GB2066274A

GB2066274A - Copolymerisation of ethylene and alpha -olefines in vapour phase

Info

Publication number: GB2066274A
Application number: GB8041313A
Authority: GB
Original assignee: Nippon Oil Corp
Current assignee: Eneos Corp
Priority date: 1979-12-26
Filing date: 1980-12-23
Publication date: 1981-07-08
Also published as: JPS6042806B2; GB2066274B; FR2472583A1; IT8026857A0; AU6553280A; IT1209378B; FR2472583B1; AU537527B2; DE3048437C2; JPS5692902A; CA1144695A; DE3048437A1

Abstract

Low density copolymers of high molecular weight are obtained by copolymerizing ethylene and alpha - olefins in vapor phase at 10 to 80 DEG C using a Ziegler type catalyst which includes (a) a solid substance containing a titanium and/or vanadium compound on a magnesium- containing inorganic solid carrier and (b) an organoaluminum compound and in the presence of hydrogen at a concentration of 0 to 5 mole % of the vapour phase.

Description

SPECIFICATION Process for preparing copolymers Background of the Invention This invention relates to a process for preparing low density ethylene copolymers having a high molecular weight.

The production of polyethylene by polymerization using a catalyst comprising a transition metal compound and an organometallic compound is generally conducted by the slurry polymerization process. And it can be said that the density of polyethylene obtained by such slurry polymerization is limited to not smaller than 0.945 which value has been considered to be the limit of density at which there will not occur polymer deposition or fouling for the inner wall and stirrer within a reaction vessel at the time of the polymerization.

Medium or low density polyethylenes with a density below 0.945 g/cm3 usually are prepared by the so-called high pressure process using a radical catalyst. Quite recently, however, a high temperature solution polymerization process has also come to be tried. Further conducted is copolymerizing ethylene with other a-olefin using a vanadium compound to produce an elastomer.

However, polymers prepared by the above methods are either crystalline resins or noncrystalline elastomers and thus their characters are clearly different. These polyolefin plastics and elastomers have respectively their own superior characteristics and are employed in various uses. But we often experience that for some applications it it required to impart some elastomeric character to plastics to thereby improve their resistance to environmental stress cracking, or conversely elastomers are required to have a strength based on crystallinity. And it is well known that if both components are mixed together for such purpose, it results in many cases in deterioration of physical properties such as tensile strength and rigidity.

As a solution to this problem if it is possible to prepare a soft or semi-hard polymer which is neither a crystalline plastic nor elastomer but has a structure intermediate therebetween and which exhibits a high extensibility, then such polymer will answer the foregoing purpose, or by blending such polymer into other plastics it is made possible to impart an elastomeric character to the plastics to improve the properties thereof. However, such soft or semi-hard polymer is not known very well.

Recently there have been made some reports on the method of preparing such polymer showing intermediate physical properties, but they involve various drawbacks and an attempt to practise them on an industrial scale encounters many problems to be solved.

For example, Japanese Patent Publication No.11028/1971 shows a solution polymerization using an aromatic hydrocarbon solvent in the preparation of ethylene/a-olefin copolymers. But this method has drawbacks such that the catalyst efficiency is poor, the separation and recovery of the solvent is troublesome because of solution polymerization, and further it is difficult to produce high molecular weight copolymers because of restriction on the solution viscosity.

Japanese Patent Publication No.26185/1972 shows the copolymerization of ethylene and a-olefins using a halogenated aliphatic hydrocarbon as a solvent. But this method is disadvantageous in that not only it is difficult to prepare high molecular weight copolymers for the same reason as mentioned above, but also there are produced large amounts of low molecular weight copolymers probably because the halogenated hydrocarbon solvent acts as a molecular weight modifier resulting in that molded articles-therefrom have sticky surfaces. In this patent publication there is also disclosed a method using lower hydrocarbons of C3 to C5 as solvents. But in the polymerization using these solvents it is necessary to raise the reaction pressure by the vapor pressure of the solvent, and in the solvent recovery step it is required to compress and cool the recovered solvent for liquefaction.

Furthermore, in Japanese Patent Laying Open Print No.41784/1976 there is disclosed a method of slurry copolymerization between ethylene and butene-1. Also in this method, however, the polymerization temperature and the composition of the starting materials are specified minutely, and outside this specified range the slurry becomes milky or porridge-like, which makes it difficult to operate the reactor and transport the slurry.

Thus various drawbacks are encountered in the conventional methods; that is, after all, since the catalyst activity is low and because of solution polymerization it is troublesome to separate and recover solvent; usually it is difficult to produce high molecular weight copolymers because of restrictions on the solution viscosity; there are produced large amounts of low molecular weight copolymers are difficult to be obtained; further, in the case of slurry polymerization, the polymerization temperature and the starting material composition must be restricted in order to maintain the polymer in a slurried condition, so that low density copolymers are difficult to be obtained.

Thus, according to either of the slurry polymerization or solution polymerization process, soft or semi-hard ethylene/a-olefin copolymers of low density and high molecular weight have heretofore been impossible to be produced industrially advantageously.

In recent years there have been made vari ous studies about the improvement of catalyst activity, and it is known that if a transition metal is attached to a magnesium-containing solid carrier such as, for example, MgO, Mg(OH)2, MgCI2, MgCO3, or Mg(OH)CI, and then combined with an organometallic compound, the resulting catalyst system can serve as a remarkably high activity catalyst in the polymerization of olefins. It is also known that the reaction product of an organomagnesium compound such as, for example, RMgX, R2Mg or RMg(OR) and a transition metal compound can serve as a high polymerization catalyst for olefins (see, for example, Japanese Patent Publications Nos. 12105/1964, 13050/1968 and 9548/1970 and Belgian Patent No.742,112).

However, even in the slurry polymerization or solution polymerization carried out using such a high activity catalyst with carrier in an effort to obtain low density polymers, the foregoing various drawbacks have not been remedied at all.

Summary of the Invention It is an object of this invention to provide a new process which has solved those problems.

It is another object of this invention to overcome various problems associated with solution polymerization or slurry polymerization such as low catalyst activity, low bulk density, polymer adhesion or agglomeration, and to provide a process for preparing low density, high molecular weight ethylene/aolefin copolymers having superior physical properties.

It is further object of this invention to provide a vapor phase polymerization process for ethylene and a-olefins which process as a whole is very simple, can perform the polymerization reaction in a stable manner and can omit the catalyst removing step.

Other objects and advantages of this invention will become apparent from the following description.

According to this invention, ethylene and 4 to 250 mole% based on the amount of ethylene of an a-olefin are copolymerized in a substantially soivent-free vapor phase condition, at a temperature of 10 to 80"C, at a hydrogen concentration in the vapor phase of 0 to 5 mole% and in the presence of a catalyst which comprises a solid substance and an organoaluminum compound, said solid substance containing a magnesium-containing inorganic solid carrier and a titanium compound and/or a vanadium compound, whereby there can be obtained a soft or semihard ethylene/a-olefin copolymer having an intrinsic viscosity of 3.0 to 10 dl/g measured in decalin at 135"C and a density of 0.850 to 0.910.It has become clear that if a vapor phase polymerization is carried out according to the process of this invention, that is, using ethylene and an a-olefin in a quantitative ratio within the range specified in the invention and using a catalyst comprising a solid substance and an organoaluminum compound which solid substance contains a magnesium-containing inorganic solid carrier and a titanium compound and/or a vanadium compound, then the polymerization is effected in an extremely high activity and the resulting polymer has a high molecular weight, is highly sticky and low in density, nevertheless the production ratio of coarse and ultra-fine particles is reduced, so the particle properties are improved, further the bulk density is high, the polymer adhesion to the reactor and agglomeration of polymer particles are minimized, and thus the vapor phase polymerization reaction can be performed in an extremely stable manner. It should be considered quite unforeseeable and surprising that according to the process of this invention not only it becomes possible to carry out a vapor phase polymerization reaction extremely smoothly, but also ethylene copolymers of high molecular weight and extremely low density can be obtained easily.

In the process of this invention, the a-olefin copolymerized with ethylene adjusts the density and molecular weight of copolymer, and the resulting copolymer is superior in transparency, outer appearance and luster, and is highly flexible and rubber-like elastic at low temperatures, not to mention at room temperature.

In addition to such a high flexibility, the strength of copolymers obtained according to the process of this invention is equal to or even higher than that of ordinary polyolefin resins. Further, they are very superior in weathering resistance, resistance to chemicals and electrical characteristics such as dielectric loss, break-down voltage and resistivity because they little contain unsaturated bond, residual catalyst or other impurities. Also in point of resistance to impact and to environmental stress cracking, the copolymers prepared according to the process of this invention exhibit excellent characteristics, which allow them to be formed into films, sheets, hollow containers, electric wires and various other products by the existing forming methods such as extrusion molding, blow molding, injection molding, press forming and vacuum forming. Thus they can be employed in various uses.

Furthermore, since the copolymers obtained according to the process of this invention contain olefins as a component, they are very similar in composition to polyolefin resins; besides, because of a low crystallinity, they are compatible with other polyolefin resins, particularly with high- and low-density polyethylenes, polypropylenes and ethylene-vinyl acetate copolymer, so their blending into these resins can improve properties of the latter such as resistance to impact, to tear, to cold and to environmental stress cracking.

Detailed Description of the Invention The catalyst system used in the process of this invention combines a solid substance with an organoaluminum compound which solid substance contains a magnesium-containing inorganic solid carrier and a titanium compound and/or a vanadium compound. As the magnesium-containing inorganic solid carrier are mentioned, for example, metallic magnesium, magnesium hydroxide, magnesium carbonate, magnesium oxide, magnesium chloride, further double salts, double oxides, carbonates, chlorides and hydroxides, which contain magnesium atom and a metal selected from silicon, aluminum and calcium, and still further these inorganic solid compounds after treatment or reaction with an oxygen-containing compound, a sulfur-containing compound, an aromatic hydrocarbon or a halogen-containing substance.And to the inorganic solid carrier exemplified above is attached a titanium compound and/or a vanadium compound in known manner.

As the above-mentioned oxygen-containing compound are exemplified water; organic oxygen-containing compounds such as alcohols, phenols, ketones, aldehydes, carboxylic acids, esters, and acid am ides; and inorganic oxygen-containing compounds such as metal alkoxides and metal oxyhalides. As the sulfurcontaining compound are exemplified organic sulfur-containing compounds such as thiol and thioethers; and inorganic sulfur-containing compounds such as sulfur dioxide, sulfur trioxide and sulfuric acid. As the aromatic hydrocarbon are exemplified mono- and polycyclic aromatic hydrocarbons such as benzene, toluene, xylenes, anthracene and phenanthrene. As the halogen-containing substance are exemplified compounds such as chlorine,hydrogen chloride, metal halides and organic halides.

By way of illustrating the titanium compound and/or vanadium compound, mention may be made of halides, alkoxyhalides and halogenated oxides of titanium and/or vanadium. Preferred titanium compounds are of the general formula Ti(OR)nX4 n wherein R is alkyl, aryl or aralkyl having 1 to 24 carbon atoms and n is 0 nS4, and also trivalent titanium compounds obtained by reducing these tetravalent titanium compounds with for example hydrogen, titanium, aluminum or an organometallic compound of a Group I-Ill metal in the Periodic Table.Examples of titanium compounds and vanadium compound are tetravalent titanium compounds such as titanium tetrachloride, titanium tetrabromide, titanium tetraiodide, monoethoxytrichlorotitanium, diethoxydichlorotitanium, triethoxymonochlorotitanium, tetraethoxytitanium, monoisopropoxytrichlorotitanium, diisopropoxydichlorotitanium and tetraisopropoxytitanium; various titanium trihalides obtained by reducing titanium tetrahalides with hydrogen, aluminum, titanium or an organometallic compound, trivalent titanium compounds such as compounds obtained by reducing various tetravalent alkoxytitanium halides with an organometallic compound; tetravalent vanadium compounds such as vanadium tetrachloride; pentavalent vanadium compounds such as vanadium oxytrichloride and orthoalkyl vanadate; and trivalent vanadium compounds such as vanadium trichloride and vanadium triethoxide.

Tetravalent titanium compounds are particularly preferred among the above-enumerated titanium compounds and vanadium compounds.

The catalyst used in the invention comprises the combination of a solid substance which contains the foregoing solid carrier and a titanium compound and/or a vanadium compound, with an organoaluminum compound.

Examples of such catalyst are combinations of organoaluminum compounds and the following solid substances (in the following formulae R represents an organic radical and X represents a halogen atom): MgO-RX-TiCI4 system (see Japanese Patent Publication No.3514/1976), Mg-SiCI4-ROH-TiCL4 system (see Japanese Patent Publication No.

23864/1975), MgCI2-Al(OR)3-TiCI4system (see Japanese Patent Publications Nos.152/1976and 15111/1977), MgCI2-SiCI4-ROH-TiCI4 system (see Japanese Patent Laying Open Print No.106581/1974), Mg(OOCR)2-Al(OR)3 TiCI4 system (see Japanese Patent Publication No.11710/1977), Mg-POCI3-TiC14 system (see Japanese Patent Publication No.153/1976) and MgCI2-AIOCI-TiCI4 system (see Japanese Patent Publication No.15316/1979).

In these catalyst systems, a titanium compound and/or a vanadium compound may be used as an adduct with an organocarboxylic acid ester, and the foregoing magnesiumcontaining inorganic solid carrier may be used after contact with an organocarboxylic acid ester. Also, using an organoaluminum compound as an adduct with an organocarboxylic acid ester causes no trouble. Further, in all possible cases in this invention, a catalyst system prepared in the presence of an organocarboxylic acid ester may be used without causing any trouble.

As the organocarboxylic acid ester there may be used esters of various aliphatic, alicyclic and aromatic carboxylic acids, preferably aromatic carboxylic acids of C7 to C12, for example, alkyl esters such as methyl and ethyl of benzoic acid, anisic acid and toluic acid.

Examples of the organoaluminum compound used in this invention are those repre sented by the general formulae R3AI, R2AIX, RAIN,, R2AIOR, RAI(OR)X and R3AI2X3 wherein R, which may be alike or different, is C1 to C20 alkyl or aryl and X is halogen, such as triethylaluminum, triisobutylaluminum, trihexylaluminum, trioctylaluminum, diethylaluminum chloride, ethylaluminum sesquichloride, and mixtures thereof.

In the presence of this invention, no special limitations are placed on the amount of the organoaluminum compound to be used, but usually it may be employed in an amount of 0.1 to 1000 moles per mole of the transition metal compound.

In the process of this invention, moreover, by contacting the foregoing catalyst system with an ethylene and/or a-olefin and thereafter using it in the vapor phase polymerization reaction, the polymerization activity can be improved to a large extent and the operation can be performed more stably than in the case where such pre-treatment is not applied.

And as the a-olefin used in such pre-treatment there may be employed various a-olefins, preferably those of C3 to C,2 and more preferably those of C3 to C8. Examples are propylene, butene-1, pentene-1 ,4-methylpentene-1, heptene-1, octene-1, and mixtures thereof. The temperature and duration of the contact between the catalyst of this invention and ethylene and/or an a-olefin can be chosen over a wide range; for example, the contact treatment may be performed for 1 minute to 24 hours at 0 to 200"C, preferably 0 to 110"C.

The amount of ethylene and/or the a-olefin to be contacted can also be chosen over a wide range, but usually it is desirable that the catalyst of this invention be treated with 1 g to 50,000, preferably 5g to 30,000g, per gram of the foregoing solid substance of ethylene and/or a-olefin to allow 1 g to 5009, preferably 1 g to 1 00g, of ethylene and/or the aolefin to be reacted per gram of the solid substance. The said contact treatment may be done at any desired pressure, but preferably -1 to 100 kg/cm2-G.

The aforesaid pre-treatment with ethylene and/or an a-olefin may be carried out by first combining the total amount of the organoaluminum compound to be used with the foregoing solid substance and then contacting with ethylene and/or the a-olefin, or alternatively, by first combining part of the organoaluminum compound with the solid substance and then contacting with ethylene and/or gaseous a-olefin and adding the remaining organoaluminum compound separately in the vapor phase polymerization. During the contact between the catalyst and ethylene and/or an aolefin there may be present hydrogen gas or other inert gas such as nitrogen, argon or helium.

In this invention there is conducted copolymerization of ethylene with an a-olefin in the presence of a catalyst comprising a solid substance and an organoaluminum compound, which solid substance contains a magnesiumcontaining inorganic solid carrier and a titanium compound and/or a vanadium compound.

As the a-olefin to be used in the copolymerization reaction, those of C3 to C8 are preferred, for example, propylene, butene-1, hexene-1, 4-methylpentene-1, and octene-1.

These a-olefin should be used in amounts ranging from 4 to 250 mole%, preferably from 5 to 100 mole%, based on the amount of ethylene. Outside this range it is impossible to obtain the object product of this invention, namely soft or semi-hard ethylene/a-olefin copolymers having an intrinsic viscosity of 3 to 10 dl/g, preferably 3.7 to 8 dl/g, measured in decalin at 1 35 C and a density of 0.850 to 0.910. The amount of a-olefin to be used can be adjusted easily be changing the composition ratio of the vapor phase in the polymerization vessel.

In the process of this invention, moreover, various dienes may be added in the copolymerization as termonomers, such as butadiene, 1,4-hexadiene, 1,5-hexadiene, vinyl norbornene, ethylidene norbornene and dicyclopentadiene.

The polymerization reaction in this invention is carried out in a substantially solvent-free vapor phase condition. As the reactor to be used, there may be employed known ones such as fluidized bed and agitation vessel.

The temperature of the polymerization reaction is in the range of from 10 to 80"C, preferably from 20 to 70"C, and the pressure thereof in the range of from atmospheric pressure to,70 kg/cm2G, preferably from 2 to 60 kg/cm2-G.

In this invention, moreover, it is necessary to add hydrogen so that the hydrogen concentration in the vapor phase is in the range of from 0 to 5 mole%. Outside this condition it is impossible to obtain the object copolymers of this invention.

It goes without saying that using the process of this invention there can be conducted without any trouble two or more stage polymerization reactions involving different polymerization conditions such as different hydrogen and comonomer concentrations and different polymerization temperatures.

Working examples of this invention are given below, but it is to be understood that these examples are for illustration only to work the invention and are not intended to restrict the invention.

Example 1 1000 9. of anhydrous magnesium chloride, 50 g. of 1,2-dichloroethane and 1 70 g. of titanium tetrachloride were subjected to ball milling for 1 6 hours at room temperature in a nitrogen atmosphere to allow the titanium compound to be supported on the carrier. The resulting solid substance contained 35 mg of titanium per gram thereof.

As an apparatus for the vapor phase polymerization there was used a stainless steel autoclave, and with a blower, a flow rate adjusting valve and a dry cyclone for separating the resulting polymer being provided to form a loop. Temperature control for the autoclave was effected by passing warm water through the jacket.

The polymerization temperature was set at 40"C, and the above solid substance and triethylaluminum were charged into the autoclave at the rates of 250 mg/hr and 50 mmol/hr, respectively, and there was made polymerization while adjusting the composition (mole ratio) of the gases fed to the autoclave with the blower so that ethylene was 69% and butene-1 31%.

The resulting polymer had an intrinsic viscosity measured in decalin at 135"C (in the following comparative and working examples this will be referred to simply as "intrinsic viscosity") of 4.5 dl/g, a bulk density of 0.38 and a density of 0.891. The polymerization activity was very high, 312,000 g.polyethy lene/g.Ti.

After continuous operation for 10 hours, the polymerization was stopped and the interior of the autoclave was checked to find that the polymer did not adhere at all to the inner wall, stirrer and polymer withdrawing pipe. In the slurry polymerization shown in the following Comparative Example 1 it was impossible to continue operation stably for a long time, while the results obtained in the above working example clearly show that according to the process of this invention it is possible continue operation for an extended period of time and that extremely stably.

Comparative Example 1 Using the same catalyst as in Example 1 there was made a continuous slurry polymerization at 40"C while feeding 5 mg/l of the solid substance, 1 mmol/l of triethylaluminum, 40 I/hr of hexane as a solvent, 8 kg/hr of ethylene, 14.0 kg/hr of butene-1 (86 mol% of ethylene) and 3 Nm3/hr of hydrogen.

The resulting polymer was in an intermediate form between slurry and solution and the polymer particles were swollen from the initial stage of polymerization, and the hexane layer was a viscous solution. After 2 hours, the slurry withdrawing pipe was blocked so the polymerization was compelled to be discontinued. The interior of the reactor was checked to find that a large amount of the polymer adhered to the inner wall and the stirrer.

The intrinsic viscosity and density of the resulting polymer were 4.1 dl/g and 0.903, respectively. Thus, despite of a large amount of butene-1 added as a comonomer, the density of the polymer was not sufficiently lowered, and the continuous polymerization did not proceed stably. It is apparent that this comparative example is an example of a very disadvantageous polymerization.

Example 2 Polymerization was made in the same manner as in Example 1 except that the polymerization temperature was set at 30"C and that the gases fed to the autoclave were ethylene, butene-1 and hydrogen in the proportions (mole ratios) of 75%, 23% and 2%, respectively.

After continuous operation for 10 hours, the polymerization was stopped and the interior of the reactor was checked to find that there was no adhesion of polymer.

The resulting polymer had an intrinsic viscosity of 5.1 dl/g, a bulk density of 0.40 and a density of 0.901. The polymerization activity was 265,000 g.polymer/g.Ti.

Example 3 830 g. of anhydrous magnesium chloride, 1 20 g. of anthracene and 1 80 g. of titanium tetrachloride were subjected to ball milling in the same manner as in Example 1 to give a solid substance, which contained 40 mg. of titanium per gram thereof.

Using the same apparatus as in Example 1 there were fed the above solid substance and triisobutylaluminum at the rates of 5.00 mg/hr and 1 50 mmol/hr, respectively, and there was made a continuous polymerization at 20"C while adjusting the composition (mole ratio) of the gases fed to the autoclave so that ethylene was 77% and propylene 23%.

The resulting polymer had an intrinsic viscosity of 4.7 dl/g, a bulk density of 0.39 and a density of 0.895. The polymerization activity was 127,000 g.polymer/g.Ti.

Example 4 A continuous polymerization was carried out in the same way as in Example 3 except that butene-1 was used in place of propylene, that the ratio (mole ratio) of the ethylene and that of butene-1 in the vapor phase were adjusted to 61% and 39%, respectively, and that the polymerization temperature was set at 50"C.

The resulting polymer had an intrinsic viscosity of 3.7 dl/g, a bulk density of 0.39 and a density of 0.886. The polymerization activity was 405,000 g.polymer/g.Ti.

Example 5 180 g. of titanium tetrachloride and 950 g.

of the reaction product resulting from reaction at 300"C for 4 hours of 400 g. magnesium oxide and 1.3 kg. aluminum chloride was subjected to ball milling in the same way as in Example 1 to give a solid substance containing 39 mg. of titanium per gram thereof.

Using the same apparatus as in Example 1 there were fed the above solid substance and diethylaluminum chloride at the rates of 500 mg/hr and 250 mmol/hr, respectively, and a continuous polymerization was conducted at 40"C while adjusting the composition (mole ratio) in the vapor phase so that ethylene was 64% and butene-1 36%.

The resulting polymer had an intrinsic viscosity of 5.3 dl/g, a bulk density of 0.37 and a density of 0.891. The polymerization activity was 105,000 g.polymer/g.Ti.

Example 6 A continuous polymerization was carried out in the same way as in Example 5 except that triethylaluminum was used in place of diethylaluminum chloride, that butene-1 was substituted by propylene and that the ratio (mole ratio) of ethylene and that of propylene in the vapor phase were adjusted to 69% and 31%, respectively.

The resulting polymer had an intrinsic viscosity of 4.8 dl/g, a bulk density of 0.40 and a density of 0.908. The polymerization activity was 335,000 g.polymer/g.Ti.

Claims

1. A process for preparing a soft or semihard ethylene/a-olefin copolymer having an intrinsic viscosity of 3.0 to 10 dl/g measured in decalin at 1 35"C and a density of 0.850 to 0.910, which process comprises copolymerizing ethylene and 4 to 250 mole% based on the amount of ethylene of an a-olefin in a substantially solvent-free vapor phase condition, at a temperature of 10 to 80"C, at a hydrogen concentration in the vapor phase of O to 5 mole% and in the presence of a catalyst, said catalyst comprising a solid substance and an organoaluminum compound, said solid substance containing a magnesiumcontaining inorganic solid carrier and at least one member selected from the group consisting of a titanium compound and a vanadium compound.

2. The process as defined in claim 1, in which said a-olefin is an a-olefin having 3 to 8 carbon atoms.

3. The process as defined in claim 1 or claim 2, in which said a-olefin is used in an amount of 5 to 100 mole% based on the amount of ethylene.

4. The process as defined in claim 1, claim 2 or claim 3, in which said titanium compound is a halide, alkoxyhalide or halgenated oxide of titanium.

5. The process as defined in claim 1, claim 2 or claim 2, in which said vanadium compound is a halide, alkoxyhalide or halogenated oxide of vanadium.

6. The process as defined in any one of claims 1 to 5, in which said organoaluminum compound is a compound represented by the general formula R3AI, R2AIX, RAIX2, R2AIOR, RAI(OR)X or R3AI2X3 wherein R, which may be alike or different, is a C1 to C20 alkyl group or aryl group and X is a halogen atom.

7. The process as defined in any one of claims 1 to 6, in which said catalyst is prepared in the presence of an organocarboxylic acid ester.

8. The process as defined in any one of claims 1 to 7, in which said catalyst is treated with ethylene and/or an a-olefin and thereafter used in the copolymerization reaction.

9. A process as claimed in claim 1 substantially as hereinbefore described with particular reference to the Examples.

10. A process as claimed in claim 1, substantially as illustrated in any one of the Examples.

11. A soft or semi-hard ethylene/a-olefin copolymer having an intrinsic viscosity of 3.0 to 10 dl/g measured in decalin at 135"C and a density of 0.850 to 0.910, when prepared by the process claimed in any of claims 1 to 10.