Production of polymers with thiol functions, e.g. thiol-terminated silicones for cosmetic applications, involves pyrolysis of the corresponding polymer with xanthate functions

THE VOICE.

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The present invention relates to a new process for preparing polymers having thiol ends from polymers of controlled architecture carrying particular xanthate functions, in particular resulting from a process of living or controlled radical polymerization.

Polymers having thiol ends can find many fields of application. Thus, in cosmetics, they can be used in the hair field (such as in the field of perms for the hair). They can also be used to generate organized layers of polymers on noble metal substrates, such as gold. In addition, taking into account the reactivity of the thiol functions, the polymers thus obtained allow access to other polymer compounds, in particular by nucleophilic substitution or by radical addition of these functions.

The polymers with controlled architecture can be polymers (homopolymers) or copolymers (random, diblock, triblock, grafted or star-shaped, or hyperbranched). More specifically, within the meaning of the invention, by polymer with controlled architecture is meant a polymer based on two or more monomers having a controlled arrangement of these different monomer units constituting it.

Polymers with controlled architecture are usually prepared by living ionic polymerization. This type of polymerization has the drawback of only allowing the polymerization of certain types of nonpolar monomers, in particular styrene and butadiene, and of requiring a particularly pure reaction medium and temperatures often below ambient so as to minimize the spurious reactions, hence severe implementation constraints.

Radical polymerization has the advantage of being easily carried out without excessive purity conditions being observed and at temperatures equal to or greater than ambient. However, until recently, there was no radical polymerization process making it possible to obtain polymers with controlled architecture, in particular block copolymers. Recently, a new radical polymerization process has developed: this is called controlled or living radical polymerization (Matyjaszewski, K., Ed. Controlled Radical Polymerizatiorr, ACS Symposium Sériés 685; American Chemical Society: Washington, DC , 1998, and ACS Symposium Series 768, 2001). In these systems, reversible termination or transfer reactions make it possible to maintain the active ends throughout the polymerization, consequently giving access to various polymers with controlled architecture.

Controlled radical polymerization ideally presents the following distinctive aspects:

1. the number of chains is fixed throughout the duration of the reaction,

2. the chains all grow at the same speed, which results in:

- a linear increase in molecular masses with conversion,

- a tight weight distribution,

3. the average molecular mass is controlled by the monomer / chain precursor molar ratio,

4. the possibility of preparing block copolymers.

The controlled character is all the more marked as the speed of reactivation of the radical chains is very high compared to the speed of growth of the chains (propagation). There are cases where this is not always true (ie the speed of reactivation of the radical chains is lower than the speed of propagation) and conditions 1 and 2 are not observed, nevertheless, it is always possible to prepare block copolymers.

Recently, living radical polymerization processes by reversible addition-fragmentation transfer have been developed. This particular type of polymerization constitutes one of the most suitable technologies for synthesizing block copolymers by the radical route. In this context, the RSC = SOR 'xanthates were used as transfer agents in patent applications WO 98/58974, WO 00/75207 and WO 01/042312 from the company Rhodia Chimie to synthesize polymers with an architecture controlled. A process for the preparation by radical polymerization under thermal activation of silicone and organic hybrid copolymers has also been described in French patent application FR 00 09722 filed by the applicant on July 25, 2000. These hybrid copolymers are prepared from a silicone precursor exhibiting reactive functions, in particular of xanthate type, of at least one organic ethylenically unsaturated monomer and of a radical polymerization initiator. It has also been described in French patent application No. 01 05144 filed by the applicant on April 13, 2001 a process for preparing polymers in the form of stars which comprises a step of radical polymerization of a composition comprising: at least one crosslinking monomer, a source of free radicals and at least one first generation polymer. This first generation polymer is itself obtained by a process comprising a radical polymerization step causing at least one crosslinking monomer to react, a source of free radicals and at least one transfer agent, in particular the xanthates of formula RSC = SOR ', as described in patent applications WO 98/58974, WO 00/75207 and WO 01/042312.

However, despite the advantages provided by these living radical polymerization processes, the polymers thus prepared exhibit reactive ends, such as in particular xanthate functions, which are fragile, since they can be hydrolyzed in a basic medium. They are therefore likely to release sulfur by-products, low molecular weight, malodorous, and / or toxic to the environment and humans.

In the remainder of the description, the term polymer is used to describe homopolymers or copolymers, unless otherwise indicated.

In addition, the term “block polymer” is understood to mean a copolymer comprising at least two successive sequences of blocks of monomer units of different chemical constitutions. The blocks can consist of a homopolymer or of a polymer obtained from a mixture of ethylenically unsaturated monomers. In this case, the block can be a random copolymer. The block copolymer may comprise two blocks each consisting of random copolymers. In this case, the ethylenically unsaturated monomers are such that the blocks obtained are of different natures. By different natures, is meant blocks consisting of monomers of different types, but also blocks consisting of monomers of the same type but in different amounts.

An aim of the present invention is to provide a method that is simple to implement, but effective, making it possible to remove the xanthates functions carried by polymers, generally obtained by radical polymerization.

Another aim of the invention is to provide a new route of access to polymers containing thiol functions.

These aims and others which will become apparent on reading the description are achieved by the present invention, which relates to a process for preparing polymers having at least one thiol function, which comprises the pyrolysis of at least one polymer having at least one thiol function. of the following formula (1):

R2 R3

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³ R1 R4

d) formula (1) in which R1, R2, R3 and R4, which may be identical or different, represent a group chosen from the hydrogen atom, the alkyl, acyl, aryl, aralkyl, alkene or alkyne, cycloalkyl or heterocycloalkyl radicals, saturated or not, aromatic, or a polymer chain, R1 and R4 or R1 and R2 which together can form a cycloalkyl or a heterocycloalkyl.

The pyrolysis temperature used in the process according to the invention depends to a large extent on the chemical nature of the radicals R1,

R2, R3 and R4. This pyrolysis temperature is chosen such that there is transformation of the function of formula (1) presented by the polymers used into a thiol function and to produce carbonyl sulfide, of formula COS, and an olefinic compound. of formula (2) below: R1R2 = R3R4. Thus, it is within the abilities of those skilled in the art to define the polymerization conditions so that the pyrolysis reaction does not take place during this polymerization. To give an order of magnitude, the pyrolysis temperature is generally between 20 and 200 ° C, preferably between 100 and 180 ° C, more particularly between 130 and 160 ° C.

The pyrolysis according to the invention is generally carried out at atmospheric pressure.

The pyrolysis according to the invention is generally carried out on a polymer which is in solution, in emulsion (in the form of a latex), solid or in the molten state.

Thus, when it is implemented on a polymer which is in solution, the solvent is preferably a solvent having a boiling point greater than or equal to the pyrolysis temperature. Mention may in particular be made of water, an organic solvent, such as in particular 1,2-dichlorobenzene.

The optionally substituted alkyl, acyl, aryl, aralkyl or alkyne groups generally have 1 to 20 carbon atoms, preferably 1 to 12, and more preferably 1 to 9 carbon atoms. They can be linear or branched. They can also be substituted by oxygen atoms, in particular in the form of esters, sulfur or nitrogen atoms.

Among the alkyl radicals, mention may in particular be made of the methyl, ethyl, propyl, butyl, pentyl, isopropyl, tert-butyl, pentyl, hexyl, octyl, decyl or dodecyl radical. Methyl or ethyl radicals are preferred.

Alkyne groups are radicals generally of 2 to 10 carbon atoms, they have at least one acetylenic unsaturation, such as the acetylenyl radical.

The acyl group is a radical generally having 1 to 20 carbon atoms with a carbonyl group.

Among the aryl radicals, mention may in particular be made of the phenyl radical, optionally substituted in particular by a nitro or hydroxyl function.

Among the aralkyl radicals, mention may in particular be made of the benzyl or phenethyl radical, optionally substituted in particular by a nitro or hydroxyl function.

The cycloalkyl radical (C₃-VS₈) is a cyclic hydrocarbon radical, such as in particular cyclopropyl, cyclopentyl or cyclohexyl. Preferably, when R1 and R4 or R1 and R2 form a cycloalkyl, this is cyclohexyl.

The heterocycloalkyl radical is a cycloalkyl radical as defined above containing, instead of one or more carbon atoms of the ring, one or more heteroatoms chosen from N, O and S.

Among the heterocycloalkyl radicals, there may therefore be mentioned in particular the piperidyl, pyrazolidinyl, piperazinyl and morpholinyl radical.

When R1, R2, R3 or R4 is a polymer chain, this polymer chain can result from a radical or ionic polymerization or result from a polycondensation.

R1, R2, R3 and R4 are preferably chosen such that the removal of the olefinic compound of formula (2) produced, indicated above, in particular by evaporation or steam stripping, is made easier.

Preferably, R1, R2, R3 and R4 represent groups chosen from: the hydrogen atom, the methyl radical, ethyl and the cyclohexyl radical for R1 and R4 or R1 and R2.

The polymer exhibiting at least one function of formula (1) used in the process of the present invention is preferably an organic polymer, a polymer of silicone type or a hybrid copolymer on the one hand formed by a polymer of silicone type and on the other hand by an organic polymer.

These polymers can be obtained by radical and / or ionic polymerization. Indeed, even if it was initially a question of removing reactive functions obtained during a process for the synthesis of polymers by the radical route, it turns out that the process according to the invention also applies to polymers such as as silicone polymers exhibiting at least one function of formula (1).

According to a particular embodiment, to have at least one end of formula (1), the polymers used in the present invention were obtained by a process, as described in one of the patent applications WO

98/58974 and WO 00/75207 from Rhodia Chimie, using at least one xanthate compound of the following formula (2):

R2 R3

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(2) in which R, R1, R2, R3 and R4, identical or different, have the meanings given for R1, R2, R3 and R4 and specified above.

Thus, the polymers used in the process of the invention may for example be polymers resulting from a controlled radical polymerization process carried out by bringing one or more ethylenically unsaturated® monomer into contact with at least one source of free radicals and at least one reversible transfer agent of xanthate type of formula (2). More specifically, the living organic polymers used in the process of the invention can be block polymers resulting from a copolymerization process comprising N successive radical polymerization steps (N being greater than or equal to 2), the first of these stages being a controlled radical polymerization carried out by contacting one or more ethylenically unsaturated® monomer®, of at least one source of free radicals and of at least one reversible transfer agent of the aforementioned type, and the following (N-1) stages being controlled radical polymerizations carried out by contacting one or more ethylenically® monomer unsaturated® different from those of the previous step, of at least one source of free radicals and of the living polymer composition resulting from the previous step.

For example, when N is equal to 2, the polymer used in the present invention can be a polymer of the following formula (!):

HR3 R1

S • oL sR4 R2

X '

- (CV = CV ') b-CH „

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- (CWZCW ') a — CR (l), with m and n, identical or different, greater than or equal to 1, preferably greater than 6, and preferably less than 500, one of the two (m or n) which may be equal to 0, when m or n&gt; 1, the repeating unit units of index m or n respectively are different or advantageously identical,

R, R1, R2, R3 and R4, identical or different, have the meanings given above for R1, R2, R3 and R4,

- V, V, W and W ', identical or different, represent: H, an alkyl group or a halogen,

- X, X ', Y and Y', identical or different, represent H, a halogen or a group R_s, GOLD₅, O₂HORN₅, NHCOH, OH, NH₂, NHR₅, N (R₅)₂, (R₅)₂NOT⁺O-, NHCOR₅, CO₂H, CO₂R_5d CN, CONH₂, CONHR₅ or CON (R₅)₂, in which R₅ is chosen from alkyl, aryl, aralkyl, alkylaryl, alkene or organosilyl groups, optionally perfluorinated and optionally substituted by one or more carboxyl, epoxy, hydroxyl, alkoxy, amino, halogen or sulfonic groups, and

- a and b are 0 or 1.

The polymer exhibiting at least one function of formula (1) used in the present invention may correspond to a star-shaped polymer. Thus, it can be obtained by a process as described in French patent application No. 01 05144 filed by the applicant on April 13, 2001. This process comprises a step of radical polymerization of a composition comprising: at least one crosslinking monomer, a source of free radicals and at least one first generation polymer. This first generation polymer is itself obtained by a process comprising a radical polymerization step causing at least one ethylenically unsaturated monomer to react, a source of free radicals and at least one xanthate compound of formula (2) as described above.

The crosslinking monomers are chosen from organic compounds comprising at least two ethylenic unsaturations and at most 10 unsaturations and known to be reactive by the radical route. Preferably, these monomers have two ethylenic unsaturations.

Thus, mention may in particular be made of acrylic, methacrylic, acrylamido, methacrylamido, vinyl ester, vinyl ether, diene, styrene, alpha-methyl styrene and allyl. As crosslinking monomers, preferred are Ν, Ν'-methylenebisacrylamide, divinylbenzene and ethylene glycol diacrylate.

The polymer exhibiting at least one function of formula (1) used in the present invention may correspond, according to another embodiment, to hybrid silicone and organic copolymers comprising units (II):

AT_xUySiO [4- (x + y)] / 2 (II) in which:

- x is equal to 0, 1, 2 or 3, y is equal to 0, 1, 2 or 3 with 2 &lt;(x + y) &lt;3 and y is different from 0 for at least one of the units of the hybrid copolymer, • the symbols A, identical or different, represent:

• a linear or branched alkyl radical containing 1 to 8 carbon atoms, optionally substituted by at least one halogen, preferably fluorine, the alkyl radicals preferably being methyl, ethyl, propyl, octyl and 3,3,3-trifluoropropyl, • a cycloalkyl radical containing between 3 and 8 cyclic carbon atoms, optionally substituted, • an aryl radical containing between 6 and 12 carbon atoms which may be substituted, preferably phenyl or dichlorophenyl, • an aralkyl part having an alkyl part containing between 5 and 14 carbon atoms and an aryl part containing between 6 and

12 carbon atoms, optionally substituted on the aryl part by halogens, alkyls and / or alkoxyls containing 1 to 3 carbon atoms, • the U symbols, which are identical or different, represent (III):

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C - (CV = CV ') a - CH

X '

C (R²R³) - (C = O) -W-Sp15 (III) in which:

- R1, R2, R3 and R4, identical or different, have the meaning given above,

- V and V, identical or different, have the meanings given above,

- X and X ', identical or different, have the meanings given above,

- R² and R³, identical or different, represent:

- an optionally substituted alkyl, acyl, aryl, alkene or alkyne group,

- a carbon ring (ii), saturated or not, optionally substituted and / or aromatic,

- a heterocycle (iii), saturated or not, optionally substituted,

- a hydrogen atom, groups; alkoxycarbonyl, cc aryloxycarbonyl (-COOR °), carboxy (-COOH), acyloxy (-O2CR), carbamoyl (-CONR 2). cyano (-CN), alkylcarbonyl, alkylarylcarbonyl, arylcarbonyl, arylalkylcarbonyl, phthalimido, maleimido, succinimido, amidino, guanidimo, hydroxy (-OH), amino (5 5

NR 2). halogen, allyl, epoxy, alkoxy (-OR), S-alkyl, S-aryl, groups having a hydrophilic or ionic character such as alkali metal salts of carboxylic acids, alkali metal salts of sulphonic acid, polyoxide chains of 'alkylene (POE,

POP), cationic substituents (quaternary ammonium salts), 5

R, identical or different, representing an alkyl or aryl group, and / or a polymer chain,

- the radicals (i), (ii) and (iii) possibly being substituted advantageously by: substituted phenyl groups, substituted aromatic groups, or groups: alkoxycarbonyl, aryloxycarbonyl (COOr5), carboxy (-COOH), acyloxy (- O2CR ^), carbamoyl (5

CONR 2). cyano (-CN), alkylcarbonyl, alkylarylcarbonyl, arylcarbonyl, arylalkylcarbonyl, phthalimido, maleimido, succinimido, 5 amidino, guanidimo, hydroxy (-OH), amino (-NR 2), halogen, allyl, 5 epoxy, alkoxy (-OR) , S-alkyl, S-aryl, groups having a hydrophilic or ionic character such as alkali metal salts of carboxylic acids, alkali metal salts of sulfonic acid, polyalkylene oxide chains (POE, POP), cationic substituents (quaternary ammonium salts), R, identical or different, representing an alkyl or aryl group, and / or a polymer chain,

- W, identical or different, represent a divalent radical chosen from

-WE R₅-, -NH-, -S-, R₅ having the meaning given above,

- Sp, identical or different, represent a ball joint consisting of an organic divalent radical of formula - (CH₂)_X.- in which x 'is between 1 and 20, this radical possibly being substituted and / or containing at least one heteroatom,

- a = 0 or 1,

- m&gt; 1, and when m&gt; 1, the repeating unit units of index m are identical or different, m preferably being less than 500.

These hybrid copolymers can be obtained by the process in which the following are brought into contact:

- at least one ethylenically unsaturated monomer of formula (IV):

CXX '(= CV - CV')_at = CH₂,

- a precursor silicone compound comprising units, identical or different, of formula (V):

AT_XU'ySiO [4_ (x + y)] / 2 in which:

- A, x and y correspond to the values ​​given previously, and the monovalent radical U 'is according to the following formula (VI):

<img file="FR2829140B1_D0003.tif" />

CR²R³- (C = O) -W-Sp

- and a radical polymerization initiator.

The precursor silicone compound of general formula (V) used in the process for preparing these hybrid copolymers can be obtained by reaction:

(i) of a silicone comprising units of formula (Vil): R_XUySiO [4_ (_X+ y)] / 2 where the monovalent radical U is according to the following formula (VIII):

L-CR²R³- (C = O) -W-Sp in which:

- R², R³, W and Sp have definitions identical to those given previously,

- L is an electrofuge group, for example: Br, Cl ', Γ, OTs; OMs', (C₆H₆) - (C = O) -O-, (CH₃) - (C = O) -O, (CF₃) - (C = O) -O '.

(ii) with a compound chosen from those of the following general formulas (IX), (X) or (XI):

<img file="FR2829140B1_D0004.tif" />

in which :

R1, R2, R3 and R4, identical or different, have the meaning given above,

- M '⁺ represents K⁺, N / A⁺, NR₄⁺, or PR / · R being of similar definition to that given for R of formula (I),

- M²⁺ represents an alkaline earth metal such as Ca²⁺, Ba²⁺and Sr²⁺⁺,

- M 'represents Ζη, Cd, m is equal to 1 or 2, n is equal to 1.2, 3 or 4 and preferably m is equal to 1 and n is equal to 2.

This silicone of formula (VII) can be obtained in particular from (i) a silicone comprising units of formula (XII): R_xU'ySiO [4- (x + y)] / 2 ° ù Ιθ monovalent radical U 'is of formula (XIII): -Sp-WH and (ii) of a compound of formula:

Besides hybrid copolymers comprising a single organic segment, the polymers used in the process according to the invention can correspond to hybrid polymers bearing organic block groups (ie multiblock). For this, their preparation process consists in repeating the implementation of the preparation process described above using:

- ethylenically unsaturated monomers different from the previous implementation, and

- instead of the precursor silicone compound (V), the hybrid copolymer comprising block units (II) resulting from the previous implementation. According to this process for the preparation of multiblock copolymers, when it is desired to obtain homogeneous block copolymers and not with a composition gradient, and if all the successive polymerizations are carried out in the same reactor, it is essential that all the monomers used during 'a step have been consumed before the polymerization of the next step begins, therefore before the new monomers are introduced.

These hybrid copolymers have been described in French patent application FR 00 09722 filed by the applicant on July 25, 2000.

As mentioned above, the polymer having at least one function of formula (1) may correspond, according to another embodiment, to a polymer of silicone type. In this case, the silicone-type polymer is of general formula (V), as described above.

The ethylenically unsaturated monomers mentioned above are more specifically according to the invention the monomers chosen from styrene or its derivatives, butadiene, chloroprene, (meth) acrylic esters, vinyl esters, vinyl nitriles, vinyl esters and amides. unsaturated carboxylic acids.

The following examples illustrate the invention without, however, limiting its scope.

EXAMPLES:

Example 1:

- Synthesis of the sodium salt of O- (2-propyI) xanthic acid

S equivalent of 2-propanol is added dropwise, at 0 ° C., to a solution (1 M) of 1.1 equivalent of NaH in THF. 4 CS equivalents₂ are added, and the reaction medium is stirred overnight at room temperature.

The THF is then evaporated off, 1 liter of petroleum ether is then added to wash the solid obtained, by filtration. The solid is then dried under vacuum.

NMR ¹H

5.45 ppm (sext. 1H (2)); 1.84 and 1.62 ppm (mult. 2x1H (3)); 1.32 ppm (doub.

2H (1)); 0.93 ppm (trip. 3H (4))

NMR ¹³VS

208.0 ppm C (5); 81.5 ppm C (2); 28.8 ppm C (3); 19.0 ppm C (1); 10.0 ppm C (4)

- Synthesis of a silicone oil (polydimethylsiloxane, DPn = 14) a, o-bis [0- (2propyl)] xanthate

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To a solution of 10 g of α, ω-hydroxylated silicone oil (polydimethylsiloxane, DPn = 14) (1 equivalent) and of 2.6 g (4 equivalents) of pyridine in ether (200 ml) is added dropwise and at room temperature, 1.9 ml (2.4 equivalents) of 2-bromopropionyl bromide.

After stirring overnight at room temperature, 50 ml of water are added to the reaction mixture. The aqueous phase is then extracted with 2 x 100 ml of ethyl acetate.

The combined organic phases are then washed successively with an aqueous solution of NaOH (1 M), an aqueous solution of 10% HCl, water and brine, then dried over magnesium sulfate. The solvents are then evaporated off. The crude product obtained is then chromatographed on a silica column (heptane 9 / ether 1) to give 11 g of brominated silicone oil.

g of brominated silicone oil is added to a solution of 0.5 g of xanthate 1 (4 eq.) dissolved in 10 ml of CH₃CN. The reaction mixture is stirred overnight at room temperature. The solvent is evaporated off, ether is then added, then filtration is carried out to remove the excess xanthate salt and the sodium salt formed. On the spectrum of the crude product obtained, the bromine is completely displaced by the xanthate salt.

NMR ¹H

5.56 ppm (sext 2H (2 ')); 4.32 ppm (quad. 2H (5)); 4.06 ppm (trip.4H (3)); 1.6 to 1.8 ppm (mult. 8H (2, 3 ')); 1.51 ppm (doub. 6H (6)); 1.30 ppm (mult. 6H (1 ')); 0.90 ppm (trip.6H (4 ')); 0.52 ppm (mult. 4H (1)); 0.1 ppm (mult. SiMe₃)

NMR ¹³VS

211.5 ppm C (5 '); 171.4 ppm C (4); 82.7 ppm C (2 '); 68.1 ppm C (3); 46.9 ppm C (5);

28.5 ppm C (3 '); 22.6 ppm C (2); 18.7, 17.0 and 9.6 ppm C (1 '), C (4') and C (6); 14.2 ppm C (1); 1.0 and 0.1 ppm (Si-CH₃).

- Synthesis of PDMS oil (polydimethylsiloxane, DPn = 14) α, ω-bisthiol

<img file="FR2829140B1_D0006.tif" />

0.2 g of silicone carrying the xanthate 2 function is dissolved in 1 ml of chlorobenzene, then refluxed. After 2 hours of stirring, little change is observed.

In solution in dichloro-benzene, the 0.2 g of silicone 2 are refluxed for 2 hours.

The solvent is then evaporated with the elimination products, to give a crude product where the characteristic signals of the xanthate function are no longer observed by NMR. ¹H and ¹³VS .

On the other hand, one always observes by NMR ¹H, 1 signal at 3.5 ppm, which should correspond to H (5). The chemical shift of the corresponding carbon in¹³C, confirms the same to us.

NMR ¹H

4.09 ppm (tripdoub. 4H (3)); 3.50 ppm (muit. 2H (5)); 1.72 ppm (mult. 4H (2)); 1.50 ppm (doub. 6H (2)); 0.55 ppm (mult. 4H (1)); 0.1 ppm (mult. SiMe₃)

NMR ¹³VS

68.0 ppm C (3); 48.2 ppm C (5); 22.7 ppm C (2); 17.0 ppm C (6); 14.1 ppm C (1); 1.1 and 0.2 ppm (Si-CH