Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1999-10-26
2001-08-07
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S240000, C361S271000, C361S437000, C361S500000
Reexamination Certificate
active
06271311
ABSTRACT:
TECHNICAL FIELD
Embodiments of the present invention generally pertain to the field of extruded elastomeric polymers. More particularly, the present invention is directed to elastomeric polymers that exhibit improved extrudability when compounded to form a useful precursor for extrudable materials. These elastomeric polymers are generally of the ethylene, alpha-olefin type made employing metallocene type catalysts.
BACKGROUND
Ethylene &agr;-olefin elastomeric polymers (EP) have been widely used in extrusion applications such as electrical insulation for decades. These products are expected to provide an extrusion surface free of melt fracture. While this can be accomplished readily by the introduction of long chain branches in an EPDM through the diene, copolymers have to rely on other structural features. For example, use of multi-sited Ziegler-Natta catalyst will provide a very broad molecular weight distribution (MWD) (Mw/Mn>20) suitable for extrusion processing.
Metallocene or single sited catalyst produced elastomeric polymers will generally have a draw back in processability when extruded compared to the previously used elastomeric polymers based on multi-sited Ziegler-Natta produced elastomeric polymers. This drawback stems from the narrow MWD (Mw/Mn about 2), characteristic of such polymers. This MWD effect manifests itself through a lack of shear sensitivity, i.e., shear sensitivity being generally lower viscosity at higher shear rates.
The challenge in providing a metallocene catalyzed elastomeric polymer, with its attendant benefits, to the extrusion and/or electrical industry, is that these materials are generally known by those of ordinary skill in the art as narrow CD, narrow MWD elastomeric polymers. Based on such a characterization, those of ordinary skill in the art would not tend to make these metallocene catalyzed elastomeric polymers their choice for extrusion processes, because to do so would be to select a material whose characteristics are opposed to those outlined above as fitting extrusion processes.
There is a commercial need, therefore, for a metallocene catalyzed elastomeric polymer material which, when compounded, can provide a compound with processability or extrudability equal to a Ziegler-Natta (Z-N) analog.
SUMMARY
We have discovered that metallocene catalyzed ethylene, alpha-olefin, diene elastomeric polymers, when produced using an unusual reactor configuration, can exhibit a relatively broad molecular weight distribution which will provide processability or extrudability equal to or better than a Z-N catalyzed analog, and substantially better than a conventional metallocene produced elastomeric polymer. This result, while desirable, is unexpected and surprising. We will refer to this reactor configuration as tailoring. This tailoring has been applied to the conventional Z-N catalysts and their elastomeric polymer products. For tailoring to work, molecular weights that are substantially higher than the average molecular weight must be synthesized as a small part of the polymer backbone. Such higher molecular weights as part of the backbone are generally quite accessible with conventional Z-N catalysts, because for instance, in the second reactor of a series reactor scheme a catalyst charged in the first reactor, due to its short life, will have expired or nearly so in the second reactor. In such a catalyst-starved second reactor the catalyst system makes very high molecular weight segments, resulting in the desired polymer configuration. By contrast, metallocene catalysts are much longer lived than conventional Z-N vanadium catalysts, effectively preventing the use of such a straight forward approach that is conveniently used in the polymerization of certain Z-N based polymers.
A reactor setup which includes little to no chain transfer agent in a first reactor is instead a method of accomplishing a high molecular weight portion, with substantial amounts of chain transfer agent in a second or subsequent reactor. The resulting molecular weight distribution shown in
FIG. 1
is surprisingly similar to the MWD of a similarly tailored vanadium (an example of Ziegler-Natta type) catalyst produced elastomeric polymer.
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Dharmarajan Narayanaswami Raja
Ravishankar Periagaram S.
Exxon Mobil Chemical Patents Inc.
Nutter Nathan M.
Prodnuk Stephen D.
Reid Frank E.
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