WO2022258907A1

WO2022258907A1 - Catalytic system for the stereospecific polymerization of dienes and use thereof in a process for synthesizing diene polymers

Info

Publication number: WO2022258907A1
Application number: PCT/FR2022/051025
Authority: WO
Inventors: Leyla PEHLIVAN; Florent VAULTIER
Original assignee: Compagnie Generale Des Etablissements Michelin
Priority date: 2021-06-10
Filing date: 2022-05-30
Publication date: 2022-12-15
Also published as: FR3123917A1; FR3123917B1; EP4352116A1

Abstract

The invention relates to a stereospecific catalyst system that comprises: - a rare earth tris(amide); - an organic magnesium compound having formula R¹R²Mg, where R¹ and R² are, independently of each other, a C₁-C₁₀ aliphatic radical, substituted or unsubstituted, or a C₆-C₂₀ aromatic radical, substituted or unsubstituted. Since this catalyst system promotes trans-1,4 insertion of the 1,3-diene monomers, the use of the system for polymerizing 1,3-diene monomers yields diene polymers having a high trans-1,4 chain content.

Description

Title: Catalytic system for the stereospecific polymerization of dienes and their use in a process for the synthesis of diene polymers

Technical area

The present invention relates to a catalytic system for the stereospecific polymerization of conjugated dienes favoring the 1,4-trans insertion of the monomers. The invention relates more particularly to a polymetallic catalytic system for the stereospecific polymerization of conjugated dienes favoring the 1,4-trans insertion of the monomers. The invention also relates to a process for the synthesis of diene polymers with a high level of 1,4-trans linkage using a polymetallic catalytic system for the polymerization of the monomers.

Prior technique

The use of polymetallic catalytic systems for the synthesis of diene polymers by coordination polymerization has been described in the past.

The literature reports in particular the combination of rare earth salts and organic magnesium compounds for the polymerization of 1,3-diene monomers capable of generating stereospecificity of the 1,4-cis or 1,4-trans configurations, and in particular of 1,4-trans configuration.

Thus, for example, the article Macromolecules 2017, 50, 7887-7894, "Regulation of the cis-1,4- and trans-l,4-Polybutadiene Multiblock Copolymers via Chain Shuttling Polymerization Using a Ternary Neodymium Organic Sulfonate Catalyst", Quanquan Dai et al., describe the synthesis of polybutadienes at controlled l,4-cis/l,4-trans levels to achieve a balance between tolerance to deformation (attributed to the cis-1,4 part of the polybutadiene) and the rigidity (attributed to the crystallinity of the trans-1,4-part of the polybutadiene). This article explains that a binary catalytic system based on neodymium trifluoromethane sulfonate and dibutylmagnesium makes it possible to synthesize by coordination catalysis a polybutadiene favoring the 1,4-trans insertion of butadiene.

Several publications report the controlled polymerization of isoprene using a catalytic system comprising a lanthanide borohydride and a dialkylmagnesium, in the presence or absence of tetrahydrofuran. These catalytic systems make it possible to provide stereoregular 1,4-trans-polyisoprene with high levels of 1,4-trans. Mention may be made, for example, of Macromolecules 2005, 38, 3162-3169 "Highly trans-Stereospecific Isoprene Polymerization by Neodymium Borohydrido Catalysts", Fanny Bonnet et al.

The document FR2567135A1 describes butadiene polymers having a 1,4-trans content between 80% and 95% by weight, prepared by coordination polymerization using a catalytic system based on an organic acid salt of lanthanum or cerium and an organic magnesium compound. Another document EP0091287 describes a catalytic system for the polymerization of butadiene comprising in particular didymium versatate and a dibutylmagnesium making it possible to achieve stereoregular polybutadiene with a high level of 1,4-trans.

If catalytic systems used in the stereospecific polymerizations of conjugated dienes have already been described in the past, a need remains to have other processes for the synthesis of diene polymers having in particular high levels of 1,4-trans linkage, it that is to say greater than 65% by weight relative to the diene part of the polymer. Moreover, in certain uses of a diene polymer, it may be advantageous for the latter not only to have a high 1,4-trans linkage rate, but also a limited 1,2 linkage rate. A process for the synthesis of diene polymers which makes it possible to satisfy both of these objectives at the same time would be of particular interest.

Technical problem

The technical problem that arises in the context of the present invention is to have a process for the synthesis of diene polymers, particularly butadiene polymers, promoting the formation of the 1,4-trans linkage, and also making it possible to limit the formation of the web 1.2.

Disclosure of Invention

The invention makes it possible to solve this problem by proposing a catalytic system of a rare earth tris(amide) and an organic magnesium compound which, used for the polymerization of 1,3-dienes, has a stereospecificity with respect to the 1,4-trans insertion.

The use of the catalytic system according to the invention in a process for the synthesis of a diene polymer makes it possible to obtain diene polymers, in particular polybutadienes, having controlled levels of 1,4-trans linkage, which levels are high with in particular values greater than 65% by weight relative to the diene part of the polymer, and a low degree of 1,2 chaining less than 10% by weight relative to the diene part of the polymer.

More particularly, the use of the catalytic system according to the invention in a process for the polymerization of butadiene allows the synthesis of a polybutadiene having the following characteristics:

- a 1,4-trans linking rate of at least 65%, or even at least 80% by weight relative to the diene part of the polybutadiene;

- a 1,2 linking rate of at most 10% by weight relative to the diene part of the polybutadiene.

In a first aspect, the invention relates to such a catalytic system.

In another aspect, the invention relates to a method of synthesizing a diene polymer using such a catalyst system.

Summary of the invention

The invention, described in more detail below, relates to at least one of the embodiments listed in the following points:

1- Catalytic system comprising

- a rare earth tris(amide),

- an organic magnesium compound of formula R ¹ R ² Mg , in which R ¹ and R ² represent, independently of each other, an aliphatic radical in Ci-Cio, substituted or not, an aromatic radical in C6- C20, substituted or not. 2- Catalytic system according to the previous embodiment in which the aliphatic radical, in the definition of R ¹ and R ² is a Ci-Cio alkyl radical, substituted or not.

3- Catalytic system according to any one of the preceding embodiments in which the aromatic radical, in the definition of R ¹ and R ² is a C6-C20 aryl radical _, substituted or not.

4- Catalytic system according to any one of the preceding embodiments in which the organic magnesium compound of formula R ¹ R ² Mg is n-butylethylmagnesium or n-butyloctylmagnesium.

5- Catalytic system according to any one of the preceding embodiments in which the rare earth metal making up the rare earth tris(amide) is a lanthanide.

6- Catalytic system according to the previous embodiment in which the rare earth metal is lanthanum or neodymium.

7- Catalytic system according to any one of the preceding embodiments in which the amide composing the rare earth tris(amide) is chosen from dialkylamides, arylalkylamides, diarylamides, N,N-bis(dialkylsilyl)amides, N,N-bis(trialkylsilyl)amides, N,N-bis(alkyaryllsilyl)amides, N,N-bis(aryldialkylsilyl)amides, N,N-bis(diarylalkylsilyl)amides and N,N-bis( triarylsilyl) amides, the alkyl groups having from 1 to 10 carbon atoms and the aryl groups from 6 to 14.

8- Catalytic system according to the previous embodiment in which the amide is an N,N-bis(trialkylsilyl)amide.

9 - Catalytic system according to the previous embodiment in which the amide is N,N-bis(trimethylsilyl)amide.

10- Catalytic system according to any one of the preceding embodiments in which the rare earth tris(amide) is N,N-bis(trimethylsilyl)lanthanum amide or N,N-bis(trimethylsilyl)neodymium amide.

11- Catalytic system according to any one of the preceding embodiments in which the molar ratio (organic magnesium compound/rare earth tris(amide)) has a value less than or equal to 40/1, preferably less than or equal to 30/ 1, preferably still less than or equal to 20/1, or even less than 20/1, in particular by at most 15/1.

12- Catalytic system according to any one of the preceding embodiments in which the molar ratio (organic magnesium compound/rare earth tris(amide)) has a value of at least 1/1, preferably greater than 1, more preferably of at least 5/1.

13- Catalytic system according to any one of the preceding embodiments further comprising at least one electron donor.

14- Catalytic system according to the previous embodiment, comprising the electron donor in a molar ratio (electron donor/organic magnesium compound) of at least 1/2.

15- Catalytic system according to the previous embodiment 13 or 14, in which the electron donor is chosen from ethers, preferably tetrahydrofuran or ethyltetrahydrofurfuryl ether. 16- Catalytic system according to any one of the preceding embodiments further comprising at least one other organometallic compound, the metal being lithium or aluminum.

17- Catalytic system according to the previous embodiment, in which the at least one other organometallic compound is an alkyllithium, a trialkylaluminum, a dialkylaluminum hydride or an aluminoxane, the alkyl radical having 1 to 4 carbon atoms.

18- Catalytic system according to any one of the preceding embodiments in which at least one of the following characteristics is respected, at least two, at least three, at least four and preferably all of them:

- the rare earth tris(amide) is a rare earth tris[N,N-bis(trialkylsilyl)amide], preferably a rare earth tris[N,N-bis(trimethylsilyl)amide]

- the rare earth is a lanthanide, preferably lanthanum or neodymium,

- the organic magnesium compound is a dialkylmagnesium, preferably n-butylethylmagnesium or n-butyloctylmagnesium,

- the molar ratio (organic magnesium compound/rare earth tris(amide)) has a value less than or equal to 40/1, preferably less than or equal to 30/1, more preferably less than or equal to 20/1, or even less than 20/1, in particular by at most 15/1,

- the catalytic system also comprises an electron donor chosen from ethers, preferably tetrahydrofuran or ethyltetrahydrofurfuryl ether.

19- Catalytic system according to any one of the preceding embodiments in which at least one of the following characteristics is respected, at least two, at least three and preferably all of them:

- the rare earth tris(amide) is lanthanum tris[N,N-bis(trimethylsilyl)amide] or neodymium tris[N,N-bis(trimethylsilyl)amide],

- the organic magnesium compound is n-butylethylmagnesium or n-butyloctylmagnesium,

- the molar ratio (organic magnesium compound/rare earth tris(amide)) has a value ranging from 5/1 to 15/1,

- the catalytic system also comprises tetrahydrofuran or ethyltetrahydrofurfuryl ether.

20- Process for the preparation of a diene polymer comprising the polymerization reaction of at least one conjugated diene monomer in a reactor in the presence of a catalytic system as defined in one of the preceding embodiments.

21- Process according to the previous embodiment, comprising, offset from the introduction of the catalytic system into the reactor, the addition to the reactor of at least one organic magnesium compound of formula R ³ R ⁴ Mg, in which each of R ³ and R ⁴ represents, independently of one another, an aliphatic radical in Ci-Cio, substituted or not, or an aromatic radical in C6-C20, substituted or not.

22. Process according to embodiment 20 or 21, in which the conjugated diene monomer to be polymerized is a 1,3-diene monomer.

23. Process according to any one of the preceding embodiments 20 to 22, in which the conjugated diene monomer is a 1,3-diene monomer having 4 to 15 carbon atoms, preferably butadiene or isoprene, more particularly butadiene. 24. Process according to any one of the preceding embodiments 20 to 23, in which the conjugated diene monomer to be polymerized is copolymerized with at least one other monomer.

25. Process according to the preceding embodiment, in which the conjugated diene monomer to be polymerized is copolymerized with at least one other monomer chosen from conjugated diene monomers having 4 to 15 carbon atoms.

26. Process according to embodiment 24 or 25, in which the conjugated diene monomer to be polymerized is copolymerized with at least one other monomer chosen from vinylaromatic compounds, preferably styrene.

27 - Process according to any one of the preceding embodiments 17 to 24 in which at least one of the following characteristics is respected, at least two, at least three, at least four, at least five, at least six and preferably all of them:

- the conjugated diene monomer to be polymerized is a 1,3-diene having 4 to 15 carbon atoms, preferably 1,3-butadiene,

- the rare earth is a lanthanide, preferably lanthanum or neodymium,

- the organic magnesium compound is a dialkylmagnesium, the alkyl radical having 1 to 10 carbon atoms, preferably n-butylethylmagnesium or n-butyloctylmagnesium,

- in the catalytic system, the molar ratio (organic magnesium compound/rare earth tris(amide)) has a value less than or equal to 40/1, preferably less than or equal to 30/1, more preferably less than or equal to 20/1, or even less than 20/1, in particular by at most 15/1.,

- the catalytic system further comprises an electron donor chosen from ethers, preferably tetrahydrofuran or ethyltetrahydrofurfuryl ether, preferably according to a molar ratio (electron donor/organic magnesium compound of formula R ¹ R ² Mg) at least 1/2,

- an organic magnesium compound of formula R ³ R ⁴ Mg, in which each of R ³ and R ⁴ represents, independently of one another, an aliphatic radical in Ci-Cio, substituted or not, an aromatic radical in C6-C20, substituted or unsubstituted, preferably n-butylethylmagnesium or n-butyloctylmagnesium, is added to the reactor independently of the catalytic system.

Definition

The terms "radical", "group" and "grouping", singular or plural, are equivalent and interchangeable.

The expression "in C _x -C _y " for a hydrocarbon radical means that said radical comprises x to y carbon atoms.

In the present description, unless otherwise expressly indicated, all the percentages (%) indicated are percentages (%) by weight (also called percentage (%) by weight). The percentages (%) expressing the microstructure of the diene polymer (for example the relative distribution of the 1,2-, 1,4-trans and 1,4-cis butadiene units) are percentages by weight relative to the diene part of the polymer . Thus a 1,4-trans linking rate of more than 70% in a diene polymer corresponds to a content of 1,4-trans diene units of more than 70% by weight relative to the weight of the diene part of the polymer.

On the other hand, any interval of values denoted by the expression "between a and b" represents the domain of values going from more than a to less than b (i.e. limits a and b excluded) while any interval of values denoted by the expression “from a to b” signifies the range of values going from a to b (that is to say including the strict limits a and b).

The compounds comprising carbon, mentioned in the description, can be of fossil origin or biobased. In the latter case, they can be, partially or totally, derived from biomass or obtained from renewable raw materials derived from biomass. In the same way, the compounds mentioned can also come from the recycling of materials already used, that is to say they can be, partially or totally, from a recycling process, or obtained from materials raw materials themselves from a recycling process. Are concerned more particularly in the present application in particular the monomers.

Thus, for example, the butadiene can advantageously be derived in a known manner directly from biomass or be obtained from a biosourced precursor, for example biosourced ethanol. The isoprene can advantageously be derived in a known manner directly from biomass or be obtained from a biosourced precursor, for example from biosourced isobutene. The styrene can, for example, advantageously be obtained in a known manner directly from biomass or else from the recycling of polystyrene.

Detailed description of the invention

The subject of the invention is a catalytic system comprising

- a rare earth tris(amide),

- an organic magnesium compound of formula R ¹ R ² Mg , in which R ¹ and R ² represent, independently of each other, an aliphatic radical in Ci-Cio, substituted or not, an aromatic radical in C ₆ -C ₂₀ , substituted or not.

In the formula R ¹ R ² Mg, R ¹ and R ² can be identical or different.

In the formula R ¹ R ² Mg, each of R ¹ and R ² can be a C ₁ -C ₁₀ aliphatic radical, substituted or unsubstituted. As an aliphatic radical representing R ¹ and R ² , mention may be made of C 10 -C ₁₀ alkyl groups, C ₂ -C ₁₀ alkenyl groups and C ₂ -C ₁₀ alkynyl groups, whether cyclic or non-cyclic . Particularly, when one of R ¹ and R ² is an aliphatic radical, it is a non-cyclic C ₁ -C ₄ alkyl radical chosen from a methyl, ethyl, n-propyl, iso-propyl, i-butyl, n-butyl, s-butyl or tert-butyl.

In the formula R ¹ R ² Mg, each of R ¹ and R ² may be a C ₆ -C ₂₀ aromatic radical, substituted or unsubstituted. As aromatic radical representing each of R ¹ and R ² , mention may be made of C6- _C20 aryl groups.

According to particular embodiments of the invention, in the formula R ¹ R ² Mg, R ¹ and R ² each denote a non-cyclic C ₁ -C ₄ alkyl radical. According to these embodiments, the organic magnesium compound of formula R ¹ R ² Mg is preferably n-butylethylmagnesium. According to one aspect of the invention, the organic magnesium compound can be a mixture of several organic magnesium compounds.

The catalytic system according to the invention also comprises a rare earth tris(amide).

According to embodiments, the term amide means an ion chosen from is chosen from dialkylamides, arylalkylamides, diarylamides, N,N-bis(dialkylsilyl)amides, N,N-bis(trialkylsilyl)amides, N, N-bis(alkyaryllsilyl)amides, N,N-bis(aryldialkylsilyl)amides,

N,N-bis(diarylalkylsilyl)amides and N,N-bis(triarylsilyl)amides, the alkyl groups having from 1 to 10 carbon atoms, preferably from 1 to 4, and the aryl groups from 6 to 14, of preference 6.

Thus the amide can be chosen from dialkylamides, in particular diisopropylamide and dimethylamide. Alternatively, the amide may be chosen from N,N-bis(dialkylsilyl)amides, in particular N,N-bis(dimethylsilyl)amide. Or the amide can be chosen from N,N-bis(aryldialkylsilyl)amides, in particular N,N-(phenyldimethyl)amide. Or else the amide can be chosen from N,N-bis(trialkylsilyl)amides, mention may be made of N,N-bis(trimethylsilyl)amide.

According to particular embodiments of the invention, the amide is an N,N-bis(trialkylsilyl)amide, preferably N,N-bis(trimethylsilyl)amide. According to these particular embodiments of the invention, the rare earth tris(amide) is preferably a lanthanum tris[N,N-bis(trialkylsilyl)amide], more preferably tris[N,N-bis(trimethylsilyl )amide] of lanthanum or tris [N,N-bis(trimethylsilyl)amide] of neodymium.

According to one aspect of the invention, the rare earth tris(amide) can be a complex of a mixture of rare earths or even a mixture of several complexes of one or more rare earths.

According to another characteristic of the invention, the neodymium is present in the catalytic system in a concentration equal to or greater than 0.010 mol/l and, preferably at least at least

0.020 mol/l, and at most 0.900 mol/l, more particularly at most 0.500 mol/l.

According to embodiments of the invention, the molar ratio (organic magnesium compound of formula R ¹ R ² Mg/rare earth tris(amide)) in said catalytic system can have a value of up to 50/1, and advantageously has a value less than or equal to 40/1, preferably less than or equal to 30/1. According to preferred embodiments, this molar ratio has a value less than or equal to 20/1, or even less than 20/1, in particular at most 15/1.

Indeed, it is found that with a molar ratio (organic magnesium compound of formula R ¹ R ² Mg / rare earth tris(amide)) of 20/1, it is possible to synthesize a polymer having a high rate of linkage 1 ,4- trans and a rate of 1,2- insertion always well below 10%. However, from this value of 20/1 the conversion rate drops. This is why, advantageously, the molar ratio (organic magnesium compound of formula R ¹ R ² Mg/rare earth tris(amide)) in said catalytic system has a value less than or equal to 20/1, or even less than 20 /1, preferably at most 15/1.

The molar ratio (organic magnesium compound of formula R ¹ R ² Mg/rare earth tris(amide)) may have a value greater than 1/1. With a view to optimizing the conversion, the molar ratio (organic magnesium compound of formula R ¹ R ² Mg rare earth tris(amide)) in said catalytic system advantageously has a value of at least at least 5/1. Also, in order to maintain conversion optimization, the molar ratio (organic magnesium compound of formula R ¹ R ² Mg / rare earth tris(amide)) in said catalytic system advantageously has a value less than or equal to 20/ 1. Thus, according to advantageous embodiments of the invention, the molar ratio (organic magnesium compound of formula R ¹ R ² Mg / rare earth tris(amide)) in said catalytic system has a value of at least 5/ 1, and less than or equal to 20/1, preferably at least 15/1.

According to very advantageous embodiments of the invention, the catalytic system can also comprise at least one electron donor.

Such an addition to the catalytic system according to the invention makes it possible to significantly improve the activity of the catalytic system and therefore to improve the conversion of the polymerization reaction.

According to these embodiments of the invention, the molar ratio (electron donor/organic magnesium compound of formula R ¹ R ² Mg) in said catalytic system advantageously has a value of at least 1/2 to observe a gain sufficient in conversion. This ratio has no upper limit because it is accompanied by a high level of 1,4-trans linkage and the maintenance of a low level of 1,2 linkage. Those skilled in the art will understand that the maximum value of the molar ratio (electron donor/organic magnesium compound of formula R ¹ R ² Mg) depends on the technical effect sought. This value can be induced for example by a conversion which n increases more beyond a certain molar ratio (electron donor/organic magnesium compound of formula R ¹ R ² Mg) or even a low rate of 1.2. By way of example, this ratio may advantageously be at most 15/1, since beyond this the conversion no longer increases.

By electron donors is meant in particular ethers, amines and thioethers. For example, as an amine, mention may be made of the family of trialkylamines and aromatic amines such as pyridine or else piperazine and its derivatives. By way of thioether, mention may be made of the family of dialkyl sulphides such as dimethyl sulphide. By way of ether, mention may be made, for example, of diethyl ether, 1,2-diethoxyethane, 1,2-di-n-propoxyethane, 1,2-di-n-butoxyethane, tetrahydrofuran, dioxane, tetrahydropyran, ethyltetrahydrofurfuryl ether. Particularly according to these embodiments, the catalytic system can comprise an ether, preferably tetrahydrofuran (THF) or ethyltetrahydrofurfuryl ether (ETE).

Very particularly according to these embodiments of the invention, when the rare earth tris(amide) is a lanthanide tris[N,N-bis(trialkylsilyl)amide], in particular tris[N,N-bis(trimethylsilyl) lanthanum amide] or neodymium tris[N,N-bis(trimethylsilyl)amide], the catalytic system advantageously comprises tetrahydrofuran or ethyltetrahydrofurfuryl ether.

Also with a view to improving the catalytic activity, the catalytic system may additionally comprise at least one other organometallic compound, the metal being lithium or aluminum.

Mention may be made, as organolithium compounds, of the compounds of formula RLi , in which R can be an aliphatic radical in Ci-Cio, substituted or not, an aromatic radical in C ₆ -C ₂₀ , substituted or not. Very particularly suitable are the compounds of formula RLi in which R is a radical noncyclic C 1 -C ₄ alkyl chosen from a methyl, ethyl, propyl or butyl radical, in particular n-butyllithium.

As organoaluminium compounds, mention may be made of alkylaluminium chosen from trialkylaluminium, or dialkylaluminium hydrides, the alkyl group comprising from 1 to 10 carbon atoms. By way of trialkylaluminum, mention may be made of triethylaluminum, tri-isopropylaluminum, tri-isobutylaluminum, tributylaluminum or trioctyaluminum. As dialkylaluminum hydride, mention may be made of diisobutylaluminum hydride.

As an organoaluminum compound that can be used in the catalytic system according to the invention, mention may also be made of aluminoxanes, compounds resulting from the partial hydrolysis of one or more trialkylaminiums, such as methylaluminoxane, triisobutylaluminoxane or else methylaluminoxanes.

When the catalytic system comprises at least one other organometallic compound, the metal being lithium or aluminium, it advantageously also comprises at least one electron donor. Such a combination of co-catalysts makes it possible to optimize the conversion while maintaining a high 1,4-trans linkage rate and maintaining a low 1,2 linkage rate.

Very particularly according to these embodiments of the invention, when the rare earth tris(amide) is a lanthanum tris[N,N-bis(trialkylsilyl)amide], in particular tris[N,N-bis(trimethylsilyl) amide] of lanthanum, the catalytic system advantageously comprises an alkyllithium, such as n-butyllithium, or an alkylaluminum, such as triethylaluminum, and tetrahydrofuran.

According to any one of the embodiments of the invention, the catalytic system can preferably comprise a hydrocarbon solvent. The catalytic system can be in the form of a solution when it is in the presence of a hydrocarbon solvent. The hydrocarbon solvent can be a low molecular weight aliphatic hydrocarbon solvent, such as for example cyclohexane, methylcyclohexane, n-heptane, or a mixture of these solvents, or else in an aromatic solvent such as toluene. It should be noted that non-aromatic solvents are particularly preferred. The hydrocarbon solvent is preferably aliphatic, more preferably methylcyclohexane.

According to certain particular embodiments of the catalytic system of the invention, at least one of the following characteristics is respected, at least two, at least three, at least four and preferably all of them:

- the rare earth tris(amide) is a rare earth tris[N,N-bis(trialkylsilyl)amide], preferably a rare earth tris[N,N-bis(trimethylsilyl)amide],

- the rare earth is a lanthanide, preferably lanthanum or neodymium,

- the molar ratio (organic magnesium compound of formula R ¹ R ² Mg / rare earth tris(amide)) has a value less than or equal to 40/1, preferably less than or equal to 30/1, preferably even less or equal to 20/1, or even less than 20/1, in particular by at most 15/1,

- the catalytic system further comprises an electron donor chosen from ethers, preferably tetrahydrofuran or ethyltetrahydrofurfuryl ether, the molar ratio (electron donor/organic magnesium compound of formula R ¹ R ² Mg) being at least 1/2.

More particularly still according to these embodiments, at least one of the following characteristics is respected, at least two, at least three and preferably all of them:

- the molar ratio (organic magnesium compound of formula R ¹ R ² Mg / rare earth tris(amide)) has a value less than or equal to 40/1, preferably less than or equal to 30/1, preferably even less or equal to 20/1, or even less than 20/1, in particular by at most 15/1.,

- the catalytic system further comprises an electron donor chosen from tetrahydrofuran (THF) or ethyltetrahydrofurfuryl ether, the molar ratio (electron donor/organic magnesium compound of formula R ¹ R ² Mg) being at least 1/2.

A method for preparing a catalytic system as defined above is also the subject of the present invention.

The process for preparing the catalytic system comprises contacting the rare earth tris(amide) and the organic magnesium compound.

Rare earth tris(amides) compounds such as rare earth tris[N,N-bis(trimethylsilyl)amide] are commercially available. They can also be synthesized according to the method described by Bradley et al. (Bradley, D. C., Ghotra, J. S., and Hart, F. A., J. Chem. Soc., Dalton Trans. 1973,

1021). and modified by Boisson et al. (Boisson, C., Barbotin, F., and Spitz, R., Macromol. Chem. Phys. 1999, 200, 1163).

Organic magnesium compounds such as dialkylmagnesiums are commercially available.

The contacting of the various components can be carried out at a temperature of between 15 and 100° C., and for 3 to 120 minutes.

The rare earth tris(amide) generally comes in solid form which is dissolved in an inert hydrocarbon solvent.

According to a variant of preparation of the catalytic system in accordance with the invention, the catalytic system is formed in situ, that is to say that the various catalytic constituents, namely the rare earth tris(amide) and the organic compound of magnesium are introduced directly into the polymerization medium. According to this variant, an order of addition of the constituents of the catalytic system according to the invention can be as follows: in a first step, the organic magnesium compound and, where appropriate, the donor of electrons. The monomer to be polymerized can be present in the medium before this addition or can be added to the medium after this step. In a second step, the rare earth tris(amide) is then added to the reaction medium.

According to another variant of preparation of the catalytic system according to the invention, the constituents of the catalytic system are pre-mixed before being brought into contact with the solvent containing the or the monomer(s) to be polymerized, by introducing the constituents of the catalytic system into an inert hydrocarbon solvent, for a time of between 0 and 120 minutes, at a temperature ranging from 10°C to 80°C, possibly above room temperature , generally ranging from 18°C to 30°C, so as to obtain a premixed catalytic system. The premixed catalytic system thus obtained is then brought into contact with the solvent containing the monomer(s) to be polymerized.

According to another variant of preparation of the catalytic system in accordance with the invention, the catalytic system is preformed prior to any polymerization reaction, that is to say by bringing the various catalytic constituents into contact, followed by aging of the constituents. catalysts before use in polymerization, optionally in the presence of a preforming conjugated diene. Before being used for example in polymerization, the catalytic system thus obtained in solution can be stored under an inert atmosphere, for example under nitrogen or argon, in particular at a temperature ranging from -20° C. to room temperature (23° C.) .

The preparation of the catalytic system according to the invention is carried out in an aliphatic or alicyclic solvent of low molecular weight, such as for example cyclohexane, methylcyclohexane, n-heptane, or a mixture of these solvents, preferably in methylcyclohexane, or else in an aromatic solvent such as toluene. It should be noted that non-aromatic solvents are particularly preferred, especially methylcyclohexane.

The catalytic system according to the invention can be advantageously used in a diene polymer synthesis process, which process is also the subject of the present invention. Indeed, it turns out that the catalytic system according to the invention, used in such a process, promotes the 1,4-trans insertion of conjugated diene monomers, thus making it possible to obtain diene polymers having a linking rate of 1 ,4-trans high while limiting linking rate 1,2. The synthesis process using a catalytic system according to the invention makes it possible in particular to obtain butadiene polymers having 1,4-trans linkage levels greater than or equal to 65% by weight and 1,2 linkage levels of less than 10 % by weight, based on the weight of the diene part of the polymer.

A subject of the invention is therefore also a process for the synthesis of a diene polymer comprising a stage of polymerization in a reactor of at least one conjugated diene monomer in the presence of a catalytic system as described above.

According to the invention, the conjugated diene monomer to be polymerized is most particularly a 1,3-diene monomer. As 1,3-diene monomer in accordance with the invention, a 1,3-diene monomer having 4 to 15 carbon atoms is very particularly suitable.

As 1,3-diene monomer, mention may be made in particular of a monomer such as butadiene, isoprene, 2,3-di(C 1 to C ₅ alkyl)-l,3-butadiene such as for example 2 ,3-dimethyl-1,3-butadiene, 2,3-diethyl-1,3-butadiene, 2-methyl-3-ethyl-1,3-butadiene, 2-methyl-3-isopropyl-1,3- butadiene, phenyl-1,3-butadiene, 1,3-pentadiene, or any other 1,3-diene monomer having 4 to 12 carbon atoms. As a 1,3-diene monomer, any non-cyclic terpene is also suitable, such as in particular a non-cyclic monoterpene (CH ) such as myrcene, a non-cyclic sesquiterpene (CH ) such as farnesene, etc. According to certain modes of realization of the invention, the conjugated diene monomer is butadiene or isoprene, advantageously butadiene.

According to certain embodiments of the invention, the polymerization step of the process is a homopolymerization step of a conjugated diene monomer in the presence of a catalytic system as described above.

According to certain embodiments of the invention, the polymerization step of the process is a step of copolymerization of at least one diene monomer in the presence of a catalytic system as described above. The diene monomer is then copolymerized with at least one other monomer.

As another monomer suitable in particular is a conjugated diene monomer having 4 to 15 carbon atoms as defined above, different from the first conjugated diene monomer. As conjugated diene monomer suitable in particular 1,3-butadiene, 2-methyl-l,3-butadiene (or isoprene), 2,3-di (C 1 to C ₅ alkyl) 1,3-butadiene such as for example 2,3-dimethyl-1,3-butadiene, 2,3-diethyl-1,3-butadiene, 2-methyl-3-ethyl-1,3-butadiene, 2-methyl-3 -isopropyl-1,3-butadiene, phenyl-1,3-butadiene, 1,3-pentadiene, 2,4-hexadiene, or any other conjugated diene having between 4 and 12 carbon atoms. By way of conjugated diene monomer, mention may also be made of non-cyclic terpene conjugated diene monomers, more particularly a farnesene or myrcene.

As another monomer, a vinylaromatic compound is also suitable. As vinyl aromatic monomer, mention may be made of a vinylaromatic monomer having from 8 to 20 carbon atoms, such as for example styrene, ortho-, meta-, para-methylstyrene, 2,4,6-trimethylstyrene, divinyl benzene and vinylnaphthalene, preferably the vinylaromatic monomer is styrene.

The polymerization step can be carried out in known manner, continuously or discontinuously, in bulk or in solution, generally and in known manner at a temperature between 40°C and 120°C.

The polymerization step can be carried out in an organic solvent conventionally used for the polymerization of diene monomers. By organic solvent is meant according to the invention an inert hydrocarbon solvent which can be for example an aliphatic or alicyclic hydrocarbon such as pentane, hexane, heptane, iso-octane, cyclohexane, methylcyclohexane, or a aromatic hydrocarbon such as benzene, toluene, xylene, or mixtures of these solvents.

It should be noted that non-aromatic solvents are particularly preferred.

The catalytic system as described above according to all its embodiments is introduced into the polymerization reactor.

According to certain embodiments of the invention, the catalytic system is used in proportions varying from 20 to 2000 pmol of rare earth metal per 100 g of monomers, preferably from 20 to 1000 pmol, even more preferably from 50 to 1000 pmol . According to certain embodiments of the invention, the polymerization step of the process is preceded by the addition of an organic magnesium compound of formula R ³ R ⁴ Mg, directly into the reaction medium, before or after the introduction monomers and staggered from the introduction of the catalytic system into the reactor. That is to say that the addition is made in the polymerization medium not at the same time and, consequently, either before, or after, or partly before and partly after, preferably before, with respect to the introduction of the catalytic system used to catalyze the polymerization reaction. The addition is preferably done before the introduction of the monomers.

It will be noted that the addition of the organic magnesium compound of formula R ³ R ⁴ Mg before the preformed catalytic system makes it possible in particular to minimize the dispersion of the characteristics of the elastomer obtained, in particular of the molecular masses.

The organic magnesium compound of formula R ³ R ⁴ Mg may be identical to or different from the organic magnesium compound of formula R ¹ R ² Mg of the catalytic system.

In the formula R ³ R ⁴ Mg, each of R ³ and R ⁴ represents, independently of one another, an aliphatic radical in Ci-Cio, substituted or not, an aromatic radical in C ₆ -C ₂₀ , substituted or not. The aliphatic and aromatic radicals are defined above in relation to R ¹ and R ² . More particularly, each of R ³ and R ⁴ is a noncyclic C ₁ -C ₄ alkyl radical chosen from a methyl, ethyl, n-propyl, iso-propyl, i-butyl, n-butyl, s-butyl or tert -butyl.

According to these embodiments of the invention, the organic magnesium compound of formula R ³ R ⁴ Mg is preferably n-butylethylmagnesium or n-butyloctylmagnesium.

According to certain particular embodiments of the method according to the invention, at least one of the following characteristics is respected, at least two, at least three, at least four, at least five, at least six and preferably all of them:

- the conjugated diene monomer to be polymerized is a 1,3 diene monomer having 4 to 15 carbon atoms, preferably 1,3-butadiene,

- the rare earth is a lanthanide, preferably lanthanum or neodymium,

- the organic magnesium compound in the catalytic system is a dialkylmagnesium, the alkyl radical having 1 to 10 carbon atoms, preferably n-butylethylmagnesium or n-butyloctylmagnesium,

- in the catalytic system, the molar ratio (organic magnesium compound of formula R ¹ R ² Mg / rare earth tris(amide)) has a value less than or equal to 40/1, preferably less than or equal to 30/1, preferably still less than or equal to 20/1, or even less than 20/1, in particular by at most 15/1,

- the catalytic system also comprises an electron donor chosen from ethers, preferably tetrahydrofuran or ethyltetrahydrofurfuryl ether, the molar ratio (electron donor/organic magnesium compound of formula R ¹ R ² Mg) preferably being d at least 1/2

- an organic magnesium compound of formula R ³ R ⁴ Mg, in which each of R ³ and R ⁴ represents, independently of one another, an aliphatic radical in C1-C10, substituted or not, an aromatic radical in C6-C20, substituted or unsubstituted, preferably n-butylethylmagnesium or n- butyloctylmagnesium, is added to the reactor in a staggered manner and independently of the catalytic system

At the end of the polymerization step, the process for synthesizing a diene polymer according to the invention can be continued in a manner known per se. Thus, in certain embodiments, the polymerization can be stopped, optionally after a step of post-polymerization modification of the diene polymer.

The process then continues in a manner known per se with the separation and recovery of the diene polymer prepared. Unreacted monomers can be removed using methods known to those skilled in the art, as can the solvent.

The aforementioned characteristics of the present invention, as well as others, will be better understood on reading the following description of several embodiments of the invention, given by way of indication and not limitation.

Examples

Measurements and tests used

Near infrared (NIR) spectroscopy:

The microstructure of elastomers is characterized by the technique of near infrared spectroscopy (NIR).

Near infrared (NIR) spectroscopy is used to determine the microstructure (relative distribution of 1,2-, 1,4-trans and 1,4-cis butadiene units). The principle of the method is based on the Beer-Lambert law generalized to a multi-component system. The method being indirect, it calls upon a multivariate calibration [Vilmin, F.; Dussap, C.; Coste, N. Applied Spectroscopy 2006, 60, 619-29] produced using standard elastomers with a composition determined by ¹³ C NMR. The microstructure is then calculated from the NIR spectrum of an elastomer film of about 750 pm thick. Spectrum acquisition is carried out in transmission mode between 7800 and 3900 cm ¹ with a resolution of 2 cm ¹ , using a Fourier transform near infrared spectrometer equipped with an InGaAs detector cooled by the Peltier effect.

Conversion:

The conversion is calculated as via the ratio between the mass of the polymer isolated at the end of the reaction and the mass of butadiene introduced into the reactor.

[Math 1] c ^m " ^{polybutadiene} _ ₁₀₀ m butadiene m _butadiene which represents the mass of butadiene introduced into the reactor, mp _oiybutadiene which represents the mass of polybutadiene obtained.

The examples which follow aim to show the great advantage of the catalytic system according to the invention for the stereospecific polymerization of conjugated diene monomers, in particular by promoting the 1,4-trans linkage while maintaining a low level of 1,2 linkage. Process for the synthesis of butadiene polymers:

Examples 1 and 18

The degassed methylcyclohexane solvent, the n-butylethylmagnesium in solution in methylcyclohexane and then the butadiene (9.1 g) are introduced into a sealed, inerted steinie bottle under nitrogen sweeping. The quantities of the reagents are mentioned in the table below. The compound La(HMDS)3 or Nd(HMDS)3 in solution in methylcyclohexane (C=0.1 mol/L) is then injected into the reaction medium. The reaction medium is heated at 70° C. for 5 h. After 5 h, the reaction is stopped using methanol (1 mL) and a conversion measurement is carried out. The solution is then anti-oxidized and dried in an oven.

Examples 2 to 13 and 18 to 25 - Polymerization in the presence of an electron donor

The degassed methylcyclohexane solvent, the butylethylmagnesium in solution in the methylcyclohexane, the electron donor (DE) and then the butadiene (9.1g) are introduced into a sealed steinie bottle, inerted under nitrogen sweeping. The quantities of the reagents are mentioned in the table below. The compound La(HMDS)3 or Nd(HMDS)3 in solution in methylcyclohexane (C=0.1 mol/L) is then injected into the reaction medium. The reaction medium is heated to 70°C. After the indicated polymerization time, the reaction is stopped using methanol (1 mL) and a conversion measurement is carried out. The solution is then anti-oxidized and dried in an oven.

Examples 14 and 15 - Polymerization in the presence of an organolithium

The degassed methylcyclohexane solvent, the n-butylethylmagnesium dissolved in methylcyclohexane, the electron donor if mentioned in the table, then the butadiene (9.1g) are introduced into a sealed steinie bottle, inerted under nitrogen sweeping. The quantities of the reagents are mentioned in the table below. The n-butyllithium is then introduced and the compound La(HMDS)3 in solution in methylcyclohexane (C=0.1 mol/L) is injected into the reaction medium. The reaction medium is heated to 70°C. After the indicated polymerization time, the reaction is stopped using methanol (1 mL) and a conversion measurement is carried out. The solution is then anti-oxidized and dried in an oven.

Examples 16 and 17 - Polymerization in the presence of an organoaluminum

The degassed methylcyclohexane solvent, the n-butylethylmagnesium in solution in methylcyclohexane, the triethylaluminum and the tetrahydrofuran if mentioned in the table, then the butadiene (9.1g) are introduced into a sealed, inerted bottle under nitrogen sweeping. The quantities of the reagents are mentioned in the table below. The compound La(HMDS)3 in solution in methylcyclohexane (C=0.1 mol/L) is then injected into the reaction medium. The reaction medium is heated to 70°C. After the indicated polymerization time, the reaction is stopped using methanol (1 mL) and a conversion measurement is carried out. The solution is then anti-oxidized and dried in an oven. Table 1:

Catalytic system: 400 mtioI Ln/100g monomer to be polymerized Solvent/monomer mass ratio is 7/1 M = rare earth metal THF = tetrahydrofuran

ETE = ethyltetrahydrofurfuryl ether All the syntheses carried out have made it possible to obtain 1,4-trans stereoregular polybutadienes, having in particular a high level of 1,4-trans of more than 80% by weight. In addition, all the syntheses made it possible to limit the formation of 1,2- linkages. Indeed, all the polybutadienes obtained have a 1,2- linkage rate of less than 10% by weight. It is noted that thanks to the use of an electron donor, the conversion of the polymerization reaction is improved, even with an DE/Mg ratio of 1/2.

It is found that the combined use of an electron donor and another organic compound of lithium or aluminum (examples 15 and 17), improves the conversion of the polymerization reaction compared to that of example 1 , with no impact on the 1,4-trans linking rate with a limited 1,2-linking rate, always less than 10%.

Claims

1. Catalytic system including

- a rare earth tris(amide),

- an organic magnesium compound of formula R ¹ R ² Mg , in which R ¹ and R ² represent, independently of each other, an aliphatic radical in Ci-Cio, substituted or not, an aromatic radical in C6- C20, substituted or not.

2. Catalytic system according to the preceding claim, characterized in that the aliphatic radical, in the definition of R ¹ and R ² is a C1-C10 alkyl radical, substituted or unsubstituted.

3. Catalytic system according to any one of the preceding claims, characterized in that the organic magnesium compound is n-butylethylmagnesium or n-butyloctylmagnesium.

4. Catalytic system according to any one of the preceding claims, characterized in that the rare earth metal making up the rare earth tris(amide) is a lanthanide, preferably lanthanum or neodymium.

5. Catalytic system according to any one of the preceding claims, characterized in that the amide is an N,N-bis(trialkylsilyl)amide, preferably N,N-bis(trimethylsilyl)amide.

6. Catalytic system according to any one of the preceding claims, characterized in that the rare earth tris(amide) is lanthanum tris[N,N-bis(trimethylsilyl)amide] or tris[N,N-bis (trimethylsilyl)amide] of neodymium.

7. Catalytic system according to any one of the preceding claims, characterized in that the molar ratio (organic magnesium compound of formula R ¹ R ² Mg / rare earth tris(amide)) has a value less than or equal to 40/ 1, preferably less than or equal to 30/1, more preferably less than or equal to 20/1, or even less than 20/1, in particular by at most 15/1.

8. Catalytic system according to any one of the preceding claims, characterized in that the molar ratio (organic magnesium compound of formula R ¹ R ² Mg / rare earth tris(amide)) has a value greater than 1/1, more preferably at least 5/1.

9. Catalytic system according to any one of the preceding claims, characterized in that it further comprises at least one electron donor according to a molar ratio (electron donor/organic magnesium compound of formula R ¹ R ² Mg ) by at least 1/2.

10. Catalytic system according to the preceding claim, characterized in that the electron donor is an ether, preferably tetrahydrofuran or ethyltetrahydrofurfuryl ether.

11. Catalytic system according to any one of the preceding claims, characterized in that at least one of the following characteristics is respected, at least two, at least three, at least four and preferably all of them:

- the rare earth is a lanthanide, preferably lanthanum or neodymium,

- the catalytic system further comprises an electron donor chosen from ethers, preferably tetrahydrofuran or ethyltetrahydrofurfuryl ether.

12. Process for the preparation of a diene polymer comprising the polymerization reaction of at least one conjugated diene monomer in a reactor in the presence of a catalytic system as defined in any one of the preceding claims.

13. Process according to the preceding claim, comprising, in a staggered manner upon introduction of the catalytic polymerization system into the reactor, the addition to the reactor of at least one organic magnesium compound of formula R ³ R ⁴ Mg, in which each of R ³ and R ⁴ represents, independently of one another, an aliphatic radical in Ci-Cio, substituted or not, an aromatic radical in C6-C20, substituted or not.

14. Process according to any one of claims 12 and 13, characterized in that the conjugated diene monomer to be polymerized is a 1,3-diene monomer having 4 to 15 carbon atoms, preferably 1,3-butadiene.

15. Method according to any one of claims 12 to 14, in which at least one of the following characteristics is respected, at least two, at least three, at least four, at least five, at least six and preferably all of them:

- the conjugated diene monomer to be polymerized is a 1,3-diene monomer having 4 to 15 carbon atoms, preferably 1,3-butadiene,

- the rare earth is a lanthanide, preferably lanthanum or neodymium,

- in the catalytic system, the molar ratio (organic magnesium compound of formula R ¹ R ² Mg / rare earth tris(amide)) has a value less than or equal to 40/1, preferably less than or equal to 30/1, preferably still less than or equal to 20/1, or even less than 20/1, in particular by at most 15/1.,

- the catalytic system also comprises an electron donor chosen from ethers, preferably tetrahydrofuran or ethyltetrahydrofurfuryl ether,

- an organic magnesium compound of formula R ³ R ⁴ Mg, in which each of R ³ and R ⁴ represents, independently of one another, an aliphatic radical in Ci-Cio, substituted or not, an aromatic radical in C6-C20, substituted or unsubstituted, preferably n-butylethylmagnesium or n-butyloctylmagnesium, is added to the reactor offset from the addition of the catalytic system.