Olefin copolymerization process with bridged hafnocenes

Details Olefin copolymerization process with bridged hafnocenes Olefin copolymerization process with bridged hafnocenes

1999-10-21

2001-10-09

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...

C526S078000, C526S128000, C526S131000, C526S348200, C526S348500, C526S348600

Reexamination Certificate

active

06300433

ABSTRACT:

TECHNICAL FIELD
This invention relates to olefin copolymerization processes using substituted hafnocene catalyst compounds with noncoordinating anions.
BACKGROUND ART
Olefin polymers comprising ethylene and at least one or more &agr;-olefin and optionally one or more diolefin make up a large segment of polyolefin polymers and will be addressed as “ethylene copolymers” herein. Such polymers range from crystalline polyethylene copolymers to largely amorphous elastomers, with a new area of semi-crystalline “plastomers” in between. In particular, ethylene copolymer plastomers are now a well established class of industrial polymers having a variety of uses associated with their unique properties, such as elastomeric properties and their thermo-oxidative stability. Uses of the plastomers include general thermoplastic olefins, films, wire and cable coatings, polymer modification (by inclusion in blends with other polyolefins), injection molding, foams, footwear, sheeting, functionalized polymers (such as by free-radical graft addition of polar monomers) and components in adhesive and sealant compounds.
Commercially prepared ethylene copolymers have been traditionally been made via Ziegler-Natta polymerization with catalyst systems largely based on vanadium or titanium. Newer metallocene catalyst compounds have received attention due to their ease of larger monomer incorporation and potential increases in polymerization activities. U.S. Pat. No. 5,324,800 describes metallocenes having substituted and unsubstituted cyclopentadienyl ligands which are suitable for producing high molecular weight olefin polymers, including linear, low density copolymers of ethylene with minor amounts of &agr;-olefin.
Noncoordinating anions useful as catalyst components with such metallocenes is known. The term “noncoordinating anion” is now accepted terminology in the field of olefin polymerization, both by coordination or insertion polymerization and carbocationic polymerization. The noncoordinating anions function as electronic stabilizing cocatalysts, or counterions, for cationic metallocenes which are active for olefin polymerization. The term “noncoordinating anion” as used here and in the references applies both to noncoordinating anions and weakly coordinating anions that are not so strongly coordinated to the cationic complex as so to be labile to replacement by olefinically or acetylenically unsaturated monomers at the insertion site. U.S. Pat. No. 5,198,401 describes a preferred noncoordinating anion tetra(perflourophenyl) boron, [B(pfp)
4
]-or [B(C
6
F
5
)
4
]-, wherein the perfluorinated phenyl ligands on the boron makes the counterion labile and stable to potential adverse reactions with the metal cation complexes.
The utility of metallocene-based ionic catalysts in high temperature olefin polymerization is described in U.S. Pat. Nos. 5,408,017 and 5,767,208, EP 0 612 768, and WO 96/33227. Each addresses suitable metallocene catalysts for high temperature processes for olefin copolymerization. High molecular weight ethylene/&agr;-olefin copolymers is an objective of EP 0 612 768 and is addressed with catalyst systems based on bis(cyclopentadienyl/indenyl/fluorenyl) hafnocenes which are combined with an alkyl aluminum compound and an ionizing ionic compound providing a non-coordinating anion.
As described above, a recognized problem for high temperature polymerization, particularly where significant content of comonomer incorporation in ethylene copolymers is to be sought, is an observed decrease in molecular weight, or increase in melt index (MI). Means of maintaining high molecular weights, or low M.I., in ethylene copolymers of low density (high comonomer content) while operating at economically preferable high polymerization reaction temperatures and high polymer production rates is highly desirable.
BRIEF SUMMARY OF THE INVENTION
The invention thus addresses specifically substituted, bridged hafnocene catalyst complexes comprising noncoordinating anions that are surprisingly stable under high temperature olefin polymerization processes such that olefin copolymers with high molecular weights can be prepared at surprisingly high production rates. More specifically, the invention relates to a polymerization process for ethylene copolymers having a density of about 0.850 to about 0.930 comprising contacting, under supercritical or solution polymerization conditions at a reaction temperature at, or above, 60° C. to 225° C., or below, ethylene and one or more comonomers capable of insertion polymerization with a hafnocene catalyst complex derived from A) a biscyclopentadienyl hafnium organometallic compound having i) at least one unsubstituted cyclopentadienyl ligand or aromatic fused-ring substituted cyclopentadienyl ligand not having additional substitutents on said ligand, ii) one substituted or unsubstituted, aromatic fused-ring substituted cyclopentadienyl ligand, and iii) a covalent bridge connecting the two cyclopentadienyl ligands, said bridge comprising a single carbon or silicon atom with two aryl groups, each substituted with a C
1
-C
20
hydrocarbyl or hydrocarbylsilyl group at least one of which is a linear C
3
or greater substitutent; and B) an activating cocatalyst, preferably a precursor ionic compound comprising a halogenated tetraaryl-substituted Group 13 anion.
DETAILED DESCRIPTION OF THE INVENTION
The bridged hafnium compounds of the invention include those having a single substituted carbon or silicon atom bridging two cyclopentadienyl-containing (Cp) ligands of the hafnium metal centers (iii), the aromatic fused-ring substituted cyclopentadienyl ligand or ligands, preferably those containing C
1
-C
30
hydrocarbyl or hydrocarbylsilyl substituents on the ii) non-cyclopentadienyl aromatic ring. The bridge substituents preferably comprise C
1
-C
20
linear or branched alkyl, or C
1
-C
20
substituted-silyl, substituted phenyl groups, the alkyl or substituted-silyl substituents located in the para- or meta-positions of the aryl groups, preferably wherein at least one of said alkyl substituents is a C
3
or higher linear n-alkyl substitutent, preferably C
4
or higher. Specific examples include methyl, ethyl, n-propyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, neopentyl, etc. Substituents present on the non-cyclopentadienyl aromatic rings of the aromatic fused-ring substituted cyclopentadienyl li,and (ii), such inclusive of indenyl and fluorenyl derivatives of cyclopentadienyl groups, typically include one or more C
1
to C
30
hydrocarbon or hydrocarbylsilyl groups selected from linear, branched, cyclic, aliphatic, aromatic or combined structure groups, including fused-ring or pendant configurations. Examples include methyl, isopropyl, n-propyl, n-butyl, isobutyl, tertiary butyl, neopentyl, phenyl, n-hexyl, cyclohexyl, and benzyl. For the purposes of this application the term “hydrocarbon” or “hydrocarbyl” is meant to include those compounds or groups that have essentially hydrocarbon characteristics but optionally contain not more than about 10 mol.% non-carbon atoms, such as boron, silicon, oxygen, nitrogen, sulfur and phosphorous. “Hydrocarbylsilyl” is exemplified by, but not limited to, dialkyl- and trialkylsilyls. Similarly the use of hetero-atom containing cyclopentadienyl rings or fused rings, where a non-carbon Group 14, 15 or 16 atom replaces one of the ring carbons in the Cp ring or in a ring fused thereto, is considered for this specification to be within the terms “cyclopentadienyl”, “indenyl”, and “fluorenyl”. See, for example, the teachings of WO 98/37106, having common priority with U.S. Ser. No. 08/999,214, filed 12/29/97, pending and WO 98/41530, having common priority with U.S. Ser. No. 09/042,378, filed Mar. 13, 1998, abandoned incorporated by reference for purposes of U.S. patent practice.
Specific bridged hafnium catalysts innclude those derived from: (1) indenyl-based complexes such as the isomers, or mixtures, of (para-n-butylphenyl) (para-t-butylphenyl)methylene (fluorenyl) (indenyl) hafnium dimethyl, (para-n-propylpheny

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