WO1998059016A1

WO1998059016A1 - Composition and method for inhibiting radical polymerisation of ethylenically unsaturated aromatic monomers

Info

Publication number: WO1998059016A1
Application number: PCT/FR1998/001302
Authority: WO
Inventors: Françoise LARTIGUE-PEYROU; Jean-Claude Galliot
Original assignee: Rhodia Chimie
Priority date: 1997-06-23
Filing date: 1998-06-22
Publication date: 1998-12-30
Also published as: FR2764882B1; AU8221098A; FR2764882A1

Abstract

The invention concerns a composition for preventing the radical polymerisation of ethylenically unsaturated aromatic monomers characterised in that it comprises at least a dinitroaromatic derivative selected among dinitrosalicylaldehydes, dinitroalkoxyphenols, dinitrodihydroxybenezenes.

Description

COMPOSITION AND METHOD FOR INHIBITING RADICAL POLYMERIZATION OF UNSATURATED AROMATIC MONOMERS

ETHYLENIC,

The subject of the present invention is a composition which can be used as an inhibitor of the radical polymerization of aromatic 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.

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 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 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 prevent 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 also 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. . JP 63 316745 indicates 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 aromatic monomers during the manufacture of said monomers.

The present invention therefore relates to a composition intended to prevent the radical polymerization of aromatic monomers containing ethylenic unsaturation, characterized in that it comprises at least one dinitroaromatic derivative chosen from dinitrosalicylaldehydes, dinitroalkoxyphenols, dinitrodihydroxybenzenes.

A variant of the invention consists in associating the dinitroaromatic 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.

More specifically, the dinitroaromatic derivative of the invention can be represented by the general formula (I):

in said formula (I), Y represents:

- an aldehyde group -CHO;

- a hydoxyl group -OH - an alkoxy group of type -O-R in which R symbolizes a lower alkyl radical, linear or branched. By "lower alkyl radical" is meant from 1 to 4 carbon atoms. Thus, R represents a methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl and tert-butyl radical. R is more preferably a methyl or ethyl radical.

The invention does not exclude compounds of formula (I) in which R represents a radical other than a lower alkyl radical, for example an alkyl radical having more than 4 carbon atoms, preferably from 5 to 16 carbon atoms. carbon or an alkenyl radical preferably having from 2 to 16 atoms of carbon, for example an allyl radical or an aryl radical, preferably a phenyl radical: the term "alkoxy" being used in a generic manner. However, from an economic point of view, these compounds are not preferred. The examples given below illustrate the dinitroaromatic derivatives preferably used. They are more particularly chosen from:

- 3,5-dinitrosalicylaldehyde,

- 3,5-dinitro-2-methoxyphenol or 3,5-dinitrogaiacol,

- 2,4-dinitro-6-methoxyphenol or 2,4-dinitrogaiacol,

- 3,5-dinitro-2-ethoxyphenol or 3,5-dinitroguétol, - 2,6-dinitrohydroquinone,

- 3,5-dinitrocatéchol.

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

The compositions of the invention are suitable for the stabilization of aromatic monomers having at least one ethylenic unsaturation.

They are more particularly suitable for monomers such as styrene, -methylstyrene, divinylbenzene, vinyltoluene, vinylnaphthalene, styrenesulfonic acids, etc.

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 necessary, however, when the solubility of the dinitroaromatic 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 another inhibitor. Indeed, a more or less significant synergy is observed by association of the inhibitor of the invention with other polymerization inhibitors. Thus, a variant of the invention consists in introducing into the composition of the invention, one or more polymerization inhibitors of known type.

Several classes of inhibitors are perfectly suitable and we can cite, among others:

- catechols and, more preferably, catechol, 3-methylcatechol, 4-methylcatechol, 3-isopropylcatechol, 3-butyl-5-methylcatechol, 4-tert-butylcatechol, 3,5-di-tert -butylcatechol, 4,6-di-tert-butylcatéchol, 3-octyl-5-methylcatéchol, 4-isopropoxycatéchol, 3,6-diisopropylcatéchol;

- p-phenylenediamines and in particular N, N '- (di-sec-butyl) -p- phenylenediamine, N, N' - (diisobutyl) -p-phenylenediamine, N, N'-di (1, 4 - dimethylpentyl) -p-phenylenediamine, N, N'-diphenyl-p-phenylenediamine, N, N'-ditolyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, N- ( 1, 3-dimethyl-butyl) -N'-phenyl-p-phenylenediamine;

- nitrosophenols and in particular 4-nitrosophenol, 2-methyl-4-nitrosophenol

- nitroxides and, more particularly, 2,2,6,6-tetramethylpiperidine-N-oxyl, 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl, 2,2,6,6 - tetramethylpiperazine-N-oxyl.

The invention does not exclude the use of any other inhibitor known in the art, provided that it is compatible with the other ingredients of the composition under the operating conditions to which the monomer to be stabilized is subjected.

The other inhibitors are added to the composition so that the ratio of the mass of the dinitroaromatic type derivatives of formula (I) to the total mass of the inhibitor type constituents is between 90/10 and 10/90, preferably between 80/20 and 20/80.

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 method for preventing the radical polymerization of an ethylenically unsaturated aromatic 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 dinitroaromatic 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 can 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 dinitroaromatic 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 previously, it is possible to add to the monomer an effective amount of one or more other polymerization inhibitors.

The proportion of the inhibitor (s) is preferably such that the ratio of the mass of the dinitroaromatic type derivatives of formula (I) to the total mass of the inhibitor type constituents is between 90/10 and 10/90, better still between 80 / 20 and 20/80. The dinitroaromatic 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 to 9

In order to evaluate the inhibition properties of the reference products, vis-à-vis the radical polymerization of vinyl monomers, inhibition tests with styrene were undertaken with the following operating protocol. Before each test, the styrene used (marketed by the Merck Company) is previously destabilized by passage over an activated alumina column (obtained from the Procatalyze Company) in order to completely eliminate the 4-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 is 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 (corresponding to the polymer formed) is dried in an oven at 40 ° C, before being weighed.

The results of the tests are summarized in Table I.

Board

The results show that the products claimed (eg 4 to 9) are excellent inhibitors of the polymerization of styrene in the same way as existing industrial products (eg 2 and 3). Furthermore, not being derived from monophenolic or cresolic products, they are less toxic than dinitrophenol. Examples 10 to 14

In these examples, the test conditions are identical to Example 1.

The nitro compounds are associated with various other known inhibitors for the stabilization of styrene.

The test results are summarized in Table II.

Table II

with IPPD = N-isopropyl-p-phenylenediamine TBC = 4-tert-butylcatechol Tempo = 2,2,6,6-tetramethylpiperidine-N-oxyl

As illustrated in Examples 10 to 14, the combination of a dinitrated compound with another inhibitor makes it possible to achieve an even better inhibitory efficiency than the dinitrated compound alone.

Claims

1. Composition intended to prevent the radical polymerization of aromatic monomers containing ethylenic unsaturation characterized in that it comprises at least one dinitroaromatic derivative chosen from dinitrosalicylaldehydes, dinitroalkoxyphenols, dinitrodihydroxybenzenes.

2. Composition according to Claim 1, characterized in that the dinitroaromatic derivative corresponds to the formula:

in said formula (I), Y represents:

- an aldehyde group -CHO;

- a hydoxyl group -OH

- an alkoxy group of type -O-R in which R symbolizes a lower alkyl radical, linear or branched.

3. Composition according to one of claims 1 or 2 characterized in that the dinitroaromatic derivative is chosen from:

- 3,5-dinitrosalicylaldehyde, - 3,5-dinitro-2-methoxyphenol,

- 2,4-dinitro-6-methoxyphenol,

- 3,5-dinitro-2-ethoxyphenol,

- 2,6-dinitrohydroquinone,

- 3,5-dinitrocatéchol.

4. Composition according to one of claims 1 to 3 characterized in that it comprises, as vehicle, one or more solvents chosen from benzene, toluene, xylene, ethylbenzene, styrene, acetophenone and methylphenylcarbinol.

5. Composition according to one of claims 1 to 4 characterized in that it comprises another inhibitor.

6. Composition according to claim 5 characterized in that the polymerization inhibitor is chosen from:

- catechols and, more preferably, catechol, 3-methylcatechol, 4-methylcatechol, 3-isopropylcatechol, 3-butyl-5-methylcatechol, 4-tert-butylcatechol, 3,5-di-tert -butylcatechol, 4,6-di-tert-butylcatechol,

3-octyl-5-methylcatechol, 4-isopropoxycatechol, 3,6-diisopropylcatechol; p-phenylenediamine and in particular N, N'-di-sec-butyl-p- phenylenediamine, N.N'-diisobutyl-p-phenylenediamine, N, N'-di (1, 4-dimethylpentyl) -p -phenylenediamine, N, N'-diphenyl-p-phenylenediamine, N, N'-ditolyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylene diamine, N-dimethyl-1, 3 -butyl-N'-phenyl-p-phenylenediamine;

- nitrosophenols and more preferably 4-nitrosophenol, 2-methyl-4-nitrosophenol; - nitroxides and, more preferably, 2,2,6,6-tetramethylpiperidine-N-oxyl, 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl, 2,2,6,6 - tetramethylpiperazine-N-oxyl.

7. Composition according to Claim 6, characterized in that the polymerization inhibitor is chosen from:

- 4-tert-butylcatechol,

- N, N'-di (1, 4-dimethylpentyl) -p-phenylenediamine,

- N-isopropyl-N'-phenyl-p-phenylene diamine,

- 2-methyl-4-nitrosophenol, - 2,2,6,6-tetramethylpiperidine-N-oxyl.

8. Composition according to any one of claims 5 to 7 characterized in that the ratio of the mass of the dinitroaromatic type derivatives of formula (I) to the total mass of the constituents of inhibitor type is between 90/10 and 10 / 90, preferably between 80/20 and 20/80.

9. A method for preventing radical polymerization of an ethylenically unsaturated monomer, comprising adding to said monomer an effective amount of one or more dinitroaromatic derivatives chosen from dinitrosalicylaldehydes, dinitroalkoxyphenols, dinitrodihydroxybenzenes.

10. Method according to claim 9 characterized in that the dinitroaromatic derivative corresponds to the formula:

in said formula (I), Y represents:

- an aldehyde group -CHO;

- a hydoxyl group -OH - an alkoxy group of type -O-R in which R symbolizes a lower alkyl radical, linear or branched.

11. Method according to one of claims 9 and 10, characterized in that at least one dinitroaromatic derivative is chosen from: - 3,5-dinitrosalicylaldehyde,

- 3,5-dinitro-2-methoxyphenol,

- 2,4-dinitro-6-methoxyphenol,

- 3,5-dinitro-2-ethoxyphenol,

- 2,6-dinitrohydroquinone, - 3,5-dinitrocatéchol.

12. Method according to one of claims 9 to 11 characterized in that the total amount of dinitroaromatic derivative of formula (I) added is between 1 and 2000 ppm, preferably between 5 and 1000 ppm relative to the total weight of said monomer.

13. Method according to one of claims 9 to 12 characterized in that the ratio of the mass of the dinitroaromatic type derivatives of formula (I) to the total mass of the constituents of inhibitor type is between 90/10 and 10 / 90, preferably 80/20 and 20/80.

14. Method according to one of claims 9 to 13, characterized in that said ethylenically unsaturated monomer is a vinylaromatic monomer, preferably chosen from styrene, α-methylstyrene, vinyltoluene, divinylbenzene and styrenesulfonic acids .