas low as 0.898 g/cm3.120 Prepolymerization at lowtemperatures (<40 °C) was shown to improve cata-lyst activity significantly.121 A catalyst comprising thedimethyl or diene complex activated by [Ct][B(C6F5)4](Ct+ ) Ph3C+, HNMe2Ph+) or B(C6F5)3 and supportedon silica with a particle size less than 15 µm can bedispersed in a hydrocarbon solvent. Settling is slowenough that the slurry can be pumped into a solutionprocess.122
Because metal alkyl complexes can be unstable andin order to remove one step from the syntheticprocess, an alternative method of generating cationicmetal alkyls was developed. The metal halide isalkylated in situ using common trialkylaluminums,then converted to the cation by contacting with [Ct]-[B(C6F5)4] or B(C6F5)3. This technique has been usedwidely in the preparation of supported single-sitecatalysts. For example, Cp′TiCl3 complexes supportedon silica are catalytically inert when combined withAlMe3, but addition of [Ph3C][B(C6F5)4] or B(C6F5)3
activates the metal complex to form a catalyst for theatactic polymerization of propylene.123 Metallocenesbearing polar groups (e.g., Et(2-t-BuMe2SiO-Ind)2-ZrCl2) were reacted with AlMe3 on silica to fix themetallocene to the surface and alkylate the metalcenter. This catalyst copolymerizes ethylene and1-butene in the presence of B(C6F5)3 or [Ph3C]-[B(C6F5)4].124
Matsumoto generated group 4 metal catalysts bycosupporting bis(cyclopentadienyl)-, mono(cyclopen-tadienyl)-, or cyclopentadienyl-free compounds withferricinium or dimethylanilinium tetrakis(pentafluo-rophenylborate) on a variety of carriers. Triisobutyl-aluminum can be added in the support step or addedto the reactor with the catalyst. Spherical particleswith bulk densities as high as 0.36 g/cm3 are formedusing this technique.
Scrubbing the carrier surface free of residualhydroxyl groups improves catalyst activites. Solu-tions of mono- or bis(cyclopentadienyl) metal dichlo-rides reacted with alkylaluminums can be evaporatedonto passivated silica and activated by B(C6F5)3,126
[HNMe2Ph][B(C6F5)4],127 or [Ph3C][B(C6F5)4].128 Cross-linked polystyrene-divinylbenzene is claimed to bea superior support to even alkylaluminum-passivatedsilica for an (Ind)2ZrCl2-[Ph3C][B(C6F5)4]-Al(i-Bu)3catalyst, though, rather surprisingly, catalyst activi-ties were essentially the same when B(C6F5)3 was theactivator.129
Simple alkylaluminums are customarily used asthe alkylating component, but other agents can beused. Metallocene dichlorides reacted with MAO aresupported and prepolymerized before contacting with[HNMe2Ph][B(C6F5)4]; final activities are low withoutthe boron component.130 Butylethylmagnesium andeven butyllithium have been successfully used asalkylating agents, giving catalysts with activitiescomparable to those when Al(n-C6H13)3 was used.131
Although the usual method of preparing supportedsingle-site catalysts is to combine the metal compo-nent and activator on a support, another means ofactivation is to combine separately supported metalcomponent and activator. For example, Me2C(Cp)-
Scheme 5
Table 4. Supported Zirconium Catalysts Activated by Trialkylaluminums and Borate Salts
metal complex activator supportpre- or post-support
Catalyst for Olefin Polymerization Chemical Reviews, 2000, Vol. 100, No. 4 1355
(Flu)ZrX2 (X ) Cl, Me) on silica132 or MgCl2133 is
combined in liquid propylene with separately sup-ported [Ph3C][B(C6F5)4] as the sole component ofanother fraction of carrier. The reactor walls are notfouled by the syndiotactic polypropylene producedtherefrom.
VI. Supported Catalysts without CocatalystsMarks and co-workers examined the solid-state 13C
NMR spectra of Cp*2ThMe2 (Cp* ) η5-C5Me5) ad-sorbed on dehydroxylated alumina. Comparisonagainst model compounds suggested that the alu-mina surface was sufficiently Lewis acidic to abstracta methyl group, forming a three-coordinate [Cp*2-ThMe]+ cation which interacted weakly, if at all, withthe oxygen functionalities of the surface (Scheme6).134 Ethylene pulsed into a helium stream was
consumed as it passed over this catalyst or one basedon Cp*2UMe2-Al2O3.135
Polymerization also takes place when Cp′2ZrMe2(Cp′ ) Cp, Cp*) or Cp*ZrMe3 are supported ondehydroxylated alumina.136 While only some 4% ofCp2ZrMe2 centers are active, about 12% of theCp*ZrMe3 is converted to cationic centers. The orderof polymerization activity is Cp*ZrMe3 > Cp2ZrMe2≈ Cp*2ZrMe2. Unlike the actinide compounds, Cp*-ZrMe3 exhibits ethylene polymerization activity evenon partially dehydroxylated alumina.
Similar results were observed when MgCl2 wasused as the support. Although only some 10% ofthorocene centers supported on alumina polymerizeethylene, about 50% are active when MgCl2 is thesupport.137 Extending these results to group 4 met-allocenes, slurrying MgCl2 with Me2C(Cp)(Flu)ZrMe2or Et(Ind)2ZrMe2 affords an active catalyst for thesyndiospecific or isospecific polymerization of pro-pylene.8b
Solid-state 13C NMR analysis of Cp*2ThMe2 ad-sorbed on dehydroxylated silica suggests that thereis a stronger interaction between the oxygen atomsof the silica and the three-coordinate thorium frag-ment (Scheme 7), and indeed this combination is
catalytically inactive at low ethylene pressures.138
However, at 80 °C and 10 bar ethylene pressure, Cp2-ZrMe2 supported on silica dehydroxylated with Me3-SiCl, AlEt3, or Al(i-Bu)3 exhibits some activity.139
Remarkably, (n-PrCp)2ZrCl2 supported on silica haslimited polymerization activity, though the mecha-nism by which an active center is generated was notexplained.140
Sulfated zirconias, prepared by thermal decompo-sition of Zr(SO4)‚4H2O, have strongly Brønsted acidichydroxyl groups on the surface. Even though thesehydroxyl groups on alumina or silica deactivate Cp*2-MMe2 cations, active catalysts are generated fromthese metallocenes on sulfonated zirconia.141 Exten-sive charge-delocalization of the conjugate base wasdeemed the reason for this phenomenon (Scheme 8).
VII. Chemically Tethered Metal ComplexesThe frequent reason given for tethering single-site
catalysts to the support is to prevent the catalystfrom leaching from the surface during polymerizationand causing fouling in the reactor. Whether thecatalyst is actually desorbed from the support duringthe polymerization process is not totally clear. It is,after all, entirely possible to polymerize olefins withheterogeneous single-site catalysts while maintainingexcellent particle morphology and narrow particlesize distribution without tethering the metal complexto the support. Nor is leaching of the catalyst fromthe support the sole reason for poor morphology,which can occur in fluidized-bed gas-phase processesas well as solvent-based processes.
Furthermore, the solvent used in many leachingexperiments78,142 has been toluene, in which manymetallocene-MAO catalysts have some solubility,especially at high Al/M ratios. However, to the bestof the author’s knowledge, few if any commercialpolymerization processes use toluene as a diluent.Aliphatic hydrocarbons, bulk monomers, and fluid-izing gas streams are used in large-scale plants.Especially at the lower excess of aluminum used inmany supported catalysts (50-200:1), metallocene-MAO catalysts are insoluble in hydrocarbon sol-vents.143 The heptane extracts from a Cp2ZrCl2-MAOcatalyst supported on silica showed no activity inethylene polymerization, even when additional MAOwas added.144
The most common techniques for tethering single-site catalysts to supports are by contacting a reactivesupport with a substituent on the metal complex,constructing all or part of the ancillary ligand set onthe carrier, then reacting with a metal component;or by polymerizing through the substituents on themetal complex. The carrier can be tethered througha substituent on the cyclopentadienyl ring, througha substituent on the bridge in ansa-metallocenecomplexes, or through a heteroatom, principally inmono(cyclopentadienyl) metal complexes and non-metallocene procatalysts.
Binding the metal complex to silica through asubstituent on the cyclopentadienyl ring can be doneby reacting a substituent on the ring with the
Scheme 6
Scheme 7
Scheme 8
1356 Chemical Reviews, 2000, Vol. 100, No. 4 Hlatky
hydroxyl groups of the silica. A variety of mono- andbis(cyclopentadienyl) complexes bearing hydroxyl-reactive substitutents on one or two rings, including((MeO)3Si(CH2)3Ind)ZrCl3,145 ((MeO)3Si(CH2)3Ind)2-ZrCl2,146 (MeO)2MeSiCpTiCl3,147 and ((MeO)Me2SiCp)-CpZrCl2,148 have been prepared and contacted withsilica to produce catalysts which are catalyticallyactive in the presence of MAO.
The thallium salt of (1,5-bis(cyclopentadienyl)-hexamethyltrisiloxyl)(indenyl)zirconium dichloridereacts with p-tolylsulfonyl-treated silica to form atethered metallocene with a cyclopentadiene groupbound to the surface (Scheme 9). This catalystpolymerizes ethylene in the presence of MAO withactivities much higher than those of Cp(Ind)ZrCl2supported on silica, but still less than that of thehomogeneous catalyst.149
Partially hydroxylated silica substituted with ClCH2-PhSi(OMe)3 quaternizes the amino groups in Me2Si-(2-Me2NInd)2ZrCl2 yielding an ionic metallocene pro-catalyst which is active in propylene polymerizationwhen contacted with MAO (Scheme 10).150
Ansa-metallocenes tethered to a silica surfacethrough the bridging group have been prepared byreacting ClMeSi(Cp)2MCl2 (M ) Zr, Hf) with partiallydehydroxylated silica, either by itself151 or modifiedby agents such as (MeO)3Si(CH2)3NH2.152 The catalystactivity in ethylene-1-hexene copolymerization is
reduced by about 75% over the homogeneous variant.It has also been suggested that (i-PrO)MeSi(C5Me4)-LMCl2 complexes (L ) C5Me4, M ) Zr;153 L ) N-t-Bu, M ) Ti154) also react with silica to form supportedprocatalysts, though no specific examples were sup-plied.
Assembling the metallocene complex on the sup-port is a second method of preparation. Silica can bemodified using (EtO)3Si(CH2)3C5H5 to give a cyclo-pentadiene-bearing silica surface. Deprotonation withBuLi and reaction with CpZrCl3 affords dSi-O-(EtO)2Si(CH2)3C5H4(Cp)ZrCl2. The activity of thiscatalyst in ethylene polymerization is twice as highas that of a homogeneous CpZrCl3-MAO catalyst,though still only a third as active as the Cp2ZrCl2analogue.155 Similarly, (MeO)Me2Si-C9H7 can bereacted with the surface hydroxyl groups of silica toafford dSi-O-SiMe2-C9H7. This is then allowed toreact with M(NMe2)4 or Cp′M(NMe2)3 to form thetethered metallocene.156 A silica-bound cyclopenta-diene is also the result of the reaction of NaCp withchlorinated silica. Subsequent treatment withM(NMe2)4 or Cp′M(NMe2)3 results in a supportedmetallocene procatalyst.157
Ansa-metallocenes attached to silica through thebridging atom were prepared by reaction of ClMeSi-(Cp)(Flu) with partially dehydroxylated silica. Depro-tonation and reaction with ZrCl4 affords a supportedcatalyst active in ethylene polymerization whencombined with MAO.158 Reacting Cl2SiCp′ (Cp )Cp159 or Ind160) with silica produces a tethered ansaligand set from which a zirconocene complex can besynthesized and used in ethylene polymerization toform polyethylene particles with good bulk density(0.38-0.39 g/cm3) and no adhesion of polymer to thereactor. A similar synthetic methodology is used toreact the Li(TMEDA) salt of cross-linked polystyrenewith Cl2Si(Ind)2 or PhClSi(Ind)2.161
Soga and co-workers assembled ancillary ligandsets by reacting partially dehydroxylated silica withSiCl4, SnCl4, or 1,1,2,2-tetrabromoethylene followedby substitution with indenyl or fluorenyl anions.162
These are used to create tethered metallocenes(Scheme 11). The indenyl-based catalysts polymerizepropylene to isotactic PP with melting points as highas 164 °C, but a substantial amount of atacticmaterial is also formed from the meso isomer. Neody-mocene catalysts synthesized from the surface-bounddianion and NdCl3 and activated by Al(i-Bu)3 poly-merize ethylene with modest activity (7.72 g of PE/mmol Nd‚h).163 In a similar synthetic methodology,silica was treated with MeSiCl3 and indenyllithiumto form tSi-O-SiMe(Ind)2. This was deprotonated
Scheme 9
Scheme 10
Catalyst for Olefin Polymerization Chemical Reviews, 2000, Vol. 100, No. 4 1357
by BuLi and metalated with ZrCl4. Polyethylene ofhigh molecular weight and narrow molecular weightdistribution is formed when this material is activatedby MAO.164
Polysiloxane-supported tethered metallocenes havebeen synthesized by reaction of brominated poly-(methylhydrogen)siloxane-poly(dimethylsiloxane) withNaCp and subsequent reaction with ZrCl4 (Scheme12).165 Cohydrolysis of Cl2Si(Cp′)(Flu) and Me2SiCl2
forms a ligand-dimethylsiloxane copolymer whichcan be deprotonated and reacted with ZrCl4 (Scheme13).166 The MAO-activated catalyst formed when Cp′) C5Me4 is only feebly active in propylene polymer-ization, but when Cp′ ) Cp, a more vigorous systemis formed which produces syndiotactic polypropylene.
Synthesizing the metallocene on a polymeric sup-port can be done by reacting a chlorinated polymersuch as chloromethylated polystyrene with cyclopen-tadienide. This can be deprotonated to form thepolymer-bound Cp anion, which can react withCpZrCl3 to form polystyrene-bound Cp2ZrCl2.167 Amore elaborate metallocene was constructed when
the polymer-bound Cp anion is allowed to react withClMe2(Flu), followed by deprotonation and metalationwith ZrCl4 (Scheme 14).168 Activated by MAO, thismetallocene polymerizes ethylene in a hexane slurry.
A polystyrene-supported rac-Ph2Si(Ind)2ZrCl2 wasprepared by the procedure indicated in Scheme 15.169
Combined with MAO (Al/Zr ) 5000), this catalystpolymerizes ethylene at temperatures as high as 150°C. Elemental mapping indicates that the catalystis evenly distributed and located only on the surfaceof the polystyrene bead, and no Zr is contained insidethe bead; polymer growth occurs, then, only on thesurface.170
Ethylene-methyl acrylate (EMA) copolymers reactwith sodium cyclopentadienide yielding a polymer-bound Cp anion, which forms an EMA-bound met-allocene when combined with CpZrCl3 or ZrCl4(THF)2(Scheme 16).171 Both catalysts polymerize ethylenein isobutane or toluene slurries to polyethylene ofrelatively narrow molecular weight distribution (Mw/Mn ) 2.3-3.0) when activated by MAO.
All or part of the ligand set can be homo- orcopolymerized prior to metalation. 2-vinylfluorene ishomopolymerized or copolymerized with styrene us-ing 2,2′-azobisisobutyronitrile (AIBN) or BF3‚OEt2 asinitiators. The polymer, with a molecular weight of5000-20 000 daltons, is then deprotonated and re-acted with CpZrCl3 to form the polymeric procata-lyst.172 The substituted styrene complex is copoly-
Scheme 11
Scheme 12
Scheme 13
1358 Chemical Reviews, 2000, Vol. 100, No. 4 Hlatky
merized with styrene in the presence of AIBN yieldinga polymeric ligand set (Scheme 17).173 The zir-conocene dichloride derived from this copolymerpolymerizes propylene to syndiotactic polypropylenewith relatively high stereospecificity (rrrr ) 0.86-0.89 at 40 °C).
Polymer-bound metallocenes are also prepared bypolymerizing through a group on the cyclopentadi-enyl ring or the bridge.174 Alkenyl- and alkynyl-
substituted metallocenes such as (H2CdCHCp)2-ZrCl2,175 (H2CdCHCH2Cp)2ZrCl2,176 1,2-C2H4(H2CdCH(CH2)nInd)(Flu)ZrCl2 (n ) 1, 4),177 1,2-C2H4(H2CdCH(CH2)4SiMe2Ind)(Flu)ZrCl2,178 and Cp(2,7-(PhCdC-)2Flu)ZrCl2
179 can be reacted with MAO andprepolymerized with ethylene under low-pressureconditions to form heterogeneous cross-linked met-allocene polymers with or without silica as a filler.These can be used under more demanding conditions
Scheme 14
Scheme 15
Scheme 16
Catalyst for Olefin Polymerization Chemical Reviews, 2000, Vol. 100, No. 4 1359
for slurry or gas-phase polymerizations free of reactorfouling. Metallocenes bearing olefinic groups in thebridge, such as 4180 and 5,181 are self-immobilized
when copolymerized with ethylene in the presenceof MAO.
Metallocenes bound to polysiloxanes through theCp ring were prepared by reacting (H2CdCH-R-Cp′)2ZrCl2 complexes (Cp′ ) Cp, Ind) with poly-(methylhydrogensiloxane) in the presence of H2PtCl6‚6H2O (Scheme 18).182 Ansa-metallocenes bound to
polysiloxanes through the bridging atom are formedfrom hydrolysis of Cl2Si(Cp)2ZrCl2 (Scheme 19).183
Alt and co-workers attached metallocenes to poly-(methylsiloxane) microgels by reacting these supportswith cyclopentadienides bearing long-chain silyl chlo-ride substituents on the ring or in the bridge.Deprotonation and metalation with ZrCl4 affords thetethered metallocene (Scheme 20).184 These are eth-ylene polymerization catalysts in the presence ofMAO with activities ranging from 0.14 to 1.44 kg/gZr‚h.
Binding the metal complex to the support througha heteroatom is done in the cases of mono(cyclopen-tadienyl) metal complexes or nonmetallocene single-site catalysts. An amine-functionalized support isproduced from the reaction of silica with 3-amino-propyltrimethoxysilane. This is then allowed to reactwith Cp*TiCl3, affording a supported metal complex(Scheme 21).185 When contacted with MAO, a catalystis formed which copolymerizes ethylene with 1-octeneto polymers with narrow molecular weight distribu-tion and high comonomer content. Styrene-4-amino-styrene copolymers react with L(N-t-Bu)VCl2 com-plexes (L ) Cp, Cl) to form supported imidovanadiumprocatalysts (Scheme 22).186 With an AlEt2Cl cocata-lyst, the Cp derivative polymerizes ethylene with 10-50 times the activity of unsupported Cp(N-t-Bu)VCl2.
A polymeric support material is prepared by react-ing R,ω-amines with 1,5-dichlorohexamethyltrisilox-ane. This is deprotonated and allowed to react withCpZrCl3 to afford a procatalyst which, when con-tacted with 1000-1500 equivalents of MAO, poly-merizes ethylene with activities as high as 1100 kg/gZr‚h (Scheme 23).187
Eisen and co-workers attached a “constrained-geometry” titanium complex to silica or aluminathrough a pendant trimethoxysilyltrimethylene groupbonded to the nitrogen atom (Scheme 24).188 Unlikemany supported single-site catalysts, the ethyleneand propylene polymerization activity of the sup-ported compound cocatalyzed by MAO is quite similarto that of the homogeneous analogue.
Scheme 17
Scheme 18
Scheme 19
1360 Chemical Reviews, 2000, Vol. 100, No. 4 Hlatky
Catalyst libraries for combinatorial screening ofdiimine-based nickel and palladium catalysts can bedeveloped by attaching a diketone to a Merrifieldresin, reacting with a variety of anilines in thepresence of a dehydrating catalyst, and complexingwith the metal (Scheme 25). After each variant isactivated with MAO or borate salt, the 96-wellmicrotiter plate is exposed to ethylene and polymer-ization activity is qualitatively determined by infra-red imaging.189
Solid-phase supports used in combinatorial chem-istry were used to prepare a cross-linked polystyrenebead containing a tetraethylene glycol spacer. Thep-nitrosulfonate derivative of the polymer was sub-stituted with NaC5HMe3Et to form a supportedcyclopentadiene, which was allowed to react withCpTiCl3, making a tethered titanocene (Scheme26).190 With MAO, this polymerizes ethylene withrelatively low activity (41 g/mmol catalyst‚h) formingpolymer with a noodle-like morphology.
VIII. Chemically Tethered Activators
A. AlumoxanesChemically tethering the activator component,
instead of the metal complex, allows for flexibility inthe choice of metal complex while retaining some ofthe advantages that chemically tethered catalystsexhibit. This technique was one of the earliest sup-
ported metallocene disclosures. Kaminsky reactedAlMe3 with starch and lignin to form a surface-supported alumoxane. This was allowed to react withCp2ZrMe2 to form a catalyst with rather low activityin ethylene polymerization (3,000-13 000 g/g M;toluene slurry).191 Simple trialkylaluminums can beused to form supported alumoxanes by contactingAlMe3 with silica containing from less than 3 to 40%water.192 Addition of metallocene dichloride andevaporation affords a solid polymerization catalyst,although another method uses separately supportedmetallocene and MAO to form the active catalyst.193
Alternatively, a metallocene/AlMe3 mixture can beadded to undehydrated silica.194 Other materials suchas Mg(OH)2,192b clays and zeolites,195 MgCl2‚6H2O,196
or Al(O)OH197 can also be used as the solid hydrolysisagent. AlEt3 can be used as a substitute, with ametallocene/AlMe3 mixture added to the surface-bound ethylalumoxane.198 Mixtures of AlMe3 withAlEt3 or Al(i-Bu)3 mixtures are also effective forgenerating the alumoxane.199 The amount of alumox-ane bound to the silica can be adjusted by alteringthe amount of water on the silica, the ratio of waterto trialkylaluminum,200 or by washing the supportedmetallocene catalyst after preparation.201 Aging of thesupported cocatalyst for 2 weeks to 3 months isclaimed to impart a modest increase in catalystactivity.202
Investigators at BASF have noted that (n-BuCp)2-ZrCl2 contacted with AlMe3-treated “wet” silica andused to polymerize ethylene in an isobutane slurryresults in severe reactor fouling. Addition of a smallamount of n-butyllithium to the autoclave eliminatesthis fouling and allows for smooth continuous reactoroperations.203
A study of the relative performance of metal-locenes, alkylaluminums, and variously hydratedsilicas shows that the activity of the surface-gener-ated alumoxanes rivals that of supported MAO or
Scheme 20
Scheme 21
Scheme 22
Catalyst for Olefin Polymerization Chemical Reviews, 2000, Vol. 100, No. 4 1361
modified MAO (MMAO) catalysts (Table 5).204 Trim-ethylaluminum on calcined silica shows negligibleactivity, whereas triethylaluminum and tributyl-aluminum are effective cocatalysts only at higherlevels of silica hydration. Cp2ZrCl2 activated bysurface-hydrolyzed diethylaluminum chloride hasonly feeble activity.
B. Boron ActivatorsAnother means of ensuring that the ionic catalyst
formed from the metal component and the activatorin non-alumoxane systems is not leached from thesupport has been to covalently bind the activator,instead of the metallocene, to the support material.Initial efforts used strongly acidic ion-exchange resinsbearing -SO3H groups to generate active catalystswhen allowed to react with Cp′2ZrCl2-Al(i-Bu)3.205 An(Ind)2ZrCl2-Al(i-Bu)3 was also successfully activatedby an ionic [Ph3C][(polymer)-SO3] support materialand used in ethylene-1-hexene copolymerization withan activity of 1000 g of polymer/g of catalyst‚h.206
Scheme 23
Scheme 24
Scheme 25
Table 5. Ethylene Polymerization with ZirconocenesSupported on Water-Laden Silicas
1362 Chemical Reviews, 2000, Vol. 100, No. 4 Hlatky
Turner postulated, but did not specifically exem-plify, using a partially hydroxylated silica surface tobind a polyfluorinated tetraphenylborate anion bear-ing a reactive group (Scheme 27).207 The essence ofthis idea was later put into practice by investigatorsat Dow and Nippon Polyolefins. Partially hydroxy-lated silica reacts with [HNMe2Ph][(C6F5)3B(C6F4-RCl)] (RCl ) SiCl3, SiMe2Cl, (CH2)8SiMe2Cl) to forma surface-bound activator for Cp′2ZrCl2-Al(i-Bu)3systems with improved control of fines (Scheme28).208 The reaction of silane-modified silicas with [R3-NH][(C6F5)3B-Ar-OH] salts (Ar ) phenyl, biphenyl,naphthyl) also affords supported activators for Me2-Si(C5Me4)(N-t-Bu)TiMe2 complexes in slurry polym-erization processes (Scheme 29).209 The same ammo-nium salts may be reacted with AlR3-treated silicasand used as activators for Me2Si(C5Me4)(N-t-Bu)Ti-(η4-diene) complexes.210
Noninterfering anions covalently bound to poly-mers have been prepared by the AIBN-initiatedcopolymerization of styrene with trialkylammonium4-styryltris(pentafluorophenyl)borate (Scheme 30).High-density polyethylene prepared from Cp2ZrCl2-Al(i-Bu)3 and this activator shows no signs of reactorfouling in a slurry polymerization.211
The reaction of neutral bis- and tris(pentafluoro-phenyl)boranes with silica surfaces can also lead tosupported ionic activators. B(C6F5)3 acts as a Lewisacid toward the surface hydroxyl groups of silica,
affording a Brønsted acid capable of reacting withCp′2ZrMe2 procatalysts. Ammonium salts, which alsofunction as ionic activators, are formed on reactionwith tertiary amines.212 Ward and Carnahan depro-tonated the hydroxyl groups with butyllithium priorto reaction with B(C6F5)3; methathesis of the lithiumsalt with Ph3CCl generates the supported tritylcomplex (Scheme 31).213
Research at Hoechst has led to the fixing of neutraltriarylborane activators to silica surfaces. This wasachieved by reacting HB(C6F5)2 with silica modifiedby vinyltriethoxysilane (Scheme 32) or substitutedtris(polyfluorophenyl)boranes with partially dehy-droxylated silica (Scheme 33). The supported neutralactivators can also be quaternized by reaction withLi(C6F5).214
The anion, even if noninterfering, can have aprofound effect on the performance of the catalyst.215
Another method of chemically anchoring ionic boron-based activators is to bind the cationic component tothe surface. This has been done by reacting (MeO)2Si-
Scheme 26
Scheme 27
Scheme 28
Scheme 29
Scheme 30
Catalyst for Olefin Polymerization Chemical Reviews, 2000, Vol. 100, No. 4 1363
(C6H4NMe2)2 with silica, protonating with HCl, andmetathesizing with Li[B(C6F5)4].216 Polymer-boundcations are prepared by reaction of secondary amineswith chloromethylated styrene, followed by reactionwith [R3NH][B(C6F5)4] salts (Scheme 34).217 Althoughthe active ionic catalyst produced from the reactionof the support with Cp′2ZrMe2 is not chemicallybound to the support, the higher dielectric of thesupport with respect to the polymerizing environ-ment (1-hexene in hexane) discourages leaching ofthe catalyst from the support and promotes goodparticle morphology.
IX. Supported Group 3 and LanthanideSingle-Site Catalysts
Soga synthesized the surface-bound ansa-neody-mocene complex 6 which was activated by a number
of alkylating agents to generate active ethylenepolymerization catalysts.218
Alkylaluminum cocatalysts such as AlMe3 andMAO generate less active catalysts (1-8 kg PE/mol
Scheme 31
Scheme 32
Scheme 33
Scheme 34
1364 Chemical Reviews, 2000, Vol. 100, No. 4 Hlatky
Nd‚h) than do butyllithium (19 kg PE/mol Nd‚h) orbutylethylmagnesium (91 kg PE/mol Nd‚h). TheBuEtMg-activated catalyst exhibits even higher ac-tivity at elevated temperatures: at 150 °C, thecatalyst rate goes up to 219 kg PE/mol Nd‚h. Cp*2-SmMe(tetrahydrofuran(THF)) supported on MgOpolymerizes ethylene in the absence of a cocatalyst,but the activity appears to be poor (1.5 kg PE/molSm‚h).219
X. Supported Group 5 Single-Site Catalysts
Compared to studies on single-site catalysts of theGroup 4 metals, research on heterogenized Group 5single-site catalysts is very limited. Apart from thepolymer-supported vanadium complexes notedabove,186 CpVCl3 and alumoxanes have been sup-ported on silica for the vapor-phase polymerizationof butadiene. The finished catalyst was prepared bya variety of methods: supporting a CpVCl3-MAOmixture on silica,220 prepolymerizing with butadienein a slurry before isolating the final catalyst,221 andgenerating the alumoxane by treating silica with aAlMe3-Al(i-Bu)3-H2O mixture, isolating the sup-ported alumoxane, and reacting with CpVCl3.222
Polybutadiene of principally cis-1,4 microstructure isformed with molecular weights over 3 000 000.
XI. Supported Group 6 Single-Site Catalysts
Of course, the first supported group 6 metallocenecatalyst which comes to mind is Cp2Cr on silica,
developed in the early 1970s.223 This should beconsidered a heterogeneous catalyst and not a truesupported single-site catalyst; the nature of the activesite remains unclear even after 25 years of research,and the polymer produced from this catalyst has abroad molecular weight distribution, suggesting thepresence of multiple polymerizing sites.
Other chromium-based catalysts have been ex-plored which, when supported, afford polyethylenewith relatively narrow molecular weight distribution.These are based on mono(cyclopentadienyl) chro-mium alkyl complexes first explored by Theopold.224
These may be Cr(II) compounds such as [Cp*-CrMe]2,225 Cr(III) oxo compounds such as Cp*Cr(O)-Me2,226 neutral and cationic Cr(III) compounds suchas Cp*CrMe2(THF) and [Cp*CrMe(THF)2][BPh4],227
mixed valence dimers such as Cp*Cr(η1-CH2Ph)(µ-η3:η6-CH2Ph)CrCp*,228 or even anionic complexessuch as [Li][Cp*Cr(CH2Ph)3] (Table 6).229
Aluminum phosphate and alumina-aluminumphosphate supports are preferred for producing cata-lysts with high activities and relatively narrowmolecular weight distributions (Mw/Mn ) 2-4). Silica-supported catalysts afford polymers with muchbroader distributions. Isobutylalumoxane was usedas the cocatalyst; some catalytic activity was observedeven in the absence of cocatalyst, and AlMe3 and BEt3
led to inferior performance. Striking as well is thevast increase in catalyst activity when the chromiumcomplexes are supported. This is contrary to thegeneral trend in group 4 complexes, where heterog-enization of the complex diminishes activity.
Table 6. Ethylene Polymerization by Chromium Catalysts
Catalyst for Olefin Polymerization Chemical Reviews, 2000, Vol. 100, No. 4 1365
XII. Supported Late-Transition Metal Single-SiteCatalysts
The nickel 1,2-diimine complexes R2C2(dNR′)2NiX2(7; R ) H, R′ ) 2-isopropylphenyl, 2,6-diisopropyl-
phenyl) have been contacted with MAO on silicaseither by itself230 or prepolymerized with ethylene231sand used to polymerize ethylene in toluene or hexaneslurry. Polymerization using the prepolymerizedcatalyst affords polymer with a high bulk density of0.40 g/cm3.
Extrapolating from solution polymerization data inthe literature, investigators at Exxon predicted thatunder gas-phase polymerization conditions employed(220 psi, 63 °C), polyethylene produced from acenaph-thalenebis(2,6-diisopropylphenylimine)nickel dibro-mide-MAO would have a melting point of 66 °C andsome 53 branches/1000 C. In a continuous fluidized-bed gas-phase polymerization, the polymer actuallyproduced from this catalyst supported on silica hada melting point of 91 °C and only 34 branches/1000C, suggesting that these catalysts can be used toprepare morphologically regular particles withoutrisk of melting and fouling.232
Supported catalysts for the alternating copolym-erization of ethylene and carbon monoxide are formedwhen palladium on alumina is reacted with [NO]-[BF4] in an acetonitrile slurry. In the presence of 1,3-diphenylphosphinopropane, an active catalyst is gen-erated which can be used in slurry or gas-phaseprocesses.233
XIII. Other Support Materials
A. Magnesium ChlorideMagnesium chloride, a widely used support in
conventional Ziegler-Natta catalysts, has been stud-ied far less extensively than silica as a carrier forsingle-site catalysts. Reaction of dibutylmagnesiumby tert-butyl chloride in a diisoamyl ether-hexanemixture produces MgCl2 with very narrow particlesize distribution. Toluene solutions of zirconocenesin the presence234 or absence235 of a proton donor suchas n-butanol are supported, then reacted with MAOto form active catalysts. Highly porous MgCl2 sup-ports are prepared by the dealcoholysis of a MgCl2‚3EtOH adduct. These are allowed to react withzirconocene-MAO mixtures to form active supported
catalysts for ethylene homo- and copolymeriza-tions.236 Lin prepared MgCl2-supported metallocenecatalysts using a one-pot method: Bu2Mg was addedto a mixture of MAO and i-BuAlCl2 or n-BuClfollowed by reaction with (n-BuCp)2ZrCl2. Thesecatalysts exhibited twice the activity in ethylenepolymerization as silica-supported analogues.237
MgCl2‚nTHF solutions, produced from the reactionof magnesium and 1,2-dichloroethane in THF, canbe reacted with a THF solution Cp2MCl2 (M ) Ti,Zr) and isolated as a solid238 or supported on silica.239
The Cp2TiCl2-MAO-MgCl2 catalyst exhibits higheractivity in the xylene slurry polymerization of eth-ylene than does the homogeneous catalyst.240 Unlikethe homogeneous catalyst, the catalyst activity in-creases with increasing temperature, but when hex-ane is the diluent, the activity declines above 50 °C.A Cp2ZrCl2-MgCl2 adduct is more active in ethylenepolymerization (heptane slurry) if treated with atrialkylaluminum before contacting with MAO. Thenumber of active sites is only about 20% of those inthe homogeneous catalyst.241
Soga and co-workers used the Lewis acidity ofMgCl2 to fix the metallocene complex Cl2Si(Ind)2ZrCl2(8).242 Activated by MAO or Al(i-Bu)3, this catalyst
polymerizes propylene to isotactic polypropylene, butwith an activity about 100 times less than that ofMe2Si(Ind)2ZrCl2-MAO. The Me2C(Cp)(Flu)ZrCl2-MAO-MgCl2 catalyst was also used in the syn-diospecific polymerization of propylene at 20 °C; inthis case, the catalyst activity was somewhat higherthan that of the homogeneous catalyst with lessatactic product formed.243
B. ZeolitesZeolites have begun to attract more interest as
supports for single-site catalysts. Unlike silica, withits amorphous structure and wide distribution of poresizes, zeolites have more regular structures, poresizes, and supercages. Because the zeolite counter-cations (Na+, H+, NH4
+) can be ion exchanged, thepossibility exists of electronically “tuning” the sup-port.
The faujasite zeolite NaY can be treated with MAOor AlMe3, then with Cp2MCl2 (M ) Ti, Zr) to formthe catalyst.244 There is no activity in MAO-activatedcatalysts below Al/Zr ) 186 and activity is negligiblewhen AlMe3 is used. Catalyst activites are lower thanthe homogeneous analogues, but the polymer molec-ular weights are higher.
1366 Chemical Reviews, 2000, Vol. 100, No. 4 Hlatky
Dealumination of NaY by NH4SiF6 leads to agradual decrease in total surface area and microporevolume, but an increase in the external surface areaand Si/Al ratio. The gradual dealumination of NaYleads to an increase in activity of a supported Cp2-ZrCl2-MAO catalyst, though again the activity waslower and the polymer molecular weights higher thanthose of the homogeneous analogue.245 Similar trendswere observed in the conversion of NaY to HY bytreatment with (NH4)2(SO4).246 Sodium mordenite hasa higher Si/Al ratio than the Y zeolites and affordsthe highest catalyst activity.
The copolymerization of ethylene with 1-olefinscatalyzed by homogeneous Cp2ZrCl2-MAO catalystsand catalysts supported on HY zeolite shows a lossin activity on heterogenization, an increase in mo-lecular weight, and a decrease in comonomer incor-poration (Table 7).247 The ansa-metallocenes Et-(Ind)2MCl2 (M ) Zr, Hf) display no attenuation ofcomonomer incorporation. The authors hypothesizethat the smaller metallocenes are in the pores of thezeolite, into which diffusion of the comonomer isdifficult, and the ansa-metallocenes, not adsorbedinside the pores, are located on the exterior and aretherefore more accessible to comonomer.
To accommodate these larger metallocenes andpolymerize larger monomers such as propylene,investigators have turned to the mesoporous molec-ular sieves MCM-41 and VPI-5. An X-ray absorptionfine structure, extended (EXAFS) analysis of Et-(Ind)2ZrCl2-MAO catalyst shows that the indenylframwork remains intact after supporting. No Zr-Cl bonds are observed but the presence of a Zr-Cbond was suggested.248 In the polymerization ofpropylene244b,249 the melting point of the polymer ishigher than that produced from the homogeneousanalogue, though the catalyst activity suffers some-what. Addition of AlMe3 as a scavenger depressescatalyst activity as well.249a In the oligomerization ofethylene and propylene by Et(Ind)2ZrMe2, the alum-oxane is best produced by in situ hydrolysis of AlMe3
by the silanol groups of MCM-41; attempts to usecommercial MAO resulted in insufficient adsorptionof the aluminum cocatalyst for significant catalystactivity.250
C. ClaysClays such as montmorillonite, hectorite, and mica
have also been employed as carriers for single-sitecatalysts. Impregnating an aqueous suspension ofclay particles averaging 10 µm with Brønsted acidssuch as HNMe2Ph+, drying, and reacting with a Cp′2-ZrCl2-AlR3 mixture affords an active catalyst forolefin polymerization.251 Catalyst activities are in-creased when longer-chain ammonium cations suchas HNMe2(n-C18H37)+ are used.252 The alkylaluminumacts only as an alkylating agent for the metalcomponent: active catalysts are obtained when Cp2-ZrMe2 is contacted with clays impregnated withtertiary ammonium cations without further recourseto alkyating agents or scavengers.253
Investigators at Mitsubishi have taken anotherapproach to using clay supports. Montmorillonite,vermiculite, and hectorite were allowed to react withAlMe3, followed by a Cp2ZrCl2-AlMe3 mixture.254 Thecatalyst activity is proportional to the pore volumeof the support. Ion-exchange reactions of montmo-rillonite with a variety of metal salts and mineralacids were used to modulate the activity of catalystsfor ethylene255 or propylene256 polymerization. Thetreated support is heat-dried or spray-dried beforecontacting with a metallocene-AlR3 mixture. Mix-tures of mica and smectite afford catalyst and poly-mer particles of greater bulk density than does micaalone or mica mixed with silica.257 Mixing TiO2 withMe2Si(H4-Ind)ZrCl2-AlEt3 on HNO3-treated smec-tite is reported to reduce adhesion of the polymerparticles to the reactor wall.258
Comparing syndiotactic polypropylene from Ph2C-(Cp)(Flu)ZrCl2-MAO as a homogeneous catalyst andsupported on silica and HY zeolite, the activity of thezeolite-supported catalyst was lower than that fromthe homogeneous catalyst or the catalyst supportedon silica, but the syndiotacticity (82-83% rrrr pen-tads) was higher than the silica-supported catalyst(77.5%) and approximately equal to that from thehomogeneous catalyst (83%).259
D. PolymersPorous polyethylene powder, either by itself260 or
impregnated with Al(OEt)3,261 acts as a carrier for
Table 7. Ethylene Copolymerizations Using Zirconocenes Supported on HY Zeolite
Catalyst for Olefin Polymerization Chemical Reviews, 2000, Vol. 100, No. 4 1367
metallocene-alumoxane catalysts for ethylene orpropylene polymerization and copolymerization.Granulated polypropylene was used as the supportfor a Me2Si(H4-Ind)2ZrCl2-MAO catalyst to producegranular elastomer in the gas-phase copolymerizationof ethylene and propylene.262 A prepolymerizationstep was added in the bulk-monomer polymerizationof propylene by a Me2Si(Me3Cp)2HfCl2-MAO catalyston polypropylene; no scaling on the reactor walls wasobserved.263 A Me2Si(Ind)2ZrCl2-MAO catalyst sup-ported on polypropylene granules loses none of itsactivity in propylene polymerization even after 2months storage.264
Polymerization of propylene by an unsupportedMe2Si(2-MeInd)2ZrCl2-MAO catalyst results in ex-tensive sheeting on the walls and stirrer of thereactor. When the same catalyst is supported onporous powdered high-density polyethylene, isotacticpolypropylene, or nylon granules, morphologicallyuniform product is produced without fouling.265 It hasalso been suggested that spray-drying microparticlesof polystyrene formed in an emulsion polymerizationagglomerate into regular macroparticles which canbe used as supports for metallocene catalysts.266
Styrene and divinylbenzene (DVB) were copolymer-ized in the pores of silica using AIBN as an activator.This polymer-silica support was treated with MAO,then Me2Si(2-Me-4-PhInd)2ZrCl2 to form a catalystfor propylene polymerization.267
Polymers with polar groups can also be used assupports for single-site catalysts. Cross-linked poly-styrene which has been chloromethylated, or acylatedwith CH3COCl-AlCl3 then reduced with NaBH4(Scheme 35), functions as a support for Et(Ind′)2ZrCl2-
MAO catalysts (Ind′ ) Ind, H4-Ind).268 In this study,unfunctionalized polystyrene or functionalized poly-styrene with insufficient cross-linking (ca. 4% DVB)gave inferior activities and extensive reactor fouling.
With a Cp2ZrCl2-MAO catalyst, the nature of thefunctional group had a profound influence on themolecular weight of the ethylene-1-hexene polymerproduced, ranging from a melt index (a measurementof molecular weight inversely proportional to Mw) of1.9-1500 (Table 8).269 When the metal component is(n-BuCp)2ZrCl2, the dramatic differences in molecularweight are largely moderated.270
Styrene, DVB, and acrylamide can be copolymer-ized using an AIBN initiator to form a functionalizedterpolymer. This support is unreactive toward Cp2-
ZrCl2, but forms a supported activator when con-tacted with MAO. This catalyst copolymerizes eth-ylene and 1-octene to a copolymer little different inits comonomer distribution from that prepared usinga homogeneous catalyst.271
Porous acrylonitrile-DVB copolymer further re-acted with diamines or triamines provides a supportfor Cp′2ZrCl2-MAO catalysts.272 The catalyst activityrivals that of silica-supported analogues and noadhesion of polymer to the reactor walls or stirrerwas observed. Polypropylene grafted with maleicanhydride allowed to react with MAO acts as asupport for a variety of metallocenes.273 The numberof gels in the polymer is lower than when silica isused as the carrier. Porous vinylpyridine-DVB274
and poly(vinyl chloride)275 have also been reportedas suitable support materials for metallocene cata-lysts.
Alt and co-workers used poly(methylsiloxane) mi-crogels as substrates for supporting MAO (Scheme36).276 These supports are amenable to functional-
ization through surface -SiHMe2 groups, thus chang-ing the properties of the support and ultimately thecatalytic performance.
E. Miscellaneous SupportsCyclodextrins treated with MAO or AlMe3 serve as
supports for Cp2ZrCl2-AlMe3 or Cp2ZrCl2-MAOcatalysts in ethylene polymerization.277 Additionalalkylaluminum (AlMe3, AlEt3, or MAO) is needed toobtain meaningful activity from the catalyst. Poly-styrene is formed when Cp*TiCl3 is the metal com-ponent. Talc treated with MgR2 complexes, then with
Scheme 35
Table 8. Ethylene Polymerization by ZirconocenesSupported on Cross-Linked Polystyrenes
1368 Chemical Reviews, 2000, Vol. 100, No. 4 Hlatky
n-butanol is contacted with Cp2ZrCl2 to form asupported metallocene. This is activated by MAO inan isobutane slurry for the polymerization or copo-lymerization of ethylene.278
Hollow MgCO3 and CaCO3 particles, either un-treated or treated with alkylaluminums, were usedas carriers for metallocene-MAO catalysts in ethyl-ene279 and propylene280 polymerizations. Rac-Me2Si-(Me3Cp)2HfCl2 and [HNMe2Ph][B(C6F5)4] can be co-supported on CaCO3 and activated by Al(i-Bu)3 toform an active catalyst for the isotactic polymeriza-tion of propylene.281
Fillers and pigments are added to polyethylene inthe extrusion stage to change the color, stiffness, ormagnetizability of the polymer. These same fillerssdyes, glass, ceramics,282 or metals283scan function assupports for metallocene-MAO catalysts, improvingthe uniformity of filler distribution through thepolymer.
XIV. Heterogeneous Single-Site Catalysts withoutCarriers
MAO is commercially available as a solution intoluene or aliphatic hydrocarbons. The solvent canbe evaporated to produce a white pyrophoric solidthat can be used as both a cocatalyst and a support.Evaporating and drying toluene solutions of MAOunder high-shear conditions ensures that a particu-late solid is formed.284
Finely divided particles of MAO are precipitatedfrom a toluene solution by addition of n-decanefollowed by evaporation. Suspension of these particlesin decane followed by reaction with toluene solutionsof Cp′2ZrCl2 (Cp′2 ) Cp2
285 or Et(Ind)2286) affords a
solid catalyst which can be used in solution or gas-phase polymerization processes using ethylene orpropylene as the monomers. Solids also separate froma toluene solution of MAO on addition of an equalvolume of hexane or isobutane.287 Insoluble gels intoluene solutions of MAO, ordinarily a nuisance, canbe filtered off, resuspended in aliphatic hydrocarbons,and reacted with metallocene dichlorides to produceactive catalysts for olefin polymerization withoutreactor fouling.288
Alumoxane solids are precipitated from mixturesof toluene and aliphatic hydrocarbons by addition ofmethylboroxine or methoxyboroxine,289 catechol bo-rane,290 and organic peroxides and carbonates.291
Reaction with metallocene dichlorides affords a cata-lyst for olefin polymerization in an isobutane slurry.Cross-linking agents such as p-hydroquinone292 andR,ω-diols such as 1,6-hexanediol293 also precipitateMAO from toluene. In the former case, activation ofEt(Ind)2ZrCl2 or Cp2ZrCl2 only occurred when ad-ditional trialkylaluminum was added.
In the presence of an emulsifier, water and AlMe3react in hexane to form MAO particles about 5-20µm in diameter. When contacted with metallocenedichlorides, solid catalysts are formed which givegood particle morphology and high bulk density inhexane-slurry polymerizations of ethylene or bulkmonomer polymerization of propylene.294
In fact, it is not necessary to isolate solid MAOparticles to achieve uniform polymer morphology. A
precontacted metallocene-MAO catalyst can be at-omized into a stirred-bed295 or fluidized-bed296 gas-phase reactor to give uniform particles of good bulkdensity. In the latter case, the catalyst is sprayed intothe reactor into a particle-lean zone such as justabove the distributor plate or in the expansion sectionat the top of the reactor. The catalyst solution, atleast part of which consists of a highly volatilecompressed or supercritical fluid such as ethane, isinjected into the reactor using a spray nozzle.297
In solution, a metallocene-MAO mixture can beprepolymerized at low temperature (10-25 °C) andpressure to form catalyst-impregnated polymer par-ticles. These are then polymerized in a second stepat more demanding conditions to form the finalpolymer product.298 The use of ultrasonic irradiationhas been claimed to aid the prepolymerization of aMe2Si(2-Me-4-Ph-Ind)2ZrCl2-MAO catalyst by pro-pylene.299 Addition of polyisobutylene as a viscositymodifier to a Cp2ZrCl2-MAO mixture in the prepo-lymerization process aids in the recovery of thepolymer-supported catalyst.300 Aging a toluene solu-tion of Me2Si(Ind)2ZrCl2 and MAO in the absence ofdaylight before addition to liquid propylene treatedwith MAO is claimed to give polypropylene particleswith narrow particle size distribution.301 Ethylene,propylene, and 1-butene are terpolymerized withoutreactor fouling by a Et(H4-Ind)2ZrCl2-tetraisobutyl-alumoxane catalyst when the 1-butene fraction in theliquid phase is greater than 15 wt %.302
XV. Supported Mixed Single-Site CatalystSingle-site catalysts characteristically produce poly-
mers with narrow molecular weight and compositiondistributions. Although this leads to many improve-ments in physical properties (clarity, impact resis-tance, environmental crack resistance), it is alsowidely held that these narrow distribution polymersare more difficult to process and have a highertendency to melt fracture, especially at higher mo-lecular weights. Controllable broadening of molecularweight distribution and composition distribution us-ing single-site catalyst is therefore desirable formaking resins suitable for certain applications.
One method is to carry out the polymerization ina two-reactor system, in which the catalyst polymer-izes monomer in a first reactor under one set ofconditions (temperature, pressure, comonomer andhydrogen concentration) and then is transferred toa second reactor operating under a different set ofconditions. Another method is to use in one or morereactors two catalysts producing polymers of differentmolecular weight and with different responses tohydrogen and comonomer.
Cp2HfCl2 and Et(Ind)2ZrCl2 were supported onsilica individually and together to determine theinfluence of ethylene and hydrogen pressure on themolecular weight distribution of the polyethyleneproduced (Table 9).303 Unimodal and bimodal poly-mers are produced depending on polymerizationconditions. The relative contribution by the zirconiumcomponent to the molecular weight distribution curveincreases with increasing ethylene pressure andtemperature. The hafnium component is more reac-
Catalyst for Olefin Polymerization Chemical Reviews, 2000, Vol. 100, No. 4 1369
tive toward hydrogen, whereas the zirconium com-ponent is relatively unaffected. At high H2 concen-trations, Cp2HfMe2 forms the low molecular weightfraction while Et(Ind)2ZrCl2 forms the high MWfraction, opposite of the contributions in the absenceof H2.
Changes in just the ligand environment around themetal are sufficient to alter the molecular charac-teristics of the polymer produced. Syndiotactic polypro-pylene with a broadened molecular weight distribu-tion (4.3-4.7) is formed when propylene is polymerizedby Ph2C(Cp)(Flu)ZrCl2 and Me2C(Cp)(2,7-(t-Bu)2Flu)-ZrCl2 co-supported on silica and activated by MAO.304
In-reactor blends of isotactic and syndiotactic polypro-pylene are prepared from Me2Si(2-MeInd)2ZrCl2 andMe2C(Cp)(Flu)ZrCl2 on silica treated with MAO.305
Blends of isotactic and elastomeric polypropyleneresult from propylene polymerization using a catalystprepared by adding an Et(Ind)2ZrCl2-MAO solutionto tetra(neophyl)zirconium supported on alumina.306
Polymers with molecular weight distributions as highas 32 are formed.
In the preparation and operation of mixed single-site catalysts, investigators at Exxon found that thebest particle morphology in propylene polymeriza-tions using a Me2Si(H4-Ind)2ZrCl2-Me2Si(2-Me-Ind)2ZrCl2-MAO catalyst on silica resulted when atoluene solution of one of the metallocenes wassupported first by a pore-filling method and dried,then contacted with a solution of the second metal-locene with MAO and dried.307 Other permutationsin catalyst preparation resulted in reactor fouling.Gas-phase copolymerization of ethylene and hexeneby a mixed (n-BuCp)2ZrCl2-Me2Si(2-MeInd)2ZrCl2-MAO catalyst could be run with the componentstogether on a silica support, injected into the reactorunsupported, or run with one of the componentssupported and the other unsupported.308
XVI. Comparison of Homogeneous andHeterogeneous Catalysts
It is, of course, most desirable that the molecularcharacteristics of the products produced from het-erogeneous single-site catalysts resemble as closelyas possible those of their homogeneous counterparts,mirroring the narrow molecular weight distribution,
random distribution of comonomer and, in the caseof stereospecific polymerization, high stereoregularityand melting point.
The most notable difference between the twofamilies is catalyst activity. With few excep-tions,29,225-229 in myriad cases, the activity of thesupported catalyst is half to a tenth that of thesoluble catalyst. This is widely ascribed to diminisheddiffusion of monomer into the interior pores of thesupported catalyst, but may also be the result offewer active centers present in the heterogeneousvariant. Catalyst centers could be deactivated whensupported, or may not be generated in the metal-cocatalyst interaction. Tait and co-workers deter-mined that 91% of zirconocene centers were activatedby MAO in solution, but when the metallocene wassupported on silica, the concentration of active sitesgenerated by MAO was only 9% of the total zirconiumsupported.309
The molecular weight of the polymer is for the mostpart unaffected or somewhat higher when a single-site catalyst is supported. This suggests that thelower activity of the catalyst is due to a reducednumber of active centers; were the propagation ratelower for a supported catalyst, the rate of terminationwould have to be reduced proportionately or more forthese molecular weight observations to hold.
An extensive study of the effect of temperature onpropylene polymerization using homogeneous andsupported Me2Si(2-Me-4,5-BenzoInd)2ZrCl2-MAOcatalysts shows that changes in activity, molecularweight, isotacticity, and polymer bulk density weremore moderate for the supported catalyst than thesolution catalyst.310 The melting point of i-PP fromthis metallocene is 147 °C for the homogeneouscatalyst, declining to 144 °C when supported. Sub-stituting [HNMe2Ph][B(C6F5)4] as the activator af-fords polymer with the same melting point as thehomogeneous catalyst.311 Although the molecularweight of the polypropylene from rac-Me2Si(2,4-Me2-Cp)(3′,5′-Me2Cp)ZrCl2-MAO catalyst increases whensupported on silica (93 000 to 190 100), the meltingpoint of the polymer is unaffected.312
The effect of heterogenization on response tocomonomer is unclear. Comparing the compositionof ethylene comonomers with 1-hexene or 1-octene,Collins and co-workers noticed a slightly less branched
Table 9. Effect of Ethylene Pressure and H2 Concentration on Cp2HfCl2-Et(Ind)2ZrCl2-MAO Catalysts
1370 Chemical Reviews, 2000, Vol. 100, No. 4 Hlatky
copolymer when a metallocene-MAO catalyst issupported on sol-gel alumina than when the catalystwas used in solution; they attributed this to greaterdiffusion barriers for the supported catalyst.94 Nodifference was observed in comonomer responsetoward 5-(N,N-diisopropylamino)1-pentene when co-polymerized with ethylene using homogeneous Me2-Si(Ind)2ZrCl2-MAO and the same catalyst supportedon silica.313
XVII. Other Process ConsiderationsHeterogeneous single-site catalysts have been run
successfully in many large-scale plants using avariety of processes, including slurry, bulk-monomer,and fluidized-bed gas-phase. In the last case, thereactor can be run with hetereogeneous metallocenecatalysts using “condensed mode” operation, in whicha liquid such as isopentane is injected to run thereactor with at least some liquid present to aid heattransfer, thus improving the capacity of the reactorand the activity of the catalyst.314 Because single-sitecatalysts have quite different responses to comono-mer and hydrogen than do conventional Ziegler-Natta catalysts, some care must be taken to avoidreactor fouling and process upsets. For example,AlEt3 is injected into the reactor as an activator andscavenger for Ziegler-Natta catalysts. With sup-ported metallocene catalysts, the presence of a scav-enger can cause fouling. Either using very smallamounts of AlEt3, operating without added AlEt3, orstopping addition after startup improves operabilityand allows for the preparation of copolymers withdensities below 0.90 g/cm3.315
In transitioning between incompatible Ziegler-Natta catalysts and metallocene catalysts in a fluid-ized-bed gas-phase process, polymerization of the firstcatalyst must be fully stopped before introducing thesecond catalyst. Small amounts of a catalyst killersuch as water or methanol, either injected directlyinto the gas stream or added as wet silica, areintroduced to deactivate the catalyst in the reactorirreversibly. The second catalyst is added afteradjustment of the feed streams.316 Addition of COabove and below the distributor plate has also beenused.317 Leftover catalyst in addition vessels can bedeactivated by heat treatment, followed by exposureto air.318
Reactor fouling can be reduced or eliminated by thejudicious addition of antistatic agents such as poly-siloxanes,319 long-chain amines, or 1,2-dimethoxy-benzene. This agent can be added to the catalystbefore introducing the catalyst into the reactor320 orinjected as a solution into the polymerizing environ-ment.321 The technique has also been used for unsup-ported catalysts in a fluidized-bed gas-phase pro-cess.322
The molecular weight and density of the polymerproduced by a metallocene catalyst in a gas-phaseprocess can be adjusted through the temperature orby injecting trace amounts of agents such as CO, CO2,Al(i-Bu)3, or acetylene.323 Addition of acetone ormethanol vapor has also been suggested to improvethe flowability of the polymer product and preventblockage of discharge lines.324
XVIII. Summary“Modern Chemistry... is much, and yet it is very
little. Much has been accomplished, for chemistry haslearned to shrink before no difficulty; little, becausewhat has been accomplished is as nothing comparedwith what remains to do. ‘Tis a fair science, yet sheowes much to chance.” Honore de Balzac, The Questof the Absolute, 1831).
This review has attempted to survey the large bodyof research into supporting single-site catalysts,tracing the development of homogeneous single-sitecatalysts as they were supported, and used in labora-tory reactors, pilot plants, commercial trials, and fullcommercial production as highly active catalystsystems which operate efficiently in many differentlarge-scale industrial polymerization processes. Thenumber of announcements of commercial productionof polyolefins produced by single-site catalysts hasincreased rapidly in the past few years. The learningcurve continues, though, even into full commercialproduction: for example, in 1997 Exxon was forcedto declare force majeure on metallocene polyethylenefrom its Mont Belvieu, TX, gas-phase polymerizationplant.325
One area which continues to attract interest isincreasing the activity of single-site catalysts whensupported, making up some of the deficit from whichthey suffer compared to their solution-soluble cous-ins. In this vein, Collins recently described in broadterms the synthesis of and polymerization usingtethered ansa-metallocenes, the activity of which iscomparable to a homogeneous analogue; we await fulldetails of catalyst structures and methods of prepa-ration.326
Another worthwhile area of endeavor is new sup-port materials, ones which are as “single-sited” as thecatalysts they carry. For example, the zeolite carriersdiscussed above have more uniform pore sizes andvolumes than the amorphous silicas hitherto widelyused. The importance of single-site catalysts lies inthe ability to characterize them comprehensively andalter them in a rational fashion in order to enhancedesired polymer properties; extending this degree ofunderstanding and control to their interaction withsupports and their performance in numerous polym-erization processes could only be beneficial.
XIX. References(1) (a) Natta, G.; Pino, P.; Mazzanti, G.; Giannini, V. J. Am. Chem.
Soc. 1957, 79, 2975. (b) Breslow, D. S.; Newburg, N. R. J. Am.Chem. Soc. 1957, 79, 5072.
(2) (a) Reichert, K. H.; Meyer, K. R. Makromol. Chem. 1973, 169,163. (b) Long, W. P.; Breslow, D. S. Liebigs Ann. Chem. 1975,463.
(4) (a) Welborn, H. C., Jr.; Ewen, J. A. U.S. Patent 5,324,800, 1994;Chem. Abstr. 1985, 102, 114142. (b) Ewen, J. A. Stud. Surf. Sci.Catal. 1986, 25, 271. A reviewer has questioned the significanceof this patent family on the grounds of its obviousness. Becausethis disclosure survived years of opposition based on exactlythose grounds in the European and Japanese patent offices, aswell as being upheld in a civil lawsuit, it seems clear that thefindings in this patent at the time it was filed were, in fact, notobvious.
Catalyst for Olefin Polymerization Chemical Reviews, 2000, Vol. 100, No. 4 1371
(5) (a) Ewen, J. A. J. Am. Chem. Soc. 1984, 106, 6355. (b) Kaminsky,W.; Kulper, K.; Brintzinger, H.-H.; Wild, F. R. W. P. Angew.Chem., Int. Ed. Engl. 1985, 24, 507.
(6) Turner, H. W.; Hlatky, G. G.; Eckman, R. R. U.S. Patent 5,198,-401, 1993; Chem. Abstr. 1995, 122, 33875.
(7) Ewen, J. A.; Elder, M. J. U.S. Patent 5,387,568, 1995; Chem.Abstr. 1991, 115, 136988.
(8) (a) Yang, X.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1991,113, 3623. (b) Ewen, J. A.; Elder, M. J. U.S. Patent 5,561,092,1996; Chem. Abstr. 1996, 125, 301814.
(9) (a) Cribbs, L. V.; Etherton, B. P.; Hlatky, G. G.; Wang, S. Proc.Ann. Technol. Conf. - Soc. Plast. Eng. 1998, 56(2), 1871. (b)Britovsek, G. J. P.; Gibson, V. C.; Wass, D. F. Angew. Chem.,Int. Ed. Engl. 1999, 38, 428.
(10) (a) Johnson, L. K.; Killian, C. M.; Brookhart, M. J. Am. Chem.Soc. 1995, 120, 6414. (b) Johnson, L. K.; Killian, C. M.; Arthur,S. D.; Feldman, J.; McCord, E. F.; McLain, S. J.; Kreutzer, K.A.; Bennett, M. A.; Coughlin, E. B.; Ittel, S. D.; Parthasarathy,A.; Tempel, D. J.; Brookhart, M. S. PCT Int. Appl. 96/23010,1996; Chem. Abstr. 1996, 125, 222773.
(11) For a discussion, see Bohm, L.; Bilda, D.; Breuers, W.; Enderle,H. F.; Lecht, R. In Ziegler Catalysts; Fink, G., Mulhaupt, R.,Brintzinger, H.-H., Eds.; Springer-Verlag: Berlin, 1995; p 387.
(12) As a colleague once put it, “Dog-bone-shaped catalyst particlesshould give dog-bone-shaped polymer particles.”
(13) (a) Olabishi, O.; Atiqullah, M.; Kaminsky, W. J. Macromol. Sci.,Rev. Macromol. Chem. Phys. 1997, C37, 519. (b) Ribeiro, M. R.;Deffieux, A.; Portela, M. F. Ind. Eng. Chem. Res. 1997, 36, 1224.(c) Ciardelli, F.; Altomare, A.; Michelotti, M. Catal. Today 1998,41, 149. (d) Jenny, C.; Maddox, P. Curr. Opin. Solid State Mater.Sci. 1998, 3, 94. (e) Abbenhuis, H. C. L. Angew. Chem., Int. Ed.Engl. 1999, 38, 1058. (f) Chien, J. C. W. Top. Catal. 1999, 7, 23.(g) Kristen, M. O. Top. Catal. 1999, 7, 89.
(14) Hlatky, G. G. Abstracts of Papers 217th National Meeting of theAmerican Chemical Society, Anaheim, CA, 1999; AmericanChemical Society, Division of Chemical Information, Washing-ton, DC, 1999; Abstract 13.
(15) The citation of a patent or patent application should not beconstrued as an endorsement of the validity of the claimscontained therein. All opinions and interpretations expressedin this review are those of the author.
(16) Donnet, J. B.; Wetzel, J. P.; Riess, G. J. Polym. Sci. A-1, 1968,6, 2359.
(17) Bocharov, J. N.; Kabanov, V. A.; Martynova, M. A.; Popov, V.G.; Smetanjuk, V. I.; Fedorov, V. V. U.S. Patent 4,161,462, 1979;Chem. Abstr. 1976, 84, 60257.
(18) Chien, J. C. W.; Hsieh, J. T. T. J. Polym. Sci., Polym. Chem.1976, 14, 1915.
(19) Slotfeldt-Ellingsen, D.; Dahl, I. M.; Ellestad, O. H. J. Mol. Catal.1980, 9, 423.
(20) Satyanarayana, G.; Sivaram, S. Macromolecules 1993, 26, 4712.(21) Oota, T.; Oonishi, M.; Suda, M. Jpn. Laid-Open Appl. 07/216014,
1995; Chem. Abstr. 1996, 124, 9669.(22) Oonishi, M.; Suda. M.; Oota, T. Jpn. Laid-Open Appl. 07/138313,
1995; Chem. Abstr. 1995, 123, 144964.(23) Oota, T.; Tange, M.; Kanamori, K.; Funabashi, H. Jpn. Laid-
Open Appl. 08/012716, 1996; Chem. Abstr. 1996, 124, 262001.(24) Mink, R. I.; Kissin, Y. V. U.S. Patent 5,397,757, 1995; Chem.
(50) Dufrenne, N. G.; Blitz, J. P.; Meverden, C. C. Microchem. J. 1997,55, 192.
(51) dos Santos, J. H. Z.; Krug, C.; da Rosa, M. B.; Stedile, F. C.;Dupont, J.; Forte, M. de C. J. Mol. Catal. A, 1999, 139, 199.
(52) dos Santos, J. H. Z.; Dorneles, S.; Stedile, F. C.; Dupont, J.; Forte,M. M. de C.; Baumvol, I. J. R. Macromol. Chem. Phys. 1997,198, 3529.
(53) dos Santos, J. H. Z.; Larentis, A.; da Rosa, M. B.; Krug, C.;Baumvol, I. J. R.; Dupont, J.; Stedile, F. C.; Forte, M. de C.Macromol. Chem. Phys. 1999, 200, 751.
(134) Toscano, P. J.; Marks, T. J. J. Am. Chem. Soc. 1985, 107, 653.(135) He, M.-Y.; Xiong, G.; Toscano, P. J.; Burwell, R. L.; Marks, T. J.
J. Am. Chem. Soc. 1985, 107, 641.(136) Dahmen, K.-H.; Hedden, D.; Burwell, R. L.; Marks, T. J.
Langmuir 1988, 4, 1212.(137) Finch, W. C.; Gillespie, R. D.; Hedden, D.; Marks, T. J. J. Am.
Chem. Soc. 1990, 112, 6221.(138) Toscano, P. J.; Marks, T. J. Langmuir 1986, 2, 820.(139) Moroz, B. L.; Semikolenova, N. V.; Nosov, A. V.; Zakharov, V.
A.; Nagy, S.; O’Reilly, N. J. J. Mol. Catal. A 1998, 130, 121.(140) Jejelowo, M. O. U.S. Patent 5,639,835, 1997; Chem. Abstr. 1995,
123, 287194.(141) Ahn, H.; Marks, T. J. J. Am. Chem. Soc. 1998, 120, 13533.(142) Semikolenova, N. V.; Zakharov, V. A. Macromol. Chem. Phys.
1997, 198, 2889.(143) Turner, H. W. U.S. Patent 4,752,597, 1988; Chem. Abstr. 1987,
107, 199105.(144) Janiak C.; Rieger, B. Angew. Makromol. Chem. 1994, 215, 47.(145) Sugimoto, R.; Asanuma, T. Jpn. Laid-Open Appl. 01/259005,
Catalyst for Olefin Polymerization Chemical Reviews, 2000, Vol. 100, No. 4 1373
(153) (a) Nickias, P. N.; Spencer, L. U.S. Patent 5,854,362, 1998; Chem.Abstr. 1999, 130, 95980. (b) Nickias, P. N.; Spencer, L. PCT Int.Appl. 97/15582, 1997; Chem. Abstr. 1997, 127, 5478.
(154) (a) Spencer, L.; Nickias, P. N. U.S. Patent 5,688,880, 1997; Chem.Abstr. 1998, 128, 35158. (b) Spencer, L.; Nickias, P. N. PCT Int.Appl. 97/15602, 1997; Chem. Abstr. 1997, 127, 18082.
(155) (a) Iiskola, E. I.; Timonen, S.; Pakkanen, T. T.; Harkki, O.;Seppala, J. V. Appl. Surf. Sci. 1997, 121/122, 372. (b) Iiskola,E. I.; Timonen, S.; Pakkanen, T. T.; Harkki, O.; Lehmus. P.;Seppala, J. V. Macromolecules 1997, 30, 2853. (c) Iiskola, E.;Suntola, T. Eur. Pat. Appl. 799,641, 1997; Chem. Abstr. 1997,127, 333465. (d) Iiskola, E.; Timonen, S.; Pakkanen, T. Eur. Pat.Appl. 799,838, 1997; Chem. Abstr. 1997, 127, 293769.
(156) Gila, L.; Proto, A.; Ballato, E.; Vigliarolo, D.; Lugli, G. U.S.Patent 5,846,895, 1998; Chem. Abstr. 1998, 128, 35163.
(157) Gila, L.; Proto, A.; Ballato, E.; Vigliarolo, D.; Lugli, G. U.S.Patent 5,861,352, 1999; Chem. Abstr. 1996, 125, 222750.
(158) Patsidis, K.; Peifer, B.; Palackal, S. J.; Alt, H. G.; Welch, M. B.;Geerts, R. L.; Fahey, D. R.; Deck, H. R. U.S. Patent 5,466,766,1995; Chem. Abstr. 1995, 122, 31709.
(167) (a) Stork, M.; Koch, M.; Klapper, M.; Mullen, K.; Gregorius, H.;Rief, U. Macromol. Rapid Commun. 1999, 20, 210. (b) Yorisue,T.; Kanejima, S. Jpn. Laid-Open Application 07/206914, 1995;Chem. Abstr. 1995, 124, 9640.
(168) Peifer, B.; Alt, H. G.; Welch, M. B.; Palackal, S. J. U.S. Patent5,473,020, 1995; Chem. Abstr. 1996, 124, 147158.
(169) Hong, S. C.; Ban, H. T.; Kishi, N.; Jin, J.; Uozumi, T.; Soga, K.Macromol. Chem. Phys. 1998, 199, 1393.
(170) Hong, S. C.; Teranishi, T.; Soga, K. Polymer, 1998, 39, 7153.(171) DiMaio, A. J. U.S. Patent 5,587,439, 1996; Chem. Abstr. 1997,
126, 31803.(172) Schertl, P.; Alt, H. G.; Peifer, B.; Palackal, S. J.; Welch, M. B.
U.S. Patent 5,770,755, 1998; Chem. Abstr. 1998, 129, 95878.(173) Kitagawa, T.; Uozumi, T.; Soga, K.; Takata, T. Polymer, 1997,
38, 615.(174) (a) Alt, H. G. J. Chem. Soc., Dalton Trans. 1999, 1703. (b) Alt,
H. G.; Jung, M. J. Organomet. Chem. 1999, 580, 1.(175) Antberg, M.; Herrmann, H.-F.; Rohrmann, J. U.S. Patent 5,-
169,818, 1992; Chem. Abstr. 1993, 118, 81632.(176) Chabrand, C. J.; Little, I. R.; McNally, J. P. U.S. Patent 5,714,-
425, 1998; Chem. Abstr. 1994, 121, 158369.(177) Jung, M.; Alt, H. G.; Welch, M. B. U.S. Patent 5,854,363, 1998;
Chem. Abstr. 1999, 130, 95982.(178) Jung, M.; Alt, H. G.; Welch, M. B. U.S. Patent 5,856,547, 1999;
Chem. Abstr. 1999, 130, 95986.(179) (a) Peifer, B.; Milius, W.; Alt, H. G. J. Organomet. Chem. 1998,
553, 205. (b) Peifer, B.; Alt, H. G.; Welch, M. B. U.S. Patent 5,-705,578, 1998; Chem. Abstr. 1998, 128, 102523.
(180) Jung, M.; Alt, H. G.; Welch, M. B. U.S. Patent 5,726,264, 1998;Chem. Abstr. 1998, 128, 205241.
(181) (a) Welch, M. B.; Alt, H. G.; Peifer, B.; Palackal, S. J.; Glass, G.L.; Pettijohn, T. M.; Hawley, G. R.; Fahey, D. R. U.S. Patent5,498,581, 1996; Chem. Abstr. 1996, 124, 147151. (b) Diefenbach,S. P. PCT Int. Appl. 99/29738, 1999; Chem. Abstr. 1999, 131,19437.
(182) Antberg, M.; Bohm, L.; Rohrmann, J. U.S. Patent 5,071,808,1991; Chem. Abstr. 1991, 115, 208842.
(186) (a) Chan, M. C. W.; Chew, K. C.; Dalby, C. I.; Gibson, V. C.;Kohlmann, A.; Little, I. R.; Reed, W. J. Chem. Soc., Chem.Commun. 1998, 1673. (b) Gibson, V. C.; Reed, W. Eur. Pat. Appl.816,384, 1998; Chem. Abstr. 1998, 128, 128395.
(187) Nagy, S.; Tyrell, J. A. U.S. Patent 5,744,417, 1998; Chem. Abstr.1998, 128, 4003.
(188) Galan-Fereres, M.; Koch, T.; Hey-Hawkins, E.; Eisen, M. S. J.Organomet. Chem. 1999, 580, 145.
(189) Weinberg, W. H.; McFarland, E.; Goldwasser, I.; Boussie, T.;Turner, H. W.; Van Beek, J. A. M.; Murphy, V.; Powers, T. PCTInt. Appl. 98/03521, 1998; Chem. Abstr. 1998, 128, 141181.
(190) Barrett, A. G. M.; de Miguel, Y. R. J. Chem. Soc., Chem.Commun. 1998, 2079.
(191) Kaminsky, W. U.S. Patent 4,431,788, 1984; Chem. Abstr. 1981,95, 151475.
(192) (a) Chang, M. U.S. Patent 4,912,075, 1990; Chem. Abstr. 1989,111, 233880. (b) Chang, M. U.S. Patent 4,914,253, 1990; Chem.Abstr. 1990, 113, 98282. (c) Chang, M. U.S. Patent 4,935,397,1990; Chem. Abstr. 1990, 113, 60082. (d) Chang, M. U.S. Patent5,008,228, 1991; Chem. Abstr. 1990, 112, 99482. (e) Herrmann,H.-F.; Bachmann, B.; Spaleck, W. U.S. Patent 5,578,537, 1996;Chem. Abstr. 1994, 121, 84221.
(193) Jejelowo, M. O. U.S. Patent 5,466,649, 1995; Chem. Abstr. 1995,123, 257788.
(194) Chang, M. U.S. Patent 5,238,892, 1993; Chem. Abstr. 1994, 120,108036.
(209) (a) Jacobsen, G. B.; Stevens, T. J. P.; Loix, P. H. H. U.S. Patent5,783,512, 1998, Chem. Abstr. 1998, 129, 109412. (b) Carnahan,E. M.; Carney, M. J.; Neithamer, D. R.; Nickias, P. N.; Shih,K.-Y.; Spencer, L. PCT Int. Appl. 97/19959, 1997; Chem. Abstr.1997, 127, 95733.
(210) Jacobsen, G. B.; Wijkens, P.; Jastrzebski, J. T. B. H.; Van Koten,G. U.S. Patent 5,834,393, 1998; Chem. Abstr. 1999, 130, 14330.
(211) Ono, M.; Hinokuma, S.; Miyake, S.; Inazawa, S. Eur. Pat. Appl.710,663, 1996; Chem. Abstr. 1996, 125, 87466.
(212) (a) Walzer, J. F. Jr., U.S. Patent 5,643,847, 1997; Chem. Abstr.1997, 127, 122104. (b) Hikuma, S.; Kibino, N.; Hori, A.; Myake,S. Inasawa, S. Jpn. Laid-Open Appl. 08/113604, 1996; Chem.Abstr. 1996, 125, 115457.
(213) Ward, D. G.; Carnahan, E. M. PCT Int. Appl. 96/23005, 1996;Chem. Abstr. 1996, 125, 196699.
(214) Fritze, C.; Kuber, F.; Bohnen, H. Eur. Pat Appl. 824, 112, 1998;Chem. Abstr. 1998, 128, 180766.
(215) (a) Chien, J. C. W.; Song, W.; Rausch, M. D. J. Polym. Chem.,Polym. Sci. 1994, 32, 2387. (b) Chen, Y.-X.; Stern, C. L.; Yang,S.; Marks, T. J. J. Am. Chem. Soc. 1996, 118, 12451.
1374 Chemical Reviews, 2000, Vol. 100, No. 4 Hlatky
(217) (a) Roscoe, S. B.; Frechet, J. M. J.; Walzer, J. F., Jr.; Dias, A. J.Science 1998, 280, 270. (b) Walzer, J. F., Jr.; Dias, A. J.; Frechet,J. M. J.; Roscoe, S. B. PCT Int. Appl. 98/55518, 1998; Chem.Abstr. 1999, 130, 52818.
(289) (a) Geerts, R. L.; Kufeld, S. E.; Hill, T. G. U.S. Patent 5,411,-925, 1995; Chem. Abstr. 1994, 121, 280872. (b) Geerts, R. L.;Palackal, S. J.; Pettijohn, T. M.; Infield, R. M. U.S. Patent 5,-496,781, 1996; Chem. Abstr. 1996, 124, 118288.
(290) Geerts, R. L. U.S. Patent 5,354,721, 1994; Chem. Abstr. 1994,121, 301611.
(291) Geerts, R. L. U.S. Patent 5,436,212, 1995; Chem. Abstr. 1995,123, 287186.
(294) Lu, B.; Wang, J.; Hong, X.; Jing, Z. U.S. Patent 5,728,640, 1998;Chem. Abstr. 1997, 126, 157932.
Catalyst for Olefin Polymerization Chemical Reviews, 2000, Vol. 100, No. 4 1375
(295) Brady, R. C.; Karol, F. J.; Lynn, T. R.; Jorgensen, R. J.; Kao,S.-C.; Wasserman, E. P. U.S. Patent 5,317,036, 1994; Chem.Abstr. 1994, 121, 206259.
(296) Goode, M. G.; Williams, C. C. U.S. Patent 5,693,727, 1997; Chem.Abstr. 1998, 128, 48604.
(297) Keller, G. E.; Carmichael, K. E.; Cropley, J. B.; Larsen, E. R.;Ramamurthy, A. V.; Smale, M. W.; Wenzel, T. T.; Williams, C.C. Eur. Pat. Appl. 764,665, 1997; Chem. Abstr. 1997, 126,264475.
(307) Speca, A. N.; Brinen, J. L.; McAlpin, J. J. U.S. Patent 5,786,-291, 1998; Chem. Abstr. 1998, 129, 149365.
(308) Nemzek, T. L.; Karol, F. J.; Kao, S.-C. PCT Int. Appl. 99/31147,1999; Chem. Abstr. 1999, 131, 45238.
(309) Tait, P. J. T.; Monteiro, M. G. K.; Yang, M.; Richardson, J. L.Proceedings of MetCon 1996, Houston, TX, 12-13 June 1996,(available from Catalyst Consultants, P.O. Box 637, SpringHouse, PA 19477).
(310) Jungling, S.; Koltzenburg, S.; Mulhaupt, R. J. Polym. Sci., Polym.Chem. 1997, 35, 1.
(312) Soga, K.; Kaminaka, M. Macromol. Rapid Commun. 1994, 15,593.
(313) Goretzki, R.; Fink, G. Macromol. Chem. Phys. 1999, 200, 881.(314) (a) DeChellis, M. L.; Griffin, J. R.; Muhle, M. E. U.S. Patent
5,405,922, 1995; Chem. Abstr. 1996, 124, 57051. (b) Griffin, J.
R.; DeChellis, M. L.; Muhle, M. E. U.S. Patent 5,462,999, 1995;Chem. Abstr. 1994, 121, 281466. (c) Goode, M. G.; Schreck, D.J.; Wenzel, T. T.; Williams, C. C. Eur. Pat. Appl. 780,404, 1997;Chem. Abstr. 1997, 127, 95744.
(315) (a) Brant, P.; Griffin, J. R.; Muhle, M. E.; Litteer, D. L.; Agapiou,A. K.; Renola, G. T. U.S. Patent 5,712,352, 1998; Chem. Abstr.1998, 128, 128404. (b) Poirot, E. E.; Sagar, V. R.; Jackson, S. K.U.S. Patent 5,712,353, 1998; Chem. Abstr. 1996, 125, 11739. (c)Muhle, M. E.; Renola, G. T.; Agapiou, A. K.; Litteer, D. L.;Griffin, J. R. U. S. Patent 5,763,543, 1998; Chem. Abstr. 1996,125, 11757; Chem. Abstr. 1998, 128, 128404. (d) Griffin, J. R.;Muhle, M. E.; Renola, G. T.; Litteer, D. L.; Brant, P. PCT Int.Appl. 96/08520, 1996; Chem. Abstr. 1996, 125, 11757.
(316) (a) Agapiou, A. K.; Muhle, M. E.; Renola, G. T. U.S. Patent 5,-442,019, 1995; Chem. Abstr. 1995, 123, 65073. (b) Muhle, M.E.; Agapiou, A. K.; Renola, G. T. U.S. Patent 5,672,666, 1997;Chem. Abstr. 1997, 126, 104568.
(318) Agapiou, A. K.; Ackermann, S. K.; LaBorde, D. M.; DeChellis,M. L. U.S. Patent 5,371,053, 1994; Chem. Abstr. 1995, 123,144878.
(319) Takeuchi, M.; Obara, Y.; Katoh, M.; Ohwaki, M. U.S. Patent 5,-270,407, 1993; Chem. Abstr. 1992, 116, 129908.
(320) (a) Agapiou, A. K.; Kuo, C.-I.; Muhle, M. E.; Speca, A. N. PCTInt. Appl. 96/11960, 1996; Chem. Abstr. 1996, 125, 59377. (b)Speca, A. N.; Brinen, J. L. PCT Int. Appl. 96/11961, 1996; Chem.Abstr. 1996, 125, 59378.
(321) (a) Fischer, D.; Frank, H.; Lux, M.; Hingmann, R. Eur. Pat. Appl.803,514, 1997; Chem. Abstr. 1997, 127, 346795. (b) Kiu, H. L.;Hussein, F. D.; Williams, C. C. Eur. Pat. Appl. 811,638, 1997;Chem. Abstr. 1998, 128, 61923.
(322) Goode, M. G.; Foster, G. N.; Williams, C. C.; Hussein, F. D.; Lee,K. H.; Cann, K. J.; Brady, R. C. PCT Int. Appl. 98/20045, 1998;Chem. Abstr. 1998, 129, 4990.
(323) (a) Cheruvu, S.; Lo. F. Y. U.S. Patent 5,608,019, 1997; Chem.Abstr. 1995, 123, 287217. (b) Cheruvu, S.; Lo, F. Y.; Ong, C. U.S.Patent 5,883,203, 1999; Chem. Abstr. 1997, 127, 95744.
![FI Catalyst for Polymerization of Olefin - IntechOpen · FI Catalyst for Polymerization of Olefin 121 bonds to become dissociated, resulting in a five-coordinated complex [36]. However,](https://static.documents.pub/doc/80x56/5f1091347e708231d449be94/fi-catalyst-for-polymerization-of-olefin-intechopen-fi-catalyst-for-polymerization.jpg)
