Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2000-08-14
2002-04-09
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...
C526S113000, C526S118000, C526S119000, C526S134000, C526S161000, C526S339000, C526S943000, C526S065000, C525S240000
Reexamination Certificate
active
06369176
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to polymer blends having a molecular weight distribution (MWD) of at least about 2. In one aspect, the invention relates to ethylene/&agr;-olefin and ethylene/&agr;-olefin/diene monomer polymer blends, particularly blends useful as elastomers, while in another aspect, the invention relates to a process of preparing such blends in a single reactor. In yet another aspect, the invention relates to a process of making the polymer blends in a single reactor using a mixed constrained geometry catalyst (CGC) system.
BACKGROUND OF THE INVENTION
Constrained geometry catalysts have found wide acceptance in the manufacture of various olefinic polymers, such as the various ethylene, propylene and diene polymers. These catalysts comprise a metal coordination complex which itself comprises a metal of group 4 of the Periodic Table of the Elements and a delocalized &pgr;-bonded moiety substituted with a constrain-inducing moiety, the complex having a constrained geometry about the metal atom such that the angle at the metal between the centroid of the delocalized, substituted &pgr;-bonded moiety and the center of at least one remaining substituent is less than such angle in a similar complex containing a similar &pgr;-bonded moiety lacking in such constrain-inducing substituent. The catalyst further comprises a cocatalyst and an activator. “Delocalized &pgr;-bonded moiety” means an unsaturated organic moiety, such as those comprising ethylenic or acetylenic functionality, in which the &pgr;-electrons are donated to the metal to form a bond.
The metal atom is the active site of each discreet CGC unit and since each such unit has a single metal atom, these catalysts tend to produce in a highly efficient manner high molecular weight (e.g., greater than about 10,000 weight average molecular weight) olefin polymers with a narrow MWD (e.g., about 2 or less) over a wide range of polymerization conditions. CGCs are especially useful for the formation of ethylene homopolymers, copolymers of ethylene and one or more &agr;-olefins (i.e., olefins having three or more carbon atoms with the ethylenic unsaturation between the first and second carbon atoms), and interpolymers of ethylene, propylene and a diene monomer (e.g., EPDM terpolymers).
While a narrow MWD can impart useful properties to ethylene-based polymers for certain applications, e.g., transparency in films, ethylene-based polymers with a broad MWD (e.g., greater than about 2) usually process more efficiently and have better physical properties, e.g., temperature performance, for such applications as injection molded or extruded articles, e.g., gaskets and wire and cable coatings, than do ethylene-based polymers with a narrow MWD. Various processes are known for producing broad MWD ethylene-based polymers or polymer blends with a CGC, but all are subject to improvement.
For example, one process for producing such polymers or polymer blends requires the use of multiple reactors deployed in parallel with each reactor containing the same CGC but operated under different polymerization conditions. The product outputs of the reactors are then blended with one another. This produces a polymer blend with a substantially uniform molecular architecture, which is often a desirable property, particularly for elastomers (i.e., polymers with a crystallinity of less than about 45%). For polymer blends of similar crystallinity, those blends of substantially uniform molecular architecture generally exhibit superior physical performance properties, e.g., tensile, modulus, tear, etc., than those blends of a relatively nonuniform molecular architecture. “Substantially uniform molecular architecture” means that each polymer molecule of the blend has substantially the same comonomer content and distribution although the polymer molecules from one reactor differ in weight average molecular weight (Mw) from the polymer molecules produced in the other reactor(s).
One difficulty with this process is that it requires balancing the operation and output of one reactor with the other reactor(s). Another difficulty is that it requires a separate, post-reaction blending step. Yet another difficulty is that with the use of multiple reactors, the ratio of high molecular weight (Mw) to low Mw components in the polymer blend is limited to the capacity of each reactor.
In another process, multiple reactors are deployed in series with each reactor operated at substantially the same polymerization conditions but with each reactor containing a different CGC. The output of the first reactor becomes, of course, a feed for the second reactor, and the product output of the second reactor is a polymer blend. While this process avoids the need for a post-reaction blending step, it still requires balancing the operation of one reactor with the other reactor(s) in the series, and the output of the process is limited by the capacity of the reactors. Moreover, this process often produces a blend in which the molecular architecture is not uniform.
Variations on both of these multiple reactor processes are known, e.g., operating the multiple reactors deployed in series at dissimilar conditions, using a catalyst other than or in addition to a CGC, etc., and U.S. Pat. No. 5,844,045 to Kolthammer and Cardwell, which is incorporated herein by reference, provides a representative description of a multiple reactor process. However, producing a polymer blend in a single reactor, i.e., a reactor blend, saves all the costs associated with running multiple reactors. Moreover, the ratio of high molecular weight (Mw) to low Mw components in the polymer blend can be controlled by controlling the weight ratio of one catalyst to another, and thus the capacity of the individual reactors is not a constraining consideration with respect to this property.
For example, U.S. Pat. No. 4,937,299 to Ewen and Welborn teaches a process for producing (co)polyolefin reactor blends comprising polyethylene and copolyethylene-&agr;-olefins. These blends are prepared in a single reactor by simultaneously polymerizing ethylene and copolymerizing ethylene and an &agr;-olefin in the presence of at least two different metallocenes and an alumoxane. However, Ewen and Welborn do not teach (i) the use of mixed CGC catalyst systems, or (ii) producing an ethylene-based polymer blend having an MWD (a) of at least about 2, and (b) at least ten percent greater than either ethylene-based polymer component of the blend prepared in a single reactor with any single component of the mixed catalyst system under similar polymerization conditions. Ewen and Welborn also do not teach the production of an ethylene-based polymer blend in which each polymer component of the blend has a uniform molecular architecture (at least with respect to the polymer units derived from ethylene and the &agr;-olefin).
U.S. Pat. No. 5,359,015 to Jejelowo teaches a process of producing polyolefins having a controllable broaden MWD utilizing transition metal metallocene catalyst systems comprising a first component comprising at least one transition metal metallocene having at least one cyclopentadienyl ring that is substituted with a first substituent having a secondary or tertiary carbon atom through which it is covalently bonded to the at least on cyclopentadienyl ring in the system, a second component comprising at least one transition metal metallocene having at least one cyclopentadienyl ring that is substituted with a second substituent that is hydrogen or optionally a second hydrocarbon substituent different from the first substituent, and an activator selected from ionic activators or alumoxane or a combination of the two. The MWD of the polymer produced by the catalyst system is generally somewhere between the high and low MWD that such catalyst system components would produce if utilized alone.
U.S. Pat. No. 5,627,117 to Mukaiyama and Oouchi teaches a process for producing a polyolefin with a wide MWD, the process employing an olefin polymerization catalyst comprising a transition metal compound having at least
Laughner Michael K.
Mangold Debra J.
Parikh Deepak R.
DuPont Dow Elastomers LLC
Rabago R.
Whyte Hirshboeck Dudek SC
Wu David W.
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