EP1358226A1

EP1358226A1 - Hydrogenation method for unsaturated block copolymers and hydrogenated unsaturated block copolymers

Info

Publication number: EP1358226A1
Application number: EP01271401A
Authority: EP
Inventors: Béatrice Boussand; Philippe Bonnet; François COURT; Michel Devic; Manuel Hidalgo; Christophe Navarro
Original assignee: Atofina SA
Current assignee: Arkema France SA
Priority date: 2000-12-21
Filing date: 2001-11-23
Publication date: 2003-11-05
Also published as: CA2436875A1; WO2002050136A1; AU2002222030A1; CN1491236A; CN1229397C; US7202308B2; FR2818650A1; FR2818650B1; US20040116615A1

Abstract

The invention concerns a selective hydrogenation method for olefinic double bonds of block copolymers whereof at least one block contains olefinic double bonds using a catalyst based on a group VIII metal in a medium comprising an organic solvent for the copolymer and an ionic liquid as solvent of the catalyst, which consists in: using a water-immiscible ionic liquid, preferably an ionic liquid whereof the anion is the hexafluorophosphate anion and the cation is the 1-butyl-3-methyl-imidazolium (bmim<+>) or 1 ethyl-3-methyl-imidazolium (emim<+>). Said method, when used for poly(styrene)-b-poly(butadiene)-b-poly(methyl methacrylate) block polymers whereof the poly(butadiene) block has in majority a 1,4 microstructure, enables to obtain copolymers whereof the hydrogenation rate is not less than 50 % and having a melting point higher than 30 DEG C.

Description

PROCESS FOR HYDROGENATION OF UNSATURATED BLOCK COPOLYMERS AND HYDROGEN BLOCK COPOLYMERS

The present invention relates to the field of block copolymers and more particularly relates to a process for the hydrogenation of unsaturated block copolymers, as well as new hydrogenated block copolymers.

Block copolymers AB or ABC having at least one block containing olefinic double bonds (polybutadiene, polyisoprene, ...) can be used alone or in admixture with other polymers such as PVDF, PVC, PVCC,. .. to improve some of their properties. However, the presence of the block containing olefinic double bonds makes them sensitive to light, to certain oxidants and to heat. The selective hydrogenation of this block makes it possible to prepare new materials containing polyolefins while improving their stability (to light, oxidants and heat) and their mechanical properties. This hydrogenation also leads to a modification of the physical properties of the polymer by creating a block containing fewer olefinic double bonds, which can become a semi-crystalline block. In addition, the presence of a polyolefin chain makes them compatible with a wider range of polymers (including polyolefins), which represents a very large potential market. The hydrogenation of these block copolymers can be carried out by non-catalytic methods, generally carried out in the presence of hydrazine derivatives such as, for example, p-toluenesulfonylhydrazine. Although these methods do not require a reactor operating under pressure, their industrial implementation cannot be envisaged because of the high cost of the reagent p-toluenesulfonylhydrazine.

Block copolymers can also be hydrogenated by heterogeneous catalysis. However, the heterogeneous catalysts having a low activity, it is necessary to operate at high temperature and hydrogen pressure and to use significant quantities of catalyst. These operating conditions can lead to degradation or crosslinking of the polymer and to a decrease in the selectivity of the hydrogenation (hydrogenation of functions other than the olefinic double bonds: esters, aromatic double bonds, ...)

The hydrogenation can also be carried out in a homogeneous medium under milder conditions by using noble metal complexes as catalysts (Wilkinson catalyst, etc.), cobalt or nickel salts with reducing agents (triethyl aluminum, butyl lithium, ...). The use of a very small quantity of catalyst can lead to an economical process even if the catalyst is not recovered; however, the latter remains partly in the polymer which can harm its properties and therefore require its purification. On the other hand, when it is necessary to use a large quantity of catalyst, it must be recovered for recycling.

The hydrogenation of block copolymers having a polybutadiene block by homogeneous catalysis in the presence of the Wilkinson catalyst has been the subject of several publications, in particular patent application DE 4 240 445, the thesis of C. Auschra at the University of Mainz (1992) entitled "Synthèse von neuartigen Multiblockcopolymeren und deren Verwendung in Polymerlegierungen", the articles by C. Auschra et al. in Polymer Bulletin 30 (1993) 257-264 and 305-311 and in Macromolecules 26 (1993) 2171-2174, and an article by R.StadIer et al. in Macromolecules 28 (1995) 3080-3097. The copolymers used have a polybutadiene block formed of butadiene having predominantly a microstructure -1, 2 (about 90%) which hydrogenates much more easily than polybutadiene having predominantly a microstructure -1, 4 (85 to 89%). On the other hand, the amount of Wilkinson catalyst used is high (8000 ppm molar per mole of double bond).

In patent application DE 19643889 and in Macromol. Chem. Phys. 199 (1998) 1063-1070 is described the hydrogenation of a polystyrene-polybutadiene-poly (ε-caprolactone) triblock in the presence of Wilkinson's catalyst (10,000 ppm), the polybutadiene block mainly having a microstructure -1, 4 . Selective hydrogenation of the polybutadiene block of an NBR copolymer

(Nitrile Butadiene Rubber) without touching the nitrile groups is described by L Mϋller et al. in Macromol. Rapid Commun. 19 (1998) 409-411. The reaction catalyzed by the RuHCI (CO) (PCy3) ₂ complex is carried out in a two-phase medium (ionic liquid + organic solvent); the ionic liquid is 1-butyl-3-methyl-imidazolium tetrafluoroborate (bmimBF ₄ ) and the NBR is dissolved in toluene. The ionic liquid solution containing the catalyst can be recycled several times.

This process which allows the catalyst to be easily recovered and recycled is also the subject of patent application BR 98 02101, of which Example 2 illustrates the same hydrogenation of an NBR with the same ionic liquid (bmimBF ₄ ), but of which generalities include many other catalysts, other unsaturated copolymers and other ionic liquids such as those in which the cation is a quaternary ammonium or phosphonium group and the anion is derived from a Lewis acid such as, for example , the anions AICU ^" , RSO ₃ ^" , BF ₄ ^" , ZnCU ^2" , ZnBr4 ^{2 "} , PF ₆ ^" , CuCI ₂ ^" , FeCI ₃ ^" , etc .... As indicated above, the hydrogenation of the copolymers containing a butadiene block mainly having a microstructure -1, 4 is difficult. Thus, when the method of Example 2 of document BR 98 02101 is applied to the hydrogenation of such a copolymer (triblock SBM) with the Wilkinson catalyst at a moderate temperature (60 ° C), a hydrogenation rate of about 30% is obtained.

It has now been found that this rate is considerably improved by using an ionic liquid immiscible with water, in particular an ionic liquid whose anion is the hexafluorophosphate anion (PF ₆ ^" ). Under the same operating conditions, we go from a hydrogenation rate of 30% to a hydrogenation rate of about 75% using as ionic liquid 1 -butyl-3-methyl-imidazolium hexafluorophosphate (bmimPFβ).

This result is surprising because, in their article relating to the hydrogenation of cyclohexene in a biphasic medium with rhodium catalysts dissolved in ionic liquids of the bmim type [Polyhedron 15, n ° 7 (1996) 1217-1219], P.A.Z.

Suarez et al. did not observe any substantial difference according to the nature of the anion: AICI ₄ ^" , BF ₄ ^" or PF ₆ ^" (entries 2, 3 and 5 in table 1).

The subject of the invention is therefore a process for the selective hydrogenation of olefinic double bonds of block copolymers of which at least one block contains olefinic double bonds using a catalyst based on a group VIII metal in a medium comprising an organic solvent and an ionic liquid, characterized in that an ionic liquid immiscible with water is used.

By ionic liquid is meant here any non-aqueous salt of ionic nature, melted at room temperature or at least at moderate temperature (<150 ° C). In these ionic liquids which can be represented by the general formula Q ⁺ A ^" , Q ⁺ is a quaternary ammonium, aromatic ammonium, quaternary phosphonium or ternary sulfonium cation.

The anion A ^′ of the ionic liquid according to the invention is preferably the hexafluorophosphate anion. As another nonlimiting example of anions A ^"in accordance with the invention, mention may be made of the anion (CF ₃ Sθ2) ₂ N ^" .

Although we prefer to use ionic liquids whose cation is an imidazolium cation of general formula:

in which X ¹ and X ³ , identical or different, are C ₁ -C ₄ alkyl radicals and X ² is a hydrogen atom or a methyl radical, preferably a cation 1, 3-dialkylimidazolium and more particularly the cations 1 -butyl-3-methyl-imidazolium (bmim ⁺ ) and 1-ethyl-3-methyl-imidazolium (emim ⁺ ), it would not go beyond the scope of the present invention to use an ionic liquid whose cation Q ⁺ corresponds to one of the following general formulas:

R ¹ R ² R ³ R ⁴ N ⁺ R ¹ R ² R ³ R ⁴ P ⁺

R ¹ R ² R ³ S ⁺ in which the symbols R ¹ to R ⁴ , identical or different, each denote a hydrocarbyl, chlorohydrocarbyl, fluorohydrocarbyl, chlorofluorohydrocarbyl or fluorocarbyl group having from 1 to 10 carbon atoms, saturated or not, cyclic or not, or aromatic, one or more of these groups can also contain one or more heteroatoms such as N, P, S or O.

The ammonium, phosphonium or sulfonium Q ⁺ cation can also be part of a saturated or unsaturated or aromatic heterocycle having from 1 to 3 nitrogen, phosphorus or sulfur atoms, this heterocycle can carry groups R ¹ to R ⁴ as defined above.

In the process according to the invention, the catalyst is dissolved in the ionic liquid and the copolymer to be hydrogenated in an organic solvent.

The catalyst used, based on a group VIII metal (in particular rhodium, ruthenium or palladium), is introduced in the form of a complex soluble in the ionic liquid. As nonlimiting examples of such complexes, mention may be made of the Wilkinson catalyst RhCl (PPh ₃ ) ₃ , the Osborn catalyst [Rh (nbd) (PPh ₃ ) 2] ⁺ PF ₆ ^" and the complexes RuCI ₂ (PPh3) 3 and PdCl2 (PPh ₃ ) 2, Ph denoting the phenyl radical and nbd norbornadiene. An excess of ligand (for example triphenylphosphine PPh ₃ in the case of the Wilkinson catalyst) can be added to the reaction mixture to avoid dissociation of the complex .

The organic solvent used to dissolve the copolymer to be hydrogenated is preferably an aromatic solvent such as benzene, toluene, xylene and ethylbenzene. For economic reasons, the concentration of the copolymer in the organic solvent is preferably as high as possible. However, this concentration must be less than or equal to the solubility of the hydrogenated copolymer at the reaction temperature. Depending on the copolymer, this concentration can be between 3 and 60% by mass, preferably between 3 and 30% and more particularly between 3 and 15%.

Between 0.01 and 5 mol% of catalyst can be used per mole of olefinic double bonds to be hydrogenated, and preferably between 0.02 and 2 mol%.

The minimum quantity of ionic liquid to be used depends on the catalyst chosen and on its solubility in the ionic liquid. Thus, it is necessary to introduce at least the volume of ionic liquid making it possible to dissolve the entire catalyst. The ratio between the volumes of ionic liquid and of organic solvent must be between 0.01 and 25, preferably between 0.05 and 5 and more particularly between 0.1 and 1.

The hydrogenation according to the invention can be carried out between 20 and 180 ° C, preferably between 20 and 150 ° C and more particularly between 50 and 125 ° C. The ionic liquid making it possible to stabilize the catalyst, it is possible to work at temperatures higher than those practiced in homogeneous hydrogenation without ionic liquid and thus to accelerate the speed of the reaction. It is preferable to add a polymer stabilizer (0.1 to 5% by mass depending on the stabilizer), the polymer being able to degrade if the temperature is too high.

The reaction can be carried out under a pressure of between 1 and 200 bars relative, preferably between 1 and 100 bars and more particularly between 20 and 60 bars.

In order to obtain good dispersion of the hydrogen in the reaction medium, it is advantageous to operate with efficient stirring, for example using a Rushton self-aspirating turbine for this purpose.

After reaction, the hydrogenated copolymer can be isolated by precipitation by introducing the reaction medium into a large amount of a non-solvent for the hydrogenated copolymer (preferably an alcohol such as methanol, ethanol or isopropanol) or, when there are two distinct phases, by decantation of the organic phase then isolation of the copolymer according to the usual methods (for example evaporation of the solvent or atomization or devolatilization or flocculation or precipitation in a non-solvent).

When the reaction medium does not settle (first case), the precipitation of the hydrogenated copolymer is carried out using a non-solvent (preferably an alcohol) in an amount which can range from 1 to 20 times the volume of the organic solvent and is d 'The less important the higher the hydrogenation rate of the copolymer. Advantageously, an amount of non-solvent ranging from 2 to 10 times the volume of the organic solvent is used, preferably 5 to 10 times. The reaction medium containing the hydrogenated copolymer is brought to a temperature between 20 and 80 ° C, preferably between 25 and 60 ° C, then is poured into the non-solvent with stirring. The temperature of the non-solvent before casting is advantageously between 0 and 60 ° C, preferably 0 to 40 ° C. After casting, stirring can be maintained and the hydrogenated copolymer is then filtered and dried under vacuum. When the polymer is not completely hydrogenated, it is preferable not to heat it during drying so as to eliminate any risk of deterioration of the polymer (crosslinking, etc.). Analysis of the hydrogenated copolymer can be carried out by NMR and its remaining double bonds can be measured by measuring the bromine index. The catalyst can be recycled in two ways, depending on the method of isolation of the hydrogenated copolymer:

1. If the ionic liquid phase has settled, it is recycled directly to the reactor with the catalyst it contains. 2. When the reaction mixture does not settle, the hydrogenated copolymer is isolated by precipitation by introduction of the reaction medium into a non-solvent. The filtrates obtained after isolation of the copolymer are concentrated by evaporation of the non-solvent and part of the organic solvent, this evaporation being preferably carried out between 60 and 100 ° C under reduced pressure. To the concentrated solution which then contains the ionic liquid and the catalytic complex which are not volatile, an amount of organic solvent is added equal to that lost during evaporation and a new charge of copolymer to effect a new hydrogenation.

The process according to the invention can be applied to the hydrogenation of any block copolymer of which at least one block contains olefinic double bonds, but it is of particular interest for the hydrogenation of block copolymers of the SBM type [ poly (styrene) -b-poly (butadiene) -b-poly (methyl methacrylate)] whose poly (butadiene) block mainly has a microstructure -1, 4.

In these SBM copolymers which are usually prepared by anionic polymerization according to known methods as described, for example, in patents EP 524 054 and EP 749 987, the mass percentage of the poly (styrene) block can range from 5 to 80 (preferably from 10 to 60), that of the poly (butadiene) block from 5 to 80 (preferably from 10 to 60) and that of the poly (methyl methacrylate) block from 90 to 15 (preferably from 80 to 30) . Their number-average molar mass is generally at least equal to 20,000 g / mol and, preferably, between 50,000 and 200,000 g / mol. These copolymers may contain synthesis intermediates, in particular poly (styrene) and the poly (styrene) -b-poly (butadiene) diblock.

The application of the process according to the invention to the selective hydrogenation of these SBM copolymers makes it possible to obtain new block copolymers partially or totally hydrogenated, the hydrogenation rate being at least equal to 50%, preferably between 70 and 100% and, more particularly, between 90 and 100%. These new copolymers are crystalline at room temperature; they generally have a melting point above 30 ° C. In the following examples which illustrate the invention without limiting it, three SBM triblock polymers and one SBS triblock defined below are hydrogenated: SBM-1: poly (styrene) -b-poly (butadiene) -b-poly ( methyl methacrylate) of composition (mass%): 34/35/31, the average molar mass of the block poly (styrene) being 27,600 g / mol and 89% of the poly (butadiene) block having a microstructure -1, 4.

SBM-2: poly (styrene) -b-poly (butadiene) -b-poly (methyl methacrylate) triblock of composition (mass%): 39/39/22, the average molar mass of the poly (styrene) block being 36,700 g / mol and 89% of the poly (butadiene) block having a microstructure -1, 4.

SBM-3: poly (styrene) -b-poly (butadiene) -b-poly (methyl methacrylate) triblock of composition (mass%): 21/21/58, the average molar mass of the poly (styrene) block being 15,900 g / mol and 88% of the poly (butadiene) block having a microstructure -1, 4.

SBS: poly (styrene) -b-poly (butadiene) -b-poly (styrene) triblock containing 19 mol% of polystyrene and 81% molar of polybutadiene and 86% of the poly (butadiene) block having a microstructure -1, 4.

EXAMPLE 1

In a glove box under a nitrogen atmosphere, a solution of

1.759 g of triblock polymer SBM-1 in 33.25 g of ethylbenzene and a solution of

15 mg of Wilkinson RhCI catalyst [P (CeH5) 3] 3 and 151.3 mg of triphenylphosphine (TPP) in 15.2 g of 1-butyl-3-methyl-imidazolium hexafluorophosphate (ionic liquid bmimPF ₆ ).

These two solutions are then mixed in the absence of air, then the two-phase mixture is introduced into a stainless steel autoclave, provided with an internal PTFE envelope and stirred by a Rushton turbine (self-aspirating turbine in stainless steel ). After checking for leaks with nitrogen at 50 bars, the reactor is pressurized with 50 bars of hydrogen and the temperature is brought to 60 ° C. for 24 hours with stirring (1000 rpm).

After cooling the reactor, 45 mg was added Irganox ^® B900 (stabilizer) and the resulting reaction mixture (little fluid stable emulsion) is then heated to 40 ° C, then poured into 350 ml of methanol at 40 ° C under stirring. A white precipitate (hydrogenated SBM) and a single clear liquid phase are obtained.

After filtration on Bϋchner and drying in a vacuum oven for 12 hours at 25 ° C, 1.75 g of hydrogenated SBM and 377 g of clear filtrates are obtained. The assay of the remaining double bonds, carried out by measuring the bromine index and by NMR, indicates that the rate of hydrogenation of the polybutadiene block is 76%.

Analysis of the hydrogenated SBM shows a content of 10 ppm of rhodium, ie a loss of 0.16 mg of Wilkinson's catalyst, which corresponds to 1% of the catalyst engaged. DSC analysis of the hydrogenated product shows a melting point of 54 ° C (precision: ± 2 ° C) while the starting product (SBM-1) is not crystalline.

EXAMPLE 2 The filtrates of Example 1 (377 g) are concentrated in a rotary evaporator at 90 ° C, under reduced pressure, to remove the methanol.

In the concentrated solution, placed in the absence of air, 1.750 g of triblock polymer SBM-1 are dissolved, then ethylbenzene is added to make up the volume of the solution to 50 ml. This solution is then loaded into the autoclave and the hydrogenation is carried out under the same conditions as in Example 1.

1.70 g of hydrogenated SBM are thus obtained having a hydrogenation rate of 66% and a rhodium content of 18 ppm.

EXAMPLE 3 (comparative.

The operation is carried out in the same apparatus and according to the same procedure as in Example 1, but without using an ionic liquid.

15 mg of Wilkinson's catalyst and 150 mg of TPP are dissolved in a solution composed of 1.759 g of SBM-1 and 48.5 g of ethylbenzene. The hydrogenation is carried out for 24 hours at 60 ° C., under a pressure of 50 bars of hydrogen.

After precipitation in methanol, 1.58 g of 75% hydrogenated SBM and having a rhodium content of 290 ppm are obtained. This corresponds to a loss of 4.13 mg of Wilkinson catalyst, a loss 29 times greater than that of Example 1 according to the invention.

EXAMPLE 4

The procedure is as in Example 1 except that the stabilizer (45 mg of Irganox ^® B900) is added before the reaction in SBM solution (1, 754 g of SBM-1 and 33.45 g of ethylbenzene), and the hydrogenation reaction is carried out at 120 ° C for 24 hours and under 50 bar of hydrogen.

At the end of the reaction, a gel-forming emulsion is obtained to which 100 ml of ethylbenzene are added and the mixture is heated to 40 ° C. to thin the gel. The emulsion is then poured into 350 ml of methanol at 40 ° C. with stirring, then the white precipitate obtained is filtered and dried as in Example 1.

1.75 g of 97% hydrogenated SBM containing 26 ppm of rhodium are obtained, corresponding to 0.42 mg of Wilkinson catalyst. EXAMPLE 5

The filtrates of Example 4 are concentrated in a rotary evaporator at 90 ° C under reduced pressure, to remove the methanol.

1.754 g of SBM-1 polymer is dissolved in the concentrated solution, sheltered from air, then ethylbenzene is added to make up the volume of the solution to 50 ml.

This solution is then loaded into the autoclave and the hydrogenation is carried out as in Example 4.

1.68 g of hydrogenated SBM are thus obtained having a hydrogenation rate of 95%.

EXAMPLE 6

The procedure is exactly as in Example 4, but replacing the Wilkinson rhodium catalyst with 15.2 mg of RuCI ₂ ruthenium catalyst.

1.75 g of hydrogenated SBM are obtained having a hydrogenation rate of 89% and a ruthenium content of 1 ppm.

EXAMPLE 7 (comparative. The operation is carried out in the same apparatus and according to the same procedure as in Example 6, but not using ionic liquid.

15.3 mg of catalyst RuCI ₂ [P (C ₆ Hs) 3] 3 and 150 mg of TPP are dissolved in a solution composed of 1.755 g of SBM-1 and 48.5 g of ethylbenzene. The hydrogenation is carried out for 24 hours at 120 ° C. under a pressure of 50 bars of hydrogen.

After precipitation in methanol, 1.53 g of 87% hydrogenated SBM are obtained, having a ruthenium content of 60 ppm. This corresponds to a loss of 0.87 mg of catalyst, a loss 60 times greater than that of Example 6 according to the invention.

EXAMPLE 8 (comparative!

The procedure is carried out in the same apparatus and according to the same procedure as in Example 1, but using as ionic liquid 1-butyl-3-methyl-imidazolium tetrafluoroborate (bmimBF4). 15 mg of Wilkinson's catalyst and 150 mg of TPP are dissolved in 15.1 g of bmimBF ₄ and a solution composed of 1.757 g of SBM-1 and 33.23 g of ethylbenzene is added. The hydrogenation is carried out for 24 hours at 60 ° C., under a pressure of 50 bars of hydrogen.

After precipitation in methanol, 1.75 g of 30% hydrogenated SBM are obtained (ie a hydrogenation rate 60% lower than that obtained with bmimPFe) and having a rhodium content of 15 ppm.

EXAMPLE 9

If in Example 1 we replace ethylbenzene with the same volume of tetrahydrofuran, we obtain a similar result.

EXAMPLE 10

The procedure is exactly as in Example 1, but using the triblock polymer SBM-2.

The hydrogenated polymer is obtained having a hydrogenation rate of 63%. Its analysis by DSC shows a melting point at 36 ° C (accuracy: ± 2 ° C) while the starting material (SBM-2) is not crystalline.

EXAMPLE 11

The procedure is exactly as in Example 1, but using the triblock polymer SBM-3.

A hydrogenated polymer is obtained having a hydrogenation rate of 70%. Its analysis by DSC shows a melting point at 45 ° C (accuracy: ± 2 ° C) while the starting material (SBM-3) is not crystalline.

EXAMPLE 12

The procedure is exactly as in Example 1, but replacing the triblock polymer SBM-1 with the SBS polymer.

A hydrogenated polymer is obtained having a hydrogenation rate of 85%. Its analysis by DSC shows a melting point at 73 ° C (precision: + 2 ° C) while the starting SBS is not crystalline.

Claims

1. Process for the selective hydrogenation of olefinic double bonds of block copolymers of which at least one block contains olefinic double bonds using a catalyst based on a group VIII metal in a medium comprising an organic solvent for the copolymer and an ionic liquid as solvent for the catalyst, characterized in that an ionic liquid immiscible with water is used.

2. Method according to claim 1 wherein the anion of the ionic liquid is the hexafluorophosphate anion.

3. Method according to claim 1 or 2 wherein the cation of the ionic liquid is a quaternary ammonium, aromatic ammonium, quaternary phosphonium or ternary sulfonium cation.

4. Method according to claim 3 wherein the cation of the ionic liquid is an imidazolium cation of general formula:

in which X ¹ and X ³ , identical or different, are C ₁ -C ₄ alkyl radicals and X ² is a hydrogen atom or a methyl radical, preferably a 1,3-dialkylimidazolium cation.

5. Method according to claim 4 wherein the cation of the ionic liquid is the cation 1-butyl-3-methyl-imidazolium (bmim ⁺ ) or 1-ethyl-3-methyl-imidazolium

(emim ⁺ ).

6. Method according to one of claims 1 to 5 wherein the organic solvent for the copolymer is an aromatic solvent.

7. Method according to one of claims 1 to 6 wherein the catalyst is based on rhodium, ruthenium or palladium and, preferably, chosen from the complexes RhCI (PPh ₃ ) ₃ , Rh (nbd) (PPh ₃ ) ₂ ⁺ PF ₆ -, RuCI ₂ (PPh ₃ ) ₃ and PdCI ₂ (PPh ₃ ) ₂ .

8. Method according to one of claims 1 to 7 wherein the ratio of the volumes of the ionic liquid to the organic solvent is between 0.05 and 5, preferably between 0, 1 and 1.

9. Method according to one of claims 1 to 8 wherein 0.01 to 5 moles of catalyst are used per 100 moles of olefinic double bonds to be hydrogenated, preferably 0.02 to 2 moles.

10. Method according to one of claims 1 to 9 wherein the hydrogenation is carried out at a temperature between 20 and 150 ° C, preferably between 50 and 125 ° C.

11. Method according to one of claims 1 to 10 wherein one operates under a hydrogen pressure between 1 and 100 bar relative, preferably between 20 and 60 bar.

12. Method according to one of claims 1 to 1 1 wherein, when the reaction mixture does not settle, the hydrogenated copolymer is precipitated by introducing the reaction mixture brought to a temperature between 20 and 80 ° C (preferably between 25 and 60 ° C) in a non-solvent for the hydrogenated copolymer, this non-solvent being used in an amount ranging from 1 to 20 times the volume of the organic solvent.

13. The method of claim 12 wherein the non-solvent is used in an amount ranging from 2 to 10 times (preferably 5 to 10 times) the volume of the organic solvent.

14. The method of claim 12 or 13 wherein the non-solvent is an alcohol.

15. Method according to one of claims 12 to 14 wherein the temperature of the non-solvent, before the introduction of the reaction mixture, is between 0 and 60 ° C, preferably between 0 and 40 ° C.

16. Application of the method according to one of claims 1 to 15 to the hydrogenation of a poly (styrene) -b-poly (butadiene) -b-poly (methacrylate) block copolymer methyl) whose poly (butadiene) block mainly has a microstructure -1, 4.

17. Block copolymers as obtained by selective total or partial hydrogenation of the poly (butadiene) block of poly (styrene) -b- poly (butadiene) -b-poly (methyl methacrylate) block copolymers including the poly ( butadiene) mainly has a microstructure -1, 4, the hydrogenation rate being at least equal to 50%.

18. Copolymers according to claim 17 in which the mass proportion of the poly (styrene) block ranges from 5 to 80% (preferably 10 to 60%), that of the initial poly (butadiene) block from 5 to 80% (preferably 10 at 60%) and that of the poly (methyl methacrylate) block from 90 to 15% (preferably 80 to 30%).

19. Copolymers according to claim 17 or 18 in which the hydrogenation rate is between 70 and 100%, preferably between 90 and 100%.

20. Copolymers according to one of claims 17 to 19 characterized in that they have a melting point above 30 ° C.