Epoxy vitrimer formulations

Abstract

The present invention refers to an epoxy monomer of formula (I): [Formula I] The invention further relates to processes for the preparation of the epoxy monomer, and to epoxy vitrimers, compositions and uses thereof.

Description

[0001] EPOXY VITRIMER FORMULATIONS

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to the field of vitrimers, and more particularly to the field of epoxy monomers for vitrimers. The present disclosure further relates to the processes of preparation of epoxy monomers, vitrimer formulations and uses thereof.

[0004] BACKGROUND

[0005] Vitrimers are polymeric materials whose network is formed by covalent bonds which can carry out bond exchange reactions, and thus be reversible. These exchanges can be either dissociative, when the bonds break first and then form again at another location resulting into an abrupt drop of its viscosity; or associative, when the covalent bonds don’t break until a new one has already formed in another position.

[0006] At service temperature, vitrimers behave like traditional thermosets, which have good thermal and mechanical properties. When under external force, exchange reactions induce a topology rearrangement and fast stress relaxation and, as a result, vitrimers can flow like a viscoelastic fluid.

[0007] Vitrimers have attracted significant attention in recent years due to their potential for several applications such as self-healing materials, re-usable adhesives, or recyclable and reconformable composite materials. The Arrhenius-type temperature dependence of the melt viscosity of vitrimers permits welding or re-adhesion while preserving the shape of the objects to be assembled. The selective cleavage of the exchange bonds can also serve as a practical route to the closed-loop recycling of vitrimer composites. It is possible for the vitrimeric thermosets to be degraded and dissolved in solvents.

[0008] Exchangeable reactions are explored for various vitrimers, especially for epoxies, including transesterification, imine metathesis or disulfide metathesis, among others. The network topology of epoxy vitrimers can be changed by these stimuli triggered (usually heat) exchangeable reactions, enabling vitrimers to be reprocessed, reshaped, remoulded, and recycled at high temperatures.

[0009] Few reports describe vitrimer networks which combine more than one exchange mechanism. Some authors have combined disulfide metathesis and carboxylate transesterification to obtain vitrimers with dual exchange reaction mechanism. Other authors obtained vitrimers with disulfide and imine metathesis exchange reaction mechanisms. Guo et al. (Polymer 2020, 197, 122483) synthesized a dialdehyde monomer with two molecules of vanillin linked with 4-bromomethyl benzaldehyde and then prepared polyimine thermosetting materials with tris(2-aminoethyl) amine and 4,4- disulfanediyldianiline as curing agents. Xiang et al. (Macromolecules, 2022, 55, 23, 10276-10284) synthesized an aminophenyl diamine and, in combination with 4- aminophenyl disulfide, used them as curing agents of a DGEBA resin.

[0010] Therefore, there remains a need in the art to develop novel self-healing, mechanically and thermally strong vitrimer materials, and epoxy monomers with the ability of forming dynamic functionalities within the vitrimer.

[0011] BRIEF DESCRIPTION OF THE INVENTION

[0012] The authors of the present invention have developed an epoxy monomer which combines more than one dynamic covalent bond, in particular, imine and disulfide, and is thus suitable for the preparation of vitrimer networks with dual exchange reaction mechanism.

[0013] Advantageously, the groups involved in the exchange reactions are part of the epoxy monomer, any curing agent suitable for epoxy resins can be used to obtain a vitrimer. Moreover, the vitrimer formulations obtained from such monomer surprisingly resulted in relatively high Tg’s and storage modulus E’ at room temperature, along with extremely fast T at low temperatures.

[0014] Therefore, in a first aspect, the present invention relates to an epoxy monomer of formula

[0015] (I): wherein:

[0016] - R1is (C2-C4)-alkylene or arylene;

[0017] - R7is hydrogen or (Ci-C3)-alkyl; - R2to R6are independently selected from hydrogen, halo, nitro, cyano, optionally substituted (Ci-Ce)-alkoxy, and glycidoxy, provided that at least one of R2to R6is glycidoxy.

[0018] In a second aspect, the invention relates to a process for the preparation of an epoxy monomer of formula (I) comprising the steps of: i) providing a vanillin derivative of formula (II): wherein Rais selected from hydrogen and (Ci-C3)-alkyl; and each Rbis a substituent independently selected from -OH, halo, nitro, cyano and (Ci-Ce)- alkoxy, wherein n is 1 , 2, 3, 4, or 5; ii) transforming one or more Rbin the vanillin derivative of formula (II); into a glycidyl ether group to yield a compound of formula (III): wherein:

[0019] - Raand each Rbare as defined above for the compound of formula (II),

[0020] - each Rcis glycidoxy,

[0021] - x is 0, 1 , 2, 3, or 4,

[0022] - y is 1 , 2, 3, 4, or 5; iii) reacting the compound of formula (III) with a compound of formula (IV): wherein R1is selected from (C2-C4)-alkylene and arylene group, to yield a compound of formula (I).

[0023] In another aspect, the invention relates to an epoxy vitrimer comprising the epoxy monomer as disclosed herein.

[0024] In a further aspect, the invention relates to a curable composition comprising the epoxy monomer as disclosed herein.

[0025] In a final aspect, the invention relates to the use of the epoxy monomer, the epoxy vitrimer or the curable composition as disclosed herein for structural and / or electronic applications.

[0026] FIGURES

[0027] Figure 1 : (a)1H-NMR and (b)13C-NMR spectra of a vanillin glycidyl ether derivative (VGE) in CDCh

[0028] Figure 2: (a)1H-NMR and (b)13C-NMR spectra of an epoxy monomer according to the invention (Cyst-BVGE) in CDCI3.

[0029] Figure 3: (a)1H-NMR and (b)13C-NMR spectra of an ethyl vanillin glycidyl ether derivative (EtVGE) in CDCI3.

[0030] Figure 4: (a)1H-NMR and (b)13C-NMR spectra of homocystamine (Homocyst) in CDCI3.

[0031] Figure 5: (a)1H-NMR and (b)13C-NMR spectra of an epoxy monomer according to the invention (Cyst-BEtVGE) in CDCI3.

[0032] Figure 6: (a)1H-NMR and (b)13C-NMR spectra of an epoxy monomer according to the invention (Homocyst-BVGE) in CDCI3.

[0033] Figure 7. (a)1H-NMR and (b)13C-NMR spectra of an epoxy monomer according to the invention (Homocyst-BEtVGE) in CDCI3.

[0034] Figure 8: Chemical structure of the amine-base curing agents employed TREN, IPDA, m- XDA, DAC.

[0035] Figure 9: (a) TGA and (b) TGA 1stderivative curves of Cyst-BVGE cured samples with different amines (TREN, IPDA, m-XDA, DAC). Figure 10: Superposed DSC thermograms of cured samples showing the Tgof Cyst-BVGE cured with TREN, I PDA, m-XDA, DAC.

[0036] Figure 11 : E’ modulus and tand as a function of temperature for the samples studied.

[0037] Figure 12: Fitting of stress relaxation results to the Arrhenius’ equation of the samples studied.

[0038] Figure 13: Angell fragility plot of the logarithm of the viscosity as a function of Tv / T. Dashed line: ideal strong liquid.

[0039] Figure 14: E’ modulus and tand as a function of temperature for the formulation Cyst- BEtVGE / lPDA.

[0040] Figure 15: Fitting of stress relaxation results to the Arrhenius’ equation for the formulation Cyst-BEtVGE / lPDA.

[0041] Figure 16: E’ modulus and tand as a function of temperature for the formulation Homocyst- BVGE / IPDA.

[0042] Figure 17: Fitting of stress relaxation results to the Arrhenius’ equation for the formulation Homocyst-BVGE / IPDA.

[0043] Figure 18: E’ modulus and tand as a function of temperature for the formulation Homocyst- BEtVGE / lPDA.

[0044] Figure 19: Fitting of stress relaxation results to the Arrhenius’ equation for the formulation Homocyst-BEtVGE / lPDA.

[0045] DETAILED DESCRIPTION OF THE INVENTION

[0046] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs. As used herein, the singular forms “a”, “an” and “the” include plural reference unless the context clearly dictates otherwise.

[0047] In the context of the present invention, the following terms have the meaning that is described in detail below.

[0048] The term “(C2-C4)-alkylene” refers to a linear or branched divalent hydrocarbon chain radical consisting of carbon and hydrogen atoms, containing no unsaturation, having between 1 and 5 carbon atoms and which is attached to the rest of the molecule by two bonds, including for example and in a non-limiting sense, e.g., ethylene, propylene, butylene, and the like, preferably ethylene, or propylene.

[0049] The term “arylene” refers to a divalent aromatic ring system which comprises 6 carbon atoms and is bound to the molecule through two bonds, e.g., arylene refers to a phenylene radical bound to the rest of the molecule by means of (1 ,2), (1 ,3) or (1 ,4) bonds.

[0050] The term “halogen” refers to bromine, chlorine, iodine, or fluorine.

[0051] The term “hydroxyl” or “hydroxy” refers to an — OH group.

[0052] The term “oxo” refers to a =0 group.

[0053] The term “carboxy” refers to a — COOH group.

[0054] The term “nitro” refers to a — NO2 group.

[0055] The terms “nitrile” or “cyano” can be used interchangeably and refer to a — CN group.

[0056] The term “(Ci-C6)-alkyl” refers to a linear or branched hydrocarbon chain radical consisting of carbon and hydrogen atoms, containing no unsaturation, having between 1 and 6 carbon atoms and which is attached to the rest of the molecule by a single bond, including for example and in a non-limiting sense, methyl, ethyl, n-propyl, i-propyl, n- butyl, t-butyl, n-pentyl, etc.

[0057] The term “(Ci-C6)-alkoxy” refers to a radical of the formula — OR’ where R’ is a radical (Ci-Ce)-alkyl as generally defined above.

[0058] The term “glycidoxy” can be used interchangeably with “glycidyl ether” or “2,3- epoxypropoxy”, and refers to a radical of the formula — OR’ where R’ is a C3 alkyl group having an oxirane ring functionality.

[0059] When the compounds of the invention have chiral centers they can exist in different stereoisomeric forms, such as enantiomeric or diastereomeric forms. Thus, any given compound referred to herein is intended to represent any one of a racemate, one or more enantiomeric forms and one or more diastereomeric forms. All the stereoisomers including enantiomers and diastereoisomers of the compounds referred to herein, and mixtures thereof (including racemic mixtures, enantiomerically enriched mixtures and diastereomerically enriched mixtures), are considered within the scope of the present invention. Also, the invention further contemplates any E / Z possible isomers.

[0060] Epoxy monomer

[0061] As defined above, a first aspect of the present invention relates to an epoxy monomer of formula (I): wherein:

[0062] - R1is (C2-C4)-alkylene or arylene;

[0063] - R7is hydrogen or (Ci-C3)-alkyl;

[0064] - R2to R6are independently selected from hydrogen, halo, nitro, cyano, (Ci-Ce)-alkoxy, and glycidoxy, provided that at least one of R2to R6is glycidoxy.

[0065] In the above compound of formula (I), R1is (C2-C4)-alkylene or arylene.

[0066] In a particular embodiment, R1is (C2-C4)-alkylene, preferably selected from the group consisting of, 1 ,2-ethylene, 1 ,3-propylene or 1 ,4-butylene. In a more preferred embodiment, R1is selected from, 1 ,2-ethylene and 1 ,3-propylene. Most preferably, R1is

[0067] 1.2-ethylene.

[0068] In another particular embodiment, R1is arylene.

[0069] In a more particular embodiment, R1is selected from the group consisting of 1 ,2-arylene,

[0070] 1.3-arylene or 1 ,4-arylene.

[0071] In a preferred embodiment, R1is 1 ,4-arylene, i. e., a phenyl ring bound with the rest of the molecule by means of (1 ,4) bonds.

[0072] In the above compound of formula (I), R7is hydrogen or (Ci-C3)-alkyl.

[0073] In a particular embodiment, R7is (Ci-C3)-alkyl selected from the group consisting of methyl, ethyl, n-propyl, isopropyl. More preferably, R7is methyl or ethyl, even more preferably R7is methyl.

[0074] In a further preferred embodiment, R7is hydrogen. In the above compound of formula (I), R2to R6are independently selected from hydrogen, halo, nitro, cyano, (Ci-Ce)-alkoxy, and glycidoxy, wherein at least one of R2to R6is glycidoxy.

[0075] In a particular embodiment, one or two of R2to R6is glycidoxy, preferably R3and / or R4.

[0076] In a particular embodiment, one of R2to R6is glycidoxy as defined above, preferably R4.

[0077] In another particular embodiment, at least one of R2to R6is (Ci-Ce)-alkoxy, preferably (Ci-Ce)-alkoxy selected from the group consisting of methoxy, ethoxy, propoxy, butoxy, pentoxy and hexoxy, more preferably (Ci-Ce)-alkoxy selected from the group consisting of methoxy, ethoxy, propoxy or butoxy, even more preferably selected from the group consisting of methoxy or ethoxy.

[0078] In a more particular embodiment, one of R2to R6is glycidoxy and the rest of R2to R6are hydrogen. In a more preferred embodiment, R4is glycidoxy and R2, R3, R5, R6are hydrogen.

[0079] In a preferred embodiment, one of R2to R6is glycidoxy, one of R2to R6is methoxy or ethoxy and the rest of R2to R6are hydrogen. In a more preferred embodiment, R4is glycidoxy, R3is methoxy or ethoxy and R2, R5, R6are hydrogen.

[0080] In a preferred embodiment, R1is selected from 1 ,2-ethylene and 1 ,3-propylene, R7is hydrogen, one of R2to R6, preferably R4, is glycidoxy, one of R2to R6, preferably R3, is methoxy or ethoxy and the rest of R2to R6are hydrogen.

[0081] In a particular embodiment, the epoxy monomer of formula (I) is selected from the group consisting of:

[0082] In a preferred embodiment, the epoxy monomer of formula (I) is selected from the group consisting of the compound of formula (la) and the compound of formula (lb).

[0083] In another particular embodiment, the epoxy monomer of formula (I) is selected from the group consisting of:

[0084] In a preferred embodiment, the epoxy monomer of formula (I) is selected from the group consisting of the compounds of formula (la) to (le). Method

[0085] A second aspect of the invention is directed to a process for the preparation of an epoxy monomer of formula (I) comprising the steps of: i) providing a vanillin derivative of formula (II): wherein Rais selected from hydrogen and (Ci-C3)-alkyl; and each Rbis a substituent independently selected from -OH, halo, nitro, cyano and (Ci-Ce)- alkoxy, wherein n is 1 , 2, 3, 4, or 5; ii) transforming one or more Rbin the vanillin derivative of formula (II); into a glycidyl ether group to yield a compound of formula (III): wherein:

[0086] - Raand each Rbare as defined above for the compound of formula (II),

[0087] - each Rcis glycidoxy,

[0088] - x is 0, 1 , 2, 3, or 4,

[0089] - y is 1 , 2, 3, 4, or 5; iv) reacting the compound of formula (III) with a compound of formula (IV): wherein R1is selected from (C2-C4)-alkylene and arylene, to yield a compound of formula (I).

[0090] Step (i)

[0091] The process of the invention comprises a step (i) of providing a vanillin derivative of formula (II) as defined above.

[0092] Vanillin (IIIPAC name: 4-hydroxy-3-methoxybenzaldehyde) is the primary component of the extract of the vanilla bean. It is a phenolic aldehyde bearing hydroxyl and ether functional groups. The compounds of formula (II) can be obtained from commercial sources or be prepared by chemical synthesis methods described in the state of the art or variations thereof which fall under the common general knowledge of one skilled in the art.

[0093] In the compound of formula (II), Rais selected from the group consisting of hydrogen and C1-C3 alkyl. In a particular embodiment, Rais selected from the group consisting of methyl, ethyl, propyl and isopropyl. In a preferred embodiment, Rais methyl or ethyl. In another preferred embodiment, Rais hydrogen.

[0094] In the compound of formula (II) as defined above, each instance of Rbis independently selected from OH, halo, nitro, cyano and (Ci-Ce)-alkoxy as defined above. Each Rbmay be attached at any available position in the benzene ring of the vanillin derivative of formula (II).

[0095] In a particular embodiment, n is 2.

[0096] In a more particular embodiment, when n is 2, one instance of Rbis -OH and another instance of Rbis (Ci-C6)-alkoxy. Preferably, the (Ci-C6)-alkoxy is selected from the group consisting of methoxy, ethoxy, propoxy, butoxy, pentoxy and hexoxy, more preferably (Ci- Ce)-alkoxy selected from the group consisting of methoxy, ethoxy, propoxy or butoxy, even more preferably selected from the group consisting of methoxy or ethoxy.

[0097] In a more preferred embodiment, one instance of Rbis -OH, and another instance of Rbis methoxy or ethoxy, preferably methoxy. More preferably, one instance of Rbis-OH at position 4 of the vanillin derivative of formula (II) and another instance of Rb is methoxy or ethoxy, preferably methoxy, at position 3 of the vanillin derivative of formula (II).

[0098] Step (ii)

[0099] The process of the invention further comprises a step (ii) of transforming at least one Rbin the vanillin derivative of formula (II) of step (i); into a glycidyl ether group to yield a compound of formula (III) as defined above. In the compound of formula (III), Rais as defined above. Preferably, Rais methyl or hydrogen, more preferably hydrogen.

[0100] Each instance of Rbis as defined above.

[0101] Each instance of Rcis glycidoxy.

[0102] In a particular embodiment, x is 1 and / or y is 1.

[0103] In a more particular embodiment, when x is 1 , Rbis (Ci-Ce)-alkoxy, preferably methoxy or ethoxy, more preferably methoxy. In a preferred embodiment, Rbis at position 3 of the compound of formula (III).

[0104] In a particular embodiment, when y is 1 , Rcis glycidoxy. In a preferred embodiment, Rcis at position 4 of the compound of formula (III).

[0105] Step (ii) is performed by conversion of one or more of the Rbgroups in the vanillin derivative of formula (II) into a glycidyl ether group.

[0106] Conversion of a Rbgroup into a glycidyl ether group can be carried out by any suitable means known in the art.

[0107] In an embodiment, step (ii) is carried out by reacting at least one instance of Rb, preferably being hydroxy, in the compound of formula (II) with a compound of formula R”-X, where R” is 2, 3-epoxy propyl, / . e., a glydicyl group, and X is a leaving group selected from halogen; more preferably chloro, bromo, iodo, even more preferably chloro, or bromo.

[0108] In a preferred embodiment, the compound of formula R”-X is selected from 2- (chloromethyl)oxirane, and 2-(bromomethyl)oxirane . Most preferably, the compound of formula R”-X is 2-(chloromethyl)oxirane, / . e., epichlorohydrin.

[0109] In a particular embodiment, the reaction is carried out by mixing a compound of formula (II) and a compound of formula R”-X in the presence of a catalyst, followed by addition of a base.

[0110] Suitable catalysts are for example phase-transfer catalysts for anionic reactants. Examples of phase transfer catalysts include, without limitation quaternary ammonium salts such as benzyltriethylammonium chloride, methyltricaprylammonium chloride, methyltributylammonium chloride, organic phosphonium salts such as hexadecyltributylphosphonium bromide, crown ethers and polyethylene glycols. In a particular embodiment, the catalyst is selected from the group consisting of benzyltriethylammonium chloride, methyltricaprylammonium chloride, methyltributylammonium chloride. In a preferred embodiment, the catalyst is benzyltriethylammonium chloride.

[0111] In a preferred embodiment, the catalyst is benzyltriethylammonium chloride.

[0112] In a particular embodiment, the compound of formula (II) and the compound of formula R”- X may be in a molar ratio ranging from 0.1 :10 to 3:1 , preferably 0.5:5 to 1 :1 , more preferably about 1 :5.

[0113] The mixing may be carried out under stirring for a period ranging from 5 min to 24 hours, preferably from 1 hour to 10 hours, more preferably about 3 hours. In an embodiment, the mixing is performed at a temperature between room temperature and 150 °C, preferably at a temperature between 50 °C and 100 °C.

[0114] Suitable bases include inorganic bases such as an alkali metal carbonate or bicarbonate (e.g. Na2CO3, K2CO3, Cs2CO3, Li2CO3, NaHCO3, KHCO3, CsHCO3, LiHCO3), an alkali metal phosphate (e.g. Na3PC>4, K3PO4, Na2HPC>4, K2HPC>4, NaH2PC>4, KH2PC>4), an alkali metal alkoxide (e.g. NaOMe, KOMe, NaOEt, KOEt, NaOtBu, KOtBu), an alkali metal hydroxide (e.g. NaOH, KOH, LiOH, CsOH). Preferably, the base is an alkali metal hydroxide. Most preferably, the base is sodium hydroxide.

[0115] In a particular embodiment, the addition of the base may be performed at a temperature ranging from -0 °C to 30 °C, preferably at room temperature.

[0116] In a particular embodiment, upon completion of the base addition, the resulting mixture is stirred for a period ranging from 5 minutes to 24 hours, preferably from 1 hour to 10 hours, more preferably for about 2 hours.

[0117] In a particular embodiment, the reaction of step (ii) such as the mixing and / or the addition of the base may be carried out in the absence of a solvent.

[0118] In another particular embodiment, the reaction of step (ii) such as the mixing and / or the addition of the base may be carried out in the presence of a solvent. Examples of suitable solvents include, without limitation, water, organic solvents such as cyclic or acyclic ethers (e.g. Et2O, iPr2O, tBu2O, MeOtBu, 1 ,4-dioxane, tetra hydrofuran, methyltetrahydrofuran), halogenated solvents (e.g. dichloromethane, chloroform, chlorobenzene), ketone (e.g. acetone, butanone, pentanone, methyl ethyl ketone, ethyl isopropyl ketone), ester (e.g. EtOAc, iPrOAc), nitrile (e.g. acetonitrile, benzonitrile), amide (e.g. DMF, DMA, HMPA, NMP), alcohol (e.g. methanol, ethanol, propanol, isopropanol, sec-butanol, t-butanol), sulfoxide (DMSO) and mixtures thereof.

[0119] In a more particular embodiment, this reaction may be carried out in the presence of a solvent, such as water, organic solvents or mixtures thereof as described above. Preferably, the solvent is selected from the group consisting of water, ketone and alcohol solvents.

[0120] Step (iii)

[0121] The process of the invention further comprises a step (iii) of reacting the compound of formula (III) from step (ii) with a disulfide derivative of formula (IV): 2to yield a compound of formula (I) as defined above.

[0122] In the compound of formula (IV), R1is selected from (C2-C4)-alkylene and arylene group. Particular and preferred embodiments are as those defined above for R1in the compound of formula (I).

[0123] Particular and preferred embodiments for the compound of formula (III) are as those defined above.

[0124] The reaction of step (iii) may be carried out in any suitable conditions known in the art for the formation of an imine bond between the carbonyl group present in the compound of formula (III) and the amine group(s) present in the compound of formula (IV).

[0125] This reaction may be carried out by mixing the compound of formula (III) and the compound of formula (IV), preferably in a molar ratio ranging between 0.5:1 to 5:1 , more preferably in a molar ratio of about 2: 1 .

[0126] In a particular embodiment, the reaction of step (iii) may be carried out at a temperature ranging from 0 to 60 °C, preferably from 10 to 30 °C, more preferably at room temperature.

[0127] In a particular embodiment, the reaction of step (iii) may be carried out for a period ranging from 5 minutes to 24 hours, preferably for a period ranging from 0.5 hours to 10 hours, more preferably for a period of about 2 hours.

[0128] In a particular embodiment, the reaction of step (iii) may be carried out in the presence of an organic solvent. Suitable organic solvents are those as defined above. In a particular embodiment, the solvent is an ether, preferably selected from the group consisting of tetrahydrofuran and methyltetrahydrofuran. In another particular embodiment, the solvent is a halogenated organic solvent, preferably, selected from the group consisting of chloroform, dichoromethane or mixtures thereof. In a more particular embodiment, step (iii) further comprises applying vacuum upon completion of the reaction to remove the solvent. In an even more particular embodiment, vacuum is applied for a period between 2 and 24 hours, optionally under heating at a temperature between 30 and 60 °C.

[0129] Epoxy vitrimer

[0130] In still another aspect of the present disclosure, there is provided an epoxy vitrimer comprising the epoxy monomer as disclosed herein, in any of its particular embodiments.

[0131] As used herein, the term ‘vitrimer’ refers to a covalently crosslinked polymer that can change its topology by internal bond-exchange reactions. Below a certain temperature (Tv - topology freezing transition temperature), vitrimers behave as a conventional thermoset polymer, but at or above said temperature (Tv) they can flow as a viscoelastic liquid.

[0132] In a particular embodiment, the vitrimer comprises: a. the epoxy monomer as disclosed herein in any of its particular embodiments; and b. a curing agent,

[0133] As used herein the term “curing agent” refers to a compound which, when mixed with the epoxy monomer, produces a cured or hardened product by generating cross links within the polymer. Curing agents may also be referred to as hardeners.

[0134] Advantageously, the epoxy monomer of formula (I) can be used with any type of curing agent and keep its vitrimer properties. Suitable epoxy curing agents include, without limitation, primary and / or secondary amines, thiols, alcohols and phenols, carboxylic acids and carboxylic acid anhydrides, or combinations thereof.

[0135] In a particular embodiment, the curing agent is one or more of amine, thiol, carboxylic acid, alcohol and phenol curing agents or combinations thereof. In a preferred embodiment, the curing agent is an amine curing agent. Non-limiting examples of amine curing agents are diethylenetriamine, triethylenetetramine or polyether amines such as polyoxyalkylene amines including diamines and triamines, for example, as those commercially available under the tradename Jeffamine®. In a more preferred embodiment, the curing agent is selected from the group consisting of 1 ,2-diaminocyclohexane (DAC), 5-amino-1 ,3,3- trimethylcyclohexanemethylamine (isophorone diamine (I PDA), m-xylylenediamine (m- XDA), tris(2-aminoethyl)amine (TREN) and combinations thereof. The epoxy vitrimer as disclosed herein has a dynamic network comprising two dynamic bonds obtained by imine and disulfide functional groups. As used herein, the terms “dynamic bond” or "dynamic bond functional group" refer to a bond or functional group that can reversibly form and dissociate in response to external stimuli such as temperature or light. In a particular embodiment, the epoxy vitrimer may comprise one or more further dynamic bonds, for example, hydroxyester, imine, disulfide, carbamate, acetal, siloxane, urea, vinylogous urethane groups, or combinations thereof.

[0136] In a particular embodiment, the epoxy monomer and the curing agent are present in a molar ratio within the vitrimer ranging from 1 :5 to 20:0.5, preferably from 1 :1 to 15:1 , more preferably from about 1 :1 to about 3:1 .

[0137] In a particular embodiment, the vitrimer has a glass transition temperature (Tg) of at least 90 °C, preferably at least 95 °C. In another particular embodiment, the vitrimer has a Tgbetween 90 and 110 °C, preferably between 95 and 105 °C. For the purpose of the present invention, glass transition temperature can be determined by DSC according to standard ISO 11357-2:2020.

[0138] In a particular embodiment, the vitrimer has a storage modulus (E’) at glassy state, such as measured at room temperature, in a range of about 2.3 to about 3.2 GPa, preferably about 2.5 to about 3.0 GPa, as determined according to EN ISO 6721-1.

[0139] The term “room temperature” as used herein and part of the general knowledge for a person skilled in the art, refers to a temperature in the range of 20 °C to 25 °C.

[0140] The epoxy vitrimer of the present invention may be obtained by (a) mixing and heating the epoxy monomer and the hardening agent to obtain a mixture; and (b) curing said mixture to obtain the vitrimer.

[0141] In a particular embodiment, the epoxy monomer and the hardening agent are mixed in a stoichiometric proportion. For example, when the hardening agent is a diamine, the epoxy monomer and the hardening agent are mixed in a proportion of 1 mole of hardening agent per 2 moles of epoxide monomer or when the hardening agent is a triamine, the epoxy monomer are mixed in a proportion of 1 mole of hardening agent per 3 moles of epoxide monomer.

[0142] In a particular embodiment, the heating of step (a) is performed at a temperature ranging from 35 °C to 80 °C, preferably from 40 °C to 60 °C. In a particular embodiment, the mixture of step (a) is cured at a temperature ranging from 90 to 160 °C for a period of 1 to 10 h.

[0143] Curable composition

[0144] In another aspect, the present invention is directed to a curable composition comprising:

[0145] (a) an epoxy compound of formula (I) as defined above in any of its particular embodiments; and

[0146] (b) a curing agent.

[0147] Suitable curing agents are as those described above for the epoxy vitrimer. In a particular embodiment, the curing agent is selected from the group consisting of amine, thiol, carboxylic acid, alcohol, phenol and carboxylic acid anhydride curing agents. In a preferred embodiment, the curing agent is an amine curing agent. More preferably, the curing agent is selected from the group consisting of 1 ,2-diaminocyclohexane (DAC), 5-amino-1 ,3,3- trimethylcyclohexanemethylamine (isophorone diamine (I PDA), m-xylylenediamine (m- XDA), tris(2-aminoethyl)amine (TREN) and combinations thereof.

[0148] In a particular embodiment, the epoxy monomer and the curing agent are present in a molar ratio in the composition ranging from 1 :5 to 20:0.5, preferably from 1 :1 to 15:1 , more preferably of about 1 : 1 to about 3: 1 .

[0149] In a particular embodiment, the curable composition is in the form of a liquid composition. The epoxy monomer is typically separated from the curing agent prior to use of the curable composition. Thus, in a particular embodiment, the epoxy monomer is present in a first portion, and the curing agent is present in a second portion of the curable composition.

[0150] Uses

[0151] In another aspect, the present invention is directed to the use of an epoxy monomer, an epoxy vitrimer or a curable composition as disclosed herein as an adhesive, coating or a matrix for composite materials, preferably as an adhesive. The epoxy monomer and related products as disclosed herein may be used for structural applications such as in construction, aerospace and automotive fields. The epoxy monomer and related product as disclosed herein may be further used for electronic applications such as a component in internal circuits, transistors, printed circuit boards. EXAMPLES

[0152] The invention is illustrated by means of the following examples which in no case limit the scope of the invention.

[0153] Materials

[0154] The following chemicals were purchased from Sigma Aldrich: Cystamine dihydrochloride (96%) (was previously neutralized with a 1 M sodium hydroxide solution and extracted with dichloromethane to obtain the free base), 3-chloropropylamine hydrochloride (98%), 1 ,2- diaminocyclohexane (DAC, 99%, mixture of cis and trans), (±)-epichlorohydrin (ECH, >99%), 3-ethoxy-4-hydroxybenzaldehyde (ethyl vanillin, >98%), 4-hydroxy-3- methoxybenzaldehyde (Vanillin, 99%), sodium thiosulfate (99%). Iodine (99%) was purchased from Glentham Life. 5-Amino-1 ,3,3-trimethylcyclohexanemethylamine (isophorone diamine (IPDA), 99%, mixture of cis and trans) and benzyltriethylammonium chloride (BTEAC, 98%) were purchased from Acres Organics. Sodium hydroxide (pellets, 97%), m-xylylenediamine (m-XDA, 99%) and Tris(2-aminoethyl)amine (TREN, 97%) were purchased from Thermo Fisher Scientific. Anhydrous magnesium sulfate (99.5%, powder) was purchased from Alfa Aesar. Absolute ethanol (EtOH) was purchased from VWR Chemicals. Anhydrous dichloromethane (HPLC grade) (DCM) was obtained from Honeywell and dispensed MBraun SPS-800 solvent purifier. All the reagents were used as received unless otherwise specified.

[0155] Monomer characterization

[0156] All the synthesized products were characterized by proton and carbon nuclear magnetic resonance (1H-NMR and13C-NMR) using a Varian VNMR-S400 NMR spectrometer. CDCh was used as solvent. All chemical shifts were quoted on the 5 scale in part per million (ppm) using the residual solvent peak as reference (1H-NMR: CDCh = 7.26 ppm and13C-NMR: CDCh = 77.16 ppm).

[0157] Thermal characterization

[0158] The curing process was performed by differential scanning calorimetry (DSC) using Mettler DSC3+ instrument calibrated using indium (heat flow calibration) and zinc (temperature calibration) standards. Samples of approximately 8-10 mg were placed in aluminium pans with pierced lids and analysed under a flow of N2 at 50 mL / min. The curing process was studied in non-isothermal mode at 10 °C / min from 30 to 250 °C. The glass transition temperature (g) of the cured samples were determined in dynamic scans at 50 °C / min from -20 to 180 °C.

[0159] The thermal stability of cured samples was studied by thermogravimetric analysis (TGA), using a Mettler-Toledo TGA 2 thermobalance. All the experiments were performed under a flow of N2 at 50 mL / min. Pieces of cured samples of a mass of approximately 10 mg were degraded between 30 and 600 °C at a heating rate of 10 °C / min. The thermal stability was also studied in isothermal mode at 160 °C for 3 h.

[0160] Thermomechanical and mechanical characterization

[0161] Thermomechanical properties were measured using a TA Instruments DMA Q800 (New Castle, DE, USA) equipped with a tension film clamp. Prismatic rectangular samples of about 30 mm x 6 mm x 1 .5 mm were analysed at 1 Hz, 0.1% strain, and from 0 °C to 150 °C at 3 °C / min. The storage modulus at glassy state (Eg) and at rubbery state (E» was obtained at 30 °C and at Tg+ 50 °C, respectively. The Tgs were determined from the maximum of the peak of tanb.

[0162] Stress relaxation tests

[0163] Stress relaxation tests were carried out using a TA Instruments DMA Q800 (New Castle, DE, USA) equipped with a film tension clamp on samples with the same dimensions as previously defined. Samples were first equilibrated at ~Tgfor 5 min, then a constant strain of 1% (this deformation is within the linear range) was applied to the sample and the consequent stress level was monitored as a function of time. The process was repeated every 10 °C until 180 °C, depending on the formulation. The stress awas normalized by the initial stress Oo and the characteristic relaxation time r was determined as the time necessary to relax 1 / e of the initial stress value Oo. The activation energy Eawas calculated for each material by using an Arrhenius-type equation: where T is the time needed to attain a given stress relaxation value of 1 / e o , R is the gas constant, T is the absolute temperature, and A is the pre-exponential factor. The topology freezing temperature Tvcan be obtained as the temperature at which the material reaches a viscosity of 1012Pa s.

[0164] Creep experiments Creep and recovery properties were studied using a TA Instruments DMA Q800 (New Castle, DE, USA) equipped with a film tension clamp with the same dimensions as previously defined. A stress of 0.1 MPa was applied for 30 min at 60 °C (depending on the formulation), then the stress was immediately released, and the sample was left to recover for another 30 min. This procedure was repeated every 10 °C up to 150 °C. The viscosity was calculated using the following equation:

[0165] The deformation rate s was determined as the slope of the linear fit of the linear part of the variation of the strain as a function of time. The Fragility Angell plot was then obtained plotting r) as a function of Tg / T.

[0166] Example 1. Preparation of vanillin glycidyl ether (VGE)

[0167] The glycidyl ether derivative of the vanillin was synthesized as follows. 10.0 g (65.7 mmol) of vanillin, 25.5 mL (325.2 mmol, 4.95 eq.) of epichlorohydrin, and 0.78 g (3.4 mmol, 5 mol%) of benzyltriethylammonium chloride (TEBAC) were introduced into a twonecked round-bottom flask equipped with a magnetic stirrer and a condenser. The mixture was stirred at 80 °C for 3 hours. Next, the mixture was cooled down in an icewater bath, and 3.0 g (75.0 mmol, 1.14 eq.) of sodium hydroxide, solubilized in 11.5 mL of water, were added dropwise into the reaction mixture. Once added, the temperature was let to rise to room temperature and let under stirring for an additional 2 hours. After the completion of the reaction, the crude reaction mixture was diluted with 250 mL of ethyl acetate and washed thrice with 150 mL of NaCI solution. The organic phase was dried over anhydrous magnesium sulfate, filtered, and the solvent eliminated under rotary evaporator. The crude product was purified through recrystallization with 250 mL of hot ethanol, obtaining the pure product as needle-like white crystals with 88 % yield.

[0168] An improved procedure for the synthesis of the vanillin glycidyl ether (VGE) was carried out by following a modification of a reported procedure (Green Chem. 2019, 21 , 1484- 1497). 100.0 g (0.66 mol) of vanillin, 258 mL (3.30 mol) of epichlorohydrin, and 7.5 g (0.03 mol) of benzyltriethylammonium chloride (BTEAC) were introduced into a twonecked round-bottom flask equipped with a magnetic stirrer and a condenser. The mixture was stirred at 80 °C for 3 hours. Next, the mixture was cooled down in an icewater bath, and 29.0 g (0.73 mol) of sodium hydroxide, solubilized in 115 mL of water, were added dropwise into the reaction mixture. Once added, the temperature was let to rise to room temperature and let under stirring for an additional 2 hours. After the completion of the reaction, a white solid precipitated from the reaction mixture, the solid was filtered through a sintered glass funnel, and the solid was washed with distilled water (5 x 300 mL) and finally washed with cold ethanol (3 x 200 mL). The solid was transferred into a 500 mL round-bottomed flask and was dried under vacuum. The pure product was obtained with 78 % yield (106.8 g). m.p. (DSC) = 101.0 °C. Figure 1 shows the NMR characterization of VGE.

[0169] ESI-MS, exact mass m / z [M+H+] = 209.0809 (Theoretical mass: 209.0809).

[0170] 1H-NMR (CDCI3, 400 MHz, TMS, 5 ppm): 9.88 (s, 1 H, -CHO), 7.42 (m, 2H, Ar.), 7.03 (d,4J = 8 Hz, 1 H, Ar.), 4.38 (dd,2J = 12 Hz,3J = 4 Hz, 1 H, CH2O-Ar.), 4.10 (m, 1 H, CH2O- Ar.), 3.93 (s, 3H, OCH3), 3.42 (m, 1 H, CH-CH2O), 2.93 (m, 1 H, CH2O), 2.78 (m, 1 H, CH2O).

[0171] 13C-NMR (CDCI3, 100.6 MHz, 5 ppm): 190.8 (-CHO), 153.3 (Ar.), 149.9 (Ar.), 130.6 (Ar.), 126.4 (Ar.), 112.2 (Ar.), 109.4 (Ar.), 69.9 (CH2O-Ar.), 55.9 (OCH3), 49.8 (CH-CH2O), 44.6 (CH2O).

[0172] Example 2. Preparation of ethyl vanillin glycidyl ether (EtVGE)

[0173] The glycidyl ether of ethyl vanillin was synthesized following a similar procedure as Example 1 with some modifications. In a typical experiment, 5.0 g (30.09 mmol) of ethyl vanillin, 12.0 mL (153.05 mmol, 5 eq.) of epichlorohydrin, 0.34 g (1.49 mmol, 5 mol%) of benzyltriethylammonium chloride (TEBAC) were introduced into a two-necked roundbottom flask equipped with a magnetic stirrer and a condenser. The mixture was stirred at 80 °C for 3 hours. Next, the mixture was cooled down in an ice-water bath, and 1.3 g (32.5 mmol, 1.08 eq.) of sodium hydroxide, solubilized in 5.3 mL of water, were added dropwise into the reaction mixture. Once added, the temperature was let to rise to room temperature and let under stirring for an additional 2 hours. After the completion of the reaction, the crude reaction mixture was diluted with 25 mL of ethyl acetate and washed thrice with 75 mL of NaCI solution. The organic phase was dried over anhydrous magnesium sulfate, filtered, and the solvent eliminated under a rotary evaporator. The crude product was purified through recrystallization with 100 mL of hot ethanol, obtaining the pure product as white crystals with 92 % yield. Figure 3 shows the NMR characterization of EtVGE.1H-NMR (CDCh, 400 MHz, TMS, 6 ppm): 9.81 (s, 1 H, -CHO), 7.40 - 7.37 (m, 2H, Ar.), 7.99 (d,4J = 8 Hz, 1 H, Ar.), 4.36 (dd,2J = 12 Hz,3J = 4 Hz, 1 H, CH2O-Ar.), 4.11 (q,3J = 8 Hz, 2H, -OCH2CH3), 4.04 (m, 1 H, CH2O-Ar.), 3.38 (m, 1 H, CH-CH2O), 2.89 (m, 1 H, CH2O), 2.76 (m, 1 H, CH2O), 1.44 (t,3J = 8 Hz, 3H, -OCH2CH3).

[0174] 13C-NMR (CDCh, 100.6 MHz, 5 ppm): 191.0 (-CHO), 153.7 (Ar.), 149.4 (Ar.), 130.7 (Ar.), 126.3 (Ar.), 112.8 (Ar.), 111.0 (Ar.), 69.9 (CH2O-Ar.), 64.6 (-OCH2CH3), 50.0 (CH-CH2O), 44.7 (CH2O), 14.7 (-OCH2CH3).

[0175] Example 3. Preparation of 3,3’-dithiobispropylamine (Homocystamine, HomoCyst)

[0176] Homocystamine was synthesized following a reported procedure (Nucleosides, Nucleotides & Nucleic Acids 2009, 28, 1076-1094). In a typical experiment, 5.60 g (43.07 mmol) of 3-chloropropylamine hydrochloride and 6.88 g (43.51 mmol) of sodium thiosulfate were introduced into a 500 mL three-necked round bottom flask and solubilized in 160 mL of 50 mL of aqueous methanol (50 %) and refluxed overnight. After that, 5.48 g (21.59 mmol) of iodine solubilized in 200 mL of methanol were added dropwise to the refluxing solution over approximately 7 hours. Then, the solution was concentrated under reduced pressure, 50 mL of 6 M aqueous sodium hydroxide solution was added and extracted with dichloromethane. The organic phase was dried over anhydrous magnesium sulfate, filtered, and the solvent eliminated under vacuum to obtain the product as a yellowish liquid with a 73 % yield. The product was used in the next step without further purification. Figure 4 shows the NMR characterization.

[0177] 1H-NMR (CDCh, 400 MHz, TMS, 5 ppm): 2.76 (t,3J = 8 Hz, 4H, -CH2-NH2), 2.72 (t,3J = 8 Hz, 4H, -CH2-S-), 1.79 (quint,3J = 7.2 Hz, 4H, -CH2CH2-S-), 1.22 (br. s, 4H, -NH2).

[0178] 13C-NMR (CDCh, 100.6 MHz, 5 ppm): 40.9 (-CH2-NH2), 36.4 (-CH2-S-), 33.0 (-CH2CH2- S-).

[0179] Example 4. Preparation of cystamine bis(vanil lin glycidyl ether) (Cyst-BVGE)

[0180] The imine derivative of vanillin glycidyl ether with cystamine (Cyst-BVGE) was synthesized as follows. 2.84 g (18.65 mmol) of cystamine (free base) was introduced into a 100 mL round-bottom flask equipped with a magnetic stirrer. Then, 7.77 g (37.32 mmol) of VGE, solubilized in 40 mL of anhydrous dichloromethane, were added. The mixture was kept under stirring at room temperature for 2 hours. After that, the solvent was evaporated under reduced pressure, and the viscous mixture was kept at 40 °C under a high vacuum overnight. The desired product was obtained as a yellowish viscous liquid with 95 % of conversion and was used in the curing process without further purification. Figure 2 shows the NMR characterization.

[0181] 1H-NMR (CDCI3, 400 MHz, TMS, 5 ppm): 8.20 (s, 2H, N=CH-), 7.40 (d,4J = 4 Hz, 2H, Ar.), 7.12 (dd,4J = 4 Hz,3J = 8 Hz, 2H, Ar.), 6.91 (d,3J = 8 Hz, 2H, Ar.), 4.29 (dd,2J = 12 Hz,3J = 4 Hz, 2H, CH2O-Ar.), 4.05 (m, 1 H, CH2O-Ar.), 3.92 (s, 6H, OCH3), 3.87 (m, 4H, =N-CH2-), 3.40 (m, 2H, CH-CH2O), 3.05 (t,3J = 8 Hz, CH2-S), 2.92 (m, 2H, CH2O), 2.75 (m, 2H, CH2O).

[0182] 13C-NMR (CDCI3, 100.6 MHz, 5 ppm): 162.1 (N=CH-), 150.4 (Ar.), 149.7 (Ar.), 129.9 (Ar.), 123.1 (Ar.), 112.7 (Ar.), 109.3 (Ar.), 70.0 (CH2O-Ar.), 60.1 (=N-CH2-), 56.0 (OCH3), 50.1 (CH-CH2O), 44.9 (CH2O), 39.6 (CH2-S).

[0183] Example 5. Preparation of cystamine bisfethylvanillin qlycidyl ether) (Cyst- BEtVGE)

[0184] The cystamine bis(ethylvanillin glycidyl ether) (Cyst-BEtVGE) was synthesized following the same procedure as Example 4 but using EtVGE instead of VGE. In a typical experiment, 1.02 g (6.67 mmol) of cystamine were introduced into a 50 mL round bottom flask, and 2.95 g (13.29 mmol) of EtVGE were added solubilized into 14 mL of anhydrous dichloromethane. The mixture was stirred at room temperature for 2 hours and then the solvent was evaporated under reduced pressure and the viscous mixture was kept at 40 °C under a high vacuum overnight. The desired product was obtained as a yellowish viscous liquid with 96 % conversion and was used in the curing process without further purification. Figure 5 shows the NMR characterization.

[0185] 1H-NMR (CDCI3, 400 MHz, TMS, 5 ppm): 8.16 (s, 2H, N=CH-), 7.37 (d,4J = 2 Hz, 2H, Ar.), 7.10 (dd,4J = 2 Hz,3J = 8 Hz, 2H, Ar.), 6.89 (d,3J = 8 Hz, 2H, Ar.), 4.27 (dd,2J = 12 Hz,3J = 4 Hz, 2H, CH2O-Ar.), 4.11 (q,3J = 7 Hz, 4H, -OCH2CH3), 4.03 - 3.99 (m, 2H, CH2O-Ar.), 3.85 (t,3J = 7 Hz, 4H, =N-CH2-), 3.39 - 3.35 (m, 2H, CH-CH2O), 3.02 (t,3J = 8 Hz, CH2-S), 2.87 (m, 2H, CH2O), 2.75 (m, 2H, CH2O), 1.43 (t,3J = 7 Hz, 6H, - OCH2CH3).

[0186] 13C-NMR (CDCI3, 100.6 MHz, 5 ppm): 162.2 (N=CH-), 150.7 (Ar.), 149.3 (Ar.), 130.1 (Ar.), 122.9 (Ar.), 113.5 (Ar.), 111.1 (Ar.), 70.0 (CH2O-Ar.), 64.5 (-OCH2CH3), 60.1 (=N- CH2-), 50.2 (CH-CH2O), 44.8 (CH2O), 39.6 (CH2-S), 14,8 (-OCH2CH3). Example 6. Preparation of homocystamine bisfvanillin glycidyl ether) (Homocyst- BVGE)

[0187] The homocystamine bis(vanillin glycidyl ether) (Homocyst-BVGE) was synthesized following the same procedure as Example 4 but using homocystamine instead of cystamine. In a typical experiment, 0.50 g (3.34 mmol) of homocystamine were introduced into a 50 mL round bottom flask, and 1.16 g (5.57 mmol) of VGE were added solubilized into 7 mL of anhydrous dichloromethane. The mixture was stirred at room temperature for 2 hours and then the solvent was evaporated under reduced pressure and the viscous mixture was kept at 40 °C under a high vacuum overnight. The desired product was obtained as a yellowish viscous liquid with 94 % conversion and was used in the curing process without further purification. Figure 6 shows the NMR characterization.

[0188] 1H-NMR (CDCI3, 400 MHz, TMS, 5 ppm): 8.19 (s, 2H, N=CH-), 7.40 (d,4J = 2 Hz, 2H, Ar.), 7.11 (dd,4J = 2 Hz,3J = 8 Hz, 2H, Ar.), 6.92 (d,3J = 8 Hz, 2H, Ar.), 4.28 (dd,2J = 12 Hz,3J = 4 Hz, 2H, CH2O-Ar.), 4.06 (dd,2J = 12 Hz,3J = 4 Hz, 2H, CH2O-Ar.), 3.92 (s, 6H, OCH3), 3.67 (t,3J = 8 Hz, 4H, =N-CH2-), 3.42 - 3.38 (m, 2H, CH-CH2O), 2.77 (m, 4H, CH2-S), 2.75 (m, 2H, CH2O), 2.09 (quint., 4H,3J = 8 Hz, -CH2CH2-S-).

[0189] 13C-NMR (CDCI3, 100.6 MHz, 5 ppm): 161.0 (N=CH-), 150.2 (Ar.), 149.7 (Ar.), 130.1 (Ar.), 122.8 (Ar.), 112.8 (Ar.), 109.3 (Ar.), 70.0 (CH2O-Ar.), 59.5 (=N-CH2-), 55.9 (OCH3), 50.0 (CH-CH2O), 44.8 (CH2O), 36.5 (CH2-S), 30.1 (-CH2CH2-S-).

[0190] Example 7. Preparation of homocystamine bisfethylvanillin glycidyl ether) (Homocyst-BEtVGE)

[0191] The homocystamine bis(ethylvanillin glycidyl ether) (Homocyst-BEtVGE) was synthesized following the same procedure as Example 4 but using homocystamine instead of cystamine and EtVGE instead of VGE. In a typical experiment, 0.46 g (2.58 mmol) of homocystamine were introduced into a 50 mL round bottom flask, and 1.15 g (5.16 mmol) of EtVGE were added solubilized into 7 mL of anhydrous dichloromethane. The mixture was stirred at room temperature for 2 hours and then the solvent was evaporated under reduced pressure and a yellowish solid was obtained. In this case the monomer was melted at 100 °C before the preparation of the formulation, m.p (DSC) = 80 °C. Figure 7 shows the NMR characterization.

[0192] 1H-NMR (CDCI3, 400 MHz, TMS, 5 ppm): 8.15 (s, 2H, N=CH-), 7.37 (d,4J = 2 Hz, 2H, Ar.), 7.10 (dd,4J = 2 Hz,3J = 8 Hz, 2H, Ar.), 6.90 (d,3J = 8 Hz, 2H, Ar.), 4.28 (dd,2J = 12 Hz,3J = 4 Hz, 2H, CH2O-Ar.), 4.12 (q,3J = 7 Hz, 4H, -OCH2CH3), 4.04 - 4.00 (m, 2H, CH2O-Ar.), 3.64 (t,3J = 8 Hz, 4H, =N-CH2-), 3.39 - 3.35 (m, 2H, CH-CH2O), 2.89 - 2.87 (m, 2H, CH2O), 2.78 - 2.74 (m, 6H, CH2-S, CH2O), 2.07 (quint.,3J = 7 Hz, 4H, -CH2CH2- S-), 1.44 (t,3J = 8 Hz, 6H, -OCH2CH3).

[0193] 13C-NMR (CDCI3, 100.6 MHz, 5 ppm): 161.1 (N=CH-), 150.6 (Ar.), 149.3 (Ar.), 130.3 (Ar.), 122.7 (Ar.), 113.6 (Ar.), 111.1 (Ar.), 70.1 (CH2O-Ar.), 64.6 (-OCH2CH3), 59.6 (=N- CH2-), 50.2 (CH-CH2O), 44.9 (CH2O), 36.6 (CH2-S), 30.2 (-CH2CH2-S-), 14.9 (- OCH2CH3).

[0194] Example 8. Preparation of formulations with different amine-based curing agents

[0195] The Cyst-BVGE was formulated with 4 different amines as shown in Figure 8 in stoichiometric proportions (Table 1): 1 mole of amine group per 2 moles of epoxide group.

[0196] Table 1. Monomer / amine proportions in prepared formulations.

[0197] Cyst-BVGE (98% w / w) Formulation Amine (g)

[0198] (g)

[0199] Cyst-BVGE / TREN 2.14 0.21

[0200] Cyst-BVGE / IPDA 2.10 0.35

[0201] Cyst-BVGE / m-XDA 1 .85 0.25

[0202] Cyst-BVGE / DAC 1.70 0.21

[0203] As a typical experiment, 2.14 g (3.94 mmol) of Cyst-BVGE (98 % w / w) were transferred into a 50 mL round-bottomed flask equipped with a Teflon-coated magnetic stirrer. Then, 0.21 g (1.44 mmol) of TREN were weighted directly into the flask, the mixture was introduced into a pre-heated thermostatic bath at 45 °C and was stirred under vacuum for 5 minutes to remove the trapped air.

[0204] Once completely homogenized, the mixture was transferred with a spatula into Teflon molds and the formulation was cured into an oven 2 h at 100 °C, 2 h at 140 °C and 1 h at 160 °C. Samples were polished with sandpaper until reaching the desired dimensions.

[0205] Chemical recycling

[0206] Degradation of Cyst-BVGE / TREN cured sample through acid hydrolysis. The acid hydrolysis of the imine bonds was carried out following a reported procedure (Liu, et al. Polymer (Guildf). 2020, 210, 123030). In a typical example, 0.39 g of a cured sample of Cyst-BVGE / TREN was immersed into 30 mL of a 0.2 M HCI solution in a mixture of H2O:THF (2:8). The sample was let to react at room temperature with only occasional manual stirring. After 72 hours the sample was completely solubilized.

[0207] Degradation of Cyst-BVGE / TREN cured sample through thiol-disulfide exchange reaction.

[0208] The cleavage of the disulfide bond through thiol-disulfide exchange reaction was carried out following a reported procedure by Zhou (Polymer (Guildf). 2017, 120, 1-8). In a typical experiment, 0.30 g of a cured sample of Cyst-BVGE / TREN was immersed into 30 mL dithiothreitol (DTT) solution in DMF in a concentration of 0.3 M. The sample was let to react at room temperature with only occasional stirring. After 48 hours the sample was almost completely solubilized with only a small amount of insoluble residue.

[0209] Thermal characterization

[0210] The thermal stability of the cured samples was studied by thermogravimetric analysis (TGA). Figure 9a shows the TGA curves and Figure 4b the 1stderivative of the TGA curves for each formulation. It can be observed in all samples a first degradation step which could correspond to the degradation of the more labile bonds such as imine and disulfide. The temperature of maximum rate of degradation and of 2 % weight loss are very similar in all the samples, ranging from 322.5 to 327.5 °C and 221.7 to 245.1 °C respectively. The major difference was observed in the char yield at 600 °C were the highest corresponds to the m-XDA and the lowest to IPDA (38.9 and 27.5 % respectively). All the thermal degradation data is summarized in Table 2.

[0211] Table 2 Thermogravimetric results of Cyst-BVGE cured samples with different amines.

[0212] Formulation T2%a(°C) Tmaxb(°C) Char yieldc(%) Tgd(°C)

[0213] Cyst-BVGE / TREN 245.1 322.5 32.8 99.1

[0214] Cyst-BVGE / IPDA 239.9 326.2 27.5 101.7

[0215] Cyst-BVGE / m-XDA 235.7 326.2 38.9 97.4

[0216] Cyst-BVGE / DAC 221.7 327.5 27.7 97.6aTemperature of 2% of weight loss.bTemperatures at the maximum rate of degradation.cChar residue at 600 °C.dGlass transition temperature determined by DSC. The glass transition temperature (g) was determined by DSC showing very similar values in all the formulations (see figure 10). In all the cases the Tgs were around 100 °C (Table 2), which indicates that the bio-based Cyst-BVGE monomer can compete with the commercials non-renewable monomers such as diglycidyl ether of bisphenol A (DGEBA). The glass transition temperatures are summarized in Table 2, as well as with the rest of thermal data.

[0217] Thermomechanical characterization

[0218] Thermomechanical properties were determined by DMA. Figure 11 shows the storage modulus (S’), and tanb as a function of temperature for the formulations studied. The main thermomechanical data obtained from those experiments are collected in Table 3.

[0219] Table 3 Thermomechanical data of the thermosetting polymers prepared. aTemperature of the peak on tan6;bFull Width at Half Maximum;cStorage modulus measured at 30 °C;dStorage modulus measured at Tg+ 50 °C.

[0220] Vitrimer characterization

[0221] Figure 12 shows the fitting of stress relaxation results to Arrhenius’ equation for each formulation.

[0222] Thermosetting polymers exhibit good resistance to creep thanks to their permanent network structure, showing a constant deformation when a constant external stress is applied, and almost no plastic deformation appears when this stress is released. In vitrimers, this behavior is observed when tested at T<TV. However, when tested at T>TV, the deformation increases progressively and the vitrimers present plastic deformation when the stress is released due to topological rearrangements of the network structure. This behavior confirms that vitrimers behave like viscoelastic liquids. From these tests, viscosity at different temperatures is determined and represented in the Angell fragility plot (Figure 13). In Table 4 are listed the activation energy of the exchange mechanism (Ea) and the adjusting parameters of the fitting to Arrhenius’ equation and the topology freezing temperature obtained from the creep experiments.

[0223] Table 4. Vitrimeric parameters of the thermosetting polymers prepared.

[0224] TvaEablnAc

[0225] Formulation R2 d

[0226] (°C) (kJ / mol) (s)

[0227] Cyst-BVGE / TREN 26 71 19.30 0.98

[0228] Cyst-BVGE / IPDA 29 70 18.12 0.99

[0229] Cyst-BVGE / m-XDA 46 45 12.01 0.98

[0230] Cyst-BVGE / DAC -38 64 14.68 0.99 aTopology freezing temperature.bActivation energy.cPre-exponential factors.dcoefficient of determination

[0231] Example 9

[0232] Table 5. Monomer / amine proportions in prepared formulations.

[0233] Formulation Cyst-BEtVGE (g) Amine (g)

[0234] Cyst-BEtVGE / lPDA 1.15 0.47

[0235] Thermomechanical characterization

[0236] Thermomechanical properties were determined by DMA. Figure 14 shows the storage modulus (E’), and tanb as a function of temperature for the formulation studied. The main thermomechanical data obtained from those experiments are collected in Table 6.

[0237] Table 6. Thermomechanical data of the thermosetting polymers prepared.

[0238] Figure 15 shows the fitting of stress relaxation results to Arrhenius’ equation for each formulation. In Table 7 are listed the activation energy of the exchange mechanism (Ea) and the adjusting parameters of the fitting to Arrhenius’ equation and the topology freezing temperature obtained from the creep experiments.

[0239] Table 7. Vitrimeric parameters of the thermosetting polymers prepared.

[0240] Formulation 7 Ea5lnAcR2 d

[0241] Thermomechanical characterization

[0242] Thermomechanical properties were determined by DMA. Figure 16 shows the storage modulus (E’), and tand as a function of temperature for the formulation studied. The main thermomechanical data obtained from those experiments are collected in Table 9.

[0243] Table 9. Thermomechanical data of the thermosetting polymers prepared.

[0244] Figure 17 shows the fitting of stress relaxation results to Arrhenius’ equation for each formulation. In Table 10 are listed the activation energy of the exchange mechanism (Ea) and the adjusting parameters of the fitting to Arrhenius’ equation and the topology freezing temperature obtained from the creep experiments.

[0245] Table 10. Vitrimeric parameters of the thermosetting polymers prepared. Thermomechanical characterization

[0246] Thermomechanical properties were determined by DMA. Figure 18 shows the storage modulus (E’), and tand as a function of temperature for the formulation studied. The main thermomechanical data obtained from those experiments are collected in Table 6. Table 6. Thermomechanical data of the thermosetting polymers prepared.

[0247] Figure 19 shows the fitting of stress relaxation results to Arrhenius’ equation for each formulation. In Table 7 are listed the activation energy of the exchange mechanism (Ea) and the adjusting parameters of the fitting to Arrhenius’ equation and the topology freezing temperature obtained from the creep experiments.

[0248] Table 7. Vitrimeric parameters of the thermosetting polymers prepared.

[0249] TvaEablnAc

[0250] Formulation R2 d

[0251] (°C) (kJ / mol) (s)

[0252] Homocyst-BEtVGE / lPDA -72 30 6.40 0.94aTopology freezing temperature.bActivation energy.cPre-exponential factors.dcoefficient of determination

Claims

CLAIMS1 . An epoxy monomer of formula (I):wherein:- R1is (C2-C4)-alkylene or arylene;- R7is hydrogen or (Ci-C3)-alkyl;- R2to R6are independently selected from H, halo, nitro, cyano, (Ci-Ce)-alkoxy and glycidoxy, provided that at least one of R2to R6is glycidoxy.

2. The epoxy monomer according to claim 1 , wherein R1is(C2-C4)-alkylene.

3. The epoxy monomer according to claim 1 , wherein R1is arylene.

4. The epoxy monomer according to any one of claims 1 to 3, wherein R7is methyl or hydrogen.

5. The epoxy monomer according to any one of claims 1 to 4, wherein R3and / or R4is glycidoxy.

6. The epoxy monomer according to any one of claims 1 to 5, wherein one of R2to R6is glycidoxy, one of R2to R6is methoxy or ethoxy and the rest of R2to R6are hydrogen.

7. The epoxy monomer according to any one of claims 1 to 6, wherein R4is glycidoxy, R3is methoxy or ethoxy and R2, R5, R6are hydrogen.

8. The epoxy monomer according to any one of claims 1 to 7, wherein said monomer is selected from the group consisting of:

109. A process for the preparation of an epoxy monomer of formula (I) comprising the steps of: i) providing a vanillin derivative of formula (II):wherein Rais selected from hydrogen and (Ci-C3)-alkyl; and each Rbis a substituent independently selected from -OH, halo, nitro, cyano, and (Ci-Ce)- alkoxy, wherein n is 1 , 2, 3, 4, or 5; ii) transforming one or more Rbin the vanillin derivative of formula (II) into a glycidyl ether group to yield a compound of formula (III):wherein:- Raand each Rbare as defined above,- each Rcis glycidyl ether,- x is 0, 1 , 2, 3, or 4,- y is 1 , 2, 3, 4, or 5; iii) reacting the compound of formula (III) with a compound of formula (IV):wherein R1is selected from (C2-C4)-alkylene and arylene group, to yield a compound of formula (I).

10. The method according to claim 9, wherein step (ii) is carried out by reacting at least one instance of Rb, preferably being hydroxy, in the compound of formula (II) with a compound of formula R”-X, where R” is a glycidyl group and X is a leaving group selected from chloro, bromo, or iodo.11 . An epoxy vitrimer comprising the epoxy monomer as defined in any one of claims 1 to8.

12. The epoxy vitrimer according to claim 11 , wherein said vitrimer has a glass transition temperature (Tg) of at least 90 °C, preferably at least 95 °C as can be determined by DSC according to standard ISO 11357-2:2020.

13. A curable composition comprising:(a) an epoxy monomer of formula (I) as defined in any one of claims 1 to 8; and(b) a curing agent.

14. The curable composition according to claim 13, wherein the curing agent is an amine curing agent, preferably selected from the group consisting of 1 ,2-diaminocyclohexane (DAC), 5-amino-1 ,3,3-trimethylcyclohexanemethylamine (isophorone diamine (I PDA), m- xylylenediamine (m-XDA), tris(2-aminoethyl)amine (TREN) and mixtures thereof.

15. Use of the epoxy monomer as defined in any one of claims 1-8, the epoxy vitrimer asdefined in any one of claims 11-12, or the curable composition as defined in any one of claims 13-14 as an adhesive, a coating or a matrix for composite materials.

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