WO2002051962A1

WO2002051962A1 - Use of a composition based on a diphenylamine derivative for inhibiting free radical polymerisation of ethylenically unsaturated aromatic monomers

Info

Publication number: WO2002051962A1
Application number: PCT/FR2001/004109
Authority: WO
Inventors: Françoise LARTIGUE-PEYROU
Original assignee: Rhodia Chimie
Priority date: 2000-12-22
Filing date: 2001-12-20
Publication date: 2002-07-04
Also published as: FR2818656A1

Abstract

The invention concerns the use for inhibiting free radical polymerisation of ethylenically unsaturated aromatic monomers of a composition comprising at least a diphenylamine derivative of general formula (I), wherein: A and B represent the radical of a cycle forming all or part of a carbocyclic, aromatic, monocyclic or polycyclic system; R1 and R2, identical or different, represent a hydrogen atom or one or several substituents; n and m represent the number of substituents on the cycle.

Description

USE OF A COMPOSITION BASED ON A DERIVATIVE OF

DIPHENYLAMINE FOR INHIBITING RADICAL POLYMERIZATION OF

AROMATIC MONOMERS WITH ETHYLENIC UNSATURATION.

The subject of the present invention is the use of a composition based on a diphenylamine derivative as an inhibitor of the radical polymerization of aromatic monomers containing ethylenic unsaturation.

The invention also relates to the process intended to inhibit the radical polymerization of such unsaturated aromatic monomers during their industrial preparation.

Ethylenically unsaturated aromatic 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 it necessary to temporarily stop production for reasons of maintenance, 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 vinyl aromatic monomers is particularly problematic when it requires the use of high temperatures: this is particularly the case of the distillation of vinyl aromatic derivatives such as styrene, α-methylstyrene and other vinylbenzenes. In order to inhibit the polymerization of vinyl aromatic 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 Patent 4,466,905 demonstrates 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.

FR-A 2787444 describes a polymerization inhibiting composition based on a diphenylamine derivative such as a mono- or dihydroxydiphenylamine. However, this composition is intended to prevent the radical polymerization of ethylenically unsaturated aliphatic monomers such as olefinic monomers such as isoprene, butadiene, vinyl chloride, acrylic derivatives, etc.

It has now been found that it is possible to use a diphenylamine derivative to inhibit the polymerization of ethylenically unsaturated aromatic monomers.

More specifically, the subject of the invention is the use to prevent the radical polymerization of aromatic ethylenically unsaturated monomers of a composition comprising at least one diphenylamine derivative corresponding to the general formula (I):

in said formula (I):

- A and B symbolize the rest of a cycle forming all or part of a carbocyclic, aromatic, monocyclic or polycyclic system,

- R and R ₂ , identical or different, represent a hydrogen atom or one or more substituents,

- n and m represent the number of substituents on the cycle.

A variant of the invention consists in associating the diphenylamine 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.

It has surprisingly been found that the same type of inhibitors can also be used to inhibit unsaturated aromatic monomers such as styrene and the like.

It should be noted that it is not at all obvious to a person skilled in the art that an inhibitor used in the field of the inhibition of aliphatic monomers unsaturated may be suitable for inhibiting the polymerization of monomers of different reactivity such as monomers of styrene type.

More specifically, the diphenylamine derivative according to the invention corresponds to the general formula (I) in which A and B represent one of the following cycles:

In the preferred compounds, A and B are identical and represent a benzene ring.

The number of substituents on rings A and B can vary. Thus, n and m, identical or different, are less than or equal to 3, preferably, equal to 0 or 1, and even more preferably equal to 0.

The residues A and B may optionally carry one or more substituents which are represented in formula (I), by the symbol Ri and R ₂ and whose preferred meanings are defined below:. a hydrogen atom,

. an alkyl radical, linear or branched, having from 1 to 12 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 ₃ -OH -R3-SH -R3-COOR4 -R3-CO-R4 -Ft3-N (R ₄ ) 2

-R ₃ -CO-N (R ₄ ) ₂ -R3-NH-CO-R4 -R3-NH-COO-R4 in said formulas, R3 represents a valential bond or a divalent hydrocarbon radical, linear or branched, saturated or unsaturated, having from 1 to 6 carbon atoms preferably, methylene, ethylene, propylene, isopropylene, isopropylidene; the identical or different R4 radicals represent a hydrogen atom or a linear or branched alkyl radical having from 1 to 6 carbon atoms.

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

in said formula (la):

- R _{1 t} R ₂ , n and m have the meaning given above.

Among the compounds of formula (la), preference is given to those which correspond to formula (I) in which R- | and R ₂ represent a hydrogen atom or an alkyl group having from 1 to 4 carbon atoms, preferably a methyl group.

The examples given below illustrate the diphenylamine derivatives preferably used. They are more particularly chosen from:

- 2,2'-dihydroxydiphenylamine, - 2,4'-dihydroxydiphenylamine,

- 3,3'-dihydroxydiphenylamine,

- 4,4'-dihydroxydiphenylamine, - 4,4'-dihydroxy-2,2'-dimethyldiphenylamine,

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

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

The compositions as defined are well suited to the stabilization of aromatic monomers having at least one ethylenic unsaturation. They are more particularly suitable for monomers such as styrene, α-methylstyrene, divinylbenzene, vinyltoluene, vinyinaphthalene, styrenesulfonic acids, etc. The invention preferably applies to styrene. The compositions used according to 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 diphenylamine 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.

Preferably, the compositions of the invention also 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 containing at least one polymerization retarder and at least one polymerization inhibitor are preferably used according to 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-trinotrophenol (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 constituents of the diphenylamine type of formula (I) to the total mass of the constituents of the nitroaromatic type 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 diphenylamine derivatives of formula (I) present in the composition to the total amount (by weight) of the nitroaromatic derivatives of the composition.

The compositions used according to the invention may contain other polymerization inhibitors such as hydroquinones; catechols of the tert-butyl-catechol type; alkylated phenols; nitrosophenols and nitrosophenylhydroxylamines or any other inhibitor known in the art, provided that these are compatible with the other ingredients of the composition under the operating conditions to which the monomer to be stabilized is subjected.

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

The compositions used according to the invention are easily prepared by mixing the various constituents in the vehicle chosen.

The subject of the invention is also a process for inhibiting the radical polymerization of an aromatic 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 diphenylamine derivative to be added to achieve effective inhibition of polymerization 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 amount of diphenylamine derivative of between 1 and 2000 ppm, preferably between 5 and 1000 ppm is generally sufficient, this amount being expressed relative to the total weight of the monomer to be stabilized. As indicated above, it is desirable to add to the monomer an effective amount of one or more nitroaromatic derivatives as a polymerization retarder. As preferred retarder, mention may again be made of 2,6-dinitro-4-methylphenol, 2,4-dinitro-6-methylphenol, and 2,4-dinitrophenol, but especially 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 the diphenylamine 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. The radical polymerization inhibitor and the nitroaromatic derivative can be added to the monomer in a completely conventional manner. The point of introduction, in the case of a distillation, is very variable: one can consider adding each of these compounds at the level of heat exchangers, pipes, pumps, reboilers, compressors or more generally of distillation columns. It should be understood that the addition can be carried out continuously or else repeated over time at one or different particular sites.

The diphenylamine derivative and the radical polymerization inhibitor can be added to the monomer in a completely conventional manner. The point of introduction into the process is very variable: it is possible to envisage adding each of these compounds to the level of heat exchangers, pipes, pumps, reboilers, compressors or more generally distillation columns. 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 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 1 and 2 Comparative example 1 a

In order to evaluate the inhibition properties of the products of the invention, with regard to the radical polymerization of vinyl aromatic 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.

This precipitate is then filtered on a millipore filter then the residue is dried in an oven at 40 ° C, before being weighed.

The test results are summarized in Table (I).

Table (I)

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

Claims

1. Use to prevent the radical polymerization of aromatic monomers containing ethylenic unsaturation of a composition comprising at least one derivative of diphenylamine corresponding to the general formula (I):

in said formula (I):

- A and B symbolize the rest of a cycle forming all or part of a carbocyclic, aromatic, monocyclic or polycyclic system, - R- _| and R ₂ , identical or different, represent a hydrogen atom or one or more substituents,

- n and m represent the number of substituents on the cycle.

2. Use according to claim 1 characterized in that the diphenylamine derivative corresponds to formula (I) in which A and B represent a benzene ring or a naphthalene cycle and preferably, A and B are identical and represent a benzene ring .

3. Use according to claim 1 characterized in that the diphenylamine derivative corresponds to formula (I) in which n and m, identical or different, are less than or equal to 3, preferably equal to 0 or 1, and even more preferably equal to 0.

4. Use according to claim 1 characterized in that the diphenylamine derivative corresponds to formula (I) in which R ^ and R ₂ represent:

. a hydrogen atom,

. an alkyl radical, linear or branched, having from 1 to 12 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: -R3-OH -R3-SH -R3-COOR4 -R3-CO-R4 -R3 "N (R ₄ ) 2

-R ₃ -CO-N (R ₄ ) ₂

-R3-NH-CO-R4

-R3-NH-COO-R4 in said formulas, R3 represents a valential bond or a divalent hydrocarbon radical, linear or branched, saturated or unsaturated, having from 1 to 6 carbon atoms preferably, methylene, ethylene, propylene, isopropylene, isopropylidene; the identical or different R4 radicals represent a hydrogen atom or a linear or branched alkyl radical having from 1 to 6 carbon atoms.

5. Use according to one of claims 1 to 4 characterized in that the diphenylamine derivative corresponds to formula (la):

in said formula (la): - R- ₍ , R ₂ , n and m have the meaning given previously in one of claims 1 to 4.

6. Use according to claim 5 characterized in that the diphenylamine derivative corresponds to formula (la) in which R- _\ and R ₂ represent a hydrogen atom or an alkyl group having from 1 to 4 carbon atoms, preferably a methyl group.

7. Use according to one of claims 1 to 6 characterized in that it comprises a diphenylamine derivative chosen from: - 2,2'-dihydroxydiphenylamine,

- 2,4'-dihydroxydiphenylamine,

- 3,3'-dihydroxydiphenylamine, - 4,4'-dihydroxy-2,2'-dimethyldiphenylamine,

- 4,4'-dihydroxydiphenylamine.

8. Use according to one of claims 1 to 7 characterized in that it comprises, as vehicle, one or more solvents chosen from benzene, toluene, xylene, ethylbenzene, styrene, acetophenone and methylphenylcarbinol.

9. Use according to one of claims 1 to 8 characterized in that it further comprises at least one nitroaromatic derivative.

10. Use according to claim 9 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.

11. Use according to one of claims 9 and 10 characterized in that the ratio of the total mass of the constituents derived from diphenylamine 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.

12. A process intended to inhibit the radical polymerization of an aromatic ethylenically unsaturated monomer, comprising the addition to said monomer of an effective amount of at least one diphenylamine derivative corresponding to the general formula (I):

in said formula (I):

- R- | and R ₂ , identical or different, represent a hydrogen atom or one or more substituents, - n and m represent the number of substituents on the ring.

13. Method according to claim 12 characterized in that the diphenylamine derivative corresponds to formula (I) in which A and B represent a benzene ring or a naphthalene cycle and preferably, A and B are identical and represent a benzene ring .

14. The method as claimed in claim 12, characterized in that the diphenylamine derivative corresponds to formula (I) in which n and m, which are identical or different, are less than or equal to 3, preferably equal to 0 or 1, and even more preferably equal to 0.

15. The method of claim 12 characterized in that the diphenylamine derivative corresponds to formula (I) in which R- | and R ₂ represent:

. a hydrogen atom,

. 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 ₃ -OH -R3-SH

-R3-COOR4 -R3-CO-R4

-R3 "N (R ₄ ) 2

-R ₃ -CO-N (R ₄ ) ₂ -R3-NH-CO-R4

-R3-NH-COO-R4 in said formulas, R3 represents a valential bond or a divalent hydrocarbon radical, linear or branched, saturated or unsaturated, having from 1 to 6 carbon atoms preferably, methylene, ethylene, propylene, isopropylene, isopropylidene; the identical or different radicals R4 represent a hydrogen atom or a linear or branched alkyl radical having from 1 to 6 carbon atoms.

16. Method according to one of claims 12 to 15 characterized in that the diphenylamine derivative corresponds to formula (la):

in said formula (la):

- Ri, R ₂ , n and m have the meaning given previously in one of claims 12 to 15.

17. The method of claim 16 characterized in that the diphenylamine derivative corresponds to formula (la) in which Ri and R ₂ represent a hydrogen atom or an alkyl group having from 1 to 4 carbon atoms, preferably a methyl group.

18. Method according to one of claims 12 to 17 characterized in that the diphenylamine derivative chosen from:

- 2,2'-dihydroxydiphenylamine,

- 2,4'-dihydroxydiphenylamine, - 3,3'-dihydroxydiphenylamine,

- 4,4'-dihydroxy-2,2'-dimethyldiphenylamine,

- 4,4'-dihydroxydiphenylamine.

19. Method according to one of claims 12 to 18 characterized in that the total amount of diphenylamine 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.

20. Method according to one of claims 12 to 19 characterized in that the ratio of the mass of the diphenylamine type derivatives of formula (I) to the total mass of the nitroaromatic type constituents is between 90/10 and 10 / 90, preferably 80/20 and 20/80.

21. Method according to one of claims 12 to 20 characterized in that the aromatic ethylenically unsaturated monomer is a vinylaromatic monomer, preferably chosen from styrene, α-methylstyrene, vinyltoluene, divinylbenzene and styrenesulfonic acids .