Catalyst composition for preparation of syndiotactic vinyl aromatic polymers

Abstract: A catalyst composition for preparation of polymers of vinyl aromatic monomers having high syndiotacticity comprises (1) a cationic metal complex of the formula [Cp m MX n X′ p ]⁺A⁻ wherein: Cp is a single η⁵-cyclopentadienyl group or a η⁵-substituted cyclopentadienyl group; M is a metal of Group 4 of the Periodic Table; each X independently is an inert anionic ligand or a group of formula R, with the proviso that at least one X is R; X′ is an inert, neutral donor ligand; each R independently is R′ or hydride, wherein R′ is hydrocarbyl, silyl or a mixture thereof, optionally substituted with one or more halogen atoms or alkoxy groups, and having up to 20 carbon and/or silicon atoms; m and p are independently 0 or 1; n is an integer greater than or equal to 1; and the sum of m and n is one less than the valence of M; and A⁻ is a noncoordinating, compatible anion; and (2) an aluminum, magnesium or zinc metal hydrocarbyl in a metal complex : metal hydrocarbyl ratio of 1:1 to 1:1000; said components (1) and (2) being combined prior to contact with a vinyl aromatic monomer.

Description: The present invention relates to a catalyst composition for polymerizing vinyl aromatic monomers, such as styrene, to produce polymers having a high degree of syndiotacticity. Such polymers may be usefully employed in the preparation of solid objects and articles such as a moldings, films, sheets and foamed objects by molding, casting or similar processes. In US-A-4,680,353 there is disclosed a process for the preparation of polymers of vinyl aromatic monomers having a stereoregular structure of high syndiotacticity by the use of certain coordination catalysts. Particularly disclosed were the reaction products of a titanium compound and an organoaluminum compound, especially polymethylaluminoxane. The process disclosed in this patent requires the use of large amounts of the polymethylaluminoxane which is very expensive and difficult to make due to its very complex structure. Also, this process requires an expensive polymer purification system to remove remaining catalyst components due to the use of large amounts of the polymethylaluminoxane. In EP-A-0277,004 there are disclosed certain bis(cyclopentadienyl) metal compounds formed by reacting a bis (cyclopentadienyl) metal complex with salts of Bronsted acids containing a non-coordinating compatible anion. The reference discloses the fact that such complexes are usefully employed as catalysts in the polymerization of olefins. EP-A-0493678 (published 8th July 1992) discloses the preparation of styrene polymers having a high degree of syndiotactic configuration using a catalyst comprising (A) a transition-metal compound without any metal-hydrogen, metal-carbon σ and metal-silicon σ bonds, (B) a coordination complex compound comprising a cation and an anion in which a plurality of radicals are bonded to a metal and (C) a compound having an alkyl group. The components (A), (B) & (C) can be admixed prior to the polymerization reaction. Exemplified transition-metal compounds include "cyclopentadienyltribenzyltitanium", "pentamethylcyclopentadienyltribenzyltitanium" and "indenyltribenzyltitanium" but these three compounds each have three metal-carbon σ bonds and hence the references to them are clearly in error. In US-A-5,006,741 (published November 19,1991 and corresponding to EP-A-0421659, published April 10, 1991), there is disclosed a process for preparing polymers of vinyl aromatic monomers having a high stereoregularity using metal complex cationic compounds of the formula: [Cp m MX n X' p ] + A - wherein: Cp is a single η 5 -cyclopentadienyl group which may optionally also be bonded to M through a substituent; M is a metal of Group 3, 4, 5, 6, 8, 9, 10 or the Lanthanide Series of the Periodic Table; each X independently is an inert anionic ligand or a group of formula R, with the proviso that at least one X is R; X' is an inert, neutral donor ligand; each R independently is hydride, or is hydrocarbyl or silyl, optionally substituted with one or more halogen atoms or alkoxy groups, and having up to 20 carbon and/or silicon atoms; m and p are independently 0 or 1; n is an integer greater than or equal to 1, the sum of m and n is one less than the valence of M, or when Cp is optionally bonded to M through the substituent, the sum of m and n is two less than the valence of M; and A - is a compatible noncoordinating anion. In Examples 12 to 15 of EP-A-0421659 a mixture of styrene and aluminum trialkyl (toluene solution) was added to cyclopentadienyldibenzyl titanium tetra(pentafluorophenyl)borate (toluene solution), the resultant mixture was shaken and then heated at 70°C for 1.5 or 2 hours to polymerize the styrene. The aluminum trialkyls used were trimethylaluminum (Example 12), triethylaluminum (Example 13) and tri(isobutyl)aluminum (Examples 14 and 15) and the polystyrene yields were 29.4% (Example 12; 2 hour polymerization; 10000:20:1 styrene:Al:Ti ratio), 76.2% (Example 13; 1.5 hour polymerization; 10000:18:1 styrene:Al:Ti ratio), 26.6% (Example 14; 1.5 hour; 65000:9:1 styrene:Al:Ti ratio), and 67.2% (Example 15; 1.5 hour; 39000:20:1 styrene:Al:Ti ratio). In Examples 17 to 22 of EP-A-0421659, 5 equivalents of triisobutyl aluminum was added to pentamethylcyclopentadienyldibenzyltitanium tetra (pentafluorophenyl) borate prior to polymerization of p-methylstyrene (Examples 17 and 18), p-methylstyrene/styrene (9.5/90.5) (Example 19), t-butylstyrene (Examples 20 and 21), or t-butylstyrene/styrene (10.1/89.9). It has now been discovered that further improvement in catalytic properties is obtained if the cationic catalysts disclosed in EP-A-0421659/US-A-5,066,741 are combined with small quantities of a metal alkyl prior to contacting with styrene monomer. According to the present invention there is now provided a catalyst composition useful for preparing polymers of vinyl aromatic monomers having high stereoregularity comprising: 1) a cationic metal complex of the formula: [Cp m MX n X' p ] + A - wherein: CP is a single η 5 -cyclopentadienyl group or a η 5 -substituted cyclopentadienyl group; M is a metal of Group 4 of the Periodic Table; each X independently is an inert anionic ligand or a group of formula R, with the proviso that at least one X is R; X' is an inert, neutral donor ligand; each R independently is R' or hydride, wherein R' is hydrocarbyl, silyl or a mixture thereof, optionally substituted with one or more halogen atoms or alkoxy groups, and having up to 20 carbon and/or silicon atoms; m and p are independently 0 or 1; n is an integer greater than or equal to 1; and the sum of m and n is one less than the valence of M; and A - is a noncoordinating, compatible anion; and 2) an aluminuum, magnesium or zinc metal hydrocarbyl, the molar ratio of the metal complex: metal hydrocarbyl being 1:1 to 1:1000 provided that, when said hydrocarbyl is triisobutyl aluminum and said metal complex is pentamethylcyclopentadienyldibenzyltitanium tetra(pentafluorophenyl)borate, said molar ratio is other than 1:5; said metal complex and metal hydrocarbyl being combined prior to contacting of the metal complex with a vinyl aromatic monomer. As used herein, the term "high stereo-regularity" refers to polymers having a stereoregular structure of greater than 50 percent syndiotactic of a racemic triad, preferably greater that 75 percent as determined by C 13 nuclear magnetic resonance spectroscopy. Such polymers may be usefully employed in the preparation of articles and objects (for example, via compression molding, injection molding or other suitable technique) having an extremely high resistance to deformation due to the effects of temperature. Examples of R' include aralkyl, alkaryl, haloalkyl, silylalkyl, haloaryl, haloalkaryl, halosilyl, halcalkarylsilyl and alkoxyalkyl. The term "inert" means non interfering with the desired catalyst preparation or with the use of the resulting catalyst composition as a polymerization catalyst. Illustrative but nonlimiting examples of X include R, halo, NR' 2 , PR' 2 , OR', SR' and BR' 2 . Illustrative but nonlimiting examples of X' include R'OR', R'SR', NR' 3 , PR' 3 and C 2-20 olefins or diolefins. Such donor ligands are able to form shared electron bonds but not a formal covalent bond. The metal complexes used in the present invention are prepared by combining at least two components as hereinafter disclosed. The first component is a derivative of a metal of Group 4 of the Periodic Table of the Elements containing at least one substituent which will combine with the cation of a second component (described hereinafter) or alternatively which is subject to oxidative activation as hereinafter described. The first component additionally must be capable of forming a cation formally having a coordination number that is one less than its valence. The second component is typically a salt of a Bronsted acid and a noncoordinating compatible anion or alternatively a salt of an oxidizing cation and a noncoordinating, compatible anion. All reference to the Periodic Table of the Elements herein shall refer to the Periodic Table of the Elements, published and copyrighted by CRC Press, Inc., 1989. Also, any reference to a Group or Series shall be to the Group or Series as reflected in this Periodic Table of the Elements, utilizing the IUPAC system for numbering groups. As used herein, the recitation "noncoordinating, compatible anion" means an anion which either does not coordinate with the first component or a derivative thereof; or which is only weakly coordinated to said component thereby remaining sufficiently labile to be displaced by the vinyl aromatic monomer to be polymerized. The recitation "noncoordinating, compatible anion" specifically refers to an anion which when functioning as a charge balancing anion in the catalyst system of this invention does not transfer an anionic substituent or fragment thereof to the cationic portion of the catalyst. Compatible anions are also anions which are not degraded to neutrality under the reaction conditions of the present invention. Preferred cyclopentadienyl and substituted cyclopentadienyl groups for use according to the present invention are depicted by the formula: wherein: each R" independently is hydrogen, halogen, R', N-R' 2 , P-R' 2 ; OR'; SR' or BR' 2 wherein R' is as previously defined. Preferably, R" is alkyl or haloalkyl of up to 6 carbons. Metal derivatives (first components) which may be used in the preparation of the metal complexes used in this invention are derivatives of titanium, zirconium and hafnium. More preferably such metal derivative compounds are those having X and R" substituents that are either devoid of reactive hydrogens or wherein potentially reactive hydrogens are protected by bulky protecting groups. Illustrative, but not limiting examples of suitable metal derivative compounds include: tetranorbornenyl titanium, tetrabenzyl zirconium, tetraneopentyl titanium, (cyclopentadienyl)dimethyl(isopropoxy)titanium, (cyclopentadienyl) dibenzyl(isopropoxy)titanium, (cyclopentadienyl)dibenzyl(phenoxy)zirconium, (cyclopentadienyl)dibenzyl(isopropoxy) hafnium, (cyclopentadienyl)dimethylzirconium chloride, bis(phenoxy)di(trimethylsilyl)zirconium, phenoxytrimethylzirconium, bis(2,6-diisopropyl-4-methyl)phenoxy)dibenzyltitanium, bis(2,4,6-trimethylphenoxy)dibenzyltitanium, tri(tertiary butyl)siloxytrimethyl zirconium, bismethoxydi(phenylmethyl)titanium, bis(2,4,6-trimethylphenoxy)dibenzyltitanium, triphenoxybenzyltitanium, butoxytris((trimethylsilyl)methyl)zirconium, dimethoxydimethylzirconium, 4-(1-methyl-1-(4-methoxyphenyl)ethyl)phenoxy tribenzyl titanium, dinorborneyldichlorotitanium, tribenzyltitanium hydride, cyclopentadienyltribenzylzirconium cyclopentadienyltribenzyltitanium, cyclopentadienyltrimethyltitanium, cyclopentadienyltrimethylzirconium, cyclopentadienyltrineopentyltitanium, cyclopentadienyltri(diphenylmethyl)zirconium, cyclopentadienyltriphenylzirconium, cyclopentadienyltrineopentylzirconium, cyclopentadienyldi(m-tolyl)zirconium, cyclopentadienyldi(p-tolyl)zirconium, cyclopentadienyltrimethyftitanium hydride, and cyclopentadienyltridiphenylmethylzirconium; hydrocarbyl-substituted cyclopentadienyl compounds such as pentamethylcyclopentadienyltrimethylzirconium, ethylcyclopentadienyltrimethylzirconium pentamethylcyclopentadienyltribenzylzirconium, n-butylcyclopentadienyltrineopentyltitanium, (t-butylcyclopentadienyl)tri(trimethylsilyl)zirconium, cyclohexylcyclopentadienyldimethylzirconium, (pentamethylcyclopentadienyl)dimethylzirconium chloride, indenyldibenzyltitanium chloride, (pentamethylcyclopentadienyl)diisopropoxyhafnium chloride, (benzylcyclopentadienyl)di(m-tolyl) titanium chloride, (diphenylcyclopentadienyl) dinorborneylzirconium chloride, methylcyclopentadienyltriphenylzirconium, tetraethylcyclopentadienyltribenzylzirconium, propylcyclopentadienyltrimethylzirconium, (n-butylcyclopentadienyl)dimethyl(n-butoxy)titanium, cyclopentadienyldiphenylisopropoxyzirconium, cyclohexylmethylcyclopentadienyltribenzylzirconium, cyclohexylmethylcyclopentadienyltrimethylzirconium, cyclopentadienylzirconium dihydride, benzylcyclopentadienyldimethylhafnium, indenyltribenzylzirconium, trimethylsilylcyclopentadienyltrimethylzirconium, (pentatrimethylsilyl)cyclopentadienyltrimethylzirconium, trimethylsilylcyclopentadienyltrimethylzirconium, penta(trimethylsilyl)cyclopentadienyltribenzyltitanium, halogen-substituted cyclopentadienyl compounds such as trifluoromethylcyclopentadienyltrimethylzirconium, trifluoromethylcyclopentadienyltrinorborneylzirconium and trifluoromethylcyclopentadienyltribenzylzirconium; silylsubstituted (cyclopentadienyl)metal compounds such as cyclopentadienyltrimethylsilylzirconium, and cyclopentadienyltri(phenyldimethylsilyl)zirconium. Other compounds which are useful as the metal complexes will, of course, be apparent to those skilled in the art. Most preferred are C 1-7 alkyl- or aralkyl-substituted titanium or zirconium compounds. Compounds useful as a second component in the preparation of the metal complexes used in this invention may, in one embodiment, comprise a cation, such as a Bronsted acid capable of donating a proton, and a compatible, noncoordinating anion. In another embodiment such compounds comprise an oxidizing cation and a compatible, non-coordinating anion. Preferred anions are those containing a single coordination complex comprising a charge-bearing metal or metalloid core which anion is relatively large (bulky), capable of stabilizing the active catalyst species (the Group 4 metal cation) formed when the two components are combined, and which will be sufficiently labile to be displaced by the polymerizable vinyl aromatic monomer. The term "metalloid", as used herein, includes non-metals such as boron, phosphorus, and silicon which exhibit semi-metallic characteristics. Suitable metals, include, but are not limited to, aluminum, gold and platinum. Compounds containing anions which comprise coordination complexes containing a single metal or metalloid atom are, of course, well known. In light of this, salts containing anions comprising a coordination complex containing a single boron atom are preferred. Preferably, second components useful in the preparation of the metal complexes used in this invention may be represented by the following general formulas: (L-H) + [A] - or Ox + [A*] - wherein: L is a neutral Lewis base; (L-H) + is a Bronsted acid; [A] - is a compatible, noncoordinating anion; Ox + is an organic or metallic oxidizing cation; and [A*] - is a compatible, noncoordinating, oxidatively inert, anion. By the term "oxidatively inert" as employed above is meant that A* of formula (II) comprises an anion which is a single coordination complex comprising a plurality of lipophilic radicals covalently coordinated to and shielding a central formally charge-bearing metal or metalloid atom, which anion is bulky and stable under the oxidation and subsequent polymerization conditions, and which anion is compatible with and noncoordinating towards the resulting polymerization catalyst. The anion is employed only to provide charge balance without interfering with the oxidizing ability of Ox + . Anions comprising boron which are particularly useful as [A*] - may be represented by the following general formula: [BX 1 X 2 X 3 X 4 ]- wherein: B is boron in a valence state of 3; X 1 to X 4 are the same or different nonreactive, organyl or silyl radicals containing from 1 to 20 carbon or silicon atoms. In addition two or more of X 1 to X 4 may be linked to each other through a stable bridging group. Preferably X 1 to X 4 lack reactive hydrogen moieties. That is, the radicals are either devoid of hydrogen, contain only hydrogen in nonactivated positions or contain sufficient steric hinderence to protect potentially active hydrogen sites. Examples of suitable radicals for X 1 to X 4 are perfluorinated hydrocarbyl radicals containing from 1 to 20 carbon atoms, 3,4,5-trifluorophenyl and 3,4-di(trifluoromethyl)phenyl. A most highly preferred compatible, non-coordinating, inert, anion for use in compounds corresponding to formula (II) is tetra(pentafluorophenyl)borate. Suitable oxidizing cations include organic and inorganic cations having sufficient electronegativity to oxidize the metal derivatives. Organic oxidizing cations for use in the compounds corresponding to formula (II) include ferrocenium ions, indenium ions and cationic derivatives of C 1-10 alkyl substituted ferrocene and indene molecules. Suitable metallic oxidizing cations include Ag +1 , Pd +2 , Pt +2 , Hg +2 , Hg 2 +2 , Au + and Cu + . The process of the invention involves a molecular oxidation. The Group 4 metal is previously fully oxidized. Highly preferred oxidizing cations have an oxidation potential of at least + 0.20 volt and preferably at least + 0.25 volt. Most highly preferred oxidizing cations are ferrocenium and Ag +1 cations. Without wishing to be bound by any particular theory of operation it is believed that the oxidizing cation causes the molecular oxidation of the metal derivative, and in the process becomes a neutral species. The oxidized metal derivative loses a hydrogen or organyl radical (.R) by a unimolecular elimination reaction. Two or more such radicals form a hydrogen molecule or a neutral organic species of the formula R(Rx) where x is an integer. These byproducts are neutral or noninterfering with any subsequent polymerization reaction and may also be removed from the reaction mixture. The preparation technique is analogous to that previously disclosed by R. Jordan, et al., J. A. C. S., 109, 4111-4113(1987). Illustrative, but not limiting, examples of oxidizing agents according to formula (II) are ferrocenium telrakis(pentafluorophenyl) borate, silver (I) tetrakis(pentafluorophenyl) borate, gold (I) tetrakis(pentafluorophenyl)borate, silver (I) tetrakis(3,4,5-trifluorophenyl) borate, silver tetra(pentafluorophenyl) borate, 1,1'-dimethylferrocenium tetrakis(pentafluorophenyl) borate, and 1,1'-dimethylferrocenium tetrakis(3,5-bistrifluoromethylphenyl) borate. Returning to above formula (I), preferably A - corresponds to the formula: [M'Q n' ] - wherein: M' is a metal or metalloid selected from Groups 5-15 of the Periodic Table of the Elements having a valency of m'; each Q independently is hydride, dialkylamido, halide, alkoxide, aryloxide, hydrocarbyl, or substituted hydrocarbyl containing up to 20 carbon atoms with the proviso that in not more than one occurrence is Q halide; n' is an integer from 2 to 8; and n'-m' = 1. Preferred second components of formula (I) are represented by the following general formula: [L-H] + [BQ 4 ] - wherein: L is a neutral Lewis base; [L-H] + is a Bronsted acid; B is boron in a valence state of 3; and Q is as previously defined. Illustrative, but not limiting, examples of boron compounds which may be used as a second component in formula (I) are trialkyl-substituted ammonium salts such as triethylammonium tetraphenylborate, tripropylammonium tetraphenylborate, tri(n-butyl)ammonium tetraphenylborate, trimethylammonium tetra(p-tolylborate) tributylammonium tetrakispentafluorophenylborate, tripropylammonium tetrakis-2,4-dimethylphenylborate, tributylammonium tetrakis-3,5-dimethylphenylborate, and triethylammonium tetrakis-(3,5-di-trifluoromethylphenyl)borate. Also suitable are N,N-dialkyl anilinium salts such as N,N-dimethyl-anilinium tetraphenylborate, N,N-diethylanilinium tetraphenylborate, and N,N-2,4,6-pentamethylanilinium tetraphenylborate; dalkyl ammonium salts such as di-(i-propyl)ammonium tetrakis-pentafluorophenylborate, and dicyclohexylammonium tetraphenylborate; and triaryl phosphonium salts such as triphenylphosphonium tetraphenylborate, tri(methylphenyl)phosphonium tetrakis-pentafluorophenylborate and tri(dimethylphenyl)phosphonium tetraphenylborate. Similar lists of suitable compounds containing other metals and metalloids which are useful as second components could be made, but such lists are not deemed necessary to a complete disclosure. In this regard, it should be noted that the foregoing list is not intended to be exhaustive and other boron compounds that would be useful as well as useful components containing other metals or metalloids would be readily apparent from the foregoing general formula and examples to those skilled in the art. In a highly preferred embodiment of the present invention Cp is pentamethylcyclopentadiene, m is zero or one, M is titanium or zirconium, n is two or three, p is zero, X is R or OR, and A - is tetrakis-pentafluorophenyl borate. In a most preferred embodiment X is C 1-20 alkyl, aryl, aralkyl, phenoxy or alkoxy and m is 0 or 1. In general, the metal complex can be prepared by combining the two components in a suitable solvent at a temperature of from -100°C to 300°C. Suitable solvents include straight and branched-chain hydrocarbons such as C 6-12 alkanes (hexane, heptane, octane); C 6-12 cyclic and alicyclic hydrocarbons such as cyclohexane, cycloheptane, methylcyclohexane and methylcycloheptane and C 6-12 aromatic and alkyl-substituted aromatic compounds such as benzene, toluene, xylene, decalin, and mixtures thereof. The catalysts' components are generally sensitive to both moisture and oxygen and should be handled and transferred in an inert atmosphere such as nitrogen, argon or helium. Preferred metal hydrocarbyls are those having from 1 to 10, more preferably from 1 to 4 carbons in the hydrocarbyl group. Most preferred are aluminum trialkyls, especially triisobutyl aluminum. The amount of metal hydrocarbyl preferably is sufficient to provide a molar ratio of metal complex:metal hydrocarbyl from 1:1 to 1:100, most preferably from 1:5 to 1:75. The components of the metal complex compound and the metal hydrocarbyl may be combined in any order. Preferably, however, the metal complex compound components are first contacted and allowed to form the desired complex and thereafter the metal hydrocarbyl is added thereto. Suitably a solution of the metal hydrocarbyl in an inert hydrocarbon such as toluene is employed. The compound are preferably combined at temperatures from 0°C to 160°C, most preferably from 25°C to 100°C. An inert atmosphere is employed as previously explained. Suitable vinyl aromatic monomers which can be polymerized using the catalyst compositions of the present invention include those represented by the formula: wherein each R is independently hydrogen; an aliphatic, cycloaliphatic or aromatic hydrocarbon group having from 1 to 10, more suitably from 1 to 6, most suitably from 1 to 4, carbon atoms; or a halogen atom. Examples of such monomers include, styrene, chlorostyrene, n-butyl styrene and p-vinyl toluene, with styrene being especially suitable. Copolymers of styrene and the above vinyl aromatic monomers other than styrene can also be prepared. The polymerization may be conducted under slurry, bulk or suspension polymerization conditions or other suitable reaction conditions including solid, powdered reaction conditions. The polymerization can be conducted at temperatures of from 0°C to 160°C, preferably from 25°C to 100°C, more preferably from 30°C to 80°C, for a time sufficient to produce the desired polymer. The catalyst composition may be employed homogeneously or supported on the surface of a suitable support. Typical reaction times are from one minute to 100 hours, preferably from 1 to 10 hours. The optimum reaction time or reactor residence time will vary depending upon the temperature, solvent and other reaction conditions employed. The polymerization can be conducted at subatmospheric pressure as well as superatmospheric pressure, suitably at a pressure within the range of 1 to 500 psig (100 kPa-3, 500 kPa). The use of ambient or low pressures, for example, 1-5 psig (100-150 kPa) is preferred in view of lower capital and equipment costs. The polymerization may be conducted in the presence of an inert diluent or solvent or in the absence thereof, that is, in the presence of excess monomer. Examples of suitable diluents or solvents include C 6-20 aliphatic, cycloaliphatic, aromatic and halogenated aliphatic or aromatic hydrocarbons, as well as mixtures thereof. Preferred diluents comprise the C 6-10 alkanes, toluene and mixtures thereof. A particularly desirable diluent for the polymerization is iso-octane, iso-nonane or blends thereof such as Isopar-E®, available from Exxon Chemical Company. Suitable amounts of solvent are employed to provide a monomer concentration from 5 percent to 100 percent by weight. The molar ratio of the vinyl aromatic monomer to the catalyst composition (in terms of Group 4 metal) may range from 100:1 to 5,000,000:1, preferably from 3,500:1 to 500,00:1. In the case of using a solvent, the catalyst may be used at a concentration with the range from 10 -7 to 10 -1 moles per liter of solvent. As in other similar polymerizations it is highly desirable that the monomers and solvents employed be of sufficiently high purity that catalyst deactivation does not occur. Any suitable technique for monomer purification such as devolatilization at reduced pressures, contacting with molecular sieves or high surface area alumina or deaeration may be employed. Additional quantities of a metal hydrocarbyl may be included in the reaction mixture if desired without departing from the scope of the present invention, it only being necessary that some of the metal hydrocarbyl be contacted with the metal complex prior to contact with the vinyl aromatic monomer. Purification of the resulting polymer to remove entrained catalyst composition may also be desired by the practitioner. Purification of the resulting polymer prepared by the process of this invention is much easier than a conventional process since the process of this invention does not use polyalkylaluminoxane which is used in large quantities as cocatalyst in the conventional process. Entrained catalyst composition may generally be identified by residues of ash on pyrolysis of the polymer that are attributable to catalyst composition metal values. A suitable technique for removing such compounds is by solvent extraction, for example, extraction utilizing hot, high boiling chlorinated solvents, acids or bases such as caustic followed by filtration. Having described the invention, the following examples are provided as further illustrative and are not to be construed as limiting. Unless stated to the contrary, all parts and percentages are based on weight. Example 1 In a argon atmosphere dry box a 0.0024M solution/suspension of the catalyst composition was prepared. A dry 2 ml volumetric flask was charged with 0.70 ml of a 0.0069M (4.8 µmol) solution of pentamethylcyclopentadienyltribenzyl titanium in toluene, 4.8 mg (4.8 µmol) of decamethylferrocenium tetra(pentafluorophenyl) boron and 26.5 µl of a 1M toluene solution of triisobutyl aluminum (TIBA, 26.5 µmol), then filled to the mark with dry, degassed toluene. The mixture was allowed to interact while being stirred for 1.5 hours, after which time a dark solution/suspension had formed. Polymerization-1 A dry 20 ml vial was charged with 10 ml (87.4 mmole) of purified styrene, 20 µl of a 1 M toluene solution of TIBA, capped with a Teflon™ coated septa and a metal crimp cap, removed from the argon atmosphere dry box and then placed in a 70°C water bath. After 10 minutes 250 µl of the above catalyst was added. Total TIBA present was 23.5 µmole. The molar ratio of styrene:Ti:TIBA was 145,000:1:39. After 1 hour the vial was removed from the water bath and the polymerization stopped by the addition of 2 ml of methanol. The off white, insoluble polymer was dried in-vacuo to give 22.4 percent yield of a resultant polymer. The resultant polymer was insoluble in methylene chloride, methylethylketone and other common solvents for atactic polystyrene. The resultant polymer had a crystalline melting point of 270°C, consistent with a polymer having >98 percent syndiotacticity. Example 2 In an argon atmosphere dry box a 0.01 M solution/suspension of the catalyst composition was prepared. A dry 2 ml volumetric flask was charged with 0.70 ml of a 0.0069M (4.8 µmol) solution of pentamethylcyclopentadienyltribenzyl titanium in toluene, 4.8 mg (4.8 µmol) of decamethylferrocenium tetra(pentafluorophenyl) boron and 100µl of a 1M toluene solution of TIBA (100 µmole), then filled to the mark with dry, degassed toluene. The mixture was allowed to interact while being stirred for 1.5 hours, after which time a dark solution/suspension had formed. Polymerization-2 A dry 20ml vial was charged with 10 ml (87.4 mmol) of purified styrene, 20 µl of a 1M toluene solution of TIBA, capped with a Teflon™ coated septa and a metal crimp cap, removed from the argon atmosphere dry box and then placed in a 70°C water bath. After 10 minutes 250 µl of the above catalyst was added. Total TIBA present was 32.5 µmole giving a molar ratio styrene:Ti:TIBA of 145,000:1:54. After 1 hour the vial was removed from the water bath and the polymerization stopped by the addition of 2 ml of methanol. The off white, insoluble polymer was dried in-vacuo to give 30.4 percent yield of a resultant polymer. The resultant polymer was insoluble in methylene chloride, methylethylketone and other common solvents for atactic polystyrene. The resultant polymer had a crystalline melting point of 270°C, consistent with a polymer having >98 percent syndiotacticity. Comparative In an argon atmosphere dry box a 0.01M solution/suspension of the catalyst composition was prepared. A dry 2 ml volumetric flask was charged with 0.70 ml of a 0.0069M (4.8 µmol) solution of pentamethylcyclopentadienyltribenzyl titanium in toluene, 4.8 mg (4.8 µmol) of decamethylferrocenium tetra(pentafluorophenyl) boron and then filled to the mark with dry, degassed toluene. The mixture was allowed to interact while being stirred for 1.5 hours after which time a dark solution/suspension had formed. Polymerization-3 A dry 20 ml vial was charged with 10 ml (87.4 mmole) of purified styrene, 20 µl of a 1M toluene solution of TIBA, capped with a Teflon™ coated septa and a metal crimp cap, removed from the argon atmosphere dry box and then placed in a 70°C water bath. After 10 minutes 250 µl of the above catalyst was added. Total TIBA present was 20 µmole. The molar ratio of styrene:Ti:TIBA was 145,000:1:33. After 1 hour the vial was removed from the water bath and the polymerization stopped by the addition of 2 ml of methanol. The off white, insoluble polymer was dried in-vacuo to give 9.4 percent yield of a resultant polymer. The resultant polymer was insoluble in methylene chloride, methylethylketone and other common solvents for atactic polystyrene. The resultant polymer had a crystalline melting point of 270°C, consistent with a polymer having >98 percent syndiotacticity. Polymerization-4 The reaction conditions of Polymerization -3 were substantially repeated excepting that 40 µl of a 1M toluene solution of TIBA was added to the styrene monomer before contacting with the catalyst. The molar ratio of styrene:Ti: TIBA was 145,000:1:67. After 1 hour the vial was removed from the water bath and the polymerization stopped by the addition of 2 ml of methanol. The off white, insoluble polymer was dried in-vacuo to give 10.3 percent yield of a resultant polymer. The resultant polymer was insoluble in methylene chloride, methylethylketone and other common solvents for atactic polystyrene. The resultant polymer had a crystalline melting point of 269°C, consistent with a polymer having >98 percent syndiotacticity. As may be seen by the above examples and the comparative experiments a significant improvement in polymerization rate is obtained when the metal complex composition is first prepared and utilized to polymerize styrene rather than preparing the complex and contacting the same with styrene contemporaneously with the metal alkyl.

Claims: A catalyst composition for preparing polymers of vinyl aromatic monomers having high stereoregularity comprising: 1) a metal complex of the formula: [Cp m MX n X' p ] + A - wherein: Cp is a single η 5 -cyclopentadienyl group or a η 5 -substituted cyclopentadienyl group; M is a metal of Group 4 of the Periodic Table; each X independently is an inert anionic ligand or a group of formula R, with the proviso that at least one X is R; X' is an inert, neutral donor ligand; each R independently is R' or hydride, wherein R' is hydrocarbyl, silyl or a mixture thereof, optionally substituted with one or more halogen atoms or alkoxy groups, and having up to 20 carbon and/or silicon atoms; m and p are independently 0 or 1; n is an integer greater than or equal to 1; and the sum of m and n is one less than the valence of M; and A - is a noncoordinating, compatible anion; and 2) an aluminum, magnesium or zinc metal hydrocarbyl, the molar ratio of the metal complex : metal hydrocarbyl being 1:1 to 1:1000, provided that, when said hydrocarbyl is triisobutyl aluminum and said metal complex is pentamethylcyclopentadienyldibenzyltitanium tetra(pentafluorophenyl)borate, said molar ratio is other than 1:5; said metal complex and metal hydrocarbyl being combined prior to contacting of the metal complex with a vinyl aromatic monomer. A catalyst composition according to Claim 1 wherein the metal hydrocarbyl is a trialkyl aluminum. A catalyst composition according to Claim 2 wherein the trialkyl aluminum is triisobutyl aluminum. A catalyst composition according to any one of the preceding claims, wherein the molar ratio of metal complex to metal hydrocarbyl is from 1:1 to 1:100. A catalyst composition according to any one of the preceding claims, wherein Cp has the formula wherein each R" is independently is hydrogen, halogen, R', NR' 2 , PR' 2 , OR', SR' or BR' 2 and R' is as defined in Claim 1. A catalyst composition according to Claim 5, wherein R" is C 1 -C 6 alkyl or C 1 -C 6 haloalkyl. A catalyst composition according to any one the preceding claims, wherein M is titanium or zirconium. A catalyst composition according to Claim 7, wherein Cp is pentamethylcyclopentadiene, m is 0 or 1, n is 2 or 3, p is 0, X is R or OR, R is as defined in Claim 1 and A - is tetrakispentafluorophenylborate. A catalyst composition according to Claim 8, wherein X is C 1 -C 20 alkyl, aryl, aralkyl, phenoxy or alkoxy. A catalyst composition according to Claim 9, comprising pentamethylcyclopentadienyldibenzyltitanium tetra(pentafluorophenyl)borate and triisobutyl aluminum. A process for preparing vinyl aromatic polymers having high stereoregularity comprising contacting a vinyl aromatic monomer with a catalyst composition comprising: 1) a metal complex of the formula: [Cp m MX n X' p ] + A - wherein: Cp is a single η 5 -cyclopentadienyl group or a η 5 -substituted cyclopentadienyl group; M is a metal of Group 4 of the Periodic Table; each X independently is an inert anionic ligand or a group of formula R, with the proviso that at least one X is R; X' is an inert, neutral donor ligand; each R independently is R' or hydride, wherein R' is hydrocarbyl, silyl or a mixture thereof, optionally substituted with one or more halogen atoms or alkoxy groups, and having up to 20 carbon and/or silicon atoms; m and p are independently 0 for 1; n is an integer greater than or equal to 1; and the sum of m and n is one less than the valence of M; and A - is a noncoordinating, compatible anion; and 2) an aluminum, magnesium or zinc metal hydrocarbyl, the molar ratio of the metal complex : metal hydrocarbyl being 1:1 to 1:1000; said metal complex and metal hydrocarbyl being combined prior to contacting of the metal complex with a vinyl aromatic monomer, provided that, when said hydrocarbyl is triisobutyl aluminum, said metal complex is pentamethylcyclopentadienyldibenzyltitanium tetra(pentafluorophenyl)borate, and molar ratio is 1:5, the vinyl aromatic monomer is other than p-methylstyrene, t-butylstyrene, a mixture of 9.5 wt% p-methylstyrene and 90.5 wt% styrene or a mixture of 10.1 wt% t-butylstyrene and 89.9 wt% styrene. A process according to Claim 11, wherein said catalyst composition is as defined in any one of Claims 2 to 10. The use of a catalyst composition according to Claim 1 as a catalyst for polymerizing vinyl aromatic monomers. A use according to Claim 13, wherein the catalyst composition is as defined in any one of Claims 2 to 10.

Inventors: CAMPBELL RICHARD E JR, CAMPBELL, RICHARD E., JR.
Applicants: DOW CHEMICAL CO, THE DOW CHEMICAL COMPANY
Application year: 1992
Main classification: C08F4
IPC codes: C08F4, C08F12