WO2015097192A1

WO2015097192A1 - Method for controlled metathesis depolymerization of synthetic rubber in a solution

Info

Publication number: WO2015097192A1
Application number: PCT/EP2014/079082
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: EP3087105A1; FR3015487B1; FR3015487A1

Abstract

The invention relates to a method for the depolymerization of a block copolymer comprising a polyisoprene block and at least one polybutadiene block for the preparation of a modified polyisoprene mainly comprising the species functionalized on the at least one polybutadiene block by one or more functional groups, wherein said method comprises the following steps: i) a step of preparing a block copolymer solution comprising the block copolymer and one or more organic solvents, then ii) a step of adding, to the block copolymer solution, one or more transfer agents comprising said functional group or groups, iii) a step of adding, to the block copolymer solution, one or more metathesis catalysts exhibiting higher activity on disubstituted carbon-carbon double bonds than on tri- and tetra-substituted carbon-carbon double bonds. The invention also relates to a modified polyisoprene obtainable using the aforementioned method. Lastly, the invention relates to an elastomeric composition made from the aforementioned modified polyisoprene.

Description

Process for the controlled depolymerization of synthetic rubber in solution by metathesis

The present invention relates to a process for the depolymerization of a block copolymer comprising a polyisoprene block and at least one polybutadiene block for the preparation of a modified polyisoprene mainly comprising the species functionalized on the polybutadiene block by one or more several functional groups.

The invention also relates to the modified polyisoprene obtainable by this process. Finally, the invention relates to a rubber composition, used in particular for the manufacture of tires, based on the aforementioned modified polyisoprene.

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 introducing chemical functions which make it possible to ensure 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 sidewalls 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.

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 carbonyl, carboxyl, ester, epoxide (or glycidyl), imine, azine, hydrobenzamide, nitrile, isocyanate or halogen.

On the other hand, in particular because of 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 the introduction of carbonyl, carboxyl, ester, epoxide (or glycidyl), imine, azine, hydrobenzamide or nitrile functional groups. , isocyanate or halogen.

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 ROMP reactions of cyclic dienes 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 polybutadiene at high rate of cis - 1,4 units 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.

This reaction requires the use of catalysts reactive with trisubstituted double bonds, especially ruthenium catalysts second generation and therefore generally very active in depolymerization. Thus, the control of this reaction to generate high molecular weight polyisoprenes (average molecular weight greater than 100 g / mol), which still possesses properties of interest in a mixture, is not easy.

To circumvent this problem of too rapid degradation of the main chain, it has been developed, and in particular in the case of the applications JP20121405 1 1, JP20 121405 12 and JP20121405 14, in the case of polybutadiene and styrene-butadiene rubbers (SBR ), functionalization methods along the chain via cross metathesis reactions between 1,2-butadiene units and a transfer agent in the presence of a Grubbs I catalyst.

However, this approach is not suitable for polyisoprenes comprising only units 1, 4 and 3, 4.

In fact, Grubbs I type catalysts are not very reactive on trisubstituted bonds and this does not make it possible specifically to introduce the functions of interest at the end of the chain.

In view of the foregoing, there is therefore a need to provide a polyisoprene metathesis metathesis depolymerization process which is versatile in terms of functions, i.e. that is adapted to a large number of functions, in order to to synthesize functional polyisoprenes at the end of the chain of high molecular weight, with a high rate of cis-1, 4 units and a high degree of functions.

A synthesis process has now been developed which makes it possible, starting from a blown copolymer comprising a polyisoprene block and at least one polybutadiene block, to obtain a modified polyisoprene comprising, for the most part, the species functionalized on the at least one polybutadiene block with a high molecular weight, a high rate of cis-1,4 units and a high rate of functions.

The subject of the invention is therefore a process for the depolymerization of a block copolymer comprising a polyisoprene block and at least one polybutadiene block for the preparation of a modified polyisoprene comprising predominantly the functionalized species on the at least one polybutadiene block. by one or more functional groups, said method comprising the following steps:

i) a step of preparing a solution of the block copolymer comprising the blister copolymer and one or more organic solvents, and

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

iii) a step of adding to the block copolymer solution of one or more metathesis reaction catalysts having a higher activity on di-substituted carbon-carbon double bonds than on tri- and carbon-carbon double bonds; tetra-substituted.

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 comprising predominantly the species functionalized on the at least one butadiene block, having a high content of cis - 1,4 units and used directly in elastomeric compositions.

Finally, the process according to the invention advantageously makes it possible to obtain a modified polyisoprene with a low polydispersity index (Ip) of less than 3.

The invention therefore also has obj and a modified polyisoprene obtainable by the process above. The subject of the invention is also a modified polyisoprene comprising predominantly the species of general formula I below or predominantly the species of general formula II below:

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 8823,

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

m, p and m ', independently of one another, being integers ranging from 1 to 184,

a and a ', independently of one another, being integers ranging from 0 to 20. This modified 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 those skilled in the art that when a block copolymer is depolymerized by metathesis in the presence of one or more transfer agents, a mixture of modified species is obtained. of this block copolymer whose composition depends in particular on the choice of the block copolymer, but also 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 "majority" or "majority" in relation to a compound, it is meant that this compound is the majority of the other compounds of the same type in the composition, that is to say that it is the one which represents the largest weight fraction among the compounds of the same type.

Thus, a functionalized species of a modified polyisoprene called majority is that representing the largest weight fraction among the functionalized species constituting the modified polyisoprene. 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 reaction product 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 various phases of manufacture of the composition, in particular during its crosslinking or vulcanization.

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

In the present application, the term "part per cent of 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.

In the present application, the term "predominantly the functionalized species on the at least one polybutadiene block", the fact that the depolymerization reaction is carried out predominantly on the at least one polybutadiene block. Once the depolymerization has been carried out, it is meant that the at least one functionalized polybutadiene block corresponds to at least one butadiene unit comprising one or more functional groups.

As previously described, the process according to the invention comprises a step of preparing a solution of the block copolymer.

The block copolymer for use in the process according to the invention comprises a polyisoprene block and at least one polybutadiene block.

Preferably, the block copolymer that can be used in the process according to the invention is chosen from a butadiene-isoprene diblock copolymer and a butadiene-isoprene-butadiene triblock copolymer.

These block copolymers are generally obtained by anionic polymerization, emulsion or Ziegler catalysis methods. In particular, the polyisoprene block of the block copolymer that can be used in the process according to the invention preferably comprises a level of isoprene units 1,4-cis greater than 90%, more preferably greater than 95%.

These high block copolymers of isoprene units 1, 4-cis can be obtained by the method described in the patent application WO0238636, that is to say by polymerization of isoprene in the presence of a catalytic system. preformed type based on at least:

- butadiene,

a salt of one or more rare earth metals, that is to say having an atomic number between 57 and 71 in the periodic table of Mendeleev elements, of an organic phosphoric acid, said salt being in suspension in at least one saturated inert hydrocarbon solvent, of aliphatic or alicyclic type,

an alkylation agent consisting of an alkylaluminium of formula A1R ₃ or HAIR 2, the molar ratio (alkylating agent / rare earth salt) having a value ranging from 1 to 5, and

a halogen donor consisting of an alkylaluminum halide.

In addition, in the case where the block copolymer is a triblock-butadiene-isoprene-butadiene copolymer, the synthesis of this copolymer further comprises a step of butadiene polymerization subsequent to the polymerization of isoprene.

Preferably, the polyisoprene block of the block copolymer that can be used in the process according to the invention has a number average molecular weight ranging from 100 to 600 kg / m 2, preferably ranging from 200 to 500 kg / m 2.

Preferably, the polybutadiene block or blocks of the block copolymer each have a number average molecular weight ranging from 0.5 to 10 kg / m 2.

As explained above, the block copolymer is lubilized in one or more organic solvents.

The organic solvent (s) that may be used in the process according to the invention may be chosen from hydrocarbon solvents. cyclic or linear, 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 block copolymer solution for use in the process according to the invention preferably has a molar concentration of isoprene unit ranging from 0.05 to 1 mol / l, more preferably ranging from 0.15 to 1 mol. / L.

As previously described, the process according to the invention comprises a step of adding to the block copolymer solution of 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 block copolymer by means of a cross-metathesis reaction with a polymer chain, mainly the polybutadiene block or blocks, in the presence of a catalyst.

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, imide, amide, nitrile, azo, diazo, hydrazo, carbamate, isocyanate, hydroxyl, carbonyl, carboxyl, ester, epoxy, sulfide, disulfide, thiocarbonyl, a trithio carbamate, 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.

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 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.

By way of 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.

By way of example of a transfer agent comprising one or more nitrile groups or nitrile groups carried by a ring, one 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.

As an 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, mention may be made of cis-2-butene-1,4-diol-diglycidyl ether, allyl glycidyl ether, glycidyl (meth) acrylate and 3,4-oxycyclohexyl (meth) acrylate.

As an 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. 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 25% by weight, and in particular from 0.02 to 10% by weight relative to number of units of isoprene units in the block copolymer.

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

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

As previously described, the process according to the invention comprises a step of adding to the block copolymer solution of one or more metathesis reaction catalysts having a higher activity on di-substituted carbon-to-carbon double bonds than on tri- and tetra-substituted carbon-carbon double bonds.

Consequently, the metathesis reaction catalyst or catalysts that can be used in the process according to the invention are advantageously very weakly active on the tri- and tetra-substituted double bonds and therefore only lead to a very low depolymerization by metathesis of the matrices. polyisoprene type.

On the other hand, they are advantageously active on the di-substituted double bonds and therefore depolymerize advantageously by metathesis mainly the butadiene block or blocks without degrading or weakly the polyisoprene block.

Preferably, the metathesis reaction catalyst or catalysts are chosen from transition metal complexes based on ruthenium, osmium or iridium, and more preferentially among ruthenium catalysts known as first generation catalysts.

By way of example, mention may be made of the Grubbs I catalyst, the Hoveyda-Grubbs I catalyst, the dichloro- (3-methyl-2- butylidene) bis (tricyclohexylphosphine) ruthenium, dichloro- (3-methyl-2-butylidene) bis (tricyclopentylphosphine) ruthenium, {[2- (i-propoxy) -5- (N, N-dimethylaminosulfonyl) phenyl] methylene} (tricyclohexylphosphine) henium dichloride, 3-phenyl-1H-inden-1-ylidene [bis (i-butylphoban)] ruthenium dichloride, bis (tricyclohexylphosphine) [(phenylthio) methylene] ruthenium

dichloride and bis (tricyclohexylphosphine) -3-phenyl-1H-indenyl-ylidenenethanenium dichloride.

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. Relative to the number of units of isoprene units in the block copolymer.

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 ii) and iii) are carried out generally with stirring of the bloated copolymer solution.

Preferably, the process according to the invention further comprises a step of controlling the temperature of the stirred block copolymer solution, said step being carried out after steps ii) and iii).

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

Once the temperature of the block copolymer solution has been reached, the block copolymer solution is generally stirred for a period of time ranging from 5 minutes to 24 hours, preferably ranging from 5 minutes to 20 hours. Preferably, the process according to the invention further comprises a step of adding one or more blocking agents to the block copolymer solution, said adding step being carried out after steps ii) to iii) and after any steps of setting the temperature and stirring of the bloated copolymer solution at the previously selected temperature and for the previously selected time.

The stopper or agents in particular make it possible to stop the depolymerization of the block copolymer.

The stopper (s) may be added to the solution of block copolymer in pure form or in solution.

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

The amount by weight of the curing 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 reaction solution. block copolymer.

The method according to the invention may furthermore comprise a step of adding one or more antioxidants, said adding step being carried out after steps ii) to iii), after the possible steps of adjusting the temperature and agitating the block copolymer solution at the previously selected temperature and during the previously selected reaction time and after the optional stop step.

Preferably, the antioxidant (s) may be chosen from 1-N- (4-methylpentan-2-yl) -4-N-phenylbenzene-1,4-diamine (Santo flex 13) and 2-tert-butyl -6- [(3-tert-butyl-2-hydroxy-5-methylphenyl) methyl] -4-methylphenol (A02246), and a mixture of these antioxidants.

Preferably, the antioxidant (s) may represent from 0.05 to 1 phr, preferably from 0.1 to 0.5 phr, relative to the block copolymer. The method according to the invention may further comprise a step of coagulating the medium.

This step makes it possible to recover the modified polyisoprene.

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

The coagulation of the medium can also be carried out by extraction by steam distillation.

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

Therefore, the object of the invention is also the modified polyisoprene obtainable by the process as described above.

In a first variant, that is to say in the case where the block copolymer comprises a polybutadiene block, the modified polyisoprene comprises mainly the species functionalized at one of its two ends by one or more functional groups.

In a second variant, that is to say in the case where the block copolymer comprises two polybutadiene blocks, the Modified polyisoprene predominantly comprises the species functionalized at both ends by one or more functional groups.

The invention also relates to a modified polyisoprene comprising predominantly the following species of general formula I or mainly the species of general formula II below:

m, p and m ', independently of one another, being integers ranging from 1 to 184, a and a ', independently of one another, being integers ranging from 0 to 20.

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

In general, the polyisoprene block of the modified polyisoprene obtained by the process according to the invention may have a number average molecular weight ranging from 100 to 600 kg / m 2, preferably ranging from 200 to 500 kg / m 2.

In general, the polybutadiene block (s) of the modified polyisoprene obtained by the process according to the invention may each have a number average molecular weight ranging from 54 to 9936 g / mol.

The modified polyisoprene according to the invention may be used as such or in admixture with one or more other compounds. The presence of one or more 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 block copolymer 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 the functional transfer agent used.

The invention therefore 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, the term "reinforcing filler" is also understood to mean mixtures of different reinforcing fillers, in particular highly dispersible siliceous and / or aluminous fillers as described below.

As reinforcing inorganic fillers other than carbon black are especially suitable mineral fillers of the siliceous type, in particular of silica (SiO ₂ ), or of the aluminous type, in particular of 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 modified polyisoprene 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 actual crosslinking system is preferably a vulcanization system, more preferably based on sulfur and a primary vulcanization accelerator, in particular a sulfenamide accelerator, such as selected from the group consisting of 2-benzothiazyl disulfide (abbreviated "MBTS"), N-cyclohexyl-2-benzothiazyl sulfenamide (abbreviated "CB S"), N, N-dicyclohexyl-2-benzothiazyl sulphenamide (abbreviated "DCBS"), N-tert-butyl-2-benzothiazyl sulphenamide (abbreviated "TBBS"), N-tert-butyl-2- benzothiazyl sulfenimide (abbreviated as "TBSI") and mixtures of these compounds.

Sulfur is used at a preferential level 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 strip of tire rolling. 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 embodiment of the invention

Measures used

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

Size exclusion chromatogram (SEC)

Size Exclusion Chromatography (or Size Exclusion Chromatography) separates macromolecules in solution according to their size through columns filled with a porous gel. The macromolecules are separated according to their hydrodynamic volume, the most voluminous being eluted first.

Without being an absolute method, the SEC allows to apprehend the distribution of the molecular masses of a polymer. From commercial standard products, the various average molecular masses (Mn) and weight (Mw) can be determined and the polymolecularity or polydispersity index (Ip = Mw / Mn) calculated via a so-called MOORE calibration. .

There is no particular treatment of the polymer sample before analysis. This is simply solubilized in a solution of tetrahydrofuran containing 1% by volume of diisopropylamine, 1% by volume of triethylamine and 1% by volume. distilled water, or in chloroform, at a concentration of about 1 g / l. Then, the solution is filtered through a 0.45 μιη porosity filter before injection.

The apparatus used is a "WATERS alliance" chromatograph. The eluting solvent is tetrahydrofuran containing 1% by volume of diisopropylamine and 1% by volume of triethylamine, or chloroform according to the solvent used for the dissolution of the polymer. The flow rate is 0.7 ml / min, the system temperature is 35 ° C and the analysis time is 90 min. A series of four WATERS columns in series, "STYRAGEL HMW7", "STYRAGEL HMW6E" and two "STYRAGEL HT6E" are used.

The volume injected from the solution of the polymer sample is 100 μΐ. The detector is a "WATERS 2410" differential refractometer and the software for the exploitation of chromatographic data is the "WATERS EMPOWER" system.

The mean calculated mass masses are relative to a calibration curve made from commercial standard polystyrene "PS S READY CAL-KIT".

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. Experience NMR quantitative ^J H, uses a simple pulse sequence 30 ° and a repeating time of 3 seconds between each acquisition. The samples are solubilized in deuterated chloroform.

The NMR spectrum ^J H quantifies silane units by integration of the signals characteristic of protons -CH = CH-Si (OEt) 3 which appear at chemical shifts δ = 3, 75-3, 65 ppm.

The NMR spectrum ^J H also quantifies the butadiene units by integration of the protons characteristic signals -CH = CH- which appear at chemical shifts δ = 5, 35 ppm.

The NMR spectrum ^! H also makes it possible to quantify the units 3, 4 and 1, 4 of the polyisoprene by integration of the characteristic signals of the protons> C = CH- which respectively appear at chemical shifts δ = 4.8 at 4.5 ppm and δ = 5, 5 to 4.8 ppm.

Origin of reagents In all of the examples mentioned below, Grubbs I and II catalysts and vinyltriethoxysilane are marketed by Aldrich and are used without further purification.

Toluene is purified by passage over alumina and bubbled with nitrogen.

Preparation and Characteristics of a Polyisoprene-Polybutadiene Block Copolymer A polyisoprene-polybutadiene block copolymer comprising a high cis-1,4 polyisoprene block was synthesized by catalyzed polymerization of isoprene in the presence of a preformed catalytic system based on butadiene, diisobutyl aluminum hydride, diethylaluminium chloride and tris [bis (2-ethylhexyl) phosphate] neodymium as described in the patent application WO0238636.

The characteristics of this block copolymer A are detailed in Table 1. Table 1

Examples 1 to 4

An example of comparative modified polyisoprene synthesis (reference 1) as well as three examples of modified polyisoprene according to the invention (references 2 to 4) are synthesized according to the following synthesis protocol and table 3 and with the reagents and the reagent contents. according to Table 2.

Table 2

(1) Quantity of isoprene units

(2) In its pure form

(3) Grubbs I catalyst solution in toluene

(concentration of 0.012 mo l / L)

(4) Grubbs II catalyst solution in toluene (0.012 mol / L concentration) Synthesis protocol

In a Schlenk tube under nitrogen containing 0.68 g of A block copolymer are added 28 ml of toluene. The mixture is then stirred for 24 hours. The desired amount of vinyltriethoxysilane and then the desired amount of metathesis catalyst solution in toluene (concentration of 0.012 mol / L) are added to the reaction medium. The reaction medium is then stirred at 60 ° C. for the desired time (see Table 3) and a solution of vinyl ethyl ether is introduced (0.5 ml). The reaction mixture is coagulated in methanol and the coagulum obtained is returned to solution in toluene. (20 mL). An antioxidant solution (Santoflex 13) in toluene at 20 g / L (0.14 ml) is added to the coagulum in solution and the latter is then dried for 48 hours at 65 ° C. under partial vacuum.

Table 3

The results of SEC and 1 H NMR are compiled in the following Table 4 and make it possible to evaluate the level of silane functions of the polyisoprene chains, the proportion of butadiene units still present in the polyisoprene chains, the average molar mass by number of the chains. polyisoprene and their polydispersity index (Ip).

Table 4

Reference 1 2 3 4

Mn (kg / mol) ⁽¹⁾ 7,285,298,280

_Ip (2) 2.2 2.2 2.1 2.2

% functions

- 0.014 0.014 0.025 silane ¹ ^

% reasons

0.1 0.1 0.1 butadiene ¹ % reasons

cis isoprene - 97.5 97.4 97.4

1, 4 < ³ >

% reasons

isoprene cis - 2.5 2.5 2.6

3, 4 < ³ >

(1) Measured by SEC

(2) Calculated from the SEC

(3) Measured by NMR ^! H (number of units per 100 isoprene units)

The level of cis-3,4 isoprenic units is comparable before and after the depolymerization reaction (see Tables 1 and 4) which results in a lack of reactivity of this type of unit in metathesis.

On the other hand, the proportion of butadiene units is reduced by five (from 0.5 to 0.1 butadiene units per hundred isoprene units) after depolymerization.

This observation indicates that the butadiene units are primarily affected by the depolymerization reaction thereby generating polybutadiene oligomers which can be partially removed in the coagulation step.

The silane grafted units are quantified at the level of 0.014 to 0.025 percent isoprene units (Table 4) or 60 to 100% functional chain ends (if Mn determined by SEC is used and if the polymer chains are mono-functional).

The SEC analysis of references 2, 3 and 4 indicates that the depolymerization of the polyisoprene main skeleton took place but very moderately.

Indeed, the average number of molar masses of these samples (Mn approximately 280-298 kg / m 2 with an Ip of 2.2) are much greater than that of reference 4 carried out in the presence of the Grubbs II catalyst. Example 5 (modified polyisoprene E5)

The modified polyisoprene was obtained under the same operating conditions as the modified polyisoprene of the preceding Example 4 but starting from 60 g of the A block copolymer. The number of silane units per 100 isoprene units is 0.023.

The average number-average molecular weight of the polyisoprene (Mn) chains is 280 kg / m 2 and their polydispersity index (Ip) is 2.1. Comparative Example (Modified Polyisoprene C2)

The modified polyisoprene C2 was obtained under the same conditions as the modified polyisoprene of Example 4 above, but starting from 60 g of the block copolymer A and in the total absence of vinyltriethoxysilane transfer agent.

The average number-average molecular weight of the polyisoprene (Mn) chains is 240 Kg / m 2 and their polydispersity index (Ip) is 2.1.

Traction tests:

These tests make it possible to determine the elastic stresses and the properties at break after firing. Unless otherwise indicated, they are carried out in accordance with the French standard NF T 46-002 of September 1988. The true eluting sequences (ie, calculated by reducing to the actual section of the test piece), expressed in MPa, at 100% elongation (modules rated M 100), at 300% elongation (M300). All these tensile measurements are carried out under normal conditions of temperature and hygrometry (23 +/- 2 ° C, 50 +/- 5% relative humidity).

Dynamic Properties

The dynamic properties AG * and tan (δ) max are measured on a viscoanalyzer (Metravib VA4000), according to ASTM D 5992- 96. The response of a sample of vulcanized composition (cylindrical specimen 4 mm in thickness and 400 mm ² in section), subjected to sinusoidal solicitation in alternating simple shear, at the frequency of 10 Hz, was recorded in normal temperature conditions (23 ° C) according to ASTM D 1349-99, or as the case may be at a different temperature (60 ° C).

A strain amplitude sweep is carried out from 0.1% to 100% (forward cycle) and then from 100% to 0.1% (return cycle). The results exploited are the complex dynamic shear modulus (G *) and the loss factor tan (δ). For the return cycle, the maximum value of tan (δ) observed, denoted tan (δ) max, as well as the complex modulus difference (AG *) between the values at 0, 1% and at 100% deformation are indicated. (Payne effect).

The value of tan (δ) at 60 ° C is representative of the hysteresis of the material and therefore of the rolling resistance: the tan (δ) at 60 ° C is lower, the lower the rolling resistance.

Examples of compositions and results

The block copolymer A, the modified polyisoprenes C2 and E5 are used for the preparation of compositions below, respectively composition F 1, composition F 2 and composition F 3.

The following tests are carried out in the following manner: the modified polyisoprene or polyisoprene is introduced into a 75 cm ³ Polylab internal mixer, filled to 70% and whose initial tank temperature is approximately 110 ° C.

Then, the carbon black and then, after one to two minutes of mixing, the various other ingredients with the exception of the vulcanization system, are introduced into the mixer. Theromechanical work (non-productive phase) is then carried out in one step (total mixing time equal to about 5 minutes), until a maximum "falling" temperature of 160 ° C. is reached. The mixture thus obtained is recovered, cooled and the system of vulcanization (sulfur and accelerator CBS) on an external mixer (homo-finisher) at 25 ° C, mixing the whole (productive phase) for about 5 to 6 min.

The compositions thus obtained are then calendered either in the form of plates (thickness of 2 to 3 mm) or thin sheets of rubber for the measurement of their physical or mechanical properties.

The rubber compositions are given in Table 5. The amounts are expressed in parts per 100 parts by weight of elastomer (phr).

Table 5

Composition Fl F2 F3

Block copolymer A 100 - -

Polyisoprene modified C2 - 100 -

Modified Polyisoprene E5 - - 100

Carbon black ¹ - ¹ 3 3 3

SIL 160MP ⁽²⁾ 50 50 50

Antioxidant ¹ - ³⁾ 2 2 2

Paraffin 1, 5 1, 5 1, 5

Stearin ¹ - ⁴⁾ 2.5 2.5 2.5

ZnO < ⁵ > 2.7 2.7 2.7 Si69 ⁽⁶⁾ 5 5 5

Sulfur 1,4 1,4 1,4

Vulcanization accelerator ¹ - ⁷ ^ 1.7 1.7 1.7

(1) N234

(2) 160MP silica: microperelated silica with a specific surface area

160 m ² / g

(3) 1,3-dimethylbutyl-N-phenyl-para-phenylenediamine ("Santoflex 6-PPD" Flexsys Company)

(4) Stearin ("Pristerene 4931" - Uniqema Company)

(5) Zinc oxide (industrial grade - Umicore company)

(6) Bis [3- (triethoxysilyl) propyl] tetrasulfide

(7) N-cyclohexyl-2-benzothiazyl sulfenamide ("Santocure CBS" Flexys company)

The dynamic properties of these compositions are measured. Traction tests are also performed.

The results are summarized in Table 6 below.

Table 6

Composition Fl F2 F3

M100 1.96 1.94 2.1

M300 2.39 2.39 2.71

M300 / M100 1.22 1.23 1.29

Deformation at break (%) 699 552 660 Δϋ * (0-100%) 60 ° C Back

100 107 99 (MPa)

91 * 100 * 88 *

Tanomax 60 ° C Back

(0.159) ** (0.174) ** (0.154) **

* relative value (in base 100)

** absolute value

The results show a significant improvement of the tanomax at 60 ° C. for the composition F3, that is to say for a composition based on the modified polyisoprene silane E5, with respect to the tanomax at 60 ° C. for the composition F2 based on a modified polyisoprene (C2) of molar mass comparable to E5. Similarly, the results show a significant improvement of the M300 / M 100 after silane functionalization (based on E5, composition F3) compared with the composition F2 based on a modified polyisoprene (C2) and with the composition F1 based on copolymer A.

Claims

1. Process for the depolymerization of a block copolymer comprising a polyisoprene block and at least one polybutadiene block for the preparation of a modified polyisoprene comprising in majority the species functionalized on the at least one polybutadiene block by one or more functional groups said method comprising the steps of:

i) a step of preparing a solution of the block copolymer comprising the block copolymer and one or more organic solvents, and

2. Process according to claim 1, characterized in that the block copolymer is chosen from a butadiene-isoprene diblock copolymer and a butadiene-isoprene-butadiene triblock copolymer.

3. Method according to claim 1 or 2, characterized in that the polyisoprene blo c of the blo cs copolymer comprises a level of isoprene units 1, 4-cis greater than 90%, preferably greater than 95%.

4. Process according to any one of the preceding claims, characterized in that the polyisoprene block of the block copolymer has a number average molecular weight ranging from 100 to 600 kg / m.sup.-1, preferably ranging from 200 to 500 kg / m.sup.2. mo l.

5. Process according to any one of the preceding claims, characterized in that the polybutadiene block (s) of the block copolymer each have a number average molecular weight ranging from 0.5 to 10 kg / mol.

6. Process according to any one of the preceding claims, characterized in that the solution of block copolymer has a molar concentration in isoprene unit varying from 0.05 to 1 mol / l, preferably ranging from 0 to 1 mol / l. 15 to 1 mo / L.

7. 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.

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,

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

9. Process according to any one of the preceding claims, characterized in that the transfer agent or agents represent from 0.01 to 50% by weight, preferably from 0.02 to 25% by weight. moles, and in particular from 0.02 to 10 mol% relative to the number of moles of isoprene units in the block copolymer.

10. Process according to any one of the preceding claims, characterized in that the metathesis reaction catalyst (s) are chosen from the Grubbs I catalyst, the Hoveyda-Grubbs I catalyst, the dichloro- (3-methyl) 2-butylidene) bis (tricyclohexylphosphine) ruthenium, dichloro- (3-methyl-2-butylidene) bis (tricyclopentylphosphine) ruthenium, {[2- (i-propoxy) -5- (N, N-dimethylaminosulfonyl) phenyl] methylene} (tricyclohexylphosphine) henium dichloride, 3-phenyl-1H-inden-1-ylidene [bis (i-butylphoban)] ruthenium dichloride, bis (tricyclohexylphosphine) [(phenylthio) methylene] ruthenium

dichloride and bis (tricyclohexylphosphine) -3-phenyl-1H-inden-1-ylidenenethanenium dichloride.

11. Process according to any one of the preceding claims, characterized in that the metathesis reaction catalyst or catalysts represent from 0.0001 to 1 mol%, preferably from 0.0001 to 0.1 mol%, and in particular from 0.002 to 0.1 mol% relative to the number of moles of isoprene units in the block copolymer.

12. Method according to any one of the preceding claims, characterized in that it further comprises a step of adjusting the temperature of the stirred block copolymer solution, 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.

13. Process according to claim 12, characterized in that, once the temperature of the block copolymer solution has been reached, the block copolymer solution is stirred for a time varying from 5 minutes to 24 hours, preferably varying from 5 to 24 hours. mn to 20 hours.

14. Method according to any one of the preceding claims, characterized in that it comprises a step of adding one or more stoppering agents to the copolymer solution. blocks, said step being carried out after steps ii) to iii), after the possible step of adjusting the temperature as defined in claim 12 and after the optional stirring step as defined in claim 13.

15. Modified polyisoprene obtainable by the process as defined in any one of claims 1 to 14.

16. Modified polyisoprene comprising predominantly the following species of general formula I or most of the following species of general formula II:

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

m, p and m ', independently of one another, being integers ranging from 1 to 84,

a and a ', independently of one another, being integers ranging from 0 to 20.

Polyisoprene according to claim 15 or 16, characterized in that the number average molecular weight of the polyisoprene block ranges from 100 to 600 kg / m 2, preferably from 200 to 500 kg / m 2.

8. An elastomeric composition based on one or more modified polyisoprenes as defined in any one of claims 15 to 17.

19. 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 18.

20. A tire characterized in that it comprises a semi-finished article as defined in claim 19.