EP1080163A1

EP1080163A1 - Composition and method for radical polymerisation of ethylenically unsaturated monomers

Info

Publication number: EP1080163A1
Application number: EP99915835A
Authority: EP
Inventors: Françoise LARTIGUE-PEYROU
Original assignee: Rhodia Chimie SAS
Current assignee: Rhodia Chimie SAS
Priority date: 1998-04-28
Filing date: 1999-04-26
Publication date: 2001-03-07
Also published as: FR2777884A1; AU3427599A; JP2002513034A; WO1999055797A1; FR2777884B1

Abstract

The invention concerns a composition for preventing radical polymerisation of ethylenically unsaturated monomers characterised in that it comprises at least a benzenetriamine derivative corresponding to general formula (I) wherein: the radicals R1, identical or different, represent a hydrogen atom and an electron donor group; the n's, identical or different represent a number equal to 0, 1 to 5.

Description

1

COMPOSITION AND METHOD FOR INHIBITING RADICAL POLYMERIZATION OF ETHYLENICALLY UNSATURATED MONOMERS.

The subject of the present invention is a composition which can be used as an inhibitor of the radical polymerization of ethylenically unsaturated monomers and a process intended to prevent the radical polymerization of such unsaturated monomers during their industrial preparation. It relates more particularly to vinyl aromatic monomers.

Ethylene unsaturated monomers are prone to spontaneously polymerize under the action of heat. However, premature polymerization must be avoided during the manufacture, purification and storage of said monomers. During manufacture or purification, early polymerization is detrimental since it causes a drop in production yields and fouling of the installations often making temporary cessation of production for maintenance reasons hence an additional cost of the production. Due to the exothermicity of the polymerization reaction, explosions and fires are also to be feared. The distillation of certain ethylenically unsaturated monomers is particularly problematic when it requires the use of high temperatures: this is particularly the case for the distillation of vinyl aromatic derivatives such as styrene, methylstyrene and other vinylbenzenes.

In order to prevent the polymerization of ethylenically unsaturated monomers, it is known in the art to add one or more polymerization inhibitors or retarders, either preventively during manufacture, or even directly to said monomers before their use.

Thus, for the inhibition of the polymerization of styrene during its manufacture, the industry commonly uses 2,4-dinitrophenol, 4,6-dinitro-o-cresol (DNOC), 2,6-dinitro-p -cresol (DNPC) [US 4,105,506] or 2,4-dinitro-6-sec-butylphenol (DNBP). US Pat. No. 4,466,905 shows that 2,6-dinitro-p-cresol associations with p-phenylenediamine compounds or with tert-butylcatechol are very effective in limiting the polymerization of styrene if a minimum of oxygen is present. . In JP 63 316745, it is indicated the possibility of using 2-methyl-4-nitrosophenol in combination with 2,6-dinitro-p-cresol.

In general, the nitrophenolic inhibitors of the state of the art are relatively toxic and are not always very stable. The object of the invention is to provide a composition intended to prevent premature polymerization of ethylenically unsaturated monomers during the production of said monomers.

The subject of the present invention is therefore a composition intended to prevent the radical polymerization of ethylenically unsaturated monomers, characterized in that it comprises at least one benzenetriamine derivative corresponding to the general formula (I):

/ ^ - 7 X ^R n

NH

(Rι>, nfc <fc H NH (R) n

^ ^ (I) in said formula (I):

- the identical or different radicals R _{1 f} represent a hydrogen atom or an electron-donor group, - the n, identical or different represent a number equal to 0.1 to 5. A variant of the invention consists in associating the benzenetriamine derivative of the invention with one or more vehicles compatible with said monomer and with each of the constituents of the composition.

Another variant of the invention is to combine it with another polymerization inhibitor.

The composition of the invention involves a compound corresponding to formula (I) in which the radical (s) R-i represent an electron donor group.

In the present text, the term “electro-donor group” is understood to mean a group as defined by H.C. BROWN in the work of Jerry MARCH - Advanced Organic Chemistry, chapter 9, pages 243 and 244 (1985).

As examples of preferred electron donor groups R- ₎ , there may be mentioned: an alkyl radical, linear or branched, having from 1 to 6 carbon atoms, preferably from 1 to 4 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, . a linear or branched alkenyl radical having from 2 to 6 carbon atoms ^* , preferably from 2 to 4 carbon atoms, such as vinyl, allyl,. a linear or branched alkoxy or thioether radical having from 1 to 6 carbon atoms, preferably from 1 to 4 carbon atoms such as the methoxy, ethoxy, propoxy, isopropoxy, butoxy radicals, an alkenyloxy radical, preferably an allyloxy radical or a phenoxy radical,. a radical of formula:

-R ₂ -OH -R ₂ -SH -R ₂ -N- (R ₃ ) ₂ in said formulas, R ₂ represents a valence bond or a divalent hydrocarbon radical, linear or branched, saturated or unsaturated, having from 1 to 6 carbon atoms such as, for example, methylene, ethylene, propylene, isopropylene, isopropylidene; the radicals R ₃ , which are identical or different, represent a hydrogen atom or a linear or branched alkyl radical having from 1 to 6 carbon atoms,

In formula (I), n is a number preferably less than or equal to 4, preferably equal to 1 or 2.

The invention does not exclude that the three benzene rings carry radicals R- | of different nature and that their number n is different.

Among the benzenetriamine derivatives of formula (I), some are particularly preferred and in particular those corresponding to formula (la):

R ₄

NH

HN NK

^R4 % a) in said formula (la): 4

- the radicals R ₄ , which are identical or different, represent a hydroxyl group, or a linear or branched alkyl or alkoxy radical having from 1 to 4 carbon atoms.

Among the compounds of formula (la), preference is given to those which correspond to formula (I) in which R ₁ represents a hydroxy group or a methoxy group or a methyl group.

The N, N ', N "-tri (p-methoxyphenyl) -1, 3,5-benzenetriamine and N, N', N" -tri (p-methylphenyl) -1, 3,5-benzenetriamine are preferably chosen.

It is also possible to use a mixture of benzenetriamine derivatives.

Thus, the compositions of the invention comprising at least one benzenetriamine derivative of formula (la) constitute a particularly preferred embodiment of the invention.

Certain benzenetriamine derivatives of formula (I) are commercial. The others are easily prepared by a person skilled in the art from commercial products.

The compositions of the invention are suitable for the stabilization of any monomer having at least one ethylenic unsaturation. The ethylenically unsaturated monomers more specifically include the aromatic ethylenically unsaturated monomers such as styrene, α-methylstyrene, divinylbenzene, vinyltoluene, vinylnaphthalene, styrenesulfonic acids, etc.

Ethylene unsaturated monomers also include olefinic monomers comprising one or two unsaturations such as isoprene and butadiene; halogenated unsaturated monomers of the type of vinyl chloride, chloroprene, vinylidene chloride, vinylidene fluoride and vinyl fluoride; unsaturated acids such as acrylic acid, methacrylic acid and crotonic acid; unsaturated esters in particular the unsaturated esters of acrylic acid of the methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, hydroxypropyl acrylate; unsaturated esters of methacrylic acid such as methyl methacrylate, butyl methacrylate, lauryl methacrylate, dimethylaminoethyl methacrylate, stearyl methacrylate; vinyl acetate; unsaturated resins such as, for example, acrylated epoxy resins and polyethylene glycol diacrylate; unsaturated amides such as acrylamide, N, N-dimethylacrylamide, methylenebisacrylamide and N-vinylpyrrolidone; unsaturated nitriles of the type of 5 acrylonitrile; unsaturated ethers such as vinyl ether; vinylpyridines; diethyl vinylphosphonate and sodium styrenesulfonate. It should be understood that this list is by no means exhaustive, the invention generally relating to the stabilization of any type of ethylenically unsaturated aliphatic monomer.

However, the compositions of the invention are particularly effective in the case of the stabilization of aromatic ethylenically unsaturated monomers, in particular vinyl aromatic monomers such as styrene, α-methylstyrene, divinylbenzene, vinyltoluene, styrenesulfonic acids.

The invention preferably applies to styrene.

The compositions of the invention form either true solutions, that is to say that they consist of perfectly miscible ingredients, or emulsions, or else suspensions. According to a preferred embodiment, however, the compositions are in the form of true solutions.

The presence in the composition of one or more vehicles is optional. It may prove to be necessary, however, when the solubility of the benzenetriamine derivatives of the composition in the monomer to be stabilized is low, or even insufficient. In this case, in fact, it is preferable to incorporate into the composition one or more vehicles compatible on the one hand with the monomer to be stabilized, and on the other hand with each of the other constituents of the composition. By "compatible" is meant according to the invention a vehicle which is chemically inert with respect to the various ingredients of the composition and of the monomer. The nature of the vehicle therefore depends on the various constituents present as well as on the very nature of the monomer.

When the monomer is a vinyl aromatic derivative, particularly suitable vehicles are benzene, toluene, xylene, ethylbenzene, styrene, acetophenone, methylphenylcarbinol or mixtures of these solvents. In this case, it is preferred to use ethylbenzene.

Depending on the nature of the monomer, a person skilled in the art will easily determine the combination of the benzenetriamine derivative and of solvents leading to the best results.

According to the invention, it is possible to combine the benzenetriamine derivative with other conventionally used components such as polymerization retarders or other polymerization inhibitors. The choice of these is easily determined by the skilled person. It depends on the nature of the polymer. Examples are given below, but they are in no way limiting.

In the case of an aromatic unsaturated aromatic monomer, the compositions of the invention advantageously contain one or more nitroaromatic derivatives. Such compounds are known in the art as a polymerization retarder. It is also known to combine them with polymerization inhibitors. Note that the polymerization inhibitor prevents polymerization until a certain time beyond which the polymerization reaction starts normally. This time is the induction time. The longer the induction time, the more effective the inhibition. The role of the self-timer is different. It does not prevent polymerization but slows down the kinetics of polymerization. A more or less significant synergy is observed by association of an inhibitor and a retarder. Thus, the compositions of the invention containing at least one polymerization retarder and at least one polymerization inhibitor form a preferred subject of the invention.

The nitroaromatic derivative is advantageously chosen from 1, 3-dinitrobenzene, 1, 4-dinitrobenzene, 2,6-dinitro-4-methylphenol, 2-nitro-4-methylphenol, 2,4-dinitro-1-naphthol, 2, 4,6-trinitrophenol (picric acid), 2,4-dinitro-6-methylphenol, 2,4-dinitrochlorobenzene, 2,4-dinitrophenol, 2,4-dinitro-6- sec-butylphenol, 4-cyano-2- nitrophenol, and 3-iodo-4-cyano-5-nitrophenol.

It is preferred to use 2,6-dinitro-4-methylphenol, 2,4-dinitro-6-methylphenol, 2,4-dinitrophenol and 2,4-dinitro-6-sec-butylphenol, 2,4-dinitro-6 - sec-butylphenol being particularly advantageous. The nitroaromatic derivatives are added to the composition so that the ratio of the total mass of the benzenetriamine type constituents of formula (I) to the total mass of the nitroaromatic type constituents is between 90/10 and 10/90, preferably between 80/20 and 20/80, better still between 60/40 and 40/60. This weight ratio is calculated by making the ratio of the total amount (by weight) of the benzenetriamine derivatives of formula (I) present in the composition to the total amount (by weight) of the nitroaromatic derivatives of the composition.

According to a variant of the invention, the compositions of the invention may contain other polymerization inhibitors such as alkylated phenols such as tert-butyl-catechol, 2,5-di-tert-octylhydroquinone, 3,5 -di-tert- octylcatechol; nitroxide compounds such as 2,2,6,6-tetramethylpiperidine-N-oxyl, 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl, 4-oxo-2,2,6 , 6-tetramethylpiperidine-N-oxyl; 4-amino-2,2,6,6- 7 tetramethylpiperidine-N-oxyl; imidazolidines / imidazolines-N-oxyl as described in FR 97/04230, preferably 2,2,3,4,5,5-hexamethylimidazolidine-1-oxyl or any other inhibitor known in the art provided that these- these are compatible with the other ingredients of the composition under the operating conditions to which the monomer to be stabilized is subjected.

In the case of an ethylenically unsaturated aliphatic monomer, it is also possible to use other inhibitors such as hydroquinone, p-methoxyphenol, phenothiazines, Le or conventional inhibitors of polymerization are added to the composition. so that the ratio of the total mass of the benzenetriamine-type constituents of formula (I) to the total mass of the other inhibitors is between 90/10 and 10/90, preferably between 80/20 and 20/80, better still between 60/40 and 40/60. The compositions of the invention are easily prepared by mixing the various constituents in the vehicle chosen.

The subject of the invention is also a process for preventing the radical polymerization of an ethylenically unsaturated monomer, preferably a vinyl aromatic monomer. This method comprises, for example, adding to said monomer, an effective amount of a composition of the invention as defined above.

The amount of benzenetriamine derivative to be added to achieve effective polymerization inhibition varies widely. It is a function of the monomer to be stabilized and of the operating conditions to which this monomer is subjected. It is clear that at high temperatures, the amount of inhibitor will be greater. The process of the invention is in fact applicable for the stabilization of the monomer, during manufacture and purification. However, it is not uncommon for the purification to be carried out by distillation of the monomer, the temperature at the reboiler being able to exceed 120 ° C.

Thus, the ideal amount of inhibitor should be assessed on a case-by-case basis. Anyway, by way of indication, a total quantity of benzenetriamine derivative of between 1 and 2000 ppm, preferably between 5 and 1000 ppm is generally sufficient, this quantity being expressed relative to the total weight of the monomer to be stabilized.

As indicated above, it is desirable to add to the ethylenically unsaturated aromatic monomer an effective amount of one or more nitroaromatic derivatives as a polymerization retarder. As 8 preferred retarder, mention may again be made of 2,6-dinitro-4-methylphenol, 2,4-dinitro-6-methylphenol, and 2,4-dinitrophenol, but above all 2,4-dinitro-6-sec- butylphenol.

The proportion of the nitroaromatic type retarder (s) is preferably such that the ratio of the total mass of benzenetriamine type constituents of formula (I) to the total mass of the nitroaromatic type constituents is between 90/10 and 10/90, better still between 80/20 and 20/80. This weight ratio is calculated by making the ratio of the total amount (by weight) of the benzenetriamine derivatives of formula (I) present in the composition to the total amount (by weight) of the nitroaromatic derivatives of the composition.

As indicated above, it is possible to add to the monomer one or more known polymerization inhibitors.

The proportion of the polymerization inhibitor (s) is preferably such that the ratio of the total mass of constituents of the benzenetriamine derivative type of formula (I) to the total mass of the other inhibitors is between 90/10 and 10/90, better still between 80/20 and 20/80.

The benzenetriamine derivative according to the invention, optionally combined with a nitroaromatic derivative or other conventional polymerization inhibitors can be added to the monomer in a completely conventional manner. The point of introduction, in the case of a distillation, is very variable: we can consider adding each of these compounds at the heat exchanger, pipes, pumps, reboilers, compressors or more usually containers. It should be understood that the addition can be carried out continuously or else repeated over time at one or different particular sites.

According to the invention, it is possible to envisage the simultaneous or separate addition of the inhibitor of the invention and / or the retarder and / or the other inhibitor. The process of the invention is particularly advantageous in terms of the effectiveness of inhibiting radical polymerization of vinyl aromatic monomers.

The following examples are given by way of illustration and relate to preferred embodiments of the invention. EXAMPLES OF APPLICATION ON AROMATIC VINYL MONOMERS *.

Example 1 Comparative example 1a

In order to evaluate the inhibition properties of the products of the invention with reference to the radical polymerization of vinyl monomers, inhibition tests with styrene were undertaken with the following operating protocol. Before each test, the styrene used (sold by the company Merck) is previously destabilized by passage over an activated alumina column (obtained from the company Procatalyse) in order to completely eliminate the tert-butylcatechol initially present at a rate of 15- 20 ppm.

The resulting styrene (10 ml) is placed in a test tube and the appropriate amount of inhibitor is then added.

Argon is introduced into the liquid phase of the reactor by bubbling (5 min) as well as into the sky of the reactor by bubbling (5 min).

The tube set closed and placed in an oil bath thermostatically controlled at 100 ° C for 2 hours. The level of polymer formed after 2 hours is determined by the methanol precipitation method.

To this end, a cooled sample of 10 ml of styrene is transferred to a glass flask containing approximately 50 ml of methanol, in order to precipitate the polystyrene formed which is insoluble in methanol. The precipitate is then filtered on a miiiipore filter and then the residue is dried in an oven at 40 ° C, before being weighed.

The test results are summarized in Table (I).

Table (I)

Ref. Inhibitor Content relative to Polymer content ex. styrene (ppm) formed (%)

1 a without inhibitor 0 5.72

1 N, N ', N "-tri (p-methoxyphenyl) -1, 3.5- 100 0 benzenetriamine

The results show that the benzenetriamine derivatives are excellent inhibitors of the polymerization of styrene. 10

EXAMPLES OF APPLICATION ON UNSATURATED ALIPHATIC MONOMERS.

In order to evaluate the inhibition properties of the products of the invention, with respect to the radical polymerization of the unsaturated aliphatic monomers, inhibition tests with methyl methacrylate were undertaken with the following operating protocol.

The effectiveness of an inhibitor according to the invention (or of a mixture of inhibitors comprising at least one inhibitor according to the invention) for methyl methacrylate is determined by measuring the induction time which represents the time to end of which the monomer begins to polymerize when it is heated in a temperature-controlled bath and in the presence of an initiator. This time is determined by a slight exothermicity of the sample studied.

The measurements are carried out in a laboratory calorimeter, the time and temperature parameters are recorded and converted on a microcomputer.

The tests were carried out with methyl methacrylate (MMA) previously destabilized by passage over an activated alumina column in order to completely eliminate the p-methoxyphenol (initial stabilizer) from the medium. 20 ml of MMA, stabilized with 20 ppm of inhibitor to be tested, then 100 ppm of azobisisobutyronitrile initiator (AIBN) are introduced into a test tube. The tube is immersed in a bath thermostatically controlled at 80 ° C. and the temperature difference between this sample and a reference tube containing silicone oil is recorded continuously. The induction time Ti corresponds to the visible exotherm which indicates the start of the polymerization of MMA. The curve T as a function of time is recorded continuously. The longer the induction time, the more effective the inhibitor tested at constant weight concentration.

The following table (II) indicates the induction time values of some "classic" inhibitors of the (meth) acrylates industry

Table (II)

Inhibitors Induction time Ti (min) phenothiazine (PTZ) 26 hydroquinone (HQ) 55

Examples 2 and 3

For each polymerization inhibitor, the operating procedure given above is repeated. 11

Table (III) summarizes the results obtained on the induction time for various inhibitors of the invention

Table (III)

Ref. Polymerization inhibitors Induction time ex. Ti (min) of MMA

2 N, N ', N "-tri (p-methylphenyl) -1, 3,5-70 benzenetriamine

3 N, N ', N "-tri (p-methoxyphenyl) -1, 3.5-53

benzenetriamine

The induction time values are better or equivalent to hydroquinone which is currently one of the best industrial inhibitors for the (meth) acrylates industry.

Example 4 In this example, the association of N, N ', N "-tri (p-methoxyphenyl) - is described.

1, 3,5-benzenetriamine of the invention with another inhibitor:

In the test, use is made of: 20 ml of MMA + 100 ppm of AIBN + mixture of inhibitors: 10 ppm of hydroquinone (HQ) + 10 ppm of inhibitor of the invention. Table (IV) summarizes the results obtained on the induction time for the mixture of inhibitors of the invention

Table (IV)

Ref. Time inhibitor e.g. induction

Ti (min) of MMA

4 HQ + N, N ', N "-tri (p-methoxyphenyl) -1, 3.5-65 benzenetriamine

Claims

12 CLAIMS

1. Composition intended to prevent the radical polymerization of ethylenically unsaturated monomers, characterized in that it comprises at least one benzenetriamine derivative corresponding to the general formula (I):

- (Rι) _

NH

^ (0 in said formula (I):

- the radicals R-j, which are identical or different, represent a hydrogen atom or an electron-donor group, - the n, which are identical or different, represent a number equal to 0.1 to 5.

2. Composition according to claim 1 characterized in that the benzenetriamine derivative corresponds to formula (I) in which n is a number less than or equal to 4, preferably equal to 1 or 2.

3. Composition according to Claim 1, characterized in that the benzenetriamine derivative corresponds to formula (I) in which R- represents:

. an alkyl radical, linear or branched, having from 1 to 6 carbon atoms, preferably from 1 to 4 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl,

. a linear or branched alkenyl radical having from 2 to 6 carbon atoms, preferably from 2 to 4 carbon atoms, such as vinyl, allyl,. a linear or branched alkoxy or thioether radical having from 1 to 6 carbon atoms, preferably from 1 to 4 carbon atoms such as the methoxy, ethoxy, propoxy, isopropoxy, butoxy radicals, an alkenyloxy radical, preferably an allyloxy radical or a phenoxy radical,. a radical of formula:

-R ₂ -OH -R ₂ -SH -R ₂ -N- (R ₃ ) ₂ 13 in said formulas, R ₂ represents a valence bond ^* or a divalent hydrocarbon radical, linear or branched, saturated or unsaturated, having from 1 to 6 carbon atoms such as, for example, methylene, ethylene, propylene, isopropylene, isopropylidene; the radicals R ₃ , which are identical or different, represent a hydrogen atom or a linear or branched alkyl radical having from 1 to 6 carbon atoms,

4. Composition according to claim 1 characterized in that the benzenetriamine derivative corresponds to formula (la):

R_

NH

^R * (la) in said formula (la):

5 Composition according to claim 1 characterized in that the benzenetriamine derivative is N, N ', N "-tri (p-methoxyphenyl) -1, 3,5-benzenetriamine and N, N', N" -tri (p-methylphenyl) -1,3,5-benzenetriamine.

6. Composition according to one of claims 1 to 5 characterized in that it comprises, as vehicle, one or more solvents chosen from benzene, toluene, xylene, ethylbenzene, styrene, acetophenone and methylphenylcarbinol.

7. Composition according to one of claims 1 to 6 characterized in that it comprises, in the case of an aromatic monomer with ethylenic unsaturation, in addition at least one nitroaromatic derivative. 14

8. Composition according to claim 7 characterized in that the nitroaromatic derivative is chosen from 2,6-dinitro-4-methylphenol, 2,4-dinitro-6-methylphenol, 2,4-dinitrophenol, 2,4 -dinitro-6-sec-butylphenol and 2-nitro-4-methylphenol, the nitroaromatic derivative preferably being 2,4-dinitro-6-sec-butylphenol.

9. Composition according to one of claims 7 and 8 characterized in that the ratio of the total mass of the constituents derived from benzenetriamine of formula (I) to the total mass of the constituents of type nitroaromatic derivative is between 90/10 and 10 / 90, preferably between 80/20 and 20/80.

10. Composition according to one of claims 1 to 9 characterized in that it further comprises another polymerization inhibitor.

11. Composition according to Claim 10, characterized in that the polymerization inhibitor is chosen from alkylated phenols such as tert-butyl-catechol, 2,5-di-tert-octylhydroquinone, 3,5-di-tert -octylcatechol; nitroxide compounds such as 2,2,6,6-tetramethylpiperidine-N-oxyl, 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl, 4-oxo-2,2,6 , 6-tetramethylpiperidine-N-oxyl; 4-amino-2,2,6,6-tetramethylpiperidine-N-oxyl; imidazolidines / imidazolines-N-oxyl, preferably 2,2,3,4,5,5-hexamethylimidazolidine-1-oxyl or any other known inhibitor.

12. Composition according to claim 10 characterized in that the polymerization inhibitor is hydroquinone; p-methoxyphenol; phenothiazines, in the case of an ethylenically unsaturated aliphatic monomer.

13. Composition according to one of claims 10 to 12 characterized in that the amount of polymerization inhibitor is such that the ratio of the total mass of constituents of benzenetriamine derivative type of formula (I) to the total mass of the others inhibitors is between 90/10 and 10/90, preferably between 80/20 and 20/80.

14. A process intended to prevent the radical polymerization of an ethylenically unsaturated monomer, comprising the addition to said monomer of an effective amount of at least one benzenetriamine derivative corresponding to the general formula (I): 15

^ ^

NH

K _^ R- ^R I) _Π

^" ^^ 7" ^~ )

^^ _(|) in said formula (I):

- the radicals R- _] , identical or different, represent a hydrogen atom or an electron-donor group, - the n, identical or different, represent a number equal to 0.1 to 5.

15. The method of claim 14 characterized in that the benzenetriamine derivative corresponds to formula (I) in which n is a number less than or equal to 4, preferably equal to 1 or 2.

16. Method according to one of claims 14 and 15 characterized in that the benzenetriamine derivative corresponds to formula (I) in which R-i represents:

. an alkyl radical, linear or branched, having from 1 to 6 carbon atoms, preferably from 1 to 4 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl,. a linear or branched alkenyl radical having from 2 to 6 carbon atoms, preferably from 2 to 4 carbon atoms, such as vinyl, allyl,. a linear or branched alkoxy or thioether radical having from 1 to 6 carbon atoms, preferably from 1 to 4 carbon atoms such as the methoxy, ethoxy, propoxy, isopropoxy, butoxy radicals, an alkenyloxy radical, preferably an allyloxy radical or a phenoxy radical,. a radical of formula:

-R ₂ -OH -R ₂ -SH

-R ₂ -N- (R ₃ ) ₂ in said formulas, R ₂ represents a valential bond or a divalent hydrocarbon radical, linear or branched, saturated or unsaturated, having from 1 to 6 carbon atoms such as, for example, methylene , ethylene, propylene, isopropylene, isopropylidene; the radicals R ₃ , identical or different 16 represent a hydrogen atom or a linear or branched alkyl radical having from 1 to 6 carbon atoms,

17. Method according to claim 14 characterized in that the benzenetriamine derivative corresponds to formula (la):

R_

NH

HN NH

^{R4 R4} (la) in said formula (la):

- the radicals R, which are identical or different, represent a hydroxyl group, or a linear or branched alkyl or alkoxy radical having from 1 to 4 carbon atoms.

18. Method according to one of claims 14 to 17 characterized in that the total amount of benzenetriamine derivative of formula (I) added, is between 1 and 2000 ppm, preferably between 5 and 1000 ppm relative to the weight total of said monomer.

19. Method according to one of claims 14 to 18 characterized in that the amount of derivative of nitroaromatic type is such that the ratio of the mass of the benzenetriamine type derivatives of formula (I) to the total mass of the type constituents nitroaromatic is between 90/10 and 10/90, preferably 80/20 and 20/80.

20. Method according to one of claims 14 to 19 characterized in that the amount of polymerization inhibitor is such that the ratio of the mass of the benzenetriamine type derivatives of formula (I) to the total mass of the other inhibitors is between 90/10 and 10/90, preferably between 80/20 and 20/80. 17

21. Method according to one of claims 14 to 20 characterized in that said ethylenically unsaturated monomer is a vinylaromatic monomer, preferably chosen from styrene, α-methylstyrene, vinyltoluene, divinylbenzene and styrenesulfonic acids.

22. Method according to one of claims 14 to 20 characterized in that the said ethylenically unsaturated aliphatic monomer is chosen from olefinic monomers comprising one or two unsaturations; halogenated unsaturated monomers; unsaturated acids; unsaturated esters; unsaturated resins; unsaturated amides; unsaturated nitriles; unsaturated ethers.

23. The method of claim 22 characterized in that said ethylenically unsaturated aliphatic monomer is chosen from isoprene and butadiene; vinyl chloride, chloroprene, vinylidene chloride, vinylidene fluoride and vinyl fluoride; acrylic acid, methacrylic acid and crotonic acid; unsaturated esters of acrylic acid of the methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, hydroxypropyl acrylate; unsaturated esters of methacrylic acid such as methyl methacrylate, butyl methacrylate, lauryl methacrylate, dimethylaminoethyl methacrylate, stearyl methacrylate; vinyl acetate; acrylated epoxy resins and polyethylene glycol diacrylate; acrylamide, N, N-dimethylacrylamide, methylenebisacrylamide and N-vinylpyrrolidone; acrylonitrile; vinyl ether; vinylpyridines; diethyl vinylphosphonate and sodium styrenesulfonate.

24. The method of claim 23 characterized in that said aliphatic monomers are the esters of acrylic acid and methacrylic acid.