Method for preparing a polyurethane foam

Abstract

The invention relates to a method for preparing a polyurethane foam (I), comprising a) reacting, at a temperature ranging from 60 to 150°C, at least one poly oxamic acid (III) with at least one polyol (II) in the presence of a hypervalent iodine oxidant; b) foaming the polyurethane (I) obtained in a) in the presence of carbon dioxide. The invention also relates to a polyurethane foam (I) obtained according to the method of the invention.

Description

Description Title of the invention: Process for preparing a polyurethane foam Technical Field

[0001] The invention relates to a process for preparing a polyurethane foam by (i) reacting at least one polyoxamic acid with at least one polyol, in the presence of an oxidant, followed by (ii) foaming the polyurethane obtained in step (i) using carbon dioxide. The invention also relates to a polyurethane foam obtained using the process according to the invention. Prior art

[0002] Polymer foams combine the inherent lightness of porous materials with low thermal and electrical conductivity, as well as good filtration and energy absorption capabilities. The polymeric nature of these materials also gives them good mechanical strength. Thanks to their specific properties, polymer foams are used in a variety of fields, such as packaging, electronics, transportation, furniture, textiles, aerospace, and construction materials, for example.

[0003] Typically, polymer foams are prepared by the nucleation of gas bubbles in a polymer or monomer mixture, followed by a phase change stabilizing the resulting porous structure (vitrification in the case of a thermoplastic polymer, gelation in the case of a thermosetting polymer). The gas bubbles can be generated by a foaming agent, which can be either "physical" (foaming agent released during a phase change) or "chemical" (foaming agent released following a chemical reaction, and in particular thermal decomposition).

[0004] In recent years, research in this field has focused in particular on the development of self-foaming systems, which meet the following criteria: (i) the foaming agent is present in the molecular structure of the polymer precursors, (ii) the foaming agent is released as a gas, ideally harmless to the environment, and (iii) no residue remains in the final polymer foam. Self-foaming processes have the advantage that the foaming step is carried out without requiring additional handling, since it is carried out concomitantly with the polymerization step through the production / / 7 s / Zz / of a foaming agent and does not generate a by-product requiring a subsequent purification step.

[0005] Various self-foaming processes have been reported, as detailed in particular in the document Monie et al., Materials Science & Engineering R, 145, 2021, 100628. Two main routes have been studied: self-foaming polymers by thermolysis for which the polymers or their precursors contain a thermolabile group allowing the generation of the foaming agent, and self-foaming polymers obtained by condensation and polycondensation for which the foaming agent is generated during the synthesis of the polymer by polycondensation.

[0006] To date, polyurethane foams are the most widely produced polymer foams in the world, notably due to their well-known and controlled preparation process, and access to a wide range of polyurethanes with varied physicochemical properties. Polyurethanes are usually prepared by the polyaddition of polyols to polyisocyanates, according to the reaction first described by Bayer.

[0007] Typically, self-foaming processes for preparing polyurethane foam use water. Partial hydrolysis of polyisocyanates during the polymerization reaction results in the formation of unstable carbamic acids, which spontaneously decompose into amine and carbon dioxide. The generated amine reacts with the isocyanate to produce urea, and the in situ generated carbon dioxide acts as a foaming agent.

[0008] The disadvantage of these processes is that (poly)isocyanates are toxic and environmentally harmful compounds, and their synthesis is made from phosgene, which is a highly toxic gas. It is therefore necessary to find alternative processes for preparing polyurethane foams, which do not require the storage and handling of (poly)isocyanates or phosgene, in order to limit the risks of environmental pollution and the risks of toxicity for operators.

[0009] Carbon dioxide is a foaming agent that has the advantage of not being highly toxic or highly harmful to the environment, of not leaving any by-products in the foam, and of making it possible to obtain polyurethane foams with physicochemical properties that meet consumer demands. Therefore, it would be desirable to have a self-foaming system capable of releasing carbon dioxide in situ to carry out the foaming of polyurethanes.

[0010] The Applicant therefore sought a self-foaming process for preparing polyurethane foams that is not only satisfactory in terms of conversion rate and physicochemical properties of the foams obtained, but also less toxic and less harmful to the environment than the process commonly used with (poly)isocyanates and polyols in the presence of water. More specifically, the Applicant sought a new route for synthesizing polyurethanes, a reagent of which makes it possible to generate in situ the polyisocyanate and carbon dioxide as a foaming agent.

[0011] Among the precursors of polyisocyanates, the Applicant was interested in polyoxamic acids. Indeed, oxamic acids are known to be stable and easily accessible by the addition of an amine to an oxalic acid derivative. Then, the oxidative decarboxylation of oxamic acid to isocyanate can be carried out either in the presence of a metal catalyst (Minisci et al., J.Chem. Soc., Chem. Commun, 1994, 679, Minisci et al., J. Org. Chem, 1995, 5430-5433), or in the presence of an oxidant, a photocatalyst and a visible light source (Goroba Pawar et al., Chem. Commun. 2018, 54, 9337-9340), or by electrochemical decarboxylation of oxamic acid (Ogbu et al., Chem. Commun. 2020, 56, 12226-12229). Although these processes allow obtaining urethanes from mono oxamic acids with good yields, the Polyurethane synthesis by these processes is limited due to the lack of solubility of polyoxamic acids, and by the heterogeneity and viscosity of the reaction mixture.

[0012] There is therefore a need for a process for preparing polyurethane foams that is reproducible, simple to implement, and provides access to a wide range of polyurethane foams. Advantageously, the process does not involve the handling of highly toxic and / or environmentally harmful reagents, such as (poly)isocyanates or phosgene. Advantageously, the reaction generates few by-products, which can be easily removed under reduced pressure and / or by heating. Thus, the process according to the invention advantageously makes it possible to easily obtain polyurethane foams. Advantageously, the process is self-foaming. Statement of the invention

[0013] The Applicant discovered that it was possible to prepare polyurethane foams by the thermal decomposition of polyoxamic acids in the presence of an oxidant, then generating in situ carbon dioxide and a polyisocyanate, this polyisocyanate being capable of reacting with a polyol to produce a polyurethane whose foaming is achieved thanks to the carbon dioxide produced.

[0014] More specifically, the process for a polyurethane foam according to the invention comprises the following steps: a) the reaction, in the presence of an oxidant and at a temperature ranging from 60 to 150°C, of ​​at least one polyoxamic acid of formula (II): ol of formula (III): in which - L1 represents a saturated, linear or branched, cyclic or acyclic hydrocarbon group in which one or more CH2s have optionally been replaced by O and / or S; or an unsaturated, linear or branched hydrocarbon group comprising at least one double bond and / or at least one aromatic ring optionally substituted by one or more alkyl and / or alkoxy groups; or a saturated, linear or branched, cyclic or acyclic hydrocarbon group comprising one or more COOH or polyethylene glycol substituents; or a fatty acid triester in which one or more CH2s have optionally been replaced by O and / or S, - L2 represents a saturated, linear or branched, cyclic or acyclic hydrocarbon group, in which one or more CH2s have optionally been replaced by O; or an unsaturated, linear or branched hydrocarbon group, in which one or more CH2s have optionally been replaced by O and comprising at least one aromatic ring optionally substituted by one or more alkyl and / or alkoxy groups or at least one aromatic heterocycle; or a fatty acid triester; or a di, tri or tetra polyester of polyalkylene glycol, - x represents an integer greater than or equal to 2, and - y represents an integer greater than or equal to 2, - it being understood that at least one of x or y is greater than or equal to 3, and b) foaming the polyurethane (I) obtained in step a) in the presence of carbon dioxide.

[0015] In step a), carbon dioxide and at least one polyisocyanate are generated in situ.

[0016] The oxidant used in step a) is advantageously a hypervalent iodinated oxidant.

[0017] The method according to the invention has the advantage of not using a highly toxic and / or environmentally harmful reagent since the polyisocyanate is generated in situ and is not isolated, and does not require the use of phosgene.

[0018] The process according to the invention has the advantage of being self-foaming.

[0019] The process according to the invention also has the advantage of generating few by-products which are easy to remove from the polyurethane foam produced.

[0020] The process according to the invention has the advantage of providing access to a wide range of polyurethane foams, with a very varied chemical structure and therefore varied physicochemical properties. Indeed, polyoxamic acids are prepared from polyamines and oxalic acid derivatives. Their synthesis is easy, and provides access to a wide variety of polyoxamic acids thanks to the wide choice of accessible polyamines.

[0021] The method according to the invention has the advantage of being reproducible and easy to implement since the operating conditions are simple.

[0022] The method according to the invention further has one or other of the following characteristics, or a combination thereof: - the carbon dioxide used for foaming in step b) is entirely generated in step a); - steps a) and b) are carried out concomitantly; - L1 is chosen from the following groups: - (CH2) m (Ll-1), - (CH2)m-CH(CH2)m'-(CH2)m" (Ll-1'), with : - RI, RI', RI", R2, R2', R3, R3', R3", R4, R4', R5, R5', R6 and R6', identical or different and representing, independently of one another, H, (CH2)i, CH3, CH3-(CH2)i, CH3O, CH3-(CH2)iO, CH3S, CH3-(CH2)iS, (CH2)iS, (CH2)iCH(CH3)S or CH3-(CH2)iCH(CH3)S, - R2 and R3 may together represent a group CH(R7a)-CH(R7b)-CH(R7c)-CH(R7d) with R7a, R7b, R7c and R7d being identical or different and independently representing H, (CH2)j, CH3, CH3-(CH2)i, CH3O or CH3-(CH2)iO, - it being understood that at least two groups among RI, RI", R2, R3, R3", R4, R5 and R6 and at least two groups among RI', R2', R3', R4', R5' and R6' represent (CH2)i, - R8, R9, R10, R11 and R12, identical or different and representing, independently of one another, H, (CH2)i, CH3, CH3-(CH2)i, O(CH2)i, CH3O or CH3-(CH2)iO, - R11 and R12 may together represent a group O-CH(R7a)-CH(R7b)-CH(R7c)-(CH(R7d))j, it being understood that at least two groups among R7a, R7b, R7c, R7d, R8, R9, R10, R11 and R12 represent (CH2)i or O(CH2)i, - R13, R14, R15, R16, R13', R14', R15' and R16', identical or different and representing, independently of one another, H, CH3(CH2) k or CH3(CH2) k O, - R17 representing H or CH3(CH2) k , - R18 and R18' representing independently of each other H, CH3(CH2) k , CH2[OCH2CH2] m OH, or CH2[OCH2CHCH3] m NHCOCOOH, - A representing a hydrocarbon chain, linear or branched, comprising from 12 to 30 carbon atoms, and of which one or more CH2 have been replaced by S, - i representing an integer ranging from 0 to 20, - j representing 0 or 1, - k representing an integer ranging from 0 to 6, - m, m' and m" being identical or different and representing independently of each other an integer ranging from 1 to 500, and - p representing an integer ranging from 1 to 6; - the at least one polyoxamic acid is such that x is equal to 2 or 3; - the at least one polyoxamic acid is such that L1 is chosen from: - (CH2) m (Ll-1), - (CH2) m -CH(CH2) m -(CH2) m „ (Ll-1'), ; - at least one polyoxamic acid is such that L1 is chosen from: (CH2) (Ll- - the at least one polyol is such that L2 is chosen from the following groups: - (CH2) t (L2-1), with : - R20, R21, R22, R23, R24 and R25 being identical or different and representing independently of one another H, (CH2) S , CH3 or CH3-(CH2)s, - R21 and R22 may together represent a group CH(R22a)-CH(R22b)- CH(R22c)-CH(R22d) with R22a, R22b, R22c and R22d identical or different and representing independently of each other H, (CH2) S , CH3 or CH3-(CH2) S , - it being understood that at least two groups among R20, R21, R22, R22a, R22b, R22c and R22d, R23, R24 and R25 represent (CH2) S , - R26, R27, R28, R29, R30 and R31 being identical or different and representing independently of one another H, (CH2) S , CH3, CH3-(CH2) S , O(CH2) S , CH3O OR CH3-(CH2) S O, it being understood that at least two groups among R26, R27, R28, R29, R30 and R31 represent (CH2) S or O(CH2) S , - R32, R33, R34, R36, R36', R45, R47, R48 and R49 representing independently of each other H, CH3 or CH3(CH2) r , - R35 representing CH3, CH3(CH2) r or HO(CH2) r , - R37, R38, R39, R40, R41, R42, R43 and R44 being identical or different and representing independently of one another H, (CH2) S , CH3, CH3-(CH2) S , O(CH2) S , CH3O OR CH3-(CH2) S O, - R46 representing (CH2) r , benzylene or cyclohexylene, - B representing a hydrocarbon chain, linear or branched, comprising from 12 to 30 carbon atoms, and comprising at least one double bond, - s representing an integer ranging from 1 to 18, - r representing an integer ranging from 1 to 6, - 1 representing an integer ranging from 1 to 500, - u representing 0, 1, 2 or 3, - w representing 0 or 1, - z representing an integer ranging from 0 to 4; - the at least one polyol is such that y is equal to 3 or 4; - the at least one polyol is such that L2 is chosen from: - (CH2) t (L2-1), (L2-6), - at least one polyol is such that L2 represents: - the oxidant is a hypervalent iodinated compound, preferably chosen from bis(trifluoroacetoxy)iodobenzene, bis(acetoxy)iodobenzene, poly[4-(diacetoxyiodo)styrene], hydroxybenziodoxole, and acetoxybenziodoxole; - the method comprises a step c), subsequent to step b), of purification of the polyurethane foam (I), preferably by heating and / or under reduced pressure; - the reaction between the at least one polyoxamic acid and the at least one polyol is carried out in the presence of a non-ionic surfactant (IV); - the surfactant (IV) is chosen from: ( ), with : - R50 representing OH, CH3-(CH2)hO or O(CO)(CH2)hCH3with h representing an integer ranging from 0 to 3, - a, b, c, d, e, f and g being identical or different and representing independently of one another an integer ranging from 0 to 500; - the process is carried out in a closed reactor and under reduced pressure; - the process is carried out in an open reactor; and - the polyurethane foam (I) is purified by a heating step and / or under reduced pressure.

[0023] The invention also relates to a polyurethane foam obtained using the method according to the invention.

[0024] Advantageously, this polyurethane foam has physicochemical properties of the same order of magnitude and comparable to those obtained by the process using polyisocyanates, polyols and water.

[0025] The polyurethane foams according to the invention further have one or other of the following characteristics, or a combination thereof: - the density of polyurethane foam (I) ranges from 10 to 1000 kg.m 3 , preferably 100 to 300 kg.m 3 ; And - the polyurethane foam has cells with a diameter between 0.1 mm and 2 mm, preferably between 0.2 mm and 1.5 mm, the diameter being measured using a scanning electron microscope at 50 Pa and 7.00 kV on sections transverse to the direction of expansion of the material. Brief description of the drawings

[0026] [Fig. 1] Figure 1 is a photograph of PU2 foam.

[0027] [Fig. 2] Figure 2 is an image of PU2 foam observed under a scanning electron microscope (FEI QUANTA, 7 kV). Description of the embodiments

[0028] The invention relates to a self-foaming process for preparing polyurethane foams (I). The process according to the invention comprises the following steps:

[0029] a) the reaction, in the presence of an oxidant and at a temperature ranging from 60°C to 150°C, of ​​at least one polyoxamic acid of formula (II):

[0030] [Chem. 1]

[0031] with at least one polyol of formula (III):

[0032] [Chem. 2] ( HO-)— L2 y (ni), and

[0033] b) foaming the polyurethane (I) obtained in step a) in the presence of carbon dioxide.

[0034] Polyurethane (I) is advantageously thermosetting.

[0035] In the context of the invention, a “poly oxamic acid” or “pluri oxamic acid” is a compound comprising several oxamic acid functions. By oxamic acid function is meant a -N(H)-C(O)-COOH group.

[0036] Preferably, the reaction temperature in step a) is from 80°C to 130°C. Preferably, the reaction is carried out at atmospheric pressure.

[0037] The process according to the invention can be carried out either in an open reactor or in a closed reactor.

[0038] In the context of the invention, x and y are both greater than or equal to two, and at least one of x or y is greater than or equal to 3. Thus, the polyurethane (I) is crosslinked.

[0039] The polyurethane (I) is prepared from one or more polyoxamic acids (II). According to a particular embodiment, the polyurethane foam (I) is prepared from a single polyoxamic acid (II).

[0040] The polyoxamic acid(s) of formula (II) comprise at least two oxamic acid functions, preferably two, three or four, and in particular two or three. In other words, x represents an integer greater than or equal to 2, preferably equal to 2, 3 or 4, and in particular equal to 2 or 3.

[0041] The polyoxamic acid(s) (II) is such that L1 represents a saturated, linear or branched, cyclic or acyclic hydrocarbon group in which one or more CH2s have optionally been replaced by O and / or S; or an unsaturated, linear or branched hydrocarbon group comprising at least one double bond and / or at least one aromatic ring optionally substituted by one or more alkyl and / or alkoxy groups; or a saturated, linear or branched, cyclic or acyclic hydrocarbon group comprising one or more COOH or polyethylene glycol substituents; or a fatty acid triester in which one or more CH2s have optionally been replaced by O and / or S.

[0042] In the context of the invention, a “hydrocarbon group” designates, unless otherwise specified, a linear or branched, cyclic or acyclic, saturated or unsaturated chain comprising only carbon and hydrogen atoms. A hydrocarbon group can therefore designate an alkyl group or an alkylene group in particular.

[0043] An "alkylene" group means a divalent alkyl group. Unless otherwise specified, an alkylene group may be branched or linear, cyclic or acyclic.

[0044] By “alkylene glycol” group is meant a divalent alkyl group substituted by two OH groups. Examples of alkylene glycol groups include ethylene glycol and propylene glycol groups in particular.

[0045] By "alkoxy" and "aryloxy" is meant respectively an -O-alkyl and -O-aryl group.

[0046] By "fatty acid" is meant an aliphatic carboxylic acid whose hydrocarbon chain comprises from 4 to 36 carbon atoms, and typically from 6 to 28 carbon atoms.

[0047] According to a preferred embodiment, L1 is chosen from the following groups:

[0048] (CH2) m (Ll-1),

[0049] (CH2)m-CH(CH2)m'-(CH2)m" (Ll-l 7 ),

[0050] [Chem. 3]

[0051] [Chem. 4] (Ll-3),

[0052] [Chem. 5]

[0053] [Chem. 6] (Ll-5),

[0054] [Chem. 7]

[0055] [Chem. 8]

[0056] [Chem. 9]

[0057] [Chem. 10] (Ll-9),

[0058] [Chem. 11]

[0059] [Chem. 12] (Ll-11),

[0060] with : - RI, RI', RI", R2, R2', R3, R3', R3", R4, R4', R5, R5', R6 and R6', identical or different and representing, independently of one another, H, (CH2)i, CH3, CH3- (CH2)i, CH3O, CH3- (CH2)iO, CH3S, CH3- (CH2)iS, (CH2)jS, (CH2)iCH(CH3)S or CH3- (CH2)iCH(CH3)S, - R2 and R3 may together represent a group CH(R7a)-CH(R7b)-CH(R7c)-CH(R7d) with R7a, R7b, R7c and R7d being identical or different and independently representing H, (CH2)i, CH3, CH3-(CH2)i, CH3O or CH3-(CH2)iO, - it being understood that at least two groups among RI, RI", R2, R3, R3", R4, R5 and R6 and at least two groups among RI', R2', R3', R4', R5' and R6' represent (CH2)i, - R8, R9, R10, R11 and R12, identical or different and representing, independently of one another, H, (CH2)i, CH3, CH3-(CH2)i, O(CH2)i, CH3O or CH3-(CH2)iO, - R11 and R12 may together represent a group O-CH(R7a)-CH(R7b)-CH(R7c)-(CH(R7d))j, it being understood that at least two groups among R7a, R7b, R7c, R7d, R8, R9, R10, R11 and R12 represent (CH2)i or O(CH2)i, - R13, R14, R15, R16, R13', R14', R15' and R16', identical or different and representing, independently of one another, H, CH3(CH2) k or CH3(CH2) k O, - R17 representing H or CH3(CH2) k , - R18 and R18' representing independently of each other H, CH3(CH2) k , CH2[OCH2CH2] m OH, or CH2[OCH2CHCH3] m NHCOCOOH, - A representing a hydrocarbon chain, linear or branched, comprising from 12 to 30 carbon atoms, and of which one or more CH2 have been replaced by S, - i representing an integer ranging from 0 to 20, - j representing 0 or 1, - k representing an integer ranging from 0 to 6, - m, m' and m" being identical or different and representing independently of each other an integer ranging from 1 to 500, and - p representing an integer ranging from 1 to 6.

[0061] According to one embodiment, the at least one polyoxamic acid (II) is such that L1 represents L1-1 or L1-1' with m, m' and m" being identical or different and independently representing an integer preferably ranging from 1 to 20, preferably from 1 to 14, and preferably from 6 to 10. According to this embodiment, x is preferably equal to 2 or 3, and advantageously is equal to 2 when L1 represents Ll-1 or equal to 3 when L1 represents Ll-1'. As examples according to this embodiment, the polyoxamic acid (II) may be such that x = 2, L1 representing (CH2) m with i = 6 or i = 10.

[0062] According to one embodiment, the at least one polyoxamic acid (II) is such that L1 represents L1-2.

[0063] According to a first preferred variant of this embodiment, L1-2 is such that RI represents (CH2)i, CH3or CH3-(CH2)i, RI" and R3" represent H, CH3or CH3-(CH2)i, R2 represents H, (CH2)i, (CH2)iS, R3 represents H, (CH2)i, CH3or CH3-(CH2)i, R4 represents H, CH3, CH3-(CH2)i or (CH2)iCH(CH3)S, R5 represents H or (CH2)i and R6 represents H. As examples of polyoxamic acids (II) according to this embodiment, the following polyoxamic acids may be mentioned:

[0064] [Chem. 13]

[0067] According to a second preferred variant of this embodiment, L1-2 is such that RI, RI", R2, R3, R3", R4, R5 and R6 are identical or different and independently represent H, (CH2)i, CH3 or CH3-(CH2)i. According to this embodiment, x is preferably equal to 2. As examples of polyoxamic acids (II) according to this embodiment, the following polyoxamic acids may be mentioned:

[0068] [Chem. 16]

[0070] According to a third preferred embodiment, L1-2 is such that R1 and R6 represent (CH2)i, R4 and R5 represent CH3 or CH3-(CH2)i, and R2 and R3 together represent a group CH(R7a)-CH(R7b)-CH(R7c)-CH(R7d) with R7a, R7b, R7c and R7d being identical or different and independently representing H, (CH2) i CH3, CH3-(CH2)i, CH3O or CH3-(CH2)iO, and preferably H, (CH2)i, CH3, OR CH3-(CH2)i. As an example of polyoxamic acid (II) according to this embodiment, the following polyoxamic acid may be mentioned:

[0071] [Chem. 18]

[0072] According to one embodiment, the at least one polyoxamic acid (II) is such that L1 represents L1-3. According to this embodiment, R1', R2', R3', R4', R5' and R6' are identical or different and preferably represent, independently of one another, H, (CH2)i, CH3 or CH3-(CH2)i. As an example of polyoxamic acid (II) according to this embodiment, the following polyoxamic acid may be mentioned:

[0073] [Chem. 19]

[0074] According to one embodiment, the at least one polyoxamic acid (II) is such that L1 represents L1-4. According to this embodiment, j preferably represents 0. Preferably according to this embodiment, R11 and R12 together represent a group O-CH(R7a)-CH(R7b)-CH(R7c)-(CH(R7d))j, with R7a, R7b, R7c and R7d as defined above and j representing 0 or 1. Preferably, R8, R9 and R10 represent H. As an example of polyoxamic acid (II) according to this embodiment, the following polyoxamic acid may be mentioned:

[0075] [Chem. 20]

[0076] According to one embodiment, the at least one polyoxamic acid (II) is such that L1 represents L1-5. According to this embodiment, i is advantageously an integer ranging from 1 to 10, preferably ranging from 1 to 6, and in particular equal to 4.

[0077] According to one embodiment, the at least one polyoxamic acid (II) is such that L1 represents L1-6. According to this embodiment, R13, R14, R15 and R16 are preferably identical or different and independently of one another represent H or CH3-(CH2) k . According to this embodiment, i is an integer preferably ranging from 1 to 10, and in particular from 1 to 4. As an example of polyoxamic acid (II) according to this embodiment, mention may be made of polyoxamic acid for which R13, R14, R15 and R16 each represent H and i is equal to 1.

[0078] According to one embodiment, the at least one polyoxamic acid (II) is such that L1 represents L1-7. According to this embodiment, R13, R14, R15, R16, R13', R14', R15' and R16' are identical or different and preferably represent, independently of one another, H, CH3O or CH3(CH2)kO. Preferably, R13, R13', R16 and R16' represent H. According to this embodiment, p preferably represents an integer ranging from 1 to 4. As an example of polyoxamic acid (II) according to this embodiment, the following polyoxamic acid may be mentioned:

[0079] [Chem. 21]

[0080] According to one embodiment, the at least one polyoxamic acid (II) is such that L1 represents L1-8. According to this embodiment, R17 represents H or CH3(CH2) k , with k preferably ranging from 0 to 4, and in particular from 0 to 2. As examples of polyoxamic acids (II) according to this embodiment, the following polyoxamic acids may be mentioned:

[0081] [Chem. 22] (II-8-1), and

[0082] [Chem. 23]

[0083] According to one embodiment, the at least one polyoxamic acid (II) is such that L1 represents L1-9. According to this embodiment, R17 represents H or CH3(CH2) k with k being an integer preferably ranging from 0 to 4, more preferably from 0 to 2, and in particular being equal to 0. According to this embodiment, R18 preferably represents H or CH3(CH2)kwith k ranging from 0 to 4, preferably from 0 to 2, and in particular being equal to 1, or R18 represents CH2[OCH2CHCH3] m NHCOCOOH or CH2[OCH2CH2] m OH. As examples of polyoxamic acids (II) according to this embodiment, the following polyoxamic acids may be mentioned:

[0084] [Chem. 24] ( ), And

[0086] [Chem. 26]

[0087] According to one embodiment, the at least one polyoxamic acid (II) is such that L1 represents L1-10. According to this embodiment, R17 represents H or CH3(CH2) k with k being an integer preferably ranging from 0 to 4, more preferably from 0 to 2, and in particular being equal to 0. According to this embodiment, R18 preferably represents H or CH3(CH2)kwith k ranging from 0 to 4, preferably from 0 to 2, and in particular being equal to 1. According to this embodiment, R18' preferably represents H, CH3(CH2) k , or CH2[OCH2CH2] m OH. As an example of polyoxamic acid (II) according to this embodiment, the following polyoxamic acid may be mentioned:

[0089] According to one embodiment, the at least one polyoxamic acid is such that L1 represents L1-11. According to this embodiment, L1-11 may represent a triester of fatty acids optionally functionalized with cysteamine. In this case, the fatty acids may in particular be a saturated fatty acid such as stearic acid, or an unsaturated fatty acid functionalized with cysteamine at the double bond(s). Among the unsaturated fatty acids, there may be include oleic acid, palmitoleic acid, erucic acid and linoleic acid.

[0090] According to a preferred embodiment of the invention, the at least one polyoxamic acid (II) is such that the group L1 is chosen from the groups Ll-1, Ll-1', Ll-2, Ll-6, Ll-9 and Ll-10, as defined above, and preferably from Ll-1 and Ll-2.

[0091] The polyurethane (I) is prepared from at least one polyol of formula (III). According to a particular embodiment, the polyurethane is prepared from a single polyol (III). According to another particular embodiment, the polyurethane (III) is prepared from two polyols (III).

[0092] The polyol(s) (III) comprise at least two hydroxyl functions, preferably two, three, four, five or six, and in particular two, three or four or even three or four. In other words, y represents an integer greater than or equal to 2, preferably equal to 2, 3, 4, 5 or 6, and in particular 2, 3 or 4, or even 3 or 4.

[0093] The polyol(s) is(are) such that L2 represents a saturated, linear or branched, cyclic or acyclic hydrocarbon group, in which one or more CH2s have optionally been replaced by O; or an unsaturated, linear or branched hydrocarbon group, in which one or more CH2s have optionally been replaced by O and comprising at least one aromatic ring optionally substituted by one or more alkyl and / or alkoxy groups or at least one aromatic heterocycle; or a fatty acid triester; or a di, tri or tetrapolyester of polyalkylene glycol.

[0094] According to a preferred embodiment, L2 is chosen from the following groups:

[0095] (CH2) t (L2-1),

[0096] [Chem. 28] (L2-2),

[0097] [Chem. 29] (L2-3)

[0098] [Chem. 30] (L2-4),

[0099] [Chem. 31]

[0100] [Chem. 32]

[0101] [Chem. 33]

[0102] [Chem. 34]

[0103] [Chem. 35]

[0104] [Chem. 36]

[0105] [Chem. 37]

[0106] [Chem. 38]

[0107] [Chem. 39] (L2-13),

[0108] [Chem. 40]

[0109] [Chem. 41]

[0113] with: - R20, R21, R22, R23, R24 and R25 being identical or different and representing independently of one another H, (CH2) S , CH3 or CH3-(CH2)s, - R21 and R22 may together represent a group CH(R22a)-CH(R22b)-CH(R22c)-CH(R22d) with R22a, R22b, R22c and R22d being identical or different and independently representing H, (CH2)s, CH3 or CH3-(CH2) S , - it being understood that at least two groups among R20, R21, R22, R22a, R22b, R22c and R22d, R23, R24 and R25 represent (CH2) S , - R26, R27, R28, R29, R30 and R31 being identical or different and representing independently of each other H, (CH2) S , CH3, CH3-(CH2) S , O(CH2) S , CH3O or CH3-(CH2) S O, provided that at least two groups among R26, R27, R28, R29, R30 and R31 represent (CH2)s or O(CH2) S , - R32, R33, R34, R36, R36', R45, R47, R48 and R49 representing independently of each other H, CH3 or CH3(CH2) r , - R35 representing CH3, CH3(CH2) r or HO(CH2) r , - R37, R38, R39, R40, R41, R42, R43 and R44 being identical or different and representing independently of one another H, (CH2) S , CH3, CH3-(CH2) S , O(CH2) S , CH3O OR CH3-(CH2) S O, - R46 representing (CH2) r , benzylene or cyclohexylene, - B representing a hydrocarbon chain, linear or branched, comprising from 12 to 30 carbon atoms, and comprising at least one double bond, - s representing an integer ranging from 1 to 18, - r representing an integer ranging from 1 to 6, - 1 representing an integer ranging from 1 to 500, - u representing 0, 1, 2 or 3, - w representing 0 or 1, - z representing an integer ranging from 0 to 4.

[0114] According to one embodiment, the at least one polyol (III) is such that L2 represents L2-1. According to this embodiment, t represents an integer preferably ranging from 1 to 18, preferably from 1 to 12, and preferably from 1 to 6. As an example of polyol (III) according to this embodiment, mention may be made of ethylene glycol OH-CH2-CH2-OH (i.e. t = 2).

[0115] According to one embodiment, the at least one polyol (III) is such that L2 represents L2-2. According to this embodiment, r is an integer preferably ranging from 1 to 4, and preferably is equal to 1, 2 or 4. As examples of polyols (III) according to this embodiment, the following polyols may be mentioned:

[0116] [Chem. 45]

[0117] [Chem. 46] (III-2-2), and

[0118] [Chem. 47]

[0119] According to one embodiment, the at least one polyol (III) is such that L2 represents L2-3. According to this embodiment, r is an integer preferably ranging from 1 to 4, and preferably is equal to 1, 2 or 3. As an example of polyol (III) according to this embodiment, the following polyol may be mentioned:

[0120] [Chem. 48] (III-3-1).

[0121] According to one embodiment, the at least one polyol (III) is such that L2 represents L2-4. According to a first preferred variant according to this embodiment, R20 and R21 are identical or different and represent (CH2) S , and R22, R23, R24 and R25 are the same or different and independently represent H, CH3 or CH3-(CH2) S . As examples of polyols (III) according to this embodiment, the following polyol may be mentioned:

[0122] [Chem. 49] (III-4-1).

[0123] According to a second preferred variant according to this embodiment, R20, R23, R24 and R25 are identical or different and preferably represent, independently of one another, H, (CH2) S , CH3 or CH3-(CH2) S , and R21 and R22 together represent a group CH(R22a)-CH(R22b)-CH(R22c)-CH(R22d) with R22a, R22b, R22c and R22d being the same or different and representing independently of each other H, (CH2)S , CH3 or CH3-(CH2) S . As examples of polyols (III) according to this embodiment, the following polyol may be mentioned:

[0124] [Chem. 50] (III-4-2).

[0125] According to one embodiment, the at least one polyol (III) is such that L2 represents L2-5. Preferably according to this embodiment, R26, R27, R28, R29, R30 and R31 represent, independently of one another, H, (CH2) S , or O(CH2) S . According to this embodiment, s preferably represents an integer ranging from 1 to 12, preferably from 1 to 6. As examples of polyols (III) according to this embodiment, the following polyols may be mentioned:

[0126] [Chem. 51] (III-5-1) and

[0127] [Chem. 52]

[0128] According to one embodiment, the at least one polyol (III) is such that L2 represents L2-6. According to this embodiment, R32 and R33 preferably represent, independently of one another, H, CH3 or CH3(CH2) r with r representing an integer ranging from 1 to 4. As an example of polyol (III) according to this embodiment, the following polyol may be mentioned:

[0129] [Chem. 53] (III-6-1).

[0130] According to one embodiment, the at least one polyol (III) is such that L2 represents L2-7. According to this embodiment, R34 preferably represents H, CH3OR CH3(CH2) r with r ranging from 1 to 4. According to this embodiment, u preferably represents 1, 2 or 3. As examples of polyols (III) according to this embodiment, the following polyols may be mentioned:

[0131] [Chem. 54] (III-7-1),

[0132] [Chem. 55] (III-7-2) and

[0133] [Chem. 56]

[0134] According to one embodiment, the at least one polyol (III) is such that L2 represents L2-8. Preferably according to this embodiment, r represents an integer ranging from 1 to 4, and preferably equal to 1 or 2. According to a first variant of this embodiment, R35 preferably represents CH3 or CH3(CH2) r with r preferably ranging from 1 to 4, and better still being equal to 1 or 2. According to a second variant of this embodiment, R35 represents HO(CH2) r , with r representing an integer preferably ranging from 1 to 4, and in particular equal to 1 or 2. As examples of polyols (III) according to this embodiment, the following polyols may be mentioned:

[0135] [Chem. 57] (III-8-1) and

[0136] [Chem. 58]

[0137] According to one embodiment, the at least one polyol (III) is such that L2 represents L2-9. According to this embodiment, R36 and R36' are identical or different and preferably represent, independently of one another, H, CH3 or CH3(CH2) r with r representing an integer ranging from 1 to 4, preferably equal to 1 or 2. As examples of polyols (III) according to this embodiment, the following polyols may be mentioned:

[0138] [Chem. 59]

[0139] [Chem. 60]

[0140] According to one embodiment, the at least one polyol (III) is such that L2 represents L2-10. According to this embodiment, R36 preferably represents H, CH3OR CH3(CH2) r with r representing an integer ranging from 1 to 4, preferably equal to 1 or 2. As examples of polyols (III) according to this embodiment, the following polyols may be mentioned:

[0141] [Chem. 61] (III-10-1) and

[0142] [Chem. 62]

[0143] According to one embodiment, the at least one polyol (III) is such that L2 represents L2-11. According to this embodiment, r preferably represents an integer ranging from 1 to 4, and preferably equal to 1 or 2. As an example of polyol (III) according to this embodiment, mention may be made of 2,5-bis(hydroxymethyl)furan, for which r = 1.

[0144] According to one embodiment, the at least one polyol (III) is such that L2 represents L2-12. According to this embodiment, u preferably represents 0 or 1. According to this embodiment, w preferably represents 0. As an example of a polyol (III) according to this embodiment, the following polyol may be mentioned:

[0145] [Chem. 63]

[0146] According to one embodiment, the at least one polyol (III) is such that L2 represents L2-13. According to this embodiment, r preferably represents an integer ranging from 1 to 4, preferably r is equal to 1. Preferably according to this embodiment, R37, R38, R39, R40, R41, R42, R43 and R44 represent, independently of one another, H, CH3, CH3-(CH2)s, CH3O or CH3-(CH2) S O, and preferably H, CH3O or CH3-(CH2) S O, with s preferably representing an integer ranging from 1 to 12, preferably from 1 to 6. According to this embodiment, R37, R38, R43 and R44 preferably represent H. According to this embodiment, R39, R40, R41 and R42 are identical or different and independently of each other represent a CH3O or CH3-(CH2) group S O with s preferably representing an integer ranging from 1 to 12, preferably 1 to 6. As an example of polyols (III) according to this embodiment, the following polyol may be mentioned:

[0147] [Chem. 64] (III-13-1).

[0148] According to one embodiment, the at least one polyol (III) is such that L2 represents L2-14. According to this embodiment, R45 preferably represents H, CH3OR CH3(CH2) r with r representing an integer ranging from 1 to 4, and preferably R45 represents H. According to this embodiment, R46 preferably represents (CH2) r with r being equal to 3, 4 or 6, benzylene or cyclohexylene. According to this embodiment z is preferably equal to 0 or 1.

[0149] [Chem. 65] with R46 = (CH2)3(III-14-1) R46 = (CH2)4(III-14-2) R46 = (CH2)6(III-14-3) R46 = CH2-Ph-CH2(III-14-4) R46 = Cy (III- 14-5)

[0150] According to one embodiment, the at least one polyol (III) is such that L2 represents L2-14'. According to this embodiment, R45 preferably represents H, CH3OR CH3(CH2) rwith r representing an integer ranging from 1 to 4, and preferably R45 represents CH3 or CH3(CH2) r with r representing an integer ranging from 1 to 4. According to this embodiment, R46 preferably represents (CH2) r with r being equal to 3, 4 or 6, benzylene or cyclohexylene. According to this embodiment, z preferably represents 0. As examples of polyols (III) according to this embodiment, the following polyols may be mentioned:

[0151] [Chem. 66] with R46 = (CH2)3(III-14'-1) R46 = (CH2)4(III-14'-2) R46 = (CH2)6(III-14'-3) R46 = CH2-Ph-CH2(III-14'-4) R46 = Cy (III-14'-5)

[0152] According to one embodiment, the at least one polyol (III) is such that L2 represents L2-15. According to this embodiment, 47 and R48 are identical or different and represent H, CH3 or CH3(CH2) rwith r preferably representing an integer ranging from 1 to 4, preferably r being equal to 1 or 2. Preferably, z is equal to 0, 1 or 4. As examples of polyols (III) according to this embodiment, the following polyols may be mentioned:

[0155] According to one embodiment, the at least one polyol (III) is such that L2 represents L2-16. According to this embodiment, R49 preferably represents H, CH3OR CH3(CH2) r with r representing an integer ranging from 1 to 4, preferably r being equal to 1 or 2. Preferably, z is equal to 0, 1 or 4. As examples of polyols (III) according to this embodiment, the following polyols may be mentioned: (III-16-2).

[0158] According to one embodiment, the at least one polyol (III) is such that L2 represents L2-17. According to this embodiment, L2-17 may represent a triester of hydroxylated unsaturated fatty acids, i.e. comprising a hydroxyl substituent on the carbon chain. According to this embodiment, the hydroxylated fatty acids are in particular chosen from ricinoleic acid, lesquerolic acid or densipolic acid.

[0159] According to a preferred embodiment of the invention, the at least one polyol is such that the group L2 is chosen from the groups L2-1, L2-2, L2-3, L2-4, L2-6, L2-8, L2-9 and L2-10, as defined above, and preferably from L2-8 and L2-9.

[0160] According to a particular embodiment of the invention, the polyurethane (I) is prepared from a polyoxamic acid (II) comprising two or three oxamic acid functions, and one or two polyols (III) each comprising two, three or four hydroxyl functions, it being understood that the number of oxamic acid functions and the number of hydroxyl functions cannot be both equal to two. In other words, according to this embodiment, the polyurethane (I) is prepared from a polyoxamic acid (II) with x = 2 or 3, and one or two polyols (III) such that for each y = 2, 3 or 4, it being understood that x and y cannot both be equal to 2.

[0161] According to a preferred embodiment of the invention, x = 2 or 3 and y = 2, 3 or 4, and preferably x = 2 and y = 3 or 4.

[0162] According to one embodiment, the at least one polyoxamic acid of formula (II) is such that the group L1 is chosen from the groups Ll-1, Ll-1', Ll-2, Ll-6, Ll-9 and Ll-10, as defined above, and preferably from Ll-1 and Ll-2, and the at least one polyol (III) is such that L2 is chosen from the groups L2-1, L2-2, L2-3, L2-4, L2-6, L2-8, L2-9 and L2-10, as defined above, and preferably from L2-8 and L2-9.

[0163] According to one embodiment, the at least one polyoxamic acid of formula (II) is such that x = 2 or 3 and group L1 is chosen from groups L1-1, L1-2, L1-6, L1-9 and L1-10, as defined above, and preferably from L1-1 and L1-2, and the at least one polyol (III) is such that y = 2, 3 or 4 and L2 is chosen from groups L2-1, L2-2, L2-3, L2-4, L2-6, L2-8, L2-9 and L2-10, as defined above, and preferably from L2-8 and L2-9, it being understood that x and y are not both equal to 2.

[0164] The reaction in step a) is carried out in the presence of an oxidant. Among the oxidants that may be suitable in the context of the invention, mention may in particular be made of hypervalent iodinated oxidants such as bis(trifluoroacetoxy)iodobenzene, bis(acetoxy)iodobenzene (or iodobenzene diacetate), poly[4-(diacetoxyiodo)styrene], hydroxybenziodoxole, and acetoxybenziodoxole. Poly[4-(diacetoxyiodo)styrene] (CAS number 36290-94-5, and also known as polystyrene iodoacetate) is, for example, marketed by the company TCI under the reference P1415. According to a preferred embodiment, the oxidant is a hypervalent iodinated oxidant chosen from bis(trifluoroacetoxy)iodobenzene, poly[4-(diacetoxyiodo)styrene] (or polystyrene iodoacetate), and bis(acetoxy)iodobenzene (or iodobenzene diacetate). According to a first particular embodiment, the iodinated oxidant hypervalent is supported, for example on a polymer, such as poly[4-(diacetoxyiodo)styrene]. According to a second embodiment, the hypervalent iodinated oxidant is not supported, and is preferably chosen from bis(trifluoroacetoxy)iodobenzene, and bis(acetoxy)iodobenzene.

[0165] Preferably, the molar ratio of oxidant to oxamic acid functions (i.e. the ratio: number of moles of oxidant / (x * number of moles of oxamic acid)) ranges from 1 to 1.2, and preferably is equal to 1.1.

[0166] Preferably, the oxamic acid:hydroxyl functional ratio ranges from 0.8:1 to 1.3:1, preferably from 0.9:1 to 1.1:1. According to a particularly preferred embodiment, the oxamic acid:hydroxyl functional ratio is 1.1:1. The term oxamic acid:hydroxyl functional ratio means the ratio between the number of oxamic acid functions of the polyoxamic acid(s) and the number of hydroxyl functions of the polyol(s). In other words, this ratio is equal to (x * number of moles of polyoxamic acid(s)) / (y * number of moles of polyol(s)).

[0167] According to a particular embodiment, the reaction in step a) is carried out in the presence of a surfactant (IV). When the process is carried out in a closed reactor, the surfactant is optional, satisfactory results being obtained with or without surfactant. When the process is carried out in an open reactor, it is more advantageous for the surfactant to be present, although it is not essential.

[0168] The surfactant (IV) is preferably non-ionic. Among the non-ionic surfactants that may be suitable in the context of the invention, mention may be made of silicone surfactants, and in particular those of the formulas below:

[0169] [Chem. 71]

[0170] [Chem. 72] (IV-2),

[0171] with : - R50 representing OH, CH3-(CH2)hO or O(CO)(CH2)hCH3with h representing an integer ranging from 0 to 3, - a, b, c, d, e, f and g being identical or different and representing independently of one another an integer ranging from 0 to 500, preferably from 0 to 20.

[0172] Preferably, R50 represents OH.

[0173] According to a first preferred embodiment, the surfactant is of formula (IV-2) with c = d = e = 1, f = 8, g = 0 and R50 = OH.

[0174] According to a second preferred embodiment, the surfactant is of formula (IV-2) with c = d = 10, e = 1, f = 8, g = 0 and R50 = OH.

[0175] When the surfactant is present, its content is less than 4% by weight, and preferably ranges from 0.1% to 2% by weight, and preferably from 0.2 to 1% by weight, relative to the total weight of the reaction mixture.

[0176] The reaction in step a) between the at least one polyoxamic acid and the at least one polyol generates in particular carbon dioxide, which is used during the polyurethane foaming step (I).

[0177] Step b) of the process according to the invention makes it possible to foam the polyurethane (I) obtained in step a).

[0178] Advantageously, the foaming step is carried out solely using the carbon dioxide generated during the synthesis of the polyurethane. The carbon dioxide generated in step a) is then the foaming agent. Thus, advantageously, the synthesis of the polyurethane (step a)) and the foaming step (step b)) can be carried out concomitantly.

[0179] An optional step c), subsequent to step b), may be carried out in order to purify the polyurethane foam (I) obtained by removing reaction by-products. For this, the polyurethane foam may be heated and / or placed under reduced pressure, using a vacuum oven for example. When this step is carried out, the foam is preferably heated to a temperature ranging from 60°C to 150°C, preferably from 80°C to 130°C, and / or placed under reduced pressure. This step is not mandatory.

[0180] The invention also relates to the polyurethane foam (I) obtained according to the process of the invention. This foam advantageously has physicochemical properties comparable to those obtained by processes described in the prior art.

[0181] In particular, polyurethane foam (I) can have a density ranging from 10 to 1000 kg.m 3 , preferably 100 to 300 kg.m 3. The density d corresponds to the apparent density of the foam, that is, the ratio of the mass m and the apparent volume V of the foam. The mass m can be measured with a balance and the apparent volume V can be determined by measuring the dimensions of the foam with a caliper.

[0182] The resulting polyurethane foam has a porous structure. The cells (or pores) of the polyurethane foam may have a diameter between 0.1 mm and 2 mm, preferably between 0.2 mm and 1.5 mm, the diameter being measured using a scanning electron microscope at 50 Pa and 7.00 kV on sections transverse to the direction of expansion of the material. The cells or pores of the polyurethane foam correspond to the empty spaces in the foam. Examples

[0183] Nine polyurethane foams according to the invention, PU1 to PU9, were prepared according to the following processes. [01841 Process for the synthesis of oxamic acid polv:

[0185] Triethylamine (11 mmol) was added to a solution of amine (10 mmol) in dichloromethane (concentration: 0.3 M) at room temperature. The solution was then cooled to 0 °C and ethyl oxalyl chloride (11 mmol) was added dropwise. The solution was then slowly brought back to room temperature over a period of 4 to 6 h while being kept stirring. The reaction was then treated with a hydrochloric acid solution (1 M, 20 mL) and extracted with dichloromethane (3 x 20 mL). The organic phases were combined and then washed with saturated sodium chloride solution. The resulting organic phase was then dried over sodium sulfate, filtered and concentrated under reduced pressure. The residue obtained was dissolved in a mixture of tetrahydrofuran (15 mL) and water (5 mL). Lithium hydroxide was then added to the solution (50 mmol). After stirring for 6 to 8 h, the solution was washed with dichloromethane (3 x 30 mL).The aqueous phase was then acidified with HCl solution (1 M). The resulting mixture was extracted with ethyl acetate (3 x 30 mL). The resulting organic phase was washed with saturated NaCl solution (30 mL) and then dried over Na2SO4. The solvent was then evaporated under reduced pressure and the residue was recrystallized from dichloromethane and hexane to obtain the desired product.

[0186] Polyurethane synthesis process in an open reactor:

[0187] The polyol(s) and surfactant were introduced into an open reactor. The oxidant and polyoxamic acid were ground and mixed together in a separate reactor, and then introduced into the reactor containing the polyol(s). The reaction mixture was mixed using a spatula and then by magnetic stirring. The reactor was heated to a temperature of 80°C, 100°C, 115°C or 130°C, depending on the reactants. The reaction mixture was stirred once the reaction mixture reached a homogeneous liquid state and foam began to form. When the foam height was stable, it was baked for 2 hours at this temperature. Once baked Once finished, the reactor was cooled to room temperature (RT). The foam was then placed in a vacuum oven at 60°C for 5 hours. FOI 881 Process for the synthesis of polyurethane in a closed reactor:

[0189] The polyol(s) and surfactant were introduced into a closed reactor. The oxidant and polyoxamic acid were ground and mixed together in a separate reactor, and then introduced into the reactor containing the polyol(s). The reaction mixture was mixed using a spatula followed by magnetic stirring. The reactor was sealed and then heated to a temperature of 100 °C. The reaction mixture was stirred once the reaction mixture reached a homogeneous liquid state. When the viscosity of the reaction mixture became significant, the reactor was opened. The resulting foam was subjected to a dynamic vacuum for 5 minutes and then cured for 2 hours at 100 °C under static vacuum. After curing was completed, the reactor was cooled to room temperature (RT) before opening. The foam was then placed in a vacuum oven at 60 °C for 5 hours.

[0190] The compositions of the polyurethane foams are detailed in Table 1 below. The percentages are percentages by mass relative to the total weight of the reactants in the reaction mixture. The ethoxylated trimethylol propane used has a number-average molar mass Mn of 1014 g. mol 1 .

[0191] [Table 1]

[0192] The physicochemical characteristics of the nine polyurethane foams were evaluated and are detailed in Table 2 below. The foaming time TM corresponds to the time of formation and stabilization of the foam, i.e. the time from which the maximum height of foam in the reactor is obtained. The density d corresponds to the apparent density of the foam, i.e. the ratio of the mass m and the apparent volume V of the foam. The mass m was measured with a balance and the apparent volume V was determined by measuring the dimensions of the foam with a caliper. The glass transition temperature Tg was measured by DSC, using a TA Instruments Q100 DSC apparatus. For each polyurethane foam, two heating cycles from -75 °C to 200 °C, with a ramp of 10 °C. min 1 , were carried out. The glass transition temperature was determined from the second cycle. The degradation temperature T d5 o / o corresponds to the temperature at which the polyurethane foam loses 5% of its initial mass. The degradation temperature T d5 o / o was determined by thermogravimetric analysis (TGA), carried out on a TGA-Q500 device from TA Instruments, under a nitrogen atmosphere, by heating to 10 °C. min 1from room temperature up to 600 °C. The mechanical properties are determined in compression by DMA, using a DMA Q850 apparatus from TA Instruments, by measuring the stress allowing to reach 50% deformation compared to the initial height of the samples, with a prestress of 0.02 N and a ramp of 100% / min. The morphologies of the foam cells are evaluated using a scanning electron microscope (SEM) FEI QUANTA 200 at 50 Pa and 7.00 kV on sections transverse to the direction of expansion of the material. The cell diameters are measured using ImageJ software and averaged for at least 100 cells per sample.

[0193] [Table 2]

[0194] The physicochemical characteristics of the new polyurethane foams are comparable to those of flexible foams synthesized by adding water to a traditional isocyanate-alcohol formulation.

[0195] The measured Tg ranges from -33.2 °C to -47.6 °C except for PU3, which is comparable to what has been described in the literature for polyurethane foams synthesized from propylene glycol and toluene diisocyanate in the presence of a silicone surfactant (Armistead et al., Journal of Applied Polymer Science, 1988, Vol. 35, pp. 601-629). Synthesis in an open or closed reactor has no influence on the Tg of the resulting foam.

[0196] The measured densities range from 112 kg.nT 3 at 318 kg.nT 3 Densities of the same order of magnitude have been reported in the literature for polyurethane foams synthesized from trifunctional propylene glycol and a mixture of 4,4'-diphenylmethylene diisocyanate (MDI) and toluene diisocyanate (TDI), in the presence of a silicone surfactant (Gwon et al., International Journal of Precision Engineering And Manufacturing, 2015, Vol. 16, No. 11, pp. 2299-2307).

[0197] The cell diameters of PU1 to PU9 foams range from 0.26 mm to 1.23 mm, which is of the same order of magnitude as described in the literature (Gwon et al., International Journal of Precision Engineering And Manufacturing, 2015, Vol. 16, No. 11, pp. 2299-2307; Yi et al.; Journal of Applied Polymer Science 2020, 7 7(46). DOI: 10.1002 / app.49510). Figure 1 is a photograph of PU2 to visualize the macroscopic appearance of the formed foam. Figure 2 shows the porous structure of the PU2 foam observed under a scanning electron microscope.

[0198] The stress to achieve 50% deformation relative to the initial height of the samples (50% stress) for foams prepared in an open reactor ranges from 0.9 kPa to 23.3 kPa, which is comparable to what is described in the Yi et al. document for a deformation of 10%. For PU4 prepared in a closed reactor, the stress 50 o / owas measured at 89.4 kPa.

[0199] The process according to the invention therefore makes it possible to obtain foams having properties comparable to those obtained by decarboxylation of isocyanate in the presence of water (i.e. one of the usual foaming methods for polyurethane foams).

Claims

Demands

1. A process for preparing a polyurethane foam (I) characterized in that it comprises: a) the reaction, in the presence of an oxidant and at a temperature ranging from 60 to 150 °C, of ​​at least one polyoxamic acid of formula (II): with at least one polyol of formula (III): ( \ HO— ) / —y L2 (HI), to generate / ns / tudu carbon dioxide and at least one polyisocyanate, wherein: - the oxidant is a hypervalent iodine compound, - L1 represents a saturated hydrocarbon group, linear or branched, cyclic or acyclic, in which one or more CH2 groups may have been replaced by O and / or S; or an unsaturated hydrocarbon group, linear or branched, comprising at least one double bond and / or at least one aromatic ring, possibly substituted by one or more alkyl and / or alkoxy groups; or a saturated hydrocarbon group, linear or branched, cyclic or acyclic, comprising one or more COOH or polyethylene glycol substituents; or a fatty acid triester in which one or more CH2 groups may have been replaced by O and / or S, - L2 represents a saturated hydrocarbon group, linear or branched, cyclic or acyclic, in which one or more CH2 groups may have been replaced by O; or an unsaturated hydrocarbon group, linear or branched, in which one or more CH2 groups may have been replaced by O and comprising at least one aromatic ring, possibly substituted by one or more alkyl and / or alkoxy groups, or at least one aromatic heterocycle; or a fatty acid triester; or a di, tri, or tetrapolymer of polyalkylene glycol, - x represents an integer greater than or equal to 2, and - y represents an integer greater than or equal to 2, - provided that at least one of x or y is greater than or equal to 3, and b) the foaming of the polyurethane (I) obtained in step a) in the presence of carbon dioxide.

2. A preparation method according to claim 1, wherein the carbon dioxide used for foaming in step b) is entirely generated in step a).

3. A preparation method according to any one of the preceding claims wherein steps a) and b) are carried out concurrently.

4. A preparation method according to any one of the preceding claims, wherein L1 is selected from the following groups: - (CH2)m (LM), - (CH2) m -CH(CH2) m '-(CH2) m "(Ll-lO, (Ll-5) with : - RI, RI', RI", R2, R2', R3, R3', R3", R4, R4', R5, R5', R6 and R6' identical or different and independently representing H, (CH2)i, CH3, CH3- (CH2)i, CH3O, CH3-(CH2)iO, CH3S, CH3-(CH2)iS, (CH2)iS, (CH2)iCH(CH3)S or CH3-(CH2)iCH(CH3)S, - R2 and R3 can together represent a group CH(R7a)-CH(R7b)-CH(R7c)-CH(R7d) with R7a, R7b, R7c and R7d being identical or different and independently representing H, (CH2)j, CH3, CH3-(CH2)i, CH3O or CH3-(CH2)iO, - it being understood that at least two groups among RI, RI", R2, R3, R3", R4, R5 and R6 and at least two groups among RI', R2', R3', R4', R5' and R6' represent (CH2)i, - R8, R9, RIO, R11 and R12 identical or different and independently representing H, (CH2)i, CH3, CH3-(CH2)i, O(CH2)i, CH3O or CH3-(CH2)iO, - R11 and R12 together can represent a group O-CH(R7a)-CH(R7b)-CH(R7c)-(CH(R7d))j, it being understood that at least two groups among R7a, R7b, R7c, R7d, R8, R9, R10, R11 and R12 represent (CH2)i or O(CH2)i, - R13, R14, R15, R16, R13', R14', R15' and R16' identical or different and independently representing H, CH3(CH2) k or CH3(CH2) k O, - R17 representing H or CH3(CH2) k , - R18 and R18' independently representing H, CH3(CH2) k , CH2[OCH2CH2] m OH, or CH2[OCH2CHCH3] m NHCOCOOH, - A representing a linear or branched hydrocarbon chain, comprising 12 to 30 carbon atoms, and in which one or more CH2s have been replaced by S, - i representing an integer ranging from 0 to 20, - j representing 0 or 1, - k representing an integer from 0 to 6, - m, m' and m" being identical or different and independently representing an integer from 1 to 500, and - p representing an integer from 1 to 6.

5. A preparation method according to any one of the preceding claims, wherein x is equal to 2 or 3.

6. A method according to any one of the preceding claims, wherein L1 is chosen from: - (CH2) m (Ll-1), - (CH2) m -CH(CH2) m -(CH2) m "(Ll- ,

7. A method according to any one of the preceding claims, wherein L1 is chosen from (Ll-2).

8. A preparation method according to any one of the preceding claims, wherein L2 is selected from the following groups: - (CH2) t (L2-1), (L2-3), , with : - R20, R21, R22, R23, R24 and R25 being identical or different and independently representing H, (CH2) S , CH3 or CH3-(CH2)s, - R21 and R22 can together represent a group CH(R22a)-CH(R22b)-CH(R22c)-CH(R22d) with R22a, R22b, R22c and R22d identical or different and independently representing H, (CH2) S , CH3 or CH3-(CH2) S , - it being understood that at least two groups among R20, R21, R22, R22a, R22b, R22c and R22d, R23, R24 and R25 represent (CH2) S , - R26, R27, R28, R29, R30 and R31 being identical or different and independently representing H, (CH2) S , CH3, CH3-(CH2) S , O(CH2) S , CH3O OR CH3-(CH2) S O, it being understood that at least two groups among R26, R27, R28, R29, R30 and R31 represent (CH2) S or O(CH2) S , - R32, R33, R34, R36, R36', R45, R47, R48 and R49 independently representing H, CH3 or CH3(CH2) r , - R35 representing CH3, CH3(CH2) r or HO(CH2) r , - R37, R38, R39, R40, R41, R42, R43 and R44 being identical or different and independently representing H, (CH2) S , CH3, CH3-(CH2) S , O(CH2) S , CH3O OR CH3-(CH2) S O, - R46 representative (CH2) r benzylene or cyclohexylene, - B representing a linear or branched hydrocarbon chain, comprising 12 to 30 carbon atoms, and comprising at least one double bond, - s representing an integer from 1 to 18, - r representing an integer from 1 to 6, - 1 representing an integer ranging from 1 to 500, - u representing 0, 1, 2 or 3, - w representing 0 or 1, - z representing an integer ranging from 0 to 4.

9. A preparation method according to any one of the preceding claims, wherein y is equal to 3 or 4.

10. A method according to any one of the preceding claims, wherein L2 is selected from: - (CH2) t (L2-1), (L2-2),

11. A method according to any one of the preceding claims, wherein L2 represents:

12. A preparation method according to any one of the preceding claims, wherein the oxidant is selected from bis(trifluoroacetoxy)iodobenzene, bis(acetoxy)iodobenzene, poly[4-(diacetoxyiodo)styrene], hydroxybenziodoxole, and acetoxybenziodoxole.

13. A method according to any one of the preceding claims, comprising a step c), subsequent to step b), of purifying polyurethane foam (I), preferably by heating and / or under reduced pressure.

14. A method according to any one of the preceding claims, wherein the reaction between at least one polyoxamic acid and at least one polyol is carried out in the presence of a nonionic surfactant (IV).

15. A method according to the preceding claim wherein the surfactant (IV) is selected from: with : - R50 representing OH, CH3-(CH2)hO or O(CO)(CH2)hCH3 with h representing an integer from 0 to 3, - a, b, c, d, e, f and g being identical or different and independently representing an integer from 0 to 500.

16. A preparation method according to any one of the preceding claims carried out in a closed reactor under reduced pressure.

17. A preparation method according to any one of claims 1 to 15 carried out in an open reactor.

18. A preparation method according to any one of the preceding claims, wherein the polyurethane foam (I) is purified by a heating step and / or under reduced pressure.

19. Polyurethane foam obtained according to the preparation process according to any one of the preceding claims.

20. Polyurethane foam according to the preceding claim, having a density from 10 to 1000 kg.m³ 3 , preferably from 100 to 300 kg.m 3 , density being the ratio of the mass of the foam measured with a scale, and the apparent volume of the foam determined by measuring the dimensions of the foam with a caliper.

21. Polyurethane foam according to claim 19 or 20 having cells with a diameter between 0.1 mm and 2 mm, preferably between 0.2 mm and 1.5 mm, the diameter being measured using a scanning electron microscope at 50 Pa and 7.00 kV on cross-sections in the direction of expansion of the material.

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