WO2010057611A1

WO2010057611A1 - Novel copolymer with thermoplastic elastomer block, method for preparing same and use thereof in an elastomer composition

Info

Publication number: WO2010057611A1
Application number: PCT/EP2009/008154
Authority: WO
Inventors: Pierre Lesage; Emmanuel Custodero; Julien Thuilliez; Marc Greiveldinger
Original assignee: Societe De Technologie Michelin; Michelin Recherche Et Technique S.A.
Priority date: 2008-11-19
Filing date: 2009-11-17
Publication date: 2010-05-27
Also published as: JP2012509370A; EA017979B1; FR2938543A1; FR2938543B1; EA201170708A1; BRPI0921540A2; EP2358776B1; EP2358776A1

Abstract

The invention relates to a novel thermoplastic elastomer of block copolymer type that includes a linear or branched elastomer block made of a polyisobutylene block (including unsaturations) and at least one thermoplastic styrene end block. The novel elastomer can advantageously be used in elastomer composition for pneumatic objects, in particular for inner tight gums for automobile tyres due to improved hysteretic properties.

Description

NOVEL THERMOPLASTIC ELASTOMERIC BLOCK COPOLYMER, PROCESS FOR PREPARING THE SAME, USE THEREOF IN ELASTOMERIC COMPOSITION

The invention relates to a novel thermoplastic block copolymer elastomer comprising an elastomeric block, linear, plugged or star composed of a polyisobutylene and at least one thermoplastic styrene end block. This thermoplastic elastomer can be advantageously used in elastomeric compositions intended for "pneumatic" objects, that is to say, by definition, objects which take their usable form when they are inflated with air or an inflation gas. equivalent, because of its gastightness properties, more particularly to pneumatic objects for motor vehicles.

[0002] Thermoplastic elastomers (abbreviated as "TPE") are compounds exhibiting both the baked properties of elastomers and the specific properties of thermoplastic compounds, in particular a facilitated implementation in the molten state.

Of intermediate structure between thermoplastic polymers and elastomers, they consist of rigid thermoplastic blocks, for example polystyrene, connected by flexible elastomeric blocks, for example polybutadiene, polyisoprene, poly (ethylene / butylene) or polyisobutylene. Typically, each of these segments or blocks contains at least more than 5, usually more than 10 base units.

Abundant literature describes this type of compounds which have the advantage, compared to simple mixtures of elastomeric compounds and thermoplastic compounds, a good structural cohesion of the material.

Among the thermoplastic elastomeric block copolymers, mention may be made of styrenic thermoplastic elastomers (abbreviated to "TPS"). They comprise a central elastomeric block and terminal styrenic blocks. It has been developed TPS whose central elastomeric block is a polyisobutylene. These thermoplastic elastomers are known by the abbreviation SIBS (styrene-isobutylene-styrene).

[0006] Various architectures of these SIBS block copolymers, controlled by their synthesis method, have been described in the prior art.

There may be mentioned, for example, US Pat. No. 4,946,899, which illustrates triblock linear SIBS and three-pointed star SIBS in which the polyisobutylene block is a three-pointed star. No. 5,428,111, which describes a process for preparing such SIBS by polymerization of styrenic monomer by initiation using live polyisobutylenes, or US Pat. No. 5,260,383 which describes the synthesis of SIBS by reaction of a living styrenic polymer with a telechelic polyisobutylene. .

[0008] Subsequently, other SIBS having various architectures have been described, such as in particular multi-branched SIBS stars and hyperbranched SIBS for example in the publications J.E. Puskas, CJ. Wilds, J. Polym. Sc /. : Part A: Polym. Chem. 36, 85 (1998); J. E. Puskas, W. Pattern, P. M. Wetmore, V. Krukonis, Rubber Chem. Technol. 72, 559 (1998); S. Jacob, J.P. Kennedy, Advances in Polym. Sci. 146, 1 (1999); J. E. Puskas, Y. Kwon, P. Antony, A. K. Bhowmick, J. Polym. ScI: Part A: Polym. Chem. 43, 1811 (2005), or in US Pat. No. 5,721,331. Many documents describe some SIBS, in various applications related to the specific properties of these elastomers, first for biomedical applications and then in various applications specific to TPE elastomers, as varied as medical equipment, parts for automobile or for household appliances, sleeves for electrical wires, sealing pieces or elastics (see for example EP 1 431 343, EP 1 561 783, EP 1 566 405, WO 2005/103146).

Furthermore, in a conventional pneumatic tire of the "tubeless" type (that is to say without a tube), the radially inner face comprises an airtight layer (or more generally any inflation gas of said tire) which allows the swelling and pressurization of the tire. Its sealing properties enable it to guarantee a relatively low rate of pressure loss, making it possible to maintain the swollen bandage in normal operating condition for a sufficient duration, normally of several weeks or several months. It also serves to protect the carcass reinforcement from the diffusion of air from the interior space to the bandage.

This function of inner layer or "inner liner" ("inner liner") waterproof is now filled with compositions based on butyl rubber (copolymer of isobutylene and isoprene), re known for a long time to their excellent sealing properties.

However, a well-known disadvantage of compositions based on rubber or butyl elastomer is that they have significant hysteretic losses, moreover over a wide temperature spectrum, a disadvantage that penalizes the rolling resistance of pneumatic tires.

The object of the present invention is to provide new materials, particularly used in rubber compositions in airtight inner layer of the tire by improving the hysteretic properties of said compositions.

The Applicants have discovered, during their research, a new thermoplastic elastomer SIBS type. This new SIBS, when used in composition optionally extended with an extension oil, induces said composition surprising and unexpected dynamic properties, which make this composition particularly suitable for the manufacture of internal sealing layers, especially for tires of motor vehicles. Advantageously, these new SIBS make it possible to obtain internal layers sealant having improved hysteresis properties while providing these said inner layers with very good sealing properties.

Thus, according to a first object, the present invention relates to a novel thermoplastic elastomer SIBS of specific structure. According to a second object, the invention relates to a process for the preparation of this new thermoplastic elastomer SIBS of specific structure.

Another object of the invention is an elastomer composition comprising this new thermoplastic elastomer SIBS specific structure majority. In the present description, unless otherwise expressly indicated, all the percentages (%) indicated are% by weight.

In the description of the invention which follows the terms "SIBS elastomer", "thermoplastic elastomeric block copolymer" and "block copolymer" are equivalent and may be used interchangeably. On the other hand, any range of values designated by the expression "between a and b" represents the range 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" signifies the range of values from a to b (that is to say, including the strict limits a and b). The invention therefore relates to a novel thermoplastic styrene elastomer in the form of a block copolymer comprising at least one elastomeric block "polyisobutylene" predominantly composed of polymerized isobutene monomer and at least at one end of the copolymer in block form, a styrenic block consisting of at least one polymerized styrenic compound. This thermoplastic block elastomeric copolymer has the following structural characteristics: I) the polyisobutylene block has a number-average molecular weight ("Mn") ranging from 25,000 g / mol to 350,000 g / mol and a glass transition temperature ("tg") less than or equal to -20 ^° C., and comprises a level of units derived from one or more conjugated dienes inserted in the polymer chain ranging from 0.5% to 6% by weight relative to the weight of the polyisobutylene block,

2) the styrenic block or blocks represent at most 16% by weight of the total weight of the block copolymer.

Thus, the novel thermoplastic styrene elastomer in the form of a block copolymer comprises at least two blocks.

According to a variant of the invention, the thermoplastic elastomeric block copolymer is in a linear triblock form. The block copolymer is then composed of a central polyisobutylene block and of two terminal styrenic blocks at each of the two ends of the polyisobutylene block.

According to another variant of the invention, the thermoplastic elastomeric block copolymer is in a star-shaped form with at least three branches. The block copolymer then consists of a polyisobutylene star block with at least three branches and a styrenic block at the end of each of the branches of the polyisobutylene. The number of branches of the polyisobutylene ranges from 3 to 12, and preferably from 3 to 6.

According to another variant of the invention, the thermoplastic elastomeric block copolymer is in a connected form or dendrimer. The block copolymer then consists of a branched central polyisobutylene block or dendrimer and a styrenic block at the end of the branches of the polyisobutylene dendrimer.

According to the invention, it is preferred that the glass transition temperature (Tg, measured according to ASTM D3418) of the thermoplastic elastomeric block copolymer is less than -20 ^° C., more preferably less than -40 ^° C. - S -

A value of Tg higher than these minima can reduce the performance of the waterproof layer during use at very low temperatures; for such use, the Tg of the block copolymer is more preferably still lower than -50 ^° C. The number-average molecular weight (denoted Mn) of the block copolymer is preferably between 30,000 and 500,000 g / mol, more preferably between 40,000 and 400,000 g / mol. Below the minima indicated, the cohesion between the SIBS elastomer chains, especially due to its possible dilution (in the presence of an extension oil), may be affected; on the other hand, an increase in the temperature of use may affect the mechanical properties, including the properties at break, resulting in reduced performance "hot". Moreover, a mass Mn that is too high can be detrimental to the flexibility of the gas-tight layer. Thus, it has been found that a value in the range of 50,000 to 300,000 g / mol is particularly well suited, particularly to use of the block copolymer in a tire composition.

The value of the polydispersity index Ip (booster: Ip = Mw / Mn with Mw weight average molecular weight) of the block copolymer is preferably less than 3; more preferably less than 2 and even more preferably less than 1.5.

According to the invention, the polyisobutylene block copolymer block has a number-average molecular weight ("Mn") ranging from 25,000 g / mol to 350,000 g / mol, preferably 35,000 g / mol to 250,000 g / mol. g / mol so as to give the TPE good elastomeric properties and sufficient mechanical strength and compatible with the internal rubber application of a tire.

According to the invention, the polyisobutylene block of the block copolymer furthermore has a glass transition temperature ("tg") less than or equal to -20 ^° C., more preferably less than -40 ^° C. A value of Tg higher than these minima can reduce the performance of the waterproof layer when used at very low temperatures; for such use, the Tg of the block copolymer is more preferably still less than -50 ^° C.

According to the invention, the polyisobutylene block of the block copolymer also comprises a level of units derived from one or more conjugated dienes inserted in the polymer chain ranging from 0.5% to 6% by weight relative to weight of the polyisobutylene block. Below 0.5%, degradation of the adhesion property of the composition containing the block copolymer of the invention is observed on the adjacent rubber compositions in the tire. Above 6%, a decrease in the resistance to thermooxidation and oxidation to ozone of the composition containing the block copolymer of the invention used in a tire is observed. This level is preferably in the range from 1.5% to 5% by weight and more preferably from 2% to 4% by weight. [00032] The conjugated dienes which can be copolymerized with isobutylene to form the "polyisobutylene" block are conjugated dienes, C ₄ - ₄ Ci. Preferably, these conjugated dienes are chosen from isoprene, butadiene, 1-methylbutadiene, 2-methylbutadiene, 2,3-dimethyl-1,3-butadiene, 2,4-dimethyl-1,3- butadiene, 1,3-pentadiene, 2-methyl-1,3-pentadiene, 3-methyl-1,3-pentadiene, 4-methyl-1,3-pentadiene, 2,3-dimethyl-1 , 3-Pentadiene, 2,5-dimethyl-1,3-pentadiene, 1,3-hexadiene, 2-methyl-1,3-hexadiene, 3-methyl-1,3-hexadiene, 4- methyl-1,3-hexadiene, 5-methyl-1,3-hexadiene, 2,5-dimethyl-1,3-hexadiene, 2-neopentylbutadiene, 1,3-cyclopentadiene, 1,3-cyclohexadiene 1-vinyl-1,3-cyclohexadiene or a mixture thereof. More preferably, the conjugated diene is isoprene or a mixture containing isoprene.

The polyisobutylene block, according to an advantageous aspect of the invention, may be halogenated and has halogen atoms in its chain. This halogenation makes it possible to increase the cooking speed of the composition comprising the block copolymer according to the invention. This halogenation makes it possible to improve the compatibility of the TPE with the other constituent elements of the TPE-based composition used in the internal rubber application of a tire. Halogenation is by means of bromine or chlorine, preferably bromine, on the units derived from conjugated dienes of the polyisobutylene block polymer chain. Only a part of these units reacts with halogen. This portion of units derived from reactive conjugated dienes must nevertheless be such that the proportion of units derived from unreacted conjugated dienes with halogen is at least 0.5% by weight relative to the weight of the block polyisobutylene. According to a variant of the invention stated above, the polyisobutylene block of the block copolymer may be star at least three branches. Preferably the number of branches is in a range from 3 to 6.

According to the invention, the terminal styrenic block or blocks represent at most 16% by weight of the total weight of the block copolymer, preferably less than 15% by weight. Beyond this value of 16% by weight, insufficient heat cohesion is observed in the composition comprising the block copolymer according to the invention. This results in particular by an increase in the module making it impossible plastic deformation of this material during the conformation of the tire.

The styrenic block (s) must be present in proportions sufficient to preserve the thermoplastic nature of the SIBS elastomer. The minimum level of styrenic blocks of the block copolymer may vary depending on the conditions of use of the copolymer. By way of example, a minimum level of 5% by weight of the total weight of the block copolymer can be envisaged for pneumatic application. The styrenic blocks consist of one or more polymerized styrenic compounds. By styrenic compound is to be understood in the present description any monomer based on styrene, unsubstituted as substituted; examples of substituted styrenes are methylstyrenes (for example for example, o-methylstyrene, m-methylstyrene or p-methylstyrene, alpha-methylstyrene, alpha-2-dimethylstyrene, alpha-4-dimethylstyrene or diphenylethylene,) butylstyrenes (e.g. para-tert-butylstyrene), chlorostyrenes (e.g. o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, 2,4-dichlorostyrene, 2,6-dichlorostyrene or 2,4,6-trichlorostyrene ), bromostyrenes (eg o-bromostyrene, m-bromostyrene, p-bromostyrene, 2,4-dibromostyrene, 2,6-dibromostyrene or 2,4,6-tribromostyrene), fluorostyrenes ( for example, o-fluorostyrene, m-fluorostyrene, p-fluorostyrene, 2,4-difluorostyrene, 2,6-difluorostyrene or 2,4,6-trifluorostyrene) or para-hydroxy-styrene. Preferably, the styrenic compound according to the invention is styrene, alpha-methylstyrene, diphenylethylene, p-methylstyrene, p-tert-butylstyrene, p-chlorostyrene or p-fluorostyrene.

The copolymers according to the invention may be prepared by synthesis methods known per se and described in the literature, in particular that cited in the presentation of the state of the art of the present description. Those skilled in the art will be able to choose the appropriate polymerization conditions and regulate the various parameters of the polymerization processes in order to achieve the specific structural characteristics of the block copolymer of the invention. Several synthetic strategies can be implemented to prepare the copolymers according to the invention.

A first consists of a first step of synthesis of the "polyisobutylene" block by living cationic polymerization of the monomers to be polymerized by means of a di-functional or polyfunctional initiator known to those skilled in the art, followed by the second step of synthesis of the styrenic blocks by adding the styrenic monomers to be polymerized on the "living polyisobutylene" obtained in the first step. Thus, these two steps are consecutive, which results in the addition sequence: monomers to be polymerized for the preparation of the "polyisobutylene" block comprising a level of units derived from one or more conjugated dienes ranging from 0.5 to 6% by weight of the total weight of the isobutylene block;

monomers to be polymerized for the preparation of styrenic blocks.

At each step, the monomer (s) to be polymerized may or may not be added in the form of a solution in a solvent as described below, in the presence or absence of an acid or a Lewis base as described below.

Each of these steps can be carried out in the same reactor or in two different polymerization reactors. Preferably, these two steps are performed in a single reactor (synthesis "one-pot").

The living cationic polymerization is conventionally carried out by means of an initiator and optionally a Lewis acid acting as a co-initiator to form a carbocation in situ. Usually electro-donating compounds are added in order to give the polymerization a living character. By way of illustration, the di-functional or polyfunctional initiators that can be used for the preparation of the copolymers according to the invention can be chosen from 1,4-di (2-methoxy-2-propyl) -benzene ( or "dicumylmethy 1 ether"), 1,3,5-tri (2-methoxy-2-propyl) -benzene (or "tricumylmethylether"), 1,4-di (2-chloro-2-propyl) - benzene (or "dicumyl chloride"), 1,3,5-tri (2-chloro-2-propyl) benzene (or "tricumyl chloride), 1,4-di (2-hydroxy-2-propyl) benzene, 1,3,5-tri (2-hydroxy-2-propyl) -benzene, 1,4-di (2-acetoxy-2-propyl) -benzene, 1,3,5-tri ( 2-acetoxy-2-propyl) -benzene, 2,6-dichloro-2,4,4,6-tetramethylheptane, 2,6-dihydroxy-2,4,4,6-heptane. Preferably, dicumyl ethers, tricumyl ethers, dicumyl halides or tricumyl halides are used. The Lewis acids may be chosen from metal halides of the general formula MXn where M is an element chosen from Ti, Zr, Al, Sn, P and B; X is a halogen such as Cl, Br, F or I and n corresponding to the degree of oxidation of the element M. For example, TiCl 4, AlCl 3, BCl 3, BF 3, SnCl 4, PCl 3, PCl 5, Among these compounds TiC14, A1C13 and BCB are used preferentially, and TiC14 even more preferentially.

The electro-donor compounds may be selected from known Lewis bases, such as pyridines, amines, amides, esters, sulfoxides and others. Among them are preferred DMSO (dimethylsulfoxide) and DMAc (dimethylacetamide).

The living cationic polymerization is carried out in an apolar inert solvent or in a mixture of nonpolar and polar inert solvents.

The apolar solvents which can be used for the synthesis of the copolymers according to the invention are, for example, hydrocarbon, aliphatic, cycloaliphatic or aromatic solvents, such as hexane, heptane, cyclohexane, methylcyclohexane, benzene or toluene.

The polar solvents which can be used for the synthesis of the copolymers according to the invention are, for example, halogenated solvents such as alkane halides, such as methyl chloride (or chloroform), ethyl chloride, chlorine and the like. butyl, methylene chloride (or dichloromethane) or chlorobenzenes (mono-, di- or tri-chloro).

Those skilled in the art will be able to choose the composition of the monomer mixtures to be used in order to prepare the copolymers according to the invention as well as the appropriate temperature conditions in order to achieve the molar mass characteristics of these copolymers.

A second synthesis strategy consists of preparing separately:

a telechelic or functional "polyisobutylene" block at its chain ends by living cationic polymerization by means of a difunctional or polyfunctional initiator, optionally followed by functionalization reaction on the chain ends,

the living styrenic blocks, for example by anionic polymerization, and then reacting one and the other to obtain a copolymer according to the invention. The nature of the reactive functions at each of the chain ends of the block and the proportion of living styrenic blocks relative to the block will be chosen by those skilled in the art to obtain a copolymer according to the invention.

The halogenation of the copolymer according to the invention is carried out according to any method known to those skilled in the art, especially those used for the halogenation of butyl rubber and can be done for example by means of bromine or chlorine. , preferably bromine, on the units derived from conjugated dienes of the polymeric chain of the polyisobutylene block.

In certain variants of the invention according to which the SIBS elastomer is star or connected, the methods described for example in the articles of Puskas J. Polym. Sci Part A: Polymer Chemistry, Vol 36, pp85-82 (1998) and Puskas, J. Polym. Sci Part A: Polymer Chemistry, vol 43, ppl 811-1826 (2005) can be implemented by analogy to obtain central blocks "polyisobutylene" star, branched or living dendrimers. Those skilled in the art will then be able to choose the composition of the monomer mixtures to be used in order to prepare the copolymers according to the invention as well as the appropriate temperature conditions in order to achieve the molar mass characteristics of these copolymers.

Preferably, the preparation of the copolymers according to the invention will be carried out by living cationic polymerization by means of a difunctional or polyfunctional initiator and by adding sequences of the monomers to be polymerized for the synthesis of the "polyisobutene" block and of the monomers polymerization for the synthesis of styrenic blocks.

Another object of the invention is an elastomer composition which comprises at least, as majority elastomer (by weight), a thermoplastic elastomer block copolymer SIBS as described above. The SIBS elastomer may alone constitute the elastomeric composition or be associated in this composition with other constituents to form an elastomeric matrix.

[00055] If any other elastomers are used in this composition, the SIBS elastomer according to the invention constitutes the majority elastomer by weight; it then preferably represents more than 50%, more preferably more than 70% by weight of all the elastomers. Such complementary elastomers, preferably minor ones, could be, for example, diene elastomers such as natural rubber or synthetic polyisoprene, butyl rubber or thermoplastic styrene elastomers (TPS) other than SIBS, within the limit of the compatibility of their microstructures. .

The SIBS elastomer previously described is sufficient on its own for the gas-tight function to be performed with respect to the pneumatic objects in which it can be used. However, according to a preferred embodiment of the invention, the latter is used in a composition which also comprises, as plasticizer, an extender oil (or plasticizing oil) whose function is to facilitate the implementation, particularly the integration into the pneumatic object by a lowering of the module and an increase in the tackifying power of the gas-tight layer.

Any extension oil, preferably of a slightly polar nature, capable of extending and plasticizing elastomers, in particular thermoplastics, may be used. At room temperature (23 ° C), these oils, more or less viscous, are liquids (that is to say, as a reminder, substances having the ability to eventually take the shape of their container), as opposed in particular to resins or rubbers which are inherently solid.

Preferably, the extender oil is chosen from the group consisting of polyolefinic oils (that is to say derived from the polymerization of olefins, monoolefins or diolefins), paraffinic oils, naphthenic oils (low or high viscosity), aromatic oils, mineral oils, and mixtures thereof.

It should be noted that the addition of an extension oil to the SIBS causes a leakage of the latter, variable depending on the type and amount of oil used. A polybutene-type oil is preferably used, in particular a polyisobutylene oil (abbreviated as "PIB"), which has demonstrated the best compromise of properties compared to the other oils tested, in particular to a conventional oil of the paraffinic type. [00061] By way of example, polyisobutylene oils are sold in particular by the company UNIVAR under the name "Dynapak PoIy" (eg "Dynapak PoIy 190"), by INEOS Oligomer under the name "INDOPOL H1200", by BASF under the name "Glissopal" (eg "Glissopal 1000") or "Oppanol" (eg "Oppanol B 12"); paraffinic oils are marketed for example by EXXON under the name "Telura 618" or by Repsol under the name "Extensol 51".

The number-average molecular mass (Mn) of the extender oil is preferably between 200 and 25,000 g / mol, more preferably still between 300 and 10,000 g / mol. For masses Mn too low, there is a risk of migration of the oil outside the composition, while too large masses can cause excessive stiffening of this composition. A mass Mn of between 350 and 4000 g / mol, in particular between 400 and 3000 g / mol, has proved to be an excellent compromise for the intended applications, in particular for use in a tire.

Those skilled in the art will be able to adjust the amount of extension oil depending on the particular conditions of use of the composition, especially as a gas-tight elastomeric layer of a pneumatic object. It is preferred that the extender oil content is greater than 5 phr, preferably between 5 and 100 phr (parts by weight per hundred parts of total elastomer, that is to say SIBS plus all any other elastomer present in the composition or elastomeric layer).

Below the minimum indicated, the elastomeric composition may have too much rigidity for certain applications while beyond the maximum recommended, there is a risk of insufficient cohesion of the composition and loss of sealing that can be harmful depending on the application.

For these reasons, in particular for use of the sealed composition in a tire, it is preferred that the extender oil content be greater than 10 phr, in particular between 10 and 90 phr, more preferably still than it is greater than 20 phr, in particular between 20 and 80 phr.

The composition described above may further comprise the various additives usually present in airtight layers known to those skilled in the art. For example, reinforcing fillers, such as carbon black or silica, non-reinforcing or inert fillers, coloring agents that can be advantageously used for coloring the composition, and lamellar fillers that further improve sealing (eg phyllosilicates such as as kaolin, talc, mica, graphite, clays or clays modified ("organo clays"), plasticizers other than the above-mentioned extension oils, protective agents such as antioxidants or antiozonants, anti-UV, various agents of implementation or other stabilizers, or promoters adapted to promote adhesion to the rest of the structure of the pneumatic object.

Compared to butyl rubbers, the new SIBS according to the invention has the advantage, because of its thermoplastic nature, to be worked as is in the molten state (liquid), and therefore to offer a possibility of simplified implementation of any elastomeric composition containing it.

Moreover, this new SIBS induces, to the composition which contains it, a high adhesion capacity on the rubber components which are adjacent to it in a pneumatic object, in particular a pneumatic tire of a motor vehicle,

In addition, this new SIBS, despite its thermoplastic nature, gives a composition which contains a good cohesion of the hot material, especially at temperatures ranging from 150 to 200 ^° C. These temperatures correspond to the cooking temperatures of motor vehicle tires. This cohesion at high temperature allows hot release of these tires without altering the integrity of the waterproof inner gum containing the new SIBS.

[00071] Thus, the novel thermoplastic elastomer SIBS according to the invention makes it possible, surprisingly, to satisfy a compromise of properties, often antinomic, of cohesion of the elastomer composition which contains it, especially when hot, and of adhesion. of it on rubber compositions adjacent thereto in a pneumatic object. In addition, the novel thermoplastic elastomer imparts to the composition containing it improved hysteretic properties in comparison with a butyl rubber composition.

These properties are achieved while imparting sealing properties and processability to the elastomeric composition containing the new SIBS.

Claims

Thermoplastic elastomeric block copolymer comprising at least one elastomeric block composed of polyisobutylene and, at least at one end of the block copolymer, a styrenic block consisting of at least one polymerized styrenic compound, characterized in that

1) the polyisobutylene block has a number-average molecular weight ranging from 25,000 g / mol to 250,000 g / mol and a glass transition temperature of less than or equal to -2O ⁰ C, and comprises a proportion of units resulting from a or more conjugated dienes inserted in the polymer chain ranging from 0.5% to 6% by weight relative to the weight of the polyisobutylene block, and in that

2) the styrenic blocks represent at most 16% by weight of the total weight of the block copolymer.

2 - block copolymer according to claim 1, characterized in that the copolymer has a triblock linear structure.

3 - block copolymer according to claim 1, characterized in that the copolymer has a star structure at least 3 branches and at most 12 branches in which the central polyisobutylene block is star at least 3 and at most 12 branches, each being terminated by a styrenic block.

4 - block copolymer according to claim 1, characterized in that the copolymer has a dendrimer structure in which the central polyisobutylene block is dendrimer, each branch of the polyisobutylene dendrimer being terminated with a styrenic block. 5 - block copolymer according to any one of claims 1 to 4, characterized in that the polyisobutylene block comprises a unit rate from one or more conjugated dienes inserted into the polymer chain ranging from 1.5% to 5% by weight relative to the weight of the polyisobutylene block,

6 - Block copolymer according to any one of claims 1 to 5, characterized in that the polyisobutylene block has a glass transition temperature of less than or equal to -50 ^° C.

7 - block copolymer according to any one of claims 1 to 6, characterized in that the conjugated dienes or dienes are chosen from isoprene, butadiene, 1-methylbutadiene, 2-methylbutadiene, 2,3- dimethyl-1,3-butadiene, 2,4-dimethyl-1,3-butadiene, 1,3-pentadiene, 2-methyl-1,3-pentadiene, 3-methyl-1,3- pentadiene, 4-methyl-1,3-pentadiene, 2,3-dimethyl-1,3-pentadiene, 2,5-dimethyl-1,3-pentadiene, 1,3-hexadiene, 2-methyl 1,3-hexadiene, 3-methyl-1,3-hexadiene, 4-methyl-1,3-hexadiene, 5-methyl-1,3-hexadiene, 2,5-dimethyl-1,3 hexadiene, 2-neopentylbutadiene, 1,3-cyclopentadiene, 1,3-cyclohexadiene, 1-vinyl-1,3-cyclohexadiene or a mixture thereof.

8 - Block copolymer according to any one of claims 1 to 7, characterized in that the polyisobutylene block is halogenated.

9 - Block copolymer according to any one of claims 1 to 8, characterized in that the styrenic blocks represent less than 15% by weight of the total weight of the block copolymer. 10 - block copolymer according to any one of claims 1 to 9, characterized in that the styrenic compound is selected from styrene, methylstyrenes, butylstyrenes, chlorostyrenes and bromostyrenes.

11 - block copolymer according to claim 10, characterized in that the styrenic compound is styrene, alpha-methylstyrene, diphenylethylene, p-methylstyrene, p-tert-butylstyrene, p-chlorostyrene or p-fluorostyrene.

12 - block copolymer according to claim 11, characterized in that the styrenic compound is styrene.

13 - Process for the preparation of a block copolymer as defined in claims 1 to 12, characterized in that it comprises

(a) a first step of synthesis of the "polyisobutylene" block comprising a level of units derived from one or more conjugated dienes ranging from 0.5 to 6% by weight of the total weight of the isobutylene block, during which reacting a mixture of monomers comprising isobutylene and one or more conjugated diene monomers with a difunctional or polyfunctional initiator in an apolar inert solvent or in a mixture of polar and nonpolar inert solvents to obtain a "polyisobutylene" alive, and

(b) a second step of synthesis of the styrenic blocks by adding the styrenic monomers in the reaction medium obtained in the first step.

14 - A method for preparing a block copolymer according to claim 13, characterized in that is added to the reaction medium of the first step a Lewis acid selected from metal halides of the general formula MXn where M is an element selected from Ti, Zr, Al, Sn, P, B, X is a halogen such as Cl, Br, F or I and n is the oxidation state of the element M.

15 - Process for preparing a block copolymer according to claim 13 or 14, characterized in that is added to the reaction medium of the first step a Lewis base.

16 - elastomer composition, characterized in that said composition comprises at least, as majority elastomer, a thermoplastic elastomeric block copolymer as defined in claims 1 to 12.

17 - Coposition according to claim 16, characterized in that the number-average molecular weight (Mn) of the block copolymer is between 30 000 and 500 000 g / mol.

18 - Composition according to claim 16 or 17, characterized in that it comprises an elastomer extension oil.

19 - Composition according to claim 18, characterized in that the extender oil is chosen from the group consisting of polyolefin oils, paraffinic oils, naphthenic oils, aromatic oils, mineral oils, and mixtures thereof. oils.

20 - Composition according to any one of claims 16 to 19, characterized in that it comprises a lamellar filler.