Vitrimers with wide processing window

Abstract

The invention relates to a process for synthesizing a single ester-containing benzoxazine monomer comprising the following steps of (i) reacting a phenolic carboxylic acid with at least one hydroxyl containing phenolic compound at a temperature of from 25°C to 200°C, during 1h-72h, in the presence of a catalyst of Bronsted acid type, resulting in a phenol terminated oligomer or molecule and of (ii) reacting said phenol terminated oligomer or molecule with a mixture of an amino-alcohol, a primary amine of formula, and paraformaldehyde at a temperature range of from 50°C to 150°C, from 1 h to 10 h, under stirring, for obtaining the single ester-containing benzoxazine monomer.

Description

[0001]VITRIMERS WITH WIDE PROCESSING WINDOW The invention is directed to the field of wide processing window benzoxazine derivatives vitrimers and to a process of manufacturing thereof and the use of said vitrimers in various applications. Technical field Vitrimers are polymeric materials owing to their dynamic nature of the covalent network, arising from reversible chemical bonds, allowing the material to be healed, recycled and reprocessed like thermoplastics. These exchange reactions are triggered by external stimulus, most frequently temperature. The viscosity of vitrimers gradually decreased upon heating providing malleability to the network while permitting internal stress to relax. Network integrity over the entire range of application ensures mechanical and solvent resistance. Following the prototypal vitrimer developed by Leibler et al. in 2011 (D. Montarnal, M. Capelot, F. Tournilhac and L. Leibler, Science, 2011, 334, 965–968), dynamic transesterification reactions demonstrated extensive interest over the last decade. These chemical exchanges induced at elevated temperatures between ester linkages and hydroxyl groups are responsible for topology rearrangements. Transesterification mechanism was implemented in cross-linked network to design self-healable, recyclable and reprocessable material with tunable properties. Demongeot et al. (A. Demongeot, R. Groote, H. Goossens, T. Hoeks, F. Tournilhac and L. Leibler, Macromolecules, 2017, 50 (16), 6117-6127) adapted the vitrimer concept to commercially available thermoplastic. Cross-linked polybutylene terephthalate (PBT) vitrimer based on transesterification exchanges was successfully prepared by reactive extrusion. In addition to improving the manufacturing techniques and the potential scope of these networks, global environmental context urges the scientific community to promote sustainable polymer derived from naturally occurring feedstocks. Altuna et al. (F. I. Altuna, V. Pettarin and R. Williams, Green Chem., 2013, 15, 3360-3366) endeavoured to generate fully bio-based polyester showing properties reminiscent of vitrimers, starting from epoxidized soybean oil and an aqueous citric acid solution. Furthermore, Legrand et al. (A. Legrand and C. Soulié-Ziakovic, Macromolecules, 2016, 49, 5893-5902) enabled to extend the scalability of applications of vitrimer networks by developing a silica−reinforced epoxy vitrimer nanocomposites with enhanced properties. Polybenzoxazines are a new type of thermoset with outstanding mechanical and thermal properties. As many other thermosets, they cannot be reshaped, re-processed nor recycled. A few examples have been reported showing a reasonable level of healability (L. Zhang, Z. Zhao, Z. Dai, L. Xu, F. Fu, T. Endo, X. Liu, ACS Macro. Lett.2019, 8, 5, 506-511 and Arslan M., Kiskan B., Y. Yagci, Sci. Rep.2017, 7, 5207). The Applicant has shown that some various chemical structures of polybenzoxazine type vitrimers exhibit among others self-healing, reshaping, reprocessability, high strength, and low melt viscosities properties owing to benzoxazine moieties of the starting monomers used for producing corresponding vitrimers, through polymerization thereof. WO 2021 / 180562 A1 relates to vitrimers obtained through the polymerization of disulfide- containing benzoxazine monomers. WO 2022 / 122735 A1, WO 2021 / 250024 and WO 2023 / 057568 A1 relate to vitrimers obtained through the polymerization of di-ester containing benzoxazine monomers. It appears that benzoxazine momomers, in particular ester-containing benzoxazine monomers, especially di-ester-containing benzoxazine monomers as starting compounds for the preparation of vitrimer polymers, exhibit too high viscosities, in most instances not less than 2 000 mPa.s, when the polymerization thereof starts (at temperatures for example of about 140°C). Besides, said high viscosity values also depend on the temperature. These undesirable high viscosities, such as until 120°C, drastically impair their industrial processability, shaping methods, for example, when curing the monomers, are then complicated to be performed. Reactive diluents may be used to overcome these drawbacks, but this addition lowers the Tg of the final material, and said solvents need to be removed during the process that may generates some defauts either in the final vitrimer structure or in the starting monomers. The invention obviates at least one of the above mentioned drawbacks, and relates to a single ester-containing benzoxazine monomer of formula (I) wherein R are, independently, selected from the group consisting of a -linear or branched C1- C6 alkyl or alkoxy group, a linear or branched C2-C6 alkenyl or alkylenoxy group, a substituted or unsubstituted linear or branched C2-C6alkynyl group, and a -C-linear or branched C1-C6alkyl or C2-C6alkenyl substituted or unsubstituted phenyl group; R* is selected from the group consisting of H, OH and a O-linear or branched C1-C6 alkyl group, a linear or branched C1-C15 alkyl group, a C2-C15 alkenyl group, a C2-C15 alkynyl group or R” and R** are, independently, selected from the group consisting of a linear or branched C1-C6 alkyl or alkoxy group; a linear or branched C2-C6 alkenyl or alkylenoxy group; a substituted or unsubstituted linear or branched C2-C6 alkynyl group; at least one linear or branched C1-C6alkyl or C2-C6alkenyl substituted or unsubstituted o-, m-, p-phenyl group, cyclo(C3-C6alkyl) group or a heterocyclo(C3- C6alkyl) group, wherein the hetero atom is selected from N, S, and O; a (CH2)n3- phenyl group, wherein n3 is an integer from 1 to 6, a -(CH2)n1-O-(CH2)n2-(CH3) group, wherein n1 and n2, independently, are an integer from 1 to 10, , and ; x’, x’’, y’, y’’ are independently from 0 to 1, y’ = 1-x’; y’’=1-x’’, x’ and x’’ values being not together 0; x’+x’’ = 2-(y’+y’’), 0 ≤ y’ + y’’< 2 with the proviso that: x’ > 0 when x” ≥ 0 and x’ ≥ 0 when x” > 0. Preferentially, R’’ and R**, independently, may be selected from the group consisting of a linear or branched C1-C4 alkyl or alkoxy group; a linear or branched C2-C4 alkenyl or alkylenoxy group; a substituted or unsubstituted linear or branched C2-C4 alkynyl group; at least one linear or branched C1-C6alkyl or C2-C6alkenyl substituted or unsubstituted o-, m-, p-phenyl group, cyclo(C3-C6alkyl) group or a heterocyclo(C3- C6alkyl) group, wherein the hetero atom is selected from N, S, and O, a (CH2)n3- phenyl group, especially a –(CH2)n3-substituted or unsubstituted furan, phenyl, and wherein n3 is an integer from 1 to 4, -(CH2)n1-O-(CH2)n2-(CH3) group, wherein n1 and n2, independently, are an integer from Preferentially, R may be selected from the group consisting of a linear or branched C1-C4 alkyl or alkoxy group, a linear or branched C2-C4 alkenyl or alkylenoxy group, a substituted or unsubstituted linear or branched C2-C4alkynyl group, and a –C-linear or branched C1-C4alkyl or C2-C4alkenyl substituted or unsubstituted phenyl group; and, independently, R* may be selected from the group consisting of H, OH, a O-linear or branched C1- C4alkyl group a linear or branched C1-C10alkyl group or a C2-C10alkenyl group, more preferentially a linear or branched C1-C6alkyl group, a C2-C6alkenyl group or a C2-C6alkynyl group or . The Applicant has surprinsingly found that one of the main advantages of the single ester-containing benzoxazine monomer of formula (I), especially in comparison with di- ester-containing benzoxazine monomers known in the art, is that said monomer exhibits constant low viscosity, for example around 50 mPa.s - 1000 mPa.s, better around 100 mPa.s - 1000 mPa.s, at a temperature range preferably of about 80°C-140°C, highly enhancing the processability and operability thereof, that renders the polymerization / curing process, for manufacturing a vitrimer based on said monomers, easier to perform. As an example, the controlled low viscosity at the temperature range mentioned above allows to carry out a shaping method under heating, such as 3D printing procedure. According to an embodiment, said viscosity may be reduced by 50%- 100% in said considered temperature range. The single ester-containing benzoxazine monomer of the invention is advantageously suited for obtaining polybenzoxazine derivatives vitrimers by a polymerization involving the benzoxazine ring opening and a self-polymerisation under heat, resulting to said polybenzoxazine derivatives vitrimers. Owing to the specific monomer starting product, the vitrimers of the invention exhibit self-healing, reshaping, reprocessability and recycling properties. For the rest of the document, benzoxazine vitrimers will always refer to the polymerized form of the ester-bond benzoxazine monomers. Besides, the single ester-containing benzoxazine monomer of the invention may be used in combination or mixed with another benzoxazine monomer such as selected from the group consisting of monofunctional amines bridged with diphenolic compounds, monophenolic compounds bridged with diamines and diamines bridged by diphenolic compounds, or a mixture thereof, to improve the processability of the single ester-containing benzoxazine monomer during the polymerization for obtaining a vitrimer thereof (improvement of the viscosity of the obtained mixture: monomer of the invention, monomer 1, and said other monomer, monomer 2). The polybenzoxazine derivatives vitrimers properties are tightly connected to the properties of the ester-containing benzoxazine monomer. The mixture of both monomers 1 & 2 may be in the ratio monomer1:monomer 2 of 1 wt%-90 wt%. As may be seen from formula (I), the monomer includes a benzoxazine ring moiety that allows the cross-linking of said monomer upon heating and that promotes the reprocessing of the obtained benzoxazine vitrimers thanks to the exchangeable ester bonds it forms once crosslinked. Benzoxazine gives thermosetting properties such as high-temperature and flammability performance, high strength, thermal stability, low water absorption, chemical resistance, low melt viscosities, and near-zero shrinkage. The presence of a moiety consisting in ester bonds and free aliphatic hydroxyl groups in the benzoxazine monomers are essential to form a dynamic and reversible network of the benzoxazine derivatives vitrimers, allowing the material to be recycled, reshaped and reprocessed. Various groups in R1and R2(R*, R** and R’’) even if they are required are not impairing enough the effect of the invention, since they are used to provide the support for OH groups and ester moieties. Accordingly, the essential features of the monomer of the invention rely on the benzoxazine- containing moiety, ester bonds and free aliphatic hydroxyl groups. The Tg of such polybenzoxazine vitrimers may be of from -50 ° to 150 °C. The invention also relates to a process for synthesizing a single ester-containing benzoxazine monomer of formula (I) comprising the following steps of: a) reacting a phenolic carboxylic acid of formula (II), (Rac)z-COOH (II), wherein Rac is R-at least one substituted or unsubstituted phenol, comprising at least one R* group on the phenolic ring, with the proviso that when the at least one R* of the phenolic acid derivative is in ortho position with regard to – OH group, then R* is H; with at least one hydroxyl containing phenolic compound of formula (III) Ral-OH (III), wherein wherein Ral is R-at least one substituted or unsubstituted phenol, comprising at least one R* group on the phenolic ring, with the proviso that when the at least one R* of the phenolic acid derivative is in ortho position with regard to –OH group, then R* is H, at a temperature of from 25°C to 200°C, during 1h-72h, in the presence of a catalyst of Bronsted acid type, resulting in a phenol terminated oligomer or molecule (compound (IV)), b) reacting the compound (IV) with a mixture of: - an amino-alcohol of formula (V): (V) - a primary amine of formula (VI), R**-NH2 (VI), and - paraformaldehyde of formula (VII) 100 at a temperature range of from 50°C to 150°C, from 1 h to 10 h, under stirring, for obtaining the compound of formula (I); wherein R, R*, R**, x’, x’’, y’ and y’’ in the monomer of formula (I) are as defined above, and x’, x’’, y’, y’’ representing the proportion between benzoxazine groups when prepared from an amino-alcohol and the other amine(s), i.e primary amine(s), z being an integer of from 1 to 3. The definition of x’, x’’, y’, y’’ may then be: being the number of aminoalcohol per R1’ group, represent the number of amines (exception the number of aminoalcohol) per group R2’ and is the total number of amino groups per R1’ and R2’ wherein being the number of aminoalcohol per R1’’ group, represent the number of amines (exception the number of aminoalcohol) per group R2’’ is the total number of amino groups per R1’’ and R2’’. The Applicant has shown that the specific starting reactants are providing a single ester-containing benzoxazine monomer, which in turn, after polymerization, is giving the polybenzoxazine derivatives vitrimers comprising polymerized benzoxazine. No reactive diluents and no solvents are required when the polymerization of such monomers is carried out, for obtaining vitrimers, allowing to control / maintain high Tg values of vitrimers, -50°C to 150 °C, that are not altered by any presence of solvents and reactive diluents. Other advantages of the obtained monomer are those mentioned above, as constant low viscosity, around 50 mPa.s - 1000 mPa.s, at a temperature range of about 80°C-140°C. These properties are of importance for an easier manufacturing of a vitrimer based on said monomers. The presence of a moiety consisting in ester bonds and free aliphatic hydroxyl groups are essential to form a dynamic and reversible network of the benzoxazine derivatives vitrimers, allowing the material to be recycled, reshaped and reprocessed. An amine terminated with a hydroxyl group allows to close the oxazine ring and allows the transesterification reactions. Accordingly, the essential features of the monomer of the invention rely on the benzoxazine-containing moiety, ester bonds and free aliphatic hydroxyl groups. Consequently, the process uses two different amine compounds, one of which is necessary bearing an hydroxyl group. The benzoxazine ring, obtained from the reaction of the specific compounds ((II)- (VII)) which allows the material to be cross-linked (processed) upon heating, also helps the reprocessing thanks to the exchangeable and reversible ester bonds, and free aliphatic hydroxyl groups. Also, the benzoxazine ring moiety gives thermosetting properties such as high-temperature and flammability performance, high strength, thermal stability, low water absorption, chemical resistance, low melt viscosities, and near-zero shrinkage. Step b) allows the formation of R1’, R1’’, R2’ and R2’’. Rac is bearing R-at least one substituted or unsubstituted phenol, meaning that substituted or unsubstituted phenol may be one, two or three phenol groups. In some embodiments, the primary amine, compound of formula (VI), may be omitted, in the case when y’ + y’’ = 0. The amino-alcohol, compound of formula (V), is used instead. The Bronsted acid type catalyst are those commonly used for a Fischer esterification include para-toluene sulfonic acid (p-TSA), anhydrous chlorohydric acid (HCl), phosphoric acid (H3PO4), methanoic acid (CH3-CO2H), sulfuric acid, tosylic acid, and Lewis acids such as scandium(III) triflate. The content of catalyst may typically be of from 0,5 wt% to 2 wt%. The step a) may advantageously be carried out at a temperature in the range of 80°C to 150°C, most preferably of from 100°C to 140°C for the best synthesis yields of higher than 95%, the chosen temperature being dependent on the nature of the reactants, i.e. the melting temperature of said reactant medium. Advantageously, step a) is performed of from 12h to 24h for the highest yield of at least 95%, and the duration is based on the kinetic of the reaction. The respective stoichiometry of starting reactants on step a), phenolic carboxylic acid: at least one hydroxyl containing phenolic compound may preferably be 1,50- 0,50 eq.:0,50-1,50 eq, resulting in an 1,0 eq. of the phenol terminated oligomer or molecule (compound (IV). In some embodiments, the stoichiometry is more preferably 1,0:1,0, or, in some embodiments, between 0,50:1,50 and 1,50:0,50. The second step of the process, step b), corresponds to a Mannich condensation type reaction of the phenol terminated oligomer or molecule of step a) ((IV)) with the amino-alcohol (formula (V)), the primary amine of formula (VI) and the paraformaldehyde (formula (VII)), optionally in presence of a catalyst. Thus, since step b) does not require the use of an external catalyst, step b) is implemented in an easier way. Step b) allows then the formation of R1’, R1’’, R2’ and R2’’. Advantageously, the amino-alcohol of formula (V) includes R* group, a linear amino- alcohol with a primary amine moiety and an aliphatic hydroxyl moiety for obtaining with the highest yield and the best reaction conditions the oxazine ring. The amino-alcohol of formula (V) may be more preferably selected from the group consisting of 2-aminoethanol, 2-amino-2-methylpropanol, 5-aminopentan-1-ol, heptaminol, 2-(2-Aminoethoxy)ethanol, and diglycolamine, or mixtures thereof. The primary amine includes the R** group as defined above. Primary amines may be further selected from the group consisting in allylamine, methylamine, ethylamine, propylamine, butylamine, isopropylamine, hexylamine, cyclohexylamine, stearylamine, 2-aminofluorene, aminophenyl acetylene, propargyl ether aniline, 4-aminobenzonitrile, furfurylamine and aniline, or mixtures thereof. The temperature range of step b) may preferably be of from 80°C to 95°C, allowing to obtain the highest conversion yields of at least 75%. Advantageously, step b) is performed from 1h to 8h, preferably of from 1h to 5h, for the highest yield of at least 75%. The respective stoichiometry of starting reactants on step b), phenol terminated oligomer or molecule (IV):amino-alcohol (V):primary amine (VI):paraformaldehyde (VII) may preferably be 1,0 eq.:z(x’+x’’);z(y’+y’’):2,0z resulting in an 1,0 eq. of the single ester-containing benzoxazine monomer, wherein, independently, x’, x’’, y’, y’’ are independently from 0 to 1, y’ = 1-x’; y’’=1-x’’, x’ and x’’ values being not together 0; x’+x’’ = 1-(y’+y’’), 0 ≤ y’+y’’ < 1; z being as defined above. It is also assumed that the higher are x’ and x’’, independently, the more efficient is the ROP. The specific range stoichiometry is depending on the respective equivalent proportion of the amino-alcohol and of the primary amine. It should be pointed out that there is a minimal quantity required for the reaction to occur. For instance, the relative molar% of amino-alcohol vs the relative molar% of primary amine derivative is 10 molar% vs 90 molar% respectively. It also means that primary amine may be omitted (0 molar%) and amino-alcohol may only be used instead (100 molar%). Besides, the selected stoichiometry ranges of both amino-alcohol / amine and paraformaldehyde preferably avoids the formation of either reaction linear and / or aliphatic by-products, such as oxazolidine, triaza derivatives, or condensation derivatives. The single ester-benzoxazine monomer synthesis may most preferably be solventless, even though a solvent could be added for the dissolution of starting reactants. The process involves a one-step synthesis, which is one of the advantages of the invention. Advantageously, the whole synthesis may generally not require any further monomer purification for the invention to be implemented. However, the purification of the monomer, if needed, may be performed by any known technic (vacuum, distillation etc.) The reaction mixtures of both steps a) and b) are stirred using a classical mechanical stirrer, or any non-limitative means. The process may be implemented by any known means known to the one skilled in the art, using appropriate vessel either at lab scale or at industrial scale. The invention also relates to a process for preparing a polybenzoxazine derivative vitrimer comprising the step of polymerization of a single ester-containing benzoxazine monomer of the invention (formula (I)) or as obtainable by the above mentioned process at temperatures within the range of from 100°C to 250°C for 1h to 24h, for obtaining polybenzoxazine derivatives vitrimers. In the context of the invention “derivative” means that the obtained vitrimer is obtained and derived through the polymerization of the benzoxazine monomer of the invention. Accordingly, “polybenzoxazine derivative vitrimer” or “polybenzoxazine vitrimer” have the same meaning. As aforementioned, no reactive diluents and no solvents are required when the polymerization of such monomers is carried out, for obtaining vitrimers, since the viscosity, around 50 mPa.s - 1000 mPa.s, at the specific temperature range of about 80°C-140°C is maintained constant. Said manufacturing process (obtention of the vitrimer) can easier be controlled and faster be carried out due to said reduced viscosity values, in comparison to known vitrimers manufacturing processes. According to the process for preparing the vitrimers of the invention, the polymerization step, which is a curing step, allows the benzoxazine ring to open and to react on itself to form a 3D network. Once cooled, the shape of the material is kept even after few months, typically 2-4 months. Once re-heated to at least 100 °C for a few minutes, the ester bonds are exchanging with the aliphatic hydroxyl group allowing the material to be reshaped, recycled, or reprocessed; while keeping structural integrity and number of covalent bound. Considering that Mannich condensation reaction is quantitative, nearly two hydroxyl groups could react with each ester bound through transesterification reaction (even after curing). The vitrimer behaviour strongly depend on the vitrimer freezing topology transition temperature (Tv) also considered as the temperature where the transesterification reaction significantly increased. The vitrimer behaviours were demonstrated through several experiments. After the curing step, by heating the vitrimer above the Tv, an initial shape of the vitrimer can be designed to other original shape. For example, vitrimers may be ground to a powder and can be reshaped or reprocessed at 150°C in a couple of minutes. However its shape remains stable at room temperature. The polymerization duration is depending on the curing temperature and / or on the nature of the single ester-containing benzoxazine monomer. The polymerization temperature is selected for a given monomer to be higher than the temperature needed to synthesize the monomer. Generally, the higher the polymerization temperature, the shorter the curing duration. For example, when the temperature of the polymerization is 250°C, the curing duration may be of at least 1h, and for a polymerization temperature of 100°C, the curing duration may be of no more than 24h. Preferably, the curing temperature may be of from 140°C to 200°C, more preferably of from 140°C to 180°C, the latter range providing curing duration of from 1,5h to 3h, preferably of from 1,5h to 2,5h. The polymerization may be performed by any known heating means, such as laser beam and infrared beam. The process may also include a post-polymerization step consisting of a heating step which may preferably be carried out at higher temperature than that the polymerization heating step. The invention is also directed to a polybenzoxazine derivative vitrimer, that may be obtained by the above depicted process, exhibiting at least one of the following characteristics: (i) Tv(topology freezing transition temperature) values of from 100°C to 250°C; preferably of from 130°C to 220°C, more preferably of from 130°C to 190°C, and (ii) Relaxation temperature values, ≥ Tvvalues, of from 100°C to 300°C, preferably of from 130°C to 200°C, more preferably of from 130°C to 180°C. The vitrimers Tvvalues are generally dependent from the nature and the content of the catalyst of step b), when present. The relaxation temperatures typically correspond to the relaxation temperatures of the vitrimers after the appliance of a strain, for example a physical deformation such as a torsion, without the observation of vitrimers degradation. Advantageously, the vitrimers may also exhibit at least one of the following characteristics selected from the group consisting of: - a relaxation time of from 0,5 s to 2 h, preferably of from 1 s to 1 h, more preferably of from 5 s to 50 min. The relaxation time is conventionally defined as the time for the sample to relax to a value corresponding 1 / e (0,37) of its original modulus. Generally, the higher is the temperature, the shorter is the relaxation time. For example, the relaxation time is about 150 min-200 s at temperatures values of 120°C-170°C, and of ≤ 200, preferably 100 s-20 s, at temperature ranges of 150°C to 200°C. In some embodiments, the vitrimer may be deformed between 0,1% to 100% of its initial size; - an activation energy related to relaxation times may be of from 50 kJ / mol to 200 kJ / mol, preferably of from 70 kJ / mol to 170 kJ / mol, more preferably of from 100 kJ / mol to 160 kJ / mol; and - a processing temperature may be of from 100°C to 250°C, preferably of from 130°C to 250°C, more preferably of from 150°C to 200°C, most preferably of from 150°C to 170°C. The vitrimers according to the invention may also very preferably exhibit the characteristics of behaving as a thermoset and / or an insolubility in many solvents, without been limited, such as water, CHCl3, CH2Cl2, DMF, THF, aromatic solvents, such as toluene and / or xylene, ketones, alcohols or carboxylic acids. Swelling properties are observed as an extent of from 0 to 500% of the initial weight thereof. Swelling experiments may be carried out in various solvents, for example in acetone, chloroform and water to assess the formation of a cross-linked network. Among them, chloroform is the solvent in which the vitrimer shows the highest swelling ratio of about 100%. In acetone and water, the vitrimers swell of 40%-50% and 20%-30%, respectively. The vitrimers of the invention present self-healing, reshaping, reprocessability, recycling and reversible adhesive properties. The vitrimers may constitute an intermediate layer between at least two substrates, such as metal, polymer, glass and ceramic material. The resulting composite material may be prepared by setting at least one ester-containing benzoxazine monomer between the two considered substrates then curing at a temperature providing the vitrimer without altering the integrity of the substrates. Each substrate may be different from the other. Metallic substrates are not limited, and may be of aluminium, iron, steel and the like. Polymer substrates may be of polycarbonate, acrylic, polyamide, polyethylene or terephthalate. Benzoxazine vitrimers may then be advantageously used in non-limited various fields of technologies, such electronics, aerospace, defense and automotive fields. The invention also relates to a composition A comprising: a) a single ester-containing benzoxazine derivative of formula (I), and b) at least one or more additional compounds of organic molecules types containing or not benzoxazine moieties. Preferably, the organic molecules types may be polymers containing or not benzoxazine moieties. The additional compound may be used to enhance the properties of either the monomer or the vitrimer (i.e. viscosity, mechanical and thermal properties), or both. Polymers may be epoxy resins, bismaleimide resins, phenolic resins or benzoxazine resins, polyurethanes, polyamides, polyolefins, polyesters, rubbers. The ester- containing benzoxazine derivative of formula I may be used in a weight ratio from 0,1 to 80 % of the final composition. The compound of formula (I) may be used to provide vitrimer properties to the above-mentioned polymers (self-healing, reprocessing, etc.). The invention also relates to a composition B comprising: a) a single ester-containing benzoxazine monomer of formula (I), and b) a material selected from the group consisting of fillers, fibers, pigments, dyes, and plasticizer. The additional compound may be used to enhance the properties of either the monomer or the vitrimer (i.e. viscosity, mechanical and thermal properties), or both. The additional compound could be carbon fibers, glass fibers, clays, carbon black, silica, carbon nanotubes, graphene, any known means for the thermal or the mechanical reinforcement of composites. The invention also concerns a use of the vitrimer according to the invention as a reversible adhesive, sealant, coating or encapsulating systems for substrates selected from the group consisting of a metal, polymer, glass and ceramic material. Preferably, the metal and the polymer are as above defined. The invention also relates to a use of the vitrimer according to the invention in 3D printing processes or in additive manufacturing processes. The following examples are intended to more detail some embodiments, with appended figures. - Figure 1 shows a synthesis reaction of a monoester with a monofunctional phenolic acid for producing 2-(3-(2-hydroxyethyl)-3,4-dihydro-2H-benzo[e][1,3]oxazin-6- yl)ethyl 3-(2-(2-hydroxyethyl)-3,4-dihydro-2H-benzo[e][1,2]oxazin-6-yl)propanoate (TYR-PA-mea); - Figure 2 shows the NMR spectrum of TYR-PA-mea ester-containing benzoxazine monomers; - Figure 3.a and Figure 3.b are respectively displaying the DSC and isothermal rheology monitoring (140°C) curves of the TYR-PA-mea and TYR-PA-fu ester- containing benzoxazine monomers, “fu” designating furfurylamine; - Figures 4 (a) and (b) show the isothermal rheology monitoring of the viscosity shear rate of TYR-PA-mea / fu ester-containing benzoxazine monomers at different temperatures; - Figure 5 shows a synthesis reaction of a monoester TYR-PA-dga ; - Figure 6 shows the NMR spectrum of TYR-PA-dga ester-containing benzoxazine monomers. Figure 7 shows a synthesis reaction of a monoester TYR-DPA-dga1.75 / ste0.25. Figure 8. shows the NMR spectra of TYR-DPA-dga1.75 / ste0.25 ester-containing benzoxazine monomers. Figure 9 displays the evolution of viscosity at 50°C and 80°C for TYR-PA-mea of Example 1 and of di-ester containing monomers PEG-DPA-mea of the prior art. Example 1: Synthesis of benzoxazine containing free aliphatic hydroxyl groups and monoester (TYR-PA-mea) with tyrosol, phloretic acid, mono-ethanolamine and paraformaldehyde The TYR-PA-mea monoester benzoxazine containing free aliphatic hydroxyl groups was synthesized in two stages (Fig. 1). The first step, step a), corresponds to a Fischer esterification between 2-(4-Hydroxyphenyl)ethanol (tyrosol, TYR) (1 eq.) and 3-(4- hydroxyphenyl) propionic acid (phloretic acid, PA) (1 eq.) in presence of para- toluene sulfonic acid introduced in catalytic amount (0,5 wt.%). The reactants were put together in melt at 130 °C and agitated by mechanical stirring for 24 hours, to provide 4-hydroxyphenethyl 3-(4-hydroxyphenyl)propanoate (TYR-PA) (1 eq.). The second step, step b), corresponds to a Mannich condensation of TYR-PA (1 eq.) with mono-ethanolamine (mea) (2 eq.) and paraformaldehyde (PFA) (4 eq,). All these reactants were agitated together by mechanical stirring and reacted in melt at 70 °C for 8 hours to provide the TYR-PA-mea monoester benzoxazine containing free aliphatic hydroxyl groups, 2-(3-(2-hydroxyethyl)-3,4-dihydro-2H- benzo[e][1,3]oxazin-6-yl)ethyl 3-(2-(2-hydroxyethyl)-3,4-dihydro-2H- benzo[e][1,2]oxazin-6-yl)propanoate. In this compound, x’ = 1, x’’ = 1; y’ = y’’ = 0. The Figure 2 is displaying the1H NMR spectrum (AVANCE III HD Bruker spectrometer) of TYR-PA-mea ester-containing benzoxazine monomers. Here, in said Example 1, no primary amine is used (y’ + y’’ = 0), mono-ethanolamine is used (which plays the role of the primary amine). Example 2 A compound named TYR-PA-fu ester-containing benzoxazine monomer is obtained as in Example 1, where furfurylamine is used instead of mono-ethanolamine. This compound is not according to the invention, and is used as a comparative example. TYR-PA-fu: 2-(3-(furan-2-ylmethyl)-3,4-dihydro-2H-benzo[e][1,3]oxazin-6-yl)ethyl 3- (2-(furan-2-ylmethyl)-3,4-dihydro-2H-benzo[e][1,2]oxazin-6-yl)propanoate. Accordingly, Figure 3.a is displaying the DSC thermogram of polyfunctional monoester containing benzoxazine. The abbreviations “mea” and “fu” correspond respectively to mono-ethanolamine (terminated by free hydroxyl groups) and furfurylamine (terminated by furan groups). The DSC thermogram of TYR-PA-fu furfurylamine containing benzoxazine monomer shows a first exothermic peak starting at a temperature of 150 °C. This peak is associated to the ring opening of the benzoxazine rings upon heating. The ring opening of the benzoxazine rings occurred at much lower temperature in the case of TYR-PA-mea benzoxazine monomers containing free alcohol groups of the invention. The first exothermic peak starts at 100 °C for a maximum located around 170 °C. Transesterification reactions between ester bonds and aliphatic hydroxyl groups promote the thermal ring opening polymerization of benzoxazine monomer. The second exothermic peak corresponds to the degradation the aliphatic ester, observed in both case (mea and fu). The curing of the TYR-PA-mea / fu ester-containing benzoxazine monomers was monitored by rheological measurement in Figure 3.b. The rheogram is performed under the following conditions: 1 Hz, with linear amplitude from 1 to 0.1%; 25 mm plates. The test is performed following a heating ramp from 80°C to 140 °C at 15 °C / min followed by an isothermal measurement at 140 °C. The complex viscosity is recorded as a function of time. The term "gelation time" is defined as the time when the complex viscosity of the soften monomer increases abruptly to transform into a gel. At 160 °C, the gelation time is reached after 410 and 2200s, respectively for TYR-PA-mea and TYR-PA-fu. Figures 4 (a) and (b) are displaying the isothermal rheology monitoring of the viscosity shear rate of the TYR-PA ester-containing benzoxazine monomers, “fu” designating furfurylamine. The rheogram is performed under the following conditions: shear rate ramp logarithmic from 100 to 0.01 s-1; 50 mm plates. The viscosity of the TYR-PA-mea / fu ester-containing benzoxazine monomers was monitored by rheological measurement in Figures 4(a) and (b). The viscosity of the TYR-PA-mea / fu ester- containing benzoxazine monomers is below 1000 mPa.s at 75 and 100 °C. The compound TYR-PA-fu is not a vitrimer, since there is no free OH groups (x’=x’’=0). The compound TYR-PA-fu (not according to the invention) has a processing window which is smaller than that according to the invention, and is longer as regards its curing duration. Example 3: Synthesis of benzoxazine containing free aliphatic hydroxyl groups and containing one ester groups from 2-(4-hydroxyphenyl)ethanol (TYR) and 3-(4- hydroxyphenyl) propionic acid (PA) as phenolic acid derivatives and diethyleneglycol (dga) as primary amine with aliphatic OH, according to the invention. The TYR-PA-dga benzoxazine monomer containing free aliphatic hydroxyl groups was synthesized in two stages (Fig.5). The first step, step a), corresponds to a Fischer esterification between 3-(4- hydroxyphenyl) propionic acid (phloretic acid, PA) (1 eq.) and 2-(4-hydroxyphenyl)ethanol (tyrosol, TYR) (1 eq.) in presence of para-toluene sulfonic acid introduced in catalytic amount (0,5 wt.%). The reactants were put together in melt at 130°C and agitated by mechanical stirring for 24 hours, to provide (TYR-PA) (1 eq.). The second step, step b), corresponds to a Mannich condensation of TYR-PA (1 eq.) with diethylene glycol amine (dga) (2 eq.) and paraformaldehyde (PFA) (4 eq,). All these reactants were agitated together by mechanical stirring and reacted in melt at 70 °C for 8 hours to provide the TYR-PA-dga benzoxazine containing free aliphatic hydroxyl groups. In said example, the primary amine is omitted, the diethylene glycol amine (dga) is used as providing the both moieties (primary amine and amino-alcohol). In this compound, x’=1, x”=1, y’=y”=0. The Figure 6 is displaying the1H NMR spectrum (AVANCE III HD Bruker spectrometer) of TYR-PA-dga ester-containing benzoxazine monomers. Here, in said Example 3, no primary amine is used (y’ + y’’ = 0 diethylene glycol amine is used (which plays the role of the primary amine). Example 4. Synthesis of benzoxazine containing free aliphatic hydroxyl groups and containing one ester groups from 2-(4-hydroxyphenyl)ethanol (TYR) and 4,4-bis(4- hydroxyphenyl)pentanoic acid (DPA) as phenolic acid derivatives and diethyleneglycol (dga) as primary amine with aliphatic OH and stearylamine (ste) as primary amine. The TYR-DPA-dga1.75 / ste0.25 benzoxazine monomer containing free aliphatic hydroxyl groups was synthesized in two stages (Fig.7). The first step, step a), corresponds to a Fischer esterification between 4,4-bis(4-hydroxyphenyl)pentanoic acid (diphenolic acid, DPA) (1 eq.) and 2-(4-hydroxyphenyl)ethanol (tyrosol, TYR) (1 eq.) in presence of para-toluene sulfonic acid introduced in catalytic amount (0,5 wt.%). The reactants were put together in melt at 130°C and agitated by mechanical stirring for 24 hours, to provide (TYR-DPA) (1 eq.). The second step, step b), corresponds to a Mannich condensation of TYR-DPA (1 eq.) with diethylene glycol amine (dga) (1.75 eq.), stearylamine (ste) (0.25 eq) and paraformaldehyde (PFA) (4 eq,). All these reactants were agitated together by mechanical stirring and reacted in melt at 70 °C for 8 hours to provide the TYR-DPA- dga1.75 / ste0.25 benzoxazine containing free aliphatic hydroxyl groups. In said example, the primary amine is omitted, the diethylene glycol amine (dga) is used as providing the both moieties (primary amine and amino-alcohol). In this compound, x’=1, x”=0.75, y’=0, y”=0.25. The Figure 8 is displaying the1H NMR spectrum (AVANCE III HD Bruker spectrometer) of TYR-PA-mea ester-containing benzoxazine monomers. Here, in said Example , no primary amine is used (y’ + y’’ = 0 diethylene glycol amine is used (which plays the role of the primary amine). Example 5: comparative example This Example 5 compares the evolution of the viscosity vs time of the TYR-PA-mea monoester benzoxazine containing free aliphatic hydroxyl groups of Example 1 and the di-ester containing monomers PEG-DPA-mea as described in WO 2021 / 250024 of the prior art (Example 1). Results are shown in Fig.9. The viscosity level is significantly lower for the TYR-PA- mea monoester benzoxazine of the current invention compared to di-ester containing monomers PEG-DPA-mea of the prior art. Conclusion The single ester-containing benzoxazine monomers, especially in comparison with di- ester-containing benzoxazine monomers known in the art, exhibit constant lower viscosity at a temperature range of for example about 80°C-140°C, due to the single- ester moiety, as it may be deduced, in a non limitative way, for example, from Example 2. The presence of a moiety consisting in ester bonds and free aliphatic hydroxyl groups in the single-ester containing benzoxazine monomers are essential to form a dynamic and reversible network of the benzoxazine derivatives vitrimers, allowing the material to be recycled, reshaped and reprocessed.

Claims

Claims 1. A single ester-containing benzoxazine monomer of formula (I)wherein R1’ and R1’’ are, independently, R2’ and R2’’ are, independently,wherein R are independently selected from the group consisting of a -linear or branched C1- C6 alkyl or alkoxy group, a linear or branched C2-C6 alkenyl or alkylenoxy group, a substituted or unsubstituted linear or branched C2-C6 alkynyl group, and a -C-linear or branched C1-C6alkyl or C2-C6alkenyl substituted or unsubstituted phenyl group; R* is selected from the group consisting of H, OH and a O-linear or branched C1-C6 alkyl group, a linear or branched C1-C15 alkyl group, a C2-C15 alkenyl group, a C2-C15 alkynyl group orR” and R** are, independently, selected from the group consisting of a linear or branched C1-C6 alkyl or alkoxy group; a linear or branched C2-C6 alkenyl or alkylenoxy group; a substituted or unsubstituted linear or branched C2-C6alkynylgroup; at least one linear or branched C1-C6alkyl or C2-C6alkenyl substituted or unsubstituted o-, m-, p-phenyl group, cyclo(C3-C6alkyl) group or a heteocyclo(C3- C6alkyl) group, wherein the hetero atom is selected from N, S, and O; a (CH2)n3- phenyl group, wherein n3 is an integer from 1 to 6, a -(CH2)n1-O-(CH2)n2-(CH3) group, wherein n1 and n2, independently, are an integer from 1 to 10,, and ; x’, x’’, y’, y’’ are independently from 0 to 1, y’ = 1-x’; y’’=1-x’’, x’ and x’’values being not together 0; x’+x’’ = 2-(y’+y’’), 0 ≤ y’+y’’ < 2; with the proviso that: x’ > 0 when x” ≥ 0 and x’ ≥ 0 when x” > 0.

2. The single ester-containing benzoxazine monomer of claim 1, wherein R’’ and R**, independently, are selected from the group consisting of a linear or branched C1-C4 alkyl or alkoxy group, a linear or branched C2-C4 alkenyl or alkylenoxy group, a substituted or unsubstituted linear or branched C2-C4alkynyl group, at least one linear or branched C1-C6 alkyl or C2-C6 alkenyl substituted or unsubstituted o-, m-, p- phenyl group, cyclo(C3-C6alkyl) group or a heteocyclo(C3-C6alkyl) group, wherein the hetero atom is selected from N, S, and O, a (CH2)n3-phenyl group, especially a - (CH2)n3-substituted or unsubstituted furan, phenyl, and wherein n3 is an integer from 1 to 4, -(CH2)n1-O-(CH2)n2-(CH3) group, wherein n1 and n2, independently, are an integer from3. The single ester-containing benzoxazine monomer of claim 1 or 2, wherein R is selected from the group consisting of a linear or branched C1-C4alkyl or alkoxy group, a linear or branched C2-C4alkenyl or alkylenoxy group, a substituted orunsubstituted linear or branched C2-C4alkynyl group, and a -C-linear or branched C1-C4alkyl or C2-C6alkenyl substituted or unsubstituted phenyl group; and, independently, R* is selected from the group consisting of H, OH, a O-linear or branched C1-C4alkyl group, a linear or branched C1-C10alkyl group or a C2-C10alkenyl group, more preferentially a linear or branched C1-C6 alkyl group, a C2-C6 alkenyl group or a C2- C6 alkynyl group or.

4. The single ester-containing benzoxazine monomer of any of claims 1 to 3, wherein said monomer exhibits a constant viscosity of 50 mPa.s - 1000 mPa.s, at a temperature range of about 80°C-140°C.

5. A process for synthesizing a single ester-containing benzoxazine monomer of formula (I) comprising the following steps of: a) reacting a phenolic carboxylic acid of formula (II), (Rac)z-COOH (II), wherein Rac is R-at least one substituted or unsubstituted phenol, comprising at least one R* group on the phenolic ring, with the proviso that when the at least one R* of the phenolic acid derivative is in ortho position with regard to – OH group, then R* is H; with at least one hydroxyl containing phenolic compound of formula (III) Ral-OH (III), wherein wherein Ral is R-at least one substituted or unsubstituted phenol, comprising at least one R* group on the phenolic ring, with the proviso thatwhen the at least one R* of the phenolic acid derivative is in ortho position with regard to –OH group, then R* is H, at a temperature of from 25°C to 200°C, during 1h-72h, in the presence of a catalyst of Bronsted acid type, resulting in a phenol terminated oligomer or molecule (compound (IV)), b) reacting the compound (IV) with a mixture of: - an amino-alcohol of formula (V): (V) - a primary amine of formula (VI), R**-NH2 (VI), and - paraformaldehyde of formula (VII)100at a temperature range of from 50°C to 150°C, from 1 h to 10 h, under stirring, for obtaining the compound of formula (I); wherein R, R*, R**, x’, x’’, y’ and y’’ in the monomer of formula (I) are as defined in any of claims 1-3, and x’, x’’, y’, y’’ representing the proportion between benzoxazine groups when prepared from an amino-alcohol and the other amine(s), z being an integer of from 1 to 3.

6. The process of claim 5, wherein the step a) may advantageously be carried out at a temperature in the range of 80°C to 150°C, most preferably of from 100°C to 140°C.

7. The process of claim 5 or 6, wherein the respective stoichiometry of starting reactants on step a), phenolic carboxylic acid: at least one hydroxyl containing phenolic compound is 1,50-0,50 eq.:0,50-1,50 eq, resulting in an 1,0 eq. of the phenol terminated oligomer or molecule (compound (IV)).

8. The process of any of claims 5 to 7, wherein the amino-alcohol of formula (V) includes the R* group, a linear amino-alcohol with a primary amine moiety and an aliphatic hydroxyl moiety.

9. The process of any of claims 5 to 8, wherein primary amines are selected from the group consisting in allylamine, methylamine, ethylamine, propylamine, butylamine, isopropylamine, hexylamine, cyclohexylamine, stearylamine, 2- aminofluorene, aminophenyl acetylene, propargyl ether aniline, 4-aminobenzonitrile, furfurylamine and aniline, or mixtures thereof. 10.The process of any of claims 5 to 9, wherein the respective stoichiometry of starting reactants on step b), phenol terminated oligomer or molecule (IV):amino- alcohol (V):primary amine (VI):paraformaldehyde (VII) is 1,0 eq.:z(x’+x’’) eq. eq.:z(y’+y’’) eq.:2,0z eq. resulting in an 1,0 eq. of the single ester-containing benzoxazine monomer, wherein, independently, x’, x’’, y’, y’’ are independently from 0 to 1, y’ = 1-x’; y’’=1-x’’, x’ and x’’values being not together 0; x’+x’’ = 1-(y’+y’’), 0 ≤ y’+y’’ < 1; z being 1, 2 or 3. 11.A process for preparing a polybenzoxazine derivative vitrimer comprising the step of polymerization of a single ester-containing benzoxazine the monomer of formula (I) of any of claims 1-4 or as obtainable by the process of any of claims 5-10 at temperatures within the range of from 100°C to 250°C for 1h to 24h, for obtaining the polybenzoxazine derivatives vitrimer. 12.A polybenzoxazine derivative vitrimer, exhibiting at least one of the following characteristics: (i) Tv values of from 100°C to 250°C; preferably of from 130°C to 220°C, more preferably of from 130°C to 190°C, and (ii) Relaxation temperature values, ≥ Tvvalues, of from 100°C to 300°C, preferably of from 130°C to 200°C, more preferably of from 130°C to 180°C.The polybenzoxazine derivative vitrimer of claim 12, exhibiting a relaxation time of from 0,5 s to 2 h, preferably of from 1 s to 1 h, more preferably of from 5 s to 50 min; an activation energy related to relaxation times of from 50 kJ / mol to 200 kJ / mol, preferably of from 70 kJ / mol to 170 kJ / mol, more preferably of from 100 kJ / mol to 160 kJ / mol; and a processing temperature of from 100°C to 250°C, preferably of from 130°C to 250°C, more preferably of from 150°C to 200°C, most preferably of from 150°C to 170°C.

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