Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1998-11-06
2002-10-08
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...
C526S160000, C526S161000, C526S348600, C526S348500, C526S916000, C526S943000, C526S347000, C526S901000, C526S352000
Reexamination Certificate
active
06462161
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to polyolefin copolymer compositions with the molecular weight maximum occurring in that part of the composition that has the highest comonomer content, and, preferably, with long chain branching, which have been produced from an &agr;-olefin monomer and one or more &agr;-olefin comonomers in a single reactor with a single metallocene catalyst, and to processes for the production of these materials and the catalysts used therefor.
BACKGROUND OF THE INVENTION
Recently there have been many advances in the production of polyolefin copolymers due to the introduction of metallocene catalysts. Metallocene catalysts offer the advantage of generally higher activity than traditional Ziegler catalysts and are usually described as catalysts which are single-site in nature. Because of their single-site nature the polyolefin copolymers produced by metallocene catalysts often are quite uniform in their molecular structure. For example, in comparison to traditional Ziegler produced materials, they have relatively narrow molecular weight distributions (MWD) and narrow Short Chain Branching Distribution (SCBD). By narrow SCBD, it is meant that the frequency of short chain branches, formed where comonomers incorporate into the polyolefin chain, is relatively independent of molecular weight. Although certain properties of metallocene products are enhanced by narrow MWD, difficulties are often encountered in the processing of these materials into useful articles and films relative to Ziegler produced materials. In addition, the uniform nature of the SCBD of metallocene produced materials does not readily permit certain structures to be obtained.
An approach to improving processability has been the inclusion of long chain branching (LCB), which is particularly desirable from the viewpoint of improving processability without damaging advantageous properties. U.S. Pat. No.'s 5,272,236; 5,278,272; 5,380,810; and EP 659,773, EP 676,421, WO 94/07930 relate to the production of polyolefins with long chain branching.
Another approach is the addition of the polymer processing aids to the polymer prior to fabrication into films or articles. This requires extra processing and is expensive.
A different approach to the problem has been to make compositions which are blends or mixtures of individual polymeric materials with the goal being to maximize the beneficial properties while minimizing the processing problems. This requires extra processing which increases the cost of materials produced. U.S. Pat. Nos. 4,598,128; 4,547,551; 5,408,004; 5,382,630; 5,382,631; and 5,326,602; and WO 94/22948 and WO 95/25141 relate to blends.
Another way to provide a solution for the processability problems and to vary SCBD has been the development of various cascade processes, where the material is produced by a series of polymerizations under different reactor conditions, such as in a series of reactors. Essentially, a material similar in some ways to a blend is produced, with a modality greater than one for various physical properties, such as the molecular weight distribution. While polyolefin compositions with superior processability characteristics can be produced this way, these methods are expensive and complicated relative to the use of a single reactor. Processes of interest are disclosed in U.S. Pat. No. 5,442,018, WO 95/26990, WO 95/07942 and WO 95/10548.
Another potentially feasible approach to improving processability and varying SCBD has been to use a multicomponent catalyst. In some cases, a catalyst which has a metallocene catalyst and a conventional Ziegler-Natta catalyst on the same support to produce a multimodal material, in other cases two metallocene catalysts have been used in polyolefin polymerizations. Components of different molecular weights and compositions are produced in a single reactor operating under a single set of polymerization conditions. This approach is difficult from the point of view of process control and catalyst preparation. Catalyst systems of interest are disclosed in WO 95/11264 and EP 676,418.
SUMMARY OF THE INVENTION
It would be desirable to be able to produce a polyolefin copolymer composition which has the molecular weight maximum occurring in that portion of the composition that has the highest number of short chain branches and which is very easy to process. Further, it would be desirable to be able to accomplish this using a single metallocene catalyst, preferably supported in a polymerization process using a single reactor, preferably gas phase, operating semi-continuously or, preferably, continuously under a single set of reactor conditions. It would be especially desirable to be able to produce a polyolefin copolymer composition which has the molecular weight maximum occurring in that portion of the composition that has the highest number of short chain branches and which has significant long chain branching.
The short chain branching distribution of a polyolefin composition, which is due to the incorporation of an &agr;-olefin comonomer during the polymerization of an &agr;-olefin monomer, can be examined by several techniques, such as, for example, ATREF-DV and GPC-FTIR. If the material of the composition is divided into portions starting at one end of the distribution or the other, the relationship between high short chain branching content due to high comonomer content and molecular weight can be determined.
In one embodiment this invention is a polyolefin copolymer composition produced with a catalyst having a metallocene complex in a single reactor in a process for the polymerization of an &agr;-olefin monomer with one or more olefin comonomers, the composition having long chain branches along the polymer backbone and a molecular weight maximum which occurs in that 50 percent by weight of the composition which has the highest weight percent comonomer content.
A preferred embodiment of this invention is a polyolefin copolymer composition wherein the composition has a comonomer partitioning factor C
pf
which is equal to or greater than 1.10 or a molecular weight partitioning factor M
pf
which is equal to or greater than 1.15, or a comonomer partitioning factor C
pf
which is equal to or greater than 1.10 and a molecular weight partitioning factor M
pf
which is equal to or greater than 1.15, where the comonomer partitioning factor C
pf
is calculated from the equation:
C
pf
=
∑
i
=
1
n
w
i
·
c
i
∑
i
=
1
n
w
i
∑
j
=
1
m
w
j
·
c
j
∑
j
=
1
m
w
j
,
where c
i
is the mole fraction comonomer content and w
i
is the normalized weight fraction as determined by GPC/FTIR for the n FTIR data points above the median molecular weight, c
j
is the mole fraction comonomer content and w
j
is the normalized weight fraction as determined by GPC/FTIR for the m FTIR data points below the median molecular weight, wherein only those weight fractions w
i
or w
j
which have associated mole fraction comonomer content values are used to calculate C
pf
and n and m are greater than or equal to 3; and where the molecular weight partitioning factor M
pf
is calculated from the equation:
M
pf
=
∑
i
=
1
n
w
i
·
M
i
∑
i
=
1
n
w
i
∑
j
=
1
m
w
j
·
M
j
∑
j
=
1
m
w
j
,
where M
i
is the viscosity average molecular weight and w
i
is the normalized weight fraction as determined by ATREF-DV for the n data points in the fractions below the median elution temperature, M
j
is the viscosity average molecular weight and w
j
is the normalized weight fraction as determined by ATREF-DV for the m data points in the fractions above the median elution temperature, wherein only those weight fractions, w
i
or w
j
which have associated viscosity average molecular weights greater than zero are used to calculate M
pf
and n and m are greater than or equal to 3.
In another embodiment this invention is a polyolefin copolymer composition produced with a catalyst having a metallocene complex in a single reactor in a continuous gas phase process for th
Cady Larry D.
Frye Christopher J.
Howard Philip
Karjala Teresa P.
Maddox Peter J.
BP Chemicals Limited
Finnegan, Henderson Farabow, Garrett and Dunner L.L.P.
Harlan R.
Wu David W.
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