NL8700797A - Low density ethylene! copolymer - with multiple melting and crystallisation points, useful in heat seal layers - Google Patents

Abstract

An ethylene polymer comprises 50-97 mole % ethylene units, 3-50 mole % 3-18C 1-alkene units and optionally other comonomer units. The polymer has density at most 910 Kg/cu.m., at least two melting points, one between -80 deg. C and (120-3x) deg. C but not above 100 deg. C and another between (120-3x) and 140 deg. C and at least two crystallisation points, one between -90 deg. C and (110-3x) deg. C but not above 90 deg. C and another between (110-3x) and 130 deg. C, where x is the total mole % of comonomers. The deviation Wc in enthalpy, defined by the formula (I), where ha and hc are the theoretical values of the specific enthalpies of 100% amorphous and 100% crystalline polypropylene resp. and h is the specific enthalpy of the polymer, is at least 1% at (120-3x) deg. C and at 23 deg. C is at most 0.87 of the Wc at -70 deg. C.

Description

8tL / WP / ag * STAMICARBON B.V.

Inventors: Vincentius B.F. Mathot in Holtum Johannes Tijssen in Spaubeek Luc M.C. Coosemans at Houthalen (Belgium) -1- (15) PN 5645

ETHENE COPOLYMER

The invention relates to a polymer comprising at least: a) 50-97 mol% ethylene b) 3-50 mol X 1 -olefin with 3 to 18 carbon atoms c) optionally one or more other monomers, with a density not exceeding 910 kg / m 2.

Such polymers are known under the name of TAFMER R. The main application is in the mixing with polyolefins in order to effect the improvement of certain properties thereof. For example, a mixture of TAFMER R and oolpropylene is suitable for use as a peelable welding layer, the impact strength and transparency of linear low density polyethylene (manufactured with a transition metal catalyst) are improved, and low density polyethylene (manufactured with a radical initiator) is obtained after mixing with TAFMER. R better adhesion to other polyolefins.

These applications are especially important for the packaging industry, where films made of various materials, as well as films consisting of several layers, are used. Usually the foil is first processed into a bag, in which a bottom is formed by squeezing two, whether or not joined together, foils and exposing them to high temperatures (e.g. 13QaC), the so-called welding.

The bag is then filled with the goods to be packed and also welded at the top.

Welding films together generally takes place using so-called welding bars between which the films are forcefully pressed together, while these welding bars have a temperature of about 125 ° C to 150 ° C. With equipment such as e.g. vertical form, f * · '«-2- (15) ΡΝ 5645 filling and sealing machines, the bag is filled with the intended content while the bottom seal is still warm. Allowing the weld to cool would entail too long a waiting time, thus extending the cycle time and thus increasing costs.

Therefore, the aim is to keep the waiting time between bag formation and filling as short as possible. This can only be achieved if the warm bag is sufficiently strong under the sudden weight of the filling. This strength is indicated by the term "hot tack".

In connection with energy costs and warm-up time, it is also desirable that the temperature at which a good weld is formed is as low as possible, without the pressure exerted by the welding beams having to be increased, or the Welding Time being extended. The conventional linear low-density polyethylene (LLDPE) has a good "hot tack" but only forms a good weld at relatively high temperatures (eg 110 ° C).

Conventional ethylene-1-olefin copolymers (such as, for example, TAFMER R) / have a low load capacity, but the "hot tack" leaves much to be desired.

The object of the invention is to find a polymer that combines the advantages of LLDPE and ethylene-1-olefin copolymers.

This object is achieved by a polymer, comprising at least a) 50-97 mol% ethylene b) 3-50 mol% 1-olefin with 3 to 18 carbon atoms c) optionally one or more other monomers, with a density of at most 910 kg / m3 / at least two melting points, one of which is between -80nc and (-3x +120) aC, but not above 1ÖQnc, and a second between (-3x +120) nC and 140nC, and at least at least two crystallization points, one of which is between -90hC and (-3x 30 +110) βο, but not above 90hC, and a second between (-3x +110) oC and 13Qnc, where x is the molar percentage of comonomer.

Polymers according to the invention already appear to form a good weld at relatively low temperatures (eg 70 ° c), while the hot tack is also very good.

8? 0 0 7 9> f -3- (15) PN 5645

The melting and crystallization curves are determined by the "Differential Scanning Calorimetry" (DSC) method and show melting respectively. crystallization peaks at certain temperatures, depending on the polymer. The peaks of these peaks are melted, respectively.

5 called crystallization points.

Surprisingly, it has been found that polymers according to the invention have a very wide melting and crystallization range compared to the known ethylene copolymers and LLDPE, that is to say melting phenomena already occur from very low temperatures (-80 ° C, in particular -70 ° C). ) which continue up to high temperatures (+ 14 ° C, in particular +135 ° C), and crystallisation phenomena (+130 ° C, in particular + 125 ** C) already occur from very high temperatures, leading to very low temperatures ( -90ac, especially -80hc) continue. It has also been found that polymers according to the invention have a DSC curve which exhibit both the low melting point (s) of the known ethylene-1-olefin copolymers and the high melting point (s) of the known LLDPE. . This may explain the fact that the polymers of the invention combine the beneficial properties of both known polymers.

Polymers with a) 6Π-96 mole% ethylene, b) 4-40 mole% 1-olefin and c) optionally one or more other monomers, with a density of at most 905 kg / rn3, at least two melting points of which one is between (-4x +70) C and (-3x +120) hC, but not above 10Qnc, and a second is between (-3x +120) e and 135hc, and at least two crystalline points of which one is between (-4x +60) πχ and (-3x +110) nC, but not above 9QöC, and a second is between (-3x + 1in> nC and 125eC, where x is the mole percentage of comonomer) the desired combination of low welding torque and high "hot tack" in particular, and in particular polymers with a) 70-95 mole% ethylene, b) 5-30 mole% 1-olefin and c) optionally one or more others monomers, with a density below 900 kg / m3, with at least two melting points, one of which is between (-4x +100) bc and (-4x +130) bC, but not above 100nc, and a second between (-x + 120) hC and 135nc, and at least two crystallization points, one of which lies t ussen (-4x +90) nc and 35 (-4x +120) nC and a second between (-x +110) ac and 125bc, where x is 8 7. '; Preferred are f4- (15) PN 5645 mol% comonomer.

Polymers according to the invention can be prepared by polymerizing ethylene with the other monomer (s) in the presence of a transition metal catalyst, in particular a Ziegler-Natta catalyst. Conventional catalysts can be used for this purpose, as described, for example, in GB-A-1,235,062. However, in order to achieve the recommended high percentages of incorporation of comonomers into the polymer molecule, it is recommended that, in addition to a titanium compound, there is also a vanadium compound present in the catalyst, especially at incorporation percentages of 5 mol% and higher, as well as halogen compound, preferably an organic halide. Particularly preferred is a catalyst containing a titanium compound, a vanadium compound, an organoaluminum compound, an organic halide and an organo-magnesium compound, especially at atomic ratios <Mg / (Ti + V) <10, preferably <5, in the especially <4, Al / (Ti + V)> 3, Al / gg> 1, preferably> 3, Ti / V <3, preferably <2. The catalyst may contain a second aluminum compound, which is separately added to the polymerization vessel is supplied. This results in a reduction in the incorporation of comonomer into the polymer molecule which makes these catalysts more suitable for the less high incorporation percentages (eg less than 5 mol%).

As titanium compounds, both four- and trivalent compounds of the general formula Ti (0R1) yield 4-ηχ1n, respectively. Ti (0R2) 3-mX2m, where R 1 and R 2 are the same or different and represent hydrocarbon radicals having 1 to 20 carbon atoms,% 1 and X 2 halogen atoms, 0 <n <4 and 0 <m <3, good results. Of these compounds, titanium acid esters, such as tetrabutoxytitanium, are preferred. It is also possible to use titanium complexes, such as, for example, TiCl3.3 decanol, TBT.AICI3, 30 TBT.2.2 Cr (acac) 2, TBT.x 003 and TBT.x diethyl zinc (0 <x <1).

Suitable vanadium compounds are compounds of the general formula V0 (0R ^) 3-px3D / in which R ^ represents a hydrocarbon radical with 1-20 carbon atoms, X ^ a halogen atom and 0 <p <3, in particular vanadyl chloride and / or vanadyl butoxide. It is also possible 6 7 C i '7 9? * -5- (15) PN 5645

It is possible to use vanadium compounds of the general formula VX ^ g or VX ^ 4 in which represents a halogen atom. X4 is preferably a chlorine atom. Also mixtures of titanium compounds, resp. vanadium compounds are useful catalyst components.

The magnesium compounds are preferably organomagnesium compounds and in particular have at least one hydrocarbon radical bonded to the magnesium atom, preferably an alkyl radical.

In particular dialkylmagnesium compounds provide a catalyst system with high activity. The organomagnesium compound may also be complexed with other organometallic compounds to obtain a soluble product. Organo-zinc, organoboron, but especially organoaluminum compounds are suitable for this. Examples of suitable organomagnesium compounds are ethylbuty (magnesium, dibutylmagnesium, and higher dialkylmagnesium compounds), as well as complexes of, for example, dibutylmagnesium 1/3 triethylaluminum and the like, or mixtures thereof.

The aluminum compound can be selected from a large group of compounds, including alkylsiloxalanes.

Preference is given to an aluminum compound of the general formula <RTI ID = 0.0> R8qALx53_q </RTI> in which the symbols are the same or different and represent a hydrocarbon radical of 1-20 carbon atoms, in particular alkyl, X ^ represents a halogen atom, in particular chlorine, and q <3. Mixtures can also be used.

It is further recommended that the catalyst also comprise one or more chlorides. These are, for example, hydrogen chloride, alkyl chlorides, acyl chlorides, aryl chlorides, inorganic chlorides or combinations thereof. Preferred are organic chlorides, in particular isopropyl chloride, benzyl chloride, etc.

In addition, the catalyst may also comprise one or more electron donors (Lewis base). These are preferably added together with one of the other compounds, for example in the form of tetrabutoxy titanium, tetraisopropoxy titanium and / or vanadyl butylate.

The polymerization can be carried out in a manner known per se, both batchwise and continuously. Generally, the pre-prepared catalyst components are added in such quantities. / V '4 μ -6- (15) PN 5645 add that the amount of titanium in the polymerization medium is 0.001 to 4 mmol / 1, preferably 0.005 to 0.5 mmol / 1 and more particularly 0.01 to 0.05 mmol / l. Depending on the catalysts used and the monomer (s) to be polymerized, a certain minimum amount of comonomer should be present in the feed line to the reactor. The comonomer / ethylene molar ratio will generally be at least 0.15, preferably at least 0.20, especially at least 0.25.

As the comonomer, 1-olefins with 3 to 18 carbon atoms are preferred, preferably with 5 to 12 carbon atoms. Mixtures of these 1-olefins, in particular combinations of 1-olefins with 3 or 4 C atoms and 1-olefins with 5 or more C atoms, also give good results. In addition, polyunsaturated compounds, such as e.g. should be co-polymerized.

As a dispersant, both in the preparation of the catalyst and in the conduct of the polymerization, any liquid which is inert to the catalyst system may be used, for example one or more saturated, straight or branched chain aliphatic hydrocarbons, such as butanes, pentanes, hexanes, heptanes, penta-20 methyl heptane or petroleum fractions such as light or regular gasoline, isopar, naphta, kerosene, gas oil. Aromatic hydrocarbons, for example benzene or toluene, are usable, but for reasons of both cost and safety reasons such solvents will generally not be used in production on a technical scale. Preferably, therefore, cheap polymeric aliphatic hydrocarbons or mixtures thereof, such as those marketed by the petrochemical industry, are used as solvents in industrial polymerizations. Pretreatments of such solvents, for example drying or purification, are often required. The average skilled person is easily capable of doing this. Cyclic hydrocarbons, such as cyclohexane, can of course also be used as a solvent.

Preferably, the polymerization is carried out at temperatures above 135 ° C, especially above 16 ° C. The temperature will generally not exceed 300 ° C for practical reasons.

β “ï fi f \ 'v <- · *? h I% i {> f; J 1 η -7- C15) ΡΝ 5645

The polymer solution obtained during the polymerization can be worked up in a manner known per se, in general the catalyst is deactivated at some stage of the work-up.

The deactivation can be carried out in a manner known per se. The catalysts are generally so active that the amount of catalyst in the polymer, especially the transition metal content, is so low that removal of catalyst residues can be omitted. Of course, if deemed necessary, one can wash the polymer to further reduce the residual catalyst components.

The polymerization can be carried out batchwise or continuously under atmospheric pressure, but also at elevated pressure up to about 1000 bar, or even higher pressure. By carrying out the polymerization under pressure, the polymer yield can be further increased, which can also contribute to the preparation of a polymer with very low levels of catalyst residues. It is preferred to polymerize under pressures of 1-200 bar, and more in particular 10-100 bar.

Pressures above 100 bar soon lead to technological problems. However, much higher pressures of 1000 bar and above can be used if the polymerization is carried out in so-called high pressure reactors.

Modifications known per se can also be applied.

For example, the molecular weight can be controlled by adding hydrogen or other customary modifiers therefor. The polymerization can also be carried out in more either parallel or series-connected stages, in which, if desired, different catalyst compositions, temperatures, residence times, pressures, hydrogen concentrations, etc. are used. For example, one can prepare products with a broad molecular weight distribution by choosing the conditions in one step, for example pressure, temperature and hydrogen concentration, so that a polymer with a high molecular weight is created, while the conditions in another step are chosen in this way. that a polymer with a lower molecular weight is produced.

Polymers according to the invention comprise, in addition to ethylene, also 35 1 -olefin and optionally other monomers. These 1-olefins have three to

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-8- (15) ΡΝ 5645 ί eighteen C atoms. Advantageously, 1-olefins having five to twelve C atoms are used, in particular 1-hexene, 1-akene and 4-methylpentene-1.

The other monomers do not need to be present to lead to good results. If desired, however, one or more other 1-olefins can be added, such as, for example, propylene or 1-butene, so that a terpolymer is formed. This can be advantageous because replacing part of the more expensive higher 1-olefin with the cheaper propylene or 1-butene does not adversely affect the properties of the polymer. The optimum ratio depends on the desired properties and can be easily determined by the skilled person.

It is also possible that polyunsaturated compounds, eg dienes (such as 1,9-decadiene) are present in small or larger amounts, or still other copolymerizable compounds.

Polymers according to the invention have a melt index which is preferably between 0.01 and 200 dg / min, in particular between 0.1 and 100 dg / min.

Polymers according to the invention are eminently suitable for use as a sealing layer on films. However, they do not necessarily have to be applied to other layers, but are themselves also suitable for processing into foil. They are also suitable for other applications, in particular injection molding, in polymers according to the invention with higher melt indices (15 dg / min, or 20 or more).

Polymers of the invention are also suitable for blending with other 1-olefin polymers, such as HDPE, LDPE, LLDPE, polypropylene, ethylene-propylene co-polymers, oropene-butene copolymers, ethylene-vinyl acetate copolymers, other polar and non-polar (co) polymers, etc. , in weight amounts of 1-99%, preferably 5-95% by weight and especially 10-90% by weight. In addition, other compounds may also be present in the mixture, such as fillers, etc. These mixtures are suitable for many applications.

The invention will now be elucidated on the basis of some examples, without however being limited thereto.

8 / c i:: 7 f -9- (15) PN 5645

Conventional ethylene-1-olefin copolymers were prepared according to B.K. Hunter et al., J. Polym. Sci: Polym. Chem. Ed., Vol. 22, 1383-1392 (1984).

Ethylene copolymers according to the invention were prepared by carrying out a number of continuous polymerizations in a 2-liter double-walled autoclave. To this end, the autoclave was completely filled with petrol which had been purified over molecular sieves. In an absorber, ethylene and, if desired, hydrogen were dissolved in purified petrol.

The copolymerizations were carried out by adding octene-1 to the ethylene and, if desired, hydrogen-containing gasoline stream and isopropyl chloride in such an amount that the concentration during the polymerization was 0.10 mmol / l. The reactor temperature was adjusted to 185 ° C with the jacket heating of the autoclave and kept at the desired value during the polymerization, optionally cooling. The pressure in the reactor was adjusted so that it remained completely filled with liquid. The catalyst composition and polymerization conditions are shown in Table 1.

The catalyst components were premixed in the feed lines during the residence time and the reactor was pumped in. (SEAC = sesqui-20 ethyl aluminum chloride, EBM = ethyl butylmagnesium, TBT = tetrabutoxy titanium, Cg = 1-octene, C2 = ethylene). The residence time in the reactor was about 10 minutes. The polymer was collected, optionally stabilized, dried and analyzed. The melt index M.I. of the polymer, expressed in dg / min, was determined according to ASTM D 1238, cond. E. The density (d), expressed in kg / m3, was measured according to ASTM D 1505.

The comonomer incorporation percentage was determined by infrared measurement. The polymer properties are shown in Table 2.

The DSC measurements in Figures 1-5, 8 and 9 used a measurement setup consisting of a Perkin-Elmer DSC-2, on-line with a Tektronix 4052, a Hewlett-Packard 3495 A scanner multiplexer , and an HP 3455A digital voltmeter (5 1/2 - 6 1/2 digit).

The measurements were made according to the "continuous" measurement method of V.R.F.

Mathot et al., J. Thermal Anal. Full. 28, 349-358, (1983).

€ / v -10- (15) PN 5645 TABLE 1

Sample SEAC EBM TBT VOCI3 H2 C8 / C2 nr.mmol / l mmol / l mmol / l mmol / l NL / h mol / mol 1 0.45 0.09 0.04 - 0.64 0.25 5 2 0, 45 0.09 0.04 - 0.21 0.28 3 0.45 0.09 0.04 - - 0.34 4 0.48 0.095 0.04 - - 0.39 5 0.50 0.10 0 .04 - - 0.44 6 0.21 0.070 0.02 0.02 0.62 0.28 10 7 0.30 0.100 0.013 0.026 0.58 0.28 ____ TABLE 2

Sample d MI mol% C2 mol% Cs melting point. krist. pt. no, kg / m3 dg / min__nC_ C 901.1 5.5 94.01 5.99 91,123,124 53,82,109 15 2 897.9 4.3 93.36 6.64 92,121.125 77,109 3 894.3 4.4 92.77 7.23 95.125 72.109 4 890.8 5.2 92.11 7.89 92,121.125 69.109 5 888.1 6.9 91.46 8.54 91,121.125 70.109 6 895.7 6.7 92.65 7. 35 80,119,124 73,105 20 7 898,9 4,7 93,43 6,57 84,121,125 75,107_ 87 0 C 7 '0 7 4 -11 “(15) PN 5645

The scanning speed used was 10aC / min. The sample weights ranged from 7 to 10 mg and were determined to 1 microgram with a Mettler HE 22/36 electronic microbalance. Each 0.2 C the measured value was recorded at the temperature reached and stored in the computer memory used.

The DSC curves in Figures 6, 7 and 10 were measured analogously, however, at a scan speed of 5ac / min.

The measurements were taken under nitrogen after warming to 18 ° C, cooling from 180 ° C to -70 ° C and then heating from -70 ° C to 180 ° C, with isothermal waiting times at -7 ° C and 18 ° C of 5 minutes. The curves associated with the last two operations, namely the cooling curve and the C2e) heating curve, are respectively lower and lower. shown at the top in Figures 1-5, 8 and 9, and above, respectively. at the bottom in fig. 6, 7 and 10.

In Figures 1-10 the temperature in aC is indicated on the horizontal axis, and the specific heat capacity in J / g / aC on the vertical axis. As a reference, the (theoretical) curves for 100% amorphous Ca) and 100% crystalline (c) linear polyethylene in Figures 1-5, 8 and 9 are also indicated, as determined in V.B.F. Mathot, Polymer, 20 Vol. 25, 579-599 (1984).

Figures 1 to 7 show the DSC curves of the resp. samples 1 to 7 from Tables 1 and 2.

For comparison, Figure 8 shows the DSC curve of a conventional ethylene propylene copolymer having a density of 896.3, a mole percent ethylene of 89.4 and a mole percent of propylene of 10.6 relative to the polymer of the invention from Fig. 2, which has approximately the same density.

In Figure 9, for comparison, the DSC curve of a conventional ethylene octene polymer of 91.74 mol% ethylene and 8.26 mol% ethylene with respect to the polymer of the invention of Figure 5, having approximately the same molar ratio, is shown. ethylene / octene.

Figure 10 shows the DSC curves of the ethylene-butene copolymer TAFHER-A-4090 and the ethylene-propylene copolymer of Figure 8 (broken).

It can be seen from the figures that with increasing comonomer incorporation 8 "i:".

-12- (15) PN 5645 it becomes more difficult to determine the lowest peak temperatures in particular because more melting and resp. crystallization processes then involve melting or crystallization points. This produces an inaccuracy of a few degrees.

The extent of the temperature ranges in the ethylene copolymers according to the invention is clarified by integrating a DSC curve and displaying the specific enthalpy curve thus obtained with the integrated (theoretical) DSC curves of 100% amorphous as reference. a) and 100% crystalline (c) polyethylene.

In Fig. 11 this is done with the DSC curve of Fig. 5. The horizontal axis shows the temperature in nc, and the left vertical axis shows the specific enthalpy in J / g. At each temperature it can now be seen to what extent the specific enthalpy of the sample deviates from the theoretical reference values. The right vertical axis shows 15% of the deviation (WC). For this purpose, at a given temperature, the difference between the values according to the a-curve and the sample curve is divided by the difference between the values according to the a-and c-curves. The broken curve represents the proportions thus obtained - multiplied by 100. This curve clearly illustrates once again that the melting process starts at the very lowest temperature and only ends at a remarkably high temperature. It is also visible that upon cooling from room temperature the sample will crystallize even further.

It also becomes clear that polymers according to the invention above a temperature of (-3x +120) t tC according to the indicated measuring method are still partly crystalline (WC is preferably 1% or more, in particular 2% or more, more particularly 3% or more). This is in contrast to the conventional ethylene copolymers which are no longer crystalline above (-3x +120) CC according to the indicated measuring method (wc = 0%).

Compared to the conventional LLDPE, the polymers of the invention differ in the degree of crystallinity decreasing at very low temperatures. Between eg -70aC and + 23aC, the WC of LLDPE hardly decreases, while that of polymers according to the invention decreases with a factor of at least 1.1, preferably with a factor of 8 5 0 v "9? -13- ¢ 15) PN 5645 1.2, in particular with a factor of 1.3 and more particularly with a factor of 1.4.

This decrease will generally not be greater than a factor of 50, preferably 10, especially 5 and more particularly 2.

This illustrates that polymers of the invention combine the melting behavior of the conventional ethylene copolymers and LLDPEs.

87 C C ":

Claims (11)

Polymer, at least comprising: a) 50-97 mol% ethylene b) 3-50 mol% 1-olefin with 3 to 18 carbon atoms c) optionally one or more other monomers, 5 with a density of at least highest 910 kg / m3, at least two melting points, one of which is between -80ac and (-3x +120) ac, but not above 100ac, and a second between C-3x +120) C and 140hC, and at least two crystallization points, one of which is between -90hc and (-3x +110) 00, but not above 90nc, and a 10 second between (-3x +110) aC and 130aC, where x is the mole percentage of comonomers. 2. Polymer, comprising at least: a) 60-96 mol% ethylene b) 4-40 mol% 1-olefin with 3 to 18 carbon atoms c) optionally one or more other monomers, with a density of at least highest 905 kg / m2, at least two melting points, one of which is between (-4x +70) ac and (-3x +120) nc, but not above 100bC, and a second between (-3x +120) ac and 135bc, and at least two crystallization points 20, one of which is between (-4x +60) «χ and (-3x +110) bc, but not above 9QbC, and a second between (-3x +110) nc and 125bc, where x is equal to the mole percentage of comonomers. 3. Polymer, comprising at least: a) 70-95 mol% ethylene 25 b) 5-30 mol% 1-olefin with 3 to 18 carbon atoms c) optionally one or more other monomers, with a density of at least highest 900 kg / m3 / at least two melting points, one of which is between C-4x + 100) hc and <-4x +130) bc, but not above 100 ° C, and a second between 30 (-x +120) HC and 135aC, and at least two crystallization points, one of which is between (-4x + 9Q) «C and (“ 4x +120) ac, but not above 90nc, and a second between (-x +110) ac and 125πς, where x is equal to the mole percentage of comonomers. 8 «.» ϋ \ & * 7 Λ * ”2 '/ ία -15- ¢ 15) PN 5645 Polymer according to claims 1-3, characterized in that the 1-olefin has 5 to 12 carbon atoms. Polymer according to claims 1-4, characterized in that the melt index is between 0.01 and 200 dg / min. A handle comprising 1-99% by weight of a polymer according to claims 1-5, and 1-99% by weight of one or more other 1-olefin olymers. Polymer according to claims 1-6, characterized in that it is prepared using a catalyst system comprising at least one organoaluminum compound, an organomagnesium compound, a titanium compound and an organic halide. Polymer according to claims 1-6, characterized in that it is prepared using a catalyst system comprising at least one organoaluminum compound, an organomagnesium compound, a titanium compound, a vanadium compound and an organic halide. Use of a polymer according to claims 1-6 as a welding layer. 10. Object made from a polymer according to claims 1-6. Foil made from a polymer according to claims 1-6. 0 C ': 7