WO2001027176A1

WO2001027176A1 - Method for producing graft polymers

Info

Publication number: WO2001027176A1
Application number: PCT/FR2000/002769
Authority: WO
Inventors: Mathias Destarac; Dominique Charmot; Samir Zard
Original assignee: Rhodia Chimie
Priority date: 1999-10-11
Filing date: 2000-10-05
Publication date: 2001-04-19
Also published as: AU7794300A; FR2799471B1; FR2799471A1

Abstract

The invention relates to a method for producing graft polymers, comprising the following steps: 1. Bringing the following into contact with each other: at least one source of free radicals; at least one compound of formula (I); at least one monomer M1 selected from 1,1 disubstituted ethylenically unsaturated monomers; 2. Then bringing the polymer resulting from the polymerisation in step 1 into contact with the following: at least one source of free radicals and at least one ethylenically unsaturated monomer M2, the proportion of radically polymerisable 1,1 disubstituted ethylenically unsaturated monomers being more than 90 wt. % in relation to the total of M2 monomers.

Description

PROCESS FOR THE PREPARATION OF GRAFT POLYMERS

The invention relates to a new process for the preparation of graft polymers.

The grafted polymers can be prepared according to three different access routes

- the "grafting onto" route, which consists of growing the grafts in the reaction medium and then, when they have finished grafting them onto the main chain,

- the "grafting from" route, which consists of preparing a main chain and growing grafts from certain motifs in this chain,

- And the "macromonomer" route, which consists in polymerizing a mixture of monomers, some of which already carry grafts. The macromonomer pathway can be implemented by radical route, but the number of macromonomers is limited and the process difficult to implement. In addition, the incorporation of the macromonomer into the graft copolymer is never complete.

The first two routes are implemented by ionic polymerization. However, ionic polymerization has the disadvantage of only allowing the polymerization of certain types of apolar monomers, in particular styrene and butadiene, and of requiring a particularly pure reaction medium and temperatures often below ambient so as to minimize parasitic reactions, hence severe implementation constraints.

Radical polymerization has the advantage of being easily carried out without excessive purity conditions being met and at temperatures equal to or above ambient. However, until recently, there was no radical polymerization process making it possible to obtain polymers grafted by "grafting onto" or "grafting from". The development of so-called "living" or "controlled" radical polymerizations has allowed access to grafted polymers by the "grafting from" route which was reserved for ionic polymerization.

Thus, "controlled" radical polymerization using nitroxide precursors makes it possible to add nitroxyl counter-radicals on polymer chains in order to grow grafts in a controlled manner in a subsequent step. However, this polymerization requires high temperatures to label the C-O bond.

Similarly, using atomic transfer polymerization (ATRP), graft copolymers have been synthesized from polymer backbones. halogens, the halogen atoms playing the role of initiating sites. However, a disadvantage of this polymerization is that there remains a significant amount of metal per chain.

The polymerization of grafts on a polymer chain carrying xanthat functions has been described in Huskic et al. Polym.lnt. 40.227 (1996). In this case, a commercial polyvinyl chloride polymer is modified by grafting xanthate functions on its chain. The grafted groups obtained are then activated under UV irradiation and brought into contact with monomers so as to create grafts of polymers on the xanthatic sites. This process has the disadvantage of implementing processes of different natures (grafting then polymerization), hence the need to purify the reaction medium between each reaction: it is therefore a heavy synthesis to industrialize. In addition, the implementation of a UV irradiation source is difficult to implement industrially.

An object of the present invention is to propose a new process for the synthesis of graft polymers by "controlled" radical polymerization.

Another object of the present invention is to propose a new process for the synthesis of grafted polymers by "controlled" radical polymerization using xanthates which do not have the above drawbacks.

For these purposes, the invention firstly relates to a process for the preparation of grafted polymers, in which the following steps are implemented:

1. we put in contact:

• at least one source of free radicals, • at least one compound of formula (I), (II) or (III):

in which :

- T and T 'represent a divalent group,

- R ¹ and R ² represent:

. an (i) alkyl, acyl, aryl, alken or alkyne group, or. a (ii) carbon cycle, saturated or not, optionally aromatic, or

. a heterocycle (iii), saturated or unsaturated, these groups and rings (i), (ii) and (iii) may be substituted by alkyl groups, substituted phenyl groups, substituted aromatic groups or groups: oxo, alkoxycarbonyl or aryloxycarbonyl ( -COOR '), carboxy (-COOH), acyloxy (-O CR'), carbamoyl (-CONR ' ₂ ), cyano (-CN), alkylcarbonyl, alkylarylcarbonyl, arylcarbonyl, arylalkylcarbonyl, isocyanate, phthalimido, maleimido, succinimido, amidino , guanidimo, hydroxy (-OH), amino (-NR ' ₂ ), halogen, allyia, epoxy, alkoxy (-OR'), S-alkyl, S-aryl, silyl, 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 ′ representing an alkyl or aryl group,. a polymer chain,

p represents an integer of between 2 and 200, • at least one monomer M1 chosen from ethylenically unsaturated monomers 1, 1 disubstituted polymerizable by the radical route,

2. then, the polymer resulting from the polymerization of step 1 is brought into contact with: • at least one source of free radicals, and • one or more ethylenically unsaturated M2 monomers, the proportion of ethylenically unsaturated monomers 1, 1 disubstituted radically polymerizable being at most 90% by weight relative to all of the monomers M2, preferably at most 50%.

The method according to the invention therefore consists in carrying out:

a first polymerization by bringing into contact a source of free radicals, at least one monomer M1 and a compound of formula (I), (II) or (III), preferably of formula (I), so as to form the main chain and then

a second polymerization by bringing this main chain into contact with a source of free radicals and at least one M2 monomer to form the grafts. In formulas (I), (II) or (III), T preferably represents a divalent group chosen from a carbonyl group (-C (O) O- or -C (O) OC _n H _2n - with n between 1 and 20), phenylene (C ₆ H ₄ or C ₆ H ₄ C _n H _2n with n between 1 and 20), acyloxy (-OC (O) - or -OC (O) C _n H ₂ n- with n between 1 and 20), alkylene or acrylamido (-C (O) NH). Preferably, T 'represents a divalent aryl, phenyl, alkyl, cycloalkyl, aralkyl or -CO ₂ R group with R aryl or cycoalkyl.

The compounds of formula (I), (II) or (III) carry a xanthate function.

According to a variant of the invention, the xanthate function of the compounds of formula (I) and (III) carries a group R ¹ substituted by at least one atom of fluorine, chlorine and / or bromine. Preferably, R ¹ is substituted by at least one fluorine atom, and even more preferably only fluorine atoms. According to a preferred variant, R ¹ represents a group of formula: -CH ₂ R ³ , in which R ³ is an alkyl group substituted by at least one fluorine, chlorine and / or bromine atom. According to this mode, the preferred groups R ¹ are the following: - CH ₂ CF ₃ ,

- CH2CF2CF2CF3,

- CH2CH2C6F13,

According to another preferred variant, R ¹ represents the group CH (CF ₃ ) ₂ . Preferably, in formula (II), R ² represents: - a group of formula CR ' ¹ R ^{, 2} R' ³ , in which:

. R ' ¹ , R' ² and R ' ³ represent groups (i), (ii) or (iii) as defined above, or. R'1 = '2 = H _e R-3 _is _an aryl, alkene or alkyne group,

- Or a group of formula -COR ' ⁴ in which R' ⁴ represents a group (i), (ii) or (iii) as defined above. For example, R ¹ can be a group chosen from:

- CH (CH ₃ ) (CO ₂ Et),

- CH (CH ₃ ) (C ₆ H ₅ ),

- CH (CO ₂ Et) _2,

- C (CH ₃ ) (CO ₂ Et) (SC ₆ H ₅ ), - C (CH ₃ ) ₂ (C ₆ H ₅ ) or

H O I II - C— C— Ph

in which Et represents an ethyl group and Ph represents a phenyl group. According to a particularly preferred mode, it is - CH (CO ₂ Et) ₂ or C (CH ₃ ) (CO ₂ Et) (SC ₆ H ₅ ).

The compounds of formulas (I) and (III) are easily accessible either by reaction of an halogenated ethylenically unsaturated compound on a xanthate salt, or by reaction of a hydroxylated ethylenically unsaturated compound with a bromopropionyl bromide and a xanthate salt . The compounds of formula (II) can also be obtained by reaction of an ethylenically unsaturated compound with CS ₂ and an alkyl halide.

The methods according to the invention using compounds of formula (II) have the advantage of limiting the crosslinking reactions of the grafts with one another and therefore the presence of gel.

The compounds of formula (III) make it possible to grow a graft on at least two active sites. With this type of compound, it is possible to save on polymerization stages in order to obtain a copolymer with several blocks. They make it possible to obtain polymers whose structure is "multi-arm" or hyperbranched.

According to the process of the invention, the source of free radicals in steps 1 and 2 is generally an initiator of radical polymerization. However, for certain monomers, such as styrene, thermal initiation is sufficient to generate free radicals.

In the first case, the radical polymerization initiator can be chosen to be chosen from the initiators conventionally used in radical polymerization. It can for example be one of the following initiators:

- hydrogen peroxides such as: tertiary butyl hydroperoxide, cumene hydroperoxide, t-butyl-peroxyacetate, t-butylperoxybenzoate, t-butylperoxyoctoate, t-butylperoxyneodecanoate, t-butylperoxyisobutarate, lauroyl peroxide, t-amylperoxypivalte, t-butylperoxypivalate, dicumyl peroxide, benzoyl peroxide, potassium persulfate, ammonium persulfate,

- azo compounds such as: 2-2'-azobis (isobutyronitrile), 2,2'-azobis (2-butanenitrile), 4,4'-azobis (4-pentanoic acid), 1, 1 ' -azobis (cyclohexane- carbonitrile), 2- (t-butylazo) -2-cyanopropane, 2,2'-azobis [2-methyl-N- (1, 1) - bis (hydroxymethyl) -2-hydroxyethyl] propionamide, 2,2'-azobis (2-methyl-N- hydroxyethyl] -propionamide, 2,2'-azobis dichloride (N, N'-dimethyleneisobutyramidine), 2,2'-azobis dichloride (2 -amidinopropane), 2,2'-azobis (N, N'-dimethyleneisobutyramide), 2,2'-azobis (2-methyl-N- [1, 1-bis (hydroxymethyl) -2-hydroxyethyl] propionamide), 2,2'-azobis (2-methyl-N- [1,1-bis (hydroxymethyl) ethyl] propionamide), 2,2'-azobis [2-methyl -N- (2-hydroxyethyl) propionamide], 2,2'-azobis (isobutyramide) dihydrate,

- redox systems comprising combinations such as:. mixtures of hydrogen peroxide, alkyl, peresters, percarbonates and the like and any of the iron salts, titanous salts, zinc formaldehyde sulfoxylate or sodium formaldehyde sulfoxylate, and reducing sugars,

. persulfates, perborate or perchlorate of alkali metals or ammonium in combination with an alkali metal bisulfite, such as sodium metabisulfite, and reducing sugars,

. alkali metal persulfate in combination with an arylphosphinic acid, such as benzene phosphonic acid and the like, and reducing sugars.

Preferably, the method is implemented in the absence of UV source.

Preferably, during step 2, the quantity of initiator to be used is determined so that the quantity of radicals generated is at most 20 mol% relative to the quantity of compound (I), (II) or (III), or even at most 5% by mole.

According to the first step of the process of the invention, the monomers M1 must be chosen from the ethylenically unsaturated monomers 1, 1 disubstituted. They can, for example, be chosen from methacrylic esters, methacrylamides, alphamethylstyrenes and their derivatives, ethers and isopropenyl esters.

Preferably, the monomers M1 are used for which the polymerization transfer constant in the presence of the compound of formula (I), (II) or (III) used as transfer agent is at most 0.1, the transfer constant corresponding to the following formula:

in which: - k _add represents the rate of addition constant of the macroradical on the compound of formula (I), (II) or (III),

- k. _add represents the reversible addition rate constant of the macroradical on the compound of formula (I), (II) or (III),

- kβ represents the fragmentation rate constant. Preferably, during step 1, the weight ratio of the compound of formula

(I), (II) or (III) relative to the monomers M1 is at most 10/90. A small amount of compound (I), (II) or (III) compared to the monomers M1 ensures a limited number of initiator sites (of grafts) by main chain and therefore minimization of the risk of crosslinking of grafts.

According to the second step of the process of the invention, the M2 monomers are ethylenically unsaturated monomers. They can be more specifically chosen from styrene or its derivatives, butadiene, chloroprene, acrylic esters, vinyl esters and vinyl nitriles. If disubstituted monomers 1, 1 are used as monomers M2, their proportion in the mixture of monomers M2 must be at most 90% by weight, preferably at most 50% by weight. By acrylic esters, esters of acrylic acid with alcohols means C ^ C- hydrogenated or fluorinated, preferably C ^ -C _j. Among the compounds of this type, there may be mentioned: methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate , t-butyl acrylate. Vinyl nitriles more particularly include those having 3 to 12 carbon atoms, such as in particular acrylonitrile and methacrylonitrile.

It should be noted that the styrene can be replaced in whole or in part by derivatives such as alphamethylstyrene or vinyltoluene.

The other ethylenically unsaturated monomers, which can be used alone or in mixtures, or copolymerizable with the above monomers are in particular:

- vinyl esters of carboxylic acid such as vinyl acetate, vinyl Versatate®, vinyl propionate,

- vinyl halides,

- ethylenic unsaturated mono- and dicarboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid and the mono-alkyl esters of dicarboxylic acids of the type mentioned with alkanois preferably having 1 to 4 carbon atoms and their N-substituted derivatives,

- the amides of unsaturated carboxylic acids such as acrylamide, methacrylamide, N-methylolacrylamide or methacrylamide, N-alkylacrylamides. ethylenic monomers comprising a sulfonic acid group and its alkali or ammonium salts, for example vinylsulfonic acid, vinylbenzene sulfonic acid, alpha-acrylamido methylpropane-sulfonic acid,

2-sulfoethylene methacrylate,

- amides of vinylamine, in particular vinylformamide or vinylacetamide, - unsaturated ethylenic monomers comprising a secondary, tertiary or quaternary amino group, or a heterocydic group containing nitrogen such as for example vinylpyridines, vinylimidazole, ( aminoalkyl meth) acrylates and aminoalkyl (meth) acrylamides such as dimethylaminoethyl acrylate or - methacrylate, ditertiobutylaminoethyl-acrylate or -methacrylate, dimethylamino methyl-acrylamide or -methacrylamide. It is likewise possible to use zwitterionic monomers such as, for example, sulfopropyl (dimethyl) aminopropyl acrylate. For the preparation of grafts based on polyvinylamines, the amides of vinylamine, for example vinylformamide or vinylacetamide, are preferably used as ethylenically unsaturated monomers. Then, the polymer obtained is hydrolyzed at acidic or basic pH.

For the preparation of grafts based on polyalcoholvinyl, vinyl esters of carboxylic acid, such as for example vinyl acetate, are preferably used as ethylenically unsaturated monomers. Then, the polymer obtained is hydrolyzed at acidic or basic pH.

Preferably, the monomer M2 is vinyl acetate.

The types and quantities of polymerizable monomers used according to the present invention vary depending on the particular final application for which the grafted polymer is intended. These variations are well known and can be easily determined by those skilled in the art.

The two polymerization stages can be carried out in bulk, in solution or in emulsion. Preferably, they are used as an emulsion. Preferably, the polymerization of the second step is carried out semi-continuously.

The temperature can vary between room temperature and 150 ° C depending on the nature of the monomers used.

The second step can take place in the presence of a solvent common to the monomers M2 and to the polymer resulting from the first step. It can also take place in the absence of solvent if the polymer from step 1 dissolves in the monomers M2.

The invention also relates to a process for the preparation of graft polymers, the grafts of which are multi-block polymers. This process consists in repeating at least once the implementation of step 2 of the polymerization process previously described using different monomers from the implementation of the previous step 2.

This step (2) can be repeated as many times as desired with new monomers to synthesize new blocks and obtain a polymer with multiblock grafts.

If we repeat step 2 once, we will obtain a polymer with diblock grafts, if we repeat it a second time, we will obtain a polymer with triblock grafts, and so after. In this way, at each new implementation, the product obtained is a block polymer having an additional polymer block.

According to this process for preparing graft polymers with multi-block grafts, when it is desired to obtain polymers with homogeneous blocks and not with a composition gradient, and if all the successive steps 2 are carried out in the same reactor, it is essential that all of the monomers used in one step have been consumed before the polymerization of the next step begins, therefore before the new monomers are introduced.

The method according to the invention has the advantage of allowing the control of the average molecular weights in number M _n of the grafts of the second polymerization step. Thus, these masses M _n are close to the theoretical values M _{n th} . M _{n th} being expressed by the following formula:

in which :

[M \ ₀ represents the initial molar concentration of monomer [P] o represents the initial concentration of precursor compound X represents the conversion of the monomer expressed as a percentage

M _Q represents the molar mass of the monomer (g / mol). The method according to the invention also has the advantage of leading to grafted polymers having a low degree of crosslinking.

Finally, the invention relates to the polymers capable of being obtained by the above process.

The invention relates more particularly to graft polymers for which the main chain is derived from the polymerization of methyl methacrylate and a compound of formula (I), (II) or (III) and the grafts are derived from the polymerization of vinyl acetate or styrene.

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

EXAMPLE 1 - SYNTHESIS OF A COMPOUND OF FORMULA (\)

Synthesis of 2 - ((2-bromopropionyl) oxy) ethyl methacrylate

2 g (0.015 mol) of 2-hydroxyethyl methacrylate are dissolved in 10 ml of dichloromethane. 2.5 ml of pyridine (0.03 mol) are then added. After cooling to 0 ° C., 1.8 ml (3.6 g, 0.033 mol) of bromopropionyl bromide are added dropwise. The mixture is stirred at this temperature for two hours. The product obtained is extracted with ether, washed with an HCl solution, then with a saline solution, and finally with water until a neutral pH is obtained. The product is dried over MgSO ₄ .

The crude reaction product is used as it is for the subsequent step (3.9 g, ie 96% yield).

Synthesis of 2 - ((0-ethylxanthylpropionyl) oxy) ethyl methacrylate

My 3.9 g of the preceding reaction crude is dissolved in 10 ml of acetone. 2.6 g (0.017 mol) of potassium salt of O-ethyl xanthic acid K ^{+ "} SCSOEt are added. The reaction mixture is stirred for 3 hours and checked by thin layer chromatography.

The product obtained is extracted with ether, washed with saline solution, then dried over MgSO4. The solvent is evaporated in vacuo and the product is purified by column chromatography (4 g or 88% yield).

EXAMPLES 2 SYNTHESIS OF STATISTICAL COPOLYMERS OF THE COMPOUND OF EXAMPLE 1 AND OF METHYL METHACRYLATE

Example 2.1

The following are introduced into a glass tube fitted with a magnetic stirrer: - 3.5 mg of azo-isobutyronitrile (AIBN) (2.14.10 ^"5 mol),

2 g of methyl methacrylate (MMA) (20 mmol), 1199,, 77 mmgg of co-combined of Example 1 (6.42 .10 ^"5 mol), and 2.15 ml of toluene.

The tube is connected to a vacuum manifold, immersed in liquid nitrogen. Three cycles are carried out "freezing / vacuum / return to ambient" on the contents of the tube in order to degas it. It is then vacuum sealed. After returning to ambient, they are immersed in an oil bath preheated to 60 ° C. After 4 hours, the tube is taken out of the oil bath and immersed in liquid nitrogen. The polymer is recovered after opening the tube and evaporation of the traces of residual monomer. After precipitation in hexane, the resulting copolymer is characterized by a UV trace at 290 nm, which shows the effective incorporation of the compound of Example 1 into the copolymer. The ¹ H NMR analysis of the copolymer confirms the presence of approximately 5 xanthate groups per polymer chain.

Gravimetric analysis gives a polymerization yield of 31%. The GPC analysis gives the following results:

- M _n = 147,400 g / mol,

- M _w / M _n = 2.4.

Example 2.2 The following are introduced into a glass tube fitted with a magnetic stirrer:

- 7 mg of azo-bis isobutyronitrile (AIBN) (4.28.10 ^"5 mol),

- 4 g of methyl methacrylate (MMA) (20 mmol),

- 7788,, 88 mmgg ddee ccoommppcosé of example 1 (1, 28 .10 ^"4 mol), and

- 4.3 ml of toluene.

The tube is degassed and sealed under vacuum as described in Example 2.1. After 3 hours, the tube is opened and the product is characterized after precipitation in hexane. The ¹ H NMR analysis confirms the presence of approximately 9 xanthate groups per polymer chain.

Gravimetric analysis gives a polymerization yield of 23.8%. Analysis by GPC gives the following results: - M _n = 137,600 g / mol, - M _w / M _n = 2.2.

EXAMPLES 3 - SYNTHESIS OF GRAFT COPOLYMERS FROM THE COPOLYMERS OF EXAMPLES 2

Example 3.1 Synthesis of a Polyvinyl Acetate Grafted Methyl Methacrylate Copolymer

The following are introduced into a glass tube fitted with a magnetic stirrer: 0.12 mg of azo-bis isobutyronitrile (AIBN) (7.4.10 ^"6 mol),

0.35 g of vinyl acetate (4 mmol), - 1.2 g of the copolymer of Example 2.1. (8.1 .10 ^{~ 6} mol), and

- 2 ml of ethyl acetate.

After 7 hours at 60 ° C, the reaction is stopped and the tube is opened. After evaporation of the solvent and of the residual monomer, the polymer is characterized.

Gravimetric analysis gives a polymerization yield of 28.5%. Analysis by GPC gives the following results: - M _n = 153,000 g / mol,

- M _w / M _n = 2.5.

The polymer obtained at the end of this second step is filtered: no solid part is retained, which proves the absence of an insoluble fraction and therefore the absence of crosslinking.

In addition, the superimposition of the RI and UV chromatograms of the polymer obtained showed the preponderance of the grafting reaction.

Example 3.2 Synthesis of a Polyvinyl Acetate Grafted Methyl Methacrylate Copolymer

A tube is prepared under the same initial concentration conditions as in Example 3.1, except that the copolymer of Example 2.1 is replaced. with the copolymer of Example 2.2. The tube is degassed, sealed, and then heated to 60 ° C for 20 h.

After evaporation of the solvent and of the residual monomer, the polymer is characterized. Gravimetric analysis gives a polymerization yield of 69.1%.

Analysis by GPC gives the following results: - M _n = 162,000 g / mol,

- M _w / M _n = 2.4.

Example 3.3 Synthesis of a Polystyrene-Grafted Methyl Methacrylate-Based Copolymer

The following are introduced into a glass tube fitted with a magnetic stirrer:

- 0.424 g of styrene (4 mmol),

- 1.2 g of the copolymer of Example 2.1 (8.1. 10 ^"6 mol), and - 2 ml of toluene.

After 5:30 at 110 ° C, the reaction is stopped and the tube is opened. After evaporation of the solvent and of the residual monomer, the polymer is characterized. Gravimetric analysis gives a polymerization yield of 21%. Analysis by GPC gives the following results: - M _n = 148,000 g / mol,

- M _w / M _n = 2.5.

The following are introduced into a glass tube fitted with a magnetic stirrer:

- 0.545 g of styrene (5.23 mmol), - 1 g of the copolymer of Example 2.2 (7.2. 10 ^"6 mol), and

- 2 ml of toluene.

After 25 hours at 110 ° C., the reaction is stopped and the tube is opened. After evaporation of the solvent and of the residual monomer, the polymer is characterized. Gravimetric analysis gives a polymerization yield of 49%.

Analysis by GPC gives the following results: - M _n = 162,000 g / mol, and

- M _w / M _n = 2.3.

Claims

1. Process for the preparation of graft polymers, in which the following steps are implemented: 1. contact is made:

• at least one source of free radicals,

• at least one compound of formula (I), (II) or (III):

in which :

- T and T 'represent divalent groups, - R ¹ and R ² represent:

. an (i) alkyl, acyl, aryl, alken or alkyne group, or

. a (ii) carbon cycle, saturated or not, optionally aromatic, or

. a heterocycle (iii), saturated or unsaturated, these groups and rings (i), (ii) and (iii) possibly being substituted by alkyl groups, substituted phenyl groups, substituted aromatic groups or groups

: oxo, alkoxycarbonyl or aryloxycarbonyl (-COOR), carboxy (-COOH), acyloxy (-O ₂ CR), carbamoyl (-CONR ₂ ), cyano (-CN), alkylcarbonyl, alkylarylcarbonyl, arylcarbonyl, arylalkylcarbonyl, isocyanate, phthalimido, maleïmido, succinimido, amidino, guanidimo, hydroxy (-OH), amino (-NR ₂ ), halogen, allyl, epoxy, aikoxy (-OR), S-alkyl, S-aryl, silyl, hydrophilic groups or ionic such as the alkali metal salts of carboxylic acids, the alkali metal salts of sulfonic acid, the polyalkylene oxide chains (POE, POP), the cationic substituents (quaternary ammonium salts), R representing an alkyl or aryl group, . a polymer chain, - p represents an integer between 2 and 200,

At least one monomer M1 chosen from ethylenically unsaturated monomers 1, 1 disubstituted which can be polymerized by the radical route,

2. then, the polymer resulting from the polymerization of step 1 is brought into contact with: ^“ at least one source of free radicals, and

• one or more ethylenically unsaturated monomer M2, the proportion of ethylenically unsaturated monomers 1, 1 disubstituted polymerizable by the radical route being at most 90% by weight relative to the totality of the monomers M2.

2. Method according to claim 1, characterized in that the polymerization implements a compound of formula (I), (II) or (III) in which:

- T represents a carbonyl group (-C (O) O- or -C (O) OC _n H ₂ n- with n between 1 and 20), phenylene (C ₆ H ₄ or C ₆ H ₄ C _n H2n with n between 1 and 20), acyloxy (-OC (O) - or -OC (O) C _n H _2n - with n between 1 and 20), alkylene or acrylamido (-C (O) NH), - T 'represents an aryl, phenyl, alkyl, cycloalkyl, aralkyl, -CO R group with R aryl or cycoalkyl.

3. Method according to claim 1 or 2, characterized in that the compounds of formula (I) and (III) bear at least one group R-i substituted by at least one atom of fluorine, chromium and / or bromine.

4. Method according to any one of the preceding claims, characterized in that the polymerization implements a compound of formula (I).

5. Method according to any one of the preceding claims, characterized in that the ethylenically unsaturated monomers M1 1, 1 disubstituted are chosen from: (meth) acrylic esters, methacryiamides, alphamethylstyrenes and their derivatives, ethers and esters d isopropenyl.

6. Method according to any one of the preceding claims, characterized in that the ethylenically unsaturated M2 monomers are chosen from: styrene or its derivatives, butadiene, chloroprene, methacrylic esters and vinyl nitriles.

7. Method according to any one of the preceding claims, characterized in that during step 1, the weight ratio of the compound of formula (I), (II) or (III) relative to the monomers M1 is not more than 10/90.

8. Process for the preparation of grafted polymers, the grafts of which are multi-block polymers, in which the method according to one of the preceding claims is implemented and the implementation of step 2 is repeated at least once using monomers different from the implementation of step 2 above.

9. grafted polymer capable of being obtained by the process according to the preceding claims.

10. Polymer according to claim 9, characterized in that it has a main chain resulting from the polymerization of methyl methacrylate and grafts resulting from the polymerization of vinyl acetate or styrene.