WO1997046593A1

WO1997046593A1 - Method for preparing telechelic 1,3-diene oligomers by the controlled free radical polymerization of 1,3-dienes in presence of a stable free radical

Info

Publication number: WO1997046593A1
Application number: PCT/FR1997/000973
Authority: WO
Inventors: Bernard Boutevin; Martine Cerf; Jean-Laurent Pradel
Original assignee: Elf Atochem S.A.
Priority date: 1996-06-04
Filing date: 1997-06-03
Publication date: 1997-12-11
Also published as: JPH11511202A; CA2229978A1; KR19990036179A; BR9702291A; EP0842198A1; CN1198750A; AU3098297A

Abstract

The invention features a method for preparing telechelic 1,3-diene oligomers that consists in effecting the free radical polymerization of at least one 1,3-diene with a heat sensitive polymerization initiator such as hydrogen peroxide in the presence of a stable nitroxide radical. The invention also features as new products the said telechelic 1,3-diene oligomers and their use for obtaining di- or multi-blocks.

Description

PROCESS FOR THE PREPARATION OF TELECHELIC 1,3-DIENE OLIGOMERS BY CONTROLLED RADICAL POLYMERIZATION OF 1,3-DIENE IN THE PRESENCE OF A

FREE STABLE RADICAL.

The present invention relates to a process for the preparation of telechelic 1,3-diene oligomers by radical polymerization of 1,3-dienes in the presence of a stable free radical. The invention also relates, as new products, to said telechelic 1,3-diene oligomers and their use for obtaining di- or multiblock copolymers.

By telechelic 1,3-diene oligomers is meant according to the present invention oligomers carrying at one of their ends (or at both) functional groups, capable of reacting with other molecules.

By way of example of such functional groups, mention may be made of the hydroxyl (-OH), cyano (-CN), amine (-NH2) and carboxylic functions.

(-COOH).

A common method for obtaining such oligomers is to carry out radical polymerization of the 1,3-dienes by initiating the polymerization with a heat-sensitive radical initiator such as hydrogen peroxide (H2O2) or an azodinitrile compound. The functionality is thus provided by the initiator itself (H2O2) or can result from a subsequent reaction (reduction of the nitrile functions provided by the azodinitrile into -CH2NH2 functions).

Thus, the dihydroxytelechelic 1,3-butadiene oligomers are obtained industrially by radical polymerization of butadiene initiated by hydrogen peroxide in an alcoholic medium (US 3,392, 1,18 - US 3,427,366). This way of operating leads to oligomers having a high polymolecularity and average functionality. In polyurethane formulation, such products lead to more or less crosslinked materials due in particular to an excess of hydroxyl functions. Stable free radicals are compounds which have been widely used in the case of radical polymerization for the study of the first stages of addition. That is to say, they made it possible to better understand the priming stage: I * + M → IM * where I is the radical resulting from the initiator and M the monomer, by immediately blocking the growth of the IM * radicals.

The literature reports numerous examples of such studies with monomers such as (meth) acrylates and styrene (E.Rizzardo et al.

August J. Chem., Vol. 35, pp 2013-2024, 1982) or vinyl monomers (G.Moad et al. Polymer Bulletin, vol. 6, pp 589-593,

1982).

By way of illustration of such compounds, mention may be made of 2,2-diphenylpicrylhydrazyl (DPPH) and very particularly the nitroxides.

Nitroxides have also been used in radical polymerization to better control the propagation step and to limit reactions of conventional endings. The following mechanism is commonly proposed:

r + M -> IIVΓ - → IM * ₂ >>-—>..—> IM *

UM IÎM! TM

where I is the radical resulting from the initiator, M the monomer and T the nitroxide.

Depending on the balance between active species and trapped species, the polymerization time can be considerably extended. This balance is displaced by the nature of T, the solvent and the temperature. However, to limit the termination reactions, the concentration of active species must remain low.

Radical polymerization in the presence of nitroxide has been widely studied, in particular for the polymerization of styrene. Thus, in international patent application WO 94/1 141 2, a process for the radical polymerization of styrene is described, in particular in the presence of a stable free radical and of benzoyl peroxide, as initiator of polymerization.

The polystyrenes obtained have a narrow polymolecularity (1, 1 to 2) and high molecular weights (approximately 100,000). The following references also relate to the radical polymerization of monomers such as polyolefins (US 5,449,724), alkyl (meth) acrylates (US 5,412,047) in the presence of a nitroxide. We have now found a process for the preparation of telechelic 1,3-diene oligomers by controlled radical polymerization, said process consisting in carrying out the radical polymerization of at least one 1,3-diene, in a dispersed medium, with a thermosensitive initiator such as hydrogen peroxide or an azodinitrile; said process being characterized in that one operates in the presence of a stable free radical.

By way of illustration of 1,3-dienes which can be used according to the present invention, mention may be made of 1,3-butadiene, 2,3-dimethyl1,3-butadiene, isoprene, 2-chloro1,3-butadiene . The present invention relates very particularly to the radical polymerization of 1,3-butadiene.

By way of illustration of azodinitriles which can be used according to the present invention as a polymerization initiator, there may be mentioned: - 2,2'-azobisisobutyronitrile,

- 2,2'-azobis (2-methylbutyronitrile),

- 2,2'-azobis (2,4-dimethylvaleronitrile),

- 1, 1 '-azobisd -cyclohexanecarbonitrile).

Preferably, 2,2'-azobisisobutyronitrile, designated below by AIBN, will be used.

By way of illustration of stable free radicals which can be used according to the present invention, mention may be made of stable nitroxide radicals, which comprise the group = NO ^# . According to the present invention, the stable nitroxide radical is chosen from the compounds represented by the following formulas:

''

R ₁ R ₂

NO in which R1, R2, R3, R4, R '1 and R'2, identical or different, represent a halogen atom such as chlorine or bromine, a linear, branched or cyclic, saturated or unsaturated hydrocarbon group having a carbon number ranging from 1 to 10 such as an alkyl, cycloalkyl or phenyl radical, or an ester group - COOR or an alkoxyl group -OR, or a phosphate group -P (O) (OR) 2 in which R is a saturated aliphatic radical having a carbon number ranging from 1 to 3; and in which R5, R6, R7, R8, R9 and R10, identical or different, may have the same meaning as R1, R2, R3, R4, R ^* 1 and R'2 or else represent a hydrogen atom, a hydroxyl group - OH or an acid group such as -COOH, -P (O) (OH) 2 or -SO3H. By way of illustration of such nitroxides, there may be mentioned:

- 2,2,5,5-tetramethyl-1 -pyrrolidinyloxy (PROXYL),

- 2,2,6,6-tetramethyl-1-piperidinyloxy, generally marketed under the name TEMPO, - N-tertiobytyl-1-phenyl-2 methyl propyl nitroxide,

- N-tertiobutyl-1 - (2-naphthyl) -2-methyl propyl nitroxide,

- N-tertiobutyl-1 -diethylphosphono-2,2-dimethyl propyl nitroxide,

- N-tertiobytyl-1-dibenzylphosphono-2,2-dimethyl propyl nitroxide,

- N-phenyl-1-diethyl phosphono-2,2-dimethyl propyl nitroxide, - N-phenyl-1 -diethyl phosphono-1 -methyl ethyl nitroxide,

- N - (- 1 -phenyl2-methylpropyl) -1 diethylphosphono-1 -methyl ethyl nitroxide TEMPO is preferably used. According to a preferred embodiment of the invention, the polymerization is carried out in a dispersed medium by mixing the initiator and the stable free radical in a solvent and then the 1,3-diene is introduced into the reaction medium having been purged and / or degassed. . The reaction is carried out under pressures ranging from 5 bars to 50 bars and, preferably, between 10 bars and 30 bars. After the introduction of 1, 3-diene, the reaction medium is brought to a temperature between 100 ° C and 150 ° C and, preferably, between 1 10 ° C and 135 ° C; for a duration which is at least equal to 1 hour and, preferably between 1 h 30 min and 6 hours.

According to the present invention, molar amounts of initiator are used between 0.1% and 10% and preferably between 0.2% and 4% relative to the 1,3-diene used.

According to the present invention, molar quantities of stable free radical are used such that the stable free radical / initiator molar ratio is between 0.05 and 5 and preferably between 0.1 and 2.5. By way of illustration of solvents which can be used according to the present invention, mention may be made of alkanes; aromatic solvents such as benzene, toluene; alcohols such as ethanol, propanol, isopropanol, cyclohexanol; ketones such as acetone, methyl ethyl ketone; ethers such as dioxane; glycols and glycol ethers such as ethylene glycol dimethyl ether (giyme) or a mixture of at least two of the above-mentioned compounds. In the case where the initiator is hydrogen peroxide, which is generally in aqueous solution, it is preferred to use as solvent alcohols such as isopropanol or ketones such as methyl ethyl ketone.

In the case where the initiator is an azodinitrile, it is preferred to use aromatic solvents such as benzene or toluene. According to the polymerization conditions, and in particular the duration, the temperature, the amounts of the reactants, in particular of initiator and of stable free radical, it is possible to obtain average molecular masses in number Mn different and different conversion rates. Thus, for given molar concentrations of initiator and of stable free radical, the number-average molecular mass Mn and the yield increase when the temperature increases for a fixed polymerization time. The functionality in stable free radical is close to 1. According to the present invention, the telechelic 1,3-diene oligomers obtained have the following general formula:

H

in which x is between 1 and 2 and n is between 1 and

500,

I represents either a hydroxyl -OH in the case where the initiator is

^H 2 ° 2 'is a monovalent organic residue comprising a nitrile group -CN, in the case where the initiator is an azodinitrile. Thus, in the case where this initiator is AIBN, I = NC-C (CH ₃ ) ₂ -.

M represents a divalent residue of 1, 3-diene. Thus, in the case of butadiene, since the 1, 3-dienes can polymerize in 1, 4 and in 1, 2, we will have the configurations, cis and trans in the case of polymerization in 1, 4:

trans configuration: -CH2-CH

^ CH-CH

CH = CH - cis configuration: -CH ₂ ^' ^ CH-

and the formation of double vinyl pendant bonds, in the case of polymerization 1, 2:

- CH ₂ -CH-

CH = CH ₂

We have a statistical distribution of the three structures with a molar percentage of vinyl type double bonds close to 20%. Thus, with butadiene, the general formula (I) of the oligomers is as follows:

Η ^ ^{^}

CH = CH ₂

The method according to the present invention makes it possible to obtain telechelic 1,3-diene oligomers having number-average molar masses Mn at most equal to 30,000 and, preferably, between 500 and 10,000. The polymolecularity Mw / Mn is less than 2 and preferably between 1, 1 and

1, 9.

This polymolecularity is less than that obtained, all other things being equal with a polymerization in the absence of a stable free radical.

According to the present invention, the telechelic 1,3-diene oligomers of structure (I) can be reduced in particular by a zinc / acetic acid system, a conventional method used for the reduction of alkoxyamines R-O-N <. In this way, one obtains in a quasi quantitative manner oligomers of difunctional telechelic 1,3-diene of general formula:

[Η ^M W ° ^H ] 2-x

The amine H-N <obtained can be reoxidized to nitroxide and thus can be used again as a stable free radical.

However, this way of operating has some drawbacks such as in particular risks of acetolysis. It also involves an expensive operation which is the regeneration of nitroxide.

It has now been found that it is possible to subject the telechelic 1,3-diene oligomer of formula (I) to a heat treatment.

The said oligomer of formula (I) is brought as such, or alternatively in solution in an inert solvent, at a temperature at least equal to

150 ° C and preferably between 160 ° C and 180 ° C for a duration which can range from 4 hours to 24 hours under reduced pressure.

The nitroxide is released quantitatively with a purity greater than 80% and a oligomer of telechelic 1,3-diene of formula:

I - M _m - X (III) in which I is the residue of the initiator (-OH, for example, in the case where the initiator is hydrogen peroxide), X a residue of the initiator or a disproportionation reaction; m represents the new number-average polymerization degree and is between 1 and 1000. The oligomers of formula (III) generally have number average molecular weights Mn greater than the oligomers of formula (II) obtained by reduction of alkoxyamines. They also exhibit superior polymolecularity. The nitroxide can be easily recovered in particular by sublimation or distillation in the case where the heat treatment is carried out without solvent or alternatively by extraction using a selective solvent when the heat treatment is carried out in a solvent medium. The telechelic 1,3-diene oligomers of formula (I) can be advantageously used for the preparation of di- or multiblock copolymers.

Indeed, the radical polymerization of 1, 3-diene in the presence of a stable free radical leads to a finished alkoxyamine block playing the role of macroinitiator.

It is possible to mix a block of formula (I) with a polymerizable monomer B such as styrene, αmethylstyrene, parachloromethyl-styrene, vinyltoluene or a different 1,3-diene and carry out the polymerization of said monomer in the presence of the oligomer of formula (I) and obtain a block copolymer of formula:

In the event that the initiator is H ₂ O ₂ , I is equal to -OH and if the reduction of the alkoxyamine is carried out by the couple Zn / acetic acid, there will be a telechelic MB diblock copolymer of formula:

The production of such block copolymers is preferably carried out in bulk, by heating the oligomer of formula (I) with the polymerizable monomer B at a temperature at least equal to 100 ° C and preferably between 1 10 ° C and 150 ° C, preferably under an inert atmosphere. It can operate at atmospheric pressure or under pressure.

The polymerization parameters such as the oligomer block concentration of formula (I), the temperature and the polymerization time make it possible to adjust the length of block B and the degree of polymerization p.

The following examples illustrate the invention:

> The polymolecularity index Ip is the ratio of the average molecular weight by weight Mw to the average molecular weight by number Mn which have been determined by gel permeation chromatography (GPC). The standard is polystyrene brought back in polybutadiene equivalent.

> The hydroxyl number IrjH 'expressed in meq / g, was determined by acetylation with acetic anhydride in pyridine medium.

> The products were identified by nuclear magnetic resonance (NMR) of the proton ( ¹ H) on a BRUCKER® AC device

The frequency for the proton is equal to 250 MHz

CDCI3 was used as the solvent. EXAMPLE 1

9.07 g d are introduced into a 300 ml stainless steel reactor fitted with a stirrer, an introduction tube, a double jacket in which a heat transfer fluid circulates. hydrogen peroxide at 30%, i.e. 0.08 mole of 100% H2O2,

1.88 g (or 0.012 mole) of 2,2,6,6-tetramethylpiperidinyloxy

(hereinafter referred to as TEMPO) and 33.7 g (or 0.56 mole) of isopropanol.

The reactor is closed and then purged with nitrogen for 15 minutes. Then introduced into the reactor 54 g (or 1 mole) of butadiene at -40 ° C. The reaction medium is heated to 130 ° C. and then kept for 4 hours at this temperature. During this time, the pressure goes from 26 bars to 19 bars. The reaction medium is cooled to room temperature and then degassed. The reaction crude is decanted in 24 hours. The densest organic phase is recovered and then evaporated under reduced pressure at 40 ° C in a rotary evaporator then under a pressure of 0.01 bar at approximately 25 ° C. 27 g of a 1,3-butadiene oligomer are obtained 2,2,6,6-tetramethylpiperidinyloxy-hydroxytelechelic which has the following physicochemical characteristics: Mn ^" (CPG) = 1700 lp = 1.7> 1 H NMR δ = 1.1 5 ppm (doublet) 1 2 H of CHPO of TEMPO δ = 3.55 to 4.32 ppm (multiplet) -CH.2O- δ = 4.8 to 5, 1 ppm (multiplet) -CH = CH.2 δ = 5.25 to 5, 7 ppm (solid) -CH = CH- (cis and trans) and -CH = CH2 Integration allows the following formula to be attributed to the oligomer:

where n = 30.

IQH ⁼ 0'61 meq / g which corresponds to an average functionality in hydroxyl functions of 1.03 calculated from Mn obtained by

CPG. EXAMPLE 2

5 g of the 1,3,6-butadiene oligomer are introduced into a 100 ml three-necked flask fitted with a thermometer, a condenser and a stirrer containing 20 ml of acetic acid, 6-tetramethylpiperidinyloxyhydroxytelechelic obtained in Example 1. The mixture is heated to 80 ° C., then 1 g of powdered zinc is introduced at once. After 2 hours of reaction, the medium is filtered.

The filtrate is concentrated under reduced pressure to constant weight.

The residue is dissolved in hexane, then extracted with a solution 10% hydrochloric acid. The organic phase is dried over sulphate, then evaporated under reduced pressure at 40 ° C in a rotary evaporator.

4.8 g of a dihydroxytelechelic oligomer of 1,3-butadiene are obtained. Analysis by proton NMR indicates the disappearance of the piperidinyl cycle and the integration makes it possible to attribute to the oligomer the following formula:

where n = 30. IpH = U 8 meq / g Mn (CPG) = 1700.

Ip = 1, 7. The average functionality in OH functions, calculated from Mn (CPG) is equal to 2.

EXAMPLE 3 (NOT CONFORM TO THE INVENTION)

The procedure is as in Example 1 but in the absence of TEMPO.

In the reactor used in Example 1, 9.07 g of 30% hydrogen peroxide is introduced, ie 0.08 mole of 100% H2O2 and

- 33.7 g (or 0.56 mole) of isopropanol.

The reactor is closed and then purged with nitrogen for 15 minutes.

Then introduced into the reactor 54 g (one mole) of butadiene at -40 ° C. The reaction medium is heated to 130 ° C and then maintained 1 h 30 min at this temperature.

During this time, the pressure goes from 26 bars to 16 bars.

The reaction medium is cooled to room temperature and then degassed. The reaction crude is decanted in 24 hours. The densest organic phase is recovered and then evaporated under reduced pressure at 40 ° C in a rotary evaporator then under a pressure of 0.01 bar at about 25 ° C. 35 g of a 1,3-butadiene dihydroxy-telechelic oligomer which has the following physicochemical characteristics are obtained:

Mn ^" (CPG) = 2800 5 Ip = 2.8> 1 H NMR δ = 3.55 to 4.2 ppm (multiplets) -CM2O- δ = 4.8 to 5.1 ppm (multiplet) -CH ≈ CH.2 δ = 5.25 to 5.7 ppm (solid) -CH ≈ CH- (cis and trans) and -CH = CH2. 10 Integration makes it possible to attribute to the oligomer the following formula:

where n = 52

HSI = ° _^'84 meq / g

The average functionality in OH functions, calculated from

Mn ^" (CPG) is 2.35. EXAMPLE 4

> Recovery of TEMPO according to the present invention.

250 g of the oligomer of 1, 3-butadiene 2,2,6,6- tetramethylpiperidinyloxyhydroxytéléchélique prepared according to the example are treated

1 and having identical physicochemical characteristics, at 165 ° C. under a reduced pressure of 5 mbar in a thin film evaporator for 5 hours.

The almost quantitatively recovered product has the following physicochemical characteristics:

Mn (CPG) = 2200 30 Ip = 3.4

IQH = 0.59

¹ H NMR analysis shows the complete disappearance of the piperidinyl cycle.

The average functionality in OH functions, calculated from Mn 35 (CPG) is equal to 1.29. The TEMPO is completely recovered at the top of the evaporator with a purity of around 80% controlled by liquid chromotography on a KROMASIL C18 column. EXAMPLE 5 The following are introduced into the reactor used in Example 1:

- 1.64 g (i.e. 0.01 mole) of azobisisobutyronitrile (hereinafter referred to as AIBN),

- 2.93 g (i.e. 0.019 mole) of TEMPO and

- 43.7 g (or 0.56 mole) of benzene. The reactor is closed and then purged with nitrogen for 15 minutes.

Then introduced into the reactor 54 g (one mole) of butadiene at -40 ° C.

The reaction medium is heated to 130 ° C. and then kept at this temperature for 4 hours. The pressure remains constant at 27 bars during this period.

The reaction medium is cooled to room temperature and then degassed.

The reaction crude is evaporated under reduced pressure at 40 ° C in a rotary evaporator, then under a reduced pressure of 0.01 bar at about 25 ° C.

13.5 g of an oiomer of 1,3-butadiene cyano, 2,2,6,6- tetramethylpiperidinyloxytelechelic which has the following physicochemical characteristics are obtained:

Mn (CPG) = 850 Ip = 1, 3

> NMR of ^" Η δ = 1.15 ppm (doublet) 12H of CH3 of TEMPO δ = 1.30 ppm (multiplet) 6H of CH3 of AIBN δ = 4.8 to 5.1 ppm (multiplet) - CH = CH2 δ = 5.25 to 5.7 ppm (solid) -CH = CH- (cis and trans) and -CH = CH2- δ = 4.20 to 4.30 ppm (solid) aminoxyl termination.

Integration allows the oligomer to be assigned the following forumule:

in which n = 10 EXAMPLE 6 The product of Example 5 is subjected to a reduction by zinc in an acetic acid medium according to the operating conditions of Example 2. An oligomer of 1,3-butadiene cyanohydroxytéléchéique is obtained. Analysis by proton NMR indicates the disappearance of the piperidinyl cycle and the integration makes it possible to attribute to the oligomer the following formula:

EXAMPLE 7 (NOT CONFORM TO THE INVENTION)

The procedure is as in Example 5, but without TEMPO.

In the reactor we introduce

- 1.64 g (or 0.01 mole) of AIBN and - 43.7 g of benzene.

The reactor is closed and then purged with nitrogen for 15 minutes.

Then introduced into the reactor 54 g (one mole) of butadiene at -40 ° C.

The medium is heated to 130 ° C. and then kept at this temperature for 1 h 30 min.

The pressure remains constant at 27 bars during this period.

The reaction medium is cooled to room temperature and then degassed.

15 g of a 1,3-butadiene dicyanotelechelic oligomer which has the following physicochemical characteristics are obtained:

Mn (CPG) = 1000 Ip = 2.3

> 1 H NMR δ = 1.30 ppm (doublet) 1 2 H of CH3 from AIBN δ = 4.8 to 5.1 ppm (multiplet) -CH = CH2 δ = 5.25 to 5.7 ppm (solid) - CH = CH (cis and trans) and -CH = CH2

Integration makes it possible to attribute the following formula to the oligomer:

in which n = 18. EXAMPLES 8 AND 9

The procedure is as in Example 1 (same quantity of reagents) but according to different operating conditions.

These conditions and results obtained are reported in Table 1 below:

TABLE 1 EXAMPLE 10

> Use of the oligomer of 1, 3-butadiene-2, 2,6,6- tetramethylpiperidinyloxyhydroxytelechelic obtained in Example 1 for the synthesis of a diblock butadiene styrene copolymer.

10 g of the oligomer obtained in Example 1 and then 30 g of styrene are introduced into a 100 ml three-necked flask fitted with a condenser, stirring and a nitrogen inlet.

Purge with nitrogen. The reaction medium is heated to 130 ° C. and then maintained for

7h30min at this temperature.

After cooling, the reaction medium is poured into 500 ml of methanol.

The precipitated product is washed and then dried. 17.5 g of a product are obtained which has the following physicochemical characteristics:

Mn ^" (CPG) = 4000 Ip = 1, 7,

The starting oligomer has completely disappeared (GPC analysis)> NMR ^" Η

Analysis by ¹ H NMR makes it possible to calculate the exact proportions of butadiene and styrene from the masses at 6.9 ppm (protons of the aromatic nuclei of styrene) and at 5.4 ppm and 5 ppm (ethylenic protons of the polybutadiene block ).

The mass and molar percentages are as follows: - molar percentage of butadiene: 31.5%. - mass percentage of butadiene: 1 9.3%. or the composition of the block copolymer: Mn of the polybutadiene block: 1,700 Mn of the polystyrene block: 7,100. This block copolymer can be represented by the formula below:

Evaluation of the mechanical properties of the polyurethanes obtained with the oligomers of 1 .3-butadiene dihydroxytéléchéliques obtained according to examples 2 and 4. We produced polyurethanes from the following products:

- PB2 oligomer of 1,3-butadiene dihydroxytelechelic from example 2

- PB4 oligomer of 1, 3-butadiene dihydroxytéléchélique of example 4

- Poly Bd® R45HT and Poly Bd® R20TLM: oligomers of 1, 3-butadiene dihydrotelechelics sold by the company ELF ATOCHEM S.A.

These 4 oligomers were polycondensed with methylene diisocyanate (hereinafter designated by MDI) using a molar ratio of -NCO functions over -OH functions equal to 1.05. The characteristics of the various starting oligomers as well as the quantities of MDI used for each test are shown in Table 2. In this table: - Mn is the average mass in number determined by GPC

. | p = Mw / Mn

- IOH ^is the hydroxyl number expressed in meq / g determined by acetylation.

- mass of MDI (in g) calculated for 50 g of oligomer used:

TABLE 2

Synthesis of polyurethanes

50 g of a 1,3-dihydroxytelechelic oligomer are charged into a glass reactor fitted with mechanical stirring, a thermocouple and a vacuum connection.

The oligomer is degassed at 80 ° C under a reduced pressure equal to 10 mbar for 1 hour. Then it is brought back to 50 ° C.

The required mass of MDI is then loaded at once as mentioned in table 2. The MDI has been previously heated to approximately 50 ° C., as is the container which is used for weighing (the melting point of the MDI being around 45 ° C). The reaction medium is stirred under reduced pressure for 4 to 5 minutes, so as to obtain a homogeneous mixture free of bubbles. The reactor is opened and the mixture is poured into a stainless steel mold, of dimensions 100 × 100 × 2 mm previously coated with a release agent.

The product is left for 24 hours at room temperature, then treated for 24 hours at 80 ° C in a ventilated oven and then 48 hours at room temperature before cutting out standard dumbbells with a punch, on which we have measured the elongation at break ε (expressed in%) and the stress at break σ (expressed in MPa) according to standard ISO 527: 1 993

1 BA (1 kN measuring cell and traction speed equal to 5 mm / min). The results obtained are collated in Table 3 below.

In this table 3, we also reported the rate of insoluble

TI expressed in%.

This insoluble level was obtained according to the following operating protocol: Approximately 1 g of polyurethane taken from a plate, synthesized as described above, and 100 ml of

DMF. The mixture is brought to reflux for 24 hours.

The solution thus obtained is filtered, the insoluble part of polyurethane is placed in a vacuum oven for 6 hours at 80 ° C. The dried insoluble residue is then weighed to determine the rate of insoluble matter by division by the mass of polyurethane initially introduced.

TABLE 3

Claims

Process for the preparation of telechelic 1,3-diene oligomers by controlled radical polymerization, said process consisting in carrying out the radical polymerization of at least 1,3-diene, in a dispersed medium with a thermosensitive initiator such as hydrogen peroxide or an azodinitrile, said method being characterized in that one operates in the presence of a stable free radical. 2. Method according to claim 1, characterized in that the stable free radical is a stable nitroxide radical which comprises the group = N-O \

Process according to Claim 2, characterized in that the stable nitroxide radical is chosen from the compounds represented by the following formulas:

R _U R ₂ C

NOT

! o - in which, R1, R2, R3, R4, R '1 and R'2, identical or different, represent a halogen atom such as chlorine or bromine, a linear, branched hydrocarbon group or cyclic, saturated or unsaturated having a carbon number ranging from 1 to 10 such as an alkyl, cycloalkyl or phenyl radical, or an ester group -COOR or an alkoxyl group -OR, or a phosphate group -P (O) (OR ) 2 in which R is a saturated aliphatic radical having a carbon number ranging from

1 to 3; and in which R5, R6, R7, R8, R9 and R10, identical or different, may have the same meaning as R1, R2, R3, R4, R '1 and R'2 or else represent a hydrogen atom, a hydroxyl group - OH or an acid group such as - COOH, -P (O) (OH) 2 or -SO3H.

4. Method according to one of claims 2 or 3, characterized in that the stable nitroxide radicals are:

- 2,2,5,5-tetramethyM -pyrrolidinyloxy (PROXYL),

2,2,6,6-tetramethyl-1-piperidinyloxy, generally marketed under the name TEMPO,

- N-tertiobytyl-1-phenyl-2 methyl propyl nitroxide,

- N-tertiobutyl-1 - (2-naphthyl) -2-methyl propyl nitroxide,

- N-tertiobutyl-1 -diethylphosphono-2,2-dimethyl propyl nitr¬ oxide, - N-tertiobytyl-1 -dibenzylphosphono-2,2-dimethyl propyl nitro¬ xyde,

- N-phenyl-1-diethyl phosphono-2,2-dimethyl propyl nitro¬ xyde,

- N-phenyl-1-diethyl phosphono-1 -methyl ethyl nitroxide, - N - (- 1 -phenyl2-methylpropyl) -1 diethylphosphono-1 -methyl ethyl nitroxide

5. Method according to one of claims 2 to 4, characterized in that the stable nitroxide radical is 2,2,6,6-tetramethyl-1 - piperidinyloxy (TEMPO). 6. Method according to claim 1, characterized in that the azodinitrile is 2,2'azobisisobutyronitrile (AIBN).

7. Method according to claim 1, characterized in that the 1, 3-diene is 1, 3-butadiene.

8. Method according to claim 1, characterized in that the polymerization is carried out in a dispersed medium by mixing the initiator and the stable free radical in a solvent, then by introducing the 1,3-diene and then the reaction medium thus obtained is brought to a temperature between 100 ° C and 1 50 ° C and, preferably between 1 10 ° C and 135 ° C.

9. Method according to claim 8, characterized in that one operates under pressures ranging from 5 bars to 50 bars and, from

5 preferably between 10 bars and 30 bars.

10. Method according to claim 8, characterized in that the temperature is maintained for a duration at least equal to 1 hour and, preferably, between 1 h 30 min and 6 hours.

1 1. Process according to either of Claims 1 and 8, characterized in that use is made of molar quantities of initiator of between 0.1% and 10% and preferably between 0.2% and 4% by compared to the 1,3-diene used.

1 2. Method according to one of claims 1, 8 or 1 1, characterized in that one uses molar amounts of free radical

Stable such that the stable free radical / initiator molar ratio is between 0.05 and 5 and preferably between 0.1 and 2.5.

13. Method according to claim 8, characterized in that the initiator is hydrogen peroxide, the stable free radical is

2,2,6,6-tetramethyl-1-piperidinyloxy, the 1,3-diene is butadiene and the solvent is isopropanol.

14. Method according to claim 8, characterized in that the initiator is azo-bisisobutyronitrile, the stable free radical is 2,2,6,6-tetramethyl-1-piperidinyloxy, the 1,3-diene is

25 butadiene and the solvent is toluene.

1 5. Telechelic 1,3-diene oligomers obtained according to any one of claims 1 to 14 of formula: W

in which x is between and 2, n is between 1 and

30,500,

I represents either a hydroxyl -OH or a monovalent organic residue comprising a nitrile group -CN, M represents a divalent residue of 1, 3-diene,> N-O- represents an alkoxyamine residue originating from a stable nitroxide radical.

35 16. Telechelic 1,3-diene oligomers of formula

(II) in which x is between 1 and 2, n is between 1 and 500,

I represents either a hydroxyl -OH, or a monovalent organic residue comprising a nitrile group -CN, 5 M represents a divalent residue of 1, 3-diene, obtained by reduction by zinc in acetic medium of the oligomers of 1, 3-diene telechelic of formula (I)

1 7. Oligomers of 1, 3-diene monohydroxytéléchéliques de fomule

M

10 in which M represents butadiene comprising at most 20 mol% of double bonds of pendant vinyl type.

1 8. Process for recovering the stable nitroxide radical from telechelic 1,3-diene oligomers of formula

in which x is between 1 and 2, n is between 1 and 500,

I represents either a hydroxyl -OH or a monovalent organic residue comprising a nitrile group -CN,

20 M represents a divalent residue of 1,3-diene,> NO- represents an alkoxyamine residue originating from a stable nitroxide radical, characterized in that said oligomer of formula (I) is heated to a temperature at least equal to 1 50 ° C and, preferably between 1 60 ° C and 180 ° C, under reduced pressure.

19. Telechelic 1,3-diene oligomers obtained according to claim 18 of formula

I - M _m m - X (III) wherein I is the residue of the initiator, X the residue of the initiator or a disproportionation reaction, m is a number 3 ₀ between 1 and 1000.

20. Use of the telechelic 1, 3-diene oligomers of formula (I) for the preparation of di- or multiblock copolymers.