Method for preparing a polyethylene or a copolymer of ethylene and 1,3-diene

Abstract

The invention relates to a method for preparing a polymer which comprises preparing a catalytic system comprising a neodymocene borohydride and a dialkylmagnesium co-catalyst in which the alkyls are primary alkyls, then polymerising a monomer selected from ethylene and a monomer mixture containing ethylene and a 1,3-diene, in the presence of the catalytic system and of an additional compound, a dialkylmagnesium compound of formula RB-Mg-RL in which RB is a secondary alkyl of formula R'2CH and RL is a primary alkyl of formula R'CH2, the R' being alkyls. The method is made less sensitive to variations in impurities in a polymerisation plant by controlling the values of the number-average molar masses.

Description

[0001] Process for the preparation of polyethylene or a copolymer of ethylene and 1,3-diene

[0002] The field of the invention is that of processes for the polymerization of ethylene or the copolymerization of ethylene and a 1,3-diene in the presence of catalytic systems which are based on rare earth metallocene.

[0003] The Applicant has described processes for the polymerization of ethylene and for the copolymerization of ethylene and a 1,3-diene in the presence of catalytic systems based on neodymium borohydride and a co-catalyst, for example in patent applications EP 1092 731, WO 2004035639, WO 2007054224 and WO 2018224776. The co-catalyst, an organometallic compound, which is most often described is an organomagnesium compound. It is also described that the ratio between the number of moles of magnesium and the number of moles of neodymium present in the polymerization medium makes it possible to define the number-average molar mass, Mn, of the polymer to be synthesized and that the lower this molar ratio, the higher the targeted Mn. Furthermore, the very high reactivity of organometallic compounds with oxygen, carbon dioxide and water is also known.Even if the polymerization reactor is cleaned, placed under an inert atmosphere, the solvents and monomers purified, impurities such as water, carbon dioxide, oxygen, may be present in the polymerization reactor containing the polymerization solvent and the monomers and react with the organomagnesium at the time of its introduction into the polymerization reactor, which has the consequence of modifying the Mg / Nd molar ratio, molar ratio between the number of moles of organomagnesium and the number of moles of Nd. For a given neodymium level, the variation undergone by the Mg / Nd molar ratio with the level of impurities is all the greater as this molar ratio is low, which can lead to less good control of the process to achieve the target Mn of the polymer to be synthesized. There is therefore a need to remedy this difficulty.

[0004] The Applicant, continuing its efforts, has developed a new process for the preparation of polyethylene and ethylene and 1,3-diene copolymer which differs from the processes already known by the introduction into the polymerization medium of a specific additional compound, a dialkylmagnesium compound of which one of the two alkyls is a secondary alkyl and the other a primary alkyl. It turns out that the process is made less sensitive to variations in the impurities of a polymerization installation in the control of the Mn values.

[0005] Thus, an object of the invention is a process for preparing a polymer which comprises the following steps: a) the preparation of a catalytic system comprising a metallocene of formula (Ia) and a co-catalyst,

[0006] P(Cp 1 CP 2 )Nd(BH4)(i + y)-Ly-N x (there)

[0007] CP 1 and Cp 2, identical or different, being chosen from the group consisting of fluorenyl groups, cyclopentadienyl groups and indenyl groups, the groups being substituted or unsubstituted, P being a group bridging the two Cp groups 1 and Cp 2 , and comprising a silicon or carbon atom,

[0008] L representing an alkali metal chosen from the group consisting of lithium, sodium and potassium,

[0009] N representing a molecule of an ether, x, an integer or not, being equal to or greater than 0, y, an integer, being equal to or greater than 0, the co-catalyst being a dialkylmagnesium of formula (IIa) in which the alkyls, identical or different, are primary alkyls, R2Mg (Ha) b) the polymerization of a monomer chosen from ethylene and a monomer mixture containing ethylene and a 1,3-diene in the presence of the catalytic system and an additional compound, a dialkylmagnesium of formula (IIa), R B -Mg-R L (Ilia) in which R B is a secondary alkyl of formula R'2CH and R L is a primary alkyl of formula R'CH2, the R's, identical or different, being alkyls.

[0010] Detailed description

[0011] Any interval of values ​​designated by the expression "between a and b" represents the domain of values ​​greater than "a" and less than "b" (i.e., excluding the limits a and b), while any interval of values ​​designated by the expression "from a to b" means the domain of values ​​from "a" to "b" (i.e., including the strict limits a and b).

[0012] The compounds mentioned in the description may be of fossil or bio-sourced origin. In the latter case, they may be, partially or totally, derived from biomass or obtained from renewable raw materials derived from biomass. Similarly, the compounds mentioned may also come from the recycling of materials already in use, that is to say, they may be, partially or totally, derived from a recycling process, or obtained from raw materials themselves derived from a recycling process.

[0013] The expression "based on" used to define the constituents of the catalytic system or catalytic composition means the mixture of these constituents, or the product of the reaction of some or all of these constituents with each other.

[0014] In the present application, metallocene is understood to mean an organometallic complex in which the metal, in this case the neodymium atom, is linked to a ligand molecule consisting of two Cp groups 1 and Cp 2 connected to each other by a P bridge.

[0015] In the formula (Ia) of the metallocene useful for the purposes of the invention, the Cp groups 1 and Cp 2, identical or different, are chosen from the group consisting of fluorenyl groups, cyclopentadienyl groups and indenyl groups, these groups being able to be substituted or unsubstituted. As substituted cyclopentadienyl, fluorenyl and indenyl groups, mention may be made of those substituted by alkyl radicals having 1 to 6 carbon atoms or by aryl radicals having 6 to 12 carbon atoms or by trialkyl radicals such as SiMej. The choice of radicals is also guided by the accessibility of the corresponding molecules which are substituted cyclopentadienyls, fluorenes and indenes, because the latter are commercially available or easily synthesized.

[0016] As substituted fluorenyl groups, mention may be made of those substituted in position 2,7, 3 or 6, particularly 2,7-ditertiobutyl-fluorenyl, 3,6-ditertiobutyl-fluorenyl. Positions 2, 3, 6 and 7 respectively designate the position of the carbon atoms of the rings as shown in the diagram below, position 9 corresponding to the carbon atom to which the P bridge is attached.

[0017] As substituted cyclopentadienyl groups, mention may be made of those substituted both in position 2 (or 5) and in position 3 (or 4), particularly those substituted in position 2, more particularly the tetramethylcyclopentadienyl group. Position 2 (or 5) designates the position of the carbon atom which is adjacent to the carbon atom to which the P bridge is attached, as shown in the diagram below.

[0018] As substituted indenyl groups, mention may be made in particular of those substituted in position 2, more particularly 2-methylindenyl, 2-phenylindenyl. Position 2 designates the position of the carbon atom which is adjacent to the carbon atom to which the P bridge is attached, as shown in the diagram below.

[0019] Preferably, Cp 1 and Cp 2 , are identical.

[0020] Preferably, Cp 1 and Cp 2 are selected from the group consisting of substituted fluorenyl groups and the unsubstituted fluorenyl group of formula C11H2. More preferably, Cp 1 and Cp 2 are identical and are selected from the group consisting of substituted fluorenyl groups and the unsubstituted fluorenyl group of formula CisHs. Advantageously, Cp 1 and Cp 2are identical and each represents an unsubstituted fluorenyl group of formula CisHs, represented by the symbol Flu.

[0021] Any ether that has the power to complex the alkali metal is suitable as an ether, especially diethyl ether and tetrahydrofuran. In formula (Ia), y can be 0 or 1 and x can be 0, 1 or 2.

[0022] The P bridge connecting the Cp groups 1 and Cp 2 and comprising a silicon or carbon atom preferably corresponds to the formula ZR 1 R 2 , in which Z represents a silicon or carbon atom, R 1 and R 2 , identical or different, each represent an alkyl group comprising from 1 to 20 carbon atoms, preferably a methyl. In the formula ZR 1 R 2 , Z advantageously represents a silicon atom, Si, according to any one of the embodiments of the invention.

[0023] The metallocene useful for the synthesis of the catalytic system may be in the form of a crystallized or non-crystalline powder, or in the form of single crystals. The metallocene may be in a monomeric or dimeric form, these forms depending on the method of preparation of the metallocene, as described for example in patent application WO 2007054224 or WO 2007054223. The metallocene may be prepared in a conventional manner by a process analogous to that described in patent application WO 2007054224 or WO 2007054223, in particular by reaction under inert and anhydrous conditions of the salt of an alkali metal of the ligand with a rare earth borohydride in a suitable solvent, such as an ether, such as diethyl ether or tetrahydrofuran or any other solvent known to those skilled in the art. After reaction, the metallocene is separated from the reaction by-products by techniques known to those skilled in the art, such as filtration or precipitation in a second solvent.The metallocene is finally dried and isolated in solid form.

[0024] According to a particularly preferred embodiment, the metallocene is of formula (I-1), (I-2), (I-3), (I-4) or (I-5):

[0025] [Me2Si(Flu)2Nd(p-BH4)2Li(THF)] (1-1) [{Me2SiFlu2Nd(p-BH4)2Li(THF)}2] (1-2) [Me2SiFlu2Nd(p-BH4)(THF)] (1-3) [{Me2SiFlu2Nd(p-BH4)(THF)}2] (1-4) [Me2SiFlu2Nd(p-BH4)] (1-5) in which Flu represents the CisHs group.

[0026] The catalytic system also has as another essential constituent a co-catalyst which is a dialkylmagnesium of formula (Ha), R2Mg (Ha) in which the R , identical or different, are primary alkyls.

[0027] Preferably, the alkyls represented by the symbols R in formula (IIa) are linear alkyls. More preferably, the co-catalyst is butyloctylmagnesium. The dialkylmagnesium compounds of formula (IIa) are well-known organometallic reagents, even some of them are commercial products. For their synthesis, one can for example also refer to the collection of volumes of "Organic Synthesis". Like any organomagnesium compound, the dialkylmagnesium compound constituting the catalytic system can be in the form of a monomeric entity or in the form of a polymeric entity. By way of illustration, the dialkylmagnesium compound can be in the form of a monomeric entity (R-Mg-R)i or in the form of a polymeric entity (R-Mg-R) p, p being an integer greater than 1, for example dimer (R-Mg-R , m being as defined previously. Furthermore, whether in the form of a monomeric or polymeric entity, the organomagnesium compound can also be in the form of an entity coordinated to one or more molecules of a solvent, preferably an ether such as diethyl ether, tetrahydrofuran or methyltetrahydrofuran.

[0028] The catalytic system in accordance with the invention can be prepared in a traditional manner by a process analogous to that described in patent application WO 2007054224 or WO 2007054223, with a dialkylmagnesium compound of formula (Ha) as co-catalyst. For example, in a hydrocarbon solvent, the co-catalyst is placed in the presence of the metallocene, typically at a temperature ranging from 20 to 80°C for a period of between 5 and 60 minutes. According to any one of the embodiments of the invention, the quantities of the co-catalyst and the metallocene reacted to form the catalytic system in step a) are such that the ratio between the number of moles of Mg in the co-catalyst and the number of moles of neodymium in the metallocene preferably ranges from 1 to 100, more preferably from 1 to less than 10. The range of values ​​from 1 to less than 10 is in particular more favorable for obtaining polymers with high molar masses.

[0029] The catalytic system is generally prepared in a hydrocarbon solvent, aliphatic such as methylcyclohexane or aromatic such as toluene. Generally after its synthesis, the catalytic system is used as is in the process for synthesizing the polymer in accordance with the invention. The catalytic system is typically in the form of a catalytic solution, i.e. in a solvent which is preferably the solvent in which it was prepared, and the metal concentration of the catalytic solution, i.e. in rare earth metallocene, is then within a range preferably ranging from 0.0001 to 0.2 mol L 1 , more preferably from 0.001 to 0.03 mol L 1 .

[0030] According to a particularly preferred embodiment, the catalytic system contains a pre-formation monomer chosen from ethylene, a 1,3-diene and a mixture of ethylene and a 1,3-diene. The 1,3-diene as pre-formation monomer may be 1,3-butadiene, isoprene or a 1,3-diene of formula CH2=CR 6 -CH=CH2, the symbol R 6representing a hydrocarbon group having 3 to 20 carbon atoms, in particular myrcene or p-farnesene. The pre-forming monomer is preferably a 1,3-diene, more preferably 1,3-butadiene. The so-called pre-formed catalytic system is typically prepared by a process analogous to that described in patent application WO 2017093654 A1 or in patent application WO 2018020122 A1. For example, the co-catalyst and the metallocene are reacted in a hydrocarbon solvent, typically at a temperature of 20 to 80°C for 10 to 20 minutes to obtain a first reaction product, then with this first reaction product, a pre-forming monomer is reacted at a temperature ranging from 40 to 90°C for 1 to 12 hours. The pre-formation monomer is preferably used in a molar ratio (pre-formation monomer / metallocene metal) ranging from 5 to 1000, preferably from 10 to 500.Before use in polymerization, the preformed type catalytic system can be stored in an inert atmosphere, in particular at a temperature ranging from -20°C to room temperature (23°C). The preformed type catalytic system therefore has the preforming monomer as its basic constituent. In other words, the so-called preformed catalytic system contains, in addition to the metallocene and the co-catalyst, the preforming monomer.

[0031] Like any synthesis carried out in the presence of organometallic compounds, the synthesis of the catalytic system takes place under anhydrous conditions under an inert atmosphere.

[0032] Typically, reactions are conducted from solvents and anhydrous compounds under anhydrous nitrogen or argon.

[0033] The catalytic system being prepared, it is used in step b) as an initiator for the polymerization reaction of a monomer, monomer M, chosen from ethylene and a monomer mixture containing ethylene and a 1,3-diene. When the monomer M is a mixture containing ethylene and a 1,3-diene, the ethylene preferably represents more than 50%, more preferably more than 60%, by mole of the monomer mixture. The monomer mixture containing ethylene and a 1,3-diene is advantageously a mixture of ethylene and a 1,3-diene. The monomer M is preferably a mixture of ethylene and a 1,3-diene, which mixture advantageously contains more than 50% by mole of ethylene, more preferably 60% by mole of ethylene.According to any one of the embodiments of the invention, the 1,3-diene of the monomer mixture containing ethylene and a 1,3-diene is preferably 1,3-butadiene, isoprene, myrcene, P-farnesene or their mixtures, more preferably 1,3-butadiene.

[0034] In step b) an additional compound is used which is a dialkylmagnesium of formula (Ilia)

[0035] R B -Mg-R L (Ilia) in which R B is a secondary alkyl of formula R'2CH and R L is a primary alkyl of formula R'CFb, the R's, identical or different, being alkyls.

[0036] In other words, the dialkylmagnesium of formula (Ilia) has the structural formula R'2CHMgCH2R'. The alkyls represented by the symbols R' can contain 1 to 10 carbon atoms.

[0037] R Lis preferably a linear alkyl, more preferably a linear alkyl having 2 to 8 carbon atoms. R L is even more preferably n-butyl of formula CH3CH2CH2CH2-.

[0038] R B is preferably an alkyl of formula R"CH2CHR", the R'', identical or different, being alkyls. The alkyl of R'' preferably has 1 to 10 carbon atoms, the alkyl of R'' preferably has 1 to 9 carbon atoms. Advantageously, R B is sec-butyl of formula CH3CH2CH(CH3)-.

[0039] A dialkylmagnesium compound of formula (Ilia) is understood to mean a single compound of formula (Ilia) or a mixture of dialkylmagnesium compounds of formula (Ilia) which are different from each other in their chemical structure, preferably a single compound of formula (Ilia). To avoid handling a multitude of compounds in the process, the dialkylmagnesium compound of formula (Ilia) denotes a single compound of formula (Ilia) (in English "one").

[0040] According to a particularly preferred embodiment of the invention, the dialkylmagnesium of formula (I11a) is of formula R B -Mg-R L in which R B is sec-butyl and R L is n-butyl, with the structural formula CH3CH2CH(CH3)MgCH2CH2CH2CH3.

[0041] Dialkylmagnesium of formula (Ilia) is used in the polymerization medium as an additional compound for better control of the polymerization process in controlling the Mn value of the polymers to be synthesized. It turns out that the use of the additional compound makes the process less sensitive to variations in impurities of a polymerization plant in controlling Mn values. The additional compound can be introduced into a reactor before the addition of the catalytic system or at the same time, the reactor containing a polymerization solvent.

[0042] In step b), a second additional compound may be added, which second additional compound is a dialkylmagnesium compound of formula (IIa). The second additional compound of formula (IIa) is preferably the same dialkylmagnesium compound as that of the catalytic system. The second additional compound is generally introduced before the additional compound of formula (IIa). When a second additional dialkylmagnesium compound of formula (IIa) is added, its amount may vary widely. The molar ratio between the amount of the second additional compound and the total amount of the second additional compound and the dialkylmagnesium compound of formula (IIa) typically varies in a range from 0 to less than 1.According to any one of the embodiments of the invention, the molar ratio between the quantity of the second additional compound and the total quantity of the second additional compound and the dialkylmagnesium of formula (IIIa) preferably varies from 0 to less than 0.95.

[0043] The total quantity of the additional compound of formula (IIa) and, where appropriate, of the additional compound of formula (Ha) introduced in step b), which is generally indexed to the quantity of neodymium, can vary to a large extent and is adjusted by a person skilled in the art according to the polymerization conditions. Preferably, the ratio between the total number of moles of the dialkylmagnesium of formula (IIa) and of the second additional compound and the number of moles of Nd in the catalytic system is less than 500 or less than 300 or less than 100. The larger ratios are preferable under conditions of high polymerization temperature or pressure; the lower ratios are preferable under conditions of lower polymerization temperature or pressure.

[0044] The polymerization is preferably carried out in solution, continuously or batchwise. The polymerization solvent is typically a hydrocarbon solvent, preferably aliphatic. As an example of an aliphatic hydrocarbon solvent, methylcyclohexane is particularly suitable. The monomer to be polymerized, monomer M, can be introduced into the reactor containing the polymerization solvent and the catalytic system or conversely the catalytic system can be introduced into the reactor containing the polymerization solvent and the monomer to be polymerized. The monomer to be polymerized and the catalytic system can be introduced simultaneously into the reactor containing the polymerization solvent, in particular in the case of continuous polymerization. The polymerization is typically carried out under anhydrous conditions and in the absence of oxygen, in the optional presence of an inert gas.The polymerization temperature generally varies in a range from 40 to 150°C, preferably 40 to 120°C. The person skilled in the art adapts the polymerization conditions such as the polymerization temperature, the concentration of each of the reactants, the pressure of the reactor, the desired microstructure and macrostructure of the polymer.

[0045] The polymerization is preferably carried out at constant monomer pressure, in particular at constant ethylene pressure. A continuous addition of monomer or one of them in the case of a monomer mixture to be polymerized can be carried out in the polymerization reactor, in which case the polymerization reactor is a fed reactor. This embodiment is particularly suitable for a random incorporation of the monomers.

[0046] According to a preferred embodiment of the invention, the polymer prepared is a copolymer of ethylene and 1,3-butadiene, preferably a random copolymer of ethylene and 1,3-butadiene.

[0047] According to a particularly preferred embodiment of the invention in which the monomer is a monomer mixture containing ethylene and 1,3-butadiene and the ligands of the catalytic system represented by Cp 1 and Cp 2 are each an unsubstituted fluorenyl group of formula C13H8, the prepared polymer contains in addition to the ethylene monomer units and the butadiene units cyclic units, 1,2-cyclohexane units of the following formula:

[0048] The cyclic units result from a particular insertion of the ethylene and 1,3-butadiene monomers into the polymer chain, in addition to the conventional ethylene and 1,3-butadiene units, respectively -(CH2-CH2)-, -(CH2-CH=CH-CH2)- and -(CH2-CH(C=CH2))-. The mechanism for obtaining such a microstructure is for example described in the document Macromolecules 2009, 42, 3774-3779. When the polymer in accordance with the invention contains 1,2-cyclohexane units, it preferably contains at most 15 mol% thereof, the percentage being expressed relative to all the repeating units constituting the polymer.

[0049] The polymerization can be stopped by cooling the polymerization medium or by adding an alcohol, preferably an alcohol containing 1 to 3 carbon atoms, for example ethanol or methanol. The polymer can be recovered using conventional techniques known to those skilled in the art, such as precipitation, evaporation of the solvent under reduced pressure or steam stripping.

[0050] In summary, the invention is advantageously implemented according to any one of the following embodiments 1 to 22.

[0051] Method 1: Process for the preparation of a polymer which comprises the following steps: a) the preparation of a catalytic system comprising a metallocene of formula (Ia) and a co-catalyst,

[0052] P(Cp 1 CP 2 )Nd(BH4)(i + y)-Ly-N x (there)

[0053] CP 1 and Cp 2, identical or different, being chosen from the group consisting of fluorenyl groups, cyclopentadienyl groups and indenyl groups, the groups being substituted or unsubstituted,

[0054] P being a group bridging the two Cp groups 1 and Cp 2 , and comprising a silicon or carbon atom,

[0055] L representing an alkali metal chosen from the group consisting of lithium, sodium and potassium,

[0056] N representing a molecule of an ether, x, an integer or not, being equal to or greater than 0, y, an integer, being equal to or greater than 0, the co-catalyst being a dialkylmagnesium of formula (IIa) in which the alkyls, identical or different, are primary alkyls,

[0057] R2Mg (Ha) b) the polymerization of a monomer chosen from ethylene and a monomer mixture containing ethylene and a 1,3-diene in the presence of the catalytic system and an additional compound, a dialkylmagnesium of formula (Ilia),

[0058] R B -Mg-R L (Ilia) in which R B is a secondary alkyl of formula R'2CH and R L is a primary alkyl of formula R'CFb, the R's, identical or different, being alkyls.

[0059] Mode 2: Method according to mode 1 in which R L is a linear alkyl.

[0060] Mode 3: Method according to mode 1 or 2 in which R B is an alkyl of formula R''CH2CHR”, the R's, identical or different, being alkyls.

[0061] Mode 4: Method according to any one of modes 1 to 3 in which R L is n-butyl.

[0062] Mode 5: Method according to any one of modes 1 to 4 in which R Bis sec-butyl.

[0063] Method 6: Process according to any one of methods 1 to 5 in which the alkyls represented by the symbols R in the formula (Ha) are linear alkyls.

[0064] Mode 7: Process according to any one of modes 1 to 6 in which the co-catalyst is butyloctylmagnesium.

[0065] Mode 8: Method according to any one of modes 1 to 7 in which Cp 1 and Cp 2 are selected from the group consisting of substituted fluorenyl groups and the unsubstituted fluorenyl group of formula C11H3. Method 9: Method according to any one of methods 1 to 8 in which Cp 1 and Cp 2 each represent an unsubstituted fluorenyl group of formula CisHs.

[0066] Mode 10: Method according to any one of modes 1 to 9 in which the bridge P corresponds to the formula ZR 1 R 2 , Z representing a silicon or carbon atom, R 1 and R2 , identical or different, each representing an alkyl group comprising from 1 to 20 carbon atoms.

[0067] Mode 11: Method according to any one of modes 1 to 10 in which the bridge P corresponds to the formula ZR 1 R 2 , Z representing a silicon or carbon atom, R 1 and R 2 , identical or different, each representing a methyl.

[0068] Method 12: Process according to any one of methods 1 to 11 in which the metallocene is of formula (1-1), (1-2), (1-3), (1-4) or (1-5): [Me2Si(Flu)2Nd(p-BH4)2Li(THF)] (1-1) [{Me2SiFlu2Nd(p-BH4)2Li(THF)}2] (1-2) [Me2SiFlu2Nd(p-BH4)(THF)] (1-3) [{Me2SiFlu2Nd(p-BH4)(THF)}2] (1-4) [Me2SiFlu2Nd(p-BH4)] (1-5) Flu representing the CisHs group.

[0069] Mode 13: Process according to any one of modes 1 to 12 in which the ratio between the number of moles of Mg of the co-catalyst and the number of moles of neodymium of the metallocene in step a) ranges from 1 to 100.

[0070] Mode 14: Process according to any one of modes 1 to 13 in which the ratio between the number of moles of Mg of the co-catalyst and the number of moles of neodymium of the metallocene in step a) ranges from 1 to less than 10.

[0071] Method 15: Process according to any one of methods 1 to 14 in which a second additional compound which is a dialkylmagnesium of formula (Ha) is added in step b) according to a molar ratio between the quantity of the second additional compound and the total quantity of the second additional compound and the dialkylmagnesium of formula (Ilia) varying in a range from 0 to less than 1 and the ratio between the total number of moles of the dialkylmagnesium of formula (Ilia) and of the second additional compound and the number of moles of Nd of the catalytic system is less than 500.

[0072] Method 16: Process according to any one of methods 1 to 15 in which a second additional compound which is a dialkylmagnesium of formula (Ha) is added in step b) according to a molar ratio between the quantity of the second additional compound and the total quantity of the second additional compound and the dialkylmagnesium of formula (Ilia) varying in a range from 0 to less than 1 and the ratio between the total number of moles of the dialkylmagnesium of formula (II la) and of the second additional compound and the number of moles of Nd of the catalytic system is or less than 300.

[0073] Method 17: Process according to any one of methods 1 to 16 in which a second additional compound which is a dialkylmagnesium of formula (Ha) is added in step b) according to a molar ratio between the quantity of the second additional compound and the total quantity of the second additional compound and the dialkylmagnesium of formula (Ilia) varying in a range from 0 to less than 1 and the ratio between the total number of moles of the dialkylmagnesium of formula (Ilia) and of the second additional compound and the number of moles of Nd of the catalytic system is less than 100.

[0074] Mode 18: A process according to any one of modes 1 to 17, wherein the catalyst system contains a pre-forming monomer selected from ethylene, a 1,3-diene and a mixture of ethylene and a 1,3-diene.

[0075] Mode 19: A process according to any one of modes 1 to 18, wherein the catalyst system contains a pre-forming monomer, the pre-forming monomer being a

[0076] 1,3-diene.

[0077] Mode 20: A process according to any one of modes 1 to 19, wherein the catalyst system contains a pre-forming monomer, the pre-forming monomer being the

[0078] 1.3-butadiene.

[0079] Mode 21: Process according to any one of modes 1 to 20 in which the monomer mixture containing ethylene and a 1,3-diene is a mixture of ethylene and 1,3-diene.

[0080] Mode 22: A process according to any one of modes 1 to 21 wherein the 1,3-diene of the monomer mixture containing ethylene and a 1,3-diene is 1,3-butadiene, isoprene, myrcene, p-farnesene or mixtures thereof.

[0081] The above-mentioned characteristics of the present invention, as well as others, will be better understood upon reading the following description of the exemplary embodiments of the invention, given for illustrative and non-limiting purposes.

[0082] Examples

[0083] Size exclusion chromatography (SEC / RI):

[0084] Size exclusion chromatography (SEC) allows the fractionation of polymer chains in a solvent according to their hydrodynamic volume. Like any chromatographic system, the technique is based on the elution of a solute (the polymer) through a column containing a stationary phase. The system is composed in this order: a solvent reservoir, a pumping system, an injector, a set of columns and detectors. The measurement chain is equipped with a Waters Alliance e2695 module and a Waters f RI410 refractometer.

[0085] The mobile phase is eluted with a flow rate of 1 mL / min. The polymer is solubilized in THF at a concentration of 1 g / L, then stirred for at least 2 h and filtered at 0.45 µm. A volume of 100 pL is injected through a set of 3 AGILENT size exclusion chromatography columns (MIXED B LS). The columns are thermostated in an oven at 35°C. The stationary phase of the columns is based on a polystyrene divinylbenzene gel with controlled porosity. The polymer chains are separated according to the hydrodynamic volume they occupy when solubilized in the solvent. The larger the volume they occupy, the less accessible the pores of the columns are and the shorter their elution time. Detection is ensured by a refractometer (RI) thermostated at 35°C. Each elution volume is associated with a mass via Moore calibration (certified standard passage: standard polystyrenes from Polymer Standard Service (Mainz).The WATERS: EMPOWER software is used for data acquisition and analysis. It is then possible to determine the number-average molar masses (Mn), the mass-average molar masses (Mw) as well as the dispersity (£) or Ip = Mw / Mn).

[0086] Preparation of polymers:

[0087] All reagents are obtained commercially, except for the metallocene which is prepared according to the procedure described in document WO 2007054224. Butyloctylmagnesium BOMAG (20% in heptane, C = 0.88 mol.L -1 ) is sourced from Chemtura and transferred to and stored in a Steinie bottle under an inert atmosphere. n-butylsecbutylmagnesium (NSBM) (20% in heptane, C = 0.88 mol.L -1) comes from Chemtura and is transferred and stored in a Steinie bottle under an inert atmosphere. The ethylene, N35 grade, comes from Air Liquide and is used without prior purification. The 1,3-butadiene is purified on alumina guards.

[0088] The catalytic system is a preformed catalytic system. It is prepared in methylcyclohexane from a metallocene, [Me2Si(Flu)2Nd(p-BH4)2Li(THF)] at 0.0065 mol / L, a co-catalyst, the organomagnesium compound BOMAG, with a Mg / Nd molar ratio equal to 2.2, and a preforming monomer, 1,3-butadiene with a 1,3-butadiene / Nd molar ratio equal to 90. The medium is heated to 80°C for a period of 5 hours. It is prepared according to a preparation method in accordance with paragraph 11.1 of patent application WO 2017093654 A1.

[0089] All ethylene and 1,3-butadiene polymerization reactions are carried out in a 500 mL glass reactor equipped with a stainless steel stirring blade. Temperature control is ensured by a thermostatically controlled oil bath connected to a double glass jacket. This reactor has all the necessary inlets and outlets for handling.

[0090] Statistical copolymers of ethylene and 1,3-butadiene are synthesized according to the procedure described below.

[0091] The additional organomagnesium compound is introduced into a 750 mL Steinie bottle containing 300 mL (231 g) of methylcyclohexane previously degassed with nitrogen. 7.9 mL (47 pmol in neodymium) of the preformed catalyst system is added to the bottle. The contents of the bottle are introduced into the polymerization reactor, previously inerted under nitrogen flushing and preheated to 80 °C. When the reactor temperature reaches 79 °C, the reactor pressure is reduced to 0.5 bar and then a gaseous mixture of ethylene and 1,3-butadiene (80 / 20 mol%) is injected into the reactor. The polymerization reaction proceeds at a constant pressure of 4 bar. When the desired monomer conversion is reached, the reactor contents are degassed. The polymer is antioxidized and then dried at 60 °C under vacuum to constant mass.

[0092] In Example 1, the additional organomagnesium compound is BOMAG. BOMAG, being a dialkymagnesium whose 2 alkyls are primary alkyls, is not an organomagnesium of formula (IIIa). In Examples 2 and 3, the additional organomagnesium compound is NSBM which satisfies formula (IIIa): Examples 2 and 3 are in accordance with the invention. In Examples 4 to 6, the additional organomagnesium compound is a mixture of NSBM and BOMAG: Examples 4 to 6 are also in accordance with the invention.

[0093] The quantities of the additional compounds BOMAG and NSBM are shown in Table 1 and are expressed as Mg content relative to the Nd content of the catalytic system. The quantities used of the catalytic system and expressed as Nd content are also shown in Table 1, as well as the polymerization results (polymerization time, mass of EBR polymer produced, its Mn, its Ip).

[0094] Table 1:

[0095] Comparing Examples 1 and 2 shows that a much higher Mn is obtained when NSBM is used instead of BOMAG for a nearly identical Mg content. Example 3 confirms that it is indeed necessary to add more NSBM than BOMAG to obtain an Mn that tends to approach that obtained with BOMAG. Higher Mg levels are required with an additional compound of formula (Ilia) than with BOMAG. In other words, to obtain a given Mn value, a higher ratio between the amount of Mg in the additional compound and the amount of Nd in the catalytic system is required when an additional compound of formula (Ilia) is used instead of BOMAG.Since the presence of impurities in a polymerization plant has the effect of varying the ratio between the amount of Mg in the additional compound and the amount of Nd in the catalytic system, the impact of a variation in the level of impurities on this ratio is lower the higher this ratio is. It follows that the polymerization process will be less sensitive to a variation in the level of impurities in the control of Mn with the use of an additional dialkylmagnesium compound of formula (I11a) such as NSBM rather than with the use of an additional dialkylmagnesium compound whose alkyls are both primary alkyls such as BOMAG.

[0096] When in Examples 4 to 6 a mixture of NSBM and BOMAG is used as the additional compound instead of BOMAG alone, almost the same Mn value is obtained even though the ratio between the amount of Mg in the additional compound and the amount of Nd in the catalytic system varies from 3.2 to 4.2, a variation of approximately 30%. These results also show that even though the Mg content varies to a certain extent, the Mn value is relatively little modified. The person skilled in the art then understands that fluctuations in the level of impurities in a polymerization installation have little impact on the Mn value. In summary, by using a dialkylmagnesium of formula (IIIa) as an additional compound in the polymerization medium, the polymerization process is made less sensitive to variations in impurities in a polymerization installation in the control of Mn values.

Claims

Claims 1. A process for preparing a polymer which comprises the following steps: a) preparing a catalytic system comprising a metallocene of formula (Ia) and a co-catalyst, P(Cp 1 CP 2 )Nd(BH4)(i + y)-Ly-N x (there) CP 1 and Cp 2 , identical or different, being chosen from the group consisting of fluorenyl groups, cyclopentadienyl groups and indenyl groups, the groups being substituted or unsubstituted, P being a group bridging the two Cp groups 1 and Cp 2 , and comprising a silicon or carbon atom, L representing an alkali metal chosen from the group consisting of lithium, sodium and potassium, N representing a molecule of an ether, x, an integer or not, being equal to or greater than 0, y, an integer, being equal to or greater than 0, the co-catalyst being a dialkylmagnesium of formula (IIa) in which the alkyls, identical or different, are primary alkyls, R2Mg (Ha) b) the polymerization of a monomer chosen from ethylene and a monomer mixture containing ethylene and a 1,3-diene in the presence of the catalytic system and an additional compound, a dialkylmagnesium of formula (Ilia), R B -Mg-R L (Ilia) in which R B is a secondary alkyl of formula R'2CH and R L is a primary alkyl of formula R'CH2, the R's, identical or different, being alkyls.

2. Method according to claim 1 in which R L is a linear alkyl.

3. Method according to claim 1 or 2 in which R Bis an alkyl of formula R"CH2CHR", the R'', identical or different, being alkyls.

4. Method according to any one of claims 1 to 3 in which R L is n-butyl.

5. Method according to any one of claims 1 to 4 in which R B is sec-butyl.

6. Process according to any one of claims 1 to 5 in which the alkyls represented by the symbols R in the formula (Ha) are linear alkyls.

7. Process according to any one of claims 1 to 6 in which the co-catalyst is butyloctylmagnesium.

8. Method according to any one of claims 1 to 7 in which Cp 1 and Cp 2 are selected from the group consisting of substituted fluorenyl groups and unsubstituted fluorenyl group of formula C11H5S, preferably each represent an unsubstituted fluorenyl group of formula C11H5S.

9. Method according to any one of claims 1 to 8 in which the bridge P corresponds to the formula ZR 1 R 2 , Z representing a silicon or carbon atom, R 1 and R 2 , identical or different, each representing an alkyl group comprising from 1 to 20 carbon atoms, preferably a methyl.

10. Process according to any one of claims 1 to 9 in which the metallocene is of formula (1-1), (1-2), (1-3), (1-4) or (1-5): [Me2Si(Flu)2Nd(p-BH4)2Li(THF)] (1-1) [{Me2SiFlu2Nd(p-BH4)2Li(THF)}2] (1-2) [Me2SiFlu2Nd(p-BH4)(THF)] (1-3) [{Me2SiFlu2Nd(p-BH4)(THF)}2] (1-4) [Me2SiFlu2Nd(p-BH4)] (1-5) Flu representing the CisHs group.

11. Process according to any one of claims 1 to 10 in which the ratio between the number of moles of Mg of the co-catalyst and the number of moles of neodymium of the metallocene in step a) ranges from 1 to 100, preferably from 1 to less than 10.

12. Process according to any one of claims 1 to 11 in which a second additional compound which is a dialkylmagnesium of formula (Ha) is added in step b) according to a molar ratio between the quantity of the second additional compound and the total quantity of the second additional compound and the dialkylmagnesium of formula (Ilia) varying in a range from 0 to less than 1 and the ratio between the total number of moles of the dialkylmagnesium of formula (Ilia) and the second additional compound and the number of moles of Nd of the catalytic system is less than 500 or less than 300 or less than 100.

13. Process according to any one of claims 1 to 12, in which the catalytic system contains a pre-formation monomer chosen from ethylene, a 1,3-diene and a mixture of ethylene and a 1,3-diene, the pre-formation monomer preferably being a 1,3-diene, more preferably 1,3-butadiene.

14. A process according to any one of claims 1 to 13 wherein the monomer mixture containing ethylene and a 1,3-diene is a mixture of ethylene and 1,3-diene.

15. A process according to any one of claims 1 to 14 wherein the 1,3-diene of the monomer mixture containing ethylene and a 1,3-diene is 1,3-butadiene, isoprene, myrcene, -farnesene or mixtures thereof.

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