Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1999-03-17
2001-08-07
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...
C526S348500, C526S160000, C526S943000
Reexamination Certificate
active
06271329
ABSTRACT:
The present invention relates to ethylene copolymers, composed of units of ethylene and at least one C
3
-C
12
&agr;-olefin, having a molecular weight distribution M
w
/M
n
exceeding 3 and a distribution of comonomers which is characterized by a standard deviation &sgr; of the average-weighted elution temperature T
a
, determined by the method of the Temperature Rising Elution Fraction (TREF), which conforms to the following equation GI:
σ
<
k
4
-
k
1
(
T
a
-
k
o
)
-
k
2
k
3
(
T
a
-
k
o
)
/
(
1
+
k
3
(
T
a
-
k
o
)
)
[
°
C
.
]
GI
where k
0
is 338.5° C., k
1
is 0.053, k
2
is 1.1318° C., k
3
is 0.00483° C.
−1
, k
4
is 0.55° C., and T
a
is <98° C.
The invention further relates to a process for the preparation of such ethylene copolymers, to the use of the ethylene copolymers for the preparation of films, hollow bodies and fibers and also to films, hollow bodies and fibers prepared using these ethylene copolymers.
When effecting copolymerizations of ethylene with other &agr;-olefins it is desirable to obtain a high degree of inclusion of these comonomers in the ethylene copolymer. The efficiency of the comonomer inclusion is particularly high when metallocene catalysts are used and can be controlled by regulating the ligand structure of these metal complexes when such catalysts are used.
It is generally assumed that the aperture angle between the cyclopentadienyl rings of the metallocene has a marked influence on the inclusion properties. A large aperture angle can be acquired eg by bridging the rings by an SiMe
2
or C
2
H
4
bridge. Such metallocene catalysts are described, for example, in EP 336,128.
The industrially most significant polymerization processes for carrying out such copolymerizations are vapor-phase polymerization processes and suspension polymerization processes. In order to carry out such copolymerization processes it is necessary to apply the catalyst to a particulate support such as silica gel.
Methods of supporting metallocene catalysts are described, for example, in WO 95/07939, WO 87/03889, WO 94/28034, EP 206,794 and EP 250,600. In these cases MAO (methyl aluminoxane) or some other aluminoxane is used as co-catalyst. In addition, methods of supporting metallocenes in which boron compounds are used as activator have already been described (cf eg WO 91/09882 WO 94/03506 WO 95/14044 EP 628,574 WO 95/15815).
The polymers prepared using these supported catalysts mostly have a very narrow molecular weight distribution combined with very uniform comonomer inclusion, which results in some desirable properties such as good strength and brightness properties of the films made from these materials. However, due to the narrow molecular weight distribution, processing on machines conventionally used in the polymer industry is hampered to a very great extent. Polymers having a broader molecular weight distribution as may be obtained, for example, when using chromium or titanium catalysts can be processed much more easily, but suffer from the drawback that the comonomer (butene, hexene, octene) is unevenly distributed over the polymer molecule. Thus the concentration of comonomers in the low molecular weight portion is distinctly higher than in the high molecular weight portion. As a result, these easy-to-process polymers have unsatisfactory mechanical properties.
All known attempts to prepare copolymers having a wider distribution of molecular weights using metallocene catalysts, have led to unsatisfactory products. Thus EP-A 613,908, for example, describes the preparation of copolymers having a molecular weight distribution M
w
/M
n
of up to 32, but these copolymers also have a broad distribution of comonomers.
WO 93/09148 also describes copolymers having a broader distribution of molecular weights, but this broadening of said molecular-weight distribution occurs at the expense of a broader distribution of comonomers and a high low-molecular content, which is reflected in a high hexane-extractable content of from 4.1 to 13.3%.
DE 19,606,167 describes supported catalyst systems with the aid of which polymers showing a narrow distribution of comonomers and a narrow distribution of molecular weights can be prepared. These catalyst systems contain metallocene complexes having bridged or unbridged metallocene ligands. This document makes no mention of copolymerizations or the products thereof.
It is thus an object of the present invention to provide ethylene copolymers comprising units of ethylene and at least one C
3
-C
12
&agr;-olefin having a molecular weight distribution of more than 3 while still exhibiting a narrow distribution of comonomers.
Accordingly, we have found the ethylene copolymers defined above. We have also found a process for the preparation of such copolymers, the use of these copolymers for the preparation of films, hollow bodies and fibers and also films, hollow bodies and fibers which have been manufactured from these copolymers.
The narrow distribution of comonomers in the copolymers of the invention can be advantageously described in terms of the standard deviation of the average-weighted elution temperature T
a
, such as can be determine by the TREF method. The TREF method is described, for example in Wild, Advances in Polymer Science, 98, pp 1 to 47, 1990, Springer-Verlag and Wild, Blatz, Polymer Mater. Sci. Eng. 67 pp 153, 1992. The average-weighted elution temperature (T
a
) and the standard deviation (&sgr;) are used in the following manner (cf Bevington, McGraw-Hill, Data Reduction and Error Analysis for the Physical Sciences, 1969):
T
a
=&Sgr;(
c
(
T
i
)*
T
i
)/&Sgr;
c
(
T
i
)[° C.]
&sgr;=([&Sgr;(
T
i
t
a
)
2*
c
(
T
i
)]/
&Sgr;c
(
T
i
))
½
[° C.]
Here T
i
denotes the temperature at point i and c(T
i
) the polymer concentration at the temperature T
i
.
The copolymers of the invention now have an unusually small standard deviation &sgr;, which can be defined by equation GI using the above values for k
0
, k
1
, k
3
, and k
4
.
Particularly preferred are copolymers in which the standard deviation &sgr; is sufficiently small to conform to equation I, where k
0
is 496.6° C., k
1
is 0.0467, k
2
is 1.1318° C., k
3
is 0.00483° C.
−1
, k
4
is 0.55° C. and T
a
is <98° C.
The advantageous properties of the copolymers of the invention result substantially from the combination of this narrow distribution of comonomers with a relatively broad molecular weight distribution. This molecular weight distribution M
w
/M
n
must have a value above 3, preferably a value greater than 3 and less than 8 and more preferably a value between 3.5 and 7.0.
The copolymers of the invention contain not only units of ethylene but also units of at least one C
3
-C
12
&agr;-olefin. Suitable &agr;-olefins are propene, butene, pentene, hexene, heptene, octene, nonene, decene, undecene and dodecene. Comonomer units derived from butene and hexene are preferred.
The amount of the comonomers in the copolymer is governed by the required mass density of the copolymer. The copolymers of the invention usually have a comonomer content which gives a mass density of from 0.87 to 0.96 g/cm
3
, preferably from 0.90 to 0.94 g/cm
3
, and more preferably from 0.910 to 0.935 g/cm
3
.
The copolymers of the invention can exhibit a wide range of molecular weights, where adjustment of the molecular weight to a desired value can be effected by methods familiar to the person skilled in the art, that is to say, for example, by altering the polymerization temperature or using reagents such as hydrogen. The copolymers usually have a molecular weight M
w
exceeding 100,000, preferably exceeding 150,000.
Moreover, copolymers having a small content of low-molecular polymer chains are preferred. This portion, which may be characterized by the heptane-extractable content, has a negative influence on the sensory examination of the copolymers, for example. The heptane-extractable content of the copolymers of the invention is preferably less than 4 wt %, more preferabl
Kristen Marc Oliver
Lilge Dieter
BASF - Aktiengesellschaft
Harlan R.
Keil & Weinkauf
Wu David W.
LandOfFree
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