PROCESS FOR THE CO-POLYMERIZATION OF AN OLEFIN AND A VINYL AROMATIC MONOMER

Abstract: A process for the co-polymerization of at least one alpha -olefin and at least one vinyl aromatic monomer. The co-polymerization is carried out in the presence of a catalyst composition including at least one co-catalyst and a reduced transition metal complex. The reduced transition metal complex contains a reduced transition metal selected from groups 4-6 of the Periodic Table of the Elements, a multidentate monoanionic ligand, and at least two monoanionic ligands. In one embodiment, the reduced transition metal is selected as titanium.

Description: PROCESS FOR THE CO-POLYMERIZATION OF AN OLEFIN AND A VINYL AROMATIC MONOMER BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a process for the co-polymerization of an olefin, especially ethylene, and a vinyl aromatic monomer. In particular, the present invention relates to the co-polymerization process conducted in the presence of a catalyst composition comprising a transition metal complex and a co-catalyst. 2. Description of the Related Art A process for the co-polymerization of ethylene and a vinyl aromatic monomer is disclosed in EP-A-416,815, in which a so-called constrained-geometry catalyst is applied. The catalysts disclosed in this reference have had success, to some extent, in co-polymerizing vinyl aromatic monomers with ethylene. A disadvantage of the process disclosed in this reference, however, is the unfavorable molecular weights of the co-polymers obtained and the insufficient percentage of vinyl aromatic monomers incorporated into the resultant co-polymers under a given set of polymerization conditions. It is known to enhance this ratio by lowering the polymerization temperature; however, the lowering of the polymerization temperature leads to decreased catalyst activity and an inferior co-polymer yield. A need therefore exists to provide a process that, under a given set of polymerization conditions, produces a co-polymer having, at a given molecular weight, a higher concentration of co-polymerized vinyl aromatic monomers than could be obtained via previously known processes conducted under similar process conditions. SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to solve the aforementioned problems associated with the related art as well as to address the need expressed above. In accordance with the principles of the present invention, this object is obtained by providing a process for the co-polymerization of at least one α-olefin and at least one vinyl aromatic monomer 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) | M - L 2 I κ m 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 -) B Y(-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 is the number of K ligands, wherein when the K ligand is an anionic ligand m is 0 for M 3+ , m is 1 for M 4 *, and m is 2 for M 5+ , 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 - A - 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 non-limiting examples of transition metal complexes according to the invention are presented below in Table 1. In the process according to the present invention, a higher catalytic activity is observed in the co-polymerization reaction between a process employing ethylene and a vinyl aromatic monomer. Consequently, the co-polymer prepared in accordance with the process of the present invention also has a higher concentration of vinyl aromatic monomers incorporated into the co-polymer than could be obtained for a co-polymer, of the same molecular weight, prepared in accordance with the above-mentioned known process conducted under similar process conditions. Another object of the present invention is the provision of a copolymer of at least one α-olefin and at least one vinyl aromatic monomer obtained by means of the above-mentioned polymerization process with utilization of the catalyst composition according to the invention. These and other objects, features, and advantages of the present invention will become apparent from the following detailed description when taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS 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. DESCRIPTION OF THE PREFERRED EMBODIMENTS 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 M 3+ for a transition metal of group 4, at most M 4+ for a transition metal of group 5 and at most M 5+ for a transition metal of group 6). ( b ) The X Ligand The X ligand is a multidentate monoanionic ligand represented by the formula: (Ar-R t -) S Y(-R t -DR '„) 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 _ λ -R t -ΩR ' n and Y(-R- DR' n ) 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, fiuorenyl, 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'„ 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-DR R-Ar 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, fiuorenyl, 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-DR It is noted that, generally, the transition metal group M is bonded to the Cp group via an ή 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' n 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 IUPAC 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' 2 CR ' 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 (C 6 R' 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 fiuorenyl group. The coordination of this Ar group in relation to the transition metal M can vary from h 1 to I") 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 fiuorenyl or a benzoindenyl group. The indenyl, fiuorenyl, 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(CH 3 ) 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 CI group and/or a C^- C 4 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 f or M 3+ m = 1 f or M 4+ m = 2 f or M 5+ On the other hand, neutral K ligands, which by definition are not anionic, are not subject to the 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 (-C 5 R' 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'„ 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(III) - L 2 ' (V) K„ 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 M 3+ ). 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) b ML 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 in the polymerization. As referred to herein, a coordinate bond is a bond (e.g., H 3 N-BH 3 ) which when broken, yields either (i) two species without net charge and without unpaired electrons (e.g., H 3 N: and BH 3 ) or (ii) two species with net charge and with unpaired electrons (e.g., H 3 N- + and BH 3 - ~ ). On the other hand, as referred to herein, a covalent bond is a bond (e.g., CH 3 - CH 3 ) which when broken yields either (i) two species without net charge and with unpaired electrons (e.g., CH 3 - and CH 3 - ) or (ii) two species with net charges and without unpaired electrons (e.g., CH 3 + and CH 3 :"). 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) - L 2 (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 6 H 5 N(CH 3 ) 2 H] + [B(C 6 F 5 ) 4 ] " ; - 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. The present invention relates to a process for the co-polymerization of one or more α-olefins and one or more vinyl aromatic monomers. As referred to herein, the term "monomer" as encompasses dimers, trimers, and oligomers. The α-olefin is preferably at least one member selected from the group consisting of ethylene, propylene, butene, pentene, heptene and octene, and any combination thereof. More preferably, at least one member selected from the group consisting of ethylene and propylene is selected as the α-olefin. Suitable vinyl aromatic monomers which can be polymerized in the process of the present invention include, without limitation, those represented by the formula: wherein each R 2 in formula (VIII) is, for example, independently selected as one of the following: hydrogen; an aliphatic, cycloaliphatic or aromatic hydrocarbon group having from 1 to 10 carbon atoms, more suitably from 1 to 6 carbon atoms, most suitably from 1 to 4 carbon atoms; and a halogen atom. Exemplary vinyl aromatic monomers include, without limitation, styrene, chlorostyrene, n- butyl styrene, and p-vinyl toluene. Especially preferred is styrene. The amount of vinyl aromatic monomer incorporated in the copolymers of the present invention is at least 0.1 mol%. Additional olefin monomers can be co¬ polymerized in the same process to thereby yield ter¬ polymers and higher polymers (which are also referred to herein as being encompassed by the term "co-polymer" and made by the "co-polymerization process"). Other olefin monomers include, by way of example and without limitation, ethylene, propylene, butene, pentene, hexene, heptene, octene and dienes such as 1,4-hexadiene, 1,7- octadiene, dicyclopentadiene (DCPD) , 5-vinylidene-2- norbornene, 5-ethylidene-2-norbornene, and 5-methylene-2- norbornene, and polyenes such as polybutadiene. The process according to the invention is also suitable for the preparation of rubber-like copolymers based on an α-olefin, a vinyl aromatic monomer and a third monomer. It is preferred to use a diene as the third monomer. Suitable dienes for preparing rubber-like copolymers include those specified above. The catalyst can be used as is, or optionally the catalyst can be supported on a suitable support or carrier, such as alumina, MgCl 2 or silica, to provide a heterogeneous supported catalyst. The transition metal complex or the co-catalyst can be supported on the carrier. It is also possible to support both the transition metal complex and co-catalyst on the same or different carriers. Where more than one carrier is provided, the carriers can be the same or different from each other. The supported catalyst systems of the invention can be prepared separately before being introduced into the co-polymerization reaction, or can be formed in situ, for example, before the co-polymerization reaction commences. By way of example, the co-polymerization reaction can be conducted under solution or slurry conditions, in a suspension utilizing a perfluorinated hydrocarbon or similar liquid, in the gas phase (for example, by utilizing a fluidized bed reactor), or in a solid phase powder polymerization. A catalytically effective amount of the present catalyst and co-catalyst are any amounts that succesfully 97/42240 PC NL97 - 21 - result in formation of the co-polymer. Such amounts can be readily determined by the routine experimentation by the skilled artisan. For instance, where the co-polymerization is conducted in a liquid reaction medium via in solution or suspension polymerization, which are preferred for the process of the invention, the quantity of transition metal complex to be used generally can be such that the concentration of the transition metal in the solution or dispersion agent is about IO -8 mol/1 to about IO -3 mol/1 , and preferably about 10 ~7 mol/1 to about IO "4 mol/1. It is to be understood that the transition metal complex described herein undergoes various transformations or forms intermediate species prior to and during the course of co-polymerization. Thus, other catalytically active species or intermediates formed from the metal complexes described herein and other metal complexes (precursors) than those described herein that achieve the same catalytic species as the complexes of the present invention are herein envisioned without departing from the scope or the present invention. Any liquid that is inert relative to the catalyst system can be used as a dispersion agent in the co-polymerization process. Suitable inert liquids that can be selected as the dispersion agent include, without limitation, the following: one or more saturated, straight or branched aliphatic hydrocarbons, including, without limitation, butane, pentane, hexane, heptane, pentamethyl heptane, and any combination thereof ? and/or one or more mineral oil fractions, including, without limitation, light or regular petrol, naphtha, kerosine, gas oil, and any combination thereof. Aromatic hydrocarbons, for instance benzene, ethylbenzene and toluene, can be also used; however, due to the high cost associated with aromatic hydrocarbons, as well as safety considerations, it is generally preferred not to use such solvents for production on a technical (or commercial) scale. In polymerization processes on a technical (or commercial) scale, it is, therefore, preferred to use as the solvent the low-priced aliphatic hydrocarbons or mixtures thereof, as marketed by the petrochemical industry. Excess vinyl aromatic or olefin monomers, including liquid vinyl aromatic or olefin monomers, can also be applied in so-called bulk polymerization processes. If an aliphatic hydrocarbon is used as the solvent, the solvent can yet contain minor quantities of aromatic hydrocarbons such as, for instance, toluene. Thus, if, for instance, methyl aluminoxane (MAO) is selected as the co-catalyst, toluene can be used as the solvent for the MAO in order to dissolve the MAO into solution and supply the solution to the polymerization reactor. Drying or purification of the solvents is desirable if such solvents are used; this can be done without undue experimentation by the skilled artisan. If solution or bulk polymerization is utilized, the polymerization is preferably carried out at temperatures well above the melting point of the polymer to be produced. Suitable temperatures generally include, without limitation, temperatures in a range of from about 120°C to about 260°C. In general, suspension or gas phase polymerization takes place at lower temperatures, that is, temperatures well below the melting temperature of the polymer to be produced. Generally, temperatures suitable for suspension or gas phase polymerization are below about 105°C. The polymer solution 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 generally be omitted, since the quantity of catalyst in the co-polymer, in particular the content of halogen and transition metal in the co-polymer, is very low due to the use of the catalyst system according to the invention. Co-polymerization can be effected at sub- atmospheric, atmospheric and elevated pressure, 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, continuously or discontinuously. If the co-polymerization is carried out under pressure, the polymer yield can be increased substantially, resulting in an even lower catalyst residue content. Preferably, the co-polymerization is performed at pressures in a range of from about 0.1 MPa to about 25 MPa. Higher pressures, typically but not limited to 100 MPa and above, can be applied if the polymerization is carried out in so-called high-pressure reactors. In such a high-pressure process, the catalyst according to the present invention can also be used with good results. The co-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., or any combination thereof can be varied from step to step. In this way, products having a wide molecular weight distribution can be obtained. EXAMPLES The process according to the invention will hereafter be elucidated with reference to the following examples, which serve to explain the present invention in more detail. It will be appreciated that the invention is not restricted to these exemplary examples and processes. 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 is published by P. Jutzi et al., Synthesis 1993, 684, the complete disclosure of which is incorporated herein by reference. TiCl 3 , the esters, the lithium reagents, 2- bromo-2-butene and 1-chlorocyclohexene each were supplied by Aldrich Chemical Company. TiCl 3 -3THF was obtained by heating TiCl 3 for 24 hours in THF with reflux. In the following example, THF refers to tetrahydrofuran, "Me" refers to methyl, "(t)Bu" refers to (tertiary) butyl, "Ind" refers to indenyl, "Flu" refers to fiuorenyl, and "iPr" refers to iso-propyl. Synthesis of bidentate monocyclopentadienyl transition metal complexes Examples I-IV set forth non-limiting processes for preparing embodiments of the transition metal complexes of the present invention. Example I Synthesis of (dimethylaminoethyl )tetramethyl- cyclopentadienyltitanium(III)diehloride (C 5 Me 4 (CH 2 ) 2 NMe 2 TiCl 2 ) . (a) Preparation of 4-hydroxy-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) over the course of 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 over a course of 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 CH 2 C1 2 . The organic phase was boiled down and the residue was distilled at reduced pressure. The yield was 51.0 g (67%). (b) Preparation of (dimethylaminoethyl)tetramethyl- cvclopentadiene The compound (21.1 g; 0.10 mol) prepared as described above in Example 1(a) was added in a single portion to p-toluenesulphonic acid H 2 0 (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 Na 2 CO 3 -10H 2 O 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 (with Na 2 S0 4 ), filtered and boiled down. Then the residue was distilled at reduced pressure. The yield was 11.6 g (60%). (c) Preparation of (dimethylaminoethyl )tetramethyl¬ cyclopentadienyltitanium(III)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 C 5 Me 4 H(CH 2 ) 2 NMe 2 of Example 1(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 TiCL 3 -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 (i.e., a C 6 hydrocarbon fraction with a boiling range of 65-70°C, obtainable from Shell or Exxon, 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. Example II Synthes is of ( dibutylaminoethyl ) tetramethyl- cyclopentadienylt itanium ( III ) dichlor ide (C 5 Me 4 ( CH 2 ) 2 NBu 2 TiCl 2 ) . (a ) Preparat ion 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 boiled down and the residue was distilled at sub-atmospheric pressure. The yield was 7.0 g (31%). (b) Preparation of bis(2-butenylHdi-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 Example IΙ(a) (7.0 g; 0.031 mol) was added with reflux over the course of approximately 5 minutes, followed by stirring for about 30 minutes. Then (200 ml) of water was carefully added dropwise. The water layer was separated off and extracted twice with 50 ml of CH 2 C1 2 . The combined organic layer was washed once with 50 ml of water, dried with K 2 C0 3 , filtered and boiled down. 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 Example IΙ(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 K 2 C0 3 , filtered and boiled down. The residue was distilled at sub-atmospheric pressure. The yield was 2.3 g (55%). (d) Preparation of (di-n-butylaminoethyl) tetramethylcvclo-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 s Me 4 H(CH 2 ) 2 NBu 2 of Example 11(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 TiCL 3 - 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 performed as in Example I. Example III As another catalyst component, (didecylaminoethyl)tetramethyl-cyclopentadienyl- titanium(III) dichloride (C 5 Me 4 (CH 2 ) 2 N(C 10 H 21 ) 2 TiCl 2 ) was prepared in an analoguous way as described in Example I, the difference being that the corresponding di-decyl- amino-propionate was applied in place of the ethyl-3-(N,N- dimethylamino)propionate. Example IV Synthesis of [l,2,4-triisopropyl-3-(dimethyl- aminoethyl)cyclopentadienyl]-titanium(III)dimethyl. (a) Reaction of cyclopentadiene with isopropyl bromide Aqueous KOH (50%; 1950g, about ca. 31.5 mol in 2.483 L water) and as a phase transfer agent Adogen 464 (31.5 g) were placed in a 3L three-neck flask fitted with a condenser, mechanical stirrer, heating mantle, thermometer, and an inlet adapter. Freshly cracked cyclopentadiene (55.3g, 0.79 mol) and isopropyl bromide (364 g, 2.94 mol) were added and stirring was begun. The mixture turned brown and became warm (50°C). The mixture was stirred vigorously over night, after which the upper layer containing the product was removed. Water was added to this layer and the product was extracted with hexane. The combined hexane layer was washed once with water and once with brine, and after drying (with MgS0 4 ) the solvent was evaporated, leaving a yellow-brown oil. GC and GC-MS analysis showed the product mixture to contain diisopropylcyclopentadiene (iPr 2 -Cp, 40%) and triisopropylcyclopentadiene (iPr 3 -Cp, 60%). iPr 2 -Cp and iPr 3 -Cp were isolated by distillation at reduced (20 mmHg) pressure. Yield depended on distillation accuracy (approx. 0.2 mol iPr 2 -Cp (25%) and 0.3 mol iPr 3 -Cp (40%)). (b) Reaction of lithium 1,2 , 4-triisopropylcvclo- pentadienyl with dimethylaminoethyl chloride In a dry 500 ml flask containing a magnetic stirrer, under dry nitrogen, a solution of 62.5 mL of n- butyllithium (1.6 M in n-hexane; 100 mmol) was added to a solution of 19.2 g (100 mmol) of iPr 3 -Cp in 250 ml of THF at -60 °C. The solution was allowed to warm to room temperature after which the solution was stirred overnight. After cooling to -60°C, dimethylaminoethyl chloride (11.3g, 105 mmol, freed from HCl (by the method of Rees W.S. Jr. & Dippel K.A. in OPPI BRIEFS vol 24, No 5, 1992, which is incorporated herein by reference) was added via a dropping funnel over the course of 5 minutes. The solution was allowed to warm to room temperature, after which it was stirred overnight. The progress of the reaction was monitored by GC. After addition of water and an alkane mixture, the organic layer was separated, dried and evaporated under reduced pressure. Next to starting material iPr 3 -Cp (30%), 5 isomers of the product (dimethylaminoethyl )-triisopropylcyclopentadiene (LH; 70%) are visible in GC. Two isomers are geminal (together 30%). Removal of the geminal isomers was feasible by precipitation of the potassium salt of the iPr 3 -Cp anion and filtration and washing with an alkane mixture (3x). The overall yield (relative to iPr 3 -Cp) was 30 mmol (30%). (c) Applied reaction sequence to r1,2 , 4-triisopropyl-3- (dimethylaminoethyl )-cvclopentadenyl 1- titaniumdll)dimethyl Solid TiCl 3 -3THF (18.53g, 50.0 mmol) was added to a solution of K iPr 3 -Cp in 160 mL of THF at -60°C at once, after which the solution was allowed to warm to room temperature. The color changed from blue to green. After all the TiCl 3 -3THF had disappeared, the reaction mixture was cooled again to -60 °C after which 2.0 equivalents of MeLi (62.5 ml of a 1.6 M solution in Et 2 0) were added. After warming to room temperature again, the black solution was stirred for an additional 30 minutes after which the THF was removed at reduced pressure. Polymerization experiments Examples V-XVII set forth non-limiting processes for preparing copolymers with the transition metal complexes of the present invention. Polymerization experiments were carried out according to the procedure described in general terms below. Unless otherwise indicated, the conditions specified in Example V were applied in each of the individual examples. Example V Styrene was distilled from CaH 2 under vacuum. 600 ml of an alkane mixture was introduced as a solvent into a stainless steel reactor with a volume of 1.5 liters under a dry N 2 atmosphere. Then, the required amount of dry styrene was introduced into the reactor. The reactor was heated to 80°C, while stirring, at an absolute ethylene pressure of 800 kPa. 25 ml of an alkane mixture was dosed as a solvent into a catalyst premixing vessel having a volume of 100 ml. The required amount of the methyl aluminoxane cocatalyst (MAO, from Witco, 10 wt.% solution in toluene) was premixed for 1 minute with the required amount of transition metal compound This mixture was subsequently dosed to the reactor, after which the polymerization started. The polymerization reaction was carried out isothermally. A constant absolute ethylene pressure of 8 bar was maintained. After the desired time, the ethylene supply was stopped and the reaction mixture was drained and quenched with the aid of methanol. The methanol-containing reaction mixture was washed with water and HCl to remove residual catalyst. Then the mixture was neutralized with the aid of NaHC0 3 . Next, an antioxidant (Irganox 1076, TM) was added to the organic fraction to stabilize the polymer. The polymer was dried in a vacuum for 24 hours at 70°C. Example VI The reactor was filled with 600 ml of alkane mixture and 45 g of styrene according to the procedure set forth above in Example V. The reactor was brought to a temperature of 80°C and was saturated with 8 bar ethylene, with stirring. 10 micromol EtCp(iPr) 3 NMe 2 TiCl 2 (Example IV) was premixed with 20 mmol MAO (Al/Ti=2000) for 1 minute in a catalyst metering vessel. After 6 minutes of polymerization, the reaction mixture was drained and quenched with the aid of methanol. After being stabilized, the polymer was dried in a vacuum. The polymer yield amounted to 15.8 kg/mol Ti-hour. The product was analyzed by means of SEC-DV, X H-NMR and DSC. The formed polymer was a copolymer with an Mw of 250,000 g/mol and a maximum melting temperature (as determined via DSC) of 93°C. Comparative experiment A With the aid of the transition metal compound Me 2 SiCp*NtBuTiCl 2 known from EP-A-416,815 a copolymerization reaction was carried out under the conditions described in Example VI, using MAO as the cocatalyst (Al:Ti ratio = 2000), for 7 minutes. The yield was 14.6 kg/mol Ti.hour. The product had an Mw of 145,000 g/mol and a maximum melting temperature of 114°C. Example VII Example VI was repeated, except that 75 g of styrene was added to the reactor contents. 10 micromol of the transition metal compound (C 5 Me 4 H(CH 2 ) 2 N(C 10 H 21 ) 2 TiCl 2 (Example III) was mixed with 10 mmol MAO (Al:Ti = 1000:1) for 1 minute in the catalyst metering vessel. The reaction mixture was subjected to co-polymerization. The yield was 6.7 g. The styrene content as determined by ^-NMR amounted to 7.5 mol.%. The Mw, as determined by means of SEC-DV, was 180,000 g/mol. Example VIII Example VII was repeated, except that 10 micromol of the transition metal compound (C 5 Me 4 (CH 2 ) 2 NBu 2 TiCl 2 (Example II) was premixed with 10 mmol MAO (Al:Ti = 1000:1) for 1 minute. The copolymer formed had an Mw (as determined by means of SEC-DV) of 180,000 g/mol. The styrene content was determined by means of ^-H-NMR and found to be 6.3 mol.%. Example IX A co-polymerization process was carried out using the transition metal compound (C 5 ME 4 (CH 2 ) 2 NMe 2 TiCl 2 (Example I) under the conditions described in Example VII. The copolymer formed contained 8.6 mol.% styrene, as determined by means of ^-NMR. The polymer had an Mw of 130,000 g/mol (SEC-DV). Comparative experiment B The copolymerization of ethylene and styrene was carried out as described in Example VII, with the exception that the catalyst composition included 10 micromol Me 2 SiCp*NtBuTiCl 2 and 20 mmol MAO (Al:Ti = 2000:1), which were mixed for 1 minute in the catalyst metering vessel. The polymer formed (6.2 g) was found to have an Mw of 82,000 g/mol (as determined by means of SEC- DV) and to contain 4.2 mol.% styrene. Example X A catalyst on a carrier was synthesised by adding 10 ml of dry toluene to 1.453 g of Si0 2 (Grace/Davidson W952, dried for 4 hours at 400°C under dry N 2 ). Then 16 ml of MAO (Witco, 30% by weight in toluene) was added over the course of 10 minutes, with stirring, at 300 K. The sample was dried for 2 hours in a vacuum, with stirring, after which 25 ml of an alkane mixture was added and the resultant mixture was stirred for 12 hours at 300K. Next, a suspension of IO "4 mol (C 5 Me 4 (CH 2 ) 2 NMe 2 TiCl 2 (Example I) was added, with stirring. After drying, the catalyst was found to contain 27.9 wt.% Al and to have an Al/Ti ratio of 328. A co-polymerization experiment was carried out using the supported catalyst described above, under conditions comparable with those of Example VI. 45 g of styrene was added to the reactor. Then 20 micromol (based on Ti) of supported catalyst was introduced into the reactor. The co-polymerization reaction was carried out at an ethylene pressure of 8 bar, at 80°C. The formed polymer (1450 kg/mol Ti.hour) was analyzed by means of SEC-DV. The Mw was found to be 490,000 g/mol at a styrene content of 3.1 mol.% (as determined via X H-NMR). Example XI A stainless steel reactor with a volume of 1.5 liters was filled with 600 ml of a mixed high-boiling alkane solvent (with a boiling range starting at 180°C) for a solution polymerization. The temperature was raised to 150°C while stirring. Then the reactor was saturated with ethylene and the ethylene pressure was brought to 21 bar. 45 g of dried styrene was introduced into the reactor. Next, 0.4 mmol aluminium alkyl (triethylaluminium) was introduced into the reactor as a scavenger. The transition metal complex (C 5 Me 4 (CH 2 ) 2 NMe 2 TiMe 2 , obtained by methylating the compound of Example I by a method similar to that described in Example IV(c), was premixed with dimethylaniline tetrakis- (pentafluorophenyl )borate (DMAHBF 20 ) in 25 ml of high- boiling alkane solvent (B/Ti ratio = 2) for 1 minute in a 100-ml catalyst metering vessel. The co-polymerization reaction was started by introducing the reaction mixture from the catalyst premixing vessel into the reactor. A constant ethylene pressure of 21 bar was maintained and the co-polymerization was carried out isothermally at 150°C. After 10 minutes the reaction mixture was drained from the reactor, quenched with methanol and stabilized with antioxidant (Irganox 1076 (TM) ) . After drying in a vacuum, the product was analyzed by means of SEC-DV. The product was found to have a molecular weight of 82,000 g/mol. The product also contained 2.7 mol.% styrene as determined by means of X H-NMR and the DSC curve indicated a maximum melting temperature of 127°C. Example XII A co-polymerization reaction was carried out as described in Example VII, with the exception that the transition metal complex was (C 5 Me 4 (CH 2 ) 2 NBu 2 TiMe 2 , obtained by methylating the compound of Example II according to the method described in Example IVc. The polymer formed was analyzed by means of SEC-DV (Mw = 80,000 g/mol) and L H-NMR (4.0 mol.% styrene content). Example XIII A co-polymerization reaction was carried out as described in Example VI, except that the transition metal complex was EtCp(iPr ) 3 NMe 2 TiMe 2 , obtained by methylating the compound of Example IV. The polymer formed was analyzed by means of SEC-DV (Mw = 105,000 g/mol) and l E- NMR (styrene content 3.8 mol.%). Example XIV A co-polymerization reaction was carried out as described in Example VI, with the difference being that 3.0 ml of dried 1,7-octadiene was additionally introduced into the reactor as a third monomer after the styrene had been introduced (terpolymerization) . Then the co-polymerization was carried out in exactly the same manner as described in Example VI. The polymer formed contained 1.6 mol.% styrene and 0.6 mol.% octadiene, both as determined by means of 13 C-NMR and 1 H- NMR, at a polymer yield of 12,000 kg/mol Ti.hour. Example XV An ethylene/styrene co-polymerization process was carried out as described in Example VI, only now 225 g of styrene was co-polymerized at an ethylene pressure of 600 KPa. The co-polymerization was carried out at 80°C using (C 5 Me 4 ) (CH 2 ) 2 NMe 2 TiCl 2 (Example I) and MAO (Al/Ti = 1000). The product formed was purified and analyzed by means of SEC-DV. The Mw was found to be 100 kg/mol and the Mn 53,000 g/mol. ^-H-NMR analysis showed that the polymer contained 19.9 mol.% styrene. Example XVI A co-polymerization experiment was carried out as described in Example XII, with the exception that the transition metal compound was EtCp(iPr ) 3 NMe 2 TiCl 2 (Example IV), which was used in combination with MAO (Al/Ti = 1000) and 135 g of styrene was added as the second monomer. SEC-DV analysis of the polymer formed revealed an Mw of 150,000 g/mol. The Mn was 47,000 g/mol. The co- polymer contained 12.3 mol.% styrene as determined by means of 1 H-NMR. Comparative experiment C A co-polymerization experiment was carried out as described in Example XIII, except that the catalyst composition included the transition metal compound Me 2 SiCp*NtBuTiCl 2 in combination with MAO (Al/Ti = 1000). At a styrene content comparable with that obtained in Example 12, the Mw and Mn were found to be only 24,000 g/mol and 9,000 g/mol, respectively. Table 1 Examples of transition metal complexes according to the invention ( see formulas I and V ) v I 10 CO I (*» It will thus be seen that the objectives and principles of this invention have been fully and effectively accomplished. It will be realized, however, that the foregoing preferred specific embodiments have been shown and described for the purpose of this invention and are subject to change without departure from such principles.

Claims: WHAT IS CLAIMED IS: 1. A process comprising co-polymerizing at least one α-olefin and at least one vinyl aromatic monomer 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: X I M - L. 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 -),Y(-R t - DR' n ) g ; 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 0 97 00239 - 39 - 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 M 3+ , m is 1 for M 4+ , and m is 2 for M 5+ , 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 fiuorenyl group. 4. A process according to claim 2, wherein said reduced transition metal complex has the following structure: R - DR 1 M(III) - L 2 , I K„ 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. A process according to claim 2, wherein said α- olefin is at least one member selected from the group consisting of ethylene, propylene, butene, hexene, octene, and any combination thereof. 14. A process according to claim 2, wherein said vinyl aromatic monomer is at least one member selected from the group consisting of styrene, chlorostyrene, n-butyl styrene, p-vinyl toluene, and any combination thereof. 15. A process according to claim 2, wherein said process further comprises co-polymerizing a diene. 16. A process according to claim 2, wherein said process further comprises a step of obtaining a rubber-like co-polymer. 17. A process according to claim 15, wherein said process further comprises a step of obtaining a rubber-like co-polymer. 18. A resin produced by a process according to claim 2. 19. A polymer blend containing one or more resins according to claim 18. 20. A film formed from a co-polymer obtained by a process according to claim 2. 21. An article manufactured from a resin according to claim 18.

Inventors: PIETERS PAULUS JOHANNES JACOBU, VAN BEEK JOHANNES ANTONIUS MAR, VAN TOL MAURITS FREDERIK HENDR, PIETERS, PAULUS, JOHANNES, JACOBUS, VAN BEEK, JOHANNES, ANTONIUS, MARIA, VAN TOL, MAURITS, FREDERIK, HENDRIK
Applicants: BEEK JOHANNES ANTONIUS MARIA V, DSM NV, PIETERS PAULUS JOHANNES JACOBU, TOL MAURITS FREDERIK HENDRIK V, DSM N.V., PIETERS, PAULUS, JOHANNES, JACOBUS, VAN BEEK, JOHANNES, ANTONIUS, MARIA, VAN TOL, MAURITS, FREDERIK, HENDRIK
Application year: 1997
Main classification: C08F212
IPC codes: C08F4, C08F210, C08F212, C08J5