WO2015097194A1

WO2015097194A1 - Method for metathesis depolymerization of natural rubber in a solution

Info

Publication number: WO2015097194A1
Application number: PCT/EP2014/079084
Authority: WO
Inventors: François JEAN-BAPTISTE-DIT-DOMINIQUE
Original assignee: Compagnie Generale Des Etablissements Michelin; Michelin Recherche Et Technique S.A.
Priority date: 2013-12-23
Filing date: 2014-12-22
Publication date: 2015-07-02
Also published as: FR3015486B1; FR3015486A1; EP3087103A1

Abstract

The invention relates to a method for the depolymerization of a deproteinized natural rubber for the preparation of a modified polyisoprene mainly comprising a mixture of the species functionalized at one of the two ends thereof by one or more functional groups and the species functionalized at both ends thereof by one or more function groups, wherein said method comprises the following steps: i) a step of preparing a deproteinized natural rubber solution comprising the deproteinized natural rubber, one or more organic solvents, and one or more surfactants, then ii) a step of adding, to the deproteinized natural rubber solution, one or more transfer agents comprising said functional group or groups, iii) a step of adding, to the deproteinized natural rubber solution, one or more metathesis catalysts. The invention also relates to a modified polyisoprene obtainable using the aforementioned method. Lastly, the invention relates to an elastomeric composition made of the aforementioned modified polyisoprene.

Description

Process for the depolymerization of natural rubber in solution by metathesis

The present invention relates to a process for the depolymerization of a deproteinized natural rubber in solution for the preparation of a modified polyisoprene comprising predominantly a mixture of the functionalized species at one of its two ends by one or more groups. functional and of the species functionalized at both ends by one or more functional groups.

The invention also relates to the modified polyisoprene obtainable by this process. Finally, the invention relates to a rubber composition, usable especially for the manufacture of tires, based on one or more of the abovementioned modified polyisoprenes.

A rubber composition reinforced with carbon black or other reinforcing filler and intended for the manufacture of tires must have specific mechanical and dynamic properties which allow the tire to obey a large number of technical requirements.

Since fuel economy and the need to protect the environment have become a priority, it has been necessary to produce tires having good adhesion properties while having reduced rolling resistance. The lowering of the hysteresis of a rubber composition is a descriptor of a lower rolling resistance for the tires comprising them.

To achieve the goal of lowering hysteresis, many solutions have already been tested. In particular, it has been proposed to modify the structure of the rubber along or at the end of the polymer chain by the introduction of chemical functions. to ensure a good dispersion and therefore a greater interaction of the reinforcing filler within the polymer.

This provides functionalized polymers which are less hysteretic than rubber compositions having unfunctionalized polymers.

In particular, end-functionalized polymers may be prepared by anionic polymerization processes, for example, by initiating the polymerization of 1,3-butadiene with a functionalized initiator or by reacting a "living" anionic polymer with a functionalization agent.

However, for the manufacture of certain tire components such as flanks or shoulders which have high performance levels, it is necessary to use stereoregular polymers such as 1, 4-cis polydienes.

These particular polymers can not be obtained by anionic polymerization processes because these methods do not allow strict control of the microstructure of the polymer, especially the level of cis-1,4 units.

In order to address this problem, catalytic systems for polymerization by catalysis have been developed.

Coordination catalysts (also known as Ziegler-Natta catalysts), such as lanthanide catalysts comprising a lanthanide compound, an alkylating agent, and a halogen-containing compound, are often highly stereoselective. These catalysts can produce conjugated diene polymers having a cis-1,4 units ratio of greater than 97%.

The 1,4-cis polydienes which are prepared by lanthanide catalyzed polymerization polymerization processes are known to possess pseudo-living polymer characteristics, i.e., some of the polymeric chains. possess reactive chain ends and are therefore potentially functionalizable. Thus, the end of the pseudo-living chains of these 1, 4-cis polydienes can react with certain functionalizing agents, comprising a reactive site of the type carbonyl, carboxyl, ester, epoxide (or glycidyl), imine, azine, hydrobenzamide, nitrile, isocyanate or halogen.

On the other hand, due in particular to the presence of alkylmetals, components of catalytic systems and the pseudo - living nature of some of the polymer chains, this method of functionalization of 1,4 - cis polydienes is therefore not compatible with introduction of carbonyl, carboxyl, ester, epoxide (or glycidyl), imine, azine, hydrobenzamide, nitrile, isocyanate or halogen functions.

In addition, the use of catalytic systems limits the ability to functionalize the resulting polymers with functional levels equivalent to those obtained for functionalization by anionic polymerization. Indeed, these catalytic systems operate by complex chemical mechanisms that involve the interaction between several catalyst components that can thus lead to many termination reactions.

Finally, this type of polymerization is generally carried out on 1,4-cis-polybutadienes and rarely on 1,4-cis polyisoprenes.

Therefore, it is necessary to develop new synthetic methods that are functionally versatile, that is, that are suitable for a large number of functions for the synthesis of 1, 4-cis polydienes, and more. particularly of 1,4-cis polyisoprenes.

Functional versatile methods for the synthesis of 1,4-cis polybutadiene and 1,4-cis polyisoprene have been developed via the Ring Opening Metathesis Polymerization (ROMP) reaction. In particular mention may be made of cyclooctadiene or 1,5-dimethyl-1,5-cyclooctadiene ROMP in the presence of a functional transfer agent.

However, the thermodynamics of the cyclic diene ROMP reactions in the presence of the ruthenium catalysts used lead to the generation of polymer whose level of trans-1,4 units is greater than 40%. Thus, in order to synthesize polydienes with both high cis units and very high functional levels, ie with at least one end of the functional chain, de-lymerisation methods have been developed. by metathesis of high cis - 1,4 unit polybutadiene to access a variety of functional oligomers.

On the other hand, there are few methods for the depolymerization of synthetic polyisoprene with a high level of cis-1,4 units by metathesis for the synthesis of telechelic oligoisoprenes.

In addition, the scarcity of raw materials from fissionable energies such as the monomers used (styrene, butadiene, isoprene) to generate these synthetic and functional elastomers pushes the pneumatic research to seek alternatives and in particular to use bio-sourced raw materials such as natural rubber.

Natural rubber appears to be an ideal matrix for metathesis depolymerization reactions by a high cis-1,4 unit ratio (greater than 99%) and on the other hand by very high molecular weight polymer chains.

However, the solubilization of most of the natural rubbers in the organic solvent leads to the formation of a macrogel. However, the kinetics of depolymerization by metathesis and thus of functionalization of the polymer chains involved in the macrogel being much slower than that of the polymer chains being solubilised, the macrostructure and the function rate are not controllable, especially when the The depolymerization reaction is not far advanced, that is, when the number average magnetic masses are greater than 100 kg / m 2.

In view of the foregoing, there is therefore a need to provide a process for the depolymerization of natural rubber by metathesis in solution which is versatile in terms of functions, i.e., which is suitable for a large number of applications. functions, in order to synthesize functional polyisoprenes at the end of the high molecular weight chain, with a high rate of cis-1, 4 units and with a high functional level. A synthetic process has now been developed to improve the depolymerization reaction of a deproteinized natural rubber in metathesis solution via the addition of a surfactant in the deproteinized natural rubber solution.

The subject of the invention is therefore a process for the depolymerization of a deproteinized natural rubber for the preparation of a modified polyisoprene mainly comprising a mixture of the species functionalized at one of its two ends by one or more functional groups and of the species functionalized at both ends by one or more functional groups, said method comprising the following steps:

i) a step of preparing a deproteinized natural rubber solution comprising the deproteinized natural rubber, one or more organic solvents, and one or more surfactants, and

ii) a step of adding to the solution of deproteinized natural rubber one or more transfer agents comprising said functional group (s),

iii) a step of adding to the solution of deproteinized natural rubber one or more metathesis reaction catalysts.

The process according to the invention is efficient and rapid and can be implemented on an industrial scale.

In addition, the process according to the invention is compatible with a large number of transfer agents.

The process according to the invention makes it possible in particular to obtain a modified polyisoprene having a high content of cis - 1,4 - units, mainly comprising a mixture of functionalized species at at least one of their two ends, which can be used directly in elastomeric compositions.

Finally, the process according to the invention advantageously makes it possible to obtain a modified polyisoprene with a monomodal chain size distribution, a low polydispersity index (Ip) of less than 10 and having a high average molecular weight. The invention therefore also relates to a modified polyisoprene obtainable by the above method, the average molecular weight of the polyisoprene ranging from 100 to 600 kg / mol.

The subject of the invention is also a modified polyisoprene comprising mainly a mixture of the following species of general formula I and the following species of general formula II:

with R 1, R ₂ , R ' ₁ and R' ₂ , independently of each other, chosen from a hydrogen atom or a methyl group, Ri being different from R ₂ and R ' ₁ being different from R' ₂ ,

n and n ', independently of one another, being integers ranging from 1470 to 8900,

R and R ', independently of one another, being functional groups comprising one or more groups selected from a halogen, an amine, an imine, an ammonium, an amide, a nitrile, an azo, a diazo, a hydrazo, carbamate, isocyanate, hydroxyl, carbonyl, carboxyl, ester, epoxy, sulfide, disulfide, thiocarbonyl, trithiocarbamate, sulfonyl, sulfinyl, silane, alkoxysilane, stannyl, a boré, a nitrogenous heterocycle, an oxygenated heterocycle, a sulfur heterocycle and an aromatic group substituted by the aforementioned groups, a and a ', independently of one another, being integers varying from 0 to 20, the average number-average molecular weight of polyisoprene ranging from 100 to 600 kg / mol.

This polyisoprene according to the invention can be obtained by the process according to the invention.

Finally, the subject of the invention is an elastomeric composition based on one or more modified polyisoprenes as defined above.

The invention as well as its advantages will be readily understood in the light of the description and examples of embodiments which follow.

In the present application, it should be noted that it is known to one skilled in the art that when a natural rubber is depolymerized by metathesis in the presence of one or more transfer agents, a mixture of modified species of this natural rubber whose composition depends in particular on the choice of the transfer agent, the amount of transfer agent, the temperature and the duration of the depolymerization reaction. This mixture may comprise, in particular, functionalized species at one or both ends, and non-functionalized species.

In the present application, by "predominantly a mixture" is meant that this mixture is predominant among the species resulting from the depolymerization reaction, that is to say that this mixture represents the largest weight fraction among the species derived from the depolymerization reaction.

Also, a functionalized species of a so-called majority modified polyisoprene is that representing the largest weight fraction among the species resulting from the depolymerization reaction. In a system comprising a single compound of a certain type, this is a majority within the meaning of the present invention.

In the same way, a so-called majority charge is that representing the largest weight fraction relative to the total weight of all the charges of the composition.

In the present application, the term "composition based on" refers to a composition comprising the mixture and / or the product of reaction of the various constituents used, some of these basic constituents being capable of, or intended to react with, each other, at least in part, during the different phases of manufacture of the composition, in particular during its crosslinking or vulcanization.

On the other hand, any range of values designated by the expression "between a and b" represents the range of values from more than a to less than b (i.e., terminals a and b excluded) while any range of values designated by the expression "from a to b" means the range from a to b (i.e., including the strict limits a and b).

In the present application, the term "part per cent elastomer" or "phr" refers to the part by weight of one component per 100 parts by weight of elastomer. Thus, a 60 phr component will mean, for example, 60 g of this component per 100 g of elastomer.

As previously discussed, the process according to the invention comprises a step of preparing a solution of deproteinized natural rubber.

Deproteinized natural rubber is understood to mean a natural rubber whose proteins have been removed by a physicochemical treatment (for example by enzymatic treatment or by multi-centrifugation in the presence of a surfactant) and whose nitrogen content is less than 0.2% by weight, preferably less than 0.15% by weight, relative to the total weight of the dry deproteinized natural rubber.

The deproteinized natural rubber that can be used in the process according to the invention is, preferably, chosen from deproteinized dry natural rubbers, previously modified or otherwise, and a mixture of these rubbers.

By modified natural rubber is meant, for example, epoxidized natural rubbers, grafted by free radical or partially hydrogenated.

Among these natural rubbers, it will be preferred to use in the process according to the invention the deproteinized natural rubbers derived from hevea, gutta percha, dandelion, guayule and a mixture of these rubbers.

As explained above, the deproteinized natural rubber is solubilized in one or more organic solvents.

The organic solvent (s) which may be used in the process according to the invention may be chosen from cyclic or linear hydrocarbon solvents, aromatic solvents, halogenated solvents and a mixture of these solvents.

As cyclic or linear hydrocarbon solvents, mention may be made of heptane, hexane, pentane, cyclohexane, methylcyclohexane, petroleum ether, decalin and a mixture of these solvents.

As aromatic solvents, mention may be made of benzene, toluene, xylene, nitrobenzene and a mixture of these solvents.

Halogenated solvents that may be mentioned include chloroform, dichloromethane, tetrachloromethane and a mixture of these solvents.

The solution of deproteinized natural rubber which can be used in the process according to the invention preferably has a molar concentration in the form of isoprene ranging from 0.05 to 0.5 mol / l, more preferably ranging from 0.15 to 0.3 mol / L.

As previously explained, the solution of deproteinized natural rubber comprises one or more surfactants.

In particular, the surfactant (s) used in the process according to the invention make it easier to homogenize the solution of deproteinized natural rubber.

The surfactant (s) that may be used in the process according to the invention may be chosen from anionic, cationic, amphoteric and nonionic surfactants.

As anionic surfactants, mention may be made especially of all anionic surfactants comprising at least one C 6 -C 40 alkyl group or at least one aromatic ring substituted by a C 6 -C 40 alkyl group, and at least one group anionic compound selected from sulfates, sulfonates, phosphates, phosphonates, and carboxylates. Preferably, the at least one anionic surfactant comprising at least one C 6 -C 40 alkyl group or at least one aromatic ring substituted by a C 6 -C 40 alkyl group is chosen from sodium stearate, sodium lauryl sulphate and lauryl ether. sodium sulphate and sodium dodecylbenzene sulphonates.

As cationic surfactants, mention may be made in particular of all cationic surfactants comprising at least one C 6 -C 40 alkyl group or at least one aromatic ring substituted by a C 6 -C 40 alkyl group, and at least one chosen cationic group. among ammoniums and pyridia.

Preferably, the cationic surfactant (s) are chosen from alkyltrimethylammonium salts such as trimethyldecylammonium chloride or bromide and benzalkonium salts.

Amphoteric surfactants that may be mentioned include amphoteric amino acids and amphoteric betaines.

The amphoteric surfactants are preferably chosen from phosphatidylcholine and N, N-dimethyl-N-dodecylglycine betaine sold under the trade name Empigen® by Sigma-Aldrich.

Nonionic surfactants that may especially be mentioned include alkanoamides and esters, and more particularly glyco esters such as ethylene glycol stearate, and glycerol esters such as glycerol stearate. sorbitan esters and polyoxyethylene sorbitan esters such as Tween® sold by Sigma-Aldrich.

There may also be mentioned alkylene oxide condensates containing one or more lipophilic chains.

The lipophilic chain (s) may be a phenol substituted by a C 6 -C 40 alkyl chain, for example nonylphenol or an alcohol, an amine or a C 6 -C 40 alkyl chain carboxylic acid.

The alkylene oxide is generally ethylene oxide or propylene oxide and generally the polyether chain contains from 18 to 30 alkylene oxide units although longer chains, for example up to 75 alkylene oxide units may sometimes be used.

By way of example, nonionic surfactants include the commercial product S innopal NP 307® sold by Cognis.

Preferably, said surfactant or surfactants are chosen from cationic and nonionic surfactants.

In a particularly preferred manner, the one or more surfactants that can be used in the process according to the invention are chosen from trimethyldecylammonium chloride, polyoxyethylene sorbitan esters and a mixture of these compounds.

Preferably, the surfactant (s) represent (s) from 1 to 20 phr, preferably from 5 to 20 phr, more preferably from 5 to 15 phr, and in particular from 10 to 15 phr, relative to the deproteinized natural rubber.

Preferably, the solution of deproteinized natural rubber may be inerted, i.e. put under an inert atmosphere, preferably by means of sparging nitrogen or argon directly into the medium. This makes it possible in particular to protect the medium from oxygen in the air.

The method according to the invention may therefore further comprise a step of inerting, preferably by bubbling the solution of deproteinized natural rubber, previously in step ii).

Preferably, this step has a duration ranging from 10 minutes to 2 hours, more preferably ranging from 10 to 60 minutes.

As previously described, the process according to the invention comprises a step of adding to the solution of deproteinized natural rubber one or more transfer agents comprising said functional group (s).

The transfer agent or agents that can be used in the process according to the invention allow the functionalization of the deproteinized natural rubber via a cross-metathesis reaction with a polymer chain in the presence of a catalyst. Therefore, the transfer agent (s) are hydrocarbon molecules having a carbon-carbon double bond, of cis or trans configuration, symmetrical or not, mono- or disubstituted.

Preferably, the transfer agent (s) may be chosen from the following compounds of formulas III, IV and V:

ni, n ₂ and n ₃ being integers ranging from 0 to 20,

Xi, X ₂ and X ₃ are functional groups comprising one or more groups selected from halogen, amine, imine, ammonium, amide, nitrile, azo, diazo, a hydrazo, carbamate, isocyanate , hydroxyl, carbonyl, carboxyl, ester, epoxy, sulfide, disulfide, thiocarbonyl, trithio carbamate, sulfonyl, sulfinyl, silane, alkoxysilane, stannyl, boron, nitrogen heterocycle , an oxygenated heterocycle, a sulfur heterocycle and an aromatic group substituted with the groups mentioned above.

As amine group, there may be mentioned primary amines protected or not, secondary or tertiary, nitrogenous heterocycles or aromatic groups substituted by the amine functions mentioned above.

By way of example of transfer agents comprising an amine function, there may be mentioned in particular amino-styrenes such as 4-vinylaniline, aminoalkyl (meth) acrylate, tert-butyl-N-allylcarbamate, N-allyl-N, N-bis (trimethylsilyl) amine, Ν, Ν, Ν ', Ν'-tetramethyl-2-butene-1,4-diamine, N, N-dialkylaminoalkyl- (meth) acrylate, such that Ν, Ν-dimethylaminoethyl (meth) acrylate and acryloyl morpholine. More particularly, as transfer agent comprising one or more nitrogenous heterocycles, mention may be made of the following compounds: olefins based on pyrrole, histidine, imidazole, triazolidine, triazole, triazine, pyridine, pyrimidine, pyrazine, indole, quinoline, purine, phenazine, pteridine, melamine.

By way of example of these compounds, mention may be made of 2-vinylpyridine, 3-vinylpyridine, 4-vinylpyridine and 2-methyl-5-vinylpyridine.

As an example of a transfer agent comprising one or more imide groups or imide groups carried by a ring, mention may be made of 2-butene-1,4-diylbis (phthalimide).

As a transfer agent comprising one or more amide groups, mention may be made of acrylamide, methacrylamide and N-alkyl (meth) acrylamide.

As an example of a transfer agent comprising one or more nitrile groups or nitrile groups carried by a ring, mention may be made of (meth) acrylonitrile, vinylidene cyanide and 1,4-dicyano-2-butene.

As an example of a transfer agent comprising one or more ammonium groups or ammonium groups carried by a ring, mention may be made of 3-butenylallylammonium chloride.

By way of example of a transfer agent comprising one or more hydroxyl groups or hydroxyl groups carried by a ring, mention may be made of cis-2-butene-1,4-diol and 2-hydroxyethyl (meth) acrylate. hydroxystyrene, m-hydroxystyrene, p-hydroxystyrene, o-hydroxy-α-methylstyrene, m-hydroxy-α-methylstyrene and p-hydroxy-α-methylstyrene.

By way of example of a transfer agent comprising one or more carboxyl groups or carboxyl groups carried by a ring, mention may be made of (meth) acrylic acid, maleic acid, fumaric acid, itaconic acid, cinnamic acid, oleic acid and linoleic acid. By way of example of a transfer agent comprising one or more ester groups or ester groups carried by a ring, 1,4-diacetoxy-but-2-ene may be mentioned.

By way of example of a transfer agent comprising one or more epoxy groups or epoxide groups carried by a ring, there may be mentioned cis-2-butene-1,4-diol-diglycidyl ether, allyl glycidyl ether, glycidyl (meth) acrylate and 3,4-oxycyclohexyl (meth) acrylate.

By way of example of a transfer agent comprising one or more stannyl groups or stannyl groups carried by a ring, mention may be made of allyltributylstannane and trans-1, 2-bis (tributylstannyl) ethene.

By way of example of a transfer agent comprising one or more silane groups or alkoxysilane groups or silane groups or alkoxysilane groups carried by a ring, mention may be made of (meth) acryloxymethyltrimethoxysilane, trimethoxyvinylsilane, triethoxyvinylsilane and 6-trimethoxysilyl - 1, 2-hexene.

Particularly preferably, in the formulas (III), (IV) and (V) as defined above, X ₁ , X ₂ and X ₃ are functional groups comprising one or more groups chosen from a halogen, an amine, an imine, ammonium, amide, nitrile, azo, diazo, hydrazo, carbamate, isocyanate, hydroxyl, carbonyl, carboxyl, epoxy, sulfide, disulfide, thiocarbonyl, trithiocarbamate , a sulphonyl, a sulfinyl, a silane, an alkoxysilane, a stannyl, a boré, a nitrogenous heterocycle, an oxygenated heterocycle, a sulfur heterocycle and an aromatic group substituted with the aforementioned groups.

In a particularly preferred manner, the transfer agent or agents are chosen from compounds of formula V.

The transfer agent (s) may be used alone or in combination of two or more of them.

Preferably, the transfer agent or agents represent from 0.01 to 50% by weight, preferably from 0.02 to 10% by weight, and in particular from 0.02 to 1 mol% relative to the number of moles of isoprene units in the deproteinized natural rubber.

In the process according to the invention, the transfer agent or agents may be added in pure form, in emulsion, or in solution in a solvent.

Preferably, the solvent used to solubilize the transfer agent or agents is chosen from those described above.

As explained above, the method according to the invention comprises a step of adding to the deproteinized natural rubber solution of one or more metathesis reaction catalysts.

The metathesis reaction catalyst (s) that can be used in the process according to the invention are preferably chosen from organometallic complexes, alone or as mixtures, whether or not they are supported.

Preferably, the metathesis reaction catalyst (s) are chosen from transition metal complexes based on ruthenium, osmium or iridium.

In a particularly preferred manner, the metathesis reaction catalyst (s) are ruthenium catalysts known as second and third generation catalysts, that is to say a catalyst comprising an N-heterocyclic carbene.

By way of example, mention may be made of Grubbs II catalysts, Hoveyda-Grubbs II catalysts, dichloro [1,3-bis (2-methylphenyl) -2-imidazolidinylidene] (2-isopropoxyphenylmethylene) ruthenium (II ), [2- (1-methylethoxy-O) phenylmethyl-C] (nitrato-0,0 ') {rel- (2R, 5R, 7S) -tricyclo [3.3.1.13,7] decane-2, 1 - diyl [3- (2,4,6-trimethylphenyl) -1-imidazolidin-2-ylidene]} ruthenium, dichloro [1,3-bis (2,4,6-trimethylphenyl) -2-imidazolidinylidene] (benzylidene) bis (3-bromopyridine) ruthenium (II), dichloro [1,3-bis (2-methylphenyl) -2-imidazolidinylidene] (benzylidene) (tricyclohexylphosphine) ruthenium (II), dichloro [1,3-bis (2) 4,6-trimethylphenyl) -2-imidazolidinylidene] (3-methyl-2-butenylidene)

(tricyclohexylphosphine) ruthenium (II), dichloro [1,3-bis (2,4,6-trimethylphenyl) -2-imidazolidinylidene] [3- (2-) pyridinyl) propylidene] ruthenium (II), dichloro [1,3-bis (2,4,6-trimethylphenyl) -2-imidazo-lidinylidene] [(tricyclohexylphosphoranyl) methylidene] ruthenium (II) tetrafluoroborate, and dichloro [1 , 3-bis (2,6-isopropylphenyl) -2-imidazo-lidinylidene] (benzylidene)

(tricyclohexylphosphine) ruthenium (II).

Preferably, the metathesis reaction catalyst or catalysts represent from 0.0001 to 1% by weight, preferably from 0.0001 to 0.1% by weight, and in particular from 0.002 to 0.1% by weight. the number of units of isoprene units in deproteinized natural rubber.

In the process according to the invention, the metathesis reaction catalyst (s) may be added in pure form or in solution in a solvent.

Preferably, the solvent used to solubilize the metathesis reaction catalyst (s) is chosen from those described above.

In the process according to the invention, steps i) to iii) are carried out generally with stirring of the solution of deproteinized natural rubber.

Preferably, the method according to the invention further comprises a step of adjusting the temperature of the solution of deproteinized natural rubber with stirring, said step being carried out after steps ii) and iii).

Thus, the temperature of the solution generally varies from 3 ° C to 100 ° C, preferably from 15 ° C to 80 ° C.

Once the temperature of the deproteinized natural rubber solution has been reached, the solution is generally stirred for a period generally ranging from 5 minutes to 24 hours, preferably ranging from 5 minutes to 8 hours, more preferably from 9 minutes to 4 hours.

Preferably, the process according to the invention further comprises a step of adding one or more stoppering agents to the deproteinized natural rubber solution, said adding step being carried out after steps ii) to iii), and after any steps of setting the temperature and stirring at the previously selected temperature and for the previously selected time.

The stopper (s) in particular make it possible to stop the depolymerization of the deproteinized natural rubber.

The stopper (s) may be added to the solution of deproteinized natural rubber in pure form or in solution.

In particular, mention may be made of ethyl vinyl ether as a stoppage agent.

The amount of the quenching agent is at least the amount of metathesis reaction catalyst introduced, and preferably at least 10 times the amount of metathesis reaction catalyst introduced into the deproteinized natural rubber solution. .

The process according to the invention may further comprise a step of coagulating the reaction mixture.

This step makes it possible to recover the modified polyisoprene.

The coagulation of the reaction mixture can be carried out in particular by the addition of a solvent selected from ketones and alcohols and in particular acetone, methanol, isopropanol and ethanol.

The coagulation of the reaction mixture can also be carried out by steam extraction.

The process according to the invention may further comprise a step of drying the modified polyisoprene obtained, once coagulated.

Preferably, the modified polyisoprene can be dried under vacuum or at atmospheric pressure while flushing with nitrogen.

Drying temperatures may vary from room temperature (25 ° C) to 130 ° C, preferably from room temperature to 100 ° C, and even more preferably from room temperature to 70 ° C.

Depending on the reaction time and temperature, the transfer agent (s) used and the amount of the agent (s) The method according to the invention can produce a modified polyisoprene comprising predominantly the species functionalized at one of its two ends, or comprising mainly the species functionalized at its two ends or comprising mainly a mixture of these two species. .

Therefore, the object of the invention is also the modified polyisoprene obtainable by the process as defined above, the average number-average molecular weight of the polyisoprene ranging from 100 to 600 kg / mol, preferably from 100 to 400 kg / mo l.

In a particularly preferred manner, this modified polyisoprene has a number average molecular weight ranging from 142 to 400 kg / mol, and in particular ranging from 142 to 1 kg / mol.

In the present application, the number and mass average weight masses are measured using the Flow-FFF / RI / MALS which is explained below.

In a first variant, the modified polyisoprene that can be obtained by the process as described comprises for the most part the species functionalized at one of its two ends by one or more functional groups.

In a second variant, the modified polyisoprene obtainable by the process as described mainly comprises the species functionalized at both ends by one or more functional groups.

The invention also relates to a modified polyisoprene comprising predominantly a mixture of the following species of general formula I and the following species of formula II:

(I)

R and R ', independently of one another, being functional groups comprising one or more groups selected from a halogen, an amine, an imine, an ammonium, an amide, a nitrile, an azo, a diazo, a hydrazo, carbamate, isocyanate, hydroxyl, carbonyl, carboxyl, ester, epoxy, sulfide, disulfide, thiocarbonyl, trithiocarbamate, sulfonyl, sulfinyl, silane, alkoxysilane, stannyl, a boré, a nitrogenous heterocycle, an oxygenated heterocycle, a sulfur heterocycle and an aromatic group substituted with the aforementioned groups, a and a ', independently of one another, being integers ranging from 0 to 20,

the number average molar mass of polyisoprene ranging from 100 to 600 kg / mol, preferably ranging from 100 to 400 kg / mol.

Preferably, this polyisoprene has a number-average molar mass ranging from 142 to 400 kg / mol, and in particular ranging from 142 to 331 kg / mol.

Preferably, in the formulas I and II, R and R ', independently of one another, are functional groups comprising one or more groups chosen from a halogen, an amine, an imine, an ammonium or an amide. , a nitrile, an azo, a diazo, a hydrazo, a carbamate, an isocyanate, a hydroxyl, a carbonyl, a carboxyl, an epoxy, a sulfide, a disulfide, a thiocarbonyl, a trithiocarbamate, a sulfonyl, a sulfinyl, a silane, an alkoxysilane, a stannyl, a boré, a nitrogenous heterocycle, an oxygenated heterocycle, a sulfur heterocycle and an aromatic group substituted with the aforementioned groups.

Preferably, this modified polyisoprene is obtained by the process according to the invention described above.

In a first preferred variant, the modified polyisoprene predominantly comprises the species of general formula (I) above.

In a second preferred variant, the modified polyisoprene predominantly comprises the species of general formula (II) above.

The modified polyisoprene according to the invention may be used as such or in admixture with one or more other compounds. The presence of functional groups at at least one of its two ends makes it possible to envisage a use in the applications usually known for modified diene polymers.

It is known, for example, to modify the nature of the diene polymers to introduce functional groups in order to optimize the interactions between the elastomer and the reinforcing filler within a reinforced rubber composition.

Thus, the particular structure of the modified polyisoprene obtained according to the invention from a deproteinized natural rubber makes it possible to envisage its use in the manufacture of various products based on reinforced rubber depending on the nature of the grafted function and therefore of the functional transfer agent used.

Finally, the invention relates to an elastomeric composition based on one or more modified polyisoprenes as defined above.

The elastomeric composition according to the invention may preferably comprise more than 40 phr of modified polyisoprene according to the invention; more preferably still, the polyisoprene content varies from 50 to 100 phr, in particular from 70 to 100 phr.

The elastomeric composition according to the invention may comprise a mixture of several modified polyisoprenes according to the invention. The elastomeric composition according to the invention may further comprise one or more reinforcing fillers and one or more crosslinking systems.

Any type of reinforcing filler known for its ability to reinforce a rubber composition that can be used for manufacturing tires, for example carbon black, a reinforcing inorganic filler such as silica, or a blend of these two types can be used. charge, especially a black carbon and silica blend.

Suitable carbon blacks are all carbon blacks, used individually or in the form of mixtures, in particular blacks of the HAF, ISAF, SAF type conventionally used in tires (so-called pneumatic grade blacks). It is also possible to use, according to the targeted applications, blacks of higher series FF, FEF, GPF, SRF. The carbon blacks could for example already be incorporated into the diene elastomer in the form of a masterbatch, before or after grafting and preferably after grafting (see, for example, applications WO 97/36724 or WO 99/16600).

As reinforcing inorganic filler other than carbon black, is meant by the present application, by definition, any inorganic or inorganic filler as opposed to carbon black, capable of reinforcing on its own, without other means than a coupling agent intermediate, a rubber composition for the manufacture of tires; such a filler is generally characterized, in known manner, by the presence of hydroxyl groups (-OH) on its surface.

The physical state under which the reinforcing filler is present is indifferent, whether in the form of powder, microbeads, granules, beads or any other suitable densified form. Of course, reinforcing filler is also understood to mean mixtures of different reinforcing fillers, in particular highly dispersible siliceous and / or aluminous fillers as described below.

Inorganic reinforcing fillers other than carbon black are suitable in particular mineral fillers of the type siliceous material, in particular silica (SiO 2), or of the aluminous type, in particular alumina (Al 2 O 3).

Preferably, the level of reinforcing filler in the composition varies from 10 to 200 phr, more preferably from 30 to 150 phr, in particular from 50 to 120 phr, the optimum being, in a manner known per se, different according to the particular applications. referred.

According to one embodiment, the reinforcing filler mainly comprises silica, preferably the content of carbon black present in the composition being less than 20 phr, more preferably less than 10 phr (for example between 0.5 and 20 phr, in particular from 1 to 10 phr).

Preferably, the reinforcing filler predominantly comprises carbon black, or is exclusively composed of carbon black.

When the reinforcing filler comprises a filler requiring the use of a coupling agent to establish the bond between the filler and the elastomer, the elastomeric composition according to the invention further comprises, in a conventional manner, an agent capable of ensuring effectively this link. When the silica is present in the composition as a reinforcing filler, an at least bifunctional coupling agent (or bonding agent) is used in known manner in order to ensure a sufficient chemical and / or physical connection between the filler inorganic (surface of its particles) and the diene elastomer, in particular organosilanes or bifunctional polyorganosiloxanes.

In the composition according to the invention, the content of coupling agent preferably varies from 0.5 to 12 phr, it being understood that it is generally desirable to use as little as possible. The presence of the coupling agent depends on that of the reinforcing inorganic filler other than carbon black. Its rate is easily adjusted by the skilled person according to the rate of this charge; it is typically in the range of 0.5 to 15% by weight relative to the amount of reinforcing inorganic filler other than carbon black. Those skilled in the art will understand that, as an equivalent load of the reinforcing inorganic filler other than carbon black, could be used a reinforcing filler of another nature, since this reinforcing filler would be covered with an inorganic layer such as silica, or would comprise on its surface functional sites, especially hydroxyl, requiring the use of a coupling agent to establish the connection between the filler and the elastomer.

The elastomeric composition according to the invention may also contain reinforcing organic fillers which may replace all or part of the carbon blacks or other reinforcing inorganic fillers described above. Examples of reinforcing organic fillers that may be mentioned are functionalized polyvinyl organic fillers as described in applications WO-A-2006/069792, WO-A-2006/069793, WO-A-2008/003434 and WO-A- 2008/003435.

The composition according to the invention may also contain, in addition to the coupling agents, activators for coupling the reinforcing filler or, more generally, processing aid agents that may be used in known manner, thanks to an improvement in the dispersion. of the charge in the rubber matrix and a lowering of the viscosity of the compositions, to improve their ability to implement in the green state.

As explained above, the composition according to the invention may also comprise a crosslinking system.

This crosslinking allows the formation of covalent bonds between the elastomer chains. It can be based on either sulfur, or sulfur and / or peroxide and / or bismaleimide donors, vulcanization accelerators, vulcanization activators.

The vulcanization system itself is preferably based on sulfur and a primary vulcanization accelerator, in particular a sulfenamide type accelerator, as chosen from the group consisting of 2-benzothiazyl disulfide (abbreviated as "MBTS"). ), N-cyclohexyl-2-benzothiazyl sulfenamide (in abbreviated "CBS"), N, N-dicyclohexyl-2-benzothiazyl sulfenamide (abbreviated "DCBS"), N-tert-butyl-2-benzothiazyl sulfenamide (abbreviated "TBB S"), N-tert-butyl-2 benzothiazyl sulfenimide (abbreviated as "TBSI") and mixtures of these compounds.

Sulfur is used at a preferential rate ranging from 0.5 to

10 phr, more preferably from 0.5 to 5.0 phr, for example from 0.5 to 3.0 phr, when the invention is applied to a tire tread. The set of primary accelerators, secondary and vulcanization activators is used at a preferential rate ranging from 0.5 to 10 phr, more preferably from 0.5 to 5.0 phr, in particular when the invention applies to a band. of tire rolling.

The elastomeric composition according to the invention may also comprise all or part of the usual additives usually used in elastomer compositions intended for the manufacture of tires, in particular treads, such as, for example, plasticizers or extension oils. that the latter are of aromatic or non-aromatic nature, pigments, protective agents such as anti-ozone waxes (such as C32 ST Ozone wax), chemical antiozonants, anti-oxidants (such as 6-para-phenylenediamine). ), anti-fatigue agents, reinforcing resins, acceptors (for example phenolic resin novo lacquer) or methylene donors (for example HMT or H3M) as described for example in the application WO 02/1 0269, adhesion promoters (cobalt salts for example).

The final composition thus obtained may then be calendered, for example in the form of a sheet, a plate or extruded, for example to form a rubber profile usable as a semi-finished rubber product for the tire.

The object of the invention is therefore a semi-finished tire rubber article comprising a crosslinkable or crosslinked rubber composition as defined above.

Finally, the object of the invention is a tire comprising a semi-finished article as defined above. The aforementioned features 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 illustration and not limitation.

Examples of realization of the invention

Measurements used The elastomers are characterized, before cooking, as indicated after.

Analysis of the macrostructure by Flow-FFF / RI / MALS (Flow Field-Flow Fractionation / Refractive Index / Multi-Angle Light Scattering)

This technique makes it possible to evaluate the macrogel of the polymer solution.

The measurement of the macrogel consists in lubilizing a sample of natural rubber (NR) at a concentration of between 0.5 and 10 g / l in an organic solvent for a period of between 1 and 14 days in a shaking water bath. at a temperature between 15 and 45 ° C.

Once the solubilization is complete, centrifugation is performed. The soluble fraction is then separated from the gel. Only this soluble fraction is analyzed in Flow-FFF / RI / MALS.

FFF is a technique that separates macromolecules (very high molecular masses) according to their hydrodynamic volume. The principle is based on a laminar flow and a longitudinal flow through a channel. The separation is done using an orthogonal force which can be of different kinds (electric potential, magnetic field, liquid flow, ...).

Flow-FFF is the most common FFF technique. The orthogonal flow is ensured by the suction of the solvent through the bottom of the channel, through a semi-permeable membrane. This is called Asymmetrical Flow FFF (AF4). The longest elastomer chains or high molar masses are eluted last.

We first start by performing a focus step. It serves to position all the compounds in the same plane so as not to distort the elution times.

When this step is finished, comes the elution step during which the orthogonal flow also called "crossflow" decreases over time.

After separation, the macromolecules are detected using a refractometer (RI) and a light scattering device (MALS). These detectors make it possible to obtain information on the molar mass distributions or on the architecture of the polymers.

Nuclear Magnetic Resonance Spectroscopy (NMR)

Determinations of the levels of functions grafted onto the polymer chain are carried out by NMR analysis. The spectra are acquired on a BRUKER 500 MHz spectrometer equipped with a BBIz-grad 5 mm wideband probe. The NMR experiment ^! H quantitative, uses a 30 ° single pulse sequence and a 3 second repetition time between each acquisition. The samples are solubilized in deuterated chloroform.

The NMR spectrum ^! H makes it possible to quantify the acetate units by integrating the characteristic signals of the protons -CH = CH-CH ₂ OCOCH ₃ , -C (CH ₃ ) = CH-CH ₂ OCOCH ₃ , -CH = CH-CH ₂ OCOCH ₃ , which appear respectively in chemical shifts δ = 5.8 at 5.4 ppm, δ = 5.3 at 5.25 ppm and δ = 4.6 at 4.4 ppm.

Origin of reagents

In the set of examples mentioned below, the Grubbs II catalyst, 1,4-diacetoxybut-2-ene, Empigen® (N- (C 1 -C 6 alkyl-N, N-dimethylglycine betaine), sodium dodecylbenzenesulfonate (SDBS), triton X® (4- (1,1,3,3-tetramethylbutyl) phenylpolyethylene glycol) and cetyltrimethylammonium (CTAC1) are marketed by Aldrich and are used without further purification. Brij35® (polyoxyethylene glycol dodecyl ether) is marketed by Acros. The dichloromethane and toluene are purified by passage on the guard of alumina and bubbling with nitrogen.

The deproteinized natural rubber used in these examples is derived from a four-fold centrifuged HANR ("High Ammonia Natural Rubber") latex, coagulated with methanol, acidified with acetic acid (98/2 by volume) and dried under vacuum at room temperature. 65 ° C. Its nitrogen content is 0.14%. Examples 1 to 5

An example of comparative modified polyisoprene synthesis (reference 1) as well as four examples of modified polyisoprene according to the invention (references 2 to 5) are synthesized according to the following synthesis protocol and with the reagents and the reagent contents according to Table 1 .

Table 1

(1) Number of isoprene units in mo

(2) Solution of 1,4-diacetoxybut-2-ene in toluene (concentration of 0.202 m 2 / L)

(3) Grubbs II catalyst solution in toluene (0.012 mol / L concentration)

Synthesis protocol

In a Schlenk tube under nitrogen containing 1.36 g of deproteinized dry natural rubber are added 90 ml of dichloromethane and the desired amount of surfactant (Brij 35®). The mixture is then stirred for 24 hours. The desired amount of the solution of 1,4-diacetoxybut-2-ene in toluene (concentration of 0.202 m 2 / l) followed by the desired amount of the catalyst solution in toluene (concentration of 0.012 m 2 / L) are added to the reaction medium. The reaction medium is then stirred at 42 ° C. for 10 minutes and a solution of vinyl ethyl ether is introduced (0.1 ml). The reaction mixture is coagulated in methanol and the coagulum is dried for 48 hours at 65 ° C. under partial vacuum. The control sample only coagulated the starting latex with methanol and the coagulum was dried for 48 hours at 65 ° C. under partial vacuum.

The results of Flow-FFF and of 1 H NMR are compiled in the following Table 2 and make it possible to evaluate the rate of acetates functions of the polyisoprene chains.

Table 2

(1) Function for Pattern 100 isoprene units measured by NMR ^the H.

(2) Number average molar mass calculated from the functional level for a linear and difunctional acetate chain. The method according to the invention makes it possible to greatly reduce the level of macrogel.

The method according to the invention allows the preparation of polyisoprene chains functionalized with good yields and having average mo lar masses in number greater than or equal to 100 kg / mo l (3 ^rd row of the table).

In addition, the functionalized polyisoprene chains (references 2 to 4) obtained with the process according to the invention have a rate of acetate functions which proves that they are predominantly the functionalized species at both ends (measured average molecular weight ^(3rd line) and calculated (5 ^th line) near).

Indeed, the Flow-FFF makes it possible to obtain the measurement of the average mass in number. NMR ^! H makes it possible to obtain the percentage of acetate function for 100 isoprene units.

Assuming that the modified polyisoprene is linear and functionalised at both ends, a theoretical number average molecular weight can be calculated.

The closer the theoretical value is to the value obtained by the Flow-FFF, the more the modified polyisoprene obtained mainly comprises difunctional species.

Examples 6 to 9 Influence of the surfactant chosen Four examples of modified polyisoprene synthesis according to the invention are carried out according to the protocol of the preceding 1 to 5 and with the reagents and the contents of reagents according to Table 3. Table 3

(1) Number of isoprene units in mo

(2) Cetyltrimethylammonium chloride

(3) Sodium dodecylbenzenesulfonate

(4) Solution of 1,4-diacetoxybut-2-ene in toluene (concentration of 0.202 m 2 / L)

(5) Grubbs II catalyst solution in toluene (0.012 mol / L concentration)

The results of Flow-FFF and of ¹ H NMR are compiled in the following Table 4 and make it possible to evaluate the level of acetate functions of the polyisoprene chains. Table 4

(1) Function for Pattern 100 isoprene units measured by NMR ^the H.

(2) Number average molar mass calculated from the functional level for a linear and difunctional acetate chain.

The method of the invention allows the preparation of polyisoprene modified with good yields and having average molecular weights well above 100 kg / mol (3 ^rd row of the table).

In addition, depending on the type of surfactant chosen and therefore the progress of the depolymerization reaction, the modified polyisoprene obtained will mainly comprise either the species mono functionalized, either the bifunctionalized species, or a mixture of the mono-functionalized species and the bifunctionalized species.

Finally, the process according to the invention makes it possible to obtain modified polyisoprenes with a low polydispersity index of less than or equal to 5.

Claims

1. Process for the depolymerization of a deproteinized natural rubber for the preparation of a modified polyisoprene comprising in majority a mixture of the species functionalized at one of its two ends by one or more functional groups and of the functionalized species at its two ends ends by one or more functional groups, said method comprising the following steps:

2. Method according to claim 1, characterized in that the deproteinized natural rubber is chosen from deproteinized dry natural rubbers previously modified or not, and a mixture of these rubbers, and preferably from the natural rubbers deproteinized from the rubber tree, gutta percha, dandelion, guayule and a mixture of these rubbers.

3. Process according to claim 1 or 2, characterized in that the solution of deproteinized natural rubber has a molar concentration of isoprene units ranging from 0.05 to 0.5 mol / l, preferably ranging from 0 to 15 to 0.3 mol / L.

4. Process according to any one of the preceding claims, characterized in that the organic solvent (s) are chosen from cyclic or linear hydrocarbon solvents, aromatic solvents, halogenated solvents and a mixture of these solvents. , and preferably from heptane, hexane, pentane, cyclohexane, methylcyclohexane, petroleum ether, decalin, benzene, toluene, xylene, nitrobenzene, chloroform, dichloromethane, tetrachloromethane and a mixture of these solvents.

5. Process according to any one of the preceding claims, characterized in that the surfactant (s) are (are) chosen from anionic, cationic, amphoteric and nonionic surfactants, and preferably from cationic and non-cationic surfactants. ionic.

6. Process according to any one of the preceding claims, characterized in that the surfactant or surfactants are chosen from trimethyldecylammonium chloride, polyoxyethylene sorbitan esters and a mixture of these compounds.

7. Process according to any one of the preceding claims, characterized in that the surfactant or surfactants represent from 1 to 20 phr, preferably from 5 to 20 phr, more preferably from 5 to 15 phr, and in particular from 10 to 20 phr. at 1 5 phr with respect to the deproteinized natural rubber.

8. Process according to any one of the preceding claims, characterized in that the transfer agent or agents are chosen from the following compounds of formula III, IV and V:

ni, n ₂ and n ₃ being integers ranging from 0 to 20,

9. Process according to claim 8, characterized in that X ₁ , X ₂ and X ₃ are functional groups comprising one or more groups chosen from a halogen, an amine, an imine, an ammonium, an amide, a nitrile and an azo. a diazo, a hydrazo, a carbamate, an isocyanate, a hydroxyl, a carbonyl, a carboxyl, an epoxy, a sulphide, a disulfide, a thiocarbonyl, a trithiocarbamate, a sulphonyl, a sulfinyl, a silane, an alkoxysilane, a stannyl , a boré, a nitrogenous heterocycle, an oxygenated heterocycle, a sulfur heterocycle and an aromatic group substituted with the aforementioned groups.

10. Process according to any one of the preceding claims, characterized in that the transfer agent or agents represent from 0.01 to 50 mol%, preferably from 0.02 to 10 mol%, and in particular from 0 to 10 mol%. , 02 to 1 mol% relative to the number of moles of isoprene units in the deproteinized natural rubber.

11. Process according to any one of the preceding claims, characterized in that the metathesis reaction catalyst (s) are chosen from Grubbs II catalysts, Hoveyda-Grubbs II catalysts and dichloro [1,3-bis (2-Methylphenyl) -2-imidazolidinylidene] (2-isopropoxyphenylmethylene) ruthenium (II), [2- (1-methylethoxy-O) phenylmethyl-C] (nitrato-0,0 ') {rele

(2R, 5R, 7S) -tricyclo [3.3.1.13,7] decane-2,1-diyl [3- (2,4,6-trimethylphenyl) -1-imidazolidin-2-ylidene]} ruthenium, dichloro [ 1,3-bis (2,4,6-trimethylphenyl) -2-imidazolidinylidene] (benzylidene) bis (3-bromopyridine) ruthenium (II), dichloro [1,3-bis (2-methylphenyl) -2-imidazolidinylidene) ] (benzylidene) (tricyclohexylphosphine) ruthenium (II), dichloro [1,3-bis (2,4,6-trimethylphenyl) -2-imidazolidinylidene] (3-methyl-2-butenylidene)

(tricyclohexylphosphine) ruthenium (II), dichloro [1,3-bis (2,4,6-trimethylphenyl) -2-imidazolidinylidene] [3- (2-pyridinyl) propylidene] ruthenium (II), dichloro [1, 3-bis (2,4,6-trimethylphenyl) -2-imidazolidinylidene] [(tricyclohexylphosphoranyl) methylidene] ruthenium m (II) tetrafluoroborate, and dichloro [1,3-bis (2,6-isopropylphenyl) -2-imidazo-lidinylidene] (benzylidene)

(tricyclohexylphosphine) ruthenium (II).

12. Process according to any one of the preceding claims, characterized in that the metathesis reaction catalyst or catalysts represent from 0.0001 to 1% by weight, preferably from 0.0001 to 0.1% by weight. and in particular from 0.002 to 0.1% by weight based on the number of units of isoprene units in the deproteinized natural rubber.

13. Method according to any one of the preceding claims, characterized in that it further comprises a step of adjusting the temperature of the solution of deproteinized natural rubber with stirring, said step being carried out after steps ii) to iii ) at a temperature ranging from 3 ° C to 100 ° C, preferably from 15 ° C to 80 ° C, followed by a stirring step of the deproteinized natural rubber solution for a period generally ranging from 5 minutes to 24 minutes. hours, preferably ranging from 5 minutes to 8 hours, more preferably from 9 minutes to 4 hours.

14. A method according to any one of the preceding claims, characterized in that it further comprises a step of adding one or more stoppering agents to the deproteinized natural rubber solution, said step being carried out after the steps ii) to iii), and after any temperature setting and stirring steps as defined in claim 13.

15. Modified polyisoprene obtainable by the process as defined in any one of claims 1 to 14, the average number-average molecular weight of the polyisoprene ranging from 100 to 600 kg / mol, preferably ranging from 100 to 400 kg / m 2, more preferably ranging from 142 to 400 kg / m 2, and in particular ranging from 142 to 33 1 kg / m 2.

16. Polyisoprene according to claim 1 5, characterized in that it comprises mainly the species functionalized at one of its two ends by one or more functional groups.

17. Polyisoprene according to claim 15, characterized in that it comprises mainly the species functionalized at both ends by one or more functional groups.

18. Modified polyisoprene comprising predominantly a mixture of the following species of general formula I and the following species of general formula II:

the number-average molar mass of polyisoprene ranging from 100 to 600 kg / mol, preferably ranging from 100 to 400 kg / mol, more preferably ranging from 142 to 400 kg / m 2, and in particular ranging from 142 to 1 kg / m 2.

Modified polyisoprene according to claim 18, characterized in that R and R ', independently of one another, are functional groups comprising one or more groups selected from halogen, amine, imine, ammonium , amide, nitrile, azo, diazo, hydrazo, carbamate, isocyanate, hydroxyl, carbonyl, carboxyl, epoxy, sulfide, disulfide, thiocarbonyl, trithiocarbamate, sulfonyl, sulfinyl, a silane, an alkoxysilane, a stannyl, a boré, a nitrogenous heterocycle, an oxygenated heterocycle, a sulfur heterocycle and an aromatic group substituted with the aforementioned groups.

20. An elastomeric composition based on one or more modified polyisoprenes as defined in any one of claims 15 to 19.

21. A rubber semi-finished article for a tire, characterized in that it comprises a cross-linkable or cross-linked rubber composition as defined in claim 20.

22. A tire characterized in that it comprises a semi-finished article as defined in claim 21.