WO1997042233A1

WO1997042233A1 - Process for the polymerization of vinyl aromatic monomers

Info

Publication number: WO1997042233A1
Application number: PCT/NL1997/000242
Authority: WO
Inventors: Maurits Frederik Hendrik Van Tol; Johannes Antonius Maria Van Beek; Paulus Johannes Jacobus Pieters
Original assignee: Dsm N.V.
Priority date: 1996-05-03
Filing date: 1997-05-01
Publication date: 1997-11-13
Also published as: AU2411897A

Abstract

The invention relates to a process for preparing vinyl aromatic polymers having a high degree of syndiotacticity and a high molecular weight comprising contacting at least one polymerizable vinyl aromatic monomer under polymerization conditions with a catalyst comprising a reduced transition metal complex and a co-catalyst. The invention is characterized in that the transition metal complex consists of a reduced transition metal, chosen from groups 4-6 of the Periodic Table of the Elements, with a multidentate monoanionic ligand and with two monoanionic ligands. In particular, the reduced transition metal is titanium (Ti).

Description

PROCESS FOR THE POLYMERIZATION OF VINYL AROMATIC MONOMERS

The present invention relates to a process for the polymerization of vinyl aromatic monomers with a transition metal complex and a co-catalyst. In particular the invention relates to a process for producing polymers having a high degree of syndiotacticity and a high molecular weight.

The syndiotactic polymerization of vinyl aromatic monomers, in particular the syndiotactic polymerization of styrene, is known from the work of Ishihara et al. - Macromolecules, 19, pp. 2464 - 2465 (1986) - who use a catalyst containing a titanium compound and an organo-aluminum compound. The syndiotactic polystyrene produced with these catalysts typically shows melting temperatures between 260 and

270 °C as reported in EP-A-210615. The titanium in the titanium compounds used has a formal oxidation state of +4.

The purpose of the present invention is to provide a process for producing polymers of vinyl aromatic monomers with an improved (i.e. higher) syndiotacticity with respect to the processes known before in the art, and which combines said higher syndiotacticity with high molecular weights of the obtained polymers. In accordance with the principles of the present invention this object is obtained by providing a process for the polymerization of vinyl aromatic monomers in the presence of the present catalyst composition. The catalyst composition includes at least one complex comprising a reduced valency transition metal (M) selected from groups 4-6 of the Periodic Table of Elements, a multidentate monoanionic ligand (X), two monoanionic ligands (L), and, optionally, additional ligands (K). More specifically, the complex of the catalyst composition of the present invention is represented by the following formula (I):

X (I)

I M - L₂

I K„

wherein the symbols have the following meanings: M a reduced transition metal selected from group 4, 5 or 6 of the Periodic Table of Elements? X a multidentate monoanionic ligand represented by the formula: (Ar-R_t-)_βY(-R_t-DR'_n)_q; Y a cyclopentadienyl, amido (-NR'-), or phosphido group (-PR'-), which is bonded to the reduced transition metal M; R at least one member selected from the group consisting of (i) a connecting group between the Y group and the DR'_n group and (ii) a connecting group between the Y group and the Ar group, wherein when the ligand X contains more than one R group, the R groups can be identical to or different from each other; D an electron-donating hetero atom selected from group 15 or 16 of the Periodic Table of Elements; R' a substituent selected from the group consisting of a hydrogen, hydrocarbon radical and hetero atom-containing moiety, except that R' cannot be hydrogen when R' is directly bonded to the electron-donating hetero atom D, wherein when the multidentate monoanionic ligand X contains more than one substituent R', the substituents R' can be identical or different from each other; Ar an electron-donating aryl group; L a monoanionic ligand bonded to the reduced transition metal M, wherein the monoanionic ligand L is not a ligand comprising a cyclopentadienyl, amido (-NR'-), or phosphido (-PR'-) group, and wherein the monoanionic ligands L can be identical or different from each other; K a neutral or anionic ligand bonded to the reduced transition metal M, wherein when the transition metal complex contains more than one ligand K, the ligands K can be identical or different from each other ; m the number of the K ligands, wherein when the K ligand is an anionic ligand m is 0, 1, or 2, and when K is a neutral ligand, m increases by one for each neutral K ligand; n the number of the R' groups bonded to the electron-donating hetero atom D, wherein when D is selected from group 15 of the Periodic Table of Elements n is 2, and when D is selected from group 16 of the Periodic Table of Elements n is 1; q,s q and s are the number of (-R_t-DR'_n) groups and (Ar-R_t-) groups bonded to group Y, respectively, wherein q + s is an integer not less than 1; and t the number of R groups connecting each of (i) the Y and Ar groups and (ii) the Y and DR'_n groups, wherein t is selected independently as 0 or 1.

A few examples of transition metal complexes according to the invention are presented in Table I. Catalysts containing compounds based on Ti,

Hf and Zr, used for the syndiotactic polymerisation of vinyl aromatic monomers are also described in EP-A-

421659.

EP-A-416815 and WO-A-93/23412 describe titanium compounds, having a constrained geometry and wherein the titanium is in the oxidation state +4, used in the copolymerisation of α-olefins with styrene. The accompanying drawings illustrate the present invention. In such drawings:

FIG. 1 is a schematic view of a cationic active site of a trivalent catalyst complex in accordance with an embodiment of the present invention; and

FIG. 2 is a schematic view of a neutral active site of a trivalent catalyst complex of a dianionic ligand of a conventional catalyst complex according to WO-A-93/19104.

Various components (groups) of the transition metal complex are discussed below in more detail.

(a) The Transition Metal (M) The transition metal in the complex is selected from groups 4-6 of the Periodic Table of Elements. As referred to herein, all references to the Periodic Table of Elements mean the version set forth in the new IUPAC notation found on the inside of the cover of the Handbook of Chemistry and Physics, 70th edition, 1989/1990, the complete disclosure of which is incorporated herein by reference. More preferably, the transition metal is selected from group 4 of the Periodic Table of Elements, and most preferably is titanium (Ti).

The transition metal is present in reduced form in the complex, which means that the transition metal is in a reduced oxidation state. As referred to herein, "reduced oxidation state" means an oxidation state which is greater than zero but lower than the highest possible oxidation state of the metal (for example, the reduced oxidation state is at most M³⁺ for a transition metal of group 4, at most M⁴⁺ for a transition metal of group 5 and at most M⁵⁺ for a transition metal of group 6). ( b ) The X L igand

The X ligand is a multidentate monoanionic ligand represented by the formula: (Ar-R_t-)_BY(-R_t-DR'_n)_q.

As referred to herein, a multidentate monoanionic ligand is bonded with a covalent bond to the reduced transition metal (M) at one site (the anionic site, Y) and is bonded either (i) with a coordinate bond to the transition metal at one other site (bidentate) or (ii) with a plurality of coordinate bonds at several other sites (tridentate, tetradentate, etc.). Such coordinate bonding can take place, for example, via the D heteroatom or Ar group(s). Examples of tridentate monoanionic ligands include, without limitation, Y-R_t-DR'_n_ι-^Rt-"^DR'n ^and Y(-R-DR'_B)₂. It is noted, however, that heteroatom(s) or aryl substituent(s) can be present on the Y group without coordinately bonding to the reduced transition metal M, so long as at least one coordinate bond is formed between an electron-donating group D or an electron donating Ar group and the reduced transition metal M. R represents a connecting or bridging group between the DR'_n and Y, and/or between the electron- donating aryl (Ar) group and Y. Since R is optional, "t" can be zero. The R group is discussed below in paragraph (d) in more detail.

(c) The Y Group

The Y group of the multidentate monoanionic ligand (X) is preferably a cyclopentadienyl, amido (-NR'-), or phosphido (-PR'-) group.

Most preferably, the Y group is a cyclopentadienyl ligand (Cp group). As referred to herein, the term cyclopentadienyl group encompasses substituted cyclopentadienyl groups such as indenyl, fluorenyl, and benzoindenyl groups, and other polycyclic aromatics containing at least one 5-member dienyl ring, so long as at least one of the substituents of the Cp group is an R_t-DR'_n group or R_t-Ar group that replaces one of the hydrogens bonded to the five-member ring of the Cp group via an exocyclic substitution.

Examples of a multidentate monoanionic ligand with a Cp group as the Y group (or ligand) include the following (with the (-R_t-DR'_n) or (Ar-R_t-) substituent on the ring) :

R R R R

The Y group can also be a hetero cyclopentadienyl group. As referred to herein, a hetero cyclopentadienyl group means a hetero ligand derived from a cyclopentadienyl group, but in which at least one of the atoms defining the five-member ring structure of the cyclopentadienyl is replaced with a hetero atom via an endocyclic substitution. The hetero Cp group also includes at least one R_t-DR'_n group or R_t-Ar group that replaces one of the hydrogens bonded to the five-member ring of the Cp group via an exocyclic substitution. As with the Cp group, as referred to herein the hetero Cp group encompasses indenyl, fluorenyl, and benzoindenyl groups, and other polycyclic aromatics containing at least one 5-member dienyl ring, so long as at least one of the substituents of the hetero Cp group is an R_t-DR'_n group or R_t-Ar group that replaces one of the hydrogens bonded to the five-member ring of the hetero Cp group via an exocyclic substitution. The hetero atom can be selected from group 14, 15 or 16 of the Periodic Table of Elements. If there is more than one hetero atom present in the five- member ring, these hetero atoms can be either the same or different from each other. More preferably, the hetero atom(s) is/are selected from group 15, and still more preferably the hetero atom(s) selected is/are phosphorus.

By way of illustration and without limitation, representative hetero ligands of the X group that can be practiced in accordance with the present invention are hetero cyclopentadienyl groups having the following structures, in which the hetero cyclopentadienyl contains one phosphorus atom (i.e., the hetero atom) substituted in the five-member ring:

R' R R' R-DR',

It is noted that, generally, the transition metal group M is bonded to the Cp group via an h_, ⁵ bond.

The other R' exocyclic substituents (shown in formula (III)) on the ring of the hetero Cp group can be of the same type as those present on the Cp group, as represented in formula (II). As in formula (II), at least one of the exocyclic substituents on the five- member ring of the hetero cyclopentadienyl group of formula (III) is the R_t-DR'„ group or the R_t-Ar group. The numeration of the substitution sites of the indenyl group is in general and in the present description based on the IϋPAC Nomenclature of Organic Chemistry 1979, rule A 21.1. The numeration of the substituent sites for indene is shown below. This numeration is analogous for an indenyl group:

Indene

The Y group can also be an amido (-NR'-) group or a phosphido (-PR'-) group. In these alternative embodiments, the Y group contains nitrogen (N) or phosphorus (P) and is bonded covalently to the transition metal M as well as to the (optional) R group of the (-R_t-DR'_n) or (Ar-R_t-) substituent.

(d) The R Group

The R group is optional, such that it can be absent from the X group. Where the R group is absent, the DR'_n or Ar group is bonded directly to the Y group (that is, the DR'_n or Ar group is bonded directly to the Cp, amido, or phosphido group). The presence or absence of an R group between each of the DR'_n groups and/or Ar groups is independent. Where at least one of the R groups is present, each of the R group constitutes the connecting bond between, on the one hand the Y group, and on the other hand the DR'_n group or the Ar group. The presence and size of the R group determines the accessibility of the transition metal M relative to the DR'_n or Ar group, which gives the desired intramolecular coordination. If the R group (or bridge) is too short or absent, the donor may not coordinate well due to ring tension. The R groups are each selected independently, and can generally be, for example, a hydrocarbon group with 1-20 carbon atoms (e.g., alkylidene, arylidene, aryl alkylidene, etc.). Specific examples of such R groups include, without limitation, methylene, ethylene, propylene, butylene, phenylene, whether or not with a substituted side chain. Preferably, the R group has the following structure:

(-CR'₂-)_p (IV)

where p = 1-4. The R' groups of formula (IV) can each be selected independently, and can be the same as the R' groups defined below in paragraph (g).

In addition to carbon, the main chain of the R group can also contain silicon or germanium. Examples of such R groups are: dialkyl silylene (-SiR'₂-), dialkyl germylene (-GeR'₂-), tetra-alkyl silylene (-SiR'₂-SiR '₂-) , or tetraalkyl silaethylene (-SiR'₂CR'₂- ). The alkyl groups in such a group preferably have 1-4 carbon atoms and more preferably are a methyl or ethyl group.

(e) The DR'_n Group

This donor group consists of an electron- donating hetero atom D, selected from group 15 or 16 of the Periodic Table of Elements, and one or more substituents R' bonded to D. The number (n) of R' groups is determined by the nature of the hetero atom D, insofar as n being 2 if D is selected from group 15 and n being 1 if D is selected from group 16. The R' substituents bonded to D can each be selected independently, and can be the same as the R' groups defined below in paragraph (g), with the exception that the R' substituent bonded to D cannot be hydrogen. The hetero atom D is preferably selected from the group consisting of nitrogen (N) , oxygen (0), phosphorus (P) and sulphur (S); more preferably, the hetero atom is nitrogen (N). Preferably, the R' group is an alkyl, more preferably an n-alkyl group having 1- 20 carbon atoms, and most preferably an n-alkyl having 1-8 carbon atoms. It is further possible for two R' groups in the DR'_n group to be connected with each other to form a ring-shaped structure (so that the DR'_n group can be, for example, a pyrrolidinyl group). The DR'_n group can form coordinate bonds with the transition metal M.

(f) The Ar Group

The electron-donating group (or donor) selected can also be an aryl group (C₆R'₅), such as phenyl, tolyl, xylyl, mesityl, cumenyl, tetramethyl phenyl, pentamethyl phenyl, a polycyclic group such as triphenylmethane, etc. The electron-donating group D of formula (I) cannot, however, be a substituted Cp group, such as an indenyl, benzoindenyl, or fluorenyl group.

The coordination of this Ar group in relation to the transition metal M can vary from I-)¹ to h_. ⁶.

(g) The R' Group

The R' groups may each separately be hydrogen or a hydrocarbon radical with 1-20 carbon atoms (e.g. alkyl, aryl, aryl alkyl and the like as shown in Table

1).

Examples of alkyl groups are methyl, ethyl, propyl, butyl, hexyl and decyl. Examples of aryl groups are phenyl, mesityl, tolyl and cumenyl. Examples of aryl alkyl groups are benzyl, pentamethylbenzyl, xylyl, styryl and trityl. Examples of other R' groups are halides, such as chloride, bromide, fluoride and iodide, methoxy, ethoxy and phenoxy. Also, two adjacent hydrocarbon radicals of the Y group can be connected with each other to define a ring system; therefore the Y group can be an indenyl, a fluorenyl or a benzoindenyl group. The indenyl, fluorenyl, and/or benzoindenyl can contain one or more R' groups as substituents. R' can also be a substituent which instead of or in addition to carbon and/or hydrogen can comprise one or more hetero atoms of groups 14-16 of the Periodic Table of Elements. Thus, a substituent can be, for example, a Si-containing group, such as Si(CH₃)₃.

(h) The L Group The transition metal complex contains two monoanionic ligands L bonded to the transition metal M. Examples of the L group ligands, which can be identical or different, include, without limitation, the following: a hydrogen atom; a halogen atom; an alkyl, aryl or aryl alkyl group; an alkoxy or aryloxy group; a group comprising a hetero atom selected from group 15 or 16 of the Periodic Table of Elements, including, by way of example, (i) a sulphur compound, such as sulphite, sulphate, thiol, sulphonate, and thioalkyl, and (ii) a phosphorus compound, such as phosphite, and phosphate. The two L groups can also be connected with each other to form a dianionic bidentate ring system.

These and other ligands can be tested for their suitability by means of simple experiments by one skilled in the art.

Preferably, L is a halide and/or an alkyl or aryl group; more preferably, L is a Cl group and/or a Ci-Cj alkyl or a benzyl group. The L group, however, cannot be a Cp, amido, or phosphido group. In other words, L cannot be one of the Y groups.

(i) The K Ligand

The K ligand is a neutral or anionic group bonded to the transition metal M. The K group is a neutral or anionic ligand bonded to M. When K is a neutral ligand K may be absent, but when K is monoanionic, the following holds for K_m: m = 0 for M³⁺ m = l for M*⁺ m = 2 for M^s+

On the other hand, neutral K ligands, which by definition are not anionic, are not subject to the 2

- 12 -

same rule. Therefore, for each neutral K ligand, the value of m (i.e., the number of total K ligands) is one higher than the value stated above for a complex having all monoanionic K ligands. The K ligand can be a ligand as described above for the L group or a Cp group (-C₅R'₅), an amido group (-NR'₂) or a phosphido group (-PR'₂). The K group can also be a neutral ligand such as an ether, an amine, a phosphine, a thioether , among others. If two K groups are present, the two K groups can be connected with each other via an R group to form a bidentate ring system.

As can also be seen from formula (I), the X group of the complex contains a Y group to which are linked one or more donor groups (the Ar group(s) and/or DR'_n group(s)) via, optionally, an R group. The number of donor groups linked to the Y group is at least one and at most the number of substitution sites present on a Y group. With reference, by way of example, to the structure according to formula (II), at least one substitution site on a Cp group is made by an R_t-Ar group or by an R_t-DR'_n group (in which case q + s = 1). If all the R' groups in formula (II) were R_t-Ar groups, R_t-DR'_n groups, or any combination thereof, the value of (q + s) would be 5.

One preferred embodiment of the catalyst composition according to the present invention comprises a transition metal complex in which a bidentate/monoanionic ligand is present and in which the reduced transition metal has been selected from group 4 of the Periodic Table of Elements and has an oxidation state of +3.

In this case, the catalyst composition according to the invention comprises a transition metal complex represented by formula (V): X

I

M ( I I I ) - L₂ , ( V )

I K_ro where the symbols have the same meaning as described above for formula (I) and where M(III) is a transition metal selected from group 4 of the Periodic Table of Elements and is in oxidation state 3+.

Such a transition metal complex has no anionic K ligands (for an anionic K, m = 0 in case of M³⁺).

It should be pointed out that in WO-A- 93/19104, transition metal complexes are described in which a group 4 transition metal in a reduced oxidation state (3+) is present. The complexes described in WO-A- 93/19104 have the general formula:

Cp_a(ZY)_bML_c (VI)

The Y group in this formula (VI) is a hetero atom, such as phosphorus, oxygen, sulfur, or nitrogen bonded covalently to the transition metal M (see p. 2 of WO-A- 93/19104). This means that the Cp_a(ZY)_b group is of a dianionic nature, and has the anionic charges residing formerly on the Cp and Y groups. Accordingly, the Cp_a(ZY)_b group of formula (VI) contains two covalent bonds: the first being between the 5-member ring of the Cp group and the transition metal M, and the second being between the Y group and the transition metal. By contrast, the X group in the complex according to the present invention is of a monoanionic nature, such that a covalent bond is present between the Y group (e.g., the Cp group) and transition metal, and a coordinate bond can be present between the transition metal M and one or more of the (Ar-R_t-) and (-R_t-DR'_n) groups. This changes the nature of the transition metal complex and consequently the nature of the catalyst that is active - 14 -

in the polymerization. As referred to herein, a coordinate bond is a bond (e.g. , H₃N-BH₃) which when broken, yields either (i) two species without net charge and without unpaired electrons (e.g., H₃N: and BH₃) or (ii) two species with net charge and with unpaired electrons (e.g., H₃N- ⁺ and BH₃-^"). On the other hand, as referred to herein, a covalent bond is a bond (e.g., CH₃-CH₃) which when broken yields either (i) two species without net charge and with unpaired electrons (e.g., CH₃- and CH₃- ) or (ii) two species with net charges and without unpaired electrons (e.g., CH₃ ⁺ and CH₃:^~). A discussion of coordinate and covalent bonding is set forth in Haaland et al. (Angew. Chem Int. Ed. Eng. Vol. 28, 1989, p. 992), the complete disclosure of which is incorporated herein by reference.

The following explanation is proposed, although it is noted that the present invention is in no way limited to this theory.

Referring now more particularly to FIG. 2, the transition metal complexes described in WO-A- 93/19104 are ionic after interaction with the co¬ catalyst. However, the transition metal complex according to WO-A-93/19104 that is active in the polymerization contains an overall neutral charge (on the basis of the assumption that the polymerizing transition metal complex comprises, a M(III) transition metal, one dianionic ligand and one growing monoanionic polymer chain (POL)). By contrast, as shown in FIG. 1, the polymerization active transition metal complex of the catalyst composition according to the present invention is of a cationic nature (on the basis of the assumption that the polymerizing transition metal complex - based on the formula (V) structure - comprises, a M(III) transition metal, one monoanionic bidentate ligand and one growing monoanionic polymer chain (POL)).

Transition metal complexes in which the transition metal is in a reduced oxidation state, but have the following structure:

Cp - M(III) - L₂ (VII)

are generally not active in co-polymerization reactions. It is precisely the presence, in the transition metal complex of the present invention, of the DR'_n or Ar group (the donor), optionally bonded to the Y group by means of the R group, that gives a stable transition metal complex suitable for polymerization.

Such an intramolecular donor is to be preferred over an external (intermolecular ) donor on account of the fact that the former shows a stronger and more stable coordination with the transition metal complex.

It will be appreciated that the catalyst system may also be formed in situ if the components thereof are added directly to the polymerization reactor system and a solvent or diluent, including liquid monomer, is used in said polymerization reactor.

The catalyst composition of the present invention also contains a co-catalyst. For example, the co-catalyst can be an organometallic compound. The metal of the organometallic compound can be selected from group 1, 2, 12 or 13 of the Periodic Table of Elements. Suitable metals include, for example and without limitation, sodium, lithium, zinc, magnesium, and aluminum, with aluminum being preferred. At least one hydrocarbon radical is bonded directly to the metal to provide a carbon-metal bond. The hydrocarbon group used in such compounds preferably contains 1-30, more preferably 1-10 carbon atoms. Examples of suitable compounds include, without limitation, amyl sodium, butyl lithium, diethyl zinc, butyl magnesium chloride, and dibutyl magnesium. Preference is given to organoaluminium compounds, including, for example and without limitation, the following: trialkyl aluminum compounds, such as triethyl aluminum and tri-isobutyl aluminum; alkyl aluminum hydrides, such as di-isobutyl aluminum hydride; alkylalkoxy organoaluminium compounds; and halogen-containing organoaluminium compounds, such as diethyl aluminum chloride, diisobutyl aluminum chloride, and ethyl aluminum sesquichloride. Preferably, linear or cyclic aluminoxanes are selected as the organoaluminium compound.

In addition or as an alternative to the organometallic compounds as the co-catalyst, the catalyst composition of the present invention can include a compound which contains or yields in a reaction with the transition metal complex of the present invention a non-coordinating or poorly coordinating anion. Such compounds have been described for instance in EP-A-426,637, the complete disclosure of which is incorporated herein by reference. Such an anion is bonded sufficiently unstably such that it is replaced by an unsaturated monomer during the co¬ polymerization. Such compounds are also mentioned in EP-A-277,003 and EP-A-277,004, the complete disclosures of which are incorporated herein by reference. Such a compound preferably contains a triaryl borane or a tetraaryl borate or an aluminum equivalent thereof. Examples of suitable co-catalyst compounds include, without limitation, the following: - dimethyl anilinium tetrakis (pentafluorophenyl) borate [C_βH₅N(CH₃)₂H]⁺ [B(C₆F_s)₄]-j dimethyl anilinium bis (7,8-dicarbaundecaborate)- cobaltate (III); tri(n-butyl)ammonium tetraphenyl borate; - triphenylcarbenium tetrakis (pentafluorophenyl) borate; dimethylanilinium tetraphenyl borate; tris(pentafluorophenyl) borane; and tetrakis(pentafluorophenyl ) borate.

If the above-mentioned non-coordinating or poorly coordinating anion is used, it is preferable for the transition metal complex to be alkylated (that is, the L group is an alkyl group). As described for instance in EP-A-500, 944, the complete disclosure of which is incorporated herein by reference, the reaction product of a halogenated transition metal complex and an organometallic compound, such as for instance triethyl aluminum (TEA), can also be used.

The molar ratio of the co-catalyst relative to the transition metal complex, in case an organometallic compound is selected as the co-catalyst, usually is in a range of from about 1:1 to about

10,000:1, and preferably is in a range of from about 1:1 to about 2,500:1. If a compound containing or yielding a non-coordinating or poorly coordinating anion is selected as co-catalyst, the molar ratio usually is in a range of from about 1:100 to about

1,000:1, and preferably is in a range of from about 1:2 to about 250:1.

As a person skilled in the art would be aware, the transition metal complex as well as the co- catalyst can be present in the catalyst composition as a single component or as a mixture of several components. For instance, a mixture may be desired where there is a need to influence the molecular properties of the polymer, such as molecular weight and in particular molecular weight distribution.

In the process according to the invention the polymerization of vinyl aromatic monomers is carried out using a catalyst composition as described above. In particular the vinyl monomer (s) is/are suitably chosen from the group comprising styrene, chlorostyrene, n- butyl styrene, p-vinyl toluene etc. with styrene being especially appropriate. Mixtures of these monomers can also be used, in particular mixtures of styrene with one or more of the other vinyl monomers mentioned, to produce co-polymers.

According to the invention the catalyst composition can be used supported as well as non¬ supported. The supported catalysts are used mainly in gas phase and slurry processes. The carrier used may be any carrier known as carrier material for catalysts, for instance Si0_2f A1₂0₃ or MgCl₂. These carriers may be used as such or modified, for example by silanes and/or aluminium alkyles and/or aluminoxane compounds, etc.

Those skilled in the art will easily understand that the catalyst systems used in accordance with this invention may also be prepared in-situ methods.

Polymerization of the vinyl aromatic monomer can be effected in a known manner, for example in a solid phase powder polymerisation, in the gas phase, i.e. utilizing a fluidized bed reactor as well as in a liquid reaction medium. In the latter case, both solution and suspension polymerization are suitable. Suspension (slurry) processes are most suitable, however, to avoid unwanted side reactions taking place at high temperatures, for example the autopolymerisation of the vinyl aromatic monomer. The quantity of transition metal to be used in case of solution or suspension polymerisation generally is such that its concentration in the dispersion agent amounts to 10^_θ - IO^-3 mol/1, preferably IO^-7 - IO^-4 mol/1. The process according to the invention will hereafter be elucidated with reference to a syndiotactic polystyrene preparation known per se, which is representative of the polymerization of vinyl aromatic monomer meant here. For the preparation of other polymers on the basis of a vinyl aromatic monomer the reader is expressly referred to the multitude of publications on this subject. The preparation of syndiotactic polystyrene relates to a process for homopolymerization or copolymerisation of styrene with one or more other vinyl aromatic monomers. It has been found that the catalyst composition of the present invention is especially suitable for suspension (slurry) polymerization of styrene.

A solvent or dispersion agent may be employed in the polymerization if desired. One or more saturated, straight or branched aliphatic hydrocarbons, such as butanes, pentanes, hexanes, heptanes, pentamethyl heptane or mineral oil fractions such as light or regular petrol, naphtha, kerosine or gas oil are suitable for that purpose as are there mixtures. Also per fluorinated hydrocarbons or similar liquids can be used.

Aromatic hydrocarbons, for instance benzene and toluene, can be used, but because of their cost as well as on account of safety considerations, it will be preferred not to use such solvents for production on a technical scale. In polymerization processes on a technical scale, it is preferred therefore to use as solvent the low-priced aliphatic hydrocarbons or mixtures thereof, as marketed by the petrochemical industry.

Suitable solvents and dispersion agents also include liquid or liquified (vinyl aromatic) monomer (so-called bulk polymerisation processes).

If an aliphatic hydrocarbon is used as solvent, the solvent may yet contain minor quantities of aromatic hydrocarbon, for instance toluene. Thus, if for instance methyl aluminoxane (MAO) is used as co¬ catalyst, toluene can be used as solvent for the MAO in order to supply the MAO in dissolved form to the polymerization reactor. Drying or purification of the solvents is desirable if such solvents are used; this can be done without problems by the average person skilled in the art.

If a solution polymerisation is utilised it is preferably carried out at temperatures well above the melting point of the polymer to be produced; in general a suspension or gasphase polymerisation takes place at lower temperatures, that is temperatures well below the melting temperature of the polymer to be produced. A slurry/suspension polymerization is preferably carried out at temperatures between -100°C and + 350°C; more preferably O°-250°C, most preferably 25° - 200°C.

The polymer suspension resulting from the polymerization can be worked up by a method known per se. In general the catalyst is de-activated at some point during the processing of the polymer. The de¬ activation is also effected in a manner known per se, e.g. by means of water or an alcohol. Removal of the catalyst residues can mostly be omitted because the quantity of catalyst in the polymer, in particular the content of halogen and transition metal is very low now owing to the use of the catalyst system according to the invention.

Polymerization can be effected at atmospheric pressure, at sub-atmospheric pressure preferably between 1 and 100 KPa, or at an elevated pressure of up to 500 MPa, and under conditions where at least one of the monomers is a liquid, which can be realized by application of suitable combinations of pressure and temperature (bulk polymerisation), continuously or discontinuously. Preferably, the polymerization is performed at pressures between 0.1 and 20 MPa. Higher pressures can be applied if the polymerization is carried out in so-called high-pressure reactors. In such a high-pressure process the process according to the present invention can also be used with good results.

The polymerization can also be performed in several steps, in series as well as in parallel. If required, the catalyst composition, temperature, hydrogen concentration, pressure, residence time, etc. may be varied from step to step. In this way it is also possible to obtain products with a wide molecular weight distribution.

The invention also relates to vinyl aromatic polymers which can be obtained by means of the polymerization process according to the invention. Because the vinyl aromatic polymers produced according to the invention have such a high isotacticity in combination with a high molecular weight, the polymers or mixtures of polymers comprising the vinylaromatic polymers are very suitable for use in rotational moulding and blow moulding techniques.

The invention will now be elucidated by means of the following non-restrictive examples.

All tests in which organometallic compounds were involved were carried out in an inert nitrogen atmosphere, using standard Schlenk equipment. A method for synthesis of (dimethylaminoethyl)-tetramethyl cyclopentadienyl was published by P. Jutzi et al., Synthesis 1993, 684. TiCl₃, the esters used and the lithium reagents, 2- bromo-2-butene and 1-chlorocyclohexene were obtained from Aldrich Chemical Company. TiCl₃.3THF was obtained by heating TiCl₃ for 24 hours in THF with reflux. (THF stands for tetrahydrofurane). In the following 'Me' means 'methyl', 'iPr' means 'isopropyl, 'Bu' means 'butyl', 'iBu' means 'isobutyl', 'tertBu' means

'tertiary butyl' 'Ind' means 'indenyl', 'Flu' means 'fluorenyl', 'Ph' means 'phenyl', Cp = cyclopentadienyl, Cp⁺ = tetramethyl Cp + additional non-methyl group as the fifth substituent. Pressures mentioned are absolute pressures. Example I

Syndiotactic polymerisation of styrene using (dimethylaminoethyl) tetramethylcyclopentadienyltitanium(III)dichloride (C₅Me₄(CH₂)₂NMe₂TiCl₂) as catalyst.

Synthesis of the catalyst

a. Preparation of 4-hvdroxy-4-(dimethylamino-ethyl)- 3,5-dimethyl-2,5-heptadiene

2-bromo-2-butene (108 g; 0.800 mol) was added to 10.0 g of lithium (1.43 mol) in diethyl ether (300 ml) in about 30 minutes with reflux. After stirring overnight (17 hours), ethyl-3-(N,N- dimethylamino)propionate (52.0 g; 0.359 mol) was added to the reaction mixture in about 15 minutes. After stirring for 30 minutes at room temperature 200 ml of water was added dropwise. After separation the water phase was extracted two times with 50 ml of CH₂C1₂. The organic phase was reduced by evaporation and the residue was distilled at reduced pressure. The yield was 51.0 g (67%) .

b. Preparation of (dimethylaminoethyl)tetramethyl- cyclopentadiene

The compound (21.1 g; 0.10 mol) prepared as described under a) was added in a single portion to p- toluenesulphonic acid.H₂0 (28.5 g; 0.15 mol), dissolved in 200 ml of diethyl ether. After stirring for 30 minutes at room temperature the reaction mixture was poured out in a solution of 50 g of Na₂CO₃.10H₂O in 250 ml of water. After separation the water phase was extracted two times with 100 ml of diethyl ether. The combined ether layer was dried (Na₂S0₄), filtered and evaporated. Then the residue was distilled at reduced pressure. The yield was 11.6 g (60%). c. Preparation of (dimethylaminoethyl)tetramethyl- cvclopentadienyltitaniumfIII)dichloride

1.0 equivalent of n-BuLi (1.43 ml; 1.6 M) was added (after cooling to -60°C) to a solution of the C₅Me₄H(CH₂)₂NMe₂ of b) (0.442 g; 2.29 mmol) in THF (50 ml), after which the cooling bath was removed. After warming to room temperature the solution was cooled to -100°C and then TiCl₃.3THF (0.85 g; 2.3 mmol) was added in a single portion. After stirring for 2 hours at room temperature the THF was removed at reduced pressure. After addition of special boiling point gasoline the complex (a green solid) was purified by repeated washing of the solid, followed by filtration and backdistillation of the solvent. It was also possible to obtain the pure complex through sublimation.

d. Polymerisation of styrene

In a roundbottom flask equipped with a mechanical stirrer, 100 ml of dry toluene was introduced. 60 ml dry styrene was added to the toluene, followed by 45 mmol on Al-basis methylaluminoxane (MAO from Witco, 10% in toluene). Then the temperature of this reaction mixture was heated to 50°C. The polymerisation reaction was started by the addition of 25 micromoles of the catalyst described under Ic above (Al/Ti ratio = 1800). The polymerisation was stopped by the addition of methanol. The reaction mixture with the methanol was rinsed with water and a solution of 10 wt. % HCI in water to remove catalyst and cocatalyst residues. The mixture was neutralized using NaHC0₃ and washed several times with water. Then an antioxidant, Irganox 1076 (TM) , was added to the organic mixture for stabilisation of the polymer. In the next step the polymer was dried under vacuum for 24 hours at 70°C. The product that had been formed (7 kg polymer/mol Ti*hour) was investigated with SEC-DV, ¹³C- NMR and DSC (Differential Scanning Calorimetry) . The Mw of the polymer was determined by SEC-DV to amount 71 kg/mol. From ¹³C-NMR measurements it was concluded that the polymer formed was polystyrene of very high syndiotacticity. DSC measurements confirmed this finding by showing a very high melting point of 274°C.

Example II

Syndiotactic polymerisation of styrene using (dibutylaminoethyl)- tetramethylcyclopentadienyltitanium(III) dichloride (C₅Me₄(CH₂)₂NBu₂TiCl₂) as catalyst.

Synthesis of the catalyst a. Preparation of ethyl 3-(N,N-di-n- butylamino)propionate

Ethyl 3-bromopropionate (18.0 g; 0.10 mol) was added carefully to di-n-butylamine (25.8 g; 0.20 mol), followed by stirring for 2 hours. Then diethyl ether (200 ml) and pentane (200 ml) were added. The precipitate was filtered off, the filtrate was evaporated and the residue was distilled at sub- atmospheric pressure. The yield was 7.0 g (31%).

b. Preparation of bis(2-butenyl) (di-n-butylaminoethyl)- methanol

2-Lithium-2-butene was prepared from 2-bromo- 2-butene (16.5 g; 0.122 mol) and lithium (2.8 g; 0.4 mol) as in example I. To this, the ester of a) (7.0 g; 0.031 mol) was added with reflux in approx. 5 minutes, followed by stirring for about 30 minutes. Then was

(200 ml) was carefully added dropwise. The water layer was separated off and extracted twice with 50 ml of CH₂C1₂. The combined organic layer was washed once with 50 ml of water, dried with K₂C0₃, filtered and evaporated. The yield was 9.0 g (100%). c. Preparation of (di-n-butylaminoethyl)tetramethyl- cvclopentadiene)

4.5 g (0.015 mol) of the compound of b) was added dropwise to 40 ml of concentrated sulphuric acid of 0°C, followed by stirring for another 30 minutes at 0°C. Then the reaction mixture was poured out in a mixture of 400 ml of water and 200 ml of hexane. The mixture was made alkaline with NaOH (60 g) while being cooled in an ice bath. The water layer was separated off and extracted with hexane. The combined hexane layer was dried with K₂C0₃, filtered and evaporated. The residue was distilled at sub-atmospheric pressure. The yield was 2.3 g (55%) .

d. Preparation of (di-n- butylaminoethyl)tetramethylcyclo¬ pentadienyltitanium(III)dichloride

1.0 equivalent of n-BuLi (0.75 ml; 1.6 M) was added (after cooling to -60°C) to a solution of the C_sMe₄H(CH₂)₂NBu₂ of c) (0.332 g; 1.20 mmol) in THF (50 ml), after which the cooling bath was removed. After warming to room temperature the solution was cooled to -100°C and then TiCl₃.3THF (0.45 g; 1.20 mmol) was added in a single portion. After stirring for 2 hours at room temperature the THF was removed at sub- atmospheric pressure. The purification was done as in example I.

e. Polymerisation of styrene A polymerisation was performed as described in example Id. The transition metal complex used was the catalyst described under lid above. The polymer that was formed (polymer yield 11 kg/mol Ti*hour) was found to be of very high syndiotacticity (¹³C-NMR data) and the DSC measurements of the polymer formed confirmed this finding by showing a very high melting point of 272°C. The Mw of the polymer formed amounted 55 kg/mol .

Comparative Example A

Under the reactor conditions as described in Example I the catalyst Me₂SiCp^*NtBuTiCl₂ was tested. The polymer yield was 7 kg/mol Ti.hour. The product was syndiotactic polystyrene; determined with ¹³C-NMR. The polymer was studied by SEC-DV. The Mw was 42000 g/mol and T_max in the DSC spectrum was 268 °C. So a polymer of lower tacticity was formed using this catalyst.

Table 1 Examples of transition metal complexes according to the invention (see formulas I and VI)

10 t

15

Claims

T NL 02 2- 28 -C L A I M S

1. A process for preparing vinyl aromatic polymers having a high degree of syndiotacticity and a high molecular weight comprising contacting at least one polymerizable vinyl aromatic monomer under polymerisation conditions in the presence of a catalyst comprising a reduced transition metal complex and a co-catalyst, wherein said reduced transition metal complex has the following structure:

M - L₂

I K.,

wherein: M is a reduced transition metal selected from group 4, 5 or 6 of the Periodic Table of the Elements;

X is a multidentate monoanionic ligand represented by the formula (Ar-R_t-)_BY(-R_t- DR'_n)_q;

Y is a member selected from the group consisting of a cyclopentadienyl, amido (-NR'-), and phosphido (-PR'-) group;

R is at least one member selected from the group consisting of (i) a connecting group between the Y group and the DR'_n group and (ii) a connecting group between the Y group and the Ar group, wherein when the ligand X contains more than one R group, the R groups can be identical as or different from each other;

D is an electron-donating hetero atom selected from group 15 or 16 of the Periodic Table of Elements; R' is a substituent selected from the group consisting of a hydrogen, hydrocarbon radical and hetero atom-containing moiety, except that R' cannot be hydrogen when R' is directly bonded to the electron-donating hetero atom D, wherein when the multidentate monoanionic ligand X contains more than one substituent R', the substituents R' can be identical or different from each other; Ar is an electron-donating aryl group;

L is a monoanionic ligand bonded to the reduced transition metal M, wherein the monoanionic ligand L is not a ligand comprising a cyclopentadienyl, amido (-NR'-), or phosphido (-PR'-) group, and wherein the monoanionic ligands L can be identical or different from each other; K is a neutral or anionic ligand bonded to the reduced transition metal M, wherein when the transition metal complex contains more than one ligand K, the ligands K can be identical or different from each other; m is the number of K ligands, wherein when the K ligand is an anionic ligand m is 0 for M³⁺, m is 1 for M⁴⁺, and m is 2 for M⁵⁺, and when K is a neutral ligand m increases by one for each neutral K ligand; n is the number of the R' groups bonded to the electron-donating hetero atom D, wherein when D is selected from group 15 of the Periodic

Table of Elements n is 2, and when D is selected from group 16 of the Periodic Table of Elements n is 1; q and s are the number of (-R_t-DR'_n) groups and (Ar-R_t-) groups bonded to group Y, respectively, wherein q + s is an integer not less than 1; and t is the number of R groups connecting each of (i) the Y and Ar groups and (ii) the Y and DR'_n groups, wherein t is selected independently as 0 or 1.

2. A process according to claim 1, wherein the Y group is a cyclopentadienyl group.

3. A process according to claim 2, wherein the cyclopentadienyl group is an unsubstituted or substituted indenyl, benzoindenyl, or fluorenyl group.

4. A process according to claim 2, wherein said reduced transition metal complex has the following structure:

Y - R - DR'_n

I

M(III) - L₂,

I κ_m

wherein:

M(III) is a transition metal from group 4 of the Periodic Table of the Elements in oxidation state 3+.

5. A process according to claim 2, wherein said reduced transition metal is titanium.

6. A process according to claim 2, wherein said electron-donating hetero atom D is nitrogen.

7. A process according to claim 2, wherein the R' group in the DR'_n group is an n-alkyl group.

8. A process according to claim 2, wherein said R group has the following structure:

(-CR'₂-)_p,

wherein p is 1, 2, 3, or 4.

9. A process according to claim 2, wherein said monoanionic ligand L is selected from the group consisting of a halide, an alkyl group, and a benzyl group.

10. A process according to claim 2, wherein the Y group is a di-, tri- or tetraalkyl- cyclopentadienyl.

11. A process according to claim 2, wherein said co¬ catalyst comprises a linear or cyclic aluminoxane or a triaryl borane or tetraaryl borate.

12. A process according to claim 2, wherein at least one member selected from the group consisting of said reduced transition metal complex and said co¬ catalyst is supported on at least one carrier.

13. Process according to claims 1-12, characterized in that the vinyl aromatic monomer is chosen from the group comprising styrene, vinyl toluene, chlorostyrene, n-butylstyrene or mixtures of these.

14. Process according to claim 13, characterized in that the vinyl aromatic monomer is styrene.

15. Polymer to be obtained by a process according to any one of claims 1-14 with a melting point higher than 270°C.

16. An article formed by rotational moulding from a vinyl aromatic polymer to be obtained by a process according to any one of claims 1 - 14.

17. An article formed by blow moulding from a vinyl aromatic polymer to be obtained by a process according to any one of claims 1 - 14.

18. A film formed from a vinyl aromatic polymer to be obtained by a process according to any one of claims 1 - 14.

19. Mixtures of vinyl aromatic polymers to be obtained by a process according to any one of claims 1 - 14.

20. Mixtures of vinyl aromatic polymers to be obtained by a process according to any one of claims 1 - 14 with other polymer materials.