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

Abstract

The invention relates to a catalytic system based at least on a borohydride neodymocene, a co-catalyst which is a dialkylmagnesium of formula RB-Mg-RL in which RB is a secondary alkyl of formula R2CH and RL is a primary alkyl of formula RCH2, with the Rs, which are identical or different, being alkyls. The catalytic system achieves the aim of better control of the macrostructure in a method for the polymerisation of ethylene or a monomer mixture containing ethylene and a 1,3-diene.

Description

[0001] Catalytic system comprising a metallocene for the synthesis of polyethylene and ethylene-1,3-diene copolymer

[0002] 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.

[0003] Rare earth metallocene-based catalyst 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 catalyst systems described in these documents are based on a neodymium metallocene and a co-catalyst for activating the metallocene. The co-catalyst is typically an organometallic compound, generally an organomagnesium compound. Like 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, the solvents and monomers purified, impurities such as water, carbon dioxide, oxygen, may be present in the polymerization reactor containing the polymerization solvent and monomers.These impurities can react with the organomagnesium when it is introduced into the polymerization reactor, which has the consequence of modifying the Mg / Nd molar ratio, the molar ratio between the number of moles of organomagnesium and the number of moles of Nd. This Mg / Nd molar ratio makes it possible 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 level of impurities is all the greater when 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 overcome this difficulty.

[0004] 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 of ethylene or a monomer mixture containing ethylene and a 1,3-diene. In other words, the catalytic system makes it possible to make the polymerization process less sensitive to variations in impurities present in the polymerization reactor which can fluctuate from one synthesis batch to another. This objective is achieved by the choice of a specific organomagnesium as a co-catalyst in a catalytic system based on a neodymium metallocene.

[0005] Thus, a first object of the invention is a catalytic system which comprises: a metallocene of formula (Ia), a co-catalyst, P(Cp 1 CP 2 )Nd(BH4)(i + y)-Ly-N x (there)

[0006] 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,

[0007] 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, integer or not, being equal to or greater than 0, y, integer, being equal to or greater than 0, the co-catalyst being a dialkylmagnesium of formula (Ha),

[0010] R B -Mg-R L (Ha) in which R B is a secondary alkyl of formula R2CH and RL is a primary alkyl of formula RCH2, the Rs, identical or different, being alkyls.

[0011] Another subject of the invention is a process for preparing a polymer which comprises a step of polymerization of a monomer M chosen from ethylene and a monomer mixture containing ethylene and a 1,3-diene in the presence of a catalytic system in accordance with the invention.

[0012] Detailed description

[0013] 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).

[0014] 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.

[0015] 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.

[0016] 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. These 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.

[0017] 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 trialkylsilyl radicals such as SiMej. The choice of radicals is also guided by the accessibility of the corresponding molecules, which are substituted cyclopentadienyl, fluorenyl and indene, because the latter are commercially available or easily synthesized.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] Preferably, Cp 1 and Cp 2 , are identical.

[0022] Preferably, Cp 1 and Cp 2are 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 2 are identical and each represents an unsubstituted fluorenyl group of formula CisHs, represented by the symbol Flu.

[0023] 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.

[0024] The P bridge connecting the Cp groups 1 and Cp 2 preferably responds to the formula ZR 1 R 2 , in which Z represents a silicon or carbon atom, R 1 and R2 , 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.

[0025] 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.

[0026] According to a particularly preferred embodiment, the metallocene is of formula (III-1), (111-2), (111-3), (111-4) or (111-5): [Me2Si(Flu)2Nd(p-BH4)2Li(THF)] (III-1) [{Me2SiFlu2Nd(p-BH4)2Li(THF)}2] (111-2) [Me2SiFlu2Nd(p-BH4)(THF)] (111-3) [{Me2SiFlu2Nd(p-BH4)(THF)}2] (111-4) [Me2SiFlu2Nd(p-BH4)] (111-5) in which Flu represents the CisHs group.

[0027] The catalytic system also has as another essential constituent an organomagnesium compound. The organomagnesium is a dialkylmagnesium of formula (IIa) R B -Mg-R L (Ha) in which R Bis a secondary alkyl of formula R2CH and RL is a primary alkyl of formula RCH2, the Rs, identical or different, being alkyls. In other words, the organomagnesium has the structural formula R2CHMgCH2R. The alkyls represented by the symbols R can contain 1 to 10 carbon atoms. Dialkylmagnesiums 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. As an illustration, the dialkylmagnesium can be in the form of a monomeric entity (R B -Mg-R L )i or in the form of a polymeric entity (R B -Mg-R L ) P, p being an integer greater than 1, for example dimer (R B -Mg-R L )2, 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] R L is 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-.

[0029] R B is preferably an alkyl of formula R"CH2CHR', R' being an alkyl and R'' being a hydrogen atom or an alkyl. The alkyl of R' preferably has 1 to 10 carbon atoms, the alkyl of R'' preferably has 1 to 9 carbon atoms. Advantageously, R Bis sec-butyl of formula CHsCFbCHfCHs)-.

[0030] According to a particularly preferred embodiment of the invention, the cocatalyst 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.

[0031] The catalytic system in accordance with the invention may be prepared in a conventional manner by a process analogous to that described in patent application WO 2007054224 or WO 2007054223, the organomagnesium useful for the purposes of the invention acting as a cocatalyst. For example, in a hydrocarbon solvent, the organomagnesium 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 the organomagnesium and the metallocene reacted to form the catalytic system are such that the ratio N Mg / N Ndwhich is the ratio between the number of moles of Mg in the organomagnesium and the number of moles of neodymium in the metallocene (NNCI) 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 particularly more favorable for obtaining polymers with high molar masses.

[0032] 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 . Alternatively, the catalytic system is prepared by a process analogous to that described in patent application WO 2017093654 A1 or in patent application

[0033] WO 2018020122 Al: it is said to be of the preformed type. For example, the organomagnesium 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 preforming monomer is reacted at a temperature ranging from 40 to 90°C for 1 to 12 hours. The preforming monomer is preferably used in a molar ratio (preforming monomer / metal of the metallocene) ranging from 5 to 1000, preferably from 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 type catalytic system has as its basic constituent a preforming monomer chosen from 1,3-dienes, ethylene and their mixtures.In other words, the so-called preformed catalytic system contains, in addition to the metallocene and the co-catalyst, a preforming monomer which is chosen from ethylene, a 1,3-diene and a mixture of ethylene and a 1,3-diene. The 1,3-diene as preforming monomer can be 1,3-butadiene, isoprene or a 1,3-diene of formula CH2=CR. 6 -CH=CH2, the symbol R 6 representing a hydrocarbon group having 3 to 20 carbon atoms, in particular myrcene or |3-farnesene. The preformation monomer is preferably 1,3-butadiene.

[0034] As with 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. Typically, reactions are carried out from solvents and anhydrous compounds under anhydrous nitrogen or argon.

[0035] 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 mol% of ethylene.

[0036] The process for preparing a polymer, which process is another subject of the invention, comprises a step of polymerizing a monomer M chosen 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, 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 advantageously being 1,3-butadiene, isoprene, myrcene, p-farnesene or their mixtures, very advantageously 1,3-butadiene.

[0037] The polymerization is preferably carried out in solution, continuously or discontinuously. 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 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.

[0038] 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.

[0039] 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.

[0040] 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 CIÎHS, 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:

[0041] 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.

[0042] 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.

[0043] In summary, the invention is advantageously implemented according to any one of the following embodiments 1 to 21:

[0044] Mode 1: Catalytic system which comprises: a metallocene of formula (Ia), a co-catalyst,

[0045] P(Cp 1 CP 2 )Nd(BH4)(i + y)-Ly-N x (there)

[0046] 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,

[0047] P being a group bridging the two Cp groups 1 and Cp 2 , and comprising a silicon or carbon atom,

[0048] L representing an alkali metal chosen from the group consisting of lithium, sodium and potassium,

[0049] N representing a molecule of an ether, x, integer or not, being equal to or greater than 0, y, integer, being equal to or greater than 0, the co-catalyst being a dialkylmagnesium of formula (Ha),

[0050] R B -Mg-R L (Ha) in which R B is a secondary alkyl of formula R2CH and RL is a primary alkyl of formula RCH2, the Rs, identical or different, being alkyls.

[0051] Mode 2: Catalytic system according to mode 1 in which R L is a linear alkyl.

[0052] Mode 3: Catalytic system according to mode 1 or 2 in which R L is a linear alkyl having 2 to 8 carbon atoms.

[0053] Mode 4: Catalytic system according to any one of modes 1 to 3 in which R B is an alkyl of formula R'CFbCHR', the R's, identical or different, being alkyls.

[0054] Mode 5: Catalytic system according to mode 4 in which the alkyl of R' has 1 to 10 carbon atoms.

[0055] Mode 6: Catalytic system according to any one of modes 1 to 5 in which R L is n-butyl.

[0056] Mode 7: Catalytic system according to any one of modes 1 to 6 in which R B is dry-butyl.

[0057] Mode 8: Catalytic system according to any one of modes 1 to 7 in which Cp 1 and Cp 2are identical.

[0058] Mode 9: Catalytic system according to any one of modes 1 to 8 in which Cp 1 and Cp 2 are selected from the group consisting of substituted fluorenyl groups and the unsubstituted fluorenyl group of formula C13H8. Mode 10: Catalytic system according to any one of modes 1 to 9 in which Cp 1 and Cp 2 each represent an unsubstituted fluorenyl group of formula CisHs.

[0059] Mode 11: Catalytic system 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 an alkyl group comprising from 1 to 20 carbon atoms.

[0060] Mode 12: Catalytic system according to mode 11 in which R 1 and R 2 each represent a methyl.

[0061] Mode 13: Catalytic system according to any one of modes 11 to 12 in which Z represents a silicon atom.

[0062] Mode 14: Catalytic system according to any one of modes 1 to 13 in which the metallocene is of formula (Il 1-1), (Il 1-2), (Il 1-3), (Il 1-4) or (Il 1-5): [Me2Si(Flu)2Nd(p-BH4)2Li(THF)] (lll-l) [{Me2SiFlu2Nd(p-BH4)2Li(THF)}2] (111-2) [Me2SiFlu2Nd(p-BH4)(THF)] (111-3) [{Me2SiFlu2Nd(p-BH4)(THF)}2] (111-4) [Me2SiFlu2Nd(p-BH4)] (111-5) Flu representing the CisHs group.

[0063] Mode 15: Catalytic system according to any one of modes 1 to 14 in which the ratio between the number of moles of Mg in the co-catalyst and the number of moles of neodymium in the metallocene ranges from 1 to 100.

[0064] Mode 16: Catalytic system according to any one of modes 1 to 15 in which the ratio between the number of moles of Mg in the co-catalyst and the number of moles of neodymium in the metallocene ranges from 1 to less than 10.

[0065] Mode 17: A 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.

[0066] Mode 18: A catalytic system according to any one of modes 1 to 17, which catalytic system contains a pre-forming monomer which is 1,3-butadiene.

[0067] Method 19: Process for preparing a polymer which comprises a step of polymerizing a monomer M chosen 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 methods 1 to 18.

[0068] Mode 20: Process according to mode 19 in which the monomer M is a mixture of a 1,3-diene and ethylene.

[0069] Method 21: Process according to method 19 or 20 in which the 1,3-diene is 1,3-butadiene, isoprene, myrcene, p-farnesene or mixtures thereof. The above-mentioned characteristics of the present invention, as well as others, will be better understood on reading the following description of the exemplary embodiments of the invention, given for illustrative and non-limiting purposes.

[0070] Examples

[0071] Size exclusion chromatography (SEC / RI):

[0072] 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.

[0073] 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).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).

[0074] Preparation of polymers:

[0075] 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.

[0076] 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 BOMAG or the organomagnesium NSBM, with a Mg / Nd molar ratio equal to 2.2, and a preformed 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. All polymerization reactions of ethylene and 1,3-butadiene 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 inlets or outlets necessary for handling.

[0077] Random copolymers of ethylene and 1,3-butadiene are synthesized according to the procedure described below. For syntheses in which the polymerization is carried out with a Mg / Nd molar ratio greater than 2.2, organomagnesium identical to that which constitutes the catalytic system is added to the polymerization medium.

[0078] The organomagnesium compound (co-catalyst) 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 gas 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.

[0079] The polymerization conditions are shown in Table 1, as well as the polymerization results (polymerization time, mass of polymer produced, Mn, Ip).

[0080] Table 1:

[0081] The catalytic system used in test 1 is not in accordance with the invention, since the cocatalyst, BOMAG, does not correspond to the formula (Ha), the alkyls of the organomagnesium being linear alkyls. The catalytic system of test 2 is in accordance with the invention, since the organomagnesium NSBM corresponds to the formula (Ha), R B -being sec-butyl and R L being n-butyl.

[0082] The results show that for the same Mg / Nd ratio and for a practically identical mass of polymer produced, the catalytic system with NSBM as co-catalyst leads to much higher number-average molar masses, Mn, than the catalytic system with BOMAG as co-catalyst. Obtaining a high Mn requires a higher Mg / Nd ratio with the use of a co-catalyst of formula (Ha) than with the use of BOMAG. Since the impact of a variation in the impurity level on a Mg / Nd ratio will be lower the higher this ratio is, the polymerization process will be less sensitive to a smaller variation in the impurity level in the control of Mn with the use of a co-catalyst of formula (IIa) such as NSBM than with the use of a dialkylmagnesium co-catalyst whose alkyls are both linear alkyls such as BOMAG.

Claims

Claims 1. Catalytic system which comprises: a metallocene of formula (Ia), 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, integer or not, being equal to or greater than 0, y, integer, being equal to or greater than 0, the co-catalyst being a dialkylmagnesium of formula (Ha), R B -Mg-R L (Ha) 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 in which R L is a linear alkyl.

3. Catalytic system according to claim 1 or 2 in which R B is an alkyl of formula R'CFbCHR', the R's, identical or different, being alkyls.

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

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

6. Catalytic system according to any one of claims 1 to 5 in which Cp 1 and Cp 2 are identical.

7. Catalytic system according to any one of claims 1 to 6 in which Cp 1 and Cp 2are selected from the group consisting of substituted fluorenyl groups and unsubstituted fluorenyl group of formula C13H8, preferably each represents an unsubstituted fluorenyl group of formula C13H8.

8. Catalytic system according to any one of claims 1 to 7 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.

9. Catalytic system according to any one of claims 1 to 8 in which the metallocene is of formula (II 1-1), (II 1-2), (II 1-3), (II 1-4) or (II 1-5): [Me2Si(Flu)2Nd(p-BH4)2Li(THF)] (HI-1) [{Me2SiFlu2Nd(p-BH4)2Li(THF)}2] (HI-2) [Me2SiFlu2Nd(p-BH4)(THF)] (HI-3) [{Me2SiFlu2Nd(n-BH4)(THF)}2] (111-4) [Me2SiFlu2Nd(n-BH4)] (HI-5) Flu representing the CIÎHS group.

10. Catalytic system according to any one of claims 1 to 9 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 ranges from 1 to 100, preferably from 1 to less than 10.

11. Catalytic system according to any one of claims 1 to 10, which catalytic system contains a pre-formation monomer chosen from ethylene, a 1,3-diene and a mixture of ethylene and a 1,3-diene, preferably a 1,3-diene.

12. A catalytic system according to any one of claims 1 to 11, which catalytic system contains a pre-forming monomer which is 1,3-butadiene.

13. Process for the preparation of a polymer which comprises a step of polymerization of a monomer M chosen 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. The method of claim 13 wherein the monomer M is a mixture of a 1,3-diene and ethylene.

15. The method of claim 13 or 14 wherein the 1,3-diene is 1,3-butadiene, isoprene, myrcene, p-farnesene or mixtures thereof.

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