Organic compounds -- part of the class 532-570 series – Organic compounds – Heavy metal containing
Patent
1995-06-07
1997-12-02
Nagumo, Mark
Organic compounds -- part of the class 532-570 series
Organic compounds
Heavy metal containing
556 53, 556 43, 556 58, 556 22, 556 38, 526127, 526160, 526129, 526348, 526351, 526943, C08F 4642, C08F 1006
Patent
active
056938365
DESCRIPTION:
BRIEF SUMMARY
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 modulus 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 if 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 high-molecular, i.e. have a viscosity index of >80 cm.sup.3 /g and a molecular weight M.sub.w of >100,000 g/mol with a polydispersity M.sub.w /M.sub.n of 4.0, or the polymer chains in the polyolefin as a whole comprise .alpha.-olefin units linked in a highly isotactic manner, with an isotactic index of >90% and a polydispersity of .ltoreq.4.0, and 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.sup.a --CH.dbd.CH--R.sup.b, in which R.sup.a and R.sup.b are identical or different and are a hydrogen atom or a hydrocarbon radical having 1 to 14 carbon atoms, or R.sup.a and R.sup.b, together with the atoms connecting them, can form a ring, at a temperature of from -60.degree. to 200.degree. 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, ##STR3## in which M.sup.1 is a metal from group IVb, Vb or VIb of the Periodic Table, C.sub.1 -C.sub.10 -alkyl group, a C.sub.1 -C.sub.10 -alkoxy group, a C.sub.6 -C.sub.10 -aryl group, a C.sub.6 -C
REFERENCES:
patent: 5145819 (1992-09-01), Winter et al.
patent: 5278264 (1994-01-01), Spaleck et al.
patent: 5304614 (1994-04-01), Winter et al.
patent: 5328969 (1994-07-01), Winter et al.
High Molecular Weight Polypropylene through Specifically Designed Zirconocene Catalysts by Walter Spaleck et al., Angewandte Chemie, Bd. 31, Nr. 10, Oct. 1992, pp. 1347-1350, Weinheim, Germany.
ansa-Metallocene derivatives by Peter Burger et al., Journal of Organometallic Chemistry, Bd. 417, No. 1-2, Oct. 1, 1991, pp. 9-27, Lausanne.
Mechanisms of Stereochemical Control in Propylene Polymerizations with Soluble Group 4B Metallocene/Methylalumoxane Catalysts by John A. Ewen, J. Am. Chem. Soc., Bd. 106, 1984, pp. 6355-6364.
Stevens, Metallocene and Other Single Site Catalysts, The Dow Chemical Co., PTO Presentation, Dec. 8, 1994.
Antberg Martin
Bachmann Bernd
Dolle Volker
Kuber Frank
Rohrmann Jurgen
Genova John M.
Hoechst Aktiengesellschaft
Nagumo Mark
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