METALLOCENE CATALYSTS HAVING MULTI-NUCLEAR CONSTRAINED GEOMETRY AND ETHYLENE/AROMATIC VINYL COMPOUND CO-POLYMERS PREPARED BY USING THE SAME Field of the Invention The present invention relates to metallocene catalysts for copolymerization of ethylene/vinyl aromatic compound. More particularly, the present invention relates to the constrained geometry metallocene catalysts having a structure linked with more than two ligands of transition metal complex, isotactic-alternating- ethylene/vinyl aromatic compound copolymers having high isotacticity, alternating index and improved physical properties, which are copolymerized using said catalysts, and a method of preparing the copolymers.

Background of the Invention In general, olefin or styrene polymers are prepared by radical polymerization, ion polymerization, or coordination polymerization using Ziegler-Natta Catalysts.

By radical polymerization or ion polymerization, atactic polymers are obtained and by coordination polymerization using a Ziegler-Natta Catalyst, isotactic polymers are mainly obtained. The polymers are classified into an atactic, an isotactic and a syndiotactic structure depending on the position of benzene rings as side chains. An atactic structure has an irregular arrangement of the benzene rings and an isotactic polystyrene has an arrangement that the benzene rings are positioned at one side of the polymer main chain. On the other hand, a syndiotactic structure has a regularly alternating arrangement of the benzene rings.

Copolymerization of ethylene and a vinyl aromatic compound such as styrene has been studied for a couple of decades. At the beginning of time, a polymerization method using a heterogeneous Ziegler-Natta catalyst was introduced

(Polymer Bulletin 20,237-241 (1988)). However, the conventional method has shortcomings in that the catalyst has poor activity, the copolymer has a low content of styrene and poor uniformity, and the copolymer is mostly a homopolymer.

Further, a copolymer of ethylene and styrene has been prepared using a homogeneous Ziegler-Natta catalyst system comprising a transition metal compound and an organoaluminum compound.

Japanese Patent Laid-Open Nos. 3-163088 and 7-53618 disclose a pseudo-random styrene/ethylene copolymer prepared by using a catalyst with a constrained geometrical structure, which does not have any head-to-tail bonds. The phenyl groups in the alternating structure of the pseudo-random styrene/ethylene copolymer do not have stereoregularity. When the larger amount of styrene was incorporated in the pseudo-random styrene/ethylene copolymer, the copolymer shows the same properties as an amorphous resin with no crystallinity.

Japanese Patent Laid-Open No. 6-49132 and Polymer Preprints (Japan 42, 2292 (1993)) disclose a method for producing a styrene/ethylene copolymer which is a pseudo random copolymer with no head-to-tail bonds. The styrene/ethylene copolymer is prepared a bridged indenyl zirconium complex and a cocatalyst.

According to the Polymer Preprints, the ethylene/styrene alternating structure in the pseudo random copolymer does not show stereoregularity.

Further, Japanese Patent Laid-Open No. 3-250007 and Stud. Surf. Sci. Catal.

517 (1990) disclose a styrene/ethylene alternating copolymer prepared by using a Ti complex having a substituted phenol type ligand. The copolymer has a styrene/ethylene alternating structure but has neither an ethylene chain nor styrene chains including head-to-head bonds and tail-to-tail bonds. The copolymer is a perfect alternating copolymer with an alternating degree of at least 70, preferably at least 90. However, as the ratio of ethylene to styrene is 50 % to 50 % by weight, it is difficult to vary the contents of the composition. The phenyl groups form isotactic streroregularity of which isotactic diad index is 0.92. As the copolymer has a molecular weight of 20,000 or below, the physical properties are poor. The catalyst has poor activity and a homopolymer such as syndiotactic polystyrene is obtained.

Therefore, the polymerization method is not successfully commercialized.

Meanwhile, Macromol. Chem., 191,2387 (1990) has reported a styrene/ethylene copolymer prepared by using CpTiCl3 as a transition metal compound and methyl aluminoxane as a cocatalyst. The copolymer includes pseudo random copolymer with no styrene chains. The catalyst shows poor activity. The publication does not mention about stereoregularity of the phenyl groups.

Eur. Polym. J., 31,79 (1995) discloses a polymerization of ethylene and styrene using a catalyst of CpTiBz3. According to the process, homopolymers such as polystyrene and syndiotactic polystyrene are obtained instead of copolymers of styrene/ethylene.

Macromolecules, 29,1158 (1996) discloses polymerization of ethylene/styrene using CpTiCl3 as a catalyst and a boron type cocatalyst, resulting to prepare a mixture of a copolymer having a high degree of alternating structure, a syndiotactic polystyrene and a polyethylene. The publication does not mention about stereoregularity of the phenyl groups.

U. S. Patent No. 5,883,213 discloses an ethylene/styrene copolymer having a weight average molecular weight of at least 81, 000, having a styrene content of from 1 to less than 55 % by mole fraction, wherein the stereoregularity of phenyl groups in the alternating structure of ethylene and styrene is represented by an isotactic diad index of more than 0.75.

According to the catalyst disclosed in EP 0 416 815 A2, the yield of copolymer per metal unit is low, a larger amount of an organoaluminum compound is used, the polymerization process is carried out at a high temperature and a high pressure, and the polymer is amorphous due to lack of stereoregularity. Further, the polymer has a pseudo-random structure.

Accordingly, the present inventors have developed new constrained geometry metallocene catalysts for olefin/styrene copolymerization, which are superior to a conventional Ziegler-Natta catalyst in activity of the catalyst, content of styrene, amount of homopolymer prepared, and heterogeneous proportion of the polymer.

Objects of the Invention A feature of the present invention is the provision of a metallocene catalyst of preparing ethylene/vinyl aromatic compound copolymer which is designed to improve low activity of catalyst, a low styrene content, an excess amount of homopolymer by-products and ununiform composition in the heterogeneous Ziegler-Natta catalyst system.

Another feature of the present invention is the provision of a metallocene catalyst of preparing a large amount of ethylene/vinyl aromatic compound copolymer using a small amount of a cocatalyst.

A further feature of the present invention is the provision of a constrained geometry metallocene catalyst with high activity.

A further feature of the present invention is the provision of a process of preparing an ethylene/vinyl aromatic compound copolymer using the metallocene catalyst.

The above and other objects and advantages of this invention will be apparent from the ensuing disclosure and appended claims.

Summary of the Invention The metallocene catalyst according to the present invention contains in one molecule 2 to 4 transition metals that are bonded with ligands. The metallocene catalyst is used for preparing an ethylene/vinyl aromatic compound copolymer. The metallocene catalyst is employed with a cocatalyst such as organometallic compound or a mixture of non-coordinated Lewis acid and alkyl aluminum. The ethylene/vinyl aromatic compound copolymer prepared by using the metallocene catalyst shows an isotacticity of at least 60 %, and especially an alternating index of at least 80 % measured by 13C NMR analysis.

Brief Description of the Drawings

Fig. 1 is a chemical formula showing a microstructure of an ethylene/styrene copolymer; Fig. 2 is a graph of the peak values of ethylene/styrene copolymers prepared in Example 7 and Comparative Example 1 measured by means of 13C NMR analysis; and Fig. 3 is a chemical formula of an ethylene/styrene copolymer having an isotactic alternating structure.

Detailed Description of the Invention The multi-nuclear constrained geometry catalyst according to the present invention is represented by the following formula (1), and the multi-nuclear constrained geometry catalysts containing 2,3, or 4 transition metals are represented by the following formulae (2), (3) and (4), respectively:

where M is the same or different Ti, Zr or Hf ; Cp'is a non-substituted cyclopentadienyl group; a cyclopentadienyl group with 1 to 4 linear alkyl substitutes; an indenyl group; a substituted indenyl group; a tetrahydroindenyl group; a substituted tetrahydroindenyl group; a fluorenyl group; an octahydrofluorenyl group; a substituted fluorenyl group; an octahydrofluorenyl group; or a substituted octahydrofluorenyl group; Y is a hydrogen atom or a silyl group of Cl l0, an alkyl group of Cl l0, an aryl group of Cl l0, or a combination thereof ; A is a hetero atom such as N, O, P, and S; X is selected from the group consisting of a hydrogen atom, a halogen atom, an alkyl group, an aryl group or a diene group; G is an alkyl group of Cl 30, a cycloalkyl group of Cl 30, an aryl group of CI-30, or an alkyl aryl group of CI 30 ; and n is 2, 3, or 4.

In the present invention, the metallocene catalyst is used with a cocatalyst.

The cocatalyst is an organometallic compound such as alkyl aluminoxane and alkyl aluminum compound, which are known to an ordinary person in the art. The representative examples of alkyl aluminoxane are methyl aluminoxane (MAO) and modified methyl aluminoxane (MMAO). The alkyl aluminoxane includes an alkyl aluminoxane having a repeating unit of the following formula (5), a linear alkyl aluminoxane represented by the following formula (6), and a cyclic alkyl aluminoxane represented by the following formula (7): where R is a hydrogen atom, an alkyl group Of CI-5 or an aryl group of Cl 6, being same or different each other, and m and n are an integer of 0-100.

Alternatively, the co-catalyst of the present invention may be a mixture of different aluminoxanes, a mixture of aluminoxane and alkyl aluminum such as

trimethylaluminum, triethylaluminum, triisobutylaluminum and dimethyl aluminum chloride.

The molar ratio of aluminum of organometallic compound to transition metal of Group IV of metallocene catalyst of the present invention is in the range from 1 : 1 to 1 x 106 : 1, preferably from 10: 1 to 1 x 104 : 1.

The co-catalyst of the present invention can be a mixture of non-coordinated Lewis acid and alkyl aluminum. Examples of the non-coordinated Lewis acid include N, N-dimethyl anilinium tetrakis (pentafluorophenyl) borate, triphenylcarbenium tetrakis (pentafluorophenyl) borate, ferrocerium tetrakis (pentafluorophenyl) borate, and tris (pentafluorophenyl) borate, and the like.

Examples of the alkyl aluminum include trimethylaluminum, triethylaluminum, diethylaluminum chloride, dimethylaluminum chloride, triisobutylaluminum, diisobutylaluminum and dimethylaluminum chloride, tri (n-butyl) aluminum, tri (n-propyl) aluminum, and triisopropylaluminum, and the like.

The molar ratio of the non-coordinated Lewis acid to the transition metal in the catalyst system according to the present invention is preferably in the range from about 0.1: 1 to about 20: 1 and more preferably in the range of about 1 : 1. If the molar ratio of the alkyl aluminum to transition metal in the catalyst system is less than 0.01: 1, it tends to be difficult to effectively activate the metal complex, and if it exceeds 100: 1, such is economically disadvantageous.

To the copolymer of the present invention, additives or adjuvants which are commonly used for polymers, may be incorporated within a range not to adversely affect the effects of the present invention. Preferred additives or adjuvants include, for example, an antioxidant, a lubricant, a plasticizer, an ultraviolet ray absorber, a stabilizer, a pigment, a colorant, a filler and/or a blowing agent.

The polymerization temperature is usually from 0 to 200 °C, preferably from 30 to 150 °C. A polymerization temperature of-78 °C or lower is practically disadvantageous, and a temperature higher than 200 °C is not suitable, since decomposition of the metal complex will take place.

The ethylene monomer polymerized by using the catalyst system of the

present invention is an ethylene, an unsaturated ethylene having a substituted group, or an a, m-diene. The ethylene monomer is copolymerized with a vinyl aromatic compound.

The representative examples of the vinyl aromatic compound include alkylstyrene, halogenated styrene, halogen-substituted alkyl styrene, alkoxy styrene, vinylbiphenyl, vinylphenylnaphthalene, vinylphenylanthracene, vinylphenylpyrene, trialkylsilylvinylbiphenyl, trialkylstanylvinylbiphenyl, alkylsilyl styrene, carboxymethyl styrene, alkyl ester styrene, vinyl benzene sulphonic acid ester, and vinylbenzyl dialkoxyphosphide.

The representative examples of alkyl styrene are styrene, methyl styrene, ethyl styrene, butyl styrene, p-methyl styrene, p-tert-butyl styrene, and dimethyl styrene; those of halogenated styrene are chlorostyrene, bromostyrene, and fluorostyrene; those of halogen-substituted alkyl styrene are chloromethyl styrene, bromomethyl styrene, and fluoromethyl styrene; those of alkoxy styrene are methoxy styrene, ethoxy styrene, and butoxy styrene; those of vinyl biphenyl ( ?) are 4-vinyl biphenyl, 3-vinyl biphenyl, and 2-vinyl biphenyl; those of vinyl phenyl naphthalene are 1- (4-vinylbiphenylnaphthalene), 2- (4-vinylbiphenylnaphthalene), 1- (3-vinylbiphenylnaphthalene), 2- (3-vinylbiphenylnaphthalene), and 1- (2-vinylbiphenylnaphthalene) ; those of vinyl phenyl anthracene are 1- (4-vinylphenyl) anthracene, 2- (4-vinylphenyl) anthracene, 9- (4-vinylphenyl) anthracene, 1- (3-vinylphenyl) anthracene, 9- (3-vinylphenyl) anthracene, and 1- (2-vinylphenyl) anthracene; those of vinyl phenyl pyrene are 1- (4-vinylphenyl) pyrene, 2- (4-vinylphenyl) pyrene, 1- (3-vinylphenyl) pyrene, 2- (3-vinylphenyl) pyrene, 1- (2-vinylphenyl) pyrene, and 2- (2-vinylphenyl) pyrene; that of trialkyl silyl vinyl biphenyl is 4-vinyl-4-trimethyl silyl biphenyl; and those of alkyl silyl styrene are p-trimethyl silyl styrene, m-trimethyl silyl styrene, o-trimethyl silyl styrene, p-triethyl silyl styrene, m-triethyl silyl styrene, and o-triethyl silyl styrene.

In the ethylenically unsaturated monomer, the representative examples of olefin are ethylene, propylene, 1-butene, 1-hexene and 1-octene ; and those of cyclic

olefin are cyclobutene, cyclopentene cyclohexene, 3-methyl cyclopentene, 3-methyl cyclohexene, and norbornene. Also, a, diene means non-conjugated diene, and the examples are 1,4-pentadiene, 1,5-hexadiene, 1,6-heptadiene, 1,7-octadiene, 1,8-nonadiene, 1, 9-decadiene, 1,4-hexadiene, dicyclopentadiene, 5-ethylene-2-norbornen, 5-vinyl norbornene, and methyl hexadiene. The content of the ethylenically unsaturated monomer in the copolymer is about 0 to 25 % by weight.

The weight average molecular weight (Mw) of ethylene/vinyl aromatic compound copolymer according to the present invention preferably exceeds 13,000, more preferably exceeds 20,000, and most preferably exceeds 30,000. The melt index (ATSM D-1238 procedure A, condition of E) is in the range from 0.001 to 1000, preferably in the range from 0.01 to 100, most preferably in the range from 0.1 to 30.

According to the present invention, monomers and solvent (if used) may be refined by vacuum distillation or by contacting alumna, silica, or Molecular Sieve before polymerization. Also, impurities may be eliminated by using a trialkyl aluminum compound, an alkali metal, or an alloy such as Na/K, etc.

It is preferable for the polymer of styrene/ethylene to have a styrene content of at least 0.1 mol%, more preferable 0.1 to 55 mol%. The polymer can be obtained at the pressure of 1 to 1, 000 bar and at room temperature to 200 °C. The polymer obtained at higher temperature than the automatic polymerization temperature of each monomer contains a small amount of homopolymer prepared by free radical polymerization.

The copolymer of the present invention shows various physical properties depending upon the styrene content in the copolymer. The melting point decreases at the lower range of styrene content from about 0 to about 20 mol%, however, increases at the higher range of styrene content from about 20 to about 30 mol%.

The melting point is constant when the styrene content reaches to a certain amount.

In case that the styrene content is over 50 mol% and the alternative index is 0.85, the melting point (Tm) is 124 °C, which is much higher by about 30 °C comparing with

the melting point of 90 °C disclosed in US Patent No. 5,883,213.

The polymer of the present invention is especially suitable for the thermoplastic elastomer used as a reinforcing material of thermoplastic or thermosetting copolymer. For the purpose of improving the physical properties, a synthetic and/or natural polymers may be blended thereto. Especially, an additional polymer such as polyethylene, ethylene/a-olefin copolymer, polypropylene, polyamide, aromatic polyester, polyisocyanate, polyurethane, polyacrylonitrile, silicon, and polyphenylene oxide may be blended with the copolymer of the present invention. The additional polymer is preferably employed in the amount of 0.5 to 50% by weight.

The ethylene/vinyl aromatic compound copolymer of the present invention is a material which retracts its original length after drawing to the length of 2 times at room temperature and exhibits physical properties of as an elastomer by ASTM Special Technical Bulletin No. 184, a thermoplastic or thermosetting resin.

Particularly, the copolymer of the present invention can be easily transformed not only by branching, grafting, hydrogenation, cross-linking but also by introducing functional groups to the double bonds, for example, by sulfonation or chlorination.

The present invention may be better understood by reference to the following examples, which are intended for the purpose of illustration and are not to be construed as in any way limiting the scope of the present invention, which is defined in the claims appended hereto.

Examples Example 1: Preparation of Catalysts (1) Preparation of [Me4CpSi (Me) 2N-C6H4-C (Me) 2-C6H4-C (Me) 2-C6H4-NSi (Me) 2Me4Cp] TiCl2 2,3,4,5-tetramethyl cyclopentadiene (2.45 g, 20 mmol) was dissolved in

dried THF (30ml) in 100 ml nitrogen filled flask, and the solution was stirred while cooling to-78 C using dry ice-acetone bath. To the solution was added n-butyl lithium (hexane solution of 1.6 M, 21 mmol) by a syringe, and then the temperature was raised to room temperature. After about 10 hours, the solvent was removed under vacuum, and then the residue was washed with pentane (50 ml x 3 times) and dried to obtain lithium tetramethylcyclopentanide (Cp*-Li+) with the yield of 98 %.

To the resultant, 30 ml of THF solvent was injected and stirred, and Si (Me) 2Cl2 (3.87 g, 30 mmol) was slowly added by a syringe at room temperature. After the reaction for over 5 hours, the solvent was removed under vacuum. The residue was refined and unreacted material was eliminated at about 70 °C to obtain greenish yellow chloro-2,3,4,5-tetramethylcyclopentadienylmethylsilane [Me4CpSi (Me) 2Cl,] with the yield of %.

(2) Preparation of Me4CpSi (Me) 2NH-C6H4-C (Me) 2-C6H4-C (Me) 2-C6H4-NHSi (Me) 2CpMe4 4,4-bi (4-aminophenyl propylidene) benzene of 6.89 g (20 mmol) was dissolved in THF (100 ml) and stirred in 250 ml nitrogen filled flask, and the solution was cooled to-78 °C using dry ice-acetone bath. To the solution was injected n-butyl lithium (hexane solution of 1.6 M, 42 mmol), and then the temperature was raised to room temperature. After about 10 hours, the solvent was removed under vacuum, and then the residue was washed with pentane and dried to obtain dilithium salt. The yield was 99 %. The dilithium salt was dissolved in THF (100 ml) and reacted with 12.9 g (60 mmol) of chloro-2, 3,4,5-tetramethyl cyclopentadienyl methyl silane at-78 °C. After overnight reaction at room temperature, the temperature was raised to 70°C. Then the solvent and unreacted material were removed under vacuum, and washed with pentane to obtain light yellow Me4CpSi (Me) 2NH-C6H4-C (Me) 2-C6H4-C (Me) 2-C6H4-NHSi (Me) 2CpMe4 with the yield of 76 %.

(3) Preparation of [Me4CpSi (Me) 2N-C6H4-C (Me) 2-C6H4-C (Me) 2-C6H4-NSi (Me) 2CpMe4] 4-4Li+4THF Me4CpSi (Me) 2NH-C6H4-C (Me) 2-C6H4-C (Me) 2-C6H4-NHSi (Me) 2Me4Cp of 7.01 g (10 mol) was dissolved in THF (50 ml) and stirred in 100 ml nitrogen filled flask, and the solution was cooled to-78°C using dry ice-acetone bath. To the solution was injected n-butyl lithium (hexane solution of 1.6 M, 42 mmol), and then the temperature was raised to room temperature. After about 10 hours, the solvent was removed under vacuum, and then the residue was washed with pentane and dried to obtain light yellow THF coordinated tetralithium salt with the yield of 95 %.

(4) Preparation of [Me4CpSi (Me) 2N-C6H4-C (Me) 2-C6H4-C (Me) 2-C6H4-NSi (Me) 2CpMe4] 4-4MgCl+4THF Me4CpSi (Me) 2NH-C6H4-C (Me) 2-C6H4-C (Me) 2-C6H4-NHSi (Me) 2CpMe4 of 7.01 g (10 mmol) was dissolved in the mixture of THF and toluene (50ml, v/v=1 : 4) and stirred in 100 ml nitrogen filled flask. To the solution was injected isopropyl magnesium chloride (42 mmol) and reacted with refluxing for over 10 hours. The solvent was removed under vacuum, and then the residue was washed with pentane and dried to obtain light pink THF coordinated tetramagnesium salt with the yield of 97%.

(5) Preparation of [Me4CpSi (Me) 2N-C6H4-C (Me) 2-C6H4-C (Me) 2-C6H4-NSi (Me) 2CpMe4] Ti2Cl4 [Me4CpSi (Me) 2N-C6H4-C (Me) 2-C6H4-C (Me) 2-C6H4-NSi (Me) 2CpMe4'4Li4 THF of 2.10 g (2.07 mmol) was dissolved in THF (30 ml) and stirred in 100 ml nitrogen filled flask. To the solution was slowly injected TiC13 (1. 54 g, 4.14 mmol)/THF (20 m). After 2 hours, a large excess amount of CH2CI2 was added by a

syringe and reacted for 3 hours. After completion of the reaction, the solvent was removed. The residual solid was extracted with toluene, and the liquid was concentrated.

[Me4CpSi (Me) 2N-C6H4-C (Me) 2-C6H4-C (Me) 2-C6H4-NSi (Me) 2CpMe4] Ti2Cl4 was obtained as a yellowish orange crystalline material after being recrystallized from the solvent mixture of hexane and toluene at-30 °C with the yield of %.

Example 2: Preparation of Catalyst Example 2 was carried out in the same manner as in Example 1 except that AgCI was used instead of CH2Cl2 [Me4CpSi (Me) 2N-C6H4-C (Me) 2-C6H4-C (Me) 2-C6H4-NSi (Me) 2CpMe4] Ti2Cl4 was obtained as a yellowish orange crystalline material and the identification was confirmed by NMR. The yield was 34%.

Example 3: Preparation of Catalyst Example 3 was carried out in the same manner as in Example 1 except that tetramagnesium salt was used instead of tetralithium salt and the reaction time is over 10 hours.

[Me4CpSi (Me) 2N-C6H4-C (Me) 2-C6H4-C (Me) 2-C6H4-NSi (Me) 2CpMe4] Ti2Cl4 was obtained and identified by NMR. The yield was 41 %.

Example 4: Preparation of Catalyst Example 4 was carried out in the same manner as in Example 1 except that AgCI was used instead of CH2Cl2 [Me4CpSi (Me) 2N-C6H4-C (Me) 2-C6H4-C (Me) 2-C6H4-NSi (Me) 2CpMe4] Ti2Cl4 was obtained and identified by NMR. The yield was 45%.

Examples 5-8 : Preparation of Polymers Polymerization was carried out in an electro-heating glass autoclave having a capacity of 1 liter or a metal autoclave having a capacity of 2 liters, which was equipped with a magnetic stirrer and completely substituted by nitrogen by repeating evacuation and nitrogen substitution. Cooling water flew through the cooling coil equipped in the reactor. A solvent such as hexane or toluene, to which Na was added and distilled, was used. The solution was contacted with Molecular Sieve, alumina, or silica under nitrogen gas.

Example 5: Homopolymerization of Ethylene In a metal autoclave having a capacity of 2 liters, hexane (100 ml) and MAO (10 mmol, A1) were charged, and the temperature of the solution was raised to 70 °C while stirring.

[Me4CpSi (Me) 2N-C6H4-C (Me) 2-C6H4-C (Me) 2-C6H4-NSi (Me) 2Me4Cp] TiCl2 containing 20, emol of Ti was polymerized with ethylene at 10 bar. After 30 minutes, ethylene gas was released. After adding a mixed solution of hydrochloric acid/methanol to stop the reaction and wash it, polyethylene was obtained in a state of powder. The product was dried under reduced pressure to obtain 59 g of polyethylene.

Example 6: Copolymerization of Ethylene/1-Octene In a metal autoclave having a capacity of 2 liters, hexane (1,000 ml), 1-octene (50 ml), and MAO (10 mmol, Al) were charged, and the temperature of the solution was raised to 70 C while stirring.

[Me4CpSi (Me) 2N-C6H4-C (Me) 2-C6H4-C (Me) 2-C6H4-NSi (Me) 2Me4Cp] TiCl2 containing 20 pmol of Ti was polymerized with ethylene at 10 bar. After 30 minutes, ethylene gas was released. After adding a mixed solution of hydrochloric

acid/methanol to stop the reaction and wash, copolymer was obtained. The product was dried under reduced pressure to obtain 65 g of the ethylene/1-octene copolymer.

13C NMR analysis of the copolymer showed that the content of 1-octene is 8.4 mol%, and Tm was 98 C.

Example 7: Copolymerization of Ethylene/Styrene In a glass autoclave having a capacity of 1 liter, SM (200 ml) and MAO (10 mmol, Al) were charged, and the temperature of the solution was raised to 70 °C while stirring.

[Me4CpSi (Me) 2N-C6H4-C (Me) 2-C6H4-C (Me) 2-C6H4-NSi (Me) 2Me4Cp] TiCl2 containing 20 umol of Ti was polymerized with ethylene at 4 bar. In the process of polymerization, a polymer insoluble in a solvent was produced in a state of powder.

After 30 minutes, ethylene gas was released. After adding a mixed solution of hydrochloric acid/methanol to stop the reaction and wash, ethylene/styrene copolymer was obtained in a state of powder. The product was dried at 130 °C for 6 hours under reduced pressure to obtain 15 g of the copolymer. 13C NMR analysis showed that it was an isotactic alternating copolymer containing 50.2 mol% of styrene. The isotacticity (diad) was 0.62 and the alternating index was 0.82.

Example 8: Copolymerization of Ethylene/Styrene In a metal autoclave having a capacity of 2 liters, SM (1,000 ml) and MAO (10 mmol, Al) were charged, and the temperature of the solution was raised to 70 °C while stirring.

[Me4CpSi (Me) 2N-C6H4-C (Me) 2-C6H4-C (Me) 2-C6H4-NSi (Me) 2Me4Cp] TiCl2 containing 20 nmol of Ti was polymerized with ethylene at 10 bar. After 30 minutes, ethylene gas was released. After adding a mixed solution of hydrochloric acid/methanol to stop the reaction and wash, ethylene/styrene copolymer was obtained in a state of powder. The product was dried at 130 °C for 6 hours under

reduced pressure to obtain 49 g of the copolymer. 13C NMR analysis showed that it was an isotactic alternating copolymer containing 50.8 mol% of styrene. The isotacticity (diad) was 65 % and the alternating index was 84 %.

Comparative Example 1: Copolymerization of Ethylene/Styrene Comparative Example was conducted in the same manner as Example 1 except that [Cp (Me) 4-Si (Me) 2-N-t-Bu] TiCl2 (CGC) was used instead of the catalyst of Example 1. Copolymer of 8.5 g was obtained after being dried at 130 °C for 6 hours under reduced pressure. 13 C NMR analysis showed that it was a pseudo-random copolymer containing 35.3 mol% of styrene. The alternating index was 41 %.

Comparative Example 2: Copolymerization of Ethylene/Styrene Comparative Example was conducted in the same manner as Example 1 except that rac- [C2H4 (Ind) 2] ZrCl2 was used instead of the catalyst of Example 1.

Copolymer of 62 g was obtained after being dried at 130 °C for 6 hours under reduced pressure. 13 C NMR analysis showed that it was a pseudo-random copolymer containing 7.9 mol% of styrene. The isotacticity (diad) was 71 % and the alternating index was 21 %.

The polymer specimens of 40-50 mg of Examples 7-8 and Comparative Examples 1-2 were dissolved in about 5 ml of a hot solvent mixture of trichlorobenzene and benzene, and the resulting solution was put into a 5 mm NMR tube, and then analyzed by means of 100 MHz 13C NMR. The test results are shown in Table 1.

Table 1 Examples Comparative Examples 7 8 1 2 Catalyst catalysta) catalysta) CGCb) EBIZ SM (ml) 200 1000 200 200 C2 (kg/cm2) 4 10 4 4 Mw (x 104) 3.88 11.3 4.12 0.61 MWD 2.09 3.26 2.23 3.54 TM (C) 124.1 124.5-91.2 Styrene content (mol%) 50.2 50.1 35.3 7.9 Isotacticity (diad, %) 63 65-71 Alternating index (%) 82 83 41 21 * Polymerization conditions: catalyst (20 mol), MAO/Ti=500, 70°C, 30 minutes Notes: a) is [Me4CpSi (Me) 2N-C6H4-C (Me) 2-C6H4-C (Me) 2-C6H4-NSi (Me) 2CpMe4] TiCl2 of the catalyst in Examples 7 and 8; b) is CGC, namely [Cp (Me) 4-Si (Me) 2-N-t-Bu] TiCl2 ; and c) is EBIZ, namely rac- [C2H4 (Ind) 2] ZrCl2.

As shown in Table 1, the ethylene/styrene copolymers by using the catalyst of the present invention have a higher styrene content as compared with conventional copolymers by using CGC or EBIZ (rac-ethylenebisindenylzirconium chloride, a common catalyst for iPP copolymerization), especially, as compared with Comparative Example 2 by using a zirconium catalyst. Further, the alternating index

is very high compared with those of Comparative Examples 1 and 2. Also, the higher isotacticities of Examples 7 and 8 over 60 % show that the copolymer of the present invention is a semi-crystalline copolymer having the melting point of 125 C even at a high styrene content. Such result is superior to the result disclosed in US Patent No. 5,883,213, in which a copolymer containing styrene of 49 mol% and having a higher isotacticity over 95 % and an alternating index of 55 % has a melting point of about 90 °C. It may be caused by the high alternating index. The product is a new isotactic alternating ethylene/styrene copolymer.

The microstructure of ethylene/styrene copolymer identified by 13C NMR is shown in Fig. 1., and the analysis of 13C NMR chemical shift is shown in Table 2.

Table 2 Carbon Chemical shift (ppm) Sa p 25.80 Sa y+ 27.89 SY Y, SY Y + 29. 99 Sa y + 35.06 Sa y 37.05 Sa a 41.61 T 45.2-46.6 In Fig. 1 and Table 2, S is a secondary carbon and T is a methine bonded to a phenyl group of styrene as a tertiary carbon. a, P and y mean that a phenyl- substituted secondary carbon is located at 2,3, and 4 position of itself respectively.

For example, Sa Y iS a secondary carbon having a phenyl substituted secondary carbon at its 2 position on one side and a secondary carbon at its 4 position on the other side. Further,"+"means that a secondary carbon exists over 5 position of itself.

The structures of the copolymers prepared in Examples 7-8, and Comparative Examples 1-2 were analyzed by means of 13C NMR, and the comparison result of Example 7 and Comparative Example 1 is shown in Fig. 2. l3C NMR analyst was carried out by using a mixed solvent of trichlorobenzene and benzene at 100°C and TMS (trimethyl silane). Such copolymer was substantially soluble in THF or CHC13 by more than 91 % by weight at room temperature, and completely soluble in boiling THF.

Distinctively, in the ethylene/styrene copolymer prepared in Example 7, the integral near 25 ppm attributable to the alternating structure was high compared with that of pseudo-random copolymer. Further, the peak attributable to the ethylene chain was nearly not observed in the vicinity of 30 ppm. It indicates that the polymer has an alternating structure. Also, Sa a peak attributable to a head-to-tail structure of styrene was nearly not observed in the vicinity of 42 ppm. It indicates that there is no styrene chain having a styrene-styrene structure.

The diad (mm) integral at 45.2 ppm is measured by the peak attributable to a secondary carbon observed in the range of 45.2 to 46.6 ppm, and the isotacticity was measured by the ratio to integral of the total secondary carbon. In Examples 7 and 8, the isotacticities were 63 % and 65 % respectively, as shown in Table 1, which are different from those of the conventional pseudo-random copolymers.

Accordingly, the multi-nuclear constrained geometry catalyst of the present invention improves the styrene content and is especially useful to prepare isotactic alternating ethylene/styrene copolymer, compared with the conventional constrained geometry catalysts. The copolymer has high activity of polymerization and exceedingly improves styrene content, as compared with a traditional ethylene/styrene copolymer, at the same polymerization condition. New copolymer having a higher alternating index over 80 % and a stereoregularity of about 60 %

can be obtained. Further, a new semi-crystalline copolymer with a high styrene content, which has the melting point of about 125 °C, can be prepared.

In the above, the present invention was described based on the preferred embodiment of the present invention, but it should be apparent to those ordinarily skilled in the art that various changes and modifications can be added without departing from the spirit and scope of the present invention. Such changes modifications should come within the scope of the present invention.