Vanillin and vanillin-like derived epoxy vitrimers containing imine bonds

Abstract

The present invention relates to imine-based epoxy monomers suitable for curing processes and methods of preparing said epoxy monomers and vitrimers based on said epoxy monomers. Curable compositions comprising the epoxy monomers of the invention and uses of the epoxy monomers, vitrimers or curable compositions are also disclosed.

Description

[0001] VANILLIN AND VANILLIN-LIKE DERIVED EPOXY VITRIMERS CONTAINING IMINE BONDS FIELD OF THE INVENTION

[0002] 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, being the epoxy monomers derived from vanillin and vanillin-like compounds the main building blocks of said vitrimers.

[0003] BACKGROUND

[0004] 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 do not break until a new one has already formed in another position.

[0005] 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.

[0006] 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.

[0007] 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.The use of imine bonds has attracted great attention due to their fast stress relaxation times and their capability to be chemically degraded under mild conditions. Several authors have reported their use in epoxy vitrimer networks in conjunction with biomass-derived feedstock to obtain sustainable materials. However, most of the examples described also the use of petrol-based raw materials for the synthesis of the epoxy monomer, which reduces the bio-based carbon content on the final monomer.

[0008] Therefore, there remains a need in the art to develop novel self-healing, mechanically and thermally strong vitrimer materials, which are more sustainable than those of the prior art. Entirely bio-based epoxy monomers with the ability of forming dynamic functionalities within the vitrimer and with potential high temperature applications should also be aimed for.

[0009] BRIEF DESCRIPTION OF THE INVENTION

[0010] The inventors have developed an epoxy monomer that may be synthesized using vanillin as renewable feedstock or commercially available vanillin-like compounds, which contain imines as exchangeable groups. The present invention describes the use of vanillin and vanillin-like building blocks, in conjunction with bio-based epichlorohydrin (Reodrin®), for obtaining an imine-containing epoxy monomer with a major content of bio-based carbon. Moreover, all the synthetic steps can be considered sustainable as no harmful solvents were used.

[0011] Advantageously, the groups involved in the exchange reactions are part of the epoxy monomer, and 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 exceptional thermal properties (high Tg’s) and storage modulus E’ at room temperature, along with extremely fast T at relatively low temperatures. The relatively low molecular weight enables the formation of a highly crosslinked network, resulting in glass transition temperatures (Tg’s) of 128 °C.

[0012] Therefore, in a first aspect, the present invention relates to an epoxy monomer of formula (I):

[0013]

[0014] (I)

[0015] wherein:

[0016] - R1and R1’ are each independently hydrogen or (Ci-C3)-alkyl;

[0017] - R2to R6and R2’ to R6’ are independently selected from the group consisting of hydrogen, halo, nitro, cyano, (Ci-Ce)-alkoxy, (Ci-Ce)-alkyl and glycidoxy, provided that at least one of R2to R6and at least one of R2’ to R6’ are glycidoxy.

[0018] In a second aspect, the invention relates to a process for the preparation of an epoxy monomer of formula (I) as defined in the first aspect, said process comprising the steps of: i) providing a compound of formula (II):

[0019]

[0020] wherein R1is selected from hydrogen and (Ci-C3)-alkyl; and

[0021] each of R2to R6is independently selected from the group consisting of hydrogen, -OH, halo, nitro, cyano, (Ci-Ce)-alkoxy and (Ci-Ce)-alkyl, provided that at least one of R2to R6is -OH; ii) reacting compound (II) with hydroxylamine or a salt thereof to obtain a compound of formula (III):

[0022]

[0023] wherein R1to R6are as defined above;

[0024] iii) reducing compound (III) in presence of an hydrogen halide of formula HX to obtain a compound of formula (IV):

[0025]

[0026] wherein R1to R6are as defined above and X is F, Cl, Br, or I;

[0027] iv) reacting compound (IV) with a compound of formula (II)’, equal to or different from that of step i),

[0028]

[0029] wherein R1’ is selected from hydrogen and (Ci-C3)-alkyl; and R2’to R6’ are independently selected from the group consisting of hydrogen, -OH, halo, nitro, cyano, (Ci-C6)-alkoxy and (Ci-C6)-alkyl, provided that at least one of R2’ to R6’ is -OH;

[0030] to obtain a compound of formula (V):

[0031]

[0032] wherein R1to R6and R1’ to R6’ are defined as above, provided that at least one of R2to R6and at least one of R2’ to R6’ are -OH; and

[0033] v) transforming each of the at least one -OH of R2to R6and at least one -OH of R2’ to R6’, in the compound of formula (V) into a glycidyl ether group to yield a compound of formula (I).

[0034] In another aspect, the invention relates to an epoxy vitrimer obtainable by curing, in the presence of a curing agent, of the epoxy monomer of formula (I), as defined in the firstaspect.

[0035] In a yet another aspect, the present invention is directed to a curable composition comprising:

[0036] (a) an epoxy compound of formula (I) as defined in the first aspect; and

[0037] (b) a curing agent.

[0038] In a final aspect, the invention relates to the use of the epoxy monomer, the epoxy vitrimer or the curable composition as defined above for structural and / or electronic applications.

[0039] FIGURES

[0040] Figure 1: DSC thermogram of the Gly-Van-Im / IPDA curing process.

[0041] Figure 2: DSC thermograms of cured sample showing the Tgof Gly-Van-Im / IPDA.

[0042] Figure 3: (a) TGA and (b) TGA 1stderivative curves of Gly-Van-lm cured with IPDA.

[0043] Figure 4: E’ modulus (a) and tanb (b) as a function of temperature of Gly-Van-lm cured / lPDA.

[0044] Figure 5: Fitting of stress relaxation results to the Arrhenius’ equation of Gly-Van-lm cured / lPDA.

[0045] Figure 6: Angell fragility plot of the logarithm of the viscosity as a function of Tg / T of Gly-Van-lm cured / lPDA. Dashed line: ideal strong liquid.

[0046] Figure 7: Superposed DSC thermograms of the Gly-Van-lm with different Jeffamine™ and Jeffamine-based curing agents.

[0047] Figure 8: Superposed DSC thermograms of cured samples showing the Tgof Gly-Van-lm cured with different Jeffamine™ and Jeffamine-based curing agents.

[0048] Figure 9: E’ modulus (a) and tanb (b) as a function of temperature of Gly-Van-lm cured with different Jeffamine™ and Jeffamine-based curing agents.

[0049] Figure 10: Fitting of stress relaxation results to the Arrhenius’ equation of Gly-Van-lm cured with different Jeffamine™ and Jeffamine-based curing agents.

[0050] Figure 11: Angell fragility plot of the logarithm of the viscosity as a function of Tg / T of Gly-Van-Im cured with different Jeffamine™ and Jeffamine-bases curing agents.

[0051] DETAILED DESCRIPTION OF THE INVENTION

[0052] 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.

[0053] In the context of the present invention, the following terms have the meaning that is described in detail below.

[0054] The term “halo” (or halogen) refers to bromine, chlorine, iodine, or fluorine.

[0055] The term “hydroxyl” or “hydroxy” refers to an — OH group.

[0056] The term “oxo” refers to a =0 group.

[0057] The term “carboxy” refers to a — COOH group.

[0058] The term “nitro” refers to a — NO2 group.

[0059] The terms “nitrile” or “cyano” can be used interchangeably and refer to a — CN group.

[0060] 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. A “(Ci-C3)-alkyl” refers to a methyl, ethyl, n-propyl, or i-propyl.

[0061] 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.

[0062] 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, that is:

[0063]

[0064] , symbol represents the rest of the epoxy monomer to which the glycidoxy is attached.

[0065] 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 anddiastereomerically enriched mixtures), are considered within the scope of the present invention. Also, the invention further contemplates any E / Z possible isomers.

[0066] Throughout the present specification, when a numeric range is indicated herein, both the lower limit and the upper limit are meant to be included in said range. The term “about” indicate a variation of ±10%, preferably ±5%, of the value it is referred to.

[0067] Epoxy monomer

[0068] As defined above, a first aspect of the present invention relates to an epoxy monomer of formula (I):

[0069]

[0070] wherein:

[0071] - R1and R1’ are each independently hydrogen or (Ci-C3)-alkyl;

[0072] - R2to R6and R2’ to R6’ are independently selected from the group consisting of hydrogen, halo, nitro, cyano, (Ci-Ce)-alkoxy, (Ci-Ce)-alkyl and glycidoxy, provided that at least one of R2to R6and at least one of R2’ to R6’ are glycidoxy.

[0073] In a particular embodiment, R1and R1’ are each independently selected from the group consisting of H, methyl, ethyl and n-propyl, even more preferably H or methyl.

[0074] In a preferred embodiment, at least one of R1and R1’ is hydrogen. In a more preferred embodiment, R1is hydrogen. In another preferred embodiment, R1’ is hydrogen. In a most preferred embodiment, R1and R1’ are H.

[0075] In another embodiment, one of R1and R1’ is hydrogen and the other one is methyl.

[0076] In another embodiment, R1and R1’ are methyl.

[0077] In the above compound of formula (I), R2to R6and R2’ to R6’ are independently selected from the group consisting of hydrogen, halo, nitro, cyano, (Ci-Ce)-alkoxy, (Ci-Ce)-alkyl and glycidoxy, provided that at least one of R2to R6and at least one of R2’ to R6’ areglycidoxy.

[0078] In a particular embodiment, in the above compound of formula (I), R2to R6and R2’ to R6’ are independently selected from the group consisting of hydrogen, (Ci-Ce)-alkoxy, (Ci-Ce)-alkyl and glycidoxy, provided that at least one of R2to R6and at least one of R2’ to R6’ are glycidoxy.

[0079] In a particular embodiment, one or two of R2to R6is / are glycidoxy, preferably R3and / or R4is / are glycidoxy, still more preferably R4is glycidoxy. In a particular embodiment, one or two of R2’ to R6’ is / are glycidoxy, preferably R3’ and / or R4’ is / are glycidoxy, still more preferably R4’ is glycidoxy.

[0080] In a particular embodiment, one of R2to R6is glycidoxy, preferably R4is glycidoxy. In a particular embodiment, one of R2’ to R6’ is glycidoxy, preferably R4’ is glycidoxy. In a preferred embodiment one of R2to R6and one of R2’ to R6’ are glycidoxy. In a more preferred embodiment R4and R4’ are glycidoxy.

[0081] 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 and ethoxy; provided that at least one of the remaining R2to R6is glycidoxy.

[0082] 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.

[0083] In a more particular embodiment, one of R2’ to R6’ is glycidoxy and the rest of R2’ to R6’ are hydrogen. In a more preferred embodiment, R4’ is glycidoxy and R2’, R3’, R5’, R6’ are hydrogen.

[0084] In a more particular embodiment, one of R2to R6is glycidoxy, one of R2’ to R6’ is glycidoxy, and the rest of R2to R6and R2’ to R6’ are hydrogen. In a more preferred embodiment, R4and R4’ are glycidoxy and R2, R3, R5, R6, R2’, R3’, R5’, R6’ are hydrogen.

[0085] 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, R4isglycidoxy, R3is methoxy or ethoxy and R2, R5, R6are hydrogen.

[0086] In a preferred embodiment, one of R2’ to R6’ is glycidoxy, one of R2’ to R6’ is methoxy or ethoxy and the rest of R2’ to R6’ are hydrogen. In a more preferred embodiment, R4’ is glycidoxy, R3’ is methoxy or ethoxy and R2’, R5’, R6’ are hydrogen.

[0087] In a preferred embodiment, one of R2to R6is glycidoxy, one of R2’ to R6’ is glycidoxy, one of R2to R6is methoxy or ethoxy, one of R2’ to R6’ is methoxy or ethoxy, and the rest of R2to R6and R2’ to R6’ are hydrogen.

[0088] In a more preferred embodiment, R4and R4’ are glycidoxy, one of R2, R3, R5and R6is methoxy or ethoxy, one of R2’, R3’, R5’ and R6’ is methoxy or ethoxy, and the rest of R2, R3, R5, R6, R2’, R3’, R5’ and R6’ are hydrogen.

[0089] In a more preferred embodiment, R4and R4’ are glycidoxy, R3and R3’ are independently of each other methoxy or ethoxy, and R2, R5, R6, R2’, R5’ and R6’ are hydrogen.

[0090] In a preferred embodiment, R1is 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.

[0091] In a preferred embodiment, R1’ is hydrogen, one of R2’ to R6’, preferably R4’, is glycidoxy, one of R2’ to R6’, preferably R3, is methoxy or ethoxy and the rest of R2’ to R6’ are hydrogen.

[0092] In a preferred embodiment, R1and R1’ are hydrogen, one of R2to R6, preferably R4, is glycidoxy, one of R2’ to R6’, preferably R4’, is glycidoxy, one of R2to R6, preferably R3, is methoxy or ethoxy, one of R2’ to R6’, preferably R3’, is methoxy or ethoxy, and the rest of R2to R6and R2’ to R6’ are hydrogen.

[0093] In a more preferred embodiment, R1and R1’ are hydrogen, R4and R4’ are glycidoxy, one of R2, R3, R5and R6is methoxy or ethoxy, one of R2’, R3’, R5’ and R6’ is methoxy or ethoxy, and the rest of R2, R3, R5, R6, R2’, R3’, R5’ and R6’ are hydrogen.

[0094] In a more preferred embodiment, R1and R1’ are hydrogen, R4and R4’ are glycidoxy, R3and R3’ are independently of each other methoxy or ethoxy, and R2, R5, R6, R2’, R5’ and R6’ are hydrogen.

[0095] In a preferred embodiment, R1= R1’, R2= R2’, R3= R3’, R4= R4’, R5= R5’, and R6= R6’. In a more preferred embodiment, R4and R4’ are glycidoxy, and R1= R1’, R2= R2’, R3=R3’, R5= R5’, and R6= R6’.

[0096] In a particular embodiment, the epoxy monomer of formula (I) is selected from the group consisting of:

[0097]

[0098]

[0099] Method

[0100] The invention according to the second aspect relates to a process for the preparation of an epoxy monomer of formula (I) as defined in the first aspect, said process comprising the steps of:

[0101] i) providing a compound of formula (II):

[0102]

[0103] wherein R1is selected from hydrogen and (Ci-C3)-alkyl; and

[0104] each of R2to R6is independently selected from the group consisting of hydrogen, -OH, halo, nitro, cyano, (Ci-Ce)-alkoxy and (Ci-Ce)-alkyl, provided that at least one of R2to R6is -OH; ii) reacting compound (II) with hydroxylamine or a salt thereof to obtain a compound of formula (III):

[0105]

[0106] wherein R1to R6are as defined above;

[0107] iii) reducing compound (III) in presence of an hydrogen halide of formula HX to obtain a compound of formula (IV):

[0108]

[0109] wherein R1to R6are as defined above and X is F, Cl, Br, or I;

[0110] iv) reacting compound (IV) with a compound of formula (II)’, equal to or different from that of step i),

[0111]

[0112] wherein R1’ is selected from hydrogen and (Ci-C3)-alkyl and R2’ to R6’ are independently selected from the group consisting of hydrogen, -OH, halo, nitro, cyano, (Ci-Ce)-alkoxy and (Ci-Ce)-alkyl, provided that at least one of R2’ to R6’ is -OH;

[0113] to obtain a compound of formula (V):

[0114]

[0115] wherein R1to R6are defined as above, provided that at least one of R2to R6and at least one of R2’ to R6’ are -OH; and

[0116] v) transforming each of the at least one -OH of R2to R6and at least one -OH of R2’ to R6’ in the compound of formula (V) into a glycidyl ether group to yield a compound of formula (I).

[0117] In step (i), the compound of formula (II) is one where R1is preferably H or methyl, more preferably hydrogen. Preferably, groups R2to R6are independently selected from hydrogen, -OH, (Ci-C6)-alkoxy and (Ci-C6)-alkyl, more preferably from hydrogen, -OH and (Ci-Ce)-alkoxy, more preferably from -OH and (Ci-C3)-alkoxy, even more preferably from -OH and -OMe; provided that at least one of R2to R6is OH.

[0118] In a particular embodiment, one or two of R2to R6is / are independently selected from -OH and (Ci-C6)-alkoxy, more preferably from-OH and (Ci-C3)-alkoxy, even more preferably from -OH and -OMe, provided that at least one of R2to R6is OH; preferably R3and / or R4is / are -OH, still more preferably R4is -OH. In a particular embodiment, one of R2to R6is -OH. In an embodiment, R4is -OH.

[0119] In another particular embodiment, at least one of R2to R6is (Ci-C6)-alkoxy, preferably (Ci-C6)-alkoxy selected from the group consisting of methoxy, ethoxy, propoxy, butoxy, pentoxy and hexoxy; more preferably (Ci-C6)-alkoxy selected from the group consisting of methoxy, ethoxy, propoxy or butoxy; even more preferably selected from the group consisting of methoxy and ethoxy; provided that at least one of the remaining R2to R6is OH.

[0120] In a more particular embodiment, one of R2to R6is -OH and the rest of R2to R6are hydrogen. In another particular embodiment, R4is -OH and R2, R3, R5, R6are hydrogen. In another embodiment, R3or R5is -OMe.

[0121] In a preferred embodiment, one of R2to R6is -OH, one of R2to R6is methoxy or ethoxy and the rest of R2to R6are hydrogen. In a preferred embodiment, R4is -OH and R3or R5is -OMe. In a more preferred embodiment, R4is -OH, R3is methoxy or ethoxy and R2, R5, R6are hydrogen.

[0122] In a preferred embodiment, R1is hydrogen or methyl, one of R2to R6, preferably R4, is -OH, one of R2to R6, preferably R3, is methoxy or ethoxy and the rest of R2to R6are hydrogen. Most preferably, R1is H, R4is -OH, R3is -OMe, and R2, R5and R6are H.In step (ii), compound (II) is reacted with hydroxylamine or a salt thereof, preferably in the presence of a base. Salts of hydroxylamine such as hydroxylamine hydrochloride, hydroxylamine hydrobromide, hydroxylamine hydroiodide, hydroxylamine sulfate, hydroxylamine nitrate, hydroxylamine phosphate, hydroxylamine perchlorate, and hydroxylamine acetate, are known in the art and would be suitable for step (ii). Preferably, hydroxylamine or its hydrochloride salt is used in step (ii), more preferably hydroxylamine hydrochloride.

[0123] The molar ratio between the compound (II) and hydroxylamine or a salt thereof may vary between 5:1 and 1:1, preferably between 2:1 and 1:1.1, even more preferably said molar ratio is about 1:1.2.

[0124] The reaction of step (ii) is preferably carried out in a polar solvent, such as water, alcohols, or mixtures thereof, more preferably in water.

[0125] Examples of suitable alcohols are methanol, ethanol, isopropanol, ethyleneglycol.

[0126] Examples of suitable bases are selected from hydroxide, carbonate and acetate of an alkali metal or alkaline earth metal. Preferably, the alkali metal or alkaline earth metal is selected from sodium, potassium, magnesium, calcium and strontium. Preferably the base is sodium hydroxide, sodium carbonate or sodium acetate, more preferably the base is sodium acetate, even more preferably the trihydrate form of sodium acetate.

[0127] In a particular embodiment the compound (II) is added to a mixture comprising hydroxylamine or a salt thereof, the base and the polar solvent, forming a suspension.

[0128] In particular embodiment, the hydroxylamine or salt thereof is dissolved in the polar solvent, preferably water, and the base, as defined in any of the above embodiments, is added, to form a homogeneous solution. In a particular embodiment, then the compound (II) is added to the solution comprising hydroxylamine or salt thereof, the sodium salt and the polar solvent, forming a suspension.

[0129] In an embodiment of step (ii), the reaction takes place at a temperature comprised between 50 °C and 150 °C, preferably between 75 °C and 125 °C, even more preferably at about 100 °C. The reaction time is not particularly limited; in an embodiment, such reaction time is comprised between 30 min and 12 hours, however when the suspension obtained after adding compound (II) turns into an homogeneous solution (with no suspended particles) the reaction may be stopped and worked up to obtain compound (III).Step (iii) is reducing the compound (III) in presence of a hydrogen halide HX to obtain the compound of formula (IV).

[0130] Step (iii) may be carried in the presence of any reducing agent suitable for reducing oximes. In a preferred embodiment, the reduction is carried out by using a catalyst and a reducing agent; preferably, the catalyst is a transition metal catalyst, for example one based on Pt, Pd, Rh, Ir, Ni, Fe, Mn, and hydrogen gas. In a most preferred embodiment, the reduction is carried out with a Pd / C catalyst and hydrogen gas. In an embodiment, the Pd / C catalyst comprises between 1 wt% and 20 wt% Pd, preferably between 5 wt% and 15 wt% Pd, more preferably the Pd content in the Pd / C catalyst is about 10 wt%. In an embodiment, the catalyst, preferably Pd / C, is added to the solvent so its concentration is comprised between 0.1 and 10.0 g / L, preferably between 0.5 g / L and 5.0 g / L, more preferably between 1.0 and 3.0 g / L.

[0131] As stated above, compound (III) is reduced in presence of a hydrogen halide HX wherein X is F, Cl, Br, or I. Preferably HX is HCI.

[0132] The molar ratio between compound (III) and HX is comprised between 1:5 and 1:1, preferably it is about 1:1.1.

[0133] Step (iii) is preferably carried out in a solvent, such as a polar organic solvent, more preferably an alcohol. The preferred solvent is ethanol but other alcohols may be employed, such as methanol or isopropanol.

[0134] In an embodiment of step (iii), compound (III) is dissolved in a solvent, preferably ethanol, then HX, preferably HCI, is added. In a particular embodiment, the catalyst, preferably a palladium-based catalyst such as Pd / C, is then added to the solution and the reducing agent, such as hydrogen gas, is added.

[0135] The reaction mixture of step (iii) may be left at room temperature or heated (such as up to 100 °C). The reaction may be left for a suitable amount of time (the conversion could be easily monitored by a skilled person, for example by thin layer chromatography (TLC) or nuclear magnetic resonance (NMR)), such as from 1 hour to 24 hours, preferably from 1 hour to 12 hours, more preferably from 2 to 6 hours. Compound of formula (IV) is then obtained.

[0136] In step iv), compound (IV) is reacted with a compound of formula (II)’, equal to or different from that of step i),

[0137]

[0138] wherein R1’ is selected from hydrogen and (Ci-C3)-alkyl and R2’ to R6’ are independently selected from the group consisting of hydrogen, -OH, halo, nitro, cyano, (Ci-C6)-alkoxy and (Ci-C6)-alkyl, provided that at least one of R2’ to R6’ is -OH;

[0139] to obtain a compound of formula (V):

[0140]

[0141] wherein R1to R6and R1’ to R6’ are defined as above, provided that at least one of R2to R6and at least one of R2’ to R6’ are -OH.

[0142] Any embodiment described above for R1to R6in compound (II) applies to R1’ to R6’ in compound (II)’. In a preferred embodiment, in the compound of formula (II)’, one of R2’ to R6’ is -OH, most preferably R4’ is -OH.

[0143] Preferably, compound (IV) is reacted with a compound of formula (II)’ equal to that of step i) (R1= R1’, R2= R2’, R3= R3’, R4= R4’, R5= R5’, and R6= R6’), thus a “symmetrical” imine (V) is obtained.

[0144] In an embodiment, compound (IV) and compound (II) are reacted in a molar ratio of 1:2 to 1:1, preferably about 1.1.

[0145] A base may be added to facilitate the reaction between compound (IV) and compound (II), such as an inorganic base. Preferably, the inorganic base is selected from the group consisting of a carbonate, a bicarbonate, and a hydroxide of an alkali metal, preferably a bicarbonate of an alkali metal. In a preferred embodiment, the inorganic base is potassium bicarbonate. The inorganic base is employed in a molar ratio comprised 1:1 and 2:1 with respect to compound (IV) or compound (II).The expression “alkali metal” refers to an element from group I of the periodic table, preferably sodium, potassium, lithium or caesium, more preferably sodium or potassium, still more preferably sodium.

[0146] The expression “alkaline earth metal” refers to an element from group II of the periodic table, preferably beryllium, magnesium, calcium, strontium, and barium.

[0147] Step iv) is preferably carried out in a solvent, more preferably a polar solvent such as water, an alcohol or a mixture thereof, even more preferably the solvent is water.

[0148] Examples of suitable alcohols are methanol, ethanol, propanol and isopropanol.

[0149] In an embodiment of step iv), compound (IV), compound (II) and an inorganic base, preferably potassium bicarbonate, are dissolved or suspended in a solvent, preferably in water.

[0150] The reaction temperature is not particularly limited and may be comprised, for example, between room temperature and 100 °C, preferably between room temperature and 50 °C, more preferably step iv) is carried out at room temperature.

[0151] Also the reaction time is not particularly limited and may be for example from 1 hour to 24 hours.

[0152] In a particular embodiment, compound (V) is obtained as a solid, preferably such solid precipitates in the solvent medium.

[0153] In step (v), the at least one -OH of R2to R6and at least one -OH of R2’ to R6’are transformed into a glycidyl ether group to yield a compound of formula (I) as defined above. Preferably, one of R2to R6and one of R2’ to R6’ are -OH are each transformed into a glycidyl ether group to yield a compound of formula (I) as defined above.

[0154] In the compound of formula (V), R1is as defined above. Preferably, R1is methyl or hydrogen, more preferably hydrogen.

[0155] Preferably, the glycidoxy is introduced at position 4, i.e. in R4and R4’, of each phenyl ring of the compound of formula (V).

[0156] Conversion of a -OH group into a glycidyl ether group can be carried out by any suitable means known in the art.

[0157] In an embodiment, step (v) is carried out by reacting at least one -OH of R2to R6and atleast one -OH of R2’ to R6’, more preferably one -OH at R4and one -OH at R4’, in the compound of formula (V) with a compound of formula R”-X, where R” is 2,3-epoxypropyl, / . e., a glycidyl group, and X is a halogen leaving group; more preferably, X is chloro, bromo, iodo, even more preferably chloro, or bromo.

[0158] 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.

[0159] In a particular embodiment, the reaction is carried out by mixing a compound of formula (V) and a compound of formula R”-X in the presence of a catalyst, followed by addition of a base.

[0160] 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.

[0161] In a preferred embodiment, the catalyst is benzyltriethylammonium chloride.

[0162] In a particular embodiment, the compound of formula (V) and the compound of formula R”-X may be in a molar ratio ranging from 0.1:10 to 1:2, preferably 0.5:10 to 1:5, more preferably is about 1:10.

[0163] The mixing may be carried out under stirring for a period ranging from 5 min to 24 hours, preferably from 30 min to 10 hours, more preferably about 1 hour. 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.

[0164] Then, the mixture may be cooled down. A base is then preferably added. Suitable bases include inorganic bases such as an alkali metal carbonate or bicarbonate (e.g. Na2COs, K2CO3, CS2CO3, l_i2CC>3, NaHCOs, KHCO3, CsHCCh, UHCO3), an alkali metal phosphate (e.g. NasPO4, K3PO4, Na2HPC>4, K2HPO4, NaH2PO4, KH2PO4), 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, thebase is sodium hydroxide.

[0165] In a particular embodiment, the addition of the base may be performed at a temperature ranging from 0 °C to 30 °C, preferably ranging from 0 °C to 10 °C.

[0166] 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 4 hours.

[0167] In a particular embodiment, the reaction of step (v) such as the mixing and / or the addition of the base may be carried out in the absence of a solvent.

[0168] In another particular embodiment, the reaction of step (v) 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. Et20, iPr2O, tBu2O, MeOtBu, 1,4-dioxane, tetrahydrofuran, 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.

[0169] 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.

[0170] Epoxy vitrimer

[0171] In still another aspect of the present disclosure, there is provided an epoxy vitrimer obtainable by curing, in presence of a curing agent, of the epoxy monomer of formula (I) as disclosed herein in any of its particular embodiments.

[0172] 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.

[0173] 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 ’’hardening agents”.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.

[0174] 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 polyoxyalkylene diamines and polyoxyalkylene 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 polyoxyalkylene amines, preferably a poly(alkylene oxide) monoamine, diamine, or triamine, having a backbone derived from repeating oxyalkylene units and terminated by one, two or three primary amino groups; 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. Most preferably, the curing agent is 5-amino-1,3,3-trimethylcyclohexanemethylamine or a poly(alkylene oxide) monoamine, diamine, or triamine. Still more preferably, the curing agent is 5-amino-1,3,3-trimethylcyclohexanemethylamine.

[0175] The epoxy vitrimer as disclosed herein has a dynamic network comprising dynamic bonds obtained by imine 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.

[0176] In a particular embodiment, the epoxy monomer and the curing agent are present in a molar ratio within the vitrimer ranging from 20:0.5 to 1:1, preferably from 5:1 to 1:0.75, more preferably is of about 2: 1.

[0177] In a particular embodiment, the vitrimer of the second aspect has a glass transition temperature (Tg) of at least 90 °C, preferably at least 100 °C, more preferably at least 100 °C. In another particular embodiment, the vitrimer has a Tgbetween 90 and 150 °C, preferably between 100 and 145 °C, more preferably between 110 and 140 °C. For thepurpose of the present invention, glass transition temperature can be determined by DSC according to standard ISO 11357-2:2020.

[0178] In a particular embodiment, the vitrimer has a storage modulus (F) at glassy state, such as measured at room temperature, in a range of about 2.0 to about 3.0 GPa, preferably from about 2.2 to about 2.8 GPa, more preferably from about 2.4 to about 2.75 GPa as determined according to EN ISO 6721-1.

[0179] 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.

[0180] The epoxy vitrimer of the present invention may be obtained by (a) pre-heating the epoxy monomer; (b) adding the curing agent to obtain a mixture and (c) curing said mixture to obtain the vitrimer.

[0181] In a particular embodiment, the epoxy monomer and the curing agent are mixed in a stoichiometric proportion. For example, when the curing agent is a diamine, the epoxy monomer and the curing agent are mixed in a proportion of 1 mole of curing agent per 2 moles of epoxide monomer or when the curing agent is a triamine, the epoxy monomer are mixed in a proportion of 1 mole of curing agent per 3 moles of epoxide monomer.

[0182] In a particular embodiment, the pre-heating of step (a) is performed at a temperature ranging from 50 °C to 120 °C, preferably from 80 °C to 120 °C.

[0183] In a particular embodiment, the mixture of step (a) is cured at a temperature varying from 100 to 200 °C for a total period of 1 to 10 h.

[0184] Curable composition

[0185] In another aspect, the present invention is directed to a curable composition comprising:

[0186] (a) an epoxy compound of formula (I) as defined above in any of its particular embodiments; and

[0187] (b) a curing agent.

[0188] 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 preferredembodiment, the curing agent is an amine curing agent. More preferably, the curing agent is selected from the group consisting of polyoxyalkylene amines, preferably a poly(alkylene oxide) monoamine, diamine, or triamine, having a backbone derived from repeating oxyalkylene units and terminated by one, two or three primary amino groups; 1,2-diaminocyclohexane (DAC), 5-amino-1,3,3-trimethylcyclohexanemethylamine (isophorone diamine (IPDA), m-xylylenediamine (m-XDA), tris(2-aminoethyl)amine (TREN) and combinations thereof.

[0189] In a particular embodiment, the epoxy monomer and the curing agent are present in a molar ratio within the vitrimer ranging from 20:0.5 to 1:1, preferably from 5:1 to 1:0.75, more preferably is of about 2: 1.

[0190] 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. An epoxy vitrimer is obtainable by curing of the curable composition as described herein. The conditions described for the synthesis of the vitrimer according to the second aspect apply to the curing of the curable composition.

[0191] Uses

[0192] 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.

[0193] EXAMPLES

[0194] The invention is illustrated by means of the following examples which in no case limit the scope of the invention.

[0195] Materials

[0196] Activated charcoal (powder, DARCO® KB-G), Celite (Diatomaceous earth, calcined), cystamine dihydrochloride (96%), which was previously neutralized with a 3 M sodiumhydroxide solution and extracted with ethyl acetate to obtain the free base, Palladium on carbon (Pd / C 10 wt.%), and trimethylolpropane tris[poly(propylene glycol), amine terminated] ether (Mn = 440 g / mol) (JeffamineTM T403), were purchased from Sigma Aldrich (St. Louis, MO, USA). Bio-based (±)-epichlorohydrin (ECH, >99%, Reodrin®) was purchased from Ineos Inovyn (Luxemburg). Bio-based 4-hydroxy-3-methoxy benzaldehyde (Vanillin, >96%) was purchased from Borregaard (Sarpsborg, Norway). 5-Amino-1,3,3-trimethylcyclohexanemethylamine (isophorone diamine, (I PDA, 99%, mixture of cis and trans)) and benzyl triethylammonium chloride (BTEAC, 98%) were purchased from Acres Organics (Geel, Belgium). Hydrogen gas (>99.999 %) was purchased from Linde (Dublin, Ireland). Hydrochloric acid (37 %), hydroxylamine hydrochloride (99%), methanol (99.8 %, extra dry), sodium acetate trihydrate (99%), potassium bicarbonate (reagent grade), and terephthalaldehyde (98%) were purchased from ThermoScientific (Waltham, MA, USA). Sodium chloride was purchased from Panreac (Castellar del Valles, Spain). Sodium hydroxide (pellets, 97%) and anhydrous magnesium sulfate (99.5%, powder) were purchased from Alfa Aesar (Haverhill, MA, USA). Absolute ethanol (EtOH, Reagent grade >99.8 %) and ethyl acetate (Reagent grade, 99%) were purchased from VWR Chemicals (Radnor, PA, USA). (Polypropylene glycol) bis(2-aminopropyl ether) (Mn = 230 g / mol) (Jeffamine™ D-230) was purchased from TCI (Tokyo, Japan). (Polypropylene glycol) bis(2-aminopropyl ether) (Mn = 400 g / mol) (Jeffamine™ D-230) was purchased from BLDpharm (Shanghai, China). All the reagents were used as received unless otherwise specified.

[0197] Monomer characterization

[0198] 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 and DMSO-cfe were used as solvents. 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, DMSO-cfe = 2.50 ppm, and13C-NMR: CDCh = 77.16 ppm, DMSO-cfe = 39.52 ppm).

[0199] Thermal characterization

[0200] 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. Thecuring 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 dynamicscans at 50 °C / min from -20 to 180 °C.

[0201] 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.

[0202] Thermomechanical and mechanical characterization

[0203] Thermomechanical properties were measured using a TA Instruments DMA 850 (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 200 °C at 3 °C / min. The storage modulus at glassy state (Eg) and at rubbery state (E’r) was obtained at 30 °C and at Tg+ 50 °C, respectively. The Tgs were determined from the maximum of the peak of tanb.

[0204] Stress relaxation tests

[0205] Stress relaxation tests were carried out using a TA Instruments DMA 850 (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 190 °C. The stress a was 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:

[0206]

[0207] 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.Creep experiments

[0208] Creep and recovery properties were studied using a TA Instruments DMA 850 (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 120 °C, 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 160 °C. The viscosity was calculated using the following equation:

[0209]

[0210] 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.

[0211] Example 1. Preparation of 4-hydroxy-3-methoxybenzaldoxime (Vanillyloxime, Van-Ox)

[0212]

[0213] The oxime of vanillin was synthesized following a reported procedure (Eur. Polym. Chem., 2015, 73, 344-362). In a typical experiment, 18.00 g (259.03 mmol) of hydroxylamine hydrochloride and 64.40 g (473.25 mmol) of sodium acetate trihydrate were introduced into a 500 mL round-bottom flask and were solubilized into 362 mL of distilled water. Then, 36.00 g (236.61 mmol) of vanillin was suspended in the solution. The mixture was heated at 100 °C for 1 hour until a clear solution was obtained. The reaction mixture was left to cool down to room temperature and the product precipitated as white crystals. The crystals were filtered, washed with cold water, and dried in a vacuum oven at 40 °C overnight, obtaining an 88 % yield of the pure product, m.p. (DSC) = 123.8 °C.

[0214] ESI-MS, exact mass m / z [M+H+] = 168.0647 (Theoretical mass: 168.0655).

[0215] 1H-NMR (DMSO-cfe, 400 MHz, 5 ppm): 10.82 (br. s, 1H, -NOH), 9.32 (br. s, 1H, Ar.-OH), 7.99 (s, 1H, CH=N), 7.16 (d,4J= 1.8 Hz, 1H, Ar.), 6.96 (dd,3J = 8.1 Hz,4J= 1.8 Hz, 1H, Ar.), 6.76 (d,3J = 8.1 Hz, 1H, Ar.), 3.77 (s, 3H, OCH3).13C-NMR (DMSO-cfe, 100.6 MHz, 5 ppm): 148.2 (CH=N), 148.1 (Ar.-OCH3), 147.9 (Ar.), 124.5 (An-CH=N), 120.6 (Ar.), 115.6 (Ar.), 109.3 (Ar.), 55.5 (OCH3).

[0216] Example 2. Preparation of 4-hydroxy-3-methoxybenzylamine hydrochloride amine Van-NH3+Cr

[0217]

[0218] The vanillyl amine hydrochloride was synthesized following a modification of a reported procedure (Eur. Polym. Chem., 2015, 73, 344-362). In a typical experiment, 9.05 g (54.14 mmol) of Van-Ox was introduced into a 1000 mL round-bottom flask and dissolved into 900 mL of absolute ethanol, once dissolved, 4.9 mL (58.68 mmol) of concentrated hydrochloric acid was added. After that, 1.80 g of Pd / C (10%) (2 g-1) was added and hydrogen gas was bubbled through the solution for 4 hours at room temperature. After the complete conversion (checked by NMR) the solution was filtered off through Celite and the solvent was removed by rotary evaporation to obtain the product as a white solid in the form of 4-hydroxy-3-methoxybenzylammonium chloride (91 % yield).

[0219] ESI-MS, exact mass m / z [M+H+] = 154.0862 (Theoretical mass: 154.0863).

[0220] 1H-NMR (DMSO-cfe, 400 MHz, 5 ppm): 9.24 (br. s, 1H, -OH), 8.48 (br. s, 3H, -NH3+), 7.21 (d, ,4J = 1.6 Hz, 1H, Ar.), 6.86 (dd, ,4J = 1.6 Hz, ,3J = 8 Hz, 1H, Ar.), 6.80 (d, ,3J = 8 Hz, 1H, Ar.), 3.86 (s, 2H, CH2-NH3+), 3.76 (s, 3H, -OCH3).

[0221] 13C-NMR (DMSO-cfe, 100.6 MHz, 5 ppm): 147.6 (Ar.), 146.9 (Ar.), 124.7 (Ar.), 121.8 (Ar.), 115.3 (Ar.), 113.6 (Ar.), 55.8 (-OCH3), 42.2 (-CH2-NH3+).

[0222] Example 3. Preparation of 4-(((4-hydroxy-3-methoxybenzyl)imino)methyl)-2- methoxyphenol (Divanillinimine, Van-Im)

[0223]

[0224] The imine of vanillin and vanillylamine hydrochloride (Van-Im) was synthesized following a reported procedure (Ind. Crops Prod., 2024, 215, 118658). In a typical experiment, 10.00 g (65.72 mmol) of vanillin, 11.22 g (59.16 mmol) of vanillylamine hydrochloride,and 7.88 g (78.71 mmol) of potassium bicarbonate, solubilized into 150 mL of distilled water, were introduced into a 250 mL round bottom flask. The mixture was stirred at room temperature overnight, and a yellow precipitate appeared afterward. The solid was filtered and thoroughly washed with distilled water and ethyl acetate. The product was dried in a vacuum oven at 60 °C overnight, obtaining 70 % yield of the pure product, m.p. (DSC) = 173.0 °C.

[0225] ESI-MS, exact mass m / z [M+H+] = 288.1219 (Theoretical mass: 288.1230).

[0226] 1H-NMR (DMSO-cfe, 400 MHz, TMS, 5 ppm): 9.15 (br. s, 2H, -OH), 8.27 (s, 1H, CH=N-), 7.36 (d,4J = 2 Hz, 1H, Ar.), 7.15 (dd,4J = 2 Hz,3J = 8 Hz, 1H, Ar.), 6.88 (d,4J= 2 Hz, 1H, Ar.), 6.85 (d,3J = 8 Hz, 1H, Ar.), 6.76 (d,3J= 8 Hz, 1H, Ar.), 6.70 (dd,4J= 2 Hz,3J = 8 Hz, Ar.), 4.59 (s, 2H, CH2-NH2), 3.78 (s, 3H, -OCH3), 3.75 (s, 3H, -OCH3).

[0227] 13C-NMR (DMSO-cfe, 100.6 MHz, 5 ppm): 160.9 (CH=N-), 149.7 (Ar.), 148.1 (Ar.), 147.6 (Ar.), 145.5 (Ar.), 130.8 (Ar.), 127.9 (Ar.), 123.1 (Ar.), 120.7 (Ar.), 115.5 (Ar.), 115.4 (Ar.), 112.5 (Ar.), 110.0 (Ar.), 63.9 (-CH2-N=), 55.7 (-OCH3), 55.6 (-OCH3).

[0228] Example 4. Preparation of N-(3-methoxv-4-(oxiran-2-vlmethoxv)benzvl)-1-(3- methoxv-4-(oxiran-2-vlmethoxv)phenvl)methanimine (Diqlvdidvl divanillinimine, Glv-Van-lm)

[0229]

[0230] The diglycidyl divanillinimine (Gly-Van-lm) was synthesized following a modification of a reported procedure for the synthesis of imine-containing epoxy monomers (Polym. Eng. Sci., 2020, 60, 2593-2605). In a typical experiment, 23.79 g (82.80 mmol) of Van-Im, 1.91 g (8.39 mmol) of benzyl triethylammonium chloride (BTEAC), and 65.0 mL (829.01 mmol) of epichlorohydrin were introduced into a 250 mL two-necked round bottom flask. The mixture was stirred at 80 °C for 1 hour, then the mixture was cooled down in an icewater bath and 7.36 g (184.00 mmol) of sodium hydroxide solubilized in 29.14 g of methanol, was added dropwise. The mixture was stirred for an additional 4 hours, and after that time, the mixture was diluted with 500 mL of ethyl acetate and washed thrice with sodium chloride solution. The organic phase was dried over anhydrous magnesium sulfate and the solvent was eliminated under reduced pressure. The product was then solubilized in 800 mL of hot ethanol, treated with activated charcoal, filtered, andrecrystallized at 4 °C overnight. The product, crystallized as a white solid, was filtered, washed with cold ethanol, and dried in a vacuum oven at 40 °C overnight. Obtaining a 41 % yield of the pure product, m.p. (DSC) = 94.8 °C

[0231] ESI-MS, exact mass m / z [M+H+] = 400.1737 (Theoretical mass: 400.1755).

[0232] 1H-NMR (CDCI3, 400 MHz, TMS, 5 ppm): 8.26 (br. s, 1H, N=CH-), 7.46 (d,4J = 2 Hz, 1H, Ar.), 7.15 (dd,4J= 2 Hz,3J = 8 Hz, 1H, Ar.), 6.92 (d,3J = 8 Hz, 1H, Ar.), 6.90 (d,3J = 8 Hz, 1H, Ar.), 6.88 (d,4J= 2 Hz, 1H, Ar.), 6.83 (dd,4J= 2 Hz,3J= 8 Hz, 1H, Ar.), 4.71 (s, 2H, =N-CH2-Ar.), 4.28 (dd,2J = 12 Hz,3J = 4 Hz, 1 H, CH2O-Ar.), 4.21 (dd,2J = 12 Hz,3J = 4 Hz, 1H, CH2O-Ar.), 4.03 (m, 1H, CH2O-Ar.), 3.90 (s, 3H, OCH3), 3.86 (s, 3H, OCH3), 3.40 - 3.34 (m, 2H, CH-CH2O), 2.90 - 2.85 (m, 2H, CH2O), 2.75 - 2.71 (m, 2H, CH2O).

[0233] 13C-NMR (CDCI3, 100.6 MHz, 5 ppm): 161.4 (N=CH-), 150.4 (Ar.), 149.9 (Ar.), 149.8 (Ar.), 147.1 (Ar.), 133.3 (Ar.), 130.2 (Ar.), 123.2 (Ar.), 120.3 (Ar.), 114.4 (Ar.), 112.9 (Ar.), 112.1 (Ar.), 109.5 (Ar.), 70.5 (CH2O-Ar.), 70.1 (CH2O-Ar.), 64.7 (=N-CH2-), 56.1 (-OCH3), 56.0 (-OCH3), 50.3 (CH-CH2O), 50.1 (CH-CH2O), 45.0(CH2O), 44.9 (CH2O).

[0234] Example 5. Preparation of formulations with different amine-based curina aqents The Gly-Van-lm was formulated with an amine (isophorone diamine) in stoichiometric proportions (Table 1): 1 mole of amine group per 2 moles of epoxide group.

[0235] Table 1. Monomer / amine proportions in the prepared formulations.

[0236] Formulation Gly-Van-lm (g) Amine (g) Gly-Van-Im / IPDA 2.5082 0.5444

[0237] As a typical experiment, 2.5082 g (6.28 mmol) of Gly-Van-lm were introduced into a 20 mL vial and placed into a pre-heated thermostatic bath at 100 °C. Once melted, the vial was removed from the thermostatic bath and 0.5444 g (3.20 mmol) of I PDA were added. The mixture was homogenized with manual stirring using a spatula and poured into Teflon molds. The formulation was cured in an oven 2 h at 120 °C, 2 h at 140 °C and 1 h at 160 °C. Samples were polished with sandpaper until the desired dimensions were obtained. Figure 1 shows the DSC thermogram of the curing process.

[0238] Chemical recycling

[0239] Degradation of Gly-Van-Im / IPDA cured sample through acid hydrolysis.The acid hydrolysis of the imine bonds was carried out following a modification of a reported procedure (Verdugo, etal. ACS Sustainable Chem. Eng., 2024, 12, 5965-5978). In a typical example, 0.40 g of a cured sample of Gly-Van-Im / IPDA was immersed into 30 mL of a 0.2 M HCI solution in a mixture of H2O:THF (2:8). The sample was left to react at 50 °C under magnetic stirring. After 24 hours the sample was completely degraded to give a viscous liquid as a degradation product.

[0240] Thermal characterization

[0241] Figure 2 shows the glass transition temperature (Tg) obtained by DSC. The thermal stability of the cured samples was studied by thermogravimetric analysis (TGA). Figure 3a shows the TGA curves and Figure 3b the 1stderivative of the TGA curve. The temperature of maximum rate of degradation is 328 °C and of 2 % weight loss is 275 °C and the char yield is 30.0 % Thermal degradation data is summarized in Table 2.

[0242] Table 2 Thermogravimetric results of Cyst-BVGE cured samples with different amines.

[0243] Formulation T2%a(°C) Tmaxb(°C) Char yieldc(%) Tgd(°C) Gly-Van-Im / IPDA 275 328 30.0 128aTemperature of 2% of weight loss.bTemperatures at the maximum rate of degradation.cChar residue at 600 °C.dGlass transition temperature determined by DSC.

[0244] Thermomechanical characterization

[0245] Thermomechanical properties were determined by DMA. Figure 4 shows the storage modulus (F). and tanb as a function of temperature. The main thermomechanical data obtained are collected in Table 3.

[0246] Table 3 Thermomechanical data of the thermosetting polymers prepared.

[0247]

[0248] Figure 5 shows the fitting of stress relaxation results to Arrhenius’ equation.

[0249] 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 behaviour is observed when tested at T<TV(or T<Tgif Tg>Tv). However,when tested at T>TV(or T>Tgif Tg<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 behaviour confirms that vitrimers behave like viscoelastic liquids. From these tests, viscosity at different temperatures is determined and represented in the Angell fragility plot (Figure 6).

[0250] 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.

[0251] Table 4. Vitrimeric parameters of the thermosetting polymer prepared.

[0252]

[0253] aTopology freezing temperature.bActivation energy.cPre-exponential factors.dcoefficient of determination

[0254] Example 6. Preparation of formulations with Jeffamine-based curing agents The Gly-Van-lm was formulated with three different polyetheramines polypropylene glycol) bis(2-aminopropyl ether) (Mn = 230 g / mol) (Jeffamine™ D230), (polypropylene glycol) bis(2-aminopropyl ether) (Mn = 400 g / mol) Jeffamine™ D440 and (Jeffamine™ T403), also denoted as D230, D440 and T403, respectively, in stoichiometric proportions (see Table 1): 1 mole of amine group per 2 moles of epoxide group. Another curing agent (TA-D230) was synthesized following the procedure described in Heliyon 2023, 9, e16945 from terephthalaldehyde and Jeffamine™ D-230 (TA-D230).

[0255] Table 5. Monomer / amine proportions in the prepared formulations.

[0256] Formulation Gly-Van-lm (g) Amine (g) Gly-Van-lm / D230 1.3628 0.3923 Gly-Van-lm / D440 1.2015 0.6618 Gly-Van-lm / T403 1.3024 0.4782 Gly-Van-lm / TA-D230 1.0123 0.7240

[0257] As a typical experiment, 1.0123 g (2.53 mmol) of Gly-Van-lm were introduced into a 20 mL vial and placed into a pre-heated thermostatic bath at 100 °C. Once melted, the vial was removed from the thermostatic bath and 0.7240 g (1.30 mmol) of TA-D230 curing agent were added. Monomer / amine proportions for other formulations were adaptedaccording to Table 5. The mixture was homogenized with manual stirring using a spatula and poured into Teflon molds. The formulation was cured in an oven 2 h at 120 °C, 2 h at 140 °C and 1 h at 160 °C. Samples were polished with sandpaper until the desired dimensions were obtained. Figure 7 shows the superposed DSC thermogram of the curing process with each curing agent.

[0258] Thermal characterization

[0259] Figure 8 shows the glass transition temperature (Tg) obtained by DSC. The values of Tgare listed in Table 6.

[0260] Table 6. Thermogravimetric results of Cyst-BVGE cured samples with different amines.

[0261] Formulation Tga(°C)

[0262] Gly-Van-lm / D230 89

[0263] Gly-Van-lm / D440 58

[0264] Gly-Van-lm / T403 92

[0265] Gly-Van-lm / TA-230 76

[0266] aGlass transition temperature determined by DSC.

[0267] Thermomechanical characterization

[0268] Thermomechanical properties were determined by DMA. Figure 9 shows the storage modulus (E*), and tanb as a function of temperature. The main thermomechanical data obtained are collected in Table 7.

[0269] Table 7. Thermomechanical data of the thermosetting polymers prepared.

[0270]

[0271] aT emperature of the peak on tand;bFull Width at Half Maximum;cStorage modulus measured at 30 °C;dStorage modulus measured at Tg+ 50 °C.

[0272] Vitrimer characterization

[0273] Figure 10 shows the fitting of stress relaxation results to Arrhenius’ equation and the viscosity at different temperatures is determined and represented in the Angell fragility plot (Figure 11).In Table 8 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.

[0274] Table 8. Vitrimeric parameters of the thermosetting polymer prepared.

[0275] TvaEablnAc

[0276] FormulationR2d (°C) (kJ / mol) (s)

[0277] Gly-Van-lm / D230 4 59 14.9 0.9511 Gly-Van-lm / D440 -90 25 5.2 0.9944 Gly-Van-lm / T403 -12 47 10.9 0.9931 Gly-Van-lm / TA-23

[0278]

[0279] -10 60 14.6 0.9906aTopology freezing temperature.bActivation energy.cPre-exponential factors.dcoefficient of determination

Claims

33CLAIMS1. An epoxy monomer of formula (I):wherein:- R1and R1’ are each independently hydrogen or (Ci-C3)-alkyl;- R2to R6and R2’ to R6’ are independently selected from the group consisting of hydrogen, halo, nitro, cyano, (Ci-Ce)-alkoxy, (Ci-Ce)-alkyl and glycidoxy, provided that at least one of R2to R6and at least one of R2’ to R6’ are glycidoxy.

2. The epoxy monomer according to claim 1, wherein R1is H or methyl.

3. The epoxy monomer according to claim 1 or 2, wherein R1’ is H or methyl.

4. The epoxy monomer according to any one of claims 1 to 3, wherein R3and / or R4is glycidoxy, and R3’ and / or R4’ is glycidoxy.

5. The epoxy monomer according to any one of claims 1 to 4, wherein one of R2to R6is glycidoxy, one of R2’ to R6’ is glycidoxy, one of R2to R6is methoxy or ethoxy, one of R2’ to R6’ is methoxy or ethoxy, and the rest of R2to R6and R2’ to R6’ are hydrogen; preferably wherein R4and R4’ are glycidoxy, one of R2, R3, R5and R6is methoxy or ethoxy, one of R2’, R3’, R5’ and R6’ is methoxy or ethoxy, and the rest of R2, R3, R5, R6, R2’, R3’, R5’ and R6’ are hydrogen.

6. The epoxy monomer according to any one of claims 1 to 5, wherein said monomer is selected from the group consisting of:

7. A process for the preparation of an epoxy monomer of formula (I) according to any one of claims 1 to 6, said process comprising the steps of:i) providing a compound of formula (II):wherein R1is selected from hydrogen and (Ci-C3)-alkyl; andeach of R2to R6is independently selected from the group consisting of hydrogen, -OH, halo, nitro, cyano, (Ci-Ce)-alkoxy and (Ci-Ce)-alkyl, provided that at least one of R2to R6is -OH; ii) reacting compound (II) with hydroxylamine or a salt thereof to obtain a compound of formula (III):wherein R1to R6are as defined above;iii) reducing compound (III) in presence of an hydrogen halide of formula HX to obtain a compound of formula (IV):wherein R1to R6are as defined above and X is F, Cl, Br, or I;iv) reacting compound (IV) with a compound of formula (II)’, equal to or different from that of step i),wherein R1’ is selected from hydrogen and (Ci-C3)-alkyl and R2’ to R6’ are independently selected from the group consisting of hydrogen, -OH, halo, nitro, cyano, (Ci-C6)-alkoxy and (Ci-C6)-alkyl, provided that at least one of R2’ to R6’ is -OH;to obtain a compound of formula (V):wherein R1to R6and R1’ to R6’ are defined as above, provided that at least one of R2to R6and at least one of R2’ to R6’ are -OH;v) transforming each of the at least one -OH of R2to R6and at least one -OH of R2’ to R6’ in the compound of formula (V) into a glycidyl ether group to yield a compound of formula (I).

8. The method according to claim 7, wherein compound (III) is reduced in presence of a transition metal catalyst based on Pt, Pd, Rh, Ir, Ni, Fe, or Mn, and hydrogen gas as reducing agent.

379. The method according to any one of claim 7 to 8, wherein in step iv) compound (IV) is reacted with a compound of formula (II)’ equal to compound (II) of step i).

10. An epoxy vitrimer obtainable by curing, in presence of a curing agent, of an epoxy monomer of formula (I) according to any one of claims 1 to 6.

11. The epoxy vitrimer according to claim 10, wherein the curing agent is an amine curing agent, preferably selected from the group consisting of a poly(alkylene oxide) monoamine, diamine, or triamine; 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.

12. The epoxy vitrimer according to claim 10 or 11, wherein said vitrimer has a glass transition temperature (Tg) of at least 120 °C, preferably at least 125 °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 6; and(b) a curing agent, preferably an amine curing agent.

14. The curable composition according to claim 13, wherein the amine curing agent is selected from the group consisting of a poly(alkylene oxide) monoamine, diamine, or triamine; 1,2-diaminocyclohexane (DAC), 5-amino-1,3,3-trimethylcyclohexanemethylamine (isophorone diamine (IPDA), 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 1-6, the epoxy vitrimer as defined in any one of claims 10-12, or the curable composition as defined in any one of claims 13-14 for making an adhesive, a coating or a matrix for composite materials.

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