Process for the preparation of olefinic polymers using...

Details Process for the preparation of olefinic polymers using... Process for the preparation of olefinic polymers using...

1999-02-03

2001-04-10

Wu, David W. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S129000, C526S348000, C526S904000, C526S943000, C502S152000

Reexamination Certificate

active

06214953

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an improved method for preparing an olefinic polymer having improved properties by polymerizing an olefinic monomer using a supported metallocene catalyst prepared by contacting a metallocene catalyst with a supported cocatalyst on a carrier in an aliphatic hydrocarbon solvent.
DESCRIPTION OF THE PRIOR ART
A metallocene compound refers to a transition metal complex having coordinated cyclopentadienyl ligands. Many studies on various catalysts based on metallocene compounds have been carried out since Kaminsky and Sinn reported that a metallocene compound, when used together with a condensation product of water and methylaluminum (e.g., methylaluminoxane, MAO), exhibits a high catalytic activity in olefin polymerization[H. Sinn and W. Kaminsky,
Adv. Organomet. Chem.,
18, 99 (1980); and H. Sinn, W. Kaminsky, H. J. Vollmer and R. Woldt,
Angew. Chem.,
92, 396 (1980)]. Such studies have shown that many metallocene catalysts exhibit high activities in polymerizing olefins, diolefins, styrenes and others(see, e.g., WO 91/14713).
When a metallocene catalyst is used in olefin polymerization, the structure and properties of the polymer produced can be better controlled than when a conventional Ziegler-Natta catalyst is used together with an alkylaluminum compound as a cocatalyst. For example, the molecular weight distribution of the polymer becomes narrower, and when used in a copolymerization, the distribution of the comonomer in the copolymer is much more uniform.
However, one drawback of metallocene catalysts is that although they readily dissolve in aromatic hydrocarbons such as benzene, toluene and substituted benzene, they are almost insoluble in aliphatic hydrocarbons. Bisindenyl zirconium dimethyl, for example, is completely soluble in toluene whereas it does not dissolve in heptane; and this difference in solubility is reflected on its catalytic activity, i.e., its catalytic activity in toluene is greater than that in heptane by a factor of 7 or more (see
J. Polym. Sci; Polym. Chem. Ed.,
123, 2117 (1985)). Because the use of an aromatic hydrocarbon solvent in a polymerization process is not advantageous due to its toxicity and unfavorable process economics in recovering the high-boiling point aromatic solvent, it is desirable to develop an efficient polyolefin manufacturing process using a metallocene catalyst in an aliphatic hydrocarbon solvent. Accordingly, there exists a need to develop a new metallocene catalyst that exhibits a high activity in an aliphatic hydrocarbon solvent.
On the other hand, when a homogeneous, i.e., solution, catalyst, which is not supported on a carrier, is used in preparing an olefinic polymer in either an aromatic or aliphatic hydrocarbon solvent, the productivity is generally low and it is difficult to separate and recover the polymer product, in addition to other problems, e.g., bulk density of the polymer produced is very low, the size of the polymer is not uniform, and reactor fouling may also occur. Accordingly, many attempts have been made to alleviate such problems by using a heterogeneous catalyst: a catalyst as well as a cocatalyst supported on a solid carrier is used (see W. Kaminsky and F. Renner,
Macromol. Chem., Rapid Commun.,
14, 239 (1993); and K. Soga and M. Kaminaka,
Macromol. Chem., Rapid Commun.,
194, 1745 (1993); a supported catalyst is prepared using a solid support having on its surface a controlled number of hydroxy groups or hydroxy groups modified by various substituents (see K. Soga and M. Kaminaka,
Macromol. Chem., Rapid Commun.,
194, 1745 (1993); and S. Collins, W. Mark Kelly and David A. Holder,
Macromolecules.
25, 1780-1785 (1992)); reactive sites are introduced on the ligand of a metallocene catalyst and the ligand is reacted with an olefin by conducting a prepolymerization reaction to anchor the metallocene catalyst within a polymer matrix, or the reactive sites having olefinic moiety on the ligand of a metallocene catalyst are polymerized to obtain a catalyst cluster(see U.S. Pat. Nos. 5,262,498 and 5,308,817); and a solid catalyst is prepared by contacting a zirconocene catalyst with methylaluminoxane in an aromatic solvent, adding silica in an aromatic solvent thereto, washing and drying the resulting catalyst several times in order to remove the unreacted metallocene catalyst, and conducting prepolymerization to obtain a solid catalyst (see U.S. Pat. No. 5,240,894).
However, these methods have problems associated with reduced efficiency and increased ash content. Specifically, a supported metallocene catalyst introduces a relatively large amount of the support material to the polymer product, and the metallocene catalyst may be deactivated by the reaction with hydroxy groups, which are catalyst poison, present on the surface of the carrier. Furthermore, when a metallocene is dissolved in an aromatic hydrocarbon solvent and contacted with an MAO to prepare a catalyst, or when a metallocene and an MAO are introduced to a slurry of a carrier in an aromatic solvent to prepare a supported catalyst, the aromatic solvent must be removed thoroughly by employing multiple washing steps or by drying under a vacuum. If the removal of the aromatic hydrocarbon solvent is not complete, the metallocene catalyst remaining dissolved in the solvent may induce homogeneous polymerization, thereby causing the broadening of the molecular weight distribution, and causing reactor fouling and non-uniform particle size. Therefore, the above methods are not conducive to the preparation of a supported metallocene catalyst which can produce a polyolefin having a high bulk density and a homogeneous particle size distribution, while preventing the reactor fouling problem and maintaining the high catalyst activity.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a method for the preparation of an olefinic polymer having a narrow molecular weight distribution and a high bulk density by way of using a supported metallocene catalyst prepared in an aliphatic hydrocarbon solvent.
In accordance with one aspect of the present invention, there is provided a method for preparing an olefinic polymer having improved properties in molecular weight distribution and bulk density by polymerizing an olefinic monomer and, optionally, a comonomer in the presence of a supported catalyst comprising a modified metallocene and an alkylaluminoxane supported on a carrier, the modified metallocene being derived from a metallocene of formula (I) by introducing at least one C
5-20
alkyl substituent into a &pgr;-ligand, C
1-4
alkylene bridge or silicon bridge thereof and the alkylaluminoxane having a repeating unit of formula (II):
wherein:
M is Ti, Zr or Hf;
X is a halogen, or a C
1-3
alkyl group;
L
1
and L
2
are each a &pgr;-ligand selected from the group consisting of cyclopentadienyl, indenyl, fluorenyl and derivatives thereof, and are optionally linked together by a C
1-4
alkylene bridge or by a silicon bridge;
m is an integer of 2 or more; and
R
1
is a C
1-20
alkyl group.
DETAILED DESCRIPTION OF THE INVENTION
The supported catalyst of the present invention may be prepared by contacting a modified metallocene, wherein at least one C
5-20
alkyl substituent is introduced into the &pgr;-ligand, the alkylene bridge or silicon bridge of the metallocene catalyst of formula (I), with an alkylaluminoxane having a repeating unit of formula (II) supported on a carrier, and optionally with an alkylaluminum of formula (III), in an aliphatic hydrocarbon solvent to provide a supported catalyst, and optionally subjecting said supported catalyst to a prepolymerization reaction of an olefinic monomer:
wherein R
2
, R
3
and R
4
are each a C
1-20
alkyl group or a halogen.
One preferred embodiment of the process for preparing the supported catalyst of the present invention is as follows:
A metallocene catalyst is contacted with a supported alkylaluminoxane in an aliphatic hydrocarbon solvent to obtain a slurry containing the supported catalyst of the pr

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