DK162940B - THE HETEROGENIC COPOLYMERS OF THE ETHYLENE, USE OF THE COPOLYMES FOR THE PREPARATION OF FILMS AND PROCEDURE FOR THE PREPARATION OF THE COPOLYMERS - Google Patents

Description

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The invention relates to heterogeneous copolymers of ethylene, the use of the copolymers for the production of films, and a process for the preparation of the copolymers.

5 In the literature, a large number of examples have been given of copolymers of ethylene and an α-olefin. Thus, catalysts capable of polymerizing ethylene are generally capable of copolymerizing ethylene with an α-olefin. However, the results of such copolymerization are highly dependent on the catalyst used and, above all, on the quality of the products, on the nature of the α-olefin. The copolymers most suitable for the production of films are those wherein the α-olefin contains at least 4 carbon atoms. Regarding such copolymers, FR patent 1,604,980 discloses firstly the importance of a narrow molecular weight distribution and secondly the importance of the comonomer's distribution between the copolymer's molecules. With respect to the latter factor, it is disclosed that homogeneous copolymers give better properties in the production of films than heterogeneous copolymers.

Thus, it is known that a copolymer of ethylene and an α-olefin intended for use in a particular method of making finished articles is, in fact, only fully defined by simultaneously giving the following seven characteristics: 1) the density or density , 2) the nature of the comonomer, 3) the melt index, 4) the molar content of the comonomer, 5) the average molecular weight, 6) the polydispersity index, which is a measure of the molecular weight distribution and defined below, and 7) the homogeneity index of the distribution. of comonomers.

If, in the case of copolymers exhibiting similar or equivalent values with respect to six of the seven characteristics mentioned above, distinctly different values are found with respect to the seventh, one must expect that these copolymers exhibit distinctly different suitability by a particular method of converting copolymer

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2 for finished articles, and thus, in short, clearly different properties of the finished articles made.

It has now surprisingly been found that it is possible to make heterogeneous copolymers of ethylene and α-olefins having at least 4 carbon atoms which, contrary to what is disclosed in FR Patent No. 1,604,980, have properties that do those suitable for forming films, having a set of properties which are technically at least equivalent to and preferably better than for similar ethylene polymers. By the term "a better set of properties" is meant that in a given set of properties, not all of the properties need necessarily be improved at the same time, but that some of these properties will be substantially improved with respect to the use of the films or films, while other properties are merely retained or slightly impaired without this deterioration outweighing the beneficial effects of the former properties. By the term "similar ethylene polymers" is meant not only those 20 ethylene copolymers whose suitability for transfer to films is mentioned in the literature, but also in particular those ethylene homopolymers known as "low density or density polyethylenes" and produced by the high pressure method. in the presence of free radical initiators.

Thus, according to the invention, copolymers of ethylene and α-olefin having at least 4 carbon atoms are provided, which copolymers have a density of between 0.905 and 0.940 g / cm 3 and a melt index of between 0.2 and 2 dg / min, and have an average content of α-olefin units of between 30 1 and 8 mol%. The new copolymers are distinguished by the distribution of the α-olefin units among the macromolecules in the copolymer, the macromolecules in the copolymer comprising both crystalline and amorphous fractions, and the content of the α-olefin units in the 35 fractions varies between 0.2 and 5. times the average content of α-olefin units in the copolymer, and - that they can be prepared by a process, by

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3 wherein ethylene and α-olefin of at least 4 carbon atoms are copolymerized in at least one reactor including at least one zone, at a temperature of between 180 degrees and 320 degrees C and under a pressure of between 300 and 2500 bar, by means of a catalyst system of The Ziegler type, which consists of an activator selected from hydrides and organometallic compounds of the metals of Groups I-III of the Periodic Table and at least one halogenated transition metal compound, the atomic ratio of the metal in the activator to the transition metal in the transition metal compound being between 1 and 10, and wherein the catalyst system exhibits a ratio of the reactivity with respect to ethylene and the reactivity with respect to α-olefin of between 5 and 15, the residence time of the catalyst in the polymerization reactor being between 2 and 100 seconds, and the gas flow introduced as feed to the reactor, contains - from stationary operation - from 10-80% by weight of ethylene and from 20-90% by weight rocent a-olefin.

In the following, the term "copolymer" 20 is used both for binary polymers containing an α-olefin and for ternary polymers containing two α-olefins in addition to ethylene. The present invention also relates to polymers containing more than two α-olefins in addition to ethylene.

The copolymers of the invention preferably have 25 crystalline fractions which exhibit a single melting point peak ranging between 116 and 130 degrees C and constitute from 20 to 50% by weight of the total copolymer.

Conveniently, the copolymers of the invention have an average molecular weight in the range of from 15,000 to 60,000 and / or a polydispersity index ranging from 3 to 9 for binary polymers and between 4 and 12 for ternary polymers. In the above definition, as is customary in the polymer technique, the average molecular weight means the average molecular weight by number of Mn and by the polydispersity index the ratio Mw / Mn, i.e. the ratio of the average molecular weight by weight to the average molecular weight

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4 by number. The α-olefins which may form part of the structure of the heterogeneous copolymers of the invention are e.g. 1-butene, 1-hexene, 4-methyl-1-pentene and 1-octene. When two α-olefins are present simultaneously in the copolymer of the invention (ie, in a terpolymer), their total average content as described above is between 1 and 8 mole percent, and furthermore, the ratio of their respective average content is preferably between 0, 25 and 4. Thus, e.g. a terpolymer of ethylene, 1-butene and Ι-ΙΟ hexene according to the invention, which contains on average 95 mol% ethylene units, have an average content of 1-4 mol% 1-butene units and an average content of 4-1 mol% 1-hexene units.

The copolymers of the invention thus defined have remarkable properties and can be converted into films having a set of properties which are technically superior to ethylene polymers known to be useful in the production of films or films.

20 The most important properties that require improvement are the elongation at break and tear strength. Thus, the copolymers of the invention usually exhibit, at a thickness of 50 microns, a rupture elongation which is between ca. 600 and 1100%, a tear strength (measured according to 25 ASTM D 1922-67), which is between approx. 150 and 900 g, depending on the longitudinal or transverse direction, an industrial extensibility less than or equal to 10 µm under the measuring conditions given in the examples below, a gloss (measured according to ASTM D 2457), which is greater than or equal to 70% and a impact strength (measured according to NF T 54 109) of up to 400 g. It should be noted that as far as the values are in the longitudinal direction, the thickness of the specimen shall always be indicated as these increase substantially, as the thickness increases.

Thus, the invention also relates to the use of the aforementioned new copolymers for the production of films and foils having a thickness of between 5 and 200 µm.

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5

The process for preparing the copolymers of the invention consists in copolymerizing ethylene and α-olefins with at least 4 carbon atoms in at least one reactor containing at least one zone at a temperature between 180 and 5 320 degrees C and under a pressure of 300 and 2500 bar by means of a Ziegler type catalytic system which contains, in part, an activator selected from hydrides and organometallic compounds of metals from groups I to III of the periodic system and partly contains at least one halogenated compound of a transition metal, the atomic ratio of the metal in the activator to the transition metal is between 1 and 10, by which process the catalyst system residence time in the polymerization reactor is between 2 and 100 seconds. The process is characterized in that, during stationary operation, the stream 15 of gas fed to the reactor contains 10-80 wt.% Ethylene and 20-90 wt.% Α-olefins, and a catalytic system exhibiting a reactivity to ethylene is used. which is 5-15 times higher than its reactivity to α-olefins.

Examples of useful transition metal compounds have the formula: (TiCl, 1/3 A1C1) (MX) (MgCl) 3 3 3 x 2 y where x is 0.3-3, y is 0-20, M is a transition metal selected from groups VB, VI B and VIII of the periodic table and X 25 is a halogen atom. When the metal M is selected from groups V B and VI B, these catalysts have a solid Ti-M binary solution solution which can be characterized by the size of its crystallites. As to the efficiency of these catalysts, it has been found that this size, as determined by radiocrystallographic analysis (Sherrer's Law) in the direction perpendicular to the plane (300), should preferably be less than or equal to 100 Å. As can be seen from the formula, in some cases (when γ> 0), these catalysts may be bonded to an inert carrier consisting of anhydrous magnesium halide. Among the metals M, vanadium, chromium and nickel are preferred, but molybdenum and tungsten are also useful. The halogen in the magnesium halide and the halide of

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The metal M may be the same or different and is selected from fluorine, chlorine, bromine and iodine.

One method of preparing such compounds consists in contacting titanium trichloride crystallized with aluminum chloride, the balogenide of the metal M and optionally anhydrous magnesium halide for a sufficient period of time. This can be achieved efficiently by subjecting the said halides to a grinding at which the grinding energy is at least 3 kWh per hectare. kg treated 10 solids. More specifically, it has been found that the greater the efficiency of these compounds, the greater the grinding energy. However, in order to optimize this efficiency, taking into account the operating costs and the need to economize with the energy, it is generally unnecessary for the milling energy to be higher than approx. 25 kWh per kg of treated solid.

The amount ratio of the activator to the halogenated compound of the transition metal is chosen such that the atomic ratio of the metal in the activator to the transition metal (or, in the case described above, the sum of Ti + M) is between 1 and 10. The average residence time of the catalytic system in the polymerization reactor is generally between 2 and 100 seconds. This residence time depends on the temperature of the reactor in that it is longer, the lower the temperature. The preferred activators are, first, trialkylaluminum compounds and, second, alkylsiloxalanes, such as those described in U.S. Patent No. 3,969,332.

The composition of the flow of gases fed to the reactor during stationary operation is understood to mean the average composition of the entire reactor, as it will be understood that this composition is not necessarily uniform and may vary throughout the reactor, especially when it comprises multiple zones. . This composition varies with the nature of the α-olefin used. Thus, for a binary polymer, the weight content of α-olefin in this stream of gas is preferably between 20 and 70% for 1-butene and between

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7 35 and 90% for 1-hexene.

When the reactor used in the process of the invention comprises several zones, it is often preferred to introduce substantially all of the α-olefin into the first 5 zones operated at temperatures between 180 and 240 degrees C, while the last zone is operated at temperature between 240 and 320 degrees C without substantial additional supply of α-olefin.

The process of the invention is carried out continuously in autoclave or in tube reactors, as is customary for polymerization of ethylene under high pressure. To accurately control the melt index of the copolymer, it may also 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 are advantageously used for the production of films having improved properties and having a thickness between 5 and 200 microns, especially less or equal to 20 microns, i.e. less than the thickness of low-density polyethylene films prepared by a radical process. These films are made by conventional methods by either blow extrusion having a blow ratio of 1.5 to 4 or by extrusion through a flat nozzle and have the special advantage of having the same firmness and solidity of films of radical polyethylene at a much lower weight . Therefore, the foils thus produced have several applications, such as, in particular, high-capacity bags, rigid foils for automatic packaging and agricultural foils.

The invention is illustrated by the following examples.

Example 1

Ethylene and 1-hexene are copolymerized in a cylindrical autoclave reactor operated under a pressure of 1000 bar and equipped internally with an agitator and 35 metal screens defining three zones of equal volume. Zone 1 maintained at a temperature of 220 degrees C and fed with a flow of 49 kg / hr 1-hexene and 24 kg / hr ethylene,

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8 receives a catalytic system comprising for the first dimethylethyl diethylsiloxalane and secondly a compound of the formula

TiCl, 1/3 A1C1, 2 VC1 3 3 3 5 in such respective quantities that the Al / Ti atomic ratio is equal to 3. Zone 2 maintained at a temperature (expressed in degrees C) is fed with a flow of 24 kg / hour ethylene and receives the same catalytic system as above. Finally, zone 3, from whose outlet the reaction mixture containing the copolymer, is fed to a separation and recycling device, is maintained at a temperature T (expressed in degrees C) 3 and receives neither monomer nor catalyst. Thus, the average weight content of the 1-hexene in the reactor is 50.5% by weight. The copolymerization is carried out in the presence of 0.12 mol% hydrogen. The average residence time of the catalyst system in the reactor is 80 seconds.

The copolymer produced is characterized by the following properties: a) the melt index (MI) measured according to ASTM D 1238-73 and expressed in dg / min, 3, b) the density p expressed in g / cm c) the average molecular weight (Mn) (d) the polydispersity index determined from Mn and the average molecular weight by weight Mw measured by the same method; e) the average content of 1-hexene units in the copolymer, expressed in mole percent and determined from the proportion of methyl groups per 1000 carbon atoms in the molecule by examining the IR absorption of ASTM D 2238-64 T as described in FR Patent No. 1,604,980; f) the homogeneity index (IH) for the distribution of comonomers determined by a fractionation study of the polymer and expressed at the multiples and sub-multiples of the average content between which the content of 1-hexene units varies, g) the melting point (MP) of the crystalline fraction of

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9 the copolymer expressed in degrees C and determined by differential enthalpy analysis.

The values of these properties, together with the values of T and T, are listed in Table I below.

Example 3

Ethylene and 1-hexene are copolymerized under a pressure of 1000 bar in the same reactor as above and under identical conditions with the following exceptions. Zone 1 is fed with a flow of 61 kg / hr 1-hexene and 25 kg / hr ethylene.

Zone 2 is fed with a flow of 25 kg / hour ethylene. Thus, the average weight content of the 1-hexene in the reactor is 55%. The copolymerization is carried out in the absence of hydrogen. The catalytic yield R <= expressed in kg of copolymer per ml. millimeters of transition metal as well as the properties of the copolymer produced are listed in Table I below.

Example 3

Ethylene and 1-hexene are copolymerized under a pressure of 600 bar in the same reactor as above and under identical conditions with the following exceptions. Zones 1 and 2 are each fed 20 with a flow of 27.5 kg / hr of ethylene and 28.5 kg / hr of 1-hexene. Thus, the average weight content of the 1-hexene in the reactor is 50.9%. The copolymerization is carried out in the presence of 0.06 mol% hydrogen. The catalytic yield and properties of the polymer produced are set forth in Table I below.

Table I

Example Tz T3 R <= MI p Ί 225 270 δΤΪ όΤβ 0.929 2 210 255 7.6 0.9 0.920 30 3 220 245 6.1 1.2 0.934

Table I (continued)

Example Mn Mw / Mn 1-hexene IH_MP

1 21.3 7.5 1.7 0.36-3.4 126 2 46.4 3.4 4.5 0.22-1.6 125 35 3 18.6 8.2 2.0 0.20 -2.5 127

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Example 4

Ethylene and 1-octene are copolymerized under a pressure of 1000 bar in the same reactor and under the same conditions as in Example 3 with the following exceptions. Zones 1 and 2 are each fed with a flow of 24 kg / hr ethylene and 29 kg / hr 1 octene. Thus, the average weight content of the 1-octane in the reactor is 55%. The copolymerization is carried out in the absence of hydrogen, and the temperatures in zones 2 and 3 are Tz = 200 ° C and T3 = 25, respectively (fC. The copolymer obtained 10 with a catalytic yield R <= = 7 kg per milliliter of starting metal, has the following properties: MI = 0.25 P = 0.933 g / cm3

Mn = 57,000 Mw / Mn = 3.3

1-octene = 1.1 mol% MP = 127 ° C

Example 5

Ethylene and 1-butene are copolymerized in a cylindrical autoclave reactor operated under 900 bar pressure and internally equipped with a stirrer and metal screens defining three zones. Zone 1, maintained at a temperature of 210 ° C and having twice the volume of each of the two following zones, is fed with a flow of 200 kg / h of a mixture containing 36 wt% 1-butene and 64 wt. % ethylene and receives a catalytic system containing partly dimethylethyl diethylsiloxalane and partly a compound of the formula

TiCl, 1/3 A1C1, 2 VC1 3 3 3 in such respective amounts that the Al / Ti atomic ratio is equal to 3. Zone 2 maintained at a temperature of 24 (f C is fed at a flow rate of 55 kg / h Finally, zone 3 from which the reaction mixture containing the copolymer is fed to a separation and recirculation device is maintained at a temperature of 28CP C and receives neither monomer nor catalyst. residence time of the catalyst system in the reactor is 43 seconds.

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The catalytic yield as well as the properties of the copolymer produced are listed in Table II below.

Example 6

Ethylene, 1-butene and 1-hexene are terpolymerized in the absence of hydrogen in the reactor described in Example 1 under a pressure of 1000 bar. Zone 1, maintained at a temperature of 180 ° C and fed with a flow of 13 kg / hr 1-hexene, 14 kg / hr ethylene and 6 kg / hr 1-butene, receives a catalytic system containing partly dimethylethyl diethylsiloxylane. and partly a compound of the formula

TiCl3, 1/3 A1C13, 6 MgCl2, 1/2 NiCl2 in such respective amounts that the Al / Ti atomic ratio is equal to 3. Zone 2 maintained at a temperature of 22? C, is fed with a flow of 14 kg / hour ethylene and 6 kg / hour 1-butene and receives the same catalytic system. Finally, zone 15 3, from which the reaction mixture containing the terpolymer, is discharged to a separation and recirculation device, is kept at a temperature of 24? C and receives neither monomer nor catalyst. Thus, the average weight content of the reactor is 53% for ethylene, 24% for 1-hexene and 23% for 1-butene. The average residence time of the catalytic system in the reactor is 85 seconds. The catalytic yield as well as the properties of the terpolymer produced are listed in Table II below.

Example 7 Ethylene, 1-butene and 1-hexene are terpolymerized in the presence of 0.15 mol% hydrogen in the reactor described in Example 1 under a pressure of 800 bar. Zone 1 maintained at a temperature of 180 ° C and fed with a flow of 27.1 kg / hr 1-hexene, 18.4 kg / hr ethylene and 1.6 kg / hr 1-butene receives the catalytic system described in Example 5.

Zones 2 and 3 maintained at temperatures of 220 and 260 ° C, respectively, are each fed with a flow of 18.4 kg / h ethylene and 1.6 kg / h 1-butene. The average residence time of the catalytic system in the reactor is 100 seconds. The catalytic yield as well as the properties of the terpolymer produced are listed in Table II below.

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12

Example 8

Ethylene and 1-butene are copolymerized in the presence of 0.1 mole percent hydrogen in the reactor described in Example 1, which is fed with a stream of gas consisting of 35 wt% ethylene 5 and 65 wt% 1-butene. Zones 1, 2 and 3 are maintained at temperatures of 200, 210 and 2355 C, respectively, and the catalytic system is described in Example 1. The average residence time of the catalytic system in the reactor is 45 seconds. The catalytic yield as well as the properties of the copolymer produced are listed in Table II below.

Table II

Example Rc MI p Mn Mw / Mn 5 672 07i 0.919 43 3 ^ 6 6 4.5 0.5 0.915 15 10.5 15 7 4.9 0.6 0.933 21.5 7.6 8 6.8 0.8 0.908 5.4

Table II (continued)

Example 1-Butene 1-hexene 1H MP

“5 372 1 0.5-2.2 Ϊ22 20 6 2.6 0.9 0.3-3.0 121 7 0.4 1.3 0.2-1.8 128 8 6.0 - 0, 5-2.0 117

Examples 9-14

The copolymers of Examples 1-3, 4, 5 and 7 are converted by blow extrusion to films of 50 µm thickness under the following conditions:

- resin temperature: 230P C

- rate of rotation of the extrusion screw: 80 rpm - inflation rate: 2.0 30 A determination is made of the following properties of these films: a) elongation elongation AR (expressed in%) in the longitudinal direction L and the transverse direction T according to ASTM D 882-67.

b) tear strength RT (expressed in g) in the longitudinal direction L and the transverse direction T according to ASTM D 1922-67.

The results of these measurements are given in Table

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13 III, where Examples 9-11 correspond to the copolymers of Examples 1-3, and Examples 12-24 correspond to the copolymers of Examples 4, 5 and 7.

Table III

Example 9_10_11_12_13_14 L 750 635 635 630 910 760

YEAR

_T 860 805_610_660_1060_850 L 190 680 160 150 300 200

10 RT

T 775 990_430_500_640_440

Furthermore, the film of Example 10 exhibits a impact strength (measured according to NF T 54 109) of 300 g.

In addition, all of the copolymers examined exhibit an industrial extensibility, defined as the film thickness which permits continuous fabrication by blow extrusion for a period of 2 hours without interruption, at 5 µm.

Example 15

The copolymer of Example 8 is converted by blow extrusion under the above conditions into a film having a thickness of 50 µm. The following properties of the foil are measured:

Impact strength: 400 g

Longitudinal tear strength: 600 g 25 Tear strength in the transverse direction: 800 g

Example 16

The optical properties of the films prepared according to Examples 10, 13 and 14, namely gloss (according to ASTM D-2457) and blur or haze (according to ASTM D-1003) are measured. The 30 results obtained, expressed in%, are listed in Table IV.

Table IV

Folie_Eks. 10_Eks. 13_Eks. 14_

Gloss (%) 95 80 85

Blur (%) 10.5_7_13_

Claims (15)

1. Copolymers of ethylene and α-olefin containing at least 4 3 carbon atoms, having a density between 0.905 and 0.940 g / cm, a melt index between 0.2 and 2 dg / min. and an average content of α-olefin units between 1 and 8 mole percent, characterized in that the distribution of α-olefin units in the macromolecules of the copolymer is heterogeneous, the copolymer's macromolecules containing crystalline and amorphous fractions, and the content of olefin units in the fractions vary between 0.2 and 5 times the average content of α-olefin units in the copolymer and can be prepared by a process in which ethylene and α-olefin having at least 4 carbon atoms are copolymerized in at least one reactor containing at least one zone at a temperature between 180 and 320 degrees C under a pressure of between 300 and 2500 bar by a Ziegler-type catalytic system comprising, in part, an activator selected from hydrides and organometallic compounds of Group I to metal metals III of the periodic system and at least one halogenated compound of a transition metal, the atomic ratio of the metal in the activator to the transition all ranges from 1 to 10, and the ratio of the catalyst system reactivity to ethylene and its reactivity to α-olefin is between 5 and 15, with the average residence time of the catalytic system in the polymerization reactor being between 2 and 100 seconds, and The gas stream fed to the reactor in stationary operation consists of 10-80 wt% ethylene and 20-90 wt% α-olefin. Copolymers according to claim 1, characterized in that their crystalline fractions exhibit a single melting point peak between 116 and 130 degrees C and constitute 20-50% by weight of the total copolymer. Copolymers according to claim 1 or 2, characterized in that their average molecular weight is between 15,000 and 60,000. Copolymers according to any one of claims 1-3, characterized in that they contain, in addition to ethylene, a single α-olefin and that their polydispersity index is between 3 and 9. Copolymers according to any one of claims 1-3, characterized in that they contain, in addition to ethylene, two α-olefins and that the ratio of the respective average proportions thereof is preferably between 0.25 and 4. Copolymers according to claim 5, characterized in that their polydispersity index is between 4 and 12. Copolymers according to any one of claims 1-6, characterized in that the α-olefins are selected from 1-butene, 1-hexene, 4-methyl-1-pentene and 1-octene. Use of copolymers according to any one of claims 1-7 for the production of foils having a thickness of between 5 and 200 µm. A process for preparing copolymers according to any one of claims 1-7, wherein ethylene and α-olefin having at least 4 carbon atoms are copolymerized in at least one reactor containing at least one zone at a temperature between 180 and 320 degrees C under a pressure of between 300 and 2500 bar by a Ziegler type catalytic system comprising, in part, an activator selected from hydrides and organometallic compounds of metals from groups I to III of the periodic system, and at least one halogenated compound of a transition metal, the atomic ratio of the metal being the activator and the transition metal are between 1 and 10, and the average residence time of the catalytic system in the polymerization reactor is between 2 and 100 seconds, characterized in that the flow of gas fed to the reactor in the stationary operation consists of 10-80 wt% ethylene and 20-90 wt% α-olefin, the ratio of the reactivity of the catalytic system to e thylene 5 and its reactivity to α-olefin are between 5 and 15. Process according to claim 9, characterized in that as halogenated compound of a transition metal one or more compounds of formula: (TiCl3, 1/3 A1C13) (ΜΧ3) χ (MgCl2) y 10 wherein x is 0.3- 3, y is 0-20, M is a transition metal selected from groups VB, VI B and VIII of the periodic table, and X is a halogen atom. Process according to claim 9 or 10, characterized in that a reactor containing several zones is used and that substantially all of the α-olefin is introduced into the first zones operated at temperatures between 180 and 240 degrees. C, while the last zone is operated at a temperature between 240 and 320 degrees C without substantial additional supply of α-olefin. A process according to any one of claims 9-11, characterized in that an activator selected from trialkyl aluminum compounds and alkylsiloxanes is used. A process according to any one of claims 9-12, characterized in that the copolymerization is carried out in the presence of up to 2 mole percent hydrogen. Process according to any one of claims 9-13, characterized in that 1-butene is used as α-olefin and the stream of gas fed to the reactor contains, in stationary operation, 20-70% by weight of 1-butene. and 30-80% by weight ethylene. DK 162940 B A process according to any one of claims 9-13, characterized in that 1-hexene is used as α-olefin and the gas stream fed to the reactor contains, in stationary operation, 35-90% by weight of 1-hexene and 10-65 5% by weight of ethylene.