Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1999-12-15
2003-06-03
Lu, Caixia (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S133000, C526S160000
Reexamination Certificate
active
06573350
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to gel-free, diene-free, branched semi crystalline high-C3 ethylene-propylene polymer compositions and a method for the preparation of branched semi-crystalline high-C3 ethylene-propylene polymer compositions using single site catalyst compounds.
BACKGROUND OF THE INVENTION
The class of rubbery ethylene-propylene copolymers, conventionally referred to as EPR polymers, is well known and has gained substantial commercial acceptance. The copolymers are known to have good properties such as weatherability, ozone resistance and thermal stability and the polymers have accepted utility in automotive applications, as construction materials and as wire and cable coatings, among others. However, conventional ethylene-propylene rubbery copolymers are often difficult to process unless compounded by relatively large amounts of other materials.
A number of proposals have been made to improve the processability of the ethylene-propylene rubbery copolymer. In Yamamoto et al, U.S. Pat. No. 4,125,699, there are disclosed ethylene-propylene copolymers having a relatively high ethylene content produced in the presence of vanadium-containing polymerization catalysts. The copolymers of Yamamoto et al. are said to have improved processability because of a relatively broad molecular weight distribution. Vanadium catalysts, however, are of relatively low activity and many, if not most, of the more recent commercial ethylene-propylene rubbery copolymers are produced with a titanium-based catalyst because of the higher catalytic activity available through the use of such catalysts.
Processability has been improved in other types of polymers due to the presence of long chain branching. For example, EP 190 889 A2 discloses high energy irradiation of polypropylene to create what is believed to be polypropylene having substantial free-end long branches of propylene units. EP 384 431 discloses the use of peroxide decomposition of polypropylene in the substantial absence of oxygen to obtain a similar product.
Other examples of long chain branched polypropylene include U.S. Pat. No. 5,541,236, which introduces long chain branching by bridging two PP backbones to form H-type polymers, and U.S. Pat. No. 5,514,761, which uses dienes incorporated in the backbones to achieve a similar effect. However, it is difficult to avoid cross-linking and gel formation in such processes.
Thus, there is still a need for ethylene-propylene copolymer compositions having improved processability.
SUMMARY OF THE INVENTION
The present invention meets that need by providing gel-free, diene-free, branched ethylene-propylene (EP) polymer compositions that have improved sprayability, elasticity, and molecular weight. The weight average branching index g′ for the higher molecular weight region of the ethylene-propylene polymer compositions is less than 0.95. Additionally, a novel process is provided for efficiently producing branched ethylene-propylene polymer compositions comprising:
a) contacting propylene monomers and ethylene monomers in a reactor with an inert hydrocarbon solvent or diluent and a catalyst composition comprising one or more single site catalyst compounds capable of producing an ethylene-propylene polymer at a temperature from about 50° C. to about 180° C., wherein the ratio in the reactor of the propylene and ethylene monomers to the inert hydrocarbon solvent or diluent is less than 2.0, and further, wherein the propylene and ethylene monomers and the inert hydrocarbon solvent or diluent comprise no more than 90 percent of the total contents of the reactor; and
b) recovering a branched ethylene-propylene polymer composition, wherein the weight average branching index g′ for the higher molecular weight region of the ethylene propylene polymer composition is less than 0.95.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a novel method for producing gel-free, diene-free, branched EP. In addition, the branched EP product of the present invention is novel. The weight average branching index g′ for the higher molecular weight region of the ethylene-propylene polymer composition is less than 0.95. In some embodiments, the weight average branching index for the higher molecular weight region of the ethylene-propylene polymer composition is less than the 0.90. In other embodiments, it is less than 0.85. These branching characteristics result in a polymer with improved rheological characteristics.
An unusual feature of the branched ethylene-propylene polymers of the present invention is the presence of a significant amount of branching in the higher molecular weight range of the polymer. This branching results in improved melt strength and shear thinning, as well as other unique physical properties. In this case, the amount of branching is determined using the weight average branching index g′ of the branched ethylene-propylene polymer. The weight average branching index g′ is defined as g′=[IV]
br
/[IV]
lin
|
Mw
wherein [IV]
br
is the intrinsic viscosity of a branched polymer sample and [IV]
lin
is the intrinsic viscosity of a linear polymer sample. It is well known in the art that as the g′ value decreases, branching increases. See B. H. Zimm and W. H. Stockmayer,
J. Chem. Phys.
17, 1301 (1949).
With regard to the molecular weight distribution of the ethylene-propylene polymer composition of the present invention, the following definitions apply:
Lower molecular weight region: That portion of the polymer product which has a molecular weight which is less than Peak MW (M
p
).
Higher molecular weight region: That portion of the polymer product which has a molecular weight which is more than Peak MW (M
p
).
Preferably, the ethylene-propylene polymers of the present invention have a high propylene content, wherein a majority of the monomeric content of the polymer is propylene. In other words, the propylene content of the ethylene-propylene polymers is greater than 50%. More preferably, the propylene content of the ethylene-propylene polymers is in the range of 75 to 95%. Most preferably, the propylene content of the ethylene-propylene polymers is in the range of 80 to 90%.
Other comonomers can be included in the branched ethylene-propylene of the present invention. Examples of these other comonomers include C
4
-C
20
&agr;-olefins, geminally disubstituted monomers, C
5
-C
25
cyclic olefins, C
8
-C
25
styrenic olefins, and lower carbon number (C
3
-C
8
) alkyl substituted analogs of the cyclic and styrenic olefins. Preferably, the other comonomers comprise from 3 to 25 mole percent of the ethylene-propylene composition. More preferably, they comprise from 5 to 20 mole percent of the ethylene-propylene composition.
In a preferred embodiment, the total comonomer content of the branched ethylene-propylene composition of the present invention is from 5 to 40 mole percent. More preferably, the total comonomer content is from 10 to 30 mole percent. Most preferably, the total comonomer content is from 15 to 25 mole percent.
Catalysts
Catalysts which are useful for producing the branched EP of the present invention include single-site catalysts which are capable of producing ethylene-propylene polymers. Single-site catalysts which are useful in the present invention include metallocene catalysts, as well as complexes such as those described in Johnson, Killian, and Brookhart,
J. Am. Chem. Soc.,
1995, 117, 6414; Small, Brookhart and Bennett,
J. Am. Chem. Soc.,
1998, 120, 4049-4050; Repo et al.,
Journal of Organometallic Chemistry,
1997, 549, 177-186; and Britovsek et al.,
Chem. Commun.,
1998, 849-850. Other useful single-site catalysts include bridged bis(arylamido) Group 4 compounds such as those described by D. H. McConville, et al, in
Organometallics
1995, 14, 5478-5480. Each of these documents is incorporated by reference for the purposes of U.S. patent practice.
In some embodiments, metallocene catalysts are used to produce the branched ethylene-p
Dekmezian Armenag H.
Markel Eric J.
Weng Weiqing
ExxonMobil Chemical Patents Inc.
Lu Caixia
Milbank Mandi
Runyan Charles E.
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