EP3609943A1 - Reactive organic product and use thereof as a cross-linking agent in self-healing coatings - Google Patents

Abstract

The invention relates to a reactive organic product comprising one or more multi-functional organic compounds of formula (I), and the use thereof as a cleavable cross-linking agent in a bi-component reactive composition. The invention also relates to cross-linkable compositions, and more particularly to coating compositions comprising a reactive organic product according to the invention. Finally, the invention relates to the use of the coating compositions according to the invention as self-healing coatings, and to a method for self-healing.

Description

 REACTIVE ORGANIC PRODUCT AND ITS USE AS RETICULATING AGENT IN SELF-HEALING COATINGS

The present invention relates to a reactive organic product comprising one or more multifunctional organic compounds of formula (I), and its use as a cleavable crosslinking agent in a two-component reactive composition. The invention also relates to crosslinkable compositions, and more particularly to coating compositions comprising such a reactive organic product. Finally, the invention relates to the use of these coatings as self-healing coatings, as well as to a self-healing process.

STATE OF THE PRIOR ART AND PURPOSE OF THE INVENTION

 The self-healing materials, designated by the English name self-healing, are able to undergo, at the molecular level as well as at the macroscopic scale, a phenomenon of chemical or physical repair in response to an external stimulus, without it is necessary to involve an outside operator.

 Currently, there are three technologies for the manufacture of self-healing materials:

 - The micro-encapsulation of healing agents which consists in enclosing in the material microcapsules or microfibers containing a healing agent, capable of breaking at the same time as the material. The healing agent present in the material is thus spread in the cracks of the material which it fills by polymerization, for example under the action of a catalyst dispersed in the matrix. This method is nevertheless of limited interest insofar as it is impossible to use the same microcapsules several times, the latter losing their self-healing properties after reaction.

- Supramolecular interactions that restore the cohesion of a material after the appearance of cracks or cuts, including at the macromolecular scale: these bonds are indeed weaker than covalent bonds, and can be restored by simple contact between both parts of the material. Several families of supramolecular interactions have been studied with a view to producing self-healing materials: hydrogen bonds seem to be the most promising, however many other types of supramolecular interactions, such as chemistry coordination metal / ligand, also seem exploitable. This method nevertheless remains sensitive to the various stimuli to which the final material would be subjected.

 - The method of reversible covalent bonds consists in incorporating in the structure of macromolecules covalent bonds capable of breaking and reforming "on command", by simple displacement of the thermodynamic equilibrium. It is possible to control this balance by an external stimulus, such as temperature, pH, humidity, etc. This method has the advantage of allowing several self-scarring at the same point of the material, while being easily controllable. In addition, the reversible covalent bonds can easily integrate into a pre-existing material: it suffices for them to be incorporated in a crosslinking agent, which requires little variations in formulation and reconciles the self-healing properties sought with the usual mechanical properties of the materials in which they are integrated.

 The inventors have today developed a new self-healing reagent organic product comprising a reversible covalent bond capable, under the effect of external stimulation and without the addition of additional chemical species, of repairing cracks, and thus of increase the life of the coatings. This new self-healing product is a reversibly cleavable crosslinking agent capable of replacing conventional crosslinking agents. The crosslinking agent of the invention carries isocyanate functions, and may advantageously be used in coatings based on polyol resins. Once the crosslinking has been carried out, the branches formed by the crosslinking agent are capable of breaking and reforming in a reversible manner on command, without modifying the urethane functions obtained in place of the alcohol functions.

 The crosslinking agent of the invention is formed and cleaved in the final coating by reaction of Diels-Alder and retro-Diels-Alder. This reaction, which won Otto Diels and Kurt Aider's Nobel Prize in Chemistry in 1950, is a cycloaddition reaction in which a conjugated diene reacts on a so-called "dienophile" alkene to form a six-atom unsaturated ring.

The reaction of furan (diene blocked in as) on maleic anhydride (dienophile bearing highly electron-withdrawing groups) is known to give a high yield, and to be easily reversible by heating:

 Diagram 1: Diels-Alder reaction between furan and maleic anhydride

The synthetic strategy of the crosslinking agent of the invention may, for example, use a diisocyanate and a hydroxyl derivative of furan, the resulting diene then reacting by Diels-Alder reaction with a bismaleimide. The resulting Diels-Alder adduct is likely to cleave by retro-Diels-Alder in response to an external stimulus.

 Scheme 2: Synthesis of a cleavable crosslinking agent according to the invention from a diisocyanate and a hydroxyl derivative of furan

Alternatively, the synthesis strategy of the crosslinking agent of the invention can use a bismaleimide (a central chain terminated by two maleimide groups, structurally very close to maleic anhydride) and a furan derivative, and makes it possible to obtain a central chain terminated on each side by a Diels-Alder adduct capable of cleaving in response to an external stimulus, the other side of the adduct carrying an alcohol function. This alcohol is reacted on a diisocyanate to obtain a crosslinking agent terminated on each side by an isocyanate function, cleavable by retro-Diels-Alder.

 Scheme 3: Synthesis of a cleavable crosslinking agent according to the invention from a bismaleimide The final self-healing coating comprising the crosslinking agent of the invention has the advantage of being activated and deactivated several times , without altering over time. It also shows quite satisfactory mechanical properties. DESCRIPTION OF THE INVENTION

According to a first aspect, the subject of the invention is a reactive organic product comprising one or more multifunctional organic compounds corresponding to the following formula (I): ## STR3 ## 2-CONH) _x -R 3 -NHCO-2-DA] _n -R 1 -AD-2-CONH-R 3

N = C = 0 (I) in which :

 X varies from 0 to 10, preferably from 0 to 5, and even more preferentially x = 0,

N varies from 1 to 2, and preferably n = 1,

■ RI is selected from aliphatic Ci-Qo _/ preferably Ci-C _{3 S,} the aromatic _groups, C ₆ -C ₂ o, preferably C ₆ -C _3, or alkylaryl groups in which the or aryl groups are C ₆ -C ₂₀ and the alkyl chain (s) are C ₁ -C ₁₀ , R 1 being advantageously a linear or branched C ₁ -C ₆ aliphatic group optionally comprising a saturated or unsaturated C ₅ -C ₆ cycloaliphatic group; , and preferably an unsaturated C ₆ cycloaliphatic group, or R 1 is a C ₆ -C ₂₀ aromatic group, or R 1 is an alkylaryl group in which the aryl group (s) are (C ₆ -C ₂₀₎ and the alkyl chain (s) are in the form of C1-C40, and even more advantageously R1 is a C1-C40 alkoxylated chain, linear or branched, preferably comprising 1 to 20 alkoxylated units, and even more preferably 1 to 15 alkoxylated units, such as ethoxy, propoxy, butoxy units; , or a mixture of ethoxy and propoxy units, or RI is an alkoxyaryl group in which the aryl groups are C 6 -C ₂₀ and or alkoxylated chains are C 1 C 0, said alcoxylaryle group preferably corresponding to the following formula (by excluding

 in which the polyether block is chosen from C1-C40 alkoxylated chains, preferably comprising 1 to 20 alkoxylated units, and even more preferably 1 to 15 alkoxylated units, such as ethoxy, propoxy or butoxy units, or a mixture of units ethoxy and propoxy, or the CrCo hydroxytelechelic polybutadiene or polyester chains,

 DA is a Diels-Alder adduct between a diene compound D carrying a chain R2 and a dienophile compound A carrying an RI group, the diene functions of the diene compound D being chemically blocked by reaction of Diels-Alder with the compound dienophile A,

R 2 is a C ₁ -C ₄ , preferably C ₁ -C ₂ , alkyl chain bearing a hydroxy group reacted with an isocyanate functional group to form a urethane linkage, ■ R 3 is selected from aliphatic C ₅ -C ₂₀ aromatic groups or C ₆ -Ci2 and preferably R3 is a cycloaliphatic C ₆ optionally substituted by one or more linear alkyl chains or branched -C C ₆ .

 For the purposes of the invention, the following terms mean:

- Aliphatic group: a hydrocarbon group in Q-Qo _/ acyclic or cyclic, linear or branched, saturated or unsaturated, excluding aromatic groups, preferably C 1 -C ₃₅ . The term "branched" means that at least one lower alkyl group such as methyl or ethyl is carried by a linear aliphatic chain.

Alkyl group: a linear or branched, preferably C 1 -C ₃₅ , saturated Q-Qo hydrocarbon aliphatic group. The term "branched" means that at least one lower alkyl group such as methyl or ethyl is carried by a linear alkyl chain.

Alkene group: an unsaturated aliphatic hydrocarbon group comprising a covalent double bond between two carbon atoms, linear or branched, C ₂ -C ₂ o, preferably C ₂ -Ci ₂ , and even more preferably Q-Ce. The term "branched" means that at least one lower alkyl group such as methyl or ethyl is carried by a linear alkenyl chain.

Cycloalkyl group: any functional group or substituent derived from a non-aromatic ring comprising at least three carbon atoms, and preferably C ₃ -C ₁₂ , optionally containing one or more heteroatoms chosen from S, O and N. Among such groups, mention may be made especially of cyclopropyl, cyclobutyl, cyclopentyl and cyclohexyl; the optionally substituted cyclohexyl group being preferred.

Aromatic group: any functional group or substituent derived from at least one aromatic ring; an aromatic ring corresponds to any planar mono- or polycyclic group comprising a delocalized π system in which each atom of the cycle comprises an orbital p, said orbital p overlapping each other; among such aromatic groups, there may be mentioned phenyl, biphenyl, naphthalene and anthracene groups. The aromatic groups of the invention are C ₆ -C ₂₀ , and preferably C ₆ -C ₃ .

Alkoxylated chain: any chain, linear or branched, comprising at least one polyether chain. Said polyether chain may comprise from 1 to 40, preferably from 1 to 20, and even more preferably from 1 to 15 alkoxylated units (or oxyalkylenated), such as ethoxy, propoxy, butoxy units, and preferably a mixture of ethoxy and propoxy units.

According to an advantageous embodiment of the invention, the diene compound D is a cyclic diene, preferably C ₅ -C ₆ , and even more preferably a C ₅ -C ₆ cyclic diene comprising a heteroatom, said diene compound. D is carrying an alkyl chain R2 in C1-C4, preferably in C _x C ₂ , carrying a hydroxyl group.

 The diene compound D preferably corresponds to the following formula:

in which :

Z represents CH ₂ , O, S, or N-Rx in which Rx is chosen from linear or branched C ₁ -C ₁₂ alkyl chains, and preferably Z = O, and

- Ra, Rb, Rc and Rd, identical or different, are selected from H or alkyl chains of C ₁ -C _12, at least one of the radicals Ra or Rd is an alkyl chain R2 -C-Q, preferably Ci-C ₂ , carrying a hydroxy group.

According to a particularly preferred embodiment, the diene compound D carrying an alkyl chain R 2 C ₁ -C 4, preferably Ci-C _2, bearing a hydroxy group is furfuryl alcohol of the formula:

According to an advantageous embodiment of the invention, the dienophile compound

A is an alkene, preferably an optionally substituted Q-Cs cyclic alkene, bearing an RI group and comprising at least one imide group. Said imide group may be an α, β-ethylenically unsaturated imide, preferably selected from the group consisting of maleimide, tetrahydrophthalimide, imide derivative of anhydride or itaconic acid.

 According to a particularly preferred embodiment, the dienophile compound A is a bismaleimide compound corresponding to the following formula:

in which :

- RI is an aliphatic C ₁ -C40 linear or branched, optionally comprising a cycloaliphatic C ₅ -C ₆ saturated or unsaturated, and preferably a cycloaliphatic C ₆ unsaturated, or RI is an aromatic group of C ₆ -C _20, or RI is an alkoxylated chain CRCW, preferably comprising 1 to 20 alkoxy units, and even more preferably 1 to 15 alkoxy units, such as ethoxy units, propoxy, butoxy, or a mixture of ethoxy units and propoxy, or RI is an alkoxyaryl group in which the aryl group (s) are C ₆ -C ₂ O and the alkoxylated chain (s) are in CrQo, said alkoxyaryl group preferably having the following formula (excluding from this

wherein the polyether block is selected from alkoxylated chain Ci-Qo _/ preferably comprising 1 to 20 alkoxy units, and even more preferably 1 to 15 alkoxy units, such as ethoxy units, propoxy, butoxy, or a mixture of units ethoxy and propoxy, or the CrCo hydroxytelechelic polybutadiene or polyester chains, - Re, Rf, Rg and Rh, identical or different, are chosen from H, the linear or branched alkyl chains in C ₁ - ₁₂ , or Re and Rf on the one hand and Rg and Rh on the other hand are interconnected to form a C ₆ aliphatic ring.

 According to an even more preferred embodiment, the dienophile compound A is a bismaleimide compound corresponding to the following formula:

in which :

R1 is a C1-C10 alkoxylated chain, preferably comprising 1 to 20 alkoxylated units, and even more preferably 1 to 15 alkoxylated units, such as ethoxy, propoxy or butoxy units, or a mixture of ethoxy and propoxy units, or RI is an alkoxyaryl group in which the aryl group (s) are C ₆ -C ₂ O and the alkoxylated chain (s) are in Q-Qo, said alkoxyaryl group preferably having the following formula (excluding from this formula both

wherein the polyether block is selected from C ₁ -C ₁₀ alkoxylated chains, preferably comprising 1 to 20 alkoxylated units, and even more preferably 1 to 15 alkoxylated units, such as ethoxy, propoxy, butoxy units, or a mixture of ethoxy and propoxy units, or polybutadiene chains or hydroxytelechelic polyesters in CrGw _/

- Re, Rf, Rg and Rh, identical or different, are chosen from H, the linear or branched alkyl chains in C ₁ -C ₁₂ , or Re and Rf on the one hand and Rg and Rh on the other hand are linked between they form a C ₆ aliphatic ring. The molecular weight of the bismaleimide of the invention advantageously varies between 600 and 1400 g. mol ^"1 , still more preferably between 700 and 1000 g mol ^-1 .

 The bismaleimide ED-600 BM marketed by the company Specifies Polymers corresponding to the following formula can advantageously be used in the context of the invention

According to an advantageous embodiment of the invention, the group -CONH-R3-NHCO- results from the reaction of a diisocyanate of formula = C = IM-R3-N = C = O with hydroxy functions. According to a particularly preferred embodiment, the diisocyanate of formula O = C = N-R 3 -N = C = O is an asymmetric aliphatic diisocyanate whose reactivity of the two isocyanate functions is slightly different, in which R 3 is preferably a cycloaliphatic group C ₅ -C _6, optionally substituted by one or more linear alkyl chains or branched Ci-C _6.

 The isophorone diisocyanate (IPDI) corresponding to the following formula may advantageously be used in the context of the invention:

The retro-Diels-Alder cleavage of the organic reactive product of the invention can be achieved by increasing the temperature, and is attainable from 60 ° C. The cleavage may optionally require temperatures up to 140 ° C. depending on the stereochemistry of the Diels-Alder adducts obtained: it is indeed easier to cleave the endo adduct than the exo adduct. As set forth below, the conditions for preparing the reactive organic product of the invention are preferably adjusted to promote the production of the endo stereochemical form. The reactive organic product comprising one or more polyfunctional organic compounds of formula (I) according to the invention can be characterized by its index Ι _{Ν∞ #} which is advantageously between 50 and 90 mgKOH.g ^"1. The index I _N co can be determined by back-titration with excess n-dibutylamine.

 Another object of the invention is a first process for preparing a reactive organic product comprising one or more multifunctional organic compounds of formula (I) according to the invention comprising the following steps:

(i) reaction between a diene compound D bearing a C ₁ -C ₆ , preferably C ₁ -C ₂ , alkyl chain R2, bearing a hydroxyl group and a diisocyanate O = C = N-R 3 -N = C = O , the molar ratio between the diene compound and the diisocyanate being preferably 1/1, to obtain a 0 = C = N-R3-NHCO-R2-D compound, then

(ii) Diels-Alder reaction between the compound O = C = N-R3-NHCO-R2-D obtained at the end of step (i) and a dienophile compound of formula R1- (A) _{n +} 1, the ratio NCO functions / OH functions being preferably greater than 1, to obtain a reactive organic product comprising one or more multifunctional organic compounds of formula (I) according to the invention,

x, n, D, A, R1, R2 and R3 being as defined above.

 The reactive organic product is advantageously prepared according to this first method when x varies from 0 to 1, and preferably x = 0 or x = 1, preferably with a molar ratio between the diene compound and the diisocyanate of 1: 1 step (i), and a ratio NCO functions / OH functions greater than 1 during step (ii).

 Steps (i) and (ii) are preferably carried out at a temperature between 20 and 40 ° C to promote the production of the endo stereochemical form. They are also preferably carried out under an inert atmosphere, for example under nitrogen, and optionally in the presence of a desiccant such as tosyl isocyanate, to avoid the presence of water and to avoid side reactions involving the isocyanate functions.

The steps (i) and (ii) may also be carried out in a polar solvent, in particular chosen from acetic acid esters such as ethyl acetate and butyl acetate, or ketones such as acetone, butan-2-one, heptan-2-one, methyl isobutyl ketone and cyclohexanone. The reactive organic product comprising one or more multifunctional organic compounds of formula (I) of the invention may also be prepared according to a second process comprising the following steps:

(I ⁷ ) Diels-Alder reaction between a diene compound D bearing a C ₁ -C ₄ , preferably C ₁ -C ₂ , alkyl chain R2, bearing a hydroxyl group and a dienophile compound of formula R 1 - (A) _{n +} 1, the ratio dienophile functions A / diene functions D being preferably equal to 1, to obtain a compound R 1 - (AD-R 2) _{n +} 1 in which each Diels-Alder adduct carries an alkyl chain R2 in Ci - C 1, preferably C ₁ -C ₂ , bearing a hydroxyl group, then

(W) reaction between the compound R1- (AD-R2) _{n +} i obtained at the end of step (0, and more precisely between the hydroxyl group of R2 and a diisocyanate O = C = N-R3-N = C = 0, to obtain a reactive organic product comprising one or more multifunctional organic compounds of formula (I) according to the invention, wherein x, n, D, A, R 1, R 2 and R 3 are as defined above.

The reactive organic product is advantageously prepared according to this second method when x varies from 0 to 1, and preferably x = 0 or x = 1, preferably with a ratio of dienophile functions A / d-diene functions of 1/1 during the step (0, and a molar ratio diisocyanate / compound R1- (AD-R2) _{n +} 1 greater than 1 during step (W).

The steps (i ⁷ ) and (ii ¹ ) are preferably carried out at a temperature between 20 and 40 ° C to promote the production of the endo stereochemical form. They are also preferably carried out under an inert atmosphere, for example under nitrogen, and optionally in the presence of a desiccant such as tosylsocyanate, to avoid the presence of water and to avoid side reactions involving the isocyanate functions.

 The steps (0 and (ϋ ') can be carried out in a polar solvent, in particular chosen from acetic acid esters such as ethyl acetate and butyl acetate, or ketones such as acetone. butan-2-one, heptan-2-one, methyl isobutyl ketone and cyclohexanone.

In the absence of a solvent, step (iiO can be carried out by adding diisocyanate O = C = N-R3-N = C = O on the compound R1- (AD-R2) _{n + 1} obtained at the end of the step (0, with for n = 1 a molar ratio diisocyanate / compound R1- (AD-R2) _{n +} 1 greater than 1, preferably ranging from 2.10 to 2.40, and even more preferably from 2, 10 to 2.20 In the presence of solvent, step (ϋ ') can be carried out by adding the compound R1- (AD-R2) _{n + 1} obtained at the end of step (0 on the dlisocyanate O = C = N-R3-N = C = O.

 The step (ϋ ') of reaction between a diene compound D carrying a chain R2, itself carrying a hydroxyl group, and the diisocyanate O = C = N-R3-N = C = O is advantageously carried out at a temperature of temperature between 20 and 40 ° C.

The diene D compound carrying an alkyl chain R2 C1-C4, preferably C1-C2, bearing a hydroxy group used during steps (i) and ^r) of the methods of the invention is preferably alcohol furfuryl.

The dienophile compound of formula R 1 - (A) _{n +} 1 used during steps (ii) and (Π of the processes of the invention is advantageously a bismaleimide compound corresponding to the following formula:

wherein R1, Re, Rf, Rg and Rh are as previously defined.

 According to a preferred embodiment, it is the bismaleimide ED-600 BM marketed by the company Specifies Polymers.

The diisocyanate of formula O = C = N-R3-N = C = O is an asymmetric aliphatic diisocyanate, in which R 3 is preferably a C ₅ -C ₆ cycloaliphatic group, optionally substituted by one or more linear or branched alkyl chains. in Ci-C ₆ .

 According to a preferred embodiment, the asymmetric aliphatic diisocyanate is isophoronediisocyanate (IPDI).

The steps (i) and (N ¹ ) of the processes of the invention can be carried out in the presence of a catalyst which influences the reactivity of the isocyanate, and makes it possible to increase the reactivity of the secondary isocyanate function. Said catalyst is preferably based on tin, bismuth, titanium, zinc, or zirconium. According to a particularly preferred embodiment, the catalyst is based on tin: it is an organotin compound, and more particularly dibutyltin dilaurate. (DBSnDL). The catalyst may be added at a molar level ranging from 0.1 to 1 mol%, and preferably from 0.2 to 0.5 mol%, relative to the total mol% of diisocyanate.

 The present invention also relates to the use of an organic reagent product according to the invention, or obtained by a process according to the invention, as a cleavable crosslinking agent in a two-component reactive composition, preferably in a two-component reactive composition. crosslinkable, and even more preferably an acrylic resin functionalized with hydroxy groups. Advantageously, the reactive organic product of the invention is a crosslinkable agent heat-cleavable reversibly in a two-component reactive composition.

 Another subject of the invention relates to a crosslinkable composition comprising an organic reagent product according to the invention, or obtained by a process according to the invention, and a component comprising at least one reactive functional group capable of reacting with said reactive organic product such as an acrylic resin functionalized with hydroxy groups.

 The crosslinkable composition of the invention is preferably a coating composition selected from paints, varnishes, inks and adhesives, a molding composition, a composite composition, or a sealant composition.

 The invention also relates to the use of a crosslinkable composition according to the invention for the self-healing of the surface of coatings or articles based on such a composition, or for the recycling of thermoplastic or thermosetting polymers, in particular composite moldings.

 Finally, a last object of the invention is a self-healing process comprising a step of applying a crosslinkable composition according to the invention to a substrate, followed by a step of de-protection (cleavage) by retro -Diels-Alder functions dienes chemically blocked from the crosslinking agent contained in said composition, under the effect of an external energy, and especially by conduction, convection, or radiation.

The step of deprotecting back-Diels-Alder is preferably a thermo-cleavage step performed by heating at a temperature ranging from 60 to 120 ° C, and preferably from 70 to 100 ° C. This heating step can be carried out for a period ranging from 5 minutes to 2 hours, and preferably between 15 minutes and 1 hour. The self-healing process of the invention may further comprise, after the step of deprotection by retro-Diels-Alder, a step of healing by cooling, preferably at a temperature ranging from 20 to 30 ° C. and even more preferably at room temperature (25 ° C).

 In addition to the foregoing, the invention also comprises other arrangements which will become apparent from the additional description which follows, which relates to examples of synthesis of reactive organic products comprising one or more multifunctional organic compounds of formula (I) according to US Pat. invention, and their evaluation in self-healing coating formulations, as well as the photographs of Figures 1 and 2 which show coatings according to the invention before and after heating.

EXAMPLES Example 1 Preparation of a crosslinking agent 1 of the invention by synthesis of the urethane, and then reacting the Diels-Alder ^st step: Synthesis of urethane

The urethane is synthesized at room temperature in a batch of 1 L, inerted with nitrogen and provided with a circulating agitation module (marine propeller) agitated at 100 revolutions.min ^{* 1} , from 46.73 g of furfuryl alcohol (Sigma-Aldrich) and 105.88 g of isophoronediisocyanate (IPDI) (Sigma-Aldrich), in the presence of 0.98 g of dibutyltin dilaurate (DBSnDL) (Sigma-Aldrich) . The reaction is conducted by adding the furfuryl alcohol dropwise to the PDI, each of which is diluted in butyl acetate (Sigma-Aldrich) (153.59 g).

 The progress of the reaction is monitored by HH NMR. The conversion rate reaches a plateau of 99.0 to 99.8% after 35 minutes of reaction.

A drying, 21.43 g of tosyl isocyanate (Sigma-Aldrich) is added at the end of the ^st step.

Step ^2: Diels-Alder

At room temperature, under nitrogen and stirring as described in the previous step: 200.00 g of bismaleimide ED-600 BM (Specified Polymers) diluted in 200.00 g of butyl acetate (Sigma-Aldrich) were added drop-by-drop over the urethane obtained after the step of ^age. The reaction is carried out respecting a ratio of dienophile functions A / diene functions D equal to 1.

As before, the reaction is followed by NMR ^X H every 30 minutes. The conversion rate reaches a 95% level after 7 days.

The index I _NC o of the crosslinking agent 1 obtained at the end of this process is determined by back-titration with excess n-dibutylamine. According to this method, the crosslinking agent 1 has an _N- index of 66 mgKOH.g ^-1 Example 2 Preparation of a crosslinking agent 2 according to the invention by reaction of Diels-Alder, then reaction with a diisocyanate ^lere stage: synthesis of the diol

 The synthesis of a crosslinking agent according to the invention is this time carried out starting with a Diels-Alder reaction between 395.7 g of ED-600 BM and 92.35 g of furfuryl alcohol. This reaction is performed at room temperature, adding the furfuryl alcohol on the ED-600 BM drip.

 The progress of the reaction is monitored by NMR H and reaches a plateau at 96.5% after 4 days.

^2nd step: addition of the diisocyanate

The 2 ^nd step corresponds to the addition of 223.90 g dlPDI the diol obtained at the end of the ^st step, in the presence 1.91 g of dibutyltin dilaurate (DBSnDL).

The progress of the ^2nd step is also followed by 1H NMR in deuterated acetone. A strong rise in viscosity is also observed, indicating the progress of the reaction.

Example 3 Formulation and Evaluation of Self-Curing Coatings Comprising a Crosslinking Agent According to the Invention 1- Preparation of coatings

The properties of the crosslinking agent 1 synthesized in Example 1 are evaluated in a polyol resin, e. Synocure® 854 BA 80 sold by Arkema. It is a resin highly functionalized with hydroxy groups, crosslinkable at room temperature by adding a prepolymer carrying isocyanate groups.

 The formulations are made by ensuring that there is the same number of hydroxy functions from the resin as isocyanate functions from the crosslinking agent:

XOH) / MOH = (M _{rs ret} XNCO) / M _N where s is the solids content of the product, and X ₀ H and χ _Ν ∞ are respectively the content of hydroxyl functions and the content of isocyanate functions of the extracts dried (for the resin used, XOH = 2, 1% and s "§ _s = 78, 9%).

The resin and the crosslinking agent are placed in a metal pot, mixed with stirring 1000 tours.min ^"1 for two minutes using a module shearing. Their dynamic viscosity η is measured using a Brookfield viscometer tray The manipulations are started at η s 300 mPa.s at 25 ° C. If the viscosity is too high at the time of mixing, butyl acetate is added.

Pot-life measurement:

 Pot life, also called pot-life, is the time during which it is possible to apply a formulation to a surface before it becomes too viscous.

 Starting from a viscosity η κ 300 mPa.s at 25 ° C., a formulation is considered as manipulable up to η <600 mPa.s at 25 ° C. Regular samples are thus taken and analyzed, and allow to extrapolate the time tpot allowing to reach η = 600 mPa.s.

The pot-life measurement of the formulation obtained is shown in Table 1 below: Table 1: Pot-life measurement of the formulation carried out

Application on metal plates:

 The formulations are then applied to QD 36 (Q-panel) type steel plates for their physicochemical analyzes. The formulations are applied by means of an apparatus for passing a metal bar at a height of 100 μm above the surface of the plate, allowing a viscous liquid of 100 μm to be uniformly spread therein. of wet thickness. 2- Physico-chemical analyzes

Drying time :

 The surface drying time (noted hereinafter tss) is measured according to the ISO 9117-3 standard, by depositing for 10 seconds on the surface of the plate a controlled quantity of glass beads having a particle size of between 125 and 250 μm. , which are then wiped with a brush; as long as the glass beads remain attached to the coating, the surface is not dry. The test is carried out at a temperature of 25 ° C ± 3 ° C and 50% ± 5% relative humidity.

 The drying time tss measured is 25 min.

Measurement of the thickness:

The thickness of the coating after drying (noted hereinafter es) is measured by magnetic induction according to ISO 2808: 2007. The measurements are carried out after one week of drying at a temperature of 25 ° C. ± 3 ° C. and 50% ± 5% relative humidity. The thickness measured is 40 ± 6 μm.

Adhesion test:

The adhesion of the coating is evaluated according to the ISO 2409: 2013 standard by streaking the surface of the QD 36 steel plate (Q-panel) with a comb with blades 1 mm apart, then removing and removing on the streaks an adhesive whose adhesion strength on steel is 750 Nm ^"1. Depending on the surface Sar of the coating torn off with the adhesive, an adhesion index of the coating on its support (noted hereinafter Iadh ) ranging from 0 (excellent adhesion) to 5 (almost zero adhesion) is attributed to coatings:

 - Iad = 0 → Sar = 0%,

 - Iadh = 1 → 0% <Sar≤ 5%,

 - Iadh = 2-5% <Sar≤ 15%,

 - Iadh = 3 → 15% <Sar≤ 35%,

 - Iadh = 4 → 35% <Sar≤ 65%,

 - Iadh = 5 → Sar> 65%,

 The adhesion test gives Iadh = 0: the adhesion of the coating on the surface of the metal plate is excellent. 3- Assessment of self-healing properties

First self-healing test:

 In a first step, the self-healing properties are evaluated hot by placing the metal plates previously used for physicochemical tests and having the streaks of the adhesion tests, in an oven at 90 ° C for 20 minutes.

Self-healing coatings of the invention are compared with a conventional coating, a control formulation using the same resin ^(® Synocure 854 BA 80) and a crosslinkable non-cleavable, e. Tolonate ™ HDT-LV2 sold by Vencorex Chemicals. The thickness of the applied reference formulation is also 100 μm wet thickness to have the same dry thickness as before, ie 40 μm ± 6 μm. Streaks are made on the reference plate in the same way for the plates of 1'nvention, streaking the surface of the plate with a comb whose blades are spaced 1 mm.

 Photographs of the plates are made before and after heating, and are shown in Figure 1 (photograph from the top: before baking - photograph of the bottom lb: after steaming).

 The plates made with the crosslinking agent 1 of the invention are compared to the reference plate (T) comprising the Tolonate ™ HDT-LV2. In contrast to the reference plate on which the striations have not evolved, it is observed that some of the striations present on the coating of the invention have closed by healing.

Second self-healing test:

 In order to verify that the self-healing properties are not modified, a second self-healing test is performed on the same plates having already undergone the first self-healing test: new striations are made, and the plates are subjected to a second passage in the oven for 20 minutes at a temperature of 90 ° C.

 Photographs of the plates are made before and after heating, and are shown in Figure 2 (top 2a photographs: before baking - bottom 2b photographs: after steaming).

 The coating of the invention still has self-healing properties and several successive hot scars seem possible, which is not the case of the reference coating.

Claims

1. A reactive organic product characterized in that it comprises one or more multifunctional organic compounds corresponding to the following formula (I): [O = C = N- (R3-NHCO-R2-DA-R1-AD-R2-CONH) _x -R3-NHCO-R2-DA] _n -R1-AD-R2-CONH-R3- N = C = 0 (I) in which: X varies from 0 to 10,  ■ n varies from 1 to 2, R 1 is chosen from aliphatic groups in Q-Qo, or aromatic groups C ₆ -C ₂ o, or RI is an alkylaryl group in which the aryl group or groups are C ₆ -C ₂ o and the alkyl chains are in C1-C40, DA is a Diels-Alder adduct between a diene compound D carrying a chain R2 and a dienophilic compound A bearing an RI group, the diene functions of the diene compound D being chemically blocked by reaction of Diels-Alder with the dienophile compound A, R2 is a C ₁ -C ₄ alkyl chain bearing a hydroxyl group reacted with an isocyanate function to form a urethane bond, R 3 is chosen from C ₅ -C ₂₀ aliphatic groups or C ₆ -C ₁₂ aromatic groups. 2. Product according to claim 1, characterized in that the diene compound D is a cyclic diene, preferably a diene cyclic C ₅ -C ₆ optionally comprising a heteroatom, said diene compound D having thereon an alkyl chain R2 C1-C4 bearing a hydroxy group.  3. Product according to claim 1 or claim 2, characterized in that the diene compound D has the following formula: Rd in which : Z represents CH ₂ , O, S, or N-Rx in which Rx is chosen from linear or branched alkyl chains in CrCi _{2 /} and - Ra, Rb, Rc and Rd, identical or different, are chosen from H or C ₁ -C ₁₂ alkyl chains, at least one of the radicals Ra or Rd being a C 1 -C 2 alkyl chain carrying a hydroxyl group; .  4. Product according to claim 3, characterized in that the diene compound D bearing a C 1 -C 2 alkyl chain R2, carrying a hydroxyl group is furfuryl alcohol of formula: 5. Product according to one of claims 1 to 4, characterized in that the dienophile compound A is an alkene, preferably an optionally substituted Q-Ce cyclic alkene, bearing an RI group and comprising at least one imide group. .  6. Product according to claim 5, characterized in that said imide group is an α, β-ethylenically unsaturated imide preferably selected from the maleimide, tetrahydrophthalimide, the imide derivative of the anhydride or itaconic acid. 7. Product according to claim 5 or claim 6, characterized in that said dienophile A compound is a bismaleimide compound corresponding to the following formula: in which :  R 1 is a C 1 -C 4 alkoxylated chain, preferably comprising 1 to 20 alkoxylated units, such as ethoxy, propoxy or butoxy units, or a mixture of ethoxy and propoxy units, - Re, Rf, Rg and Rh, identical or different, are chosen from H, the linear or branched alkyl chains in CrCi ₂ , or Re and Rf on the one hand and Rg and Rh on the other hand are linked together to form a C ₆ aliphatic ring. 8. Product according to one of claims 1 to 7, characterized in that R3 is a cycloaliphatic group C ₅ -C _{6 /} optionally substituted by one or more linear or branched alkyl chains C Cs.  9. Process for preparing a reactive organic product comprising one or more multifunctional organic compounds of formula (I) according to one of claims 1 to 8, characterized in that it comprises the following steps:  (i) reaction between a diene compound D bearing a C2 alkyl chain carrying a hydroxy group and a diisocyanate O = C = N-R3-N = C = O, to obtain a compound O = C = N-R3 -NHCO-R2-D, then (ii) Diels-Alder reaction between the compound O = C = N-R3-NHCO-R2-D obtained at the end of step (i) and a dienophile compound of formula R1- (A) _{n +} 1, to obtain a reactive organic product comprising one or more multifunctional organic compounds of formula (I), x, n, D, A, R 1, R 2 and R 3 being as defined in claims 1 to 8.  10. Process for preparing a reactive organic product comprising one or more multifunctional organic compounds of formula (I) according to one of claims 1 to 8, characterized in that it comprises the following steps: (0 Diels-Alder reaction between a diene compound D bearing an alkyl chain R2 Ci-C ₄ bearing a hydroxy group and a dienophile compound of formula R1- (A) _{n + 1} , to obtain a compound R1- (AD-R2) _{n + 1} , then (ii ') reaction between the compound R1- (AD-R2) _n + i obtained at the end of step (O) and a diisocyanate O = C = N-R3-N = C = O, to obtain a product organic reagent comprising one or more multifunctional organic compounds of the formula (D, x, n, D, A, R 1, R 2 and R 3 being as defined in claims 1 to 8. 11. The method of claim 9 or claim 10, characterized in that the diene compound D bearing a C 1 -C 2 alkyl chain carrying a hydroxy group is furfuryl alcohol, and the dienophile compound of formula R1- (A _{n +} i is a bismaleimide compound having the following formula: wherein R1, Re, Rf, Rg and Rh are as defined in claim 7. 12. The method of claim 10 or claim 11, characterized in that step (ϋ ') is carried out, in the absence of solvent, by addition of diisocyanate 0 = C = N-R3-N = C = 0 on the compound R1- (AD-R2) _{n + 1} obtained at the end of step (O, with for n = 1 a molar ratio of diisocyanate / compound R1- (AD-R2) _{n +} 1 ranging from 2.10 to 2 , 40, and preferably from 2.10 to 2.20.  13. Method according to one of claims 9 to 12, characterized in that step (i) or 00 is carried out in the presence of a catalyst, and preferably in the presence of a tin-based catalyst, bismuth, titanium, zinc, or zirconium.  14. Use of a reactive organic product comprising one or more multifunctional organic compounds of formula (I) according to one of claims 1 to 8, or obtained by a process according to one of claims 9 to 13, as cleavable crosslinking agent. in a two-component reactive composition, and preferably in a crosslinkable two-component reactive composition.  15. Use according to claim 14, characterized in that said bi-component reactive composition comprises an acrylic resin functionalized with hydroxyl groups. 16. Crosslinkable composition characterized in that it comprises a reactive organic product comprising one or more multifunctional organic compounds of formula (I) according to one of claims 1 to 8, or obtained by a process according to one of claims 9 to 13, and a component comprising at least one reactive functional group capable of reacting with said reactive organic product. 17. Composition according to claim 16, characterized in that said component comprising at least one reactive functional group capable of reacting with said reactive organic product is an acrylic resin functionalized with hydroxyl groups.  18. A composition according to claim 16 or claim 17, characterized in that it is a coating composition chosen from paints, varnishes, inks and adhesives, a molding composition, a composition of composite, or a sealing composition.  19. Use of a crosslinkable composition according to one of claims 16 to 18 for the self-healing of the surface of coatings or articles based on said composition, or for the recycling of thermoplastic or thermosetting polymers, in particular composite molded parts.  20. A method of self-healing characterized in that it comprises a step of applying a crosslinkable composition according to one of claims 16 to 18 on a substrate, followed by a step of protection-deprotection by Diels-Alder diene functions chemically blocked organic reactive product according to one of claims 1 to 8 contained in said composition, under the effect of an external energy such as conduction, convection, or radiation.  21. The method according to claim 20, characterized in that the step of protection by retro-Diels-Alder is a thermo-cleavage step performed by heating at a temperature ranging from 60 to 120 ° C, and preferably from 70 to 100 ° C.