Ethylene polymer composition

0001The present invention relates to a process for preparing an ethylene polymer composition, using several reactors arranged in series. In particular, it relates to a process for preparing an ethylene polymer composition further comprising an alpha-olefin.

0002Patent application EP-A-0528523 not yet published on the priority date of the present invention, but part of the prior art according to Article 54 (3) EPC discloses a polymerization process in two gas phase reactors in series by means of a catalyst supported on silica.

0003In patent EP-22376-B1 (MITSUI PETROCHEMICAL INDUSTRIES), there is described a process for preparing an ethylene polymer composition, according to which at least two reactors in series are used, a first part of the ethylene is polymerized in the presence of a catalyst in a first reactor of the series, a polymer is withdrawn from it and the catalyst these are circulated successively in the other reactors in each of which is made to arrive another part of the ethylene, that we polymerize, and recovering from the last reactor an ethylene polymer composition. This known process uses in each reactor polymerization conditions different from those used in other reactors, so that in each reactor, a polymer having a different viscosity - and hence a different melt index - is produced. those produced in other reactors. In particular, the ethylene polymer composition obtained by this known method comprises a first polymer having an intrinsic viscosity of 0.3 to 3 and a second polymer having an intrinsic viscosity of 1 to 12, the ratio of these viscosities being at least equal to 1.5.

0004This known method does not make it possible to achieve a high difference in the viscosities or the melt indices of the polymers produced in the different reactors, so that it does not make it possible to obtain polymers combining good properties of implementation (their own properties). polymers with a high melt index) and good mechanical properties (specific to low melt index polymers).

0005Moreover, this known method is poorly suited to adjusting the molecular weight distribution of the final composition. Therefore, it does not allow access to a final composition suitable for the implementation of objects by injection (composition having a molecular weight distribution characterized by a ratio M_w/ M_not less than 10), nor to compositions usable for the manufacture of films by calendering (compositions in which the ratio M_w/ M_not above is greater than 40).

0006This known process also has the disadvantage of causing, when the polymer of low viscosity or high melt index is manufactured in one of the reactors in a hydrocarbon diluent in the presence of hydrogen, a rapid saturation of the diluent hydrogen.

0007The present invention overcomes the drawbacks stated above by providing a novel process employing several reactors, which makes it possible to obtain a pronounced difference in the fluidity indices of the polymers obtained in the various reactors, which has great flexibility in controlling the molecular weight distribution of the final polymer composition, and which also makes it possible to produce a polymer with a very high melt index in the presence of a hydrocarbon diluent and hydrogen, without risk of premature saturation of the diluent with hydrogen.

0008Consequently, a process for preparing an ethylene polymer composition comprising a high melt index polymer and a low melt index polymer in at least two reactors, according to which a part of the ethylene is introduced into a first reactor, a transition metal-derived catalyst selected from Group IIIB elements, IVB, VB and VIB of the periodic table, and free of silica and a cocatalyst, it carries out a polymerization of ethylene, a medium containing one of these polymers is withdrawn from this reactor, the catalyst and the cocatalyst, the medium and another part of the ethylene which is polymerized to form the other polymer are introduced into a subsequent reactor, the weight ratio of the polymers being equal to (30 to 70) :( 70 to 30); according to the invention, the catalyst has an intrinsic molecular weight distribution defined by a ratio M_w/ M_not intrinsic less than or equal to 10 and a deactivation constant less than or equal to 0.5 h^-1, and the high melt index polymer has a melt index MI₂, measured under a load of 2.16 kg at 190 ° C according to ASTM D 1238, from 5 to 1000 g / 10 min, and the low melt index polymer has a melt index MI₅, measured under a load of 5 kg at 190 ° C according to ASTM D 1238, of 0.01 to 2 g / 10 min, the ratio between these melt indexes being 500 to 50,000.

0009By intrinsic molecular weight distribution of a catalyst is meant the molecular weight distribution of a polymer obtained in a single polymerization step and under constant polymerization conditions, in the presence of this catalyst. The M report_w/ M_not intrinsic characterization of this intrinsic molecular weight distribution refers to the ratio of the weight average molecular weight (M_w) of the polymer thus obtained and the number average molecular weight (M_not) of this polymer, this ratio being measured by steric exclusion chromatography performed in 1,2,4-trichlorobenzene at 135 ° C on a chromatograph of WATERS type 150 C.

0010Catalyst deactivation constant means the angular coefficient characterizing the linear relationship between the logarithm of the ratio of the polymerization rate and the initial polymerization rate, and the polymerization time, the polymerization being carried out in the presence of this catalyst. The angular coefficient is calculated by means of a linear regression.

0011MI flow index₂ (MI respectively₅) of a polymer means the flow rate of the molten polymer at 190 ° C., which flows through a die with a diameter of 2 mm and a length of 8 mm, under the action of a piston weighted with a mass of 2.16 kg (respectively 5 kg), this flow rate being expressed in g / 10 min according to ASTM D 1238.

0012In the process according to the invention, the ethylene is polymerized in the presence of a catalyst. An essential feature of the process lies in the properties of the catalyst used. According to the invention, the catalyst has an intrinsic molecular weight distribution defined by a ratio M_w/ M_not intrinsic maximum of 10, preferably less than 8, the values ​​less than or equal to 7 being the most advantageous, for example about 6.5 or 5. The ratio M_w/ M_not intrinsic is usually greater than 3, with values ​​greater than 4 being the most common. The catalyst used in the process according to the invention also has a deactivation constant of less than or equal to 0.5 h.¹, preferably not more than 0.3 h-¹, values ​​less than or equal to 0.2 h-¹, for example about 0.15 h-¹ being recommended. The deactivation constant is generally greater than 0.05 h.¹, values ​​greater than or equal to 0.1 h-¹ being the most common.

0013The catalyst used in the process according to the invention may be chosen from Ziegler type catalysts, in particular those derived from titanium, and from metallocene catalysts, which is a cyclopentadienyl derivative of a transition metal, in particular zirconium.

0014As catalysts of the Ziegler type, mention may be made, by way of non-limiting examples, of compounds comprising a transition metal chosen from the groups IIIB, IVB, VB or VIB of the periodic table, of magnesium and a halogen, obtained by mixing a compound of magnesium with a transition metal compound and a halogenated compound. The halogen may optionally be an integral part of the magnesium compound or the transition metal compound.

0015Examples of metallocene-type catalysts include aluminoxane-activated metallocenes and ionic-ion-activated ionic metallocenes as described, for example, in EP-500944-A1 (MITSUI TOATSU CHEMICALS).

0016Ziegler catalysts are preferred. Of these, those comprising at least one transition metal selected from groups IIIB, IVB, VB and VIB, magnesium and at least one halogen are very suitable. Good results are obtained with those including:<ul id="ul0001" list-style="dash" compact="compact"><li>from 10 to 30% by weight of transition metal, preferably from 15 to 20% by weight, typically about 17% by weight,</li><li>from 20 to 60% by weight of halogen, the values ​​of 30 to 50% by weight (for example about 40% by weight) being preferred,</li><li>from 0.5 to 20% by weight of magnesium, usually from 1 to 10% by weight, for example about 5% by weight,</li><li>from 0.1 to 10% by weight of aluminum, generally from 0.5 to 5% by weight, the values ​​of 1 to 3% by weight being the most common; the balance usually consists of elements from products used for their production such as carbon, hydrogen and oxygen. The transition metal and the halogen are preferably titanium and chlorine.</li></ul>

0017In the process according to the invention, the polymerization is carried out in the presence of a cocatalyst. Any cocatalyst known in the art may be used, in particular compounds comprising at least one aluminum-carbon chemical bond, such that the optionally halogenated organoaluminium compounds may comprise oxygen or a group 1 element of the periodic table; and aluminoxanes. Examples of organoaluminium compounds that may be mentioned include trialkylaluminums such as triethylaluminium, trialkenylaluminiums such as triisopropenylaluminium, aluminum mono- and dialcoolates such as diethylaluminum ethoxide, and mono- and dihalogenated alkylaluminums such as chloride. diethylaluminum, alkylaluminum mono- and dihydrides such as dibutylaluminum hydride and organoaluminium compounds comprising lithium such as LiAl (C₂H₅)₄. Organoaluminum compounds, especially those which are not halogenated, are well suited. Triethylaluminum and triisobutylaluminum are especially advantageous.

0018In the process according to the invention, an installation is used comprising at least two polymerization reactors arranged in series and interconnected. Each reactor is fed with ethylene. The catalyst and the cocatalyst are preferably introduced only into the first reactor, in which ethylene is polymerized until a polymer having the characteristics specific to the polymerization conditions of this reactor is obtained. A medium from the first reactor comprising the polymer obtained therein, the catalyst and the cocatalyst is introduced into the second reactor, preferably continuously. In this second reactor, the ethylene introduced therein is polymerized with the aid of the catalyst and the cocatalyst from the first reactor, and polymerization conditions (temperature, transfer agent concentration, concentration in the second reactor) are used in this second reactor. possible comonomer) different from those used in the first reactor. Thus, the polymer produced in the second reactor has a melt flow rate different from that produced in the first reactor, and the overall polymer composition collected from the second reactor combines characteristics specific to the operating conditions of the first reactor and characteristics specific to the operating conditions of the first reactor. second reactor.

0019In the process according to the invention the high melt index polymer and the low melt index polymer can be prepared in any order.

0020The installation can obviously include more than two reactors connected in series. In this case, the first reactor of the series is fed with the catalyst and the cocatalyst, and each reactor is fed with ethylene and with the medium from the preceding reactor of the series, this medium comprising the catalyst, the cocatalyst and a mixture of the polymers produced in the previous reactors of the series.

0021In the case where the installation comprises more than two reactors in series, the high melt index polymer and the low melt index polymer as defined above can be produced in two contiguous or non-contiguous reactors of the series. . In this particular case of implementation of the process according to the invention, it is possible to carry out, in the other reactors of the series, operating conditions for which an MI polymer is indifferently produced.₂ less than 5, from 5 to 1,000 or greater than 1,000 or a MI flow index₅ less than 0.01, from 0.01 to 2 or greater than 2, MI flow indices₂ and MI₅ having been defined above.

0022It is preferably limited to two reactors.

0023In a first embodiment of the process according to the invention, the formation of the high melt index polymer precedes that of the low melt index polymer. This embodiment is particularly advantageous when it is desired to obtain an ethylene polymer composition that can be used for manufacturing artifacts whose surface is free of imperfections such as hard spots.

0024In a second embodiment of the process according to the invention, at least one of the hydrogen reactors acting as transfer agent modulating the melt index of the polymer produced in this reactor is fed. The partial pressure of the hydrogen in the reactor (s) is advantageously from 0.001 to 2 MPa, more particularly from 0.002 to 1.5 MPa, preferably from 0.005 to 1.3 MPa, the ratio between partial pressures. hydrogen and ethylene generally not exceeding 5, preferably not 3, and being for example between 0.01 to 2.5.

0025In a variant of this second embodiment, hydrogen is introduced continuously into all the reactors, the ratio between the partial pressures of ethylene and hydrogen in the first reactor being different from that used in other reactors. In this variant it is important to maintain these ratios constant in each reactor during the polymerization time. The quotient of these two ratios is advantageously greater than 20, preferably 40; it is desirable that it does not exceed 300, for example 200. A quotient selected from 45 to 175 is particularly suitable.

0026This embodiment of the process according to the invention has the advantageous feature of making it possible to obtain a polymer of very high melt index in the presence of a hydrocarbon diluent while avoiding a rapid saturation of the hydrocarbon diluent by the hydrogen.

0027In the process according to the invention, the polymerization process in the reactors can be selected from the processes in solution, in suspension or in the gas phase, regardless of the properties of the polymer which it is desired to prepare therein and the choice of the process used in the process. other reactor. For example, the polymerization can be carried out in two gas phase reactors, or in a first suspension reactor and in a second gas phase reactor or vice versa. The polymerization is preferably carried out in suspension in two reactors.

0028In the case of suspension polymerization, this is generally carried out in a hydrocarbon diluent which is inert with respect to the catalyst, the cocatalyst and the product polymer (such as aliphatic, cycloaliphatic and aromatic liquid hydrocarbons), a temperature such that at least 50% (preferably at least 70%) of the polymer formed therein is insoluble. Preferred diluents are linear alkanes such as n-butane, n-hexane and n-heptane, or branched alkanes such as isobutane, isopentane, isooctane and 2,2-dimethylpropane, or cycloalkanes such as cyclopentane and cyclohexane or mixtures thereof. The polymerization temperature is generally from 20 to 200 ° C, preferably from 50 to 100 ° C. The ethylene partial pressure is most often chosen from 0.1 to 5 MPa, preferably from 0.2 to 2 MPa, more particularly from 0.4 to 1.5 MPa.

0029In the process according to the invention, it is possible to supply the second reactor and / or, where appropriate, at least one of the following reactors with catalyst and / or fresh cocatalyst. However, it is preferred to introduce the catalyst and cocatalyst exclusively into the first reactor.

0030In a particular embodiment of the process according to the invention, at least one of the reactors is additionally introduced with an alpha-olefin so as to produce in this reactor a copolymer of ethylene and of this alpha-olefin. The alpha-olefin may be selected from olefinically unsaturated monomers comprising from 3 to 8 carbon atoms, for example propylene, 1-butene, 1-pentene, 3-methyl-1-butene and 1-hexene. 3- and 4-methyl-1-pentenes and 1-octene. Other examples of alpha-olefin are diolefins comprising from 4 to 18 carbon atoms, preferably unconjugated aliphatic diolefins such as 4-vinylcyclohexene and 1,5-hexadiene, alicyclic diolefins having an endocyclic bridge such as that dicyclopentadiene, methylene and ethylidene norbornene; and conjugated aliphatic diolefins such as 1,3-butadiene, isoprene and 1,3-pentadiene. Preferred alpha-olefins are propylene, 1-butene, 1-hexene, 1-octene and 1,5-hexadiene. Good results are obtained with 1-butene and 1-hexene.

0031In this particular embodiment of the process according to the invention, the alpha-olefin or the diolefin comprising from 4 to 18 carbon atoms is generally introduced into that of the reactors in which the polymer of low melt index is produced, in an amount adjusted so that said polymer comprises from 0.5 to 20% by weight of alpha-olefin or diolefin comprising from 4 to 18 carbon atoms, preferably from 1 to 10% by weight, for example 2% by weight, weight. In a variant, a part of the alpha-olefin or of the diolefin comprising from 4 to 18 carbon atoms can also be introduced into the other reactor, in a limited amount so that the alpha-olefin or diolefin content comprising from 4 to 18 carbon atoms of the polymer of high melt index does not exceed 5% by weight, preferably 3% by weight, for example 1% by weight; the alpha-olefin or diolefin content comprising from 4 to 18 carbon atoms of the high melt index polymer is usually at least 0.1%.

0032The process according to the invention is applicable to the preparation of ethylene polymer compositions which may comprise one or more homopolymers of ethylene and / or one or more ethylene copolymers.

0033The process according to the invention makes it possible to obtain polymer compositions of ethylene and optionally alpha-olefins or diolefins comprising from 4 to 18 carbon atoms, wherein each individual polymer has a melt index sufficiently different from that of the other or each of the other polymers to simultaneously benefit from the process-specific properties of a high melt index polymer and good properties. mechanical properties of a polymer of low melt index.

0034The process according to the invention also has great flexibility in controlling the molecular weight distribution of the final composition. Thus, the process according to the invention makes it possible to manufacture a wide range of ethylene polymer compositions ranging from those suitable for the use of injection-molded articles to those that can be used for the production of films by extrusion or calendering. .

0035In addition, the process according to the invention makes it possible to obtain polymer compositions of ethylene and optionally of alpha-olefins or of diolefins comprising from 4 to 18 carbon atoms comprising an alpha-olefin or a diolefin in a variable amount. up to 10% by weight, preferably from 0.5 to 6% by weight, for example about 1% by weight.

0036The process according to the invention proves particularly efficient for the manufacture of ethylene polymer compositions and optionally of alpha-olefins or diolefins comprising from 4 to 18 carbon atoms which can be used for the manufacture of objects having a high resistance. to stress cracking and whose surface is free of imperfections such as hard spots.

0037The invention therefore also relates to ethylene polymer compositions obtainable by the process according to the invention having the properties mentioned above, these compositions comprising, on the one hand, a first polymer having a MI fluidity₂ from 5 to 1000 g / 10 min, preferably from 10 to 500 g / 10 min, and secondly, a second polymer having a melt index MI₅ from 0.01 to 2 g / 10 min, preferably from 0.03 to 1 g / 10 min, in particular from 0.05 to 0.7 g / 10 min, the ratio of these melt indexes being from 500 to 50,000, preferably 1,000 to 10,000. The weight ratio of these two polymers is generally equal to (30 to 70) :( 70 to 30), preferably to (40 to 60) :( 60 to 40), for example to (42 to 58) :( 58 to 42). The first aforementioned polymer may optionally comprise an alpha-olefin or a diolefin comprising from 4 to 18 carbon atoms in an amount equal to at most 5% by weight and the second polymer comprises from 0.5 to 20% by weight of a alpha-olefin or a diolefin comprising from 4 to 18 carbon atoms. Advantageous compositions comprise a high melt index ethylene homopolymer and a low melt index ethylene copolymer containing, for example, from 0.5 to 6% by weight of an alpha-olefin or a diolefin comprising from 4 to 18 carbon atoms. The compositions according to the invention have a molecular weight distribution defined by a ratio M_w/ M_not ranging from 5 to 70, in particular from 7 to 50, for example from 10 to 40. In addition, the compositions according to the invention have a melt index MI₅ from 0.1 to 10 g / 10 min, in particular from 0.5 to 5 g / 10 min and a dynamic viscosity η expressed in dPa.s and measured at a speed gradient of 100 s^-1 at 190 ° C, responding to the relationship<maths id="math0001"><math display="block"><mrow><mtext>0.652 ≥ </mtext><mfrac><mrow><msub><mrow><mtext>[Log (177470 / MI</mtext></mrow><mrow><mtext>5</mtext></mrow></msub><mtext>) - logη] </mtext></mrow><mrow><msub><mrow><mtext>2 - log (2.53 x MI</mtext></mrow><mrow><mtext>5</mtext></mrow></msub><mtext>)</mtext></mrow></mfrac></mrow></math><img file="EP1544244A1_D0001.tif" /></maths>

0038The compositions according to the invention commonly contain from 0.5 to 10% by weight of an alpha-olefin or a diolefin comprising from 4 to 18 carbon atoms, preferably from 1 to 6% by weight.

0039The compositions according to the invention find a particularly advantageous use in a wide range of industrial applications, because they combine good properties of implementation and good mechanical properties such as resistance to impact and stress cracking. . The compositions according to the invention are capable of being used by all the conventional processes for converting plastics and more particularly by extrusion, extrusion-blow molding, extrusion-thermoforming, calendering and extrusion processes. injection. These compositions are suitable for the manufacture of shaped articles such as films, sheets, plates, containers, bags and sachets; they are particularly suitable for the manufacture of tubes.

0040The present invention therefore also relates to the use of the compositions described above for the manufacture of tubes.

0041The examples, the description of which follows, serve to illustrate the invention.

0042The meaning of the symbols used in these examples, the units expressing the quantities mentioned and the methods of measurement of these quantities are explained below.<dl id="dl0001" compact="compact"><dt>MID₂ =</dt><dd>melt index of a polymer designating the flow rate of molten polymer at 190 ° C, which flows through a die with a diameter of 2 mm and a length of 8 mm, under the action of a weighted piston with a mass of 2.16 kg, this flow rate being expressed in g / 10 min, according to the ASTM D 1238 standard.</dd><dt>MID₅ =</dt><dd>melt index of a polymer (or polymer composition) designating the flow rate of the molten polymer (or melt composition) at 190 ° C, which flows through a die having a diameter of 2 mm and a length of 8 mm, under the action of a weighted piston of a mass of 5 kg, this flow being expressed in g / 10 min, according to the standard ASTM D 1238.</dd><dt>M_w/ M_not =</dt><dd>ratio of the weight average molecular weight (M_w) of a polymer (or a polymer composition) and the number average molecular weight (M_not) of this polymer (or of this composition), measured by steric exclusion chromatography carried out in 1,2,4-trichlorobenzene at 135 ° C. on a chromatograph of WATERS type 150 C.</dd><dt>η =</dt><dd>dynamic viscosity of a polymer (or a polymer composition) expressed in dPa.s and measured at a speed gradient of 100 s^-1 at 190 ° C.</dd><dt>K_d =</dt><dd>constant of deactivation of a catalyst expressed in h-¹, which is the angular coefficient characterizing the linear relationship between the logarithm of the ratio of the polymerization rate and the initial polymerization rate, and the polymerization time, the polymerization being carried out in the presence of this catalyst. The angular coefficient is calculated by means of a linear regression.</dd><dt>α =</dt><dd>catalytic activity in grams of insoluble polymer obtained per hour and per gram of catalyst and divided by the mole fraction of ethylene in the diluent.</dd></dl>

<u>Example 1 (in accordance with the invention)</u>

AT. <u>Catalyst preparation</u>

0043Magnesium diethylate was reacted at 150 ° C. for 4 hours with titanium tetrabutylate in such amounts that the molar ratio of titanium to magnesium was 2. Then the resulting reaction product was chlorinated and precipitated. by contacting it with a solution of ethylaluminum dichloride for 90 minutes at 45 ° C. The solid thus obtained, collected from the suspension, included (% by weight):    Ti: 17; Cl: 41; Al: 2; Mg: 5.

B. <u>Polymerization of ethylene in a single reactor</u>

00441.5 liter autoclave equipped with a stirrer was charged with 1 liter of hexane and 1 mmol of triethylaluminum. The temperature was then raised to 85 ° C., which was kept constant during the polymerization time. A single dose of hydrogen was then introduced at a pressure of 0.4 MPa and ethylene. Then 7 mg of the solid catalyst obtained in A. The ethylene partial pressure was kept constant at 1 MPa for 1 hour. The autoclave was then degassed and cooled. The polyethylene collected from the autoclave had a ratio M_w/ M_not of 6.7 and the catalyst had a K_d 0.15.

C. <u>Polymerization of ethylene into two reactors</u>

0045The polymerization process in two successive reactors was simulated in a single reactor in two stages separated by an intermediate expansion and reinitialization of the operating parameters.

<u>Polymerization of a first polymer (i)</u> :

0046A 2 liter hexane and 2 mmol triethylaluminum were charged to a 5 liter autoclave equipped with a stirrer. The temperature was then raised to 85 ° C., which was kept constant during the polymerization time. A single dose of hydrogen was then introduced at a pressure of 1.3 MPa and ethylene. The ethylene partial pressure was kept constant at 0.6 MPa. Then 22 mg of the solid catalyst obtained in A was injected. After 73 minutes the autoclave was degassed. 200 g of polymer (i) were obtained. The catalyst had an α activity of 10.3.

<u>Polymerization of a second polymer (ii)</u> :

0047200 ml of hexane were added to the autoclave. The temperature was brought to 75 ° C and kept constant during the polymerization time. A dose of hydrogen at a pressure of 0.08 MPa, ethylene and a dose of butene was then introduced so as to obtain a butene / ethylene molar ratio in the liquid phase of 0.38. The ethylene partial pressure was kept constant at 0.4 MPa until an additional 169 g of polymer (ii) was obtained. After degassing, 369 g of a polymer composition (i) and (ii) were collected from the autoclave. The catalyst had an α activity of 7.3. The following results were obtained:

<u>Polymer (i)</u> :

0048<dl id="dl0002" compact="compact"><dt>MID₂ =</dt><dd>168</dd></dl>

<u>Polymer (ii)</u> :

0049<dl id="dl0003" compact="compact"><dt>MID₅ =</dt><dd>0.21</dd></dl>

<u>Composition comprising polymers (i) and (ii)</u>

:

0050<dl id="dl0004" compact="compact"><dt>MID₅ =</dt><dd>15.9</dd><dt>η =</dt><dd>6700</dd><dt>M_w/ M_not =</dt><dd>21.</dd></dl>

<u>Example 2 (reference)</u>

0051In this example, a catalyst having an intrinsic distribution defined by a ratio M_w/ M_not greater than 10, which was then used in a two-reactor ethylene polymerization process.

AT. <u>Catalyst preparation</u>

0052Magnesium diethylate, titanium tetrabutylate and zirconium tetrabutylate were reacted for 4 hours at 150 ° C. in amounts such that the Ti / Mg molar ratio was 0.6 and the Zr / Ti molar ratio equal to 1.2. Then, the resulting reaction product was chlorinated and precipitated by contacting it with a solution of isobutylaluminum dichloride first at 45 ° C and then at 60 ° C. The solid thus obtained, collected from the suspension, included (% by weight):    Ti: 6; Zr: 12; Cl: 50; Al: 2; Mg: 5.

B. <u>Polymerization of ethylene in a single reactor</u>

0053The operations of Example 1 (B) were repeated under the following operating conditions:<ul id="ul0002" list-style="dash" compact="compact"><li>initial hydrogen partial pressure: 1.2 MPa</li><li>partial pressure of ethylene: 0.6 MPa</li><li>amount of catalyst used: 12 mg</li><li>polymerization time: 42 min</li><li>amount of polyethylene produced: 60 g.</li></ul>

0054The polymer thus obtained had a ratio M_w/ M_not of 19 and the catalyst had a K_d from 1.

C. <u>Polymerization of ethylene into two reactors</u>

0055The operations of Example 1 (C) were repeated under the following operating conditions:

<u>Polymerization of a first polymer (i)</u> :

0056<ul id="ul0003" list-style="dash" compact="compact"><li>polymerization temperature: 85 ° C</li><li>initial hydrogen partial pressure: 1.2 MPa</li><li>partial pressure of ethylene: 0.6 MPa</li><li>amount of catalyst used: 12 mg</li><li>amount of polyethylene produced: 54 g.</li></ul> The catalyst had an α activity of 19.3.

<u>Polymerization of a second polymer (ii)</u> :

0057<ul id="ul0004" list-style="dash" compact="compact"><li>polymerization temperature: 70 ° C</li><li>initial hydrogen partial pressure: 0.2 MPa</li><li>partial pressure of ethylene: 0.6 MPa</li><li>molar ratio butene / ethylene: 0.28</li><li>amount of polyethylene produced in the second stage: 80 g</li><li>total amount of polyethylene produced: 134 g.</li></ul>

0058The following results were obtained:

<u>Polymer (i):</u>

0059<dl id="dl0005" compact="compact"><dt>MID₂ =</dt><dd>1.4</dd></dl>

<u>Polymer (ii):</u>

0060<dl id="dl0006" compact="compact"><dt>M15 =</dt><dd>0.03</dd></dl>

0061Composition comprising polymers (i) and (ii):<dl id="dl0007" compact="compact"><dt>MI5 =</dt><dd>0.09</dd><dt>η =</dt><dd>23500</dd><dt>Mw / Mn =</dt><dd>18.</dd></dl>

0062A comparison of the results of Example 2 with those of Example 1 shows the progress made by the invention with regard to the spacing between the melt indexes of polymers (i) and (ii) obtained in both reactors.