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Polyolefin compositions

Polyolefin compositions description/claims

This application is a divisional of co-pending application Ser. No. 10/503,104, which is a national phase filing under 35 U.S.C. §371 of International Application PCT/EP03/05787, filed May 30, 2003, claiming priority to European Patent Application 02077339.6 filed Jun. 13, 2002; the disclosures of application Ser. No. 10/503,104, International Application PCT/EP03/05787, and European Patent Application 02077339.6, each as filed, are incorporated herein by reference.

The present invention relates to the process for the preparation of ethylene copolymers, to the catalyst components used for such preparation and to specific elastomeric ethylene copolymers.

Ethylene copolymers represent a very broad family of products having a prominent importance in the polyolefin field.

One of the most important groups of ethylene copolymers is constituted by the Linear low-density polyethylene (LLDPE). Due to its characteristics, it finds application in many sectors and in particular in the field of wrapping and packaging of goods where, for example, the use of stretchable films based on LLDPE constitutes an application of significant commercial importance. LLDPE is commercially produced with liquid phase processes (solution or slurry) or via the gas-phase processes. Both processes involve the widespread use of Ziegler-Natta MgCl2-supported catalysts that are generally formed by the reaction of a solid catalyst component, in which a titanium compound is supported on a magnesium halide, with an alkylaluminium compound. In order to be advantageously usable in the preparation of LLDPE, said catalysts are required to show high comonomer incorporation properties and good comonomer distribution suitably coupled with high yields. The above characteristics in fact would ensure the preparation of a product having the desired density and, at the same time, a low content of hydrocarbon soluble fractions.

Another important group of ethylene copolymers is represented by the elastomeric ethylene copolymers such as ethylene/propylene (EPM) elastomers optionally containing smaller proportions of dienes (EPDM). The said elastomers are produced industrially by solution processes or slurry processes carried out, for example, in the presence of certain Ziegler-Natta catalysts based on vanadium compounds such as vanadium acetylacetonate. These catalysts in fact, in view of their good capability to randomly distribute the comonomers, are able to produce a softer and more elastomeric product with respect to the catalysts based on titanium compounds. Their basic downside however, is the fact that they are not able to produce predominantly isotactic crystalline polypropylene and therefore they cannot be used in the production of in-situ heterophasic copolymers such as polypropylene impact copolymers constituted by crystalline polypropylene matrix within which an elastomeric rubbery phase is dispersed. On the other hand, the titanium based catalysts generally do not have a good capability to distribute the comonomer and therefore the quality of the rubbery phase is not particularly high especially when EPR/EPDM polymers with an amount of ethylene in the range of 40-70% by weight (having a satisfactory behavior during vulcanization) are to be produced. In these conditions in fact, the fraction of crystalline ethylene copolymers produced would be so high to deteriorate the properties of the rubber. The availability of this kind of product would be of high importance because the elastomeric copolymers obtained by titanium based catalysts, generally show a better homogeneity with the crystalline matrix.

We have now surprisingly found a process capable to produce ethylene copolymers endowed with good comonomer distribution comprising the copolymerization of ethylene with olefins CH2═CHR, in which R is a hydrocarbyl radical with 1-12 carbon atoms carried out in the presence of a catalyst comprising the product obtained by contacting (i) a solid catalyst component comprising Mg, Ti, halogen and the 1,3-diethers of formula (I)

in which R is a C1-C10 hydrocarbon group, R1 is methyl or ethyl, optionally containing a heteroatom, and R2 is a C4-C12 linear alkyl group optionally containing a heteroatom, with (ii) an organo-Al compound.

Preferably, R is a C1-C5 alkyl group, R1 is methyl and R2 is a C7-C10 linear alkyl group.

Examples of representative 1,3 diethers that are included in the above formula (I) are: 2-methyl-2-pentyl-1,3-dimethoxypropane, 2-methyl-2-n-hexyl-1,3-dimethoxypropane, 2-n-heptyl-2-methyl-1,3-dimethoxypropane, 2-n-octyl-2-methyl-1,3-dimethoxypropane, 2-n-decyl-2-methyl-1,3-dimethoxypropane, 2-ethyl-2-butyl-1,3-dimethoxypropane, 2-ethyl-2-pentyl-1,3-dimethoxypropane, 2-ethyl-2-n-hexyl-1,3-dimethoxypropane, 2-n-heptyl-2-ethyl-1,3-dimethoxypropane, 2-n-octyl-2-ethyl-1,3-dimethoxypropane, 2-n-decyl-2-ethyl-1,3-dimethoxypropane. The use of 2-n-octyl-2-methyl-1,3-dimethoxypropane is particularly preferred.

Particularly preferred are the solid catalyst components comprising a titanium compound, containing at least one Ti-halogen bond, and an internal electron-donor compound chosen from the above mentioned 1,3-diethers, supported on magnesium halide.

In a particular embodiment, the Mg-halide is in active form. The active form of the magnesium halides present in the catalyst components of the invention is recognizable by the fact that in the X-ray spectrum of the catalyst component the major intensity reflection which appears in the spectrum of the non-activated magnesium halides (having surface area smaller than 3 m2/g) is no longer present, but in its place there is a halo with the position of the maximum intensity shifted with respect to the position of the major intensity reflection, or by the fact that the major intensity reflection presents a half-peak breadth at least 30% greater that the one of the corresponding reflection of the non-activated Mg halide. The most active forms are those in which the halo appears in the X-ray spectrum of the solid catalyst component.

Among the magnesium halides, the chloride is the preferred compound. In the case of the most active forms of the magnesium chloride, the halo appears in place of the reflection which in the spectrum of the non-activated magnesium chloride is situated at the interplanar distance of 2.56 Å.

Preferred titanium compounds are the halides or the compounds of formula TiXn(OR4)4-n, where 0≦n≦3, X is halogen, preferably chlorine, and R4 is a C1-C10 hydrocarbon group. The titanium tetrachloride is the preferred compound. Satisfactory results can also be obtained with the trihalides, particularly TiCl3 HR, TiCl3 ARA, and with the halogen alcoholates such as TiCl3 OR, where R is a C1-C10 hydrocarbon radical.

The 1,3-diethers of the present invention can be prepared according to the methods disclosed in the European patent application No. 0361493. Said diethers, used in the preparation of Ziegler-Natta catalysts, are generally synthesized by the reaction of alkylating agents with the diols corresponding to the above diethers. A way of synthesis of said diols consists in the reduction of the corresponding malonates.

The preparation of the solid catalyst components can be carried out using various methods.

For example, the magnesium halide (preferably used in a form containing less than 1% of water), the titanium compound and the electron-donor compound are milled together under conditions that cause the activation of the magnesium halide; the milled product is then caused to react one or more times with TiCl4 in excess, optionally in the presence of an electron-donor, at a temperature ranging from 80 to 135° C., and then repeatedly washed with a hydrocarbon (such as hexane) until no chlorine ions can be detected in the wash liquid.

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