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

Abstract

The invention relates to a process for preparing a polymer comprising the preparation of a catalytic system including neodymocene borohydride and a dialkylmagnesium cocatalyst wherein the alkyls are primary alkyls, followed by the polymerization of a monomer selected from ethylene and a monomer mixture containing ethylene and a 1,3-diene in the presence of the catalytic system and an additive, a dialkylmagnesium of formula RB-Mg-RL, wherein RB is a secondary alkyl of formula R'2CH and RL is a primary alkyl of formula R'CH2, the R's being alkyls. The process is made less sensitive to variations in impurities in a polymerization plant in controlling the number-average molar masses.

Description

Title of the invention: Process for preparing a polyethylene or a copolymer of ethylene and 1,3-diene.

[0001] The field of the invention is that of processes for the polymerization of ethylene or for the copolymerization of ethylene and a 1,3-diene in the presence of catalytic systems which are based on rare earth metallocene.

[0002] The Applicant has described processes for the polymerization of ethylene and the copolymerization of ethylene and a 1,3-diene in the presence of catalytic systems based on neodymocene borohydride and a co-catalyst, for example in patent applications EP 1 092 731, 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 of the number of moles of magnesium to the number of moles of neodymium present in the polymerization medium allows the number-average molar mass, Mn, of the polymer to be synthesized to be defined, and that the lower this molar ratio, the higher the target Mn. Furthermore, the very high reactivity of organometallic compounds with oxygen, carbon dioxide and water is also known.Even when the polymerization reactor is cleaned, placed under an inert atmosphere, and the solvents and monomers are purified, impurities such as water, carbon dioxide, and oxygen can still be present in the polymerization reactor containing the polymerization solvent and monomers. These impurities can react with the organomagnesium compound upon its introduction, altering the Mg / Nd molar ratio, the ratio between the number of moles of organomagnesium compound and the number of moles of Nd. For a given neodymium concentration, the variation in the Mg / Nd molar ratio with the impurity concentration is greater when this molar ratio is low. This can lead to less precise control of the process in achieving the target Mn concentration of the polymer being synthesized. Therefore, there is a need to address this difficulty.

[0003] The Applicant, continuing its efforts, has developed a new process for preparing polyethylene and ethylene-1,3-diene copolymer which differs from known processes by the introduction into the polymerization medium of a specific additive, a dialkylmagnesium compound in which one of the two alkyl groups is a secondary alkyl and the other a primary alkyl. It turns out that the process is less sensitive to variations in impurities in a polymerization plant in controlling the Mn values.

[0004] 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 (la) and a co-catalyst, P(Cp1Cp2)Nd(BH4)(1+y>Ly-Nx (la) Cp1 and Cp2, identical or different, being chosen from the group consisting of fluorenyl groups, cyclopentadienyl groups and indenyl groups, the groups being substituted or unsubstituted, Pending a group bridging the two groups Cp1 and Cp2, and comprising a silicon or carbon atom, L represents 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 dialkylmagnesian of formula (lia) in which the alkyls, identical or different, are primary alkyls, R2Mg (Ha) b) the polymerization of a monomer selected from ethylene and a monomer mixture containing ethylene and a 1,3-diene in the presence of the catalytic system and an additive, a dialkylmagnesian of formula (Ilia), RB-Mg-RL (Ilia) in which RB is a secondary alkyl of formula R'2CH and RL is a primary alkyl of formula R'CH2, the R's, whether identical or different, being alkyls. Detailed description

[0005] 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., bounds a and b excluded) 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 bounds a and b).

[0006] The compounds mentioned in the description may be of fossil origin or bio-based. 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 used, 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.

[0007] 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.

[0008] In the present application, metallocene means an organometallic complex in which the metal, in this case the neodymium atom, is linked to a ligand molecule consisting of two Cp1 and Cp2 groups linked together by a P bridge.

[0009] In the formula (la) of the metallocene useful for the purposes of the invention, the Cp1 and Cp2 groups, whether identical or different, are chosen from the group consisting of fluorenyl groups, cyclopentadienyl groups, and indenyl groups, these groups being either substituted or unsubstituted. Examples of substituted cyclopentadienyl, fluorenyl, and indenyl groups include those substituted by alkyl radicals having 1 to 6 carbon atoms, by aryl radicals having 6 to 12 carbon atoms, or by trialkylsilyl radicals such as SiMe3. The choice of radicals is also guided by the accessibility of the corresponding molecules, namely the substituted cyclopentadienes, fluorenes, and indenes, because these are either commercially available or easily synthesized.

[0010] Examples of substituted fluorenyl groups include those substituted at positions 2,7, 3, or 6, particularly 2,7-ditertiobutyl-fluorenyl and 3,6-ditertiobutyl-fluorenyl. Positions 2, 3, 6, and 7 respectively designate the positions of the carbon atoms in the rings, as shown in the diagram below, with position 9 corresponding to the carbon atom to which the P-bridge is attached. P

[0011] Examples of substituted cyclopentadienyl groups include those substituted at position 2 (or 5) as well as at position 3 (or 4), particularly those substituted at position 2, more specifically the tetramethylcyclopentadienyl group. Position 2 (or 5) refers to the position of the carbon atom adjacent to the carbon atom to which the P-bridge is attached, as shown in the diagram below. P

[0012] By way of substituted indenyl groups, particular examples may be given to those substituted in position 2, more specifically 2-methylindenyl, 2-phenylindenyl. Position 2 designates the position of the carbon atom that is adjacent to the carbon atom to which the P-bridge is attached, as shown in the diagram below.

[0013] Preferably, Cp1 and Cp2 are identical.

[0014] Preferably, Cp1 and Cp2 are chosen from the group consisting of substituted fluorenyl groups and the unsubstituted fluorenyl group of formula Ci3H8.

[0015] More preferably, Cp1 and Cp2 are identical and are chosen from the group consisting of substituted fluorenyl groups and the unsubstituted fluorenyl group of formula CnH8. Advantageously, Cp1 and Cp2 are identical and each represent an unsubstituted fluorenyl group of formula CnH8, represented by the symbol Flu.

[0016] Any ether that has the ability to complex the alkali metal is suitable, in particular diethyl ether and tetrahydrofuran. In formula (la), y can be equal to 0 or 1 and x can be equal to 0, 1 or 2.

[0017] The bridge P connecting the Cp1 and Cp2 groups and comprising a silicon or carbon atom preferably conforms to the formula ZR'R2, in which Z represents a silicon or carbon atom, and R1 and R2, identical or different, each represent an alkyl group comprising from 1 to 20 carbon atoms, preferably a methyl group. In the formula ZR'R2, Z advantageously represents a silicon atom, Si, according to any one of the embodiments of the invention.

[0018] The metallocene useful for the synthesis of the catalytic system may be in the form of a crystalline or non-crystalline powder, or in the form of single crystals. The metallocene may be in monomeric or dimeric form, these forms depending on the method of preparation of the metallocene, as described, for example, in patent applications WO 2007054224 or WO 2007054223. The metallocene may be prepared in a traditional manner by a process analogous to that described in patent applications WO 2007054224 or WO 2007054223, in particular by reacting, under inert and anhydrous conditions, the salt of an alkali metal of the ligand with a rare-earth borohydride in a suitable solvent, such as an ether, like diethyl ether or tetrahydrofuran, or any other solvent known to those skilled in the art. After the reaction, the metallocene is separated from the reaction by-products using known techniques. The expert uses methods such as filtration or precipitation in a second solvent. The metallocene is then dried and isolated in solid form.

[0019] According to a particularly preferred embodiment, the metallocene has the 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) where Flu represents the CnH8 group.

[0020] The catalytic system also has as another essential constituent a co-catalyst which is a dialkylmagnesium compound of formula (lia), R2Mg (lia) in which the Rs, identical or different, are primary alkyls.

[0021] Preferably, the alkyls represented by the symbols R in formula (lia) are linear alkyls. More preferably, the co-catalyst is butyloctyl-magnesium.

[0022] Magnesium dialkyl compounds of formula (lia) are well-known organometallic reagents, some of which are even commercial products. For their synthesis, one can, for example, refer to the collection of volumes of "Organic Synthesis". Like all organomagnesium compounds, the magnesium dialkyl compound constituting the catalytic system can be in the form of a monomeric entity or in the form of a polymer entity. By way of illustration, the magnesium dialkyl compound can be in the form of a monomeric entity (R-Mg-R)i or in the form of a polymer entity (R-Mg-R)p, p being an integer greater than 1, for example, the dimer (R-Mg-R)2, m being as defined previously.Furthermore, whether in the form of a monomeric or polymeric entity, the organomagnesium compound can also be presented as an entity coordinated to one or more molecules of a solvent, preferably an ether such as diethyl ether, tetrahydrofuran or methyltetrahydrofuran.

[0023] The catalytic system according to the invention can be prepared conventionally by a process analogous to that described in patent application WO 2007054224 or WO 2007054223, with a dialkylmagnesium compound of formula (lia) as the 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 The number of moles of Mg in the co-catalyst and the number of moles of neodymium in the metallocene preferably range from 1 to 100, more preferably from 1 to less than 10. The range of values ​​from 1 to less than 10 is particularly more favorable for obtaining polymers with high molar masses.

[0024] 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 according to the invention. The catalytic system is typically in the form of a catalytic solution, that is to say, in a solvent which is preferably the solvent in which it was prepared, and the metal concentration of the catalytic solution, that is to say, rare earth metallocene, is then in the range preferably from 0.0001 to 0.2 mol L⁻¹, more preferably from 0.001 to 0.03 mol L⁻¹.

[0025] According to a particularly preferred embodiment, the catalytic system contains a preforming monomer selected from ethylene, a 1,3-diene, and a mixture of ethylene and a 1,3-diene. The 1,3-diene as the preforming monomer may be 1,3-butadiene, isoprene, or a 1,3-diene of the formula CH2=CR6-CH=CH2, the symbol R6 representing a hydrocarbon group having 3 to 20 carbon atoms, in particular myrcene or 3-farnesene. The preforming monomer is preferably a 1,3-diene, more preferably 1,3-butadiene.The so-called preformed catalytic system is typically prepared by a process analogous to that described in patent application WO 2017093654 Al or in patent application WO 2018020122 AL. For example, the co-catalyst and the metallocene are typically reacted in a hydrocarbon solvent 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 preforming monomer is reacted at a temperature of 40 to 90°C for 1 to 12 hours. The preforming monomer is preferably used with a molar ratio (preforming monomer / metal of the metallocene) of 5 to 1000, preferably 10 to 500. Before its use in polymerization, the preformed type catalytic system can be stored under an inert atmosphere, in particular at a temperature ranging from -20°C to room temperature (23°C).The preformed 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.

[0026] As with any synthesis carried out in the presence of an organometallic compound, the synthesis of the catalytic system takes place under anhydrous conditions in an inert atmosphere. Typically, the reactions are conducted using solvents and anhydrous compounds. under nitrogen or anhydrous argon.

[0027] Once the catalytic system has been prepared, it is used in step b) as an initiator for the polymerization reaction of a monomer, monomer M, selected 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%, and 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, and more advantageously 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, 3-farnesene or mixtures thereof, more preferably 1,3-butadiene.

[0028] In step b) an additive is used which is a dialkylmagnesian of formula (Ilia), RB-Mg-RL (Ilia) in which RB is a secondary alkyl of formula R'2CH and RL is a primary alkyl of formula R'CH2, the R's, identical or different, being alkyls. In other words, the dialkylmagnesium compound with formula (Ilia) has the structural formula R'2CHMgCH2R'. Alkyl groups represented by the symbols R' can contain 1 to 10 carbon atoms. RL is preferentially a linear alkyl, more preferably a linear alkyl having 2 to 8 carbon atoms. RL is even more preferably n-butyl with the formula CH3CH2CH2CH2-, RB is preferably an alkyl group with the formula R”CH2CHR”, the R” groups, whether identical or different, being alkyl groups. The alkyl group of R” preferably has 1 to 10 carbon atoms, and the alkyl group of R” preferentially has 1 to 9 carbon atoms. Advantageously, RB is a sec-butyl group with the formula CH3CH2CH(CH3)-.

[0029] 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) that differ from one another 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) designates a single compound of formula (Ilia) (in English, "one").

[0030] According to a particularly preferred embodiment of the invention, the dialkylmagnesian of formula (Ilia) has the formula RB-Mg-RL in which RB is sec-butyl and RL is n-butyl, or has the developed formula CH3CH2CH(CH3)MgCH2CH2CH2 CH3.

[0031] The dialkylmagnesium compound of formula (Ilia) is used in the polymerization medium as an additive to improve control of the polymerization process by regulating the Mn content of the polymers to be synthesized. It has been found that the use of this additive makes the process less sensitive to variations in impurities within a polymerization plant, thus controlling the Mn values. The additive can be introduced into a reactor before the addition of the catalytic system or simultaneously with the addition of the reactor containing a polymerization solvent.

[0032] In step b), a second additive may be added, which second additive is a dialkylmagnesium compound of formula (Ilia). The second additive of formula (Ilia) is preferably the same dialkylmagnesium compound as that of the catalytic system. The second additive is generally introduced before the additive of formula (Ilia). When a second dialkylmagnesium compound of formula (Ilia) is added, its quantity can vary considerably. The molar ratio between the quantity of the second additive and the total quantity of the second additive and the dialkylmagnesium compound of formula (Ilia) typically varies in the range of 0 to less than 1. According to any one embodiment of the invention, the molar ratio between the quantity of the second additive and the total quantity of the second additive and the dialkylmagnesium compound of formula (Ilia) preferably varies from 0 to less than 0.95.

[0033] The total amount of additive of formula (Ilia) and, where applicable, of additive of formula (lia) introduced in step b), which is generally indexed to the amount of neodymium, can vary considerably and is adjusted by those skilled in the art according to the polymerization conditions. Preferably, the ratio between the total number of moles of the dialkylmagnesium compound of formula (Ilia) and the second additive and the number of moles of Nd in the catalytic system is less than 500, less than 300, or less than 100. Larger ratios are preferable under high polymerization temperature or pressure conditions; smaller ratios are preferable under lower polymerization temperature or pressure conditions.

[0034] Polymerization is preferably carried out in solution, either continuously or batchwise. The polymerization solvent is typically a hydrocarbon solvent, preferably aliphatic. Methylcyclohexane is a particularly suitable example of an aliphatic hydrocarbon solvent. 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, particularly in the case of continuous polymerization. Polymerization is typically carried out under anhydrous conditions and in the absence of oxygen, possibly in the presence of an inert gas. The temperature The polymerization temperature generally varies in a range of 40 to 150°C, preferably 40 to 120°C. A person skilled in the art adapts the polymerization conditions such as the polymerization temperature, the concentration of each of the reactants, the reactor pressure, to the desired microstructure and macrostructure of the polymer.

[0035] Polymerization is preferably carried out at constant monomer pressure, particularly 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 made in the polymerization reactor, in which case the polymerization reactor is a fed reactor. This embodiment is particularly suitable for the statistical incorporation of monomers.

[0036] According to a preferred embodiment of the invention, the prepared polymer is a copolymer of ethylene and 1,3-butadiene, preferably a statistical copolymer of ethylene and 1,3-butadiene.

[0037] 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 Cp1 and Cp2 are each an unsubstituted fluorenyl group of formula Ci3H8, 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: 0¾—CHg \. Y CH— CH f Y

[0038] The cyclic units result from a specific insertion of 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 described, for example, in Macromolecules 2009, 42, 3774-3779. When the polymer according to the invention contains 1,2-cyclohexane units, it preferably contains at most 15% by mole, the percentage being expressed relative to all the repeating units constituting the polymer.

[0039] 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 by pre precipitation, by evaporation of the solvent under reduced pressure or by steam stripping.

[0040] In summary, the invention is advantageously implemented according to any one of the following embodiments 1 to 22.

[0041] Mode 1: A process for preparing a polymer comprising the following steps: a) the preparation of a catalytic system comprising a metallocene of formula (la) and a co-catalyst, P(Cp1Cp2)Nd(BH4)(1+y)_Ly-Nx (la) Cp1 and Cp2, identical or different, being chosen from the group consisting of fluorenyl groups, cyclopentadienyl groups and indenyl groups, the groups being substituted or unsubstituted, Pending a group bridging the two groups Cp1 and Cp2, and comprising a silicon or carbon atom, L represents an alkali metal chosen from the group consisting of lithium, sodium, and potassium, N representing a molecule of an ether, x, whether 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 compound of formula (lia) in which the alkyls, whether identical or different, are primary alkyls, R2Mg (lia) b) the polymerization of a monomer selected from ethylene and a monomer mixture containing ethylene and a 1,3-diene in the presence of the catalytic system and an additive, a dialkylmagnesian of formula (Ilia), RB-Mg-RL (Ilia) in which RB is a secondary alkyl of formula R'2CH and RL is a primary alkyl of formula R'CH2, the R's, identical or different, being alkyls.

[0042] Mode 2: Process according to mode 1 in which RL is a linear alkyl.

[0043] Mode 3: A process according to mode 1 or 2 in which RB is an alkyl of formula R”CH2CHR”, the R”, identical or different, being alkyls.

[0044] Mode 4: Process according to any one of modes 1 to 3 in which RL is n-butyl.

[0045] Mode 5: Method according to any one of modes 1 to 4 in which RB is sec- butyl.

[0046] Mode 6: A process according to any one of modes 1 to 5 in which the alkyls represented by the symbols R in formula (lia) are linear alkyls.

[0047] Mode 7: Process according to any one of modes 1 to 6 in which the co-catalyst is butylctylmagnesium.

[0048] Mode 8: A method according to any one of modes 1 to 7 in which Cp1 and Cp2 are chosen from the group consisting of substituted fluorenyl groups and the unsubstituted fluorenyl group of formula CnH8.

[0049] Mode 9: A method according to any one of modes 1 to 8 in which Cp1 and Cp2 each represent an unsubstituted fluorenyl group of formula CnH8.

[0050] Mode 10: Method according to any one of modes 1 to 9 in which the bridge P corresponds to the formula ZR'R2, Z representing a silicon or carbon atom, R1 and R2, identical or different, each representing an alkyl group comprising from 1 to 20 carbon atoms.

[0051] Mode 11: Method according to any one of modes 1 to 10 in which the bridge P corresponds to the formula ZR'R2, Z representing a silicon or carbon atom, R1 and R2, identical or different, each representing a methyl.

[0052] Mode 12: Process according to any one of modes 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)] (I-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 Ci3H8 group.

[0053] Mode 13: A 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) goes from 1 to 100.

[0054] Mode 14: A 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) is from 1 to less than 10.

[0055] Mode 15: A process according to any one of modes 1 to 14 in which a second additive, which is a dialkylmagnesian of formula (Ilia), is added in step b) in a molar ratio between the amount of the second additive and the total amount of the second additive and the dialkylmagnesian of formula (Ilia) varying in a range from 0 to less than 1 and the ratio between the total number of moles of the dialkylmagnesian of formula (Ilia) and the second additive and the number of moles of Nd in the catalytic system is less than 500.

[0056] Mode 16: A process according to any one of modes 1 to 15 in which a second additive, which is a dialkylmagnesium compound of formula (Ilia), is added in step b) in a molar ratio between the amount of the second additive and the total amount of the second additive and the dialkylmagnesium compound of formula (Ilia) varying in the range of 0 to less than 1, and the ratio between the total number of moles of the dialkylmagnesium compound of formula (Ilia) and the second additive and the number of moles of Nd in the catalytic system is or less than 300.

[0057] Mode 17: A process according to any one of modes 1 to 16 in which a second additive, which is a dialkylmagnesian of formula (Ilia), is added in step b) in a molar ratio between the amount of the second additive and the total amount of the second additive and the dialkylmagnesian of formula (Ilia) varying in a range from 0 to less than 1 and the ratio between the total number of moles of the dialkylmagnesian of formula (Ilia) and the second additive and the number of moles of Nd in the catalytic system is less than 100.

[0058] Mode 18: A method according to any one of modes 1 to 17, wherein the catalytic system contains a preforming monomer selected from ethylene, a 1,3-diene and a mixture of ethylene and a 1,3-diene.

[0059] Mode 19: A method according to any one of modes 1 to 18, wherein the catalytic system contains a preforming monomer, the preforming monomer being a 1,3-diene.

[0060] Mode 20: A process according to any one of modes 1 to 19, wherein the catalytic system contains a preforming monomer, the preforming monomer being 1,3-butadiene.

[0061] Mode 21: A 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.

[0062] Mode 22: A process according to any one of modes 1 to 21 in which the 1,3-diene of the monomer mixture containing ethylene and a 1,3-diene is 1,3-butadiene, isoprene, myrcene, [3-famesene or mixtures thereof.

[0063] The aforementioned features of the present invention, as well as others, will be better understood upon reading the following description of examples of embodiments of the invention, given by way of illustration and not limitation. Examples

[0064] Size exclusion chromatography fSEC / RI): 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 consists, in this order, of 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 fRI410 refractometer. The mobile phase is eluted at a flow rate of 1 mL / min. The polymer is solubilized in THF at a concentration of 1 g / L, then stirred for a minimum of 2 h and filtered. A 100 pL volume is injected through a set of three AGELENT size-exclusion chromatography columns (MIXED B LS). The columns are temperature-controlled 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, the less accessible the column pores are to them, and the shorter their elution time. Detection is performed using a refractometer (RI) temperature-controlled at 35°C. Each elution volume is associated with a mass via Moore calibration (certified standard: Polymer Standard Service (Mainz) standard polystyrenes). 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 (D or Ip = Mw / Mn).

[0065] Polymer preparation: All reagents are commercially available, except for metallocene, which is prepared according to the procedure described in document WO 2007054224. Butyl-loctylmagnesium BOMAG (20% in heptane, C = 0.88 mol / L*) is sourced from Chemtura and is transferred and then stored in a Steinie bottle under an inert atmosphere. α-butylsecbutylmagnesium (NSBM) (20% in heptane, C = 0.88 mol / L*) is sourced from Chemtura and is transferred and then stored in a Steinie bottle under an inert atmosphere. The N35 grade ethylene is sourced from Air Liquide and is used without prior purification. 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 cocatalyst, the organomagnesium compound BOMAG, with a Mg / Nd molar ratio of 2.2, and a preforming monomer, 1,3-butadiene, with a 1,3-butadiene / Nd molar ratio of 90. The medium is heated to 80°C for 5 hours. It is prepared according to a method conforming to paragraph II.1 of patent application WO 2017093654 AL

[0066] All the polymerization reactions of ethylene and 1,3-butadiene are carried out in a 500 mL glass reactor equipped with a stainless steel stirring paddle. Temperature control is achieved by means of a thermostatically controlled oil bath connected to a double-walled glass jacket. This reactor has all the necessary inlets and outlets for the experiments.

[0067] Statistical copolymers of ethylene and 1,3-butadiene are synthesized according to the procedure described below.

[0068] The organomagnesium additive is introduced into a 750 mL Steinie bottle containing 300 mL (231 g) of methylcyclohexane that has been previously degassed with nitrogen. 7.9 mL (47 pmol neodymium) of the preformed catalytic system are added to the bottle. The bottle contents are introduced into the polymerization reactor, which has been previously inert under nitrogen purging and preheated to 80 °C. When the reactor temperature reaches 79 °C, the reactor pressure is reduced to 0.5 bar, and 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 conversion to monomers is achieved, the reactor contents are degassed. The polymer is antioxidized and then dried at 60 °C under vacuum to constant mass.

[0069] In Example 1, the organomagnesium additive is BOMAG. Since BOMAG is a dialkymagnesium compound whose two alkyl groups are primary alkyls, it is not an organomagnesium compound of formula (Ilia). In Examples 2 and 3, the organomagnesium additive is NSBM, which conforms to formula (Ilia): Examples 2 and 3 are in accordance with the invention. In Examples 4 to 6, the organomagnesium additive is a mixture of NSBM and BOMAG: Examples 4 to 6 are also in accordance with the invention.

[0070] The quantities of the BOMAG and NSBM additives are shown in Table 1 and are expressed as the Mg content relative to the Nd content of the catalytic system. The quantities of catalytic system used, expressed as the Nd content, are also shown in Table 1, as well as the polymerization results (polymerization time, mass of EBR polymer produced, its Mn content, its Ip content).

[0071] Table 1: Example 1 2 3 4 5 6 Nd (pmol) 46.7 47.9 47.9 46.0 46.0 47.9 BOMAG / Nd 2.8 0 0 2.5 2.1 1.4 NSBM / Nd 0 2.7 5.5 0.7 1.4 2.8 EBR (g) 13.96 13.93 14.15 13.90 14.07 14.26 Mn 33085 57156 42831 31988 34039 32863 IP 1.17 1.13 1.13 1.15 1.14 1.13

[0072] Comparing Examples 1 and 2 highlights that a significantly higher Mn concentration is obtained when NSBM is used instead of BOMAG for a virtually identical Mg concentration. Example 3 confirms that it is indeed necessary to add more NSBM than BOMAG to obtain an Mn concentration that approaches that obtained with BOMAG. Higher Mg concentrations are required with an additive of formula (Ilia) than with BOMAG. In other words, to obtain a Given a given Mn value, a higher ratio of additive Mg to catalytic system Nd is required when an additive of formula (Ilia) is used instead of BOMAG. Since the presence of impurities in a polymerization plant causes the ratio of additive Mg to catalytic system Nd to vary, the higher the ratio, the less significant the impact of a change in impurity levels on this ratio. Consequently, the polymerization process will be less sensitive to changes in impurity levels in Mn control when using a dialkylmagnesium additive of formula (Ilia) such as NSBM than when using a dialkylmagnesium additive in which both alkyl groups are primary alkyls, such as BOMAG.

[0073] When, in Examples 4 to 6, a mixture of NSBM and BOMAG is used as an additive instead of BOMAG alone, virtually the same Mn value is obtained, even though the ratio between the amount of Mg in the additive and the amount of Nd in the catalytic system varies from 3.2 to 4.2, i.e., a variation of approximately 30%. These results also show that even when the Mg content varies to some extent, the Mn value is relatively little affected. Those skilled in the art can therefore understand that fluctuations in the impurity level in a polymerization plant have little impact on the Mn value.

[0074] In summary, by using a dialkylmagnesian of formula (Ilia) as an additive in the polymerization medium, the polymerization process is made less sensitive to variations in impurities of a polymerization installation in the control of Mn values.

Claims

Demands

1. A process for preparing a polymer comprising the following steps: a) the preparation of a catalytic system comprising a metallocene of formula (la) and a co-catalyst, PtCp'CpWH^i^Nx (la) Cp1 and Cp2, identical or different, being selected 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 groups Cp1 and Cp2, and comprising a silicon or carbon atom, L representing an alkali metal selected 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 compound of formula (lia) in which the alkyls, identical or different, are primary alkyls,R2Mg (lia) b) the polymerization of a monomer selected from ethylene and a monomer mixture containing ethylene and a 1,3-diene in the presence of the catalytic system and an additive, a dialkylmagnesium compound of formula (nia), RB-Mg-RL (nia) in which RB is a secondary alkyl of formula R'2CH and RL is a primary alkyl of formula R'CH2, the R's, identical or different, being alkyls.,

2.

3. A method according to claim 1 wherein RL is a linear alkyl. A method according to claim 1 or 2 wherein RB is an alkyl of formula R”CH2CHR”, the R”, identical or different, being alkyls.

4. A method according to any one of claims 1 to 3 wherein RL is n-butyl.

5. A process according to any one of claims 1 to 4 wherein RB is sec-butyl.

6. A method according to any one of claims 1 to 5 wherein the alkyls represented by the symbols R in formula (lia) are linear alkyls.

7. A process according to any one of claims 1 to 6 wherein the co-catalyst is butyloctylmagnesium.

8. A method according to any one of claims 1 to 7 wherein Cp1 and Cp2 are selected from the group consisting of substituted fluorenyl groups and the unsubstituted fluorenyl group of formula CnH8, preferably each representing an unsubstituted fluorenyl group of formula CnH8.

9. A method according to any one of claims 1 to 8 wherein the bridge P corresponds to the formula ZR'R2, Z representing a silicon or carbon atom, R1 and R2, identical or different, each representing an alkyl group comprising from 1 to 20 carbon atoms, preferably a methyl.

10. A process according to any one of claims 1 to 9 wherein the metallocene is of formula (1-1), (1-2), (1-3), (1-4) or (1-5): [Me2Si(Flu)2Nd(p-BH4)2Li(THF)] (I-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 Ci3H8 group.

11. A method according to any one of claims 1 to 10 wherein the ratio of the number of moles of Mg of the co-catalyst to the number of moles of neodymium of the metallocene in step a) is from 1 to 100, preferably from 1 to less than 10.

12. A process according to any one of claims 1 to 11 wherein a second additive which is a dialkylmagnesian of formula (Ilia) is added in step b) in a molar ratio between the amount of the second additive and the total amount of the second additive and the dialkylmagnesian of formula (Ilia) varying in a range from 0 to less than 1 and the ratio between the total number of moles of the dialkylmagnesian of formula (Ilia) and the second additive and the number of moles of Nd of the catalytic system is less than 500 or less than 300 or less than 100.

13. A method according to any one of claims 1 to 12, wherein the catalytic system contains a preforming monomer selected from ethylene, a 1,3-diene and a mixture of ethylene and a 1,3-diene, the preforming monomer being preferably a 1,3-diene, more preferably 1,3-butadiene.

14. A method 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 method 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, 3-farnesene or mixtures thereof.