DD203730A5 - HETEROGENIC AETHYLENE COPOLYMERS - Google Patents

Abstract

The invention relates to heterogeneous ethylene copolymers which can be used for the production of films. The aim of the invention is to provide heterogeneous copolymers based on ethylene and alpha-olefins, which possess a set of properties which are at least technically equivalent and preferably better than those of similar or analogous ethylene polymers. The present invention provides copolymers of ethylene and alpha-olefins having at least four carbon atoms, having a density between 0.905 and 0.940 g / cm 3, a flow index between 0.2 and 2 dg / min, and an average alpha-olefin content between 1 and 8 mole percent. The distribution of alpha-olefin units in the copolymer is heterogeneous in the present invention, said copolymer containing crystalline and amorphous fractions, and the content of the alpha-olefin unit copolymer varies between at least 0.2 depending on the fractions contemplated - and at most 5 times their average salary.

Description

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Heterogeneous Ethylene Copolymers Field of the Invention

The invention relates to copolymers and terpolymers of ethylene, which are suitable for being processed into films, and to a process for the preparation of said copolymers and terpolymers _o

Γ " Characteristic of the known technical solutions

The literature reveals a large number of examples of copolymers of ethylene and a dC- olefin. Thus, the catalysts suitable for polymerizing the ethylene are generally capable of copolymerizing the ethylene with an £ -olefin. However, the results of such copolymerization are highly dependent on the catalyst used and, above all, on the quality of the product, on the nature of the α-olefin. The copolymers most suitable for processing into films are those in which the For such copolymers, FR-PS 1 604 980 shows, on the one hand, the importance of a narrow distribution of molecular masses and, on the other hand, the importance of the distribution of the comonomer between the molecules of the copolymer the cited document that the homogeneous copolymers have better properties for the production of films than heterogeneous copolymers.

However, it is known that a copolymer of ethylene and an o <f -O-olefin, which is intended to be certainly processed into finished articles, can only be obtained by the simultaneous existence of the following seven

17th of January. 1933 * üfc2i; .3

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Characteristics is defined; 1) density, 2) type of comonomer, 3) flow index, 4) molar content of oomonomer, 5) average molecular weight, 6) the polydispersity number, which is the distribution of molecular masses and defined below, and 7) the homogeneity of the distribution of the gomonomer.

If, in the presence of copolymers having the same equivalent values for six of the seven preceding features, the values for the seventh feature are quite different, then for these copolymers having very differentiated capabilities for a particular type of processing, it is necessary to make finished articles and thus Finally, count on completely different properties of the finished items.

Object of the invention

The object of the invention is to provide heterogeneous copolymers based on ethylene and α-olefins having at least four carbon atoms, which are processible into films and possess a set of properties which is at least technically equivalent and preferably better than those of similar or analogous ethylene polymers _e

By the term "better totality of properties" it is to be understood that in the totality of the properties contemplated not all properties are necessarily and simultaneously improved, but that some of these properties are substantially improved for the benefit of the user of the films, while the other properties either simply obtained or degraded, without this deterioration, the favorable effects of the former

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The term "similar or analogous ethylene polymers" should be understood to mean not only those ethylene copolymers whose suitability for processing into films is described in the literature, but also and especially the homopolymers of ethylene, the so-called "polyethylenes" Density * ¹ as produced by a high pressure process and in the presence of free radicals as initiators.

Explanation of the essence of the invention

The invention is αίβ _λ object of finding a suitable distribution of ethylene and o ^ -Offineinheiten in the copolymer _o

Other objects of the present invention are to provide mimetics having improved properties prepared from said copolymers and methods for preparing said copolymers.

It has now surprisingly been discovered that it is possible to obtain heterogeneous copolymers of ethylene and ° C olefins having at least four carbon atoms which, unlike the teaching of PR-PS 1 604 980, have suitable properties for their processing into films *

In the following description, the term copolymer is used to designate at the same time binary polymers which contain, in addition to the ethylene, an .alpha.- C-olefin and, in addition to the ethylene, ternary polymers containing two .alpha.-olefins. In a broader sense, the invention also relates to polymers containing more than two oC- olefins in addition to ethylene,

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In the first place, the invention consists of copolymers of ethylene and <= C- olefins having at least four carbon atoms, which copolymers have a density between 0.905 and 0.940 g / cm, a flow index between 0.2 and 2 dg / min and a Average content of cC- olefin units between 1 and 8 mole percent and characterized in that the distribution of the aC- olefin units in the copolymer is heterogeneous, said copolymer containing crystalline and amorphous fractions, and in that the content of the copolymer oC-olefin units, depending on the considered fractions between at least 0.2 and at most 5 times their average content varies · The copolymers of this invention can be further characterized in that their crystalline fractions C a single melting peak between 110 ⁰ and 130 ⁰ C. and account for 20 to 50% by weight of the total copolymer.

Further, the copolymers of the present invention may have an average molecular weight between 15,000 and β0,000 and / or a polydispersity number between 3 and 9 in the case of binary polymers and between 6 and 12 in the case of ternary polymers. In. the above definition is to be understood in the conventional manner in polymer technology, the average molecular weight as the average molecular weight Mn in numbers and the polydispersity number as the ratio Mw / Mn of the average molecular weight by weight to the average molecular mass in numbers. On the other hand, the α-olefins which can be used to form heterogeneous copolymers of the invention are, for example, butene-1, hexene-1, methyl-4-pentene-1 and octene-1. When two Γ-olefins are co-present in the copolymer of the invention (the case of a terpolymer), their average total content, as described above, is between 1 and 8 mole percent and that

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Ratio of their respective average shares between 0.25 and 4 off. So z. For example, an inventive terpolymer ethylene / butene-i / hexene-1 having an average of 95 mole percent of ethylene units will contain an average of 1 to 4 mole percent of butene-1 units and 4 to 1 mole percent of hexene-1 units.

The copolymers of the invention so determined are endowed with remarkable properties and can be made into films having a set of properties which are technically superior to ethylene polymers known to be processable into films. The most important properties to which this improvement has an effect are the elongation at break and the tear strength. Thus, in the case of films of a thickness of 50 / μm, the copolymers according to the invention generally have an elongation at break of between about 600 % and 1100%, a tensile strength (measured according to ASTM D 1922-67) between about 150 and 900 g, depending on whether in the longitudinal or transverse direction, an industrial drawability of 10 μm or less, depending on the measurement conditions indicated in the examples below, a gloss (measured according to ASTM D -2457) of 70 % or more and an impact strength (measured according to the Horm IF T 54 109),. which can reach up to 400g. It should be noted that in terms of longitudinal properties, the thickness of the test sample must always be given as these properties increase significantly as the thickness increases.

The process for the preparation of copolymers according to the invention consists in copolymerizing the ethylene and the γ - olefins having at least four carbon atoms in at least one reactor, the at least one zone having a temperature between 180 ⁰ C and 320 ⁰ C and under a pressure between 300 and 2500 bar by means of a Ziegler catalyst

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system comprising on the one hand an activator selected from the group consisting of the hydrides and organometallic compounds of metals of groups I to III of the Periodic Table and on the other hand at least one halogen compound of a transition metal, wherein the atomic ratio between the metal of the activator and the transition metal is between 1 and 10 and the average residence time of the catalyst system in the polymerization reactor is between 2 and 100 s, and is characterized in that on the one hand the gas stream feeding the reactor is constantly formed from 10 to 80% by weight of ethylene and 20 to 90% by weight of ε - olefin and on the other hand, the catalyst system has a reactivity towards the ethylene which is much larger, preferably 5 to 15 times greater than its reactivity with the <* T-01efins.

A limiting example of such compounds has the formula.

(TiCl ₃ , j AlCl ₃ ) (MX ₃ ) _χ (MgCl ₂ ) _y ,

wherein 0.3 < x <0.3.0 ^ y <20, M is a transition metal selected from Groups VB, VIB and VIII of the Periodic Table and X is a halogen. When metal M is selected from Groups VB and VIB, the catalysts have a binary Ti-M mixed crystal structure which can be characterized by the size of their crystallites. It has been found that, in view of the efficiency of these catalysts, this size measured by the radio-crystallographic analysis method (Sherrer's law) in the direction perpendicular to plane (300) should preferably be less than or equal to 100 Sngstroms (51) of these catalysts, these may optionally (if y > o) be attached to an inert support formed by anhydrous magnesium halide.

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Among the metals M, vanadium, chromium and nickel are added, but molybdenum and tungsten may also be used. The halogen of the magnesium halide and that of the halide of the metal M may be identical or different and will be selected from the group consisting of fluorine, chlorine, bromine and iodine selected.

One method of making these compounds is by contacting mixed crystals of titanium trichloride and aluminum chloride, the halide of the metal M and optionally the anhydrous magnesium halide for a sufficient duration. This can be effectively achieved by subjecting the three mentioned chlorides to a comminution step in which the comminution energy is at least 3 kY / kg of the treated pest. More specifically, it has been observed that the higher the said comminuting energy, the greater the efficiency of these compounds. However, in order to optimize this efficiency, it is generally not necessary for the crushing energy to be greater than about 25 kWh / kg of the treated pulp, taking into account operating costs and the need for energy conservation.

The proportions of the activator and the halogen compound of the transition metal are selected so that the atomic ratio of the activator metal to the transition metal (or in the case described above to the sum Ti + M) is between 1 and 10. The average residence time of the catalyst system in the polymerization reactor is generally between 2 and 100 s, This residence time depends on the temperature in the reactor so that it is higher than the temperature low; is. The preferred activators are, on the one hand, the trialkylaluminum compounds and the alkylsiloxalanes, as described in US Pat. No. 3,969,332.

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The composition of the gas stream feeding the reactor in a constant manner as a characteristic of the process according to the invention is to be understood as average composition throughout the reactor, it being understood that this composition is not necessarily uniform and may vary along the reactor, especially if it has multiple zones contains. This composition varies according to the nature of the contemplated o-olefin. Thus, in a binary copolymer, the weight fraction of oC- olefin in the gas stream is preferably between 15 and 70 % for the butene-1 and between 35 and 90 % for the hexene-1. Contains the reactor used for the inventive method a plurality of zones, is preferably in most cases the majority of the oC-olefins in the first injected at temperatures between 180 ⁰ C and 240 ⁰ C-working zones, while the last "zone at a temperature between 240 ⁰ G and 320 ⁰ C without significant additional injection of o ^ * - working 01efinen.

The process according to the invention is carried out continuously, using reactors in the form of autoclaves or tubular reactors, as is customary in the art of the polymerization of ethylene under high pressure. In order to precisely control the flow index of the copolymer, it may be advantageous to carry out the copolymerization in the presence of up to 2 mole percent hydrogen.

As stated above, the heterogeneous copolymers of the invention find favored use in the production of films of improved performance and a thickness of between 5 and 200 microns, especially 20 microns or less, i. h, among those of the low density polyethylene films as obtained by the radical route. These films are after

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obtained usual Extrusionsblastechniken with a blow-up ratio between 1.5 and 4, and have the exceptional advantage that they allow the same use at a much lower weight and have the same strength as the radical Polyethylene _o The thus produced films have numerous applications, such insbesonder for bags with high passability, rigid films for automatic packaging and films for agriculture,

embodiment

The invention is explained in more detail below with reference to some examples. The following examples are illustrative and not limiting.

example 1

Ethylene and hexene-1 are copolymerized in a reactor in the form of a cylindrical autoclave which operates under a pressure of 1000 bar and is internally equipped with a stirrer and metallic diaphragms delimiting three zones of equal volume. The zone 1, which is maintained at a temperature of 200 ⁰ C and fed with a stream of 49 kg hexene-1 / h and 24 kg of ethylene / h, receives a catalyst system consisting of one hand Dimethyläthy1-diethylsiloxalan and on the other hand of a compound of Formula TiCIo, 4 AlGIo, 2 VGIo in such respective amounts that the atomic ratio Al / Ti is equal to 3. The zone 2, which is kept at a temperature T ₂ (in ⁰ G), is charged with a stream of 24 kg ethylene / h and receives the same catalyst system as described above. Finally, Zone 3, at the outlet of which the reaction mixture containing the copolymer is evacuated to a separating and recycling device, is heated to a temperature T,

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(in ⁰ C) and receives neither a monomer nor a catalyst. The average weight fraction of hexene-1 in the reactor is therefore 50.5%. The copolymerization is carried out in the presence of 0.12 mole percent Y / acid. The average residence time of the catalyst system in the reactor is 80 s.

The resulting copolymer is characterized by the following properties:

a) pouring index (IP) measured according to ASTBiTD 1238-73 and expressed in dg / min.,

b) density £ in g / cm x ³ ,

c) mean molecular mass Mn in numbers, "measured by gel permeation chromatography, expressed in thousands,

d) polydispersity number, determined from Mn and the average molecular weight Mw measured by the same method, by weight,

e) average content of hexene-1 units in the copolymer, expressed in mole percent and based on the percentage of methyl groups per 1000 carbon atoms in the molecule by infrared radiation absorption analysis according to ASTM D 2238-64 T, as described in PR-PS 1 604 980 is, measured,

f) index of homogeneity of the distribution of the comonomer determined by a polymer prilling test and expressed by the multiple and fraction of the average content between which the content of hexene-1 units varies;

g) Melting point of the crystalline fraction of the copolymer, expressed in ⁰ C, and determined by differential thermal analysis.

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The values of these properties are with the values of T _? and To are summarized in Table 1 below.

Example 2

Ethylene and hexene-1 are copolymerized while maintaining a pressure of 1000 "bar in the same reactor as in the same conditions except for the following exceptions: Zone 1 is charged with a stream of 61 kg hexene-1 / h and 25 kg ethylene Zone 2 receives a flow of 25 kg ethylene / h, the average weight fraction of hexene-1 in the reactor is thus 55 %. " The copolymerization is carried out in the absence of hydrogen, The catalytic efficiency R ^, expressed in kg of copolymer per 10 gram atom of transition metal, as well as the properties of the resulting copolymer are shown in the following Table I.

Example 3

Ethylene and hexene-1 are copolymerized while maintaining a pressure of 600 bar in the same reactor as before and under the same conditions except for the following exceptions. Zones 1 and 2 are each fed with a stream of 27.5 kg ethylene / h and 28.5 kg hexene-1 / h. Accordingly, the average weight fraction of hexene-1 in the reactor is 50.9 %. The copolymerization is carried out in the presence of 0.06 mol % of 7% acid. The catalytic efficiency and the properties of the resulting copolymer are shown in Table I below.

Table I

example φ -2. H R C IP 6 O, 929 1 225 270 5 ,1 O, 9 O, 920 2 210 255 7 , 6 O, 2 O, 934 3 220 245 6 ,1 1,

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Table I (Continuation) 3 MW / Mn Hexene-1 7 0 IH 4 F 1 ⁰ C example Mn 4 7.5 1, 5 0 , 36-3, 6 1 26 1 21 6 3.4 4, 0 0 , 22-1, 5 1 25 2 , 46 8.2 2, , 20-2, 27 3 18 Example 4

Ethylene and octene-1 are copolymerized while maintaining a pressure of 1000 bar in the same reactor as before and under the same conditions as in Example 3 except for the following exceptions. Zones 1 and 2 are each fed with a stream of 24 kg ethylene / h and 29 kg octene-1 / h. The average weight fraction of octene-1 in the reactor is thus 55% <. The copolymerization is carried out in the absence of hydrogen, wherein the temperatures Tp and Τ-, the zones 2 and 3 are 200 ⁰ G and 250 ⁰ G. · The average residence time of the catalyst system in the reactor is 90 s. That with a catalytic efficiency R _rt of 7 kg per 10 ^ gram atom of transition metal

The copolymer obtained has the following properties: I.j? * = 0.25 Mn = 57,000 octene-1 = 1.1 Mo1%

e = 0 , 933 g / cm ³ G Mw / Mn = 3.3 j? - · Ί 27 ° Ex iel 5

Ethylene and butene-1 are copolymerized in a reactor in the form of a cylindrical autoclave operating under a pressure of 900 bar and in its interior with a stirrer and three-zone metallic diaphragms

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The first zone, held at a temperature of 210 ^° C., has a volume twice that of each of the two zones below, and is at a rate of 200 kg / h of a 36% by weight of butene-1 and 64 wt .-% ethylene existing mixture and receives a catalyst system containing on the one hand Dimethyläthyldiäthylsiloxalan and on the other hand, a compound of formula TiClO, 1 AlClO, VCIo in such respective amounts that the atomic ratio Al / Ti is equal to 3. The maintained at a temperature of 240 ⁰ C Zone 2 is fed with a flow of 55 kg / h of the same mixture as above and receives the same catalyst system * Finally, the zone 3, at the output of which the copolymer-containing reaction mixture against a separation and Recirculation is evacuated, is maintained at a temperature of 280 ⁰ C and receives neither a monomer nor a catalyst. The average residence time of the catalyst system in the reactor is 43 s.

The catalytic efficiency and the properties of the copolymer obtained are shown in the following Table II,

Example 6

In the absence of hydrogen, ethylene, butene-1 and hexene-1 in the described in Example 1, under a pressure of 1000 bar working reactor terpolymerisiert «The zone 1, which is maintained at a temperature of 180 ⁰ C, with a Stream of 13 kg hexene-1 / h, fed 14 kg of ethylene / h and 6 kg butene-1 / h and receives a catalyst system consisting of one hand Dimethyläthyldiäthylsiloxalan and on the other hand of a compound of formula TiCIo, 4 AlClO, 6 MgCl ₂ , 0 , 5 NiCl ₂ in such jewelery

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The amount of Al / Ti atomic is equal to 3. The zone 2 maintained at a temperature of 225 ^° C. is fed with a stream of 14 kg ethylene / h and 6 kg butene-1 / h and obtains the same catalyst system as above Finally, zone 3, at the outlet of which the reaction mixture containing the terpolymer is evacuated against a separation and recycling device, becomes open. maintained at a temperature of 245 ⁰ C and receives neither a monomer nor a catalyst. The average proportions by weight in the reactor are thus 53 % ethylene, 24 % hexene-1 and 23 % Baten-1. The average residence time of the catalyst system in the reactor is 85 s. The catalytic "efficiency and properties of the obtained terpolymer are given in Table II below"

Example 7

In the presence of 0.15 % of hydrogen terpolymerized ethylene, butene-1 and hexene-1 in the described in Example 1 and operating under a pressure of 800 bar reactor, the held at a temperature of 180 ⁰ C Zone 1 is. With a Stream of 27.1 kg hexene-1 / h, 18.4 kg ethylene / h and 1.6 kg butene-1 / h fed and receives the catalyst system described in Example 5, Zones 2 and 3, to 220 temperatures ⁰ G and 260 ⁰ C, each fed with a stream of 18.4 kg ethylene / h and 1.6 kg butene-1 / h «The average residence time of the catalyst system in the reactor is 100 s. The catalytic efficiency and the properties of the obtained. Terpolymers result from the following Table II.

Example 8

In the presence of 0.1% Y / averstoff copolymerized ethylene and butene-1 in the reactor described in Example 1, which with a constantly formed gas stream from

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35 wt ~% ethylene and 65 wt -.% Butene-1 is fed. The zones 1,2 and 3 operate at temperatures of 200 ⁰ C, 210 ° <or 235 ⁰ C, and the catalyst system used is the i] described in Example 1. The average residence time of the catalyst system in the reactor is 45 s. The catalytic efficiency and the properties of the copolymer obtained are shown in Table II below,

Table II ^E c IF 8th O, Butene-1 14 919 - - Mn m / Ma. , 6 example 6.2 0 5 O, 3.2 915 43 3 , 5 5 4.5 O, 6 O, 2.6 933 ! 3 15 10 , 6 6 4.9 O, 8th '0, 0.4 908 - 21.5 7 , 4 7 6.8 0 Table II (continued) 6.0 25 5 8th example 9 to Hexene-1 F 5 122 6 C IH 5 to 2.2 121 7 0 3 to 3.0 128 8th O, 2 to 1.8 117 Examples 0 5 to 2.0 0

The copolymers of Examples 1 to 3, 4, 5 and 7 are made into 50 μm thick films by extrusion blow molding under the following conditions:

- Resin temperature: 230 ⁰ C

- Rotationsgeschwindigkeit'der extruder screw: 80 U / min

Blowing ratio: 2.0

The properties measured on these films are: a) The elongation at break AR (in %) in the longitudinal direction L and in the transverse direction T, determined according to ASTM D 882-67.

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b) The tear strength RD (in g) in the longitudinal direction L and in the transverse direction T, determined according to ASTM D 1922-67.

The results of these measurements are listed in Table III, it being understood that Examples 9 to 11 refer to the copolymers of Examples 1 to 3 and Examples 12 to 14 to the copolymers of Examples 4, 5 and 7 ».

Table III 9 10 11 12 13 14 example 750 635 635 630 910 760 Ar L 360 805 610 660 1060 850 T 190 680 .160 150 300 200 RD L 775 900 430 500 640 440 T

The PiIm of Example 10 also has an impact strength (measured according to the standard IIP T 54 109) of 300 g.

In addition, all of the copolymers studied above have an industrial elongation determined by that pore thickness of 5 μm, which allows for continuous production by extrusion blown for 2 hours without disturbances.

Example 15 *

The copolymer of Example 8 is extrusion blown under the above conditions to a thickness of 50 μm. The following properties are measured on this PiIm:

- Impact resistance: 400 g

- Tear strength in the longitudinal direction: 600 g

- Tear resistance in the transverse direction: 800 g.

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Example 16

The films obtained according to Examples 10, 13 and 14 are subjected to measurement of the following optical properties: gloss (according to ASTM D-2457) and haze (according to ASTM D-1003) .These percent properties are those given in Table IV Values,

table IV example 13 Example 14 Movie . Example 10 80 7 13 Gloss turbidity 95 10.5

Claims (13)

invention claim 1. A process for the preparation of copolymers of ethylene and cC-olefins having at least four carbon atoms, which has a density between 0.905 u &gt; 0.940 g / cm, a flow index between 0.2 and 2 dg / min and an average content of <--olefin units between 1 and 8 mole percent, consisting in copolymerizing the Äthylens and the <£, -Olefine having at least four carbon atoms in at least one reactor containing at least one zone with a temperature between 180 and 320 G and a pressure between 300 and 2500 bar, means a Ziegler catalyst system having on the one hand an activator selected from the group consisting of the hydrides and organometallic compounds of metals of groups I to III of the Periodic Table and on the other hand at least one halogen compound of a transition metal, wherein the , Atomic ratio between the metal of the activator and the transition metal between 1 and 10 and the average residence time of the catalyst system in the polymer! onsreakt or between 2 and 100 s, characterized in that on the one hand the gas stream feeding the reactor is constantly formed from 10 to 80 wt .-% of ethylene and 20 to 90 wt .-% tC- olefin and on the other hand, the catalyst system has a reactivity to the Ethylene, which is much larger than its reactivity with the cC- olefins. 2. The method according to item 1, characterized in that the ratio of the reactivity of the catalyst system relative to the ethylene to its reactivity towards cC-olefins is between 5 and 15. 3. The method according to item 1 or 2, characterized in that the halogen compound of the transition material, the formula _Λ
(TiCl. ,, 4 AlGl.) (MX-) 241592 3 / Z - 61 110/18 wherein 0.3 <x <0.3, O <y < 20, M 'is a transition metal selected from Groups VB, VIB and VIII of the Periodic Table and Σ is a halogen. 4 · A method according to any one of 1 "to 3, characterized in that the reactor has a plurality of zones and that the main part of the oC-olefins in the first, * temperatures case of temperature between 180 ⁰ G and 240 G working zones is injected, while the last zone operates at a temperature between 240 ⁰ C and 320 ⁰ G without significant complementary Irgizierung of <C- olefins. 5. The method according to any one of items 1 to 4, characterized in that the activator is selected from the group consisting of the trialkylaluminum compounds and the alkylsiloxalanes. 6. The method according to any one of items 1 to 5, characterized in that the copolymerization is carried out in the presence of up to 2 mole percent Y / ass first of fjt . Process according to one of the items 1 to 6, characterized in that the distribution of the cC-olefin units in the copolymer is heterogeneous, said copolymer containing crystalline and amorphous fractions, and that the content of the copolymer of cC-olefin Sinities Depending on the fractions considered, between at least 0.2 and at most 5 times their average content varies. 8. The method according to any one of items 1 to 7, characterized in that their crystalline fractions have a single melting peak between 110 ⁰ C and 130 ⁰ C and constitute 20 to 50 wt .-% of the total copolymer. 9. The method according to item 7 or 8, characterized in that their average molecular mass between 15 000 and 15 9 2 3 - ^ - 61 60,000 lies. 10. The method according to any one of items 1 'to 9, characterized in that they contain a single cC-olefin and that their polydispersity number is between 3 and 9. 11. The method according to any one of items 1 'to 9, characterized in that they contain two oC-olefins, wherein the ratio between their respective average proportions between 0.25 and 4. 12. The method according to item 11, characterized in that their polydispersity number is between 6 and 12. 13. The method according to any one of items 1 to 12, characterized in that the ε-olefins are selected from the group consisting of butene-1, hexene-1, methyl-4-pentene-1 and octene-1.