Catalytic system comprising a metallocene for the synthesis of polyethylene and ethylene-1,3-diene copolymer.

Abstract

The invention relates to a catalytic system based on at least one neodymocene borohydride, a co-catalyst which is a dialkylmagnesium compound of formula RB-Mg-RL, in which RB is a secondary alkyl of formula R2CH and RL is a primary alkyl of formula RCH2, the Rs, identical or different, being alkyls. The catalytic system addresses the objective of improved macrostructure control in a polymerization process of ethylene or a monomer mixture containing ethylene and a 1,3-diene.

Description

Title of the invention: Catalytic system comprising a metallocene for the synthesis of polyethylene and ethylene copolymer and 1,3-diene.

[0001] The field of the invention is that of catalytic systems which are based on rare earth metallocene and which are intended to be used in the polymerization of ethylene or mixtures containing ethylene and a 1,3-diene.

[0002] Rare-earth metallocene-based catalytic systems for polymerizing ethylene and a 1,3-diene are known, for example, from patent applications EP 1 092 731, WO 2004035639, WO 2007054224, and WO 2018224776. The catalytic systems described in these documents are based on a neodymium metallocene and a co-catalyst to activate the metallocene. The co-catalyst is typically an organometallic compound, generally an organomagnesium compound. As with any synthesis carried out in the presence of organometallic compounds, the implementation of the polymerization process requires anhydrous conditions under an inert atmosphere. Even if 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 may be present in the polymerization reactor containing the polymerization solvent and monomers.These impurities can react with the organomagnesium compound upon its introduction into the polymerization reactor, thereby altering the Mg / Nd molar ratio, the ratio between the number of moles of organomagnesium compound and the number of moles of Nd. This Mg / Nd molar ratio is used, in particular, to define the number-average molar mass (Mn) of the polymer to be synthesized. The higher the target Mn, the lower this molar ratio. For a given neodymium content, the variation in the Mg / Nd molar ratio with the impurity content is greater when this molar ratio is low, which can lead to less precise control of the process in achieving the target Mn of the polymer to be synthesized. Therefore, there is a need to address this difficulty.

[0003] The Applicant, continuing its efforts, has developed a new catalytic system that meets this objective of better control of the macrostructure in a polymerization process for ethylene or a monomer mixture containing ethylene and a 1,3-diene. In other words, the catalytic system makes the polymerization process less sensitive to variations in impurities present in the polymerization reactor, which can fluctuate from one batch to another. This objective is achieved by selecting a specific organomagnesium compound as a co-catalyst in a metallocene-based catalytic system. neodymium.

[0004] Thus, a first object of the invention is a catalytic system comprising: a metallocene of formula (la), 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), RB-Mg-RL (lia) in which RB is a secondary alkyl of formula R2CH and RL is a primary alkyl of formula RCH2, the Rs, identical or different, being alkyls.

[0005] Another object of the invention is a process for preparing a polymer which includes a step of polymerizing a monomer M selected from ethylene and a monomer mixture containing ethylene and a 1,3-diene in the presence of a catalytic system according to the invention. Detailed description

[0006] 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).

[0007] 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.

[0008] By the expression "based on" used to define the constituents of the system ca catalytic or catalytic composition, we mean the mixture of these constituents, or the product of the reaction of some or all of these constituents with each other.

[0009] In the present application, the term 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. These Cp1 and Cp2 groups, 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.

[0010] Examples of substituted cyclopentadienyl, fluorenyl, and indenyl groups include those substituted by alkyl radicals having 1 to 6 carbon atoms, or by aryl radicals having 6 to 12 carbon atoms, or by trial-kylsilyl 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.

[0011] 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.

[0012] 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

[0013] As examples of substituted indenyl groups, particular examples include those substituted at position 2, more specifically 2-methylindenyl and 2-phenylindenyl. Position 2 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.

[0014] Preferably, Cp1 and Cp2 are identical.

[0015] Preferably, Cp1 and Cp2 are chosen from the group consisting of substituted fluorenyl groups and the unsubstituted fluorenyl group of formula Ci3H8.

[0016] 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.

[0017] 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.

[0018] The bridge P connecting the Cp1 and Cp2 groups preferably corresponds to the formula ZR'R2, in which Z represents a silicon or carbon atom, R1 and R2, identical or different, each represent an alkyl group comprising from 1 to 20 carbon atoms, preferably a methyl. In the formula ZR'R2, Z advantageously represents a silicon atom, Si.

[0019] 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.

[0020] According to a particularly preferred embodiment, the metallocene has the formula (III-1), (III-2), (III-3), (III-4) or (III-5): [Me2Si(Flu)2Nd(p-BH4)2Li(THF)] (III-1) [{Me2SiFlu2Nd(p-BH4)2Li(THF)}2] (III-2) [Me2SiFlu2Nd(p-BH4)(THF)] (III-3) [{Me2SiFlu2Nd(p-BH4)(THF)}2] (III-4) [Me2SiFlu2Nd(p-BH4)] (III-5) in which Flu represents the Ci3H8 group.

[0021] The catalytic system also has as another essential component an organo-magnesium compound. The organo-magnesium compound is a dialkylmagnesium compound of formula (lia)RB-Mg-RL (lia) in which RB is a secondary alkyl of formula R2CH and RL is a primary alkyl of formula RCH2, the Rs, whether identical or different, being alkyls. In other words, the organo-magnesium compound has the structural formula R2CHMgCH2R. The alkyls represented by the symbols R can contain from 1 to 10 carbon atoms.

[0022] Dialkylmagnesium compounds are well-known organometallic reagents; some are even commercial products. For their synthesis, one can, for example, refer to the collection of volumes in "Organic Synthesis". Like all organomagnesium compounds, the dialkylmagnesium compound constituting the catalytic system can be in the form of a monomer or a polymer. By way of illustration, the dialkylmagnesium compound can be in the form of a monomer (RB-Mg-RL)1 or a polymer (RB-Mg-RL)P, where p is an integer greater than 1, for example, a dimer (RB-Mg-RL)2, where m is 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] RL is preferably 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-,

[0024] RB is preferably an alkyl group with the formula R”CH2CHR', where R' is an alkyl group and R” is a hydrogen atom or an alkyl group. The alkyl group of R' preferably has 1 to 10 carbon atoms, and the alkyl group of R” preferably has 1 to 9 carbon atoms. Advantageously, RB is a sec-butyl group with the formula CH3CH2CH(CH3)-.

[0025] According to a particularly preferred embodiment of the invention, the cocatalyst has the formula RB-Mg-RL in which RB is sec-butyl and RL is n-butyl, or with the developed formula CH3CH2CH(CH3)MgCH2CH2CH2CH3.

[0026] 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, the organomagnesium compound useful for the purposes of the invention acting as a co-catalyst. For example, in a hydrocarbon solvent, the organomagnesium compound 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. The quantities of organomagnesium and metallocene reacted to form the catalytic system are such that the NMg / NNd ratio, which is the ratio between the number of moles of Mg of the organomagnesium and the number of moles of neodymium of the metallocene (NNd), preferably goes 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.

[0027] 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.

[0028] Alternatively, the catalytic system is prepared by a process analogous to that described in patent application WO 2017093654 A1 or in patent application WO 2018020122 A1: it is said to be of the preformed type. For example, the organomagnesium compound 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 a preformed monomer is reacted with this first reaction product at a temperature ranging from 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 has as its basic constituent a preforming monomer chosen from among 1,3-dienes, ethylene, and mixtures thereof. In other words, the so-called preformed catalytic system contains, in addition to the metallocene and the cocatalyst, a preforming monomer chosen from among ethylene, a 1,3-diene, and a mixture of ethylene and a 1,3-diene. The 1,3-diene used as a preforming monomer can be 1,3-butadiene, isoprene, or a 1,3-diene with the formula CH2=CR6-CH=CH2, where the symbol R6 represents a hydrocarbon group with 3 to 20 carbon atoms, particularly myrcene or 3-farnesene. The preferred preforming monomer is 1,3-butadiene.

[0029] 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 in anhydrous nitrogen or argon.

[0030] The catalytic system according to the invention is intended to be used in polymer synthesis processes, preferably in the synthesis of polymers containing ethylene, more particularly in the synthesis of polymers containing more than 50% by mole of ethylene.

[0031] The process for preparing a polymer, which process is another object of the invention, comprises a step of polymerizing a monomer M selected from ethylene and a monomer mixture containing ethylene and a 1,3-diene in the presence of the catalytic system according to the invention. The monomer M, the monomer to be polymerized in the presence of the catalytic system according to the invention, is preferably ethylene or a mixture of ethylene and a 1,3-diene, the 1,3-diene being advantageously 1,3-butadiene, isoprene, myrcene, 3-farnesene or mixtures thereof, most advantageously 1,3-butadiene.

[0032] 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 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 polymerization temperature generally varies in a range of 40 to 150°C, preferably 40 to 120°C. Those skilled in the art adapt the polymerization conditions, such as the polymerization temperature, the concentration of each of the reactants, and the reactor pressure, to achieve the desired microstructure and macrostructure of the polymer.

[0033] Polymerization is preferably carried out at constant monomer pressure, in particular at constant ethylene pressure. A continuous addition of monomer or one of In the case of a monomer mixture to be polymerized, this can be done 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.

[0034] 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.

[0035] 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 CnH8, 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: CH2—CHg \ CH2 x / CH- CH x / X

[0036] 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.

[0037] 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.

[0038] In summary, the invention is advantageously implemented according to any one of the following embodiments 1 to 21:

[0039] Mode 1: Catalytic system comprising: a metallocene of formula (la), 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), RB-Mg-RL (lia) in which RB is a secondary alkyl of formula R2CH and RL is a primary alkyl of formula RCH2, the Rs, identical or different, being alkyls.

[0040] Mode 2: Catalytic system according to mode 1 in which RL is a linear alkyl.

[0041] Mode 3: Catalytic system according to mode 1 or 2 in which RL is an alkyl linear having 2 to 8 carbon atoms.

[0042] Mode 4: Catalytic system according to any one of modes 1 to 3 in which RB is an alkyl of formula R'CH2CHR', the R's, identical or different, being alkyls.

[0043] Mode 5: Catalytic system according to mode 4 in which the alkyl of R' has 1 to 10 carbon atoms.

[0044] Mode 6: Catalytic system according to any one of modes 1 to 5 in which RL is n-butyl.

[0045] Mode 7: Catalytic system according to any one of modes 1 to 6 in which RB is sec-butyl.

[0046] Mode 8: Catalytic system according to any one of modes 1 to 7 in which Cp1 and Cp2 are identical.

[0047] Mode 9: Catalytic system according to any one of modes 1 to 8 in which Cp1 and Cp2 are chosen from the group consisting of the substituted fluorenyl groups and the unsubstituted fluorenyl group of formula Ci3H8.

[0048] Mode 10: Catalytic system according to any one of modes 1 to 9 in which Cp1 and Cp2 each represent an unsubstituted fluorenyl group of formula Ci3H8.

[0049] Mode 11: Catalytic system 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 an alkyl group comprising from 1 to 20 carbon atoms.

[0050] Mode 12: Catalytic system according to mode 11 in which R1 and R2 each represent a methyl.

[0051] Mode 13: Catalytic system according to any one of modes 11 to 12 in which Z represents a silicon atom.

[0052] Mode 14: Catalytic system according to any one of modes 1 to 13 in which the metallocene is of formula (III-1), (III-2), (III-3), (III-4) or (III-5): [Me2Si(Flu)2Nd(p-BH4)2Li(THF)] (III-1) [{Me2SiFlu2Nd(p-BH4)2Li(THF)}2] (III-2) [Me2SiFlu2Nd(p-BH4)(THF)] (III-3) [{Me2SiFlu2Nd(p-BH4)(THF)}2] (III-4) [Me2SiFlu2Nd(p-BH4)] (III-5) Flu representing the CnH8 group.

[0053] Mode 15: Catalytic system according to any one of modes 1 to 14 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 goes from 1 to 100.

[0054] Mode 16: Catalytic system according to any one of modes 1 to 15 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 goes from 1 to less than 10.

[0055] Mode 17: Catalytic system according to any one of modes 1 to 16, which catalytic system contains a preforming monomer selected from ethylene, a 1,3-diene and a mixture of ethylene and a 1,3-diene.

[0056] Mode 18: Catalytic system according to any one of modes 1 to 17, which catalytic system contains a preforming monomer which is 1,3-butadiene.

[0057] Mode 19: A process for preparing a polymer that includes a step of polymerizing a monomer M selected from ethylene and a monomer mixture containing ethylene and a 1,3-diene in the presence of a catalytic system defined in any one of modes 1 to 18.

[0058] Mode 20: Process according to mode 19 in which the monomer M is a mixture of a 1,3-diene and ethylene.

[0059] Mode 21: Process according to mode 19 or 20 in which the 1,3-diene is 1,3-butadiene, isoprene, myrcene, [3-farnesene or mixtures thereof.

[0060] 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

[0061] Size exclusion chromatography (SEC / RI): Size exclusion chromatography (SEC) allows the fractionation of chains of polymers 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: 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 through a 0.45 µm filter. A volume of 100 pL is injected through a set of three AGELENT (MIXED B LS) size-exclusion chromatography columns. The columns are oven-heated 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) 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 (D or Ip = Mw / Mn).

[0062] 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 co-catalyst, the organomagnesium compound BOMAG or the organomagnesium compound NSBM, 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 preparation method conforming to paragraph II.1 of patent application WO 2017093654 AL

[0063] . All polymerization reactions of ethylene and 1,3-butadiene are shown. The experiments are conducted in a 500 mL glass reactor equipped with a stainless steel stirring paddle. Temperature control is achieved via a thermostatically controlled oil bath connected to a double-walled glass enclosure. This reactor has all the necessary inlets and outlets for the experiments.

[0064] Statistical copolymers of ethylene and 1,3-butadiene are synthesized according to the procedure described below. For syntheses in which polymerization is carried out with a Mg / Nd molar ratio greater than 2.2, organomagnesium compound identical to that which constitutes the catalytic system is added to the polymerization medium.

[0065] The organomagnesium compound (co-catalyst) 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 is added to the bottle. The contents of the bottle 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 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 conversion to monomers is achieved, the contents of the reactor are degassed. The polymer is antioxidantized and then dried at 60 °C under vacuum to constant mass.

[0066] The polymerization conditions are shown in Table 1, as well as the polymerization results (polymerization time, mass of polymer produced, Mn, Ip).

[0067] Table 1: Mg / Nd Organomagnesium Test n Polymer Mass (g) Polymerization Time (min) Mn (g / mol) IP 1 2.8 BOMAG 13.96 82 33085 1.17 2 2.8 NSBM 13.87 113 66098 1.12

[0068] The catalytic system used in Test 1 is not in accordance with the invention, since the co-catalyst, BOMAG, does not correspond to formula (Ha), the alkyls of the organomagnesium compound being linear alkyls. The catalytic system of Test 2 is in accordance with the invention, since the organomagnesium compound NSBM corresponds to formula (Ha), RB being sec-butyl and RL being n-butyl.

[0069] The results show that for the same Mg / Nd ratio and for a mass of polymer The product is practically identical. The catalytic system using NSBM as a co-catalyst leads to significantly higher number-average molar masses (Mn) than the catalytic system using BOMAG as a co-catalyst. Obtaining a high Mn value requires a higher Mg / Nd ratio with a co-catalyst of formula (lia) than with BOMAG. Since the impact of a variation in impurity content on the Mg / Nd ratio will be weaker as this ratio increases, the polymerization process will be less sensitive to even a small variation in impurity content in controlling Mn content with a co-catalyst of formula (lia) such as NSBM than with a dialkylmagnesium co-catalyst whose alkyl groups are both linear alkyls, such as BOMAG.

Claims

Demands

1. A catalytic system comprising: a metallocene of formula (la), a co-catalyst, P^'Cp2»^^ (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, Pent 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), RB-Mg-RL (lia) in which RB is a secondary alkyl of formula R2CH and RL is a primary alkyl of formula RCH2, the Rs, identical or different, being alkyls.

2. Catalytic system according to claim 1 wherein RL is a linear alkyl.

3. Catalytic system according to claim 1 or 2 wherein RB is an alkyl of formula R'CH2CHR', the R's, identical or different, being alkyls.

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

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

6. Catalytic system according to any one of claims 1 to 5 wherein Cp1 and Cp2 are identical.

7. Catalytic system according to any one of claims 1 to 6 wherein Cp1 and Cp2 are selected from the group consisting of substituted fluorenyl groups and the unsubstituted fluorenyl group of formula Ci3H8, preferably each representing an unsubstituted fluorenyl group of formula Ci3H8.

8. Catalytic system according to any one of claims 1 to 7 in which the P bridge 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.

9. Catalytic system according to any one of claims 1 to 8 wherein the metallocene is of formula (III-1), (III-2), (III-3), (III-4) or (III-5): [Me2Si(Flu)2Nd(p-BH4)2Li(THF)] (III-1) [ {Me2SiFlu2Nd(p-BH4)2Li(THF)} 2] (III-2) [Me2SiFlu2Nd(p-BH4)(THF)] (III-3) [ {Me2SiFlu2Nd(p-BH4)(THF)} 2] (III-4) [Me2SiFlu2Nd(p-BH4)] (III-5) Flu representing the Ci3H8 group.

10. Catalytic system according to any one of claims 1 to 9 wherein the ratio of the number of moles of Mg of the co-catalyst to the number of moles of neodymium of the metallocene is from 1 to 100, preferably from 1 to less than 10.

11. Catalytic system according to any one of claims 1 to 10, wherein catalytic system contains a preforming monomer selected from ethylene, a 1,3-diene and a mixture of ethylene and a 1,3-diene, preferably a 1,3-diene.

12. Catalytic system according to any one of claims 1 to 11, wherein catalytic system contains a preforming monomer which is 1,3-butadiene.

13. A process for preparing a polymer comprising a step of polymerizing a monomer M selected from ethylene and a monomer mixture containing ethylene and a 1,3-diene in the presence of a catalytic system defined in any one of claims 1 to 12.

14. A process according to claim 13 wherein the monomer M is a mixture of a 1,3-diene and ethylene.

15. A process according to claim 13 or 14 wherein the 1,3-diene is 1,3-butadiene, isoprene, myrcene, [3-famesene or mixtures thereof.