Ethylene copolymerization process

Details Ethylene copolymerization process Ethylene copolymerization process

2002-08-19

2004-03-30

Choi, Ling-Siu (Department: 1713)

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

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S127000, C526S943000, C526S348000, C526S335000, C526S352000, C502S152000, C502S117000

Reexamination Certificate

active

06713574

ABSTRACT:

TECHNICAL FIELD
This invention relates to the preparation of ethylene-&agr;-olefin polymers under solution polymerization conditions using catalyst compositions based on biscyclopentadienyl derivatives of zirconium.
BACKGROUND OF THE INVENTION
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 for convenience as “ethylene-&agr;-olefin-diolefin 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-&agr;-olefin-diolefin elastomers are a well established class of industrial polymers having a variety of uses associated with their elastomeric properties, their thermo-oxidative stability, their solubility in hydrocarbon oleaginous fluids, and their capability for modifying the properties of polyolefin blends. Included in this terminology are the commercially available EPM (ethylene-propylene monomer) and EPDM (ethylene-propylene-diene monomer) rubbery polymers, both being vulcanizable by cross-linking, the addition of the diolefin, also known as diene monomer, providing increased ease of both cross-linking and functionalization.
Commercially prepared ethylene-&agr;-olefin-diolefin elastomers have been traditionally been made via Ziegler-Natta polymerization with homogenous catalyst compositions 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. WO95/277147 describes bridged and unbridged Group 4 metallocene compounds wherein the cyclopentadienyl ligands have two or four adjacent substituents forming one or two alkylenic cycles of from 4 to 8 carbon atoms. These compounds are said to be useful for ethylene copolymerization and propylene polymerization, including elastomeric copolymers of ethylene, &agr;-olefins and non-conjugated diolefins. Ethylene copolymerization with propylene is reported in examples 28-30 and in Table 3. U.S. Pat. No. 5,543,373 describes bridged metallocenes having two differing &pgr; ligands which are said to be of high activity. Copolymers of ethylene with 1-olefins and/or one or more diene monomers are produced in a preferred process according to the invention. Example R illustrates an ethylene-propylene-diene terpolymer rubber prepared with dimethylsilanediyl(2-methyl-4-phenyl-1-indenyl)(2,3,5-trimethyl-1-cyclopentadienyl) zirconium dichloride.
Ethylene copolymerization is described in WO 95/27717 with zirconocenes having a Cp cyclopentadienyl group with one or two alkylenic cycles of 4 to 8 carbon atoms and a Cp′ cyclopentadienyl group having up to 4 R substituents. Example 12 illustrates the preparation of isopropyliden(cyclopentadienyl) (2,3-cyclotetramethyleneinden-1-yl) zirconium dichloride. Example 19 illustrates syndiotactic propylene polymerization with this catalyst.
A high temperature solution process for the preparation of ethylene-&agr;-olefin copolymers is described in EP-A-0 612 769. The catalyst compositions are based on bis(cyclopentadienyl/indenyl/fluorenyl) titanocenes/zirconocenes which are combined with an alkyl aluminum compound and an ionizing ionic compound which provides a non-coordinating anion. Asymmetrically substituted catalysts are illustrated. The solution process conditions are described to range from 120 to 300° C. at pressures from atmospheric to 200 kg/cm
2
. In the examples of this process the metallocene compound is reacted with the organoaluminum compound, then reacted with ionizing ionic compound, and subsequently added to the polymerization reactor. High molecular weight polymer is said to be produced at high efficiency.
A high activity supported catalyst suitable for ethylene copolymers is described in U.S. Pat. No. 5,240,894. The catalyst isopropylidene(cyclopentadienyl)(fluorenyl) zirconium dichloride is a preferred metallocene embodiment. Example 10 illustrates an ethylene-propylene copolymerization.
It remains important in industry to develop efficient copolymerization processes, and in particular, those capable of high productivity of polymer per unit weight of catalyst compound.
INVENTION DISCLOSURE
The invention is a polymerization process for the preparation of ethylene-&agr;-olefin-diolefin copolymers comprising contacting ethylene, one or more &agr;-olefin monomer, and optionally, one or more cyclic diolefin monomer, with a catalyst composition prepared from at least one a catalyst activator and at least one bridged, bis(cyclopentadienyl) zirconium compound having an unsubstituted cyclopentadienyl ligand, a bulky, substituted cyclopentadienyl ligand, said ligands bridged by a covalent bridging group containing one or more Group 14 element, said process conducted in a solution polymerization process. The invention process exhibits high catalyst activity, high comonomer incorporation and high diene monomer conversion rates.
BEST MODE AND EXAMPLES OF THE INVENTION
The ethylene-&agr;-olefin-diolefin copolymers of this invention (hereinafter referred to as “EPC”) is meant to include copolymers, terpolymers, tetrapolymers, etc. It typically comprises ethylene, one or more alpha-olefins, and optionally, one or more cyclic diolefin monomers; it is typically substantially amorphous; and it will typically have a substantially random arrangement of at least the ethylene and the alpha-olefin monomers. Thus both of ethylene-containing elastomer and plastomer copolymers can be prepared by the invention process.
The EPC capable of preparation in accordance with the invention process generally can have a molecular weight range typically between about 20,000 and up to about 500,000 or higher, more typically between about 60,000 and 300,000 where the molecular weight is number-average (“M
n
”).
Typically elastomeric EPC is “substantially amorphous”, and when that term is used to define the EPC elastomers of this invention it is to be taken to mean having a degree of crystallinity less than about 25% as measured by means known in the art, preferably less than about 15%, and more preferably less than about 10%. The three major known methods of determining crystallinity are based on specific volume, x-ray diffraction, and infrared spectroscopy. Another well-established method, based on measurement of heat content as a function of temperature through the fusion range, is carried out using differential scanning calorimetric measurements. It is known that these independent techniques lead to reasonably good experimental agreement. The degree of randomness of the arrangement of monomers in the EPC elastomeric polymers also affects the crystallinity and is appropriately characterized by the degree of crystallinity.
Additionally, it is known in the art that the tendency of a particular combination of catalyst composition and monomers to produce blocky, random, or alternating polymers can be characterized by the product of the reactivity ratios defined for the given monomers under the specific reaction conditions encountered. If this product is equal to 1.0, the sequence distribution will be perfectly random; the more the product is less than 1.0, the more the monomers will tend to have a “blocky” sequence distribution. Generally speaking, the segments of a polymer which crystallize are linear segments of a polymer which have a number of identical (both by chemical make-up and stereo-specific orientation) units in a row. Such segments are said to be “blocky”. If there is little or no such sequential order within the segments making up a polymer chain, that chain will be very unlikely to conform itself into the correct shape to fit into the spatial order

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