EP4352115A1

EP4352115A1 - Preformed catalytic system for the stereospecific polymerization of dienes and use thereof in a process for synthesizing diene polymers

Info

Publication number: EP4352115A1
Application number: EP22733699.7A
Authority: EP
Inventors: Leyla PEHLIVAN; Stéphanie PINEL; Philip-Christopher GEORGE
Original assignee: Compagnie Generale des Etablissements Michelin SCA
Current assignee: Compagnie Generale des Etablissements Michelin SCA
Priority date: 2021-06-10
Filing date: 2022-05-30
Publication date: 2024-04-17
Also published as: FR3123916A1; WO2022258906A1

Abstract

The invention relates to a preformed stereospecific catalytic system comprising: • - an organic phosphoric acid salt of neodymium, • - a preforming diene monomer, and • - an organic magnesium compound having formula R1R2Mg, wherein R1 and R2 each represent, independently of each other, an optionally-substituted C1-C10 aliphatic radical or an optionally-substituted C6-C20 aromatic radical. The use of this catalytic system for the polymerization of 1,3-dienes, which promotes trans-1,4 insertion of 1,3-diene monomers, yields diene polymers with a high trans-1,4 chaining rate.

Description

PREFORMED CATALYTIC SYSTEM FOR THE STEREOSPECIFIC POLYMERIZATION OF DIENES AND THEIR USE IN A PROCESS FOR THE SYNTHESIS OF DIENIC 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 1,4-trans linking rate 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 organic compounds of rare earths and organic compounds of magnesium for the polymerization of 1,3-diene monomers capable of generating a 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 allowing to regulate the ratio of 1,4-cis and 1,4-trans levels to achieve a balance between tolerance to deformation (attributed to the cis-1,4 part of the polybutadiene) and stiffness (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 a polybutadiene by coordination catalysis by promoting the 1,4-trans insertion of butadiene.

Several publications report the controlled polymerization of isoprene using a catalytic system comprising a neodymium borohydride and a dialkylmagnesium, in the presence or absence of tetrahydrofuran. These catalytic systems make it possible to provide stereoregular 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.

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 high levels of 1,4-trans linkage, that is 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.

Disclosure of Invention

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

The invention makes it possible to solve this problem by proposing a preformed catalytic system combining a neodymium organophosphate and an organic magnesium compound which, used for the polymerization of 1,3-dienes, has a stereospecificity with respect to the insertion 1 ,4-trans while maintaining satisfactory polymerization reaction conversion. 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 having high levels of 1,4-trans linkage, with in particular values of at least 65% by weight relative to the diene part of the polymer, and a low 1,2-linking rate, in particular with values less than or equal to 10% by weight relative to the diene part of the polymer.

More particularly, the use of the preformed 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% by weight relative to the diene part of the polybutadiene;

- a 1,2- vinyl linking rate less than or equal to 10% by weight relative to the diene part of the polybutadiene.

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

In another aspect, the invention relates to a method of synthesizing a diene polymer using such a preformed 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- Preformed catalytic system based on at least

- a neodymium salt of an organic phosphoric acid,

- a preformation diene monomer, and

- 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 R ² Mg is a Ci-Cio alkyl radical, substituted or not.

3- 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 chosen from a methyl or ethyl radical, propyl, butyl, pentyl, hexyl, heptyl radicals , octyls, nonyls and decyls.

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 preformation monomer is a conjugated diene monomer having 4 to 15 carbon atoms.

6- Catalytic system according to the previous embodiment in which the preformation monomer is a 1,3-diene monomer having 4 to 15 carbon atoms, preferably 1,3-butadiene.

7- Catalytic system according to any one of the preceding embodiments in which the neodymium salt of an organic phosphoric acid is a neodymium tris(organophosphate).

8- Catalytic system according to the previous embodiment in which the organophosphate is a phosphoric acid diester.

9- Catalytic system according to the previous embodiment in which the neodymium salt of an organic phosphoric acid is neodymium tris[bis(2-ethylhexyl)phosphate].

10- Catalytic system according to any one of the preceding embodiments in which the molar ratio (R ¹ R ² Mg / neodymium) has a value of at most 15/1 and preferably of at most 12/1, more preferably of at most 11/1.

11- Catalytic system according to any one of the preceding embodiments in which the molar ratio (R ¹ R ² Mg / neodymium) has a value of at least 1/2, preferably of at least 1/1, more preferably of at least 2/1.

12- Catalytic system according to any one of the preceding embodiments in which the molar ratio (preformation monomer/neodymium) has a value of at least 5/1, preferably of at least 15/1.

13- 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 organic phosphoric acid salt of neodymium is a phosphoric acid diester of neodymium, preferably tris [bis (2-ethylhexyl) phosphate] of neodymium,

- the preformation monomer is 1,3-butadiene,

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

- the molar ratio (R ¹ R ² Mg / neodymium) has a value of at most 15/1, preferably of at most 12/1, more preferably of at most 11/1, - the molar ratio (preformation monomer/neodymium) has a value of at least 5/1, preferably of at least 15/1.

14- Catalytic system according to any one of the preceding embodiments in which the catalytic system is bimetallic.

15- Catalytic system according to any one of the preceding embodiments in which the catalytic system is ternary.

16- 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 preformed catalytic system as defined in one of the preceding embodiments

17- Process according to embodiment 16 comprising, offset from the introduction of the preformed 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.

18- Process according to the previous embodiment in which the molar ratio (organic magnesium compounds / neodymium) is at most 15/1, preferably at most 12/1, more preferably at most 11/1, the molar quantity of organic magnesium compounds being the sum of the molar quantities of the magnesium compounds R ¹ R ² Mg and R ³ R ⁴ Mg.

19- Process according to any one of embodiments 16 to 18 in which the conjugated diene monomer to be polymerized is a 1,3-diene monomer.

20- Process according to any one of embodiments 16 to 19 in which the conjugated diene monomer to be polymerized is a 1,3-diene monomer having 4 to 15 carbon atoms, preferably butadiene or isoprene, more preferably butadiene .

21. Process according to any one of the preceding embodiments 16 to 20, in which the conjugated diene monomer to be polymerized is copolymerized with at least one other monomer.

22. 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.

23. Process according to embodiment 21 or 22, in which the conjugated diene monomer to be polymerized is copolymerized with at least one other monomer chosen from vinylaromatic compounds, preferably styrene.

24 - Process according to any one of the preceding embodiments 16 to 23 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 neodymium organic phosphoric acid salt of the preformed catalytic system is the neodymium tris[bis(2-ethylhexyl)phosphate],

- the preformation monomer is 1,3-butadiene,

- the organic magnesium compound of the preformed catalytic system is n-butylethylmagnesium or n-butyloctylmagnesium,

- in the preformed catalytic system, the molar ratio (R ¹ R ² Mg / neodymium) has a value of at most 15/1, preferably of at most 12/1, more preferably of at most 11/1 ,

- in the preformed catalytic system, the molar ratio (preformation monomer/neodymium) has a value of at least 5/1, preferably at least 15/1,

- an organic magnesium compound 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, preferably n-butylethylmagnesium or n-butyloctylmagnesium, is added to the reactor independently of the catalytic system provided that the molar ratio (organic magnesium compounds / neodymium) is at most 15/1, preferably of at most 12/1, more preferably of at most 11/1, the molar quantity of organic magnesium compounds being the sum of the molar quantities of the magnesium compounds R ¹ R ² Mg and R ³ R ⁴ Mg .

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 mass). 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 65% in a diene polymer corresponds to a 1,4-trans diene unit rate of more than 65% by weight relative to the weight of the diene part of the polymer .

In the present description, the term “high level of 1,4-trans linkage” means a level of 1,4-trans linkage of more than 65% 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).

By the expression “based on” used to define the constituents of the catalytic system, is meant the mixture of these constituents and/or the product of the reaction between these constituents. 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 preformed catalytic system based on at least

- a neodymium salt of an organic phosphoric acid,

- a preformation monomer, and

- 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.

The catalytic system according to the invention is based on at least one neodymium salt of an organic phosphoric acid. The organic phosphoric acid salt of neodymium is advantageously a tris(organophosphate) of neodymium, the organophosphate being able to be chosen from the diesters of phosphoric acid of general formula (R'0)(R"0)P0(OH), in which R' and R", which are identical or different, represent a C ₁ -C ₁₀ alkyl radical or a C ₆ -C ₂₀ aryl or C ₇ -C ₂₅ alkylaryl radical. By way of example, mention may be made of a tris [dibutyl phosphate] of neodymium, a tris [dipentyl phosphate] of neodymium, a tris [dioctyl phosphate] of neodymium, a tris [bis (2-ethylhexyl) phosphate] of neodymium, a neodymium tris[bis(1-methylheptyl)phosphate], neodymium tris[bis(p-nonylphenyl)phosphate], neodymium tris[butyl(2-ethylhexyl)phosphate], neodymium tris[(1-methylheptyl) ( neodymium tris [(2-ethylhexyl) (p-nonylphenyl) phosphate], neodymium tris [bis (2-ethylhexyl) phosphate], tris [bis(oleyllyl) phosphate] neodymium or a neodymium tris[bis(lineolyl)phosphate].

According to embodiments of the invention, the organic phosphoric acid salt of neodymium is neodymium tris[bis(2-ethylhexyl)phosphate].

The neodymium salt can be in the form of a powder, of a solution in an inert hydrocarbon solvent, of a suspension in an inert hydrocarbon solvent or else of a gel in an inert hydrocarbon solvent. According to embodiments of the invention, neodymium is present in the catalytic system in a concentration equal to or greater than 0.005 mol/l and at most 0.1 mol/l, more particularly at most 0.08 mol/l.

The catalytic system according to the invention is also based on at least one organic magnesium compound of formula R ¹ R ² Mg

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, at least one of R ¹ and R ² can be a Ci-Cio aliphatic radical, substituted or not. As an aliphatic radical, mention may be made of C 1 -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 noncyclic C ₁ -C ₁₀ alkyl radical chosen from the methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyls, nonyls and decyls.

In the formula R ¹ R ² Mg, at least one of R ¹ and R ² can be a C -C aromatic radical, substituted or not. By way of aromatic radical, mention may be made of C -C aryl groups.

By substituted aliphatic radical or substituted aromatic radical, is meant a radical substituted by one or more hydrocarbon groups having from 1 to 10 carbon atoms.

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 -C alkyl radical. According to this embodiment, the organic magnesium compound of formula R ¹ R ² Mg is n-butylethylmagnesium or n-butyloctylmagnesium.

According to particular embodiments of the invention, the molar ratio (R ¹ R ² Mg/neodymium) in said catalytic system has a value of at least 1/2, preferably of at least 1/1. There is no maximum value for this ratio which is linked to the 1,4-trans linkage rate to be achieved. Nevertheless, so that the achievement of a high level of 1,4-trans linkage greater than 65% by weight relative to the diene part of the polymer does not occur to the detriment of the 1,2- linkage level, the molar ratio (R ¹ R ² Mg/neodymium) in said catalytic system is preferably at most 15/1. Preferably the molar ratio (R ¹ R ² Mg / neodymium) is at most 12/1 to maintain a 1,2 linking rate of less than 10% by weight relative to the diene part of the polymer, more preferably still of at most 11/1.

Furthermore, with a view to maintaining optimization of the conversion, the molar ratio (R ¹ R ² Mg/neodymium) in said catalytic system advantageously has a value of at least 1/1, or even preferably of at least 2/ 1. Also, with a view to maintaining optimization of the conversion, the molar ratio (R ¹ R ² Mg/neodymium) in said catalytic system advantageously has a value of at most 12/1, even more preferably of at most 11/ 1. Thus, according to advantageous embodiments of the invention, the molar ratio (R ¹ R ² Mg / neodymium) in said catalytic system has a value of at least 1/1, preferably of at least 2/1, and at most 12/1, more preferably at most 11/1.

The catalytic system according to the invention is also based on at least one diene monomer intended for the preformation of the catalytic system. By way of diene monomer which can be used to preform the catalytic system according to the invention, mention may be made of conjugated diene monomers and very particularly conjugated diene monomers having 4 to 15 carbon atoms.

Suitable as preformation diene monomer are in particular 1,3-butadiene, 2-methyl-

1,3-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.

As diene monomer that can be used to preform the catalytic system according to the invention, mention may also be made of non-cyclic terpene conjugated diene monomers, more particularly a farnesene or myrcene.

According to particular embodiments of the invention, the preforming diene monomer is a conjugated diene monomer having 4 to 12 carbon atoms, particularly isoprene or

1,3-butadiene, preferably butadiene.

According to embodiments of the invention, the molar ratio (preformation monomer/neodymium) can have a value of at least 5/1, more particularly of at least 15/1. Those skilled in the art will understand that there is no maximum value for this molar ratio which is linked to the activity of the catalyst. The quantity of preformation monomer is mainly linked to the process for manufacturing the catalytic system and to its exothermic nature which is difficult to control industrially. For example, it may be advantageous to have a molar ratio (preformation monomer / neodymium) of at most 100:1, or even at most 70:1.

According to any one of the embodiments of the invention, the catalytic system preferably comprises 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. Generally, the catalytic system is stored in the form of a solution in the hydrocarbon solvent before being used in polymerization.

According to any one of the embodiments of the invention, the catalytic system is bimetallic and therefore contains as metallic compounds only the neodymium salt and the organic magnesium compound.

According to any one of the embodiments of the invention, the catalytic system is ternary and therefore only contains, apart from a possible solvent as mentioned above, the neodymium salt, the preformation monomer and the compound organic magnesium.

Those skilled in the art will understand that the embodiments of the invention mentioned above can be combined with one another in all their particular and preferential aspects, provided that they are compatible. Thus, 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 preformation diene monomer is a conjugated diene monomer having 4 to 15 carbon atoms, preferably 1,3-butadiene,

- the organic magnesium compound R ¹ R ² Mg is n-butylethylmagnesium or n-butyloctylmagnesium,

- the molar ratio (R ¹ R ² Mg / neodymium) has a value of at most 15/1, preferably of at most 12/1, more preferably of at most 11/1,

- the molar ratio (preformation monomer/neodymium) has a value of at least 5/1, preferably of at least 15/1.

The catalytic system according to the invention can be prepared in a conventional manner.

According to a variant, the method for preparing the catalytic system according to the invention comprises the following steps a) and b):

- a) reacting the organic phosphoric acid salt of neodymium and the organic magnesium compound in a hydrocarbon solvent, then

- b) reacting the preformation diene monomer with the reaction product of step a).

The organic phosphoric acid salt of neodymium used for the preparation of the catalytic system can be in the form of a powder; said salt is then previously placed in suspension or in solution in the hydrocarbon solvent.

Stage b) corresponds to the preformation stage of the catalytic system. The hydrocarbon solvent used in the preparation of the catalytic system is generally an aliphatic hydrocarbon solvent such as methylcyclohexane or an aromatic solvent such as toluene. Most often, it is identical to the solvent of the catalytic solution defined previously. Indeed, the hydrocarbon solvent used in the preparation of the catalytic system is, preferably, also the solvent of the catalytic solution.

In step a), the neodymium salt can be added to the hydrocarbon solvent, then the organic magnesium compound. Step a) can take place at a temperature ranging from 10 to 60°C. The reaction time of step a) can vary between 5 and 60 minutes, more preferably from 10 to 20 minutes.

In step b), the preforming monomer is added to the reaction product of step a). Step b) can be carried out at a temperature ranging from 20 to 70°C. The reaction time of step b) can typically vary from 10 minutes to 24 hours, preferably from 20 minutes to 12 hours.

Stage b) can be followed by a degassing stage to eliminate the preformation monomer which would not have reacted during stage b).

Like any synthesis carried out in the presence of an organometallic compound, the synthesis takes place under anhydrous conditions under an inert atmosphere both for step a) and for step b) and, where appropriate, the degassing step. Typically, the reactions are carried out starting from solvents and anhydrous monomers under anhydrous nitrogen or argon. Steps a) and b) are generally carried out with stirring.

Before being used, 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 ambient temperature (of the order of 23° C. ).

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 1,3-diene monomers, thus making it possible to obtain diene polymers having a rate of high 1,4-trans linkage. 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 rates greater than or equal to 65% and having a linkage rate

1.2- less than or equal to 10%.

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

According to the invention, the conjugated diene monomer to be polymerized is most particularly a monomer

1.3-diene. By way of 1,3-diene monomer in accordance with the invention, mention may very particularly be made of 1,3-diene monomers having 4 to 15 carbon atoms.

As 1,3-diene monomer, butadiene, isoprene, 2,3-di(C 1 to C ₅ alkyl)-l,3-butadiene such as for example 2,3-dimethyl-l ,3-butadiene, 2,3-diethyl-l,3-butadiene, 2-methyl-3-ethyl-l,3-butadiene, 2-methyl-3-isopropyl-l,3-butadiene, phenyl-l ,3-butadiene, 1,3-pentadiene, or any other 1,3-diene monomer having 4 to 12 carbon atoms. As 1,3-diene monomer, any non-cyclic terpene is also suitable, such as in particular a non-cyclic monoterpene (C10H16) such as myrcene, a non-cyclic sesquiterpene (C15H24) such as farnesene, etc.

According to certain embodiments of the invention, the conjugated diene monomer to be polymerized 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 conjugated diene monomer in the presence of a catalytic system as described above. The conjugated 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 than 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 preformed catalytic system as described above according to all its embodiments is introduced into a reactor and used for the polymerization of at least one conjugated diene monomer in a reaction medium comprising the monomers to be polymerized and, where appropriate, the solvent of polymerization.

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 to the polymerization medium, independently of the introduction of the preformed catalytic system used for the polymerization reaction and in a staggered manner, a quantity of at least one organic magnesium compound of formula R ³ R ⁴ Mg. That is to say that the addition is made in the polymerization medium not at the same time and, therefore, either before, or after, or partly before and partly after, with respect to the introduction of the system preformed catalyst used to catalyze the polymerization reaction. The addition can advantageously take place before the introduction of the monomers in order to avoid degassing.

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.

Advantageously, the quantity of organic magnesium compound of formula R ³ R ⁴ Mg is such that the molar ratio (organic magnesium compounds/neodymium) is preferably at most 15/1, and more preferably of at most 12/1 with a view to maintaining a 1,2 linking rate of less than or equal to 10%, more preferably of at most 11/1. It is necessary to understand here by molar quantity of organic magnesium compounds the sum of the molar quantity of magnesium compound R ³ R ⁴ Mg used during the polymerization and of the molar quantity of magnesium compound R ¹ R ² Mg of the catalytic system.

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 ₁₀ alkyl radical chosen from a methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl and decyl radical.

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 process for synthesizing a diene polymer according to the invention, at least one of the following characteristics is observed, at least two, at least three, at least four, at least five, at least six and preferably all:

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

- the neodymium organic phosphoric acid salt of the catalytic system is a neodymium phosphoric acid diester, preferably neodymium tris [bis (2-ethylhexyl) phosphate],

- the preformation diene monomer of the catalytic system is a conjugated diene monomer having 4 to 15 carbon atoms, preferably 1,3-butadiene,

- the organic magnesium compound of the catalytic system is n-butylethylmagnesium or n-butyloctylmagnesium,

- in the catalytic system, the molar ratio (R ¹ R ² Mg / neodymium) is at most 15/1, preferably at most 12/1, more preferably at most 11/1,

- in the catalytic system, the molar ratio (preformation monomer / neodymium) is at least 5/1, preferably at least 15/1

- an organic magnesium compound R ³ R ⁴ Mg, each of R ³ and R ⁴ represents, independently of one another, a C ₁ -C ₁₀ aliphatic radical, substituted or not, an aromatic C ₆ radical -C ₂₀ , substituted or unsubstituted, preferably n-butylethylmagnesium or n-butyloctylmagnesium, is added to the polymerization medium independently of the catalytic system at a rate such that the molar ratio (organic magnesium compounds/neodymium) is less than 15/ 1, preferably at most 12/1, more preferably at most 11/1, the molar amount of organic magnesium compounds being the sum of the molar amount of R ³ R ⁴ Mg and the molar amount of R ¹ R ² Mg.

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 by 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 present invention, given by way of indication and not limitation.

Examples

Measurements and tests used

Near infrared spectroscopy (NIR): 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 by the ratio between the mass of the polymer isolated at the end of the reaction and the mass of butadiene introduced into the reactor. c ^m " ^{polybutadiene} _ ₁₀₀ m butadiene rri _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 interest of the catalytic system according to the invention for the polymerization of conjugated diene monomers, in particular by favoring the 1,4-trans linkages while maintaining a low level of 1,2 linkage. Process for the synthesis of catalytic systems:

For Al, A2 and A3 catalytic systems:

Neodymium tris[bis(2-ethylhexyl)phosphate] is dissolved for 12 hours in methylcyclohexane. In a sealed steinie bottle inerted under nitrogen flushing are introduced the degassed methylcyclohexane solvent, tris [bis (2-ethylhexyl) phosphate] of neodymium in solution in methylcyclohexane (the concentration of Nd in the catalytic system is 0.03 mol/L), butylethylmagnesium in solution in methylcyclohexane, then butadiene (butadiene/Nd molar ratio = 30). The reaction medium is heated at 30° C. for 60 minutes. The quantities of the reactants (molar ratios) are mentioned in the table below. The A4 catalytic system is not preformed. Its method of preparation therefore does not include the addition of preformation butadiene (molar ratio butadiene/Nd=0).

Table 1

Process for the synthesis of butadiene polymers: Into an inerted sealed steinie bottle under nitrogen flushing are introduced the degassed methylcyclohexane solvent, n-butylethylmagnesium (denoted Mg _p0iy ) in solution in methylcyclohexane then butadiene (8.7g). For all of the tests, the mass ratio (solvent/monomer) is 7.4/1. The quantities of the reagents are mentioned in the table below. The catalytic system AX is then introduced into the reaction medium. The reaction medium is heated to the temperature indicated in the tables. After a polymerization time of 5 hours, the reaction is stopped using methanol (1 mL). A conversion measurement is carried out if necessary. The solution is then anti-oxidized and dried in an oven.

Presentation of the tests Table 2 presents the degree of conversion of the polymerization reactions with the various catalytic systems AX, as well as the microstructures of the polybutadienes obtained.

Table 2

Catalyst 400 pmol Nd/100g monomer to be polymerized nd = the quantity of polymer synthesized is insufficient to be able to carry out the microstructure measurements by NIR.

On reading the results presented in Table 2: Effect of the preformation of the catalytic system and of the Mg/Nd molar ratio in the catalytic system on the optimization of the microstructure of polybutadiene:

It is found that a catalytic system not preformed with butadiene does not make it possible to achieve a satisfactory conversion rate allowing the production of a sufficient quantity of elastomer to determine the microstructure.

It is observed that the 1,4-trans level in the polybutadiene decreases and the 1,2 linking level increases with an increasing Mg _ca taiyseur/Nd molar ratio in the catalytic system. It is thus possible to modulate the 1,4-trans linking rate by varying the Mgc _a t _a iyseuri/Nd molar ratio with a preferential maximum value of the order of 10/1 in order to maintain a linking rate of 1 .2 to a value less than or equal to 10%.

Effect of the Mg/Nd molar ratio in the catalytic system on the conversion of the reaction of the polymerization of butadiene:

It can be seen, on reading the results in Table 2, that the conversion in 5 hours of polymerization of butadiene at 90° C. increases and then decreases with an increasing Mg _ca catalyst/Nd molar ratio in the catalytic system in a range of values ranging from 2/1 to 10/1.

Table 3 shows the microstructures of the polybutadienes obtained by varying the amount of organic magnesium compound added to the reaction medium outside the catalytic system.

Table 3

On reading the results presented in Table 3:

Effect of the molar ratio M to Neodymium:

It is found that the 1,2-linkage rate increases with an increasing Mg _to t _ai / Nd molar ratio while maintaining a high 1,4-trans linking rate, Mg _to t _ai being the total molar amount of organomagnesium compound comprising the magnesium compound added during the polymerization process and the magnesium compound which enters into the composition of the catalytic system.

It is also noted that to maintain a 1,2 linking rate at a value less than or equal to 10%, when an organomagnesium compound is added during the butadiene polymerization process, the Mg _totai / Nd molar ratio is preferably lower to 12/1, or even at most 11/1.

Claims

1. Preformed catalytic system based on at least

- a salt of an organic neodymium phosphoric acid,

- a preformation diene monomer, and

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

2. Preformed catalytic system according to claim 1, in which the aliphatic radical, in the definition of R ¹ R ² Mg is a C1-C10 alkyl radical, substituted or unsubstituted.

3. Preformed catalytic system according to claim 1 or 2, characterized in that the organic magnesium compound of formula R ¹ R ² Mg is n-butylethylmagnesium or n-butyloctylmagnesium.

4. Preformed catalytic system according to any one of the preceding claims, characterized in that the preformation monomer is a conjugated diene monomer having 4 to 15 carbon atoms, preferably 1,3-butadiene.

5. Preformed catalytic system according to any one of the preceding claims, characterized in that the salt of an organic phosphoric acid of neodymium is a tris (organophosphate) of neodymium.

6. Preformed catalytic system according to any one of the preceding claims, characterized in that the salt of an organic phosphoric acid of neodymium is tris [bis (2-ethylhexyl) phosphate] of neodymium.

7. Preformed catalytic system according to any one of the preceding claims, characterized in that the molar ratio (organic magnesium compound/neodymium) has a value of at most 15/1, preferably of at most 12/1, plus preferably still at most 11/1.

8. Preformed catalytic system according to any one of the preceding claims, characterized in that the molar ratio (organic magnesium compound / neodymium) has a value of at least 1/2, preferably at least 1/1, more preferably still of at least 2/1.

9. Preformed catalytic system according to any one of the preceding claims, characterized in that the molar ratio (preformation monomer/neodymium) has a value of at least 5/1, advantageously of at least 15/1.

10. Preformed 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 organic magnesium compound is a dialkylmagnesium, each of the alkyl radicals being Ci-Cio, substituted or unsubstituted, preferably n-butylethylmagnesium or n-butyloctylmagnesium,

- the molar ratio (organic magnesium compound/neodymium) has a value of at most 15/1, preferably at most 12/1, more preferably at most 11/1,

11. 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 preformed catalytic system as defined in any one of the preceding claims.

12. Process according to claim 11 comprising, staggered upon introduction of the preformed 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.

13. Process according to claim 12, characterized in that the molar ratio (organic magnesium compounds/neodymium) is at most 15/1, preferably at most 12/1, more preferably at most 11/ 1, the molar amount of organic compounds of magnesium being the sum of the molar amounts of the magnesium compounds R ¹ R ² Mg and R ³ R ⁴ Mg.

14. Process according to any one of claims 11 to 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 11 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 organic magnesium compound R ¹ R ² Mg of the catalytic system is a dialkylmagnesium, each of the alkyl radicals being Ci-Cio, substituted or unsubstituted, preferably n-butylethylmagnesium or n-butyloctylmagnesium,

- the molar ratio (R ¹ R ² Mg / neodymium) has a value of at most 15/1, preferably of at most 12/1, more preferably of at most 11/1

- the molar ratio (preformation monomer/neodymium) has a value of at least 5/1, preferably at least 15/1,

- an organic magnesium compound 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, provided that the molar ratio (organic magnesium compounds / neodymium) is at most 15/1 , preferably at most 12/1, more preferably at most 11/1, the molar quantity of organic magnesium compounds being the sum of the molar quantities of the magnesium compounds R ¹ R ² Mg and R ³ R ⁴ Mg.