Self-blowing and recyclable vitrimer foams

Abstract

The invention relates to a process for preparing self-blowing and recyclable vitrimer foams comprising the steps of polymerizing a monomer compound of benzoxazine containing free aliphatic hydroxyl groups and monoester said steps consisting of a) a conditioning step of the monomer compound (I) at a melting temperature selected within the range of from 100°C to 130°C, and followed by b) a temperature increasing step to reach a foaming temperature within the range of from 170°C to 230°C, both steps a) and b), independently, being carried out for 10 min to 1h, for obtaining a self-blowing and recyclable vitrimer foam originating from said benzoxazine monomers compounds.

Description

[0001] SELF-BLOWING AND RECYCLABLE VITRIMER FOAMS

[0002] Field of invention

[0003] The invention is directed to the field of self-blowing and recyclable vitrimer foams derived from benzoxazine compounds based on transesterification mechanism.

[0004] Technical field

[0005] Vitrimers are polymeric materials that can be classified as covalent adaptable networks owing to the dynamic nature of their reversible chemical bonds, allowing the material to be healed, recycled and reprocessed like thermoplastics. These exchange reactions are triggered by external stimuli, most frequently by temperature. The viscosity of vitrimers gradually decreases upon heating providing malleability to the network while permitting internal stress to relax. Network integrity over the entire range of application ensures dimensional stability, mechanical, and solvent resistance.

[0006] 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).

[0007] 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 viscosity properties owing to the benzoxazine moieties contained in the starting monomers and 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 and WO 2021 / 250024 relate to vitrimers obtained through the polymerization of ester containing benzoxazine monomers. Some other vitrimers originate from ester and acrylate moieties containing benzoxazine monomers (PCT / EP2023 / 025539).

[0008] Vitrimer foams, especially based on benzoxazine monomers, are already available (patent applications IN202441042130 and CN11 1218054). EP4306577 discloses a process to obtain lightweight foaming composites based on vitrimer resins such as benzoxazine resin (BOz) with dynamic S-S bond, epoxy resin with dynamic imine-amine bond, epoxy resin with carboxylate bond. However, said composites are not self-blowing and thus require the use of an external blowing agent, that can lead to difficult formulation, chemical compatibilities, foams uniformity and control, weakened mechanical properties and lowered thermal and chemical stability.

[0009] Self-blowing foams have also been described, for example in W02021004993A1 , which relates to polyurethane foams, but they do generally not present any recyclable ability. References are also made to patent applications US20240043647 and JP01170623.

[0010] It appears that vitrimer foams, especially those originating from benzoxazine monomers, in particular ester-containing benzoxazine monomers, still need to present some improved properties for specific uses, especially that are both selfblowing and recyclable.

[0011] Disclosure of the invention

[0012] It is an object of the present invention to alleviate at least one above mentioned drawbacks. More specifically, the invention has for generic technical problem to provide a self-blowing and recyclable vitrimer foam originating from specific benzoxazine monomer compounds or presenting a structural backbone issued from benzoxazine monomer compounds.

[0013] For this purpose, one aspect of the invention is directed to a process for preparing self-blowing and recyclable vitrimer foams comprising the steps of polymerizing a monomer compound of benzoxazine containing free aliphatic hydroxyl groups and monoester of formula (I) said steps consisting of: a) a conditioning step of the monomer compound (I) at a melting temperature selected within the range of from 100°C to 130°C, and followed by b) a temperature increasing step to reach a foaming temperature within the range of from 170°C to 230°C, both steps a) and b), independently, being carried out for 10 min to 1 h, for obtaining a self-blowing and recyclable vitrimer foam originating from said benzoxazine monomers compounds, wherein the monomer compound of benzoxazine containing free aliphatic hydroxyl groups and a monoester of formula (I) is wherein

[0014] R is selected from the group consisting of a linear or branched C1-C12 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, a cyclo(C3-Ce alkyl) group, a heteocyclo(C3-Ce alkyl), a linear or branched C1-C6 alkyl or C2-C6 alkenyl substituted or unsubstituted phenyl group and a (CH2)n3-phenyl group, wherein n3 is an integer from 1 to 10;

[0015] R’ is selected from the group consisting of at least one of -CH, a C-(CH2)n3-CH3 group, a C-(CH2)n3-CH-(CH3)2 group, a C-(CH2)n3-(CHZ)n4-(CH3)2 group, a C-(CH2)n3- (CHZ)n4-(CH2)n3-CH3gTOUp, a C-(CHZ)n4-(CH2)n3-CH3group, a C-(CHZ)n4-[(CH2)n3- CHS]2 group, a C-substituted or unsubstituted C2-C6 linear or branched alkenyl group, a linear or branched Ci-Ce alkyl substituted or unsubstituted phenyl or phenyl including at least one hetero atom selected from N, O and S, a C-(CH2)n3-Ci-Ce linear or branched alkyl substituted or unsubstituted phenyl or phenyl including at least one heteroatom selected from N, O and S, a C-(CH2)n3-Ci-Ce linear or branched alkyl substituted or unsubstituted phenyl or phenyl including at least one heteroatom selected from N, O and S-(CH2)n3-CH3, a C-(CH2)n3-Ci-Ce linear or branched alkyl substituted or unsubstituted phenyl or phenyl including at least one heteroatom selected from N, O and S-(CH2)n3-CH-(CH3)2, a C-(CH2)n3-Ci-Ce linear or branched alkyl substituted or unsubstituted phenyl or phenyl including at least one heteroatom selected from N, O and S-(CH2)n3-(CHZ)n4-(CH3)2 group, a C-(CH2)n3-Ci- Ce linear or branched alkyl substituted or unsubstituted phenyl or phenyl including at least one heteroatom selected from N, O and S-(CHZ)n4-(CH2)n3-CH3 group and a C- (CH2)n3-(CHZ)n4-Ci-C6 linear or branched alkyl substituted or unsubstituted phenyl or phenyl including at least one heteroatom selected from N, O and S-(CH2)n3-CH3 group, wherein n3 and n4, independently, are an integer from 1 to 10 and Z is selected from the group consisting in a linear or branched Ci-Ce alkyl or alkoxy group, linear or branched C2-C6 alkenyl or alkylenoxy group and a linear or branched Ci-Ce alkyl or C2-C6 alkenyl substituted or unsubstituted phenyl group, and at least one O atom is present or not between two adjacent C, or R’ is omitted.

[0016] R* is selected from the group consisting of a linear or branched C1-C20, preferably Ci-Ce, alkyl or alkoxy group, a cyclo(C3-Ce alkyl) group, a heteocyclo(C3-Ce alkyl) group, wherein the hetero atom is selected from N, S, and O, linear or branched C2- Ce alkenyl or alkylenoxy group, substituted or unsubstituted linear or branched C2-C6 alkynyl group, a linear or branched Ci-Ce alkyl or C2-C6 alkenyl substituted or unsubstituted phenyl group, a (CH2)n3-phenyl group and -(CH2)n3-O-(CH2)n4, wherein n3 and n4, independently, are an integer from 1 to 10;

[0017] R** is the same as R* and further includes a member selected from a O-, N- or S- (CH2)n3-CH-(CHs)2 group, a O-, N- or S-(CH2)n3-(CHZ)n4-(CH3)2 group, a O-, N- or S- (CH2)n3-(CHZ)n4-(CH2)n3-CH3 group, a O-, N- or S-(CHZ)n4-(CH2)n3-CH3 group, a O-, N- or S-(CHZ)n4-[(CH2)n3-CH3]2 group and a O-substituted or unsubstituted C2-C6 linear or branched alkynyl group, Z being as defined for R’, a -(CH2)n3-C=N group, a polycyclic aromatic or heteroaromatic hydrocarbon, such as naphthalene, anthracene, fluorene, phenanthrene, optionally substituted by a linear or branched Ci-Ce alkyl or alkoxy group, a cyclo(C3-Ce alkyl) group, a heterocyclo(C3-C6alkyl) group, a linear or branched C2-C6 alkenyl or alkylenoxy group, or by a substituted or unsubstituted linear or branched C2-C6 alkynyl group, wherein n3 and n4, independently, are an integer from 1 to 10; R*** is selected from the group consisting in H, OH and a O-linear or branched Ci-Ce alkyl group, and further includes a linear or branched C1-C15 alkyl group or a C2-C15 alkenyl group or x value is of from 0 to 1 and y value is 1-x, preferably of from 0,1 to 1 , more preferentially from 0,5 to 1 ;

[0018] In the context of the invention, x and y, in formula (I) represent the proportion between benzoxazine groups when prepared from an aminoalcohol and the other amine(s). In other words, x and y can be defined as whereinn«n?nes and naminoaicohoi being the number of aminoalcohol per molecules of monomer compound , Uamines represent the number of amines (excepting the number of aminoalcohol) per molecule of monomer compound and ’ S the total number of amino groups per molecule of monomer compound.

[0019] In the context of the invention, “monomer compound of benzoxazine containing free aliphatic hydroxyl groups and monoester of formula (I) and “monomer compound(s)” have the same meaning.

[0020] The Applicant has surprisingly found that the self-blowing vitrimer foams originating from benzoxazine monomer compounds (I) are obtained in such a specific foaming temperature range of 170°C and 230°C, which are also presenting recyclable abilities. More specifically, the monomer compounds are melted (step a)) at a melting temperature selected within the range from 100°C to 130°C, more preferably from 100°C to 120°C, or in some embodiments from 110°C to 130°C, to ensure their liquid state an initiate the benzoxazine ring opening at a low extent. This step is crucial to melt the monomer compounds and initiate their oligomerization. As the temperature selected in step a) rises within the range of 170-230°C, depending on the monomer compounds, preferably 180°C-220°C, more preferably 185°C-220°C, or even preferably 190°C-220°C, the polymerization takes place. This triggers both benzoxazine polymerization and the transesterification reaction. The latter is responsible for the release of an alcohol compound (step b)), while the former, benzoxazine polymerization, leads to an increase in viscosity and freezing, or fixing, of the structure (foaming) by cross-linking. It is because these two phenomena occur concomitantly with the considered duration that the production of self-blowing and recyclable vitrimers foams originating from benzoxazine monomers compounds is possible.

[0021] The main aspect of the invention is starting from a monomer compound (A) (such as of formula (I) containing an ester and an alcohol group (aliphatic hydroxyl group), to produce the corresponding typical structure (B) after polymerization of the benzoxazine rings (ring-opening polymerization) and polycondensation of the monoesters releasing the self-blowing blowing agent (degenerative transesterification). This is illustrated by a following non limitative theoretical example.

[0022] (A) (B)

[0023] Thus, the foaming temperature of step b) is higher than the temperature of polymerization of benzoxazines and higher than the temperature of degenerative transesterification temperature which is the dynamic exchange temperature allowing to release the alcohol compound and then to allow the foaming to take place.

[0024] However, a foaming temperature higher than that of step b) is impairing the native structure of the foaming vitrimer, the porosity and the expansion volume thereof partly explained by the possible deterioration of the covalent bonds such as Mannich bridges Ar-CH2-N (Ar being an aromatic) or ester bonds, leading to reduced mechanical properties, such as the compression modulus, of the vitrimer foam.

[0025] The invention addresses the gap by combining self-blowing and recyclability into a single material.

[0026] In the foaming temperature range of step b), there may very advantageously be an optimal temperature at which each of the monomer compounds of formula (I) allows to obtain the optimal structure and shape defined by both evolution of the expansion of the vitrimer foam (originating from monomer compounds of formula (I)). It should be understood that each vitrimer foam is produced at such optimal temperature, within the range of step b), that is the best compromise of both extent rate of degenerative transesterification which is limited by the deterioration of the vitrimer foam characteristics, for example the recycling ability, and volumetric expansion which is achieved when said expansion volume is no longer evolving.

[0027] Same consideration applies for the duration of step b) in which there may very advantageously be an optimal duration at which each of the monomer compounds of formula (I) allows to obtain the optimal structure and shape defined by both evolution of the extent rate of degenerative transesterification and volumetric expansion for obtaining the vitrimer foam. It should be understood that each vitrimer foam is produced at such optimal foaming duration that is the best compromise of both extent rate of degenerative transesterification which is observed by the deterioration of the vitrimer foam characteristics, for example the recycling ability, and volumetric expansion which is achieved when said expansion volume is no longer evolving.

[0028] The optimal temperature and duration of step b) does not exclude the fact that vitrimer foams could be produced at any temperature and duration given for said step b), preferred ranges thereof being of from 10 min to 55 min, more preferably of from 10 min to 50 min, especially of from 10 min to 45 min. Very preferably, the increasing of the temperature between step a) and step b) is carried out at a heating ramp between 2°C / min and 20°C / min.

[0029] The presence of a conditioning step a) followed by a high heating ramp in one the reasons which explains why foaming has been observed.

[0030] Melt viscosities at melting temperatures of step a) may advantageously range from 50 to 1000 mPa.s, these melt viscosities increase as alcohol is released during step b). It should be pointed out that depending on the chemical definition of each monomer compound, said monomer compound may be a viscous liquid or paste, or a powder at ambient temperature. Step a) allows to obtain a melt monomer compound as viscous liquid or paste.

[0031] The polymerization duration (step b)), otherwise named curing, may advantageously depend on the polymerization temperature and / or on the nature of the 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 polymerization duration. For example, when the temperature of the polymerization is 230°C, the curing duration may be of 10 min, and for a polymerization temperature of 170°C, the curing duration may be of no more than 1 h, preferably no more than 55 min, more preferably no more than 50 min.

[0032] In some embodiments, the foaming temperature may be of from 180°C to 220°C, more preferably of from 185°C to 220°C, said ranges providing duration of step b) of from 10 min to 50 min, preferably of from 10 min to 45 min with the production of the of self-blowing and recyclable vitrimers foams originating from benzoxazine monomers compounds. The polymerization may be performed by any known heating means, such as, and not limited to, laser beam and infrared beam.

[0033] It is very advantageous to carry out the step b) for practical reasons, at reduced pressure, typically of from 0.09 to 0.1 mBar. Such reduced pressure allows to obtain a vitrimer foam with a duration and / or temperature decreased by about 20%-30% compared to the duration and / or temperature at atmospheric pressure, said decreased duration and / or temperature being within the defined corresponding ranges thereof (step b)). According to the monomer compounds of formula (I), R’ is structure making the bridge between the ester bond and the phenolic ring, and R*** is a substituent of the phenolic ring. It is preferred that R*** is on meta position(s).

[0034] In the monomer compound of formula (I):

[0035] R may preferably 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, an unsubstituted linear or branched C2-C4 alkynyl group, an unsubstituted phenyl group and a (CH2)n3-phenyl group, wherein n3 is an integer from 1 to 6.

[0036] R’ may preferably be selected from the group consisting of at least one of -CH, a C- (CH2)n3-CHs group, a C-(CH2)n3-CH-(CH3)2 group, a C-(CH2)n3-(CHZ)n4-(CH3)2 group, C-(CH2)n3-(CHZ)n4-(CH2)n3-CH3group, C-(CHZ)n4-(CH2)n3-CH3group, a C-(CHZ)n4- [(CH2)n3-CHs]2 group, a C-substituted or unsubstituted C2-C4 linear or branched alkenyl group, an unsubstituted phenyl or phenyl including at least one heteroatom selected from N, O and S, a C-(CH2)n3-unsubstituted phenyl or phenyl including at least one heteroatom selected from N, O and S, a C-(CH2)n3-unsubstituted phenyl or phenyl including at least one heteroatom selected from N, O and S-(CH2)n3-CH3, a C- (CH2)n3-unsubstituted phenyl or phenyl including at least one heteroatom selected from N, O and S-(CH2)n3-CH-(CH3)2, a C-(CH2)n3-unsubstituted phenyl or phenyl including at least one heteroatom selected from N, O and S-(CH2)n3-(CHZ)n4-(CH3)2 group, a C-(CH2)n3-unsubstituted phenyl or phenyl including at least one heteroatom selected from N, O and S-(CHZ)n4-(CH2)n3-CH3 group and a C-(CH2)n3-(CHZ)n4- unsubstituted phenyl or phenyl including at least one heteroatom selected from N, O and S-(CH2)n3-CH3 group, wherein n3 and n4, independently, are an integer from 1 to 6 and Z is selected from the group consisting in a linear or branched C1-C4 alkyl or alkoxy group, linear or branched C2-C4 alkenyl or alkylenoxy group and an unsubstituted phenyl group, and at least one O atom is present or not between two adjacent C.

[0037] R* may preferably be selected from the group consisting of a linear or branched C1- Ce, preferably Ci-Ce, alkyl or alkoxy group, a linear or branched C2-C4 alkenyl or alkylenoxy group, an unsubstituted linear or branched C2-C4 alkynyl group, an unsubstituted phenyl group, a (CH2)n3-phenyl group and -(CH2)n3-O-(CH2)n4, wherein n3 and n4, independently, are an integer from 1 to 6; Preferably, R** is the same as R* and may further include a member selected from O-, N- or S-(CH2)n3-CH-(CH3)2group, a O-, N- or S-(CH2)n3-(CHZ)n4-(CH3)2group, a O-, N- or S-(CH2)n3-(CHZ)n4-(CH2)n3-CH3group, a O-, N- or S-(CHZ)n4-(CH2)n3-CH3group, a O-, N- or S-(CHZ)n4-[(CH2)n3-CH3]2group and a O-substituted or unsubstituted C2-C4 linear or branched alkynyl group, Z being as defined above, a - (CH2)n3-C=N group, a cyclo(C3-C4 alkyl) group, a heteocyclo(C3-C4 alkyl) group, a polycyclic aromatic or heteroaromatic hydrocarbon, wherein the hetero atom is selected from N, S, and O, such as naphthalene, anthracene, fluorene, furane, which may optionally be substituted by a linear or branched C1-C4 alkyl or alkoxy group, a linear or branched C2-C4 alkenyl or alkylenoxy group, or by a substituted or unsubstituted linear or branched C2-C4 alkynyl group, wherein n3 and n4, independently, are an integer from 1 to 6;

[0038] R*** may preferably be selected from the group consisting in H, OH and a O-linear or branched C1-C4 alkyl group, and may further include a linear or branched C1-C10 alkyl group or C2-Cw alkenyl group or

[0039] More preferably, R may be selected from the group consisting of groups -CH3, - (CH2)n3-CH3, -(CH2)n3-CH-[(CH2)n3-CH3]2, -C(CH3)3, -(CH2)n3-(C6H5), -(CH2)n3- CH=CH2and -(CH2)n3-C=CH, wherein n3 is an integer from 1 to 5.

[0040] More preferably, R’ may be selected from the group consisting of groups -CH, -C(CH3), -C-CH(CH2CH3), -C(CH2CH2CH3), -C-CH2(CH2)3CH3, -C-CH2(CH2)4CH3, -C(C6H5), -C(CH3)CH2, C(CH3)CH2CH2and -C(C6H5)CH2-CH3.

[0041] More preferably, R* may be selected from the group consisting of groups -CH3, - (CH2)n3-CH3, -(CH2)n3-CH-[(CH2)n4-CH3]2, -C(CH3)3, (CH2)n3-(C6H5), -(CH2)n3- CH=CH2, -(CH2)n3-C=CH, -(CH2)n3-O-(CH2)n4 wherein n3 and n4 independently are integer from 1 to 4, phenyl, and -(CH2)3-phenyl. More preferably, R** can be the group R*, or may be selected from the group consisting of groups CH3, -(CH2)n3-CH3, -(CH2)n3-CH-[(CH2)n4-CH3]2, -C(CH3)3, (CH2)n3-(C6H5), -(CH2)n3-CH=CH2, -(CH2)n3-C CH, O-(CH2)n3-C CH, O-(CH2)n3-C N, (CH2)n3-C=N, and -(CH2)n3-substituted or unsubstituted furan, phenyl, and wherein n3 and n4, independently, are integer from 1 to 4.

[0042] R*** may preferably be selected from the group consisting in H, OH and a O-linear or branched C1-C3 alkyl group, and may further include linear or branched Ci-Ce alkyl group or C2-C6 alkenyl group or . .

[0043] The depicted R, R’, R*, R**, R*** and combination thereof may be used independently one from the other.

[0044] The expression “substituted” as defined above, relates to the presence of some linear or branched alkyl groups in Ci-Ce.

[0045] Examples of a process and operating conditions for producing monomer compounds of formula (I) are given in WO2022122882.

[0046] In the context of the invention, it should be understood that a mixture of monomer compounds of formula (I) could be used.

[0047] A second aspect of the invention is self-blowing and recyclable vitrimer foams presenting a backbone issued from benzoxazine monomer compounds according to the invention, exhibiting at least one of the following characteristics selected from the group consisting of: a) an experimental weight loss (W%), defined by the ratio expressed as a percentage between the weight of a dried vitrimer foam to the weight of a monomer compound used for the preparation of said vitrimer foam according to a process of the invention, in the range of from 3% to 30%; b) a volume expansion (V%), defined by the ratio expressed in percentage between the height of a vitrimer foam to the height of a monomer compound used for the preparation of said vitrimer foam according to a process of the invention, in the range of 5% to 1000%; c) an extent rate of degenerative transesterification (Y%), defined as the percentage of the experimental weight loss to the theoretical weight loss corresponding to the maximal weight loss when the degenerative transesterification (Y%) is 100%, of from 15 to 95%.

[0048] More specifically: with Wexperimentai corresponding to the experimental weight loss and Wtheoretical corresponding to the theoretical ones. with Wexperimentai corresponding to the experimental weight loss and Wtheoretical corresponding to the theoretical ones. with Hmonomer corresponding to the initial height of the monomer and Htoam the final height of the foam after surfaces’ polishing.

[0049] The vitrimer foams may very advantageously further exhibit a porosity of 60%-90%, a density of from 50 kg / m3to 400 kg / m3, a glass transition temperature, Tgof from 50°C to 200°C, a compression modulus, Ocompression, of from 2 MPa to 50 MPa and / or a break modulus, Obreak, of from 1 MPa to 100 MPa, both measured according to the ASTM-D1621 standard.

[0050] The vitrimer foams are presenting open pores, mean diameter of each pore being within the range of from 100 to 10000 nm.

[0051] The monomer compounds of formula (I) can be formulated with other monomer compounds different from those of formula (I) to obtain hybrid self-blown foams. The ratio of monomer compounds of formula (I) in the final formulation must exceed 50 wt.% to ensure an efficient self-blowing process. Additionally, the melt viscosities at melting temperatures should be advantageously kept from 50 to 1000 mPa.s.

[0052] The specific vitrimer foams are self-blowing and are exhibiting recyclability properties, due to specific mechanical properties, especially appropriate compression modulus, that can make them used in various fields such as automotive and aerospace, packaging, construction, electronics and appliances, footwear and textiles and medical devices.

[0053] As an example, the self-blowing foams are grinded into powder and compressed at temperatures of about 200°C for 30 min-50 min under 10-30 MPa pressure in a support mold. Translucid homogeneous reprocessed resins can be obtained via compression molding at 200°C.

[0054] The invention also relates to a material comprising a support covered by a layer of self-blowing and recyclable vitrimer foam of the invention. The support may be a polymeric or non polymeric support, based on a metallic or not metallic compound, a ceramic, a part of a device and the like.

[0055] The invention also relates to a use of a monomer compound of benzoxazine containing free aliphatic hydroxyl groups and monoester of formula (I) for producing a self-blowing and recyclable vitrimer foam presenting a backbone issued from said benzoxazine monomer compound of formula (I).

[0056] The invention is described more specifically with some examples including the following figures.

[0057] Figure 1 shows the optimization of the temperature of self-foaming process of Me- DPA-mea monomer.

[0058] Figure 2 shows the optimization of the duration of self-foaming process of Me-DPA- mea monomer.

[0059] Figures 3a and 3ba show the evolution of the complex viscosity and release of selfblowing agent as function as the optimal self-foaming process of monomer compounds (I).

[0060] Figure 4 depicts the three-dimensional tomography images of self-blown polybenzoxazine foams according to some embodiments of the invention.

[0061] Figure 5a shows the evolution of the compressive stress of 4 various self-blowing vitrimer foams.

[0062] Figure 5b shows the thermogravimetric analyses of 4 various vitrimer self-blowing foams.

[0063] Figure 6 shows the recycling of self-blown polybenzoxazine foams by thermocompression.

[0064] Figure 7 shows the digital images of polybenzoxazine vitrimer foams of example 6.

[0065] Experimental section

[0066] 1) Example 1 : Synthesis of monomer compounds (I)

[0067] The synthesis of monomer compound of benzoxazine containing free aliphatic hydroxyl groups and monoester of formula (I) followed a similar two-steps chemical pathway reported in WO2022122882 with minor modification. Phenolic acid precursors, such as -(4-hydroxyphenyl) propionic acid (phloretic acid, PA) and 4,4- bis(4-hydroxyphenyl)valeric acid (diphenolic acid, DPA), were reacted with an excess of alcohol solvents, such as methanol, ethanol, propanol, and butanol, in the presence of acid catalyst (0.5 wt.%), such as para-toluene sulfonic acid (p-TSA), anhydrous chlorhydric acid (HCI), phosphoric acid (H3PO4), methanoic acid (CH3- CO2H), sulfuric acid, tosylic acid, and Lewis acids such as scandium(lll) triflate, via Fischer esterification. After 12-24 h of reaction at the reflux temperature of alcohol solvents under magnetic stirring (200 rpm-500 rpm), the reaction media was cooled to room temperature and concentrated under reduced pressure. Then, the extract was redissolved in an appropriate solvent, such as chloroform and butanone, and purified by three liquid-liquid extractions with 5% sodium bicarbonate (NaHCOs), followed by three liquid-liquid extractions with ultrapure water. The organic layer was dried over magnesium sulfate (MgSC ), evaporated under reduced pressure, dried overnight under reduced pressure (<1 mBar, 50°C) and recovered mostly as fine powder (pure yield > 70%). In a second step, the monoester precursors obtained (1.0 equiv) were reacted solventless with paraformaldehyde (PFA, 2.0 or 4.0 equiv), and an amino-alcohol such as mono-ethanolamine (mea, 1.0 or 2.0 equiv) at 60°C- 80°C for 3h-12h under magnetic or mechanical stirring via a Mannich-like condensation. All monoester-based benzoxazine precursors were solubilized in an appropriate solvent, such as chloroform, and thoroughly dried over MgSCU. After evaporation of the solvent under reduced pressure, the monomer compounds obtained were dried overnight under reduced pressure (<1 mBar, 50°C), and used without any other purification. Monomer compounds were obtained in almost quantitiative mass yield as viscous liquid or solid powder.

[0068] Some examples of monomer compounds are:

[0069] Me-PA-mea : methyl 3-(3-(2-hydroxyethyl)-3,4-dihydro-2Hbenzo[e][1 ,3]oxazin-6- yl)propanoate

[0070] Et-PA-mea : ethyl 3-(3-(2-hydroxyethyl)-3,4-dihydro-2Hbenzo[e][1 ,3]oxazin-6- yl)propanoate

[0071] Pr-PA-mea : Propyl 3-(3-(2-hydroxyethyl)-3,4-dihydro-2Hbenzo[e][1 ,3]oxazin-6- yl)propanoate

[0072] Bu-PA-mea : Butyl 3-(3-(2-hydroxyethyl)-3,4-dihydro-2Hbenzo[e][1 ,3]oxazin-6- yl)propanoate

[0073] Me-DPA-mea: methyl 4,4-bis(3-(2- hydroxyethyl)-3,4-dihydro-2H- benzo[e][1 ,3]oxazin-6-yl)pentanoate.

[0074] Et-DPA-mea: ethyl 4,4-bis(3-(2- hydroxyethyl)-3,4-dihydro-2H-benzo[e][1 ,3]oxazin-6- yl)pentanoate.

[0075] Pr-DPA-mea: propyl 4,4-bis(3-(2- hydroxyethyl)-3,4-dihydro-2H-benzo[e][1 ,3]oxazin- 6-yl)pentanoate.

[0076]

[0077] Bu-DPA-mea: butyl 4,4-bis(3-(2- hydroxyethyl)-3,4-dihydro-2H-benzo[e][1 ,3]oxazin- 6-yl)pentanoate.

[0078] 2) Example 2: Preparation of self-blowing and recyclable vitrimer foams:

[0079] The foaming process, using monomer compounds of Example 1 , was performed in a convection oven using typically 2.5 g of monomer compounds placed into a sealed 15 mL polytetrafluoroethylene sample tub (PTFE, chemically inert and autoclavable). For larger container, a similar ratio between monomer compounds weight and container’s capacity was maintained. The sample is heated from room tempreature to 130°C or directly introduced in the convection oven at 130°C. After complete softening of the monomer compound at 130°C during 10 minutes, the temperature is then increased to 180, 200, or 220°C at a 5°C.min'1rate and maintained for a period of 20 min to maximize the rate of cross-linking reactions.

[0080] The sample is weighted before and after the process to calculate the experimental weight loss with formula (1): with Wi corresponding to the weight of the dried monomer before the foaming process and Wf corresponding to the weight of the sample after the foaming process. Table 1 summarizes the theoretical weight loss for each monomer compounds considering that all monomer compound (1 eq.) has quantitatively reacted to release the alcohol solvent adduct of degenerative transesterification reactions.

[0081] Table 1 Theoretical weight loss considering quantitative degenerative transesterification of monomer compounds.

[0082] Assuming that the monomer compounds are properly dried and only the alcohol solvent is released during the foaming process (and responsible for the weight loss), the extent rate of degenerative transesterification (Y) can be calculated according to equation (2): with Wexperimentai corresponding to the experimental weight loss and Wtheoretical corresponding to the theoretical ones.

[0083] The volumetric expansion of the vitrimer foam is controlled by the release of the selfblowing agent and buble coalescence filling the free-volume of the container. The upper surface of the regular cylinder was polished to obtain parallel surface (Tegramin-25 Stuers®, silicon carbide grinding paper grit 80). As the foam expansion is oriented solely toward the vertical direction, the volumetric expansion can be calculated as follows equation (3): with Hmonomer corresponding to the initial height of the monomer and Hfoam the final height of the foam after surfaces’ polishing.

[0084] 3) Example 3: Optimization of the foaming process of Me-DPA-mea: evolution of the extent rate of degenerative transesterification and volumetric expansion as function of the foaming temperature and the foaming duration.

[0085] The purpose of this example is to determine the optimal temperature and duration of the foaming process to obtain vitrimer foams from a specific monomer compound, with an optimal compromise between the extent rate of degenerative transesterification (Y%) and volumetric expansion (V%).

[0086] Figure 1 shows the optimization of the foaming process of Me-DPA-mea: evolution of the extent rate of degenerative transesterification Y% (-•-) and volumetric expansion V% (-■-) as function of the foaming temperature. As can be seen, the best compromise between V% together with the optimal Y% is for a temperature at 180°C or even 185°C. Temperatures higher than 180°C or 185°C, lower the V% and increase Y% leading to an insufficient volumetric expansion.

[0087] Figure 2 depicts the evolution of the extent rate of degenerative transesterification Y% (-•-) and volumetric expansion V% (-■-) as function of the foaming duration for Me-DPA-mea between 20 min and 60 min. Said figure shows that both Y% and V% remain more or less unchanged. The optimal duration is then 20 min at 185°C. 4) Example 4: Self-foaming of monomer compounds (I): monitoring of selfblowing process, microstructure, and thermo-mechanical properties.

[0088] Based on the optimization study reported in Example 3, the purpose of Example 4 is to depict the optimal self-foaming conditions for some monomer compound (I).

[0089] Figure 3. a and Figure 3.b gathers the evolution of the complex viscosity ( / ]*) and the release of self-blowing agent (Aaicohoi) of some monomer compounds (I) as function of their optimal self-foaming conditions. The temperature program follows the similar steps ( / .e. heating rates, foaming temperature, and time) as established for the optimal conditions. For all monomers, the complex viscosity remains constant during the isothermal step at 130°C suggesting that no cross-linking reactions occurs. Once the temperature is elevated, the increase in the complex viscosity is concomitant with the release of self-blowing mono-alcohol solvent. The release of mono-alcohol solvent adduct of degenerative transesterification measured by thermogravimetric analysis coupled with gaz chromatography (TGA-pGC) provides the direct evidence of the release of the self-blowing agent.

[0090] Table 2 summarizes the extent rate of degenerative transesterification (Y%) and volumetric expansion (V%) as function of the optimal self-foaming conditions for each monomer compounds.

[0091] Table 2 Optimal foaming conditions for monomer compounds

[0092] The microstructure of the self-blown polybenzoxazine foams was analysed by microcomputed X-ray tomography (pCT) in Figure 4. The three-dimensional reconstruction reveals an open-cell morphology with interconnected cell attributed to the fast release of the self-blowing agent across the cross-linked material. The gradual decrease of the porosity (e) from e= 85.9 % for f(Me-DPA-mea) to e= 66.7 % for f(Pr- DPA-mea) is attributed to the higher release of self-blowing agent during the foaming process. The higher porosity determined for f(Bu-DPA-mea) is attributed to the restricted gas diffusion of long-alkyl side-chain blowing agent resulting in the formation of larger pores (e= 74.8 %)

[0093] The compressive profile depicted in Figure 5. a is characteristic of rigid foam with three different regimes: the elastic deformation (initial linear slope at strain deformation ranging from 0 to 1 %), the crushing domain (collapse of cell walls), and finally the densification (drastic increase of the compressive stress). The compressive modulus gradually decreases from oComPression= 39 and 23 MPa with increasing length of the alkyl side-chain (from f(Me-DPA-mea) and f(Bu-DPA-mea)). The thermal properties of the self-blown polybenzoxazine foams were analyzed by thermogravimetric analyses (TGA, Figure 5.b). The thermal degradation of the selfblown polybenzoxazine foams starts at 235°C.

[0094] 5) Example 5: Recycling of Me-DPA-mea self-blowing foams (I)

[0095] As the degenerative TER of monoester occurring during the self-foaming process is not guantitative, two types of ester bonds are present in the network: 1 ) the unreacted monoester and 2) the p-aminoester adduct of degenerative TER. Upon recycling, the remaining p-aminoalcohol moieties may further exchange with these ester groups though degenerative or reversible transesterification.

[0096] The self-blown polybenzoxazine foams were grinded into powder and compressed in a hydraulic press at 190°C for 30 min under 20 MPa pressure in a disk shape mold (h= 1 mm, 0= 20 mm). The foam-to-resin mechanical recycling of the self-blown polybenzoxazine foams is shown in Figure 6. Translucid homogeneous reprocessed resins can be obtained via compression molding at 190°C. The mechanical recycling was extended to four cycles.

[0097] 6) Example 6: Self-foaming process of different monomer compounds (I) Other monomer coumpounds are reported in this Example 6:

[0098] Me-PHBA-mea : methyl 3-(2-hydroxyethyl)-3,4-dihydro-2H-benzo[e][1 ,3]oxazine- 7-carboxylate

[0099] Pe-DPA-mea : pentyl 4,4-bis(3-(2-hydroxyethyl)-3,4-dihydro-2H- benzo[e][1 ,3]oxazin-6-yl)pentanoate iPr-DPA-dga isopropyl 4,4-bis(3-(2-(2-hydroxyethoxy)ethyl)-3,4-dihydro-2H- benzo[e][1 ,3]oxazin-6-yl)pentanoate

[0100]

[0101] The foaming process, using monomer compounds of Example 6, was performed in a convection oven using typically 2.5 g of monomer compounds placed into a sealed 15 mL polytetrafluoroethylene sample tub (PTFE, chemically inert and autoclavable). The sample is heated from room tempreature to 130°C or directly introduced in the convection oven at 130°C. After complete softening of the monomer compound at 130°C during 10 minutes, the temperature is then increased to 180 or 200°C at a 5°C.min'1rate and maintained for a period of 20 min to maximize the rate of crosslinking reactions. The Figure 7 shows the digital images of polybenzoxazine vitrimer foams of example 6, wherein HR means heating ramp

[0102] Table 3 summarizes the extent rate of degenerative transesterification (Y%) and volumetric expansion (V%) as function of the optimal self-foaming conditions for each monomer compounds. Table 3 Optimal foaming conditions for monomer compounds

Claims

CLAIMS1 . A process for preparing self-blowing and recyclable vitrimer foams comprising the steps of polymerizing a monomer compound of benzoxazine containing free aliphatic hydroxyl groups and monoester of formula (I) said steps consisting of a) a conditioning step of the monomer compound (I) at a melting temperature selected within the range of from 100°C to 130°C, and followed by b) a temperature increasing step to reach a foaming temperature within the range of from 170°C to 230°C, both steps a) and b), independently, being carried out for 10 min to 1 h, for obtaining a self-blowing and recyclable vitrimer foam originating from said benzoxazine monomers compounds, wherein the monomer compound of benzoxazine containing free aliphatic hydroxyl groups and a monoester of formula (I) iswherein, in formula (I)R is selected from the group consisting of a linear or branched C1-C12 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, a cyclo(C3-Ce alkyl) group, a heteocyclo(C3-Ce alkyl), a linear or branched Ci-Ce alkyl or C2-C6 alkenyl substituted or unsubstituted phenyl group and a (CH2)n3-phenyl group, wherein n3 is an integer from 1 to 10;R’ is selected from the group consisting of at least one of -CH, a C-(CH2)n3-CH3 group, a C-(CH2)n3-CH-(CH3)2 group, a C-(CH2)n3-(CHZ)n4-(CH3)2 group, a C-(CH2)n3- (CHZ)n4-(CH2)n3-CH3gTOUp, a C-(CHZ)n4-(CH2)n3-CH3group, a C-(CHZ)n4-[(CH2)n3- CHS]2 group, a C-substituted or unsubstituted C2-C6 linear or branched alkenyl group, a linear or branched Ci-Ce alkyl substituted or unsubstituted phenyl or phenyl including at least one hetero atom selected from N, O and S, a C-(CH2)n3-Ci-Ce linear or branched alkyl substituted or unsubstituted phenyl or phenyl including at least one heteroatom selected from N, O and S, a C-(CH2)n3-Ci-Ce linear or branched alkyl substituted or unsubstituted phenyl or phenyl including at least one heteroatom selected from N, O and S-(CH2)n3-CH3, a C-(CH2)n3-Ci-Ce linear or branched alkyl substituted or unsubstituted phenyl or phenyl including at least one heteroatom selected from N, O and S-(CH2)n3-CH-(CH3)2, a C-(CH2)n3-Ci-Ce linear or branched alkyl substituted or unsubstituted phenyl or phenyl including at least one heteroatom selected from N, O and S-(CH2)n3-(CHZ)n4-(CH3)2 group, a C-(CH2)n3-Ci- Ce linear or branched alkyl substituted or unsubstituted phenyl or phenyl including at least one heteroatom selected from N, O and S-(CHZ)n4-(CH2)n3-CH3 group and a C- (CH2)n3-(CHZ)n4-Ci-C6 linear or branched alkyl substituted or unsubstituted phenyl or phenyl including at least one heteroatom selected from N, O and S-(CH2)n3-CH3 group, wherein n3 and n4, independently, are an integer from 1 to 10 and Z is selected from the group consisting in a linear or branched Ci-Ce alkyl or alkoxy group, linear or branched C2-C6 alkenyl or alkylenoxy group and a linear or branched Ci-Ce alkyl or C2-C6 alkenyl substituted or unsubstituted phenyl group, and at least one O atom is present or not between two adjacent C, or R’ is omitted.R* is selected from the group consisting of a linear or branched C1-C20, preferably Ci-Ce, alkyl or alkoxy group, a cyclo(C3-Ce alkyl) group, a heteocyclo(C3-Ce alkyl) group, wherein the hetero atom is selected from N, S, and O, linear or branched C2- Ce alkenyl or alkylenoxy group, substituted or unsubstituted linear or branched C2-C6 alkynyl group, a linear or branched Ci-Ce alkyl or C2-C6 alkenyl substituted or unsubstituted phenyl group, a (CH2)n3-phenyl group and -(CH2)n3-O-(CH2)n4, wherein n3 and n4, independently, are an integer from 1 to 10;R** is the same as R* and further includes a member selected from a O-, N- or S- (CH2)n3-CH-(CH3)2 group, a O-, N- or S-(CH2)n3-(CHZ)n4-(CH3)2 group, a O-, N- or S-(CH2)n3-(CHZ)n4-(CH2)n3-CH3 gCOUp, a O-, N- or S-(CHZ)n4-(CH2)n3-CH3 group, a O-, N- or S-(CHZ)n4-[(CH2)n3-CH3]2 group and a O-substituted or unsubstituted C2-C6 linear or branched alkynyl group, Z being as defined for R’, a -(CH2)n3-C=N group, a polycyclic aromatic or heteroaromatic hydrocarbon, such as naphthalene, anthracene, fluorene, phenanthrene, optionally substituted by a linear or branched Ci-Ce alkyl or alkoxy group, a cyclo(C3-Ce alkyl) group, a heterocyclo(C3-C6alkyl) group, a linear or branched C2-C6 alkenyl or alkylenoxy group, or by a substituted or unsubstituted linear or branched C2-C6 alkynyl group, wherein n3 and n4, independently, are an integer from 1 to 10;R*** is selected from the group consisting in H, OH and a O-linear or branched Ci-Ce alkyl group, and further includes a linear or branched C1-C15 alkyl group or a C2-C15 alkenyl group orx value is of from 0 to 1 and y value is 1 -x, preferably of from 0,1 to 1 , more preferentially from 0,5 to 1 ; and wherein x and y are defined aswhereinnatt^Lsand naminoaicohoi being the number of aminoalcohol per molecules of monomer compound , Uamines represent the number of amines (excepting the number of aminoalcohol) per molecule of monomer compound and ’^m^esis the total number of amino groups per molecule of monomer compound;2. The process according to claim 1 , wherein in the monomer compound of formula (I):R is 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, an unsubstituted linear or branched C2-C4 alkynyl group, an unsubstituted phenyl group and a (CH2)n3- phenyl group, wherein n3 is an integer from 1 to 6.R’ is selected from the group consisting of at least one of -CH, a C-(CH2)n3-CH3 group, a C-(CH2)n3-CH-(CH3)2 group, a C-(CH2)n3-(CHZ)n4-(CH3)2 group, C-(CH2)n3- (CHZ)n4-(CH2)n3-CH3group, C-(CHZ)n4-(CH2)n3-CH3group, a C-(CHZ)n4-[(CH2)n3- CHS]2 group, a C-substituted or unsubstituted C2-C4 linear or branched alkenyl group, an unsubstituted phenyl or phenyl including at least one heteroatom selected from N, O and S, a C-(CH2)n3-unsubstituted phenyl or phenyl including at least one heteroatom selected from N, O and S, a C-(CH2)n3-unsubstituted phenyl or phenyl including at least one heteroatom selected from N, O and S-(CH2)n3-CH3, a C- (CH2)n3-unsubstituted phenyl or phenyl including at least one heteroatom selected from N, O and S-(CH2)n3-CH-(CH3)2, a C-(CH2)n3-unsubstituted phenyl or phenyl including at least one heteroatom selected from N, O and S-(CH2)n3-(CHZ)n4-(CH3)2 group, a C-(CH2)n3-unsubstituted phenyl or phenyl including at least one heteroatom selected from N, O and S-(CHZ)n4-(CH2)n3-CH3 group and a C-(CH2)n3-(CHZ)n4- unsubstituted phenyl or phenyl including at least one heteroatom selected from N, O and S-(CH2)n3-CH3 group, wherein n3 and n4, independently, are an integer from 1 to 6 and Z is selected from the group consisting in a linear or branched C1-C4 alkyl or alkoxy group, linear or branched C2-C4 alkenyl or alkylenoxy group and an unsubstituted phenyl group, and at least one O atom is present or not between two adjacent C.R* is selected from the group consisting of a linear or branched Ci-Ce, preferably C1- Ce, alkyl or alkoxy group, a linear or branched C2-C4 alkenyl or alkylenoxy group, an unsubstituted linear or branched C2-C4 alkynyl group, an unsubstituted phenyl group, a (CH2)n3-phenyl group and -(CH2)n3-O-(CH2)n4, wherein n3 and n4, independently, are an integer from 1 to 6;R** is the same as R* and may further include a member selected from O-, N- or S- (CH2)n3-CH-(CH3)2 group, a O-, N- or S-(CH2)n3-(CHZ)n4-(CH3)2 group, a O-, N- or S-(CH2)n3-(CHZ)n4-(CH2)n3-CH3 gCOUp, a O-, N- or S-(CHZ)n4-(CH2)n3-CH3 group, a O-, N- or S-(CHZ)n4-[(CH2)n3-CH3]2 group and a O-substituted or unsubstituted C2-C4 linear or branched alkynyl group, Z being as defined above, a -(CH2)n3-C=N group, a cyclo(C3-C4 alkyl) group, a heteocyclo(C3-C4 alkyl) group, a polycyclic aromatic or heteroaromatic hydrocarbon, wherein the hetero atom is selected from N, S, and O, such as naphthalene, anthracene, fluorene, furane, which may optionally be substituted by a linear or branched C1-C4 alkyl or alkoxy group, a linear or branched C2-C4 alkenyl or alkylenoxy group, or by a substituted or unsubstituted linear or branched C2-C4 alkynyl group, wherein n3 and n4, independently, are an integer from 1 to 6;R*** is selected from the group consisting in H, OH and a O-linear or branched C1-C4 alkyl group, and may further include a linear or branched C1-C10 alkyl group or C2- C10 alkenyl group or3. The process according to claim 1 or 2, wherein in formula (I)R is selected from the group consisting of groups -CH3, -(CH2)n3-CH3, -(CH2)n3-CH- [(CH2)n3-CH3]2, -C(CH3)3, -(CH2)n3-(C6H5), -(CH2)n3-CH=CH2 and -(CH2)n3-C=CH, wherein n3 is an integer from 1 to 5;R’ is selected form the group consisting of groups -CH, -C-(CH2)2-C(CH3), -C- CH(CH2CH3), -C(CH2CH2CH3), -C-CH2(CH2)3CH3, -C-CH2(CH2)4CH3, -C(C6H5), - C(CH3)CH2, C(CH3)CH2CH2 and -C(C6H5)CH2-CH3;R* is selected from the group consisting of groups -CH3, -(CH2)n3-CH3, -(CH2)n3-CH- [(CH2)n4-CH3]2, -C(CH3)3, (CH2)n3-(C6H5), -(CH2)n3-CH=CH2, -(CH2)n3-C CH , -(CH2)n3-O-(CH2)n4 wherein n3 and n4 independently are integer from 1 to 4, phenyl, and -(CH2)3-phenyl.R** is selected from the group consisting of groups CH3, -(CH2)n3-CH3, -(CH2)n3-CH- [(CH2)n4-CH3]2, -C(CH3)3, (CH2)n3-(C6H5), -(CH2)n3-CH = CH2, -(CH2)n3-C=CH , O- (CH2)n3-C=CH, O-(CH2)n3-C=N, (CH2)n3-C=N, and -(CH2)n3-substituted or unsubstituted furan, phenyl, and wherein n3 and n4 independently are integer from 1 to 4;R*** is selected from the group consisting in H, OH and O-linear or branched C1-C3 alkyl group, and further includes linear or branched Ci-Ce alkyl group or C2-C6 alkenyl group or4. The process of any of claims 1 to 3, wherein in step a) the melting temperature is selected within the range of from 100°C to 120°C.

5. The process of any of claims 1 to 4, wherein in step b), the foaming temperature is of from 180°C to 220°C, more preferably of from 185°C to 220°C.

6. The process of any of claims 1 to 5, wherein step b) and / or step a) are carried out at reduced pressure of from 0,09 to 0.1 mBar.

7. The process of any of claims 1 to 6, wherein the increasing of the temperature between step a) and step b) is carried out at a heating ramp between 2°C / min and 20°C / min.

8. Self-blowing and recyclable vitrimer foams presenting a backbone issued from benzoxazine monomer compounds as defined in any of claims 1 to 4,exhibiting at least one of the following characteristics selected from the group consisting of: a weight loss (W%), defined by the ratio expressed as a percentage between the weight of a dried vitrimer foam to the weight of a monomer compound used for the preparation of said vitrimer foam according to a process of the invention, in the range of from 3% to 30%; a volume expansion (V%), defined by the ratio expressed in percentage between the height of a vitrimer foam to the height of a monomer compound used for the preparation of said vitrimer foam according to a process of the invention, in the range of 5% to 1000%; an extent of degenerative transesterification (Y%), defined as the percentage of the experimental weight loss to the theoretical weight loss corresponding to the maximal weight loss when the degenerative transesterification (Y%), is 100%, of from 15 to 95%.

9. Self-blowing and recyclable vitrimer foams according to claim 9, further exhibiting a density in the range of from 100 to 400 kg / m3; a porosity of 60%- 90%, a glass transition temperature, Tgof from 50°C to 150°C, a compression modulus, Ocompression, of from 2 MPa to 50 MPa and / or a break modulus, Obreak, of from 1 MPa to 100 MPa, both measured according to the ASTM-D1621 standard.

10. A material comprising a support covered by a layer of self-blowing and recyclable vitrimer foam as defined in claim 8 or 9 or as obtained by the process of any of claims 1-7.

11. Use of a monomer compound of benzoxazine containing free aliphatic hydroxyl groups and monoester of formula (I) wherein the monomer compound of benzoxazine containing free aliphatic hydroxyl groups and a monoester of formula (I) iswherein, in formula (I)R is selected from the group consisting of a linear or branched C1-C12 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, a cyclo(C3-Ce alkyl) group, a heteocyclo(C3-Ce alkyl), a linear or branched Ci-Ce alkyl or C2-C6 alkenyl substituted or unsubstituted phenyl group and a (CH2)n3-phenyl group, wherein n3 is an integer from 1 to 10;R’ is selected from the group consisting of at least one of -CH, a C-(CH2)n3-CH3 group, a C-(CH2)n3-CH-(CH3)2 group, a C-(CH2)n3-(CHZ)n4-(CH3)2 group, a C-(CH2)n3- (CHZ)n4-(CH2)n3-CH3gTOUp, a C-(CHZ)n4-(CH2)n3-CH3group, a C-(CHZ)n4-[(CH2)n3- CHS]2 group, a C-substituted or unsubstituted C2-C6 linear or branched alkenyl group, a linear or branched Ci-Ce alkyl substituted or unsubstituted phenyl or phenyl including at least one hetero atom selected from N, O and S, a C-(CH2)n3-Ci-Ce linear or branched alkyl substituted or unsubstituted phenyl or phenyl including at least one heteroatom selected from N, O and S, a C-(CH2)n3-Ci-Ce linear or branched alkyl substituted or unsubstituted phenyl or phenyl including at least one heteroatom selected from N, O and S-(CH2)n3-CH3, a C-(CH2)n3-Ci-Ce linear or branched alkyl substituted or unsubstituted phenyl or phenyl including at least one heteroatom selected from N, O and S-(CH2)n3-CH-(CH3)2, a C-(CH2)n3-Ci-Ce linear or branched alkyl substituted or unsubstituted phenyl or phenyl including at least one heteroatom selected from N, O and S-(CH2)n3-(CHZ)n4-(CH3)2 group, a C-(CH2)n3-Ci- Ce linear or branched alkyl substituted or unsubstituted phenyl or phenyl including at least one heteroatom selected from N, O and S-(CHZ)n4-(CH2)n3-CH3 group and a C- (CH2)n3-(CHZ)n4-Ci-C6 linear or branched alkyl substituted or unsubstituted phenyl or phenyl including at least one heteroatom selected from N, O and S-(CH2)n3-CH3group, wherein n3 and n4, independently, are an integer from 1 to 10 and Z is selected from the group consisting in a linear or branched Ci-Ce alkyl or alkoxy group, linear or branched C2-C6 alkenyl or alkylenoxy group and a linear or branched Ci-Ce alkyl or C2-C6 alkenyl substituted or unsubstituted phenyl group, and at least one O atom is present or not between two adjacent C, or R’ is omitted.R* is selected from the group consisting of a linear or branched C1-C20, preferably Ci-Ce, alkyl or alkoxy group, a cyclo(C3-Ce alkyl) group, a heteocyclo(C3-Ce alkyl) group, wherein the hetero atom is selected from N, S, and O, linear or branched C2- Ce alkenyl or alkylenoxy group, substituted or unsubstituted linear or branched C2-C6 alkynyl group, a linear or branched Ci-Ce alkyl or C2-C6 alkenyl substituted or unsubstituted phenyl group, a (CH2)n3-phenyl group and -(CH2)n3-O-(CH2)n4, wherein n3 and n4, independently, are an integer from 1 to 10;R** is the same as R* and further includes a member selected from a O-, N- or S- (CH2)n3-CH-(CH3)2 group, a O-, N- or S-(CH2)n3-(CHZ)n4-(CH3)2 group, a O-, N- or S- (CH2)n3-(CHZ)n4-(CH2)n3-CH3 group, a O-, N- or S-(CHZ)n4-(CH2)n3-CH3 group, a O-, N- or S-(CHZ)n4-[(CH2)n3-CH3]2 group and a O-substituted or unsubstituted C2-C6 linear or branched alkynyl group, Z being as defined for R’, a -(CH2)n3-C=N group, a polycyclic aromatic or heteroaromatic hydrocarbon, such as naphthalene, anthracene, fluorene, phenanthrene, optionally substituted by a linear or branched Ci-Ce alkyl or alkoxy group, a cyclo(C3-Ce alkyl) group, a heterocyclo(C3-C6alkyl) group, a linear or branched C2-C6 alkenyl or alkylenoxy group, or by a substituted or unsubstituted linear or branched C2-C6 alkynyl group, wherein n3 and n4, independently, are an integer from 1 to 10;R*** is selected from the group consisting in H, OH and a O-linear or branched Ci-Ce alkyl group, and further includes a linear or branched C1-C15 alkyl group or a C2-C15 alkenyl group orx value is of from 0 to 1 and y value is 1 -x, preferably of from 0,1 to 1 , more preferentially from 0,5 to 1 ; and wherein x and y are defined aswhereinnmmes, and naminoaicohoi being the number of aminoalcohol per molecules of monomer compound , Uamines represent the number of amines (excepting the number of aminoalcohol) per molecule of monomer .^£ £tl^ compound and ’ nesis the total number of amino groups per molecule of monomer compound, for producing a self-blowing and recyclable vitrimer foam presenting a backbone issued from said benzoxazine monomer compound of formula (I).

12. Use according to claim 11 wherein in the monomer compound of formula (I):R is 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, an unsubstituted linear or branched C2-C4 alkynyl group, an unsubstituted phenyl group and a (CH2)n3- phenyl group, wherein n3 is an integer from 1 to 6.R’ is selected from the group consisting of at least one of -CH, a C-(CH2)n3-CH3 group, a C-(CH2)n3-CH-(CH3)2 group, a C-(CH2)n3-(CHZ)n4-(CH3)2 group, C-(CH2)n3- (CHZ)n4-(CH2)n3-CH3group, C-(CHZ)n4-(CH2)n3-CH3group, a C-(CHZ)n4-[(CH2)n3- CHS]2 group, a C-substituted or unsubstituted C2-C4 linear or branched alkenyl group, an unsubstituted phenyl or phenyl including at least one heteroatom selected from N, O and S, a C-(CH2)n3-unsubstituted phenyl or phenyl including at least one heteroatom selected from N, O and S, a C-(CH2)n3-unsubstituted phenyl or phenyl including at least one heteroatom selected from N, O and S-(CH2)n3-CH3, a C- (CH2)n3-unsubstituted phenyl or phenyl including at least one heteroatom selected from N, O and S-(CH2)n3-CH-(CH3)2, a C-(CH2)n3-unsubstituted phenyl or phenyl including at least one heteroatom selected from N, O and S-(CH2)n3-(CHZ)n4-(CH3)2group, a C-(CH2)n3-unsubstituted phenyl or phenyl including at least one heteroatom selected from N, O and S-(CHZ)n4-(CH2)n3-CH3 group and a C-(CH2)n3-(CHZ)n4- unsubstituted phenyl or phenyl including at least one heteroatom selected from N, O and S-(CH2)n3-CH3 group, wherein n3 and n4, independently, are an integer from 1 to 6 and Z is selected from the group consisting in a linear or branched C1-C4 alkyl or alkoxy group, linear or branched C2-C4 alkenyl or alkylenoxy group and an unsubstituted phenyl group, and at least one O atom is present or not between two adjacent C.R* is selected from the group consisting of a linear or branched Ci-Ce, preferably C1- Ce, alkyl or alkoxy group, a linear or branched C2-C4 alkenyl or alkylenoxy group, an unsubstituted linear or branched C2-C4 alkynyl group, an unsubstituted phenyl group, a (CH2)n3-phenyl group and -(CH2)n3-O-(CH2)n4, wherein n3 and n4, independently, are an integer from 1 to 6;R** is the same as R* and may further include a member selected from O-, N- or S- (CH2)n3-CH-(CHs)2 group, a O-, N- or S-(CH2)n3-(CHZ)n4-(CH3)2 group, a O-, N- or S- (CH2)n3-(CHZ)n4-(CH2)n3-CH3 group, a O-, N- or S-(CHZ)n4-(CH2)n3-CH3 group, a O-, N- or S-(CHZ)n4-[(CH2)n3-CH3]2 group and a O-substituted or unsubstituted C2-C4 linear or branched alkynyl group, Z being as defined above, a -(CH2)n3-C=N group, a cyclo(C3-C4 alkyl) group, a heteocyclo(C3-C4 alkyl) group, a polycyclic aromatic or heteroaromatic hydrocarbon, wherein the hetero atom is selected from N, S, and O, such as naphthalene, anthracene, fluorene, furane, which may optionally be substituted by a linear or branched C1-C4 alkyl or alkoxy group, a linear or branched C2-C4 alkenyl or alkylenoxy group, or by a substituted or unsubstituted linear or branched C2-C4 alkynyl group, wherein n3 and n4, independently, are an integer from 1 to 6;R*** is selected from the group consisting in H, OH and a O-linear or branched C1-C4 alkyl group, and may further include a linear or branched C1-C10 alkyl group or C2- C10 alkenyl group or13. The process according to claim 11 or 22, wherein in formula (I)R is selected from the group consisting of groups -CH3, -(CH2)n3-CH3, -(CH2)n3-CH- [(CH2)n3-CH3]2, -C(CH3)3, -(CH2)n3-(C6H5), -(CH2)n3-CH=CH2 and -(CH2)n3-C=CH, wherein n3 is an integer from 1 to 5;R’ is selected form the group consisting of groups -CH, -C-(CH2)2-C(CH3), -C- CH(CH2CH3), -C(CH2CH2CH3), -C-CH2(CH2)3CH3, -C-CH2(CH2)4CH3, -C(C6H5), - C(CH3)CH2, C(CH3)CH2CH2 and -C(C6H5)CH2-CH3;R* is selected from the group consisting of groups -CH3, -(CH2)n3-CH3, -(CH2)n3-CH- [(CH2)n4-CH3]2, -C(CH3)3, (CH2)n3-(C6H5), -(CH2)n3-CH=CH2, -(CH2)n3-C CH, - (CH2)n3-O-(CH2)n4 wherein n3 and n4 independently are integer from 1 to 4, phenyl, and -(CH2)3-phenyl.R** is selected from the group consisting of groups CH3, -(CH2)n3-CH3, -(CH2)n3-CH- [(CH2)n4-CH3]2, -C(CH3)3, (CH2)n3-(C6H5), -(CH2)n3-CH = CH2, -(CH2)n3-C=CH , O- (CH2)n3-C=CH, O-(CH2)n3-C=N, (CH2)n3-C=N, and -(CH2)n3-substituted or unsubstituted furan, phenyl, and wherein n3 and n4 independently are integer from 1 to 4;R*** is selected from the group consisting in H, OH and O-linear or branched C1-C3 alkyl group, and further includes linear or branched Ci-Ce alkyl group or C2-C6 alkenyl group or

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