WO2020070442A1

WO2020070442A1 - Method for synthesising a copolymer of ethylene and myrcene

Info

Publication number: WO2020070442A1
Application number: PCT/FR2019/052326
Authority: WO
Inventors: Vincent LAFAQUIERE; Emma MORESO
Original assignee: Compagnie Generale Des Etablissements Michelin
Priority date: 2018-10-04
Filing date: 2019-10-02
Publication date: 2020-04-09
Also published as: FR3086945A1; FR3086945B1; KR20210069703A

Abstract

The invention relates to a method for producing a copolymer of ethylene and myrcene, comprising ethylene units and myrcene units, the ethylene units in the copolymer representing between 50 mol % and 95 mol % of the ethylene units and the myrcene units of the copolymer, and the myrcene units with a 1,2 and 3,4 configuration in the copolymer representing more than 50 mol % of the myrcene units of the copolymer, said method comprising the polymerisation of ethylene and myrcene in a reactor in the presence of a catalytic system at least containing one metallocene and one organomagnesium compound, ethylene and myrcene being continuously added into the reactor during the polymerisation.

Description

Process for the synthesis of ethylene and myrcene copolymer

The field of the invention is that of the preparation of conjugated diene and ethylene copolymers, rich in ethylene unit and usable as elastomers in a rubber composition for tires.

The most widely used diene elastomers in the manufacture of tires are polybutadienes, polyisoprenes, in particular natural rubber, and copolymers of 1,3-butadiene and styrene. The common point with these elastomers is the high molar proportion of diene units in the elastomer, generally much greater than 50%, which can make them sensitive to oxidation, in particular under the action of ozone.

The Applicant has described elastomers which, on the contrary, are relatively poor in diene units, in particular with a view to reducing their sensitivity to the phenomena of oxidation. These elastomers are for example described in the document WO 2007054223. They are copolymers of 1,3-butadiene and ethylene containing more than 50 mol% of ethylene unit. These elastomers are called diene elastomers rich in ethylene.

The ethylene-rich copolymers of 1,3-butadiene and ethylene are crystalline and see their crystallinity increase with the level of ethylene. The presence of crystalline parts in the copolymer can be problematic when the copolymer is used in a rubber composition. The melting of the crystalline parts of the copolymer resulting in a reduction in its rigidity, a rubber composition containing such a copolymer and used in a tire also sees its rigidity decrease when it is brought to temperatures equal to or exceeding the melting temperature of the crystalline parts , which may be the case during the repeated braking and acceleration phases of the tire. This dependence on stiffness as a function of temperature can therefore lead to uncontrolled fluctuations in the performance of the tire. It is of interest to have diene polymers rich in ethylene units whose crystallinity is reduced, or even eliminated.

In document WO 2007054224, the Applicant has described diene copolymers rich in ethylene which have a reduced crystallinity. These copolymers are copolymers of 1,3-butadiene and ethylene which also contain 6-membered saturated hydrocarbon cyclic units. However, these copolymers introduced into a rubber composition can confer too high rigidity on the rubber composition. The high rigidity of the rubber composition is attributed to an equally high rigidity of the elastomer. High stiffness of a rubber composition can be problematic, as it too can make the rubber composition unsuitable for certain applications. To produce these ethylene and 1,3-butadiene copolymers rich in ethylene and comprising 6-membered saturated hydrocarbon cyclic units, the Applicant has developed a catalytic system based on a metallocene of formula (I) and d an organomagnesium, as described for example in the document WO 2007054224,

P (Cp ¹ ) (Cp ² ) Nd (BH ₄ ) _{(i + y)} -L _y -N _x (I)

Cp ¹ and Cp ² , identical or different, being chosen from the group consisting of substituted fluorenyl groups and the unsubstituted fluorenyl group of formula C _I3 H ₈ , P being a group bridging the two groups Cp ¹ and Cp ² and representing a group ZR ³ R ⁴ , Z representing a silicon or carbon atom, R ³ and R ⁴ , identical or different, each representing an alkyl group comprising from 1 to 20 carbon atoms, preferably a methyl, y, whole number, being equal to or greater than 0, x, whole number or not, being equal to or greater than 0, L representing an alkali metal chosen from the group consisting of lithium, sodium and potassium, N representing a molecule of an ether, preferably diethyl ether or tetrahydrofuran.

As everyone knows, the capacity of a production unit for a given polymer is linked to the productivity of the production unit. One way to increase the productivity of a production unit involving polymerization in the presence of a metallocene-based catalytic system is to increase the catalytic activity. This gain in catalytic activity is therefore constantly sought to make a process for synthesizing a polymer more productive with a view to minimizing the production costs of a polymerization unit and increasing its production capacity.

Pursuing its aim of synthesizing diene elastomers rich in ethylene, the Applicant has discovered a new process for the preparation of a polymer which makes it possible to solve the problems mentioned with the synthesis of a polymer having an improved compromise between its crystallinity, its rate of ethylene and its glass transition temperature.

Thus, the invention relates to a process for the preparation of a copolymer of ethylene and myrcene which comprises ethylene units and myrcene units,

the ethylene units in the copolymer representing between 50% and 95% by moles of the ethylene units and of the myrcene units of the copolymer,

the myrcene units of configuration 1,2 and 3,4 in the copolymer representing more than 50 mol% of the myrcene units of the copolymer,

which process comprises the polymerization of ethylene and myrcene in a reactor in the presence of a catalytic system based at least on a metallocene of formula (I) and an organomagnesium of formula (II),

P (Cp ¹ Cp ² ) Nd (BH ₄ ) _{(i + y} , -L _y -N (l) MgR ¹ R ² (II)

Cp ¹ and Cp ² , identical or different, being chosen from the group consisting of substituted fluorenyl groups and the unsubstituted fluorenyl group of formula C _I3 H ₈ ,

P being a group bridging the two groups Cp ¹ and Cp ² and representing a group ZR ³ R ⁴ , Z representing a silicon or carbon atom, R ³ and R ⁴ , identical or different, each representing an alkyl group comprising of 1 with 20 carbon atoms, preferably methyl,

y, an integer, being equal to or greater than 0,

x, whole number or not, being equal to or greater than 0,

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

N representing a molecule of an ether, preferably diethyl ether or tetrahydrofuran,

R ¹ and R ² , identical or different, representing a carbon group, ethylene and myrcene being added continuously to the reactor during the polymerization.

I. DETAILED DESCRIPTION OF THE INVENTION

In the present description, any range of values designated by the expression "between a and b" represents the range of values greater than "a" and less than "b" (ie limits a and b excluded) while any range of values designated by the expression "from a to b" means the range of values from "a" to "b" (ie including the strict bounds a and b).

The expression “based on” used to define the constituents of a catalytic system or of a composition means the mixture of these constituents, or the product of the reaction of part or all of these constituents. between them.

Unless otherwise indicated, the levels of the units resulting from the insertion of a monomer into a copolymer are expressed in molar percentage relative to the totality of the monomer units of the copolymer. The rate of ethylene unit in the copolymer expressed in "x mole% of the ethylene units and the myrcene units of the copolymer" is calculated by the ratio between the number of moles of ethylene units in the copolymer and the total number of units monomers of the copolymer, ratio multiplied by 100, the total number of monomer units of the copolymer being the sum of the moles of the ethylene units and of the moles of the myrcene units present in the copolymer. The compounds mentioned in the description can be of fossil origin or bio-based. In the latter case, they can be, partially or totally, from biomass or obtained from renewable raw materials from biomass. The monomers are concerned in particular.

Since myrcene is a substituted 1,3-diene, myrcene can give rise to units of configuration 1,2 represented by formula (1), of configuration 3,4 represented by formula (2) and of configuration 1,4 of which the trans form is represented below by formula (3). The units resulting from the polymerization of myrcene are called myrcene units.

(1) (2) (3)

As is also well known, the ethylene unit is a unit of motif - (CH ₂ -CH ₂ ) -.

The process according to the invention makes it possible to prepare a copolymer of ethylene and myrcene, which implies that the monomer units of the copolymer are units resulting from the polymerization of ethylene and myrcene, namely ethylene units and myrcene units. The copolymer therefore comprises ethylene units and myrcene units.

The copolymer of ethylene and myrcene comprises between 50% and 95% in moles of ethylene unit. In other words, the ethylene units in the copolymer represent between 50% and 95% by moles of the ethylene units and of the myrcene units of the copolymer. Another essential characteristic is also to include myrcene units which are more than 50% by mole of the myrcene units of configuration 1,2 and 3,4. In other words, the myrcene units in the copolymer, whether they are of the 1,2 or 3,4 configuration, represent more than 50 mol% of the myrcene units of the copolymer. Preferably, the myrcene units in the copolymer of configuration 1,2 and 3,4 represent more than 55 mol% of the myrcene units of the copolymer. The complement to 100% by mole of the myrcene units in the copolymer consists of all or part of myrcene units of configuration 1.4. According to any one of the embodiments of the invention, preferably more than half of the myrcene units of configuration 1.4 are of 1,4-trans configuration, more preferably all of the myrcene units of configuration 1.4 are of configuration 1,4-trans. According to a preferred embodiment of the invention, the ethylene units in the copolymer represent at least 60% by mole of the ethylene units and of the myrcene units of the copolymer. More preferably, the ethylene units in the copolymer represent from 60 to 90% by mole of the ethylene units and of the myrcene units of the copolymer.

According to a more preferred embodiment of the invention, the ethylene units in the copolymer represent at least 70% by mole of the ethylene units and of the myrcene units of the copolymer. More preferably, the ethylene units in the copolymer represent from 70% to 90% by mole of the ethylene units and of the myrcene units of the copolymer.

Preferably, the copolymer has a glass transition temperature below -35 ° C, in particular between -70 ° C and -35 ° C.

More preferably, the copolymer prepared according to any one of the embodiments of the invention, in particular those described according to any one of claims 1 to 12, is an elastomer.

The catalytic system useful, if necessary, of the invention is a catalytic system based at least on a metallocene of formula (I) and an organomagnesium of formula (II)

PiCp'Cp ² ) Nd (BH ₄ ) _{(i + y) -} L _y -N _x (I)

MgR ¹ R ² (II)

y, an integer, being equal to or greater than 0,

x, whole number or not, being equal to or greater than 0,

R ¹ and R ² , identical or different, representing a carbon group. As substituted fluorenyl groups, mention may be made of those substituted by alkyl radicals having 1 to 6 carbon atoms or by aryl radicals having 6 to 12 carbon atoms. The choice of radicals is also guided by the accessibility to the corresponding molecules that are substituted fluorenes, because the latter are available commercially or easily synthesized.

As substituted fluorenyl groups, there may be mentioned more particularly the groups 2,7 - ditertiobutyle-fluorenyl and 3,6-ditertiobutyle-fluorenyl. Positions 2, 3, 6 and 7 respectively designate the position of the carbon atoms of the rings as shown in the diagram below, position 9 corresponding to the carbon atom to which the P bridge is attached.

The catalytic system is generally introduced into the reactor containing the polymerization solvent and the monomers.

The catalytic system can be prepared in the traditional way by a process analogous to that described in patent application WO 2007054224. For example, the organomagnesium and metallocene is typically reacted in a hydrocarbon solvent at a temperature ranging from 20 to 80 ° C. for a period of between 5 and 60 minutes. The catalytic system is generally prepared in a hydrocarbon solvent, aliphatic such as methylcyclohexane or aromatic such as toluene. Generally after its synthesis, the catalytic system is used as it is in the process for synthesizing the copolymer according to the invention.

Alternatively, the catalytic system can be prepared by a process analogous to that described in patent application WO 2017093654 A1 or in patent application WO 2018020122 A1. According to this alternative, the catalytic system also contains a preformation monomer chosen from a conjugated diene, ethylene or a mixture of ethylene and a conjugated diene, in which case the catalytic system is based at least on metallocene, organomagnesium and the preformation monomer. For example, the organomagnesium and metallocene is typically reacted in a hydrocarbon solvent typically at a temperature of 20 to 80 ° C for 10 to 20 minutes to obtain a first reaction product, then with this first reaction product, a reaction is carried out. temperature ranging from 40 to 90 ° C for 1 hour to 12 hours the preformation monomer chosen from a conjugated diene, ethylene or a mixture of ethylene and a conjugated diene. The catalytic system thus obtained can be used immediately in the process according to the invention or be stored under an inert atmosphere before its use in the process according to the invention.

The metallocene used to prepare the catalytic system can be in the form of powder, crystallized or not, or in the form of single crystals. The metallocene can be in a monomer or dimer form, these forms depending on the method of preparation of the metallocene, as for example that is described in patent application WO 2007054224. The metallocene can be prepared in a traditional manner by a process analogous to that described in patent application WO 2007054224, in particular by reaction under inert and anhydrous conditions of the salt of an alkali metal of the ligand with a rare earth borohydride in a suitable solvent, such as an ether, such as diethyl ether or tetrahydrofuran or any other solvent known to those skilled in the art. After reaction, the metallocene is separated from the reaction by-products by techniques known to those skilled in the art, such as filtration or precipitation in a second solvent. The metallocene is finally dried and isolated in solid form.

Like any synthesis carried out in the presence of an organometallic compound, the synthesis of the metallocene and that of the catalytic system takes place under anhydrous conditions under an inert atmosphere. Typically, the reactions are carried out using solvents and anhydrous compounds under anhydrous nitrogen or argon.

Preferably, the metallocene is of formula (la), (Ib), (le), (Id) or (le) in which the symbol Flu presents the fluorenyl group of formula C _I3 H ₈ .

[{Me ₂ SiFlu ₂ Nd (p-BH ₄ ) 2Li (THF)} ₂ ] (la)

[Me ₂ SiFlu ₂ Nd (p-BH ₄ ) ₂ Li (THF)] (Ib)

[Me ₂ SiFlu ₂ Nd (p-BH ₄ ) (THF)] (le)

[{Me ₂ SiFlu ₂ Nd (p-BH ₄ ) (THF)} ₂ ] (Id)

[Me ₂ SiFlu ₂ Nd (p-BH ₄ )] (le)

The organomagnesium useful for the needs of the invention is of formula MgR ¹ R ² in which R ¹ and R ² , identical or different, represent a carbon group. Carbon group means a group which contains one or more carbon atoms. Preferably, R ¹ and R ² contain 2 to 10 carbon atoms. More preferably, R ¹ and R ² each represent an alkyl. The organomagnesium is advantageously a dialkylmagnesium, better butylethylmagnesium or butyloctylmagnesium, even better butyloctylmagnesium.

According to any one of the embodiments of the invention, the molar ratio of the organomagnesium to the metal Nd constituting the metallocene is preferably within a range from 1 to 100, more preferably is greater than or equal to 1 and less than 10. The range of values from 1 to less than 10 is in particular more favorable for obtaining copolymers of high molar masses.

Those skilled in the art also adapt the polymerization conditions and the concentrations of each of the reactants (constituents of the catalytic system, monomers) according to the material (tools, reactors) used to conduct the polymerization and the various chemical reactions. As is known to a person skilled in the art, the copolymerization as well as the handling of the monomers, of the catalytic system and of the polymerization solvent (s) takes place under anhydrous conditions and under an inert atmosphere. The polymerization solvents are typically hydrocarbon, aliphatic or aromatic solvents.

The polymerization is preferably carried out in solution, continuously or discontinuously. The polymerization solvent can be a hydrocarbon, aromatic or aliphatic solvent. Examples of polymerization solvents that may be mentioned include toluene and methylcyclohexane. Advantageously, the polymerization is carried out in solution in a hydrocarbon solvent.

The copolymerization, namely the polymerization of ethylene and myrcene, is typically carried out under anhydrous conditions and in the absence of oxygen, in the possible presence of an inert gas. The polymerization temperature generally varies in a range from 30 to 150 ° C, preferably from 30 to 120 ° C. These temperature ranges can be applied to any of the embodiments of the invention, in particular those described according to any one of claims 1 to 12. Preferably, the copolymerization is carried out at constant ethylene pressure .

The polymerization can be stopped by cooling the polymerization medium or by adding an alcohol, preferably an alcohol containing 1 to 3 carbon atoms, for example ethanol. The polymer can be recovered according to conventional techniques known to those skilled in the art, for example by precipitation, by evaporation of the solvent under reduced pressure or by stripping with steam.

The preparation process in accordance with the invention also has the essential characteristic of comprising a continuous addition of ethylene and myrcene to the reactor during the polymerization. In other words, the reactor is a powered reactor. The incorporation of myrcene and ethylene into the growing polymer chain being typically statistical, this continuous addition participates in the regulation of the rate of incorporation of the monomers in the growing polymer chain, in particular by controlling the composition of monomers in the polymerization medium. It makes it possible to compensate for the consumption of each of the monomers in the reactor during the polymerization. This addition allows better control of the composition of the copolymer while along the synthesis of the copolymer. It therefore makes it possible to prepare copolymers whose composition along the chain is controlled throughout their synthesis and provides access to copolymers having low levels of crystallinity even when the molar concentration of ethylene units is very high. In particular, it also allows the preparation of copolymers whose composition is almost constant from one end to the other of the chain.

The ethylene and the myrcene to be added continuously to the reactor can be mixed before being introduced into the reactor and thus form a monomer mixture which is then introduced continuously into the reactor. Alternatively, ethylene and myrcene are introduced individually into the reactor, in other words, they do not come into contact with each other before their introduction into the reactor. When ethylene and myrcene are continuously added in the form of a monomer mixture in the reactor, the molar ratio between ethylene in the monomer mixture and myrcene in the monomer mixture is within a range preferably ranging from 1/9 to 19/1, more preferably from 1/1 to 9/1. Thus, the mixture added has an ethylene / myrcene molar composition preferably ranging from 10/90 to 95/5, more preferably from 50/50 to 90/10. When ethylene and myrcene are continuously added individually to the reactor, the flow rates of ethylene and myrcene are such that the molar ratio between the ethylene added in the reactor and the myrcene added in the reactor is included in a range from 1/9 to 19/1, more preferably from 1/1 to 9/1.

The device for implementing the method may comprise one or more means for measuring on the one hand the concentration of myrcene in the reaction medium, on the other hand the pressure of ethylene in the reactor or the concentration of ethylene in the reaction medium. By way of example and without limitation, the measurement means can be carried out by absorbance type methods in the infrared range, absorbance type methods in the ultraviolet / visible range, or by gas chromatography.

According to a particular embodiment of the invention, a system for managing the addition of monomers can be coupled to the reactor in order to maintain constant the ethylene and myrcene concentration in the reactor and thus guarantee a statistical polymer free from a composition gradient. .

In one operating mode, the ethylene concentration in the reaction medium is kept constant by managing the pressure within the reactor with a continuous addition of ethylene. In fact, by keeping the ethylene pressure constant within the reactor and by continuously injecting ethylene, at a rate which can vary, the ethylene consumption is compensated for. Similarly, in this operating mode, the consumption of myrcene is compensated for by adding myrcene to the reactor. Alternatively, ethylene and myrcene are injected at a predetermined flow rate. Thus, the injection of the monomers is controlled by the ethylene pressure in the reactor and by the myrcene concentration in the reaction medium and by a flow rate ratio known by the various tools available from those skilled in the art (experimentation , numerical simulation), and adapted to the catalytic system used. According to this variant, the myrcene is advantageously injected in liquid form. According to this variant, ethylene is advantageously injected in gaseous form. The reactor typically includes a means for measuring the pressure within the reactor connected to an automatic reactor pressure controller which controls the ethylene injection flow rates. The ethylene and myrcene injection flow rates, regulated by the opening of valves and measured respectively by flow measurement means are also controlled by a controller of the ratio of feed flow rates of ethylene and myrcene to respect the pre-established flow ratio.

In a second variant, a mixture of ethylene and myrcene is injected. The reactor includes means for measuring the concentration of ethylene and myrcene in the reaction medium. This measurement means is connected to an automatic controller which controls the injection rate of the mixture of ethylene and myrcene via a valve. According to this second variant, the mixture of ethylene and myrcene is advantageously injected in liquid form.

The process is advantageously a semi-continuous process, process in which ethylene and myrcene are continuously added to the reactor during the polymerization. The polymerization reaction medium is advantageously stirred. The reactor advantageously comprises at least one stirring means, for example with several blades. The temperature of the reaction medium is advantageously kept constant during the polymerization. The total pressure of the reactor is advantageously kept constant.

The copolymer, particularly when it is elastomeric, can be used in a rubber composition.

The rubber composition includes a crosslinking system.

The crosslinking system can be based on sulfur, sulfur donors, peroxides, bismaleimides or their mixtures. The crosslinking system is preferably a vulcanization system, that is to say a system based on sulfur (or a sulfur donor agent) and on a primary vulcanization accelerator. To this basic vulcanization system can be added various secondary accelerators or known vulcanization activators such as zinc oxide, stearic acid or equivalent compounds, guanidic derivatives (in particular diphenylguanidine), or also known vulcanization retarders. Preferably, the rubber composition comprises a reinforcing filler. The rubber composition can comprise any type of so-called reinforcing filler, known for its capacity to reinforce a rubber composition which can be used for the manufacture of tires, for example an organic filler such as carbon black, an inorganic reinforcing filler such as silica to which is associated in known manner with a coupling agent, or a mixture of these two types of filler. Such a reinforcing filler typically consists of nanoparticles whose average size (by mass) is less than a micrometer, generally less than 500 nm, most often between 20 and 200 nm, in particular and more preferably between 20 and 150 nm. The rate of reinforcing filler is adjusted by a person skilled in the art according to the use of the rubber composition.

The rubber composition may also contain other additives known for use in rubber compositions for tires, such as plasticizers, anti-ozonants, antioxidants.

The rubber composition is typically produced in suitable mixers, using two successive preparation phases well known to those skilled in the art: a first working phase or thermomechanical kneading (so-called "non-productive" phase) at high temperature, up to '' at a maximum temperature between 130 ° C and 200 ° C, followed by a second mechanical working phase (so-called "productive" phase) to a lower temperature, typically below 110 ° C, for example between 40 ° C and 100 ° C, finishing phase during which the crosslinking system is incorporated.

The rubber composition, which can either be in the raw state (before crosslinking or vulcanization), or in the cooked state (after crosslinking or vulcanization), can be used in a semi-finished article for a tire.

The tire comprises the rubber composition as defined above according to any of the variants described.

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

II. EXAMPLES OF EMBODIMENT OF THE INVENTION All the reagents are obtained commercially except the metallocenes [{Me ₂ SiFlu ₂ Nd (p- BH ₄ ) ₂ Li (THF)}] and [Me ₂ SiCpFluNd (p-BH ₄ ) ₂ Li (THF)] which are prepared according to the procedures described in patent applications WO 2007054224 and WO 2007054223.

BOMAG butyloctylmagnesium (20% in heptane, C = 0.88 mol L ¹ ) comes from Chemtura and is stored in a Schlenk tube under an inert atmosphere. The ethylene, of N35 quality, comes from the company Air Liquide and is used without prior purification. Myrcene (purity> 95%) is obtained from Sigma-Aldrich.

1) Determination of the microstructure of the polymers:

The spectral characterization and the measurements of the ethylene-myrcene copolymer microstructure are carried out by Nuclear Magnetic Resonance (NMR) spectroscopy.

Spectrometer: For these measurements, a Bruker Avance III HD 400 MHz spectrometer is used, equipped with a Bruker cryo-BBFO z-grad 5 mm probe.

Experiments: 1H experiments are recorded using a radio frequency pulse with a tilt angle of 30 °, the number of repetitions is 128 with a recycling time of 5 seconds. The 1H-13C correlation NMR experiments HSQ.C (Heteronuclear Single Quantum Coherence) and HMBC (Heteronuclear Multiple-Bond Correlation) are recorded with a repetition number of 128 and an increment number of 128. The experiments are performed at 25 ° C.

Sample preparation: 25 mg of sample are dissolved in 1 mL of deuterated chloroform (CDCI3).

Calibration of the sample: The axes of the chemical displacements ¹ and ¹³ C are calibrated with respect to the protonated impurity of the solvent (CHCI ₃ ) at di _H = 7.2 ppm and ôi _3C = 77 ppm.

Spectral attribution: The signals of the forms of insertion of myrcene A, B and C (diagram 1) were observed on the different recorded spectra. According to S. Georges et al., (S. Georges, M. Bria, P. Zinck and M. Visseaux, Polymer 55 (2014) 3869-3878) the signal of the grouping -CH = n ° 8 '' characteristic of form C has chemical shifts ¹ and ¹³ C identical to the group -CH = n ° 3.

The chemical shifts of the signals characteristic of the patterns A, B and C are presented in Table 1. The patterns A, B and C correspond respectively to the units of configuration 3,4, configuration 1,2 and configuration 1,4-trans . Diagram 1:

Ri and R ₂ representing the points of attachment of the unit to the polymer chain.

Table 1: Allocation of the ¹ H and ¹³ C signals of Ethylene-Myrcene copolymers

5IH (ppm) 5i ₃ c (ppm) Grouping

5.54 146.4 8

5.07 124.6 3 + 8 "

4.97 - 4.79 112.0 9 '

4.67 108.5 7

2.06 26.5 4

31.8 5 + 5 '+ 5 "

2.0 - 1.79

44.5 8

1.59 25.9 and 17.0 1

1.2 36.8 - 24.0 CH ₂ ethylene

The quantifications were carried out from the integration of ¹ H NMR ¹ H spectra using the Topspin software.

The integrated signals for the quantification of the different patterns are:

Ethylene: signal at 1.2 ppm corresponding to 4 protons

Total myrcene: signal assigned to group no.1 (1.59 ppm) corresponding to 6 protons

Form A: signal assigned to group No.7 (4.67 ppm) corresponding to 2 protons Form B: signal allocated to group No.8 '(5.54 ppm) corresponding to 1 protons

The quantification of the microstructure is carried out in molar percentage (molar%) as follows: molar% of a motif = 1H integral of a motif * 100 / å (1H integrals of each motif)

2) Determination of the glass transition temperature of the polymers:

The glass transition temperature is measured by means of a differential scanning calorimeter (ASTM D3418 (1999)).

3) Determination of the degree of crystallinity of the polymers:

ISO 11357-3: 2011 is used to determine the temperature and enthalpy of fusion and crystallization of the polymers used by differential scanning calorimetry (DSC). The reference enthalpy of polyethylene is 277.1 J / g (from Handbook of Polymer 4th Edition, J. BRANDRUP, E. H. IMMERGUT, and E. A. GRULKE, 1999)

4) Synthesis of polymers:

4.1- Control synthesis: example 1

The polymer is synthesized according to the following procedure: In a 500 ml glass reactor containing 300 ml of toluene, the cocatalyst, butyloctylmagnesium (BOMAG) and then the metallocene [Me ₂ SiCpFluNd (p- BH ₄ ) ₂ Li (THF)] are added. The alkylation time is 10 minutes, the reaction temperature is 20 ° C. The respective amounts of the constituents of the catalytic system are shown in Table 2. Next, the monomers are added in the respective proportions indicated in Table 2, ethylene (Eth) and 1,3-butadiene (Bde) being in the form of a gas mixture. The polymerization is carried out at 80 ° C. and at a constant ethylene pressure of 4 bars. The polymerization reaction is stopped by cooling, degassing of the reactor and addition of 10 ml of ethanol. An antioxidant is added to the polymer solution. The copolymer is recovered by drying in an oven under vacuum to constant mass. The mass weighed makes it possible to determine the average catalytic activity of the catalytic system expressed in kilogram of polymer synthesized per mole of neodymium metal and per hour (kg / mol. H).

4.2 - Example not in accordance with the invention: example 2

The polymer is synthesized according to the following procedure:

In a 500 ml glass reactor containing 300 ml of methylcyclohexane, the cocatalyst, butyloctylmagnesium (BOMAG) is added, followed by the metallocene [Me ₂ Si (Flu) ₂ Nd (p- BH ₄ ) ₂ Li (THF)] . The alkylation time is 10 minutes, the reaction temperature is 20 ° C. The respective amounts of the constituents of the catalytic system are shown in Table 2. Next, the monomers are added in the respective proportions indicated in Table 2, ethylene (Eth) and 1,3-butadiene (Bde) being in the form of a gas mixture. The polymerization is carried out at 80 ° C. and at a constant ethylene pressure of 4 bars. The polymerization reaction is stopped by cooling, degassing of the reactor and addition of 10 ml of ethanol. An antioxidant is added to the polymer solution. The copolymer is recovered by drying in an oven under vacuum to constant mass. The mass weighed makes it possible to determine the average catalytic activity of the catalytic system expressed in kilogram of polymer synthesized per mole of neodymium metal and per hour (kg / mol. H).

4.3- Example not in accordance with the invention: example 3

The polymer is synthesized according to the following procedure:

In a 500 ml glass reactor containing 300 ml of methylcyclohexane, the cocatalyst, butyloctylmagnesium (BOMAG) is added, followed by the metallocene [Me ₂ Si (Flu) ₂ Nd (p- BH ₄ ) ₂ Li (THF)] . The alkylation time is 10 minutes, the reaction temperature is 20 ° C. The respective amounts of the constituents of the catalytic system are shown in Table 2. Next, the myrcene (10.3 mL, Table 2) is added to the reactor before the injection of the ethylene gas. The polymerization is carried out at 80 ° C. and at a constant ethylene pressure of 4 bars. The polymerization reaction is stopped by cooling, degassing of the reactor and addition of 10 ml of ethanol. An antioxidant is added to the polymer solution. The copolymer is recovered by drying in a vacuum oven until constant mass. The mass weighed makes it possible to determine the average catalytic activity of the catalytic system expressed in kilogram of polymer synthesized per mole of neodymium metal and per hour (kg / mol. H).

4.4- Example not in accordance with the invention: example 4

The polymer is synthesized according to the following procedure:

In a reactor containing at 80 ° C. methylcyclohexane, ethylene and butadiene in the proportions indicated in table 3, butyloctylmagnesium (BOMAG) is added to neutralize the impurities of the reactor, then the catalytic system (see table 3) . At this time, the reaction temperature is controlled at 80 ° C and the polymerization reaction starts. The polymerization reaction takes place at a constant pressure of 8 bars. The reactor is supplied throughout the polymerization with ethylene and butadiene in the proportions defined in Table 3. The polymerization reaction is stopped by cooling, degassing of the reactor and addition of ethanol. An antioxidant is added to the polymer solution. The copolymer is recovered by drying in an oven under vacuum to constant mass. The mass weighed makes it possible to determine the average catalytic activity of the catalytic system expressed in kilogram of polymer synthesized per mole of neodymium metal and per hour (kg / mol. H). The catalytic system is a preformed catalytic system. It is prepared in methylcyclohexane from a metallocene, [Me ₂ Si (Flu) 2Nd (p-BH ₄ ) 2Li (TH F)], a co-catalyst, butyloctylmagnesium (BOMAG), and d 'a preformation monomer, 1,3-butadiene, in the contents indicated in Table 3. It is prepared according to a preparation method in accordance with paragraph ll.l of patent application WO 2017093654 A1.

4.5- Examples in accordance with the invention: example 5 to 6

The polymer is synthesized according to the following procedure:

In a reactor containing at 80 ° C. methylcyclohexane, ethylene and myrcene in the proportions indicated in table 3, butyloctylmagnesium (BOMAG) is added to neutralize the impurities of the reactor, then the catalytic system (see table 3) .

At this time, the reaction temperature is controlled at 80 ° C and the polymerization reaction starts. The polymerization reaction takes place at a constant pressure of 8 bars. The reactor is fed throughout the polymerization with ethylene and myrcene in the proportions defined in Table 3. The polymerization reaction is stopped by cooling, degassing of the reactor and addition of ethanol. An antioxidant is added to the polymer solution. The copolymer is recovered by drying in an oven under vacuum to constant mass. The mass weighed makes it possible to determine the average catalytic activity of the catalytic system expressed in kilogram of polymer synthesized per mole of neodymium metal and per hour (kg / mol. H). The catalytic system is a preformed catalytic system. It is prepared in methylcyclohexane from a metallocene, [Me ₂ Si (Flu) 2Nd (p-BH ₄ ) 2Li (THF)], a co-catalyst, butyloctylmagnesium (BOMAG), and a preformation monomer, 1,3-butadiene, in the contents indicated in the Table 3. It is prepared according to a preparation method in accordance with paragraph ll.l of patent application WO 2017093654 Al.

5) Results:

The characteristics of the polymers are given in Tables 4 and 5.

In Example 1 (control), the diene copolymer rich in ethylene and synthesized by polymerization of ethylene and 1,3-butadiene in the presence of the metallocene [Me2SiCpFluNd (p-BH ₄ ) 2Li (THF)] has a high crystallinity (31%) which can make it unsuitable for certain uses.

In Example 2 (non-conforming), the diene copolymer rich in ethylene synthesized in the presence of the metallocene [Me2Si (Flu) 2Nd (p-BH ₄ ) 2Li (THF)] has cyclic units. Although it contains a level of ethylene comparable to that of the control, it is not crystalline.

In Examples 5 and 6 (conforming), the ethylene-rich diene copolymers are copolymers of ethylene and of myrcene synthesized according to a process in accordance with the invention. Their ethylene level is much higher than that of the control, even though their crystallinity level is much lower than that of the control.

Note that the copolymer of Example 5 has an ethylene content identical to the copolymer of Example 3 which is also a copolymer of ethylene and myrcene, but which is synthesized according to a process not in accordance with the invention (not addition throughout the polymerization of both myrcene and ethylene). However, the copolymer of Example 5 has a lower degree of crystallinity than the copolymer of Example 3. The process according to the invention therefore makes it possible to synthesize ethylene and myrcene copolymers which have both very high contents high in ethylene and crystallinity levels which remain relatively low taking into account the ethylene content in the copolymers.

It is also noted that in Examples 5 and 6, the catalytic activity is much higher than that of Example 4. Surprisingly, the use of myrcene in place of 1,3-butadiene as a comonomer of ethylene significantly increases the catalytic activity of the catalytic system.

Table 2:

Table 3

Table 4:

Table 5:

Claims

1. Process for the preparation of a copolymer of ethylene and myrcene which comprises ethylene units and myrcene units,

which process comprises the polymerization of ethylene and myrcene in a reactor in the presence of a catalytic system based at least on a metallocene of formula (I) and an organomagnesium of formula (II)

P (Cp ¹ Cp ² ) Nd (BH ₄ ) (i _{+ y} ) -Ly-N _x (I)

MgR ¹ R ² (II)

y, an integer, being equal to or greater than 0,

x, whole number or not, being equal to or greater than 0,

2. Method according to claim 1 in which the metallocene is of formula (la), (Ib), (le),

(Id) or (le)

[{Me ₂ SiFlu ₂ Nd (p-BH ₄ ) 2Li (THF)} ₂ ] (la)

[Me ₂ SiFlu ₂ Nd (p-BH ₄ ) ₂ Li (THF)] (Ib)

[Me ₂ SiFlu ₂ Nd (p-BH ₄ ) (THF)] (le)

[{Me ₂ SiFlu ₂ Nd (p-BH ₄ ) (THF)} ₂ ] (Id)

[Me ₂ SiFlu ₂ Nd (p-BH ₄ )] (le) the symbol Flu having the fluorenyl group of formula C _I3 H ₈ .

3. Method according to any one of claims 1 to 2 wherein R ¹ and R ² contain 2 to 10 carbon atoms.

4. Method according to any one of claims 1 to 3 wherein R ¹ and R ² each represent an alkyl.

5. Method according to any one of claims 1 to 4 wherein the organomagnesium is a dialkylmagnesium, preferably butylethylmagnesium or butyloctylmagnesium, more preferably butyloctylmagnesium.

6. Process according to any one of claims 1 to 5, in which the ethylene and the myrcene are added continuously in the form of a monomer mixture in the reactor and the mixture added has an ethylene / myrcene molar composition preferably going from 10/90 to 95/5, more preferably from 50/50 to 90/10.

7. Method according to any one of claims 1 to 5 wherein the ethylene and the myrcene are continuously added individually to the reactor, the flow rates of ethylene and of myrcene are such that the molar ratio between the ethylene added in the reactor and the myrcene added to the reactor is in a range from 1/9 to 19/1, more preferably from 1/1 to 9/1.

8. Method according to any one of claims 1 to 7 wherein the polymerization of ethylene and myrcene is carried out at constant ethylene pressure.

9. Method according to any one of claims 1 to 8, which method is a semi-continuous process.

10. Process according to any one of claims 1 to 9, in which the catalytic system is also based on a preformation monomer chosen from a conjugated diene, ethylene or a mixture of ethylene and a conjugated diene .

11. Method according to any one of claims 1 to 10, in which the ethylene units in the copolymer represent from 60 to 90% by mole, preferably from 70 to 90% by mole of the ethylene units and of the myrcene units of the copolymer.

12. Method according to any one of claims 1 to 11, in which the polymerization is carried out in solution, preferably in a hydrocarbon solvent.