Method for Preparing Ethylene Copolymer

FIG. 1 shows a .sup.13 C-NMR spectrum of a copolymer obtained in Example 1.

In the formula I representing a transition metal compound which is used as one component of a catalyst in the present invention, each of A.sup.1 and A.sup.2 is an unsubstituted or substituted cyclopentadienyl group, indenyl group or fluorenyl group. Typical examples of A.sup.1 and A.sup.2 include a cyclopentadienyl group, methylcyclopentadienyl group, dimethylcyclopentadienyl group, tetramethylcyclopentadienyl group, indenyl group, 3-methylindenyl group, tetrahydroindenyl group, fluorenyl group, methylfluorenyl group and 2,7-di-tert-butylfluorenyl group.

In the formula I, each of A.sup.3 and A.sup.4 is a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 20 carbon atoms, an alkylaryl group having 6 to 20 carbon atoms, an arylalkyl group having 6 to 20 carbon atoms, halogenated aryl group having 6 to 20 carbon atoms, or a hydrocarbon group having 1 to 20 carbon atoms and containing a hetero-atom such as oxygen, nitrogen, sulfur or silicon. Typical examples of A.sup.3 and A.sup.4 include a hydrogen atom, methyl group, ethyl group, propyl group, phenyl group, toluyl group, fluorophenyl group, methoxyphenyl group and benzyl group.

Q which couples with A.sup.1 and A.sup.2 is a hydrocarbon group having 2 to 10 carbon atoms, a hydrocarbon group having 1 to 10 carbon atoms and containing silicon, germanium or tin, or a carbon, silicon, germanium or tin atom. Preferably, Q is the hydrocarbon group having 2 to 10 carbon atoms, a carbon atom or silicon atom. Furthermore, A.sup.3 and A.sup.4 may combine with each other to form a ring structure comprising A.sup.3, A.sup.4 and Q. In this case, examples of the group comprising A.sup.3, A.sup.4 and Q include a cyclopentylidene group, cyclohexylidene group and tetrahydropyran-4-ylidene group.

Each of R.sup.1 and R.sup.2 is a halogen atom, a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkyl group having silicon, or an aryl group, alkylaryl group or arylalkyl group having 6 to 20 carbon atoms. Preferable typical examples of R.sup.1 and R.sup.2 include a chlorine atom, methyl group, phenyl group and trimethylsilyl group.

A metallocene compound represented by the formula I in the present invention is characterized by having a crosslinkable ligand. The employment of such a metallocene compound allows the copolymerization of ethylene and the aromatic vinyl compound to proceed. Suitable examples of the metallocene compound having the crosslinkable ligand which can be used in the present invention include metallocene compounds mentioned in U.S. Pat. Nos. 4,769,510 and 4,892,851 as well as Japanese Patent Laid-open Nos. 274703/1990, 274704/1990 and 69394/1992.

Typical examples of the metallocene compound include ethylenebis(1-indenyl)zirconium dichloride, ethylene-bis(tetrahydro-1-indenyl)zirconium dichloride, isopropylidene(cyclopentadienyl)(fluorenyl)zirconium dichloride, methylphenylmethylene(cyclopentadienyl)(fluorenyl)zirconium dichloride and diphenylmethylene(cyclopentadienyl)(fluorenyl)zirconium dichloride.

In the present invention, a known cocatalyst can be used as a component (B) in combination with the metallocene compound. Known aluminoxanes are preferable examples of the cocatalyst. In addition, other usable examples of the cocatalyst include compounds which can stabilize cationic transition metal complexes mentioned in WO 88 05792, WO 88 05793 and U.S. Pat. No. 5,155,080. Furthermore, as compounds which can stabilize the cationic transition metal complexes, compounds showing Lewis acid properties and solid acids can also be used. Preferred examples of the compounds showing Lewis acid properties include compounds containing elements in the group III a of the periodic table such as triphenylboron, tris(pentafluorophenyl)boron and triphenyl aluminum. Examples of the solid acid include magnesium chloride, aluminum chloride and alumina.

The aluminoxanes are compounds represented by the formulae II and III ##STR2## (wherein R is a hydrocarbon group, particularly, an alkyl group having 1 to 10 carbon atoms, and n is an integer of 2 or more, preferably an integer of from 2 to 100), and in the aluminoxane which can be particularly preferably used, R is a methyl group and n is 5 or more, preferably 10 or more. Even if the aluminoxane is contaminated with a small amount of an alkyl aluminum compound, there is no problem. Further, aluminoxanes having two or more kinds of alkyl groups mentioned in Japanese Patent Laid-open Nos. 247201/1990 and 103407/1991, a fine particle aluminoxane mentioned in U.S. Pat. No. 4,952,540 and aluminum oxy-compounds obtained by bringing into contact with a compound containing active hydrogen such as water and alcohols mentioned in U.S. Pat. Nos. 5,171,799 and 4,990,640 can also be used.

In the present invention, the amount of a cocatalyst such as the aluminoxane is usually from 1 to 100000 moles, preferably from 10 to 10000 moles per mole of the above-mentioned transition metal compound.

In the present invention, the transition metal compound and/or a cocatalyst such as the aluminoxane may be used as is, or may be carried on a known carrier such as SiO.sub.2, Al.sub.2 O.sub.3 or MgCl.sub.2 which is used in a conventional Ziegler catalyst.

Furthermore, the catalyst comprising the transition metal compound and the cocatalyst which can be used in the present invention can be used in the presence of an organic aluminum compound, if necessary. In this case, the ethylene copolymer can be produced in a smaller amount of the aluminoxane.

The usable organic aluminum compound can be represented by the formula IV

(wherein each of R' and R" is a hydrocarbon group having 1 to 20 carbon atoms, and R' and R" may be mutually identical or different; X is a halogen atom; j is an integer of from 1 to 3; each of k, l and m is an integer of from 0 to 2, and j+k+l+m=3).

Typical examples of the organic aluminum compound include trimethyl aluminum, triethyl aluminum, triisobutyl aluminum, diethyl aluminum chloride, ethyl aluminum dichloride and diisobutyl aluminum hydride. Above all, trimethyl aluminum and triisobutyl aluminum are suitably used.

The amount of the organic aluminum compound is preferably from 1 to 1000 moles, more preferably from 50 to 500 moles per mole of the transition metal compound.

The important conception of the present invention is that an ethylene-aromatic vinyl compound copolymer can be prepared by polymerizing ethylene with at least one aromatic vinyl compound.

Examples of the aromatic vinyl compound which can be used in the present invention include styrene; o-methylstyrene, p-methylstyrene, o,p-dimethylstyrene, o-ethylstyrene, m-ethylstyrene, p-ethylstyrene, o-chlorostyrene, p-chlorostyrene and .alpha.-methylstyrene.

No particular restriction is put on the polymerization process and polymerization conditions in the present invention, and a known process for use in a usual olefin polymerization can be employed. A solvent polymerization using an inert hydrocarbon solvent, a bulk polymerization which is carried out under substantially inert hydrocarbon-free conditions, or a gaseous phase polymerization can be utilized. Polymerization temperature is in the range of from -100.degree. to 200.degree. C. preferably from -50.degree. to 100.degree. C. and polymerization pressure is in the range of from atmospheric pressure to 100 kg/cm.sup.2, preferably from atmospheric pressure to 50 kg/cm.sup.2.

Examples of the hydrocarbon solvent which can be used in the polymerization of the present invention include saturated hydrocarbons such as butane, pentane, hexane, heptane, octane, nonane, decane, cyclopentane and cyclohexane, and aromatic hydrocarbons such as benzene, toluene and xylene.

The ethylene-aromatic vinyl compound copolymer obtained by the method of the present invention contains 0.1 to 50 mole %, preferably 1 to 45 mole % of an aromatic vinyl compound unit. This kind of copolymer is a random copolymer which is free from a chain of the aromatic vinyl compounds combined with each other.

Heretofore, it is known that the ethylene-aromatic vinyl compound copolymer, for example, ethylene-styrene copolymer can be obtained by copolymerizing butadiene with styrene in accordance with an anionic polymerization technique, and then hydrogenating the resultant polymer. However, in the thus obtained copolymer, a styrene-styrene chain is present, and therefore the copolymer is poor in compatibility with another resin. For this reason, the applications of the copolymer are limited.

On the contrary, the copolymer obtained by the method of the present invention is a random copolymer as described above, and therefore the copolymer which is excellent in transparency, flexibility and compatibility with another resin such as polypropylene can be produced by suitably selecting the content of the aromatic vinyl compound unit.

Furthermore, in copolymerizing with a diene for the purpose of modifying the polymer, the solvent which can be used in the method of the present invention can be applied. Examples of the diene compound which can be used for such a purpose include 1,4-hexadiene, 4-methyl-1,4-hexadiene, ethylidenenorbornene and dicyclopentadiene.

Now, the present invention will be described in more detail in reference to examples. It should be noted that the scope of the present invention is not limited to these examples.

A .sup.13 C-NMR spectrum of each polymer was measured in a chloroform-d solution at 27.degree. C. by the use of an FX-100 spectrometer made by JEOL, Ltd. The attribution of the spectrum was carried out in the light of the attribution of Japanese Patent Application Laid-open No. 250007/1991.

In a 100 cm.sup.3 glass flask sufficiently purged with a nitrogen gas were placed 30 cm.sup.3 of toluene, 20 mg of isopropylidene(cyclopentadienyl)(9-fluorenyl)zirconium dichloride synthesized as described in U.S. Pat. No. 4,892,851, 2.7 g of methyl aluminoxane purchased from Toso Akzo Co., Ltd. and 9.1 g of styrene in turn. After the temperature in the system was adjusted to 40.degree. C., ethylene was fed to the flask to start polymerization. After the polymerization was carried out for one hour, a small amount of methanol was added to the system to terminate the polymerization. Next, the resultant reaction product was poured into a large amount of methanol/hydrochloric acid to precipitate the polymer. The thus precipitated polymer was washed with methanol and then dried to obtain 12.2 g of a rubbery-like polymer.

An intrinsic viscosity ([.eta.]) of the resulting polymer measured in a tetralin solution at 135.degree. C. was 0.26 dl/g. Furthermore, this polymer was analyzed by measuring .sup.13 C-NMR. As a result, a peak was not observed at 42-44 ppm, which meant that any styrene-styrene chain was not present in the polymer, and it was apparent that the polymer was ethylene-styrene random copolymer having a styrene content of 22.6 mole %. The .sup.13 C-NMR spectrum of this polymer is shown in FIG. 1.

In accordance with the same procedure as in Example 1 except that 20 mg of dicyclopentadienylzirconium dichloride were used as a metallocene catalyst component, ethylene-styrene copolymerization was tried. However, the resulting polymer is polyethylene alone, and a copolymer of ethylene and styrene could not be prepared.

In accordance with the same procedure as in Example 1 except that 20 mg of ethylenebis(tetrahydro-1-indenyl)zirconium dichloride were used as a metallocene catalyst component, ethylene-styrene copolymerization was carried out. As a result, 12.4 g of a polymer were obtained. A styrene content in this polymer measured in the same manner as in Example 1 was 19.6 mole %, and any styrene-styrene chain was not present. An intrinsic viscosity ([.eta.]) of the obtained polymer measured in a tetralin solution at 135.degree. C. was 0.54 dl/g.

In accordance with the same procedure as in Example 1 except that 0.9 g of styrene was used, polymerization was carried out. As a result, 4.8 g of a polymer were obtained. A styrene content in this polymer measured in the same manner as in Example 1 was 2.1 mole %, and any styrene-styrene chain was not present.

According to the method of the present invention, an ethylene-aromatic vinyl compound random copolymer containing 0.1 to 50 mole % of an aromatic vinyl compound unit can be obtained in a good yield.