Process for the preparation of polyolefins

Details Process for the preparation of polyolefins Process for the preparation of polyolefins

1999-10-28

2002-03-19

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, C526S348600, C526S351000, C526S352000, C526S282000

Reexamination Certificate

active

06359095

ABSTRACT:

For the preparation of highly isotactic polyolefins by means of stereospecific racemic metallocene/cocatalyst systems, the highest possible isotacticity is desired. This means that very stereoselective racemic metallocene types are employed which are able to build up polymer chains having very few construction faults. The consequence of this is that products having high crystallinity, high melting point and thus also high hardness and excellent modules of elasticity in flexing are obtained as desired.
However, it is disadvantageous that these polymers are difficult to process, and in particular problems occur during extrusion, injection molding and thermoforming. Admixing of flow improvers and other modifying components could help here, but results in the good product properties, such as, for example, the high hardness, being drastically reduced. In addition, tackiness and fogging also occur. The object was thus to improve the processing properties of highly isotactic polyolefins of this type without in this way impairing the good properties of the moldings produced therefrom.
Surprisingly, we have found that it rac/meso mixtures of certain metallocenes are used, the processing problems can be eliminated without the abovementioned good product properties being lost.
In addition, the use of these specific metallocenes in their pure meso-form makes it possible to prepare high-molecular-weight atactic polyolefins which can be homogeneously admixed, as additives, with other polyolefins.
This was not possible with the low-molecular weight polyolefins accessible hitherto due to the large differences in viscosity between the polyolefin matrix and the atactic component.
Such admixtures improve polyolefin moldings with respect to their surface gloss, their impact strength and their transparency. In addition, the processing properties of such polyolefins are likewise improved by admixing the high-molecular-weight atactic polyolefin. Likewise, tackiness and fogging do not occur.
Homogeneous miscibility of the atactic component is so important because only with a homogeneous material can a usable molding with a good surface and long service life be produced and only in the case of homogeneous distribution do the qualities of the atactic component come out in full.
The invention thus relates to the preparation of polyolefins which
1) are atactic, i.e. have an isotactic index of ≦60%, and are high-molecular, i.e. have a viscosity index of >80 cm
3
/g and a molecular weight M
w
of >100,000 g/mol with a polydispersity M
w
/M
n
of ≦4.0, or
2) comprise at least two types of polyolefin chains, namely
a) a maximum of 99% by weight, preferably a maximum of 98% by weight, of the polymer chains in the polyolefin as a whole comprise &agr;-olefin units linked in a highly isotactic manner, with an isotactic index of >90% and a polydispersity of ≦4.0, and
b) at least 1% by weight, preferably at least 2% by weight, of the polymer chains in the polyolefin as a whole comprise atactic polyolefins of the type described under 1).
Polyolefins which conform to the description under 2) can either be prepared directly in the polymerization or are prepared by melt-mixing in an extruder or compounder.
The invention thus relates to a process for the preparation of an olefin polymer by polymerization or copolymerization of an olefin of the formula R
a
—CH═CH—R
b
, in which R
a
and R
b
are identical or different and are a hydrogen atom or a hydrocarbon radical having 1 to 14 carbon atoms, or R
a
and R
b
, together with the atoms connecting them, can form a ring, at a temperature of from −60 to 200° C., at a pressure of from 0.5 to 100 bar, in solution, in suspension or in the gas phase, in the presence of a catalyst formed from a metallocene as transition-metal compound and a cocatalyst, wherein the metallocene is a compound of the formula I which is used in the pure meso-form for the preparation of polyolefins of type 1 and used in a meso:rac ratio of greater than 1:99, preferably greater than 2:98, for the preparation of type 2 polyolefins,
in which
M
1
is a metal from group IVb, Vb or VIb of the Periodic Table,
R
1
and R
2
are identical or different and are a hydrogen atom, a C
1
-C
10
-alkyl group, a C
1
-C
10
-alkoxy group, a C
6
-C
10
-aryl group, a C
6
-C
10
-aryloxy group, a C
2
-C
10
-alkenyl group, a C
7
-C
40
-arylalkyl group, a C
7
-C
40
-alkylaryl group, at C
8
-C
40
-arylalkenyl group, or a halogen atom,
the radicals R
4
and R
5
are identical or different and are a hydrogen atom, a halogen atom, a C
1
-C
10
-alkyl group, which may be halogenated, a C
6
-C
10
-aryl group, which may be halogenated, and an —NR
10
2
, —SR
10
, —OSiR
10
3
, —SiR
10
3
or —PR
10
2
radical in which R
10
is a halogen atom, a C
1
-C
10
-alkyl group or a C
6
-C
10
aryl group,
R
3
and R
6
are identical or different and are as defined as for R
4
, with the proviso that R
3
and R
6
are not hydrogen,
or two or more of the radicals R
3
to R
6
, together with the atoms connecting them, form a ring system,
═BR
11
, ═AlR
11
, —Ge—, —Sn—, —O—, —S—, ═SO, ═SO
2
, ═NR
11
, ═CO, ═PR
11
or ═P(O)R
11
, where
R
11
, R
12
and R
13
are identical or different and are a hydrogen atom, a halogen atom, a C
1
-C
10
-alkyl group, a C
1
-C
10
-fluoroalkyl group, a C
6
-C
10
-aryl group, a C
6
-C
10
-fluoroaryl group, a C
1
-C
10
-alkoxy group, a C
2
-C
10
-alkenyl group, a C
7
-C
40
-arylalkyl group, a C
8
-C
40
-arylalkenyl group or a C
7
-C
40
-alkylaryl group, or R
11
and R
12
or R
11
and R
13
, in each case together with the atoms connecting them, form a ring,
M
2
is silicon, germanium or tin,
R
8
and R
9
are identical or different and are as defined for R
11
, and
m and n are identical or different and are zero, 1 or 2, where m plus n is zero, 1 or 2.
Alkyl is straight-chain or branched alkyl. Halogen (halogenated) means fluorine, chlorine, bromine or iodine, preferably fluorine or chlorine.
The substitutents R
3
, R
4
, R
5
and R
6
may be different in spite of the same indexing.
The catalyst to be used for the process according to the invention comprises a cocatalyst and a metallocene of the formula I.
In the formula I, M
1
is a metal from group IVb, Vb or VIb of the Periodic Table, for example titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum or tungsten, preferably zirconium, hafnium or titanium.
R
1
and R
2
are identical or different and are a hydrogen atom, a C
1
-C
10
-, preferably C
1
-C
3
-alkyl group, a C
1
-C
10
-, preferably C
1
-C
3
-alkoxy group, a C
4
-C
10
-, preferably C
6
-C
8
-aryl group, a C
6
-C
10
-, preferably C
4
-C
8
-aryloxy group, a C
2
-C
10
-, preferably C
2
-C
6
-alkenyl group, a C
7
-C
40
-, preferably C
7
-C
10
-arylalkyl group, a C
7
-C
40
-, preferably a C
7
-C
12
-alkylaryl group, a C
8
-C
40
-, preferably a C
8
-C
12
-aryalkenyl group, or a halogen atom, preferably chlorine.
The radicals R
4
and R
5
are identical or different and are a hydrogen atom, a halogen atom, preferably a fluorine, chlorine or bromine atom, a C
1
-C
10
-, preferably C
1
-C
4
-alkyl group, which may be halogenated, a C
6
-C
10
-, preferably a C
6
-C
9
-aryl group, which may be halogenated, an —NR
10
2
, —SR
10
, —OSiR
10
3
, —SiR
10
3
or ═PR
10
2
radical, in which R
10
is a halogen atom, preferably a chlorine atom, or a C
1
-C
10
-, preferably a C
1
-C
3
-alkyl group, or a C
6
-C
10
- preferably C
6
-C
8
-aryl group. R
4
and R
5
are particularly preferably hydrogen, C
1
-C
4
-alkyl or C
6
-C
9
-aryl.
R
3
and R
6
are identical or different and are defined for R
4
, with the proviso that R
3
and R
6
must not be hydrogen. R
3
and R
6
are preferably (C
1
-C
4
)-alkyl or C
6
-C
9
-aryl, both of which may be halogenated, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, trifluoromethyl, phenyl, tolyl or mesityl, in particular methyl, isopropyl or phenyl.
Two or more of the radicals R
3
to R
6
may alternatively, together with the atoms connecting them, form an aromatic or aliphatic ring syst

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