Rigid polymer foams obtained by aza-michael addition

Abstract

The invention relates to a process for preparing a rigid or semi-rigid foam, comprising reacting, in the presence of a blowing agent: - at least one polyfunctional acrylate; and - at least one polyamine, wherein, in the reaction medium of step (E): (i) the polyfunctional acrylates comprise at least 3 acrylate functions; and (ii) the polyamines comprise from 5 to 8 N-H bonds present in primary or secondary amine functions.

Description

Description Title of the invention: Rigid polymer foams obtained by Michael's aza addition

[0001] The present invention relates to the field of polymer materials in the form of foams. More specifically, the invention relates to rigid or semi-rigid polymer foams having characteristics similar to those of foams based on cross-linked polyurethane (PUR) or cross-linked polyisocyanurate (PIR), but obtained by another synthesis method.

[0002] A polymer foam is a well-known type of material resulting from a cluster of gas bubbles trapped within a continuous network of polymer. The polymer forms the foam matrix and the walls of its structure, which contains numerous cavities (or cells). This type of material is well-established and allows for combining the advantages of the matrix polymer with those of the foam itself, notably enabling a reduction in density (resulting in lightweight materials), increased compressibility or a higher surface-to-volume ratio, or lower thermal conductivity. By modifying the type of gas trapped within the cells, the properties of the polymer foam can also be altered.

[0003] Among polymer foams of this type, polyurethane foams are a notable example, where the matrix polymer is most often a cross-linked polyurethane (PUR). These polyurethane foams are generally obtained by reacting polyisocyanates (typically containing 2 to 3 isocyanate groups -NCO) and polyols (typically containing more than 2 OH groups), the polyaddition of which forms the polyurethane that constitutes the foam walls. This polyaddition is generally carried out in the presence of a catalyst (for example, a tertiary amine, which promotes the deprotonation of the polyol).

[0004] Other polymer foams known from the prior art are polyisocyanurate (PIR) foams. These foams are similar to the polyurethane (PUR) foams described in the previous paragraph, but where the polymer constituting the walls is a modified polyurethane composed of The majority of the foam consists of isocyanurate structures, which generally provides greater rigidity and stability to the foam structure (in addition to improved fire resistance). The formation of PIR foam typically uses the same polyisocyanate and polyol reagents as those used for PUR foams, but with the addition of a catalyst that induces a trimerization reaction of isocyanates to isocyanurate. An isocyanurate, resulting from the trimerization of three isocyanates, has the following cyclic structure: where each of A1, A2 and A3 (usually identical) is a substituent, for example an alkyl group.

[0005] In the aforementioned PUR and PIR foams, foam formation is induced by the production of a gas during the polyurethane or polyisocyanurate formation reaction. To achieve this, water can be introduced into the reaction medium, resulting in the formation of CO2, which acts as a chemical blowing agent. To further increase expansion, a physical blowing agent is generally added, which generates additional gas bubbles in the polyurethane or polyisocyanurate formation medium due to the exothermic nature of the reaction. Such an additional physical blowing agent can be chosen from hydrocarbons, ethers, or, more advantageously, hydrofluoroolefins (HFOs) or hydrochlorofluoroolefins (HCFOs).

[0006] PUR and PIR foams are typically synthesized by mixing (i) a polyisocyanate, such as polymeric MDI (4,4'-diphenylmethylene diisocyanate); and (ii) a premix comprising: a polyol; one or more blowing agents; and one or more additives.

[0007] In particular, to allow optimal mixing of the polyol and the blowing agent in the premix, good incorporation of the bubbles forming in the reaction medium and then stabilization of the alveoli formed, a surfactant can advantageously be introduced into the premix, for example a silicone surfactant, such as a polyether-polysiloxane copolymer, suitable for ensuring both a role of emulsifier (making the polyol and the blowing agent compatible), of nucleating agent (allowing suitable incorporation of the gas bubbles forming) and of stabilization of the bubbles formed in the mixture, which optimizes the quality of the foam obtained in the end.

[0008] The aforementioned PUR and PIR foams prove to be of practical value. They are particularly well-suited as thermal insulation materials. They are especially effective when their cells contain a gas with low thermal conductivity: in this case, they provide better thermal insulation than other common insulators such as fiberglass. Furthermore, they can easily incorporate additives introduced into the foam formation process, allowing for enhanced performance, such as flame-retardant compounds, including halogenated or phosphorus-based ones.

[0009] However, in addition to these advantages, PUR and PIR foams have the drawback of requiring the use of polyisocyanates such as polymeric MDI during their synthesis. While these compounds offer advantages in terms of reactivity and cost, their use remains problematic, particularly regarding safety and their impact on health and the environment.

[0010] One object of the present invention is to provide a means of access to foams similar to the aforementioned PUR and PIR foams, which in particular allow to obtain performances similar to those of PUR and PIR foams, but without requiring the use of polyisocyanates.

[0011] To this end, the invention proposes a foam synthesis process using a particular Michael aza addition, making it possible to do away with the use of polyisocyanates and which proves to be suitable for the preparation of foams exhibiting performance similar to that of PUR and PIR foams.

[0012] More specifically, according to a first aspect, the present invention relates to a process for preparing a material in the form of a rigid or semi-rigid foam, comprising a step (E) in which the following are reacted in the presence of a blowing agent: - a polyfunctional acrylate or a mixture of several polyfunctional acrylates; and - a polyamine or a mixture of several polyamines, characterized in that, in the reaction medium of step (E): (i) the polyfunctional acrylates present comprise at least 3 acrylate functions; and (ii) the polyamines present comprise 5 to 8 NH bonds present in primary or secondary amine functions.

[0013] The acrylates present in the reaction medium of step (E) are said to be "polyfunctional" in that they include several acrylate functions.

[0014] Furthermore, the polyamines present in the reaction medium of step (E) are compounds bearing several amine functions, including at least two primary and / or secondary amine functions. They are characterized by the number of NH bonds present in the primary and / or secondary amine functions they comprise.

[0015] According to a particular embodiment, the polyfunctional acrylates present in the reaction medium of step (E) are compounds which preferably comprise from 3 to 7 acrylate functions, for example from 3 to 5 acrylate functions.

[0016] According to another embodiment, compatible with the preceding one, the polyamines present in the reaction medium of step (E) include preferably with 5 to 6 NH bonds present in primary or secondary amine functions.

[0017] According to a specific embodiment, the polyfunctional acrylates present in the reaction medium of step (E) can be compounds, referred to herein as "prepolymers," which are produced by a reaction between polyfunctional acrylates and polyamines. In this case, these prepolymers are generally produced in a step (E0), prior to step (E), where the prepolymers are prepared by contacting polyfunctional acrylates with a substoichiometric amount of polyamines.

[0018] The polyfunctional acrylates used in step (E0) are generally non-polymer compounds, and they preferably include 3 to 7 acrylate functions, for example 3 to 5 acrylate functions.

[0019] The polyamines used in step (E0) generally comprise 5 to 8 NH bonds, for example, 5 to 6 NH bonds, present in primary or secondary amine groups. The polyamines used in step (E0) are generally the same as those used in step (E), and the sequence of steps (E0) then (E) thus amounts to reacting the polyfunctional acrylates in two steps with the polyamines. However, according to another possible approach, the polyamines used in steps (E0) and then (E) can be different.

[0020] In another aspect, the invention also relates to materials in the form of rigid or semi-rigid foams obtained by implementing the aforementioned process. These foam materials, which can be obtained according to the process of the invention, typically have a density of less than 500 kg / m³ and a cell size of less than 500 microns, with a closed cell content typically above 50%.

[0021] The process of the invention implements in its step (E) (and optionally also in its preceding step (E0)) a Michael aza addition which is carried out rapidly and uses amine functions as Michael donors and acrylate functions (bearing a bond including an a,[3-unsaturated C=C-(C=O)-O) chain as a Michael acceptor (the non-bonding pair of the amine attacks the nucleophilic site of the acrylate, namely the electrophilic carbon of the C=C double bond which is in the beta position of the carbon of the electron-withdrawing C=O group, which leads to the formation of "aminoester" covalent bonds including an NCC-(C=0)-O chain ensuring a role similar to that of the urethane N-(C=0)-O covalent bonds formed in polyurethane foams).

[0022] The amine functions used in step (E) and / or (E0) also act as a basic proton-capturing compound, which eliminates the need for an additional basic catalyst and allows the reaction to be carried out under mild conditions.

[0023] Furthermore, the use of polyamines and polyfunctional acrylates, which are inherently highly reactive, according to the invention, leads to rapid and exothermic crosslinking suitable for use with physical blowing agents of the type used in PUR and PIR foams. The exothermic nature of the reaction also has the advantage of not requiring any external energy input (no heating in particular), which constitutes another significant benefit of the process, especially in terms of process costs.

[0024] The process of the invention also has the advantage of using polyamines and polyfunctional acrylates that are readily available commercially.

[0025] The work carried out by the inventors in connection with the present invention has now established that, with the specific functionalities employed according to the invention for polyfunctional acrylates (namely, with 3 to 5 acrylate groups per acrylate compound) and polyamines (namely, with 5 or 6 NH bonds present per amine compound), the reaction in step (E) makes it possible to obtain foams similar to PIR and PUR type foams. The functionalities employed according to the invention correspond to reagents having well-suited reactivities and leading to a particularly advantageous crosslinking density.

[0026] According to the invention, particularly interesting foams are obtained in particular when: - each of the polyfunctional acrylates present in the reaction medium of step (E) comprises exactly 3 acrylate functions or exactly 4 acrylate functions: and / or - Each of the polyamines present in the reaction medium of step (E) comprises exactly 5 NH bonds within an amine group (primary or secondary). In this context, and interestingly, the polyamines present in step (E) comprise: - two primary amine functions (monovalent function with the formula -NH2, containing two NH bonds); and - a single secondary amine function (divalent function of formula -NH- containing an NH bond).

[0027] In a particularly interesting way: - each of the polyfunctional acrylates present in the reaction medium of step (E) comprises exactly 3 acrylate functions or exactly 4 acrylate functions and each of the polyamines present in the reaction medium of step (E) comprises exactly 5 NH bonds present in a primary or secondary amine function.

[0028] The specific choice of functionalities of polyamines and polyfunctional acrylates according to the invention makes it possible, in particular, to achieve sufficient rigidity to prevent foam collapse, yet sufficiently low to allow foam expansion under the effect of blowing agents. It should be emphasized in this regard that the inventors' work has unexpectedly established that the optimal functionalities to be implemented using Michael's aza addition are distinct from those required for PUR or PIR type foams (for foams of this type, much lower functionalities are recommended, with polyols exhibiting on the order of 2 or 3 -OH and polyisocyanates with functionalities more in the order of 2.5-2.9).

[0029] However, and just as unexpectedly, it has now been highlighted by the inventors that the surfactants used for the synthesis PUR and PI R type foams proved to be well suited within the framework of the present invention, which is a result that nothing suggested.

[0030] Based on this, it appears that the process of the present invention constitutes an interesting alternative to prior art methods for preparing PUR and PIR foams, avoiding the use of polyisocyanates and thus simplifying the process. Furthermore, the process retains many of the advantages of those used for preparing PUR and PIR foams, in particular that it does not require the use of any additional solvent.

[0031] Various features and possible embodiments of the invention are described in more detail in the following paragraphs.

[0032] Multifunctional acrylates

[0033] Step (E) of the process of the invention specifically employs compounds bearing several acrylate functions.

[0034] An acrylate group has a C=C bond in the vicinal position of an electron-withdrawing C=O group. It is typically a monovalent group with the formula [CH2=CH-C(=O)-O-]-.

[0035] The compounds bearing multiple acrylate functional groups used in step (E) are referred to in this description as polyfunctional acrylates. The term "polyfunctional" as used in this description and in the claims refers to the presence of multiple acrylate functional groups in the compound. In addition to the acrylate functional group, a polyfunctional acrylate may optionally include functional groups other than acrylates, in which case it is both a polyfunctional compound (i.e., bearing multiple acrylate functional groups) and a "multifunctional" compound (i.e., bearing multiple types of functional groups).

[0036] Generally, in step (E) polyfunctional acrylates are used which are not multifunctional, namely which are only carriers of several acrylate functions on a hydrocarbon chain without other functional groups.

[0037] However, according to particular embodiments of the invention, it is not excluded that the polyfunctional acrylates used in step (E) may be multifunctional acrylates. According to this embodiment, the polyfunctional acrylates preferably comprise functional groups that do not interfere with the Michael aza addition reaction, and these groups are ultimately found in the material in the form of foam prepared in step (E).

[0038] Whatever their exact nature, the polyfunctional acrylates used in step (E) comprise between 3 and 5 acrylate functions.

[0039] According to a first particularly interesting embodiment, all the polyfunctional acrylates used in step (E) comprise at most 3 acrylate functions and at most 5 acrylate functions.

[0040] Step (E) may implement: - a single multifunctional acrylate comprising exactly 3, 4 or 5 acrylate functions, and more preferably comprising exactly 3 acrylate functions or exactly 4 acrylate functions; or - a mixture of several polyfunctional acrylates of this type (each of the polyfunctional acrylates in the mixture can independently contain 3, 4 or 5 acrylate functions and more preferably exactly 4 functions). By way of non-limiting examples of multifunctional acrylates usable according to the invention, the following multifunctional acrylates may be cited: - Pentaerythritol tetracrylaye (PETA), containing 4 acrylate functions, which corresponds to the following formula: - trimethylolpropane triacrylate (TMPTA - available notably under the trade name SR 351 from ARKEMA SARTOMER), containing 3 functions acrylates, which corresponds to the following formula:

[0041] Other interesting multifunctional acrylates include, but are not limited to: - dipentaerythritol pentaacrylate (CAS 60506-81-2) which contains 5 acrylate functions; - diTMPTA (CAS 94108-97-1) which contains 4 acrylate functional groups; or - SR 494 (ethoxylated version of PETA (Cas 144086-02-2), available notably in the form of the commercial product Ebecryl 50 (Allnex).

[0042] According to a second conceivable mode, step (E) can implement a mixture of polyfunctional acrylates where some of the polyfunctional acrylates present do not have exactly 3, 4 or 5 acrylate functions, but where the average number of acrylate functions in the polyfunctional acrylates of the mixture remains between 3 and 5 (advantageously between 3 and 4).

[0043] According to this particular method, the polyfunctional acrylates of step (E) are preferably in the form of a mixture comprising: (i) at least one polyfunctional acrylate comprising exactly 3, 4 or 5 acrylate functions; and (ii) at least one polyfunctional acrylate comprising a number of acrylate functions other than 3, 4 or 5, with a proportion between compounds (i) and (ii) such that the average number of acrylate functions in the polyfunctional acrylates of the mixture is between 3 and 5, preferably between 3 and 4.

[0044] A mixture of this type, usable according to the invention, comprises, for example, a mixture of pentaerythritol tetracrylae (PETA) mixed with tricyclodecane dimethanol diacrylate (TCDDA, available notably under the trade name Ebecryl 130 (Allnex)) comprising two acrylate functional groups, in proportions such that the average number of acrylate groups in the mixture remains between 3 and 5, preferably between 3 and 4. The formula of TCDDA is:

[0045] The "average number of acrylate functions" in the polyfunctional acrylates of a given polyfunctional acrylate mixture is calculated by the ratio of the total number of acrylate functions present in the mixture (in moles) to the total number of polyfunctional acrylate molecules in the mixture (in moles).

[0046] Polyamines

[0047] The polyamines used in step (E) are molecules bearing at least two primary and / or secondary amine groups. In other words, the polyamines of step (E) comprise several amine groups selected from primary amines, secondary amines, and mixtures of primary and secondary amines.

[0048] Typically, a polyamine used in step (E) does not include a tertiary amine group.

[0049] In this description, reference is made to amine groups in their unprotonated form. The polyamines used in step (E) are characterized by the number of NH bonds present, which refers to the number of covalent NH bonds in the primary (-NH2) and secondary (-NH-) amine groups in their unprotonated forms (and therefore not in deep forms (-NH3) + or -NH2 + -) which contains additional NH bonds). It is understood that the reference made here to amines in non-deep form concerns only the form of the amine to be considered for counting the number of NH bonds, which simply means that a primary amine function is present within the polyamine (namely a monovalent -NH2 group, deep or not in its -NH3 form). + ) is counted as 2 NH bonds; and a secondary amine (namely a divalent -NH- group, deep or not in its -NH2 form) +-,) is counted as 1 NH bond (and a tertiary amine is counted as 0 NH bonds, even if it is in its deep form). -E, in other words, the proton possibly bonded to the amine group is not counted when determining the number of NH bonds in the polyamine. That being said, and regardless of the formal counting method used in this description to describe the polyamines adapted according to the invention, it should be understood that, in practice, under the conditions of the process of the invention, the different amine groups of the polyamine can be independently in protonated or unprotonated form.

[0050] The polyamines used according to the invention comprise 5 to 6 NH bonds present in amine functions. These NH bonds may be present (in pairs) in primary amine functions (-NH2) and / or be the NH bond of a secondary amine (-NH-).

[0051] When the polyamine has 5 NH bonds, it advantageously comprises two primary amines and one secondary amine.

[0052] When the polyamine has 6 NH bonds, it advantageously comprises two primary amines and two secondary amines; or three primary amines.

[0053] As an example of a useful polyamine according to the invention, dipropylene triamine (DPTA) may be mentioned, which comprises 5 NH bonds (in two primary amine groups and one secondary amine group). Dipropylene triamine (DPTA) has the following formula: In this compound, the two primary amine groups -NH2 each include two NH bonds, and the central secondary amine group -NH- includes a single NH bond, for a total of 5 NH bonds in the molecule.

[0054] Particularly interesting results were observed within the scope of the invention when using DPTA as a polyamine in step (E). DPTA is especially advantageous when using PETA or TMTPA, as defined above, as polyfunctional acrylates.

[0055] Step (E)

[0056] The formation of the material in the form of foam in step (E) takes place by reacting the polyamine (or mixture of polyamines) and the polyfunctional acrylate (or mixture of polyfunctional acrylates) in the presence of a blowing agent activated during the formation of the material and which allows progressive expansion as the material forms which crosslinks under the effect of the reactions between the amine groups and the acrylate groups.

[0057] The reaction that takes place between a monoamine and monoacrylates in the context of Michael aza additions can be described as follows:

[0058] According to the invention, compounds bearing several amines and compounds bearing several acrylates are used, which leads to a multiplication of this type of reaction between the species present, which create covalent bonds of the aminoester type and progressively form a network of molecules cross-linked together of the polyaminoester type.

[0059] Polyamine (or a mixture of polyamines) and polyfunctional acrylate (or a mixture of polyfunctional acrylates) are generally introduced in substantially stoichiometric quantities of functions, namely with a molar ratio of the total quantity of acrylate functions contributed by polyfunctional acrylates to the total number of NH bonds contained in an amine group of the order of 1, for example between 0.8 and 1.2.

[0060] According to an interesting embodiment, step (E) is carried out by mixing the polyfunctional acrylate (or the mixture of polyfunctional acrylates) with a premix comprising: - the polyamine (or mixture of polyamines); and - the blowing agent.

[0061] This premix advantageously comprises an additional surfactant, in addition to the polyamine (or polyamine mixture) and the blowing agent. The primary role of this additional surfactant is to ensure compatibility between the polyamines and the blowing agent (emulsifying effect). Generally, like the surfactants used in the manufacture of PUR and PIR foams, the surfactants employed in the context of the present invention most often also act as nucleating agents (allowing for the proper incorporation of air bubbles during mixing and of the gas bubbles forming) and as a stabilizer of the bubbles formed in the mixture, thereby optimizing the final quality of the foam.

[0062] The premix comprising the polyamines and the blowing agent, and advantageously an additional surfactant, may also contain additives which will be found in the structure of the foam obtained in the end.

[0063] The premix is ​​preferably free of additional solvent.

[0064] Thus, according to an interesting embodiment, step (E) is carried out by bringing into contact: - a premix comprising: the polyamine (or mixture of polyamines); the blowing agent, and optionally a surfactant plus possibly other additives; and - polyfunctional acrylate (or a mixture of polyfunctional acrylates)

[0065] According to an alternative embodiment, step (E) can be carried out by bringing into contact: - a premix comprising: the polyfunctional acrylate (or the mixture of polyfunctional acrylates); the blowing agent, and optionally a surfactant plus possibly other additives; and - the polyamine (or the mixture of polyamines).

[0066] The blowing agent

[0067] The blowing agent ensuring foam expansion during step (E) can be any compound that does not interfere with the Michael aza addition reaction and is capable of forming gas bubbles within the reaction medium under the conditions of step (E). Given the exothermic nature of the reaction in step (E), the blowing agent used can typically be chosen from among the physical blowing agents commonly employed in the preparation of PUR and PIR foams. For example, the blowing agent can be chosen from hydrocarbons, which vaporize upon increasing temperature. An interesting blowing agent according to the invention is pentane (particularly n-, iso-, and cyclopentane, as well as mixtures thereof). Cyclopentane is especially suitable. Other useful blowing agents according to the invention include ethers, hydrofluoroolefins (HFOs), and hydrochlorofluoroolefins (HCFOs).

[0068] During step (E), it is preferred that the molar ratio of blowing agent / polyamine be between 0.20 and 1.20, preferably between 0.40 and 0.90.

[0069] Furthermore; during step (E), it is preferred that the blowing agent / polyfunctional acrylate molar ratio be between 0.1 and 0.70, preferably between 0.25 and 0.45.

[0070] The surfactant

[0071] The surfactant that can advantageously be added to the premix comprising the polyamines and the blowing agent may, in particular, be a silicone surfactant, such as a polyether-polysiloxane copolymer).

[0072] Furthermore, it is preferred that the surfactant / polyamine molar ratio be between 0.01 and 0.05; preferably between 0.02 and 0.04.

[0073] Possible additives

[0074] The premix in step (E) may optionally include other additives to give the foams additional performance characteristics. These additives may, for example, be flame-retardant compounds, particularly halogenated and / or phosphorus-containing compounds.

[0075] EXAMPLE

[0076] Step 1: Preparing a premix The following compounds were mixed under mechanical stirring at a temperature of 23°C: 6.89 g of DPTA (DPTE or Baxxodur EC 110 marketed by BASF) 0.21 g of surfactant (polyether polysiloxane Tegostab B84501 marketed by Evonik) 2.17 g of cyclopentane type blowing agent (sold by Dehon Group).

[0077] Step 2: Michael's aza addition To the premix formed above, 23.11 g of PETA (SR295 marketed by ARKEMA SARTOMER) was added in one go. The foam formed in 20 seconds without any external energy input. The foam exhibits a glass transition temperature of 72°C. The density was measured at 150 ± 10 kg / m³. 3 After observation under an optical microscope, the size of the cells is measured at 150±40pm.

Claims

Demands

1. A process for preparing a material in the form of a rigid or semi-rigid foam, comprising a step (E) in which the following are reacted in the presence of a blowing agent: - a polyfunctional acrylate or a mixture of several polyfunctional acrylates; and - a polyamine or a mixture of several polyamines, characterized in that in the reaction medium of step (E): (i) the polyfunctional acrylates present comprise at least 3 acrylate functions, preferably 3 to 7 acrylate functions; and (ii) the polyamines present comprise 5 to 8 NH functions present in primary or secondary amine functions, preferably 5 to 6 NH functions present in primary or secondary amine functions.

2. A method according to claim 1 wherein each of the polyfunctional acrylates used in step (E) comprises at least 3 acrylate functions and at most 5 acrylate functions.

3. A process according to claim 2 wherein each of the polyfunctional acrylates present in the reaction medium of step (E) comprises exactly 3 acrylate functions or exactly 4 acrylate functions.

4. A process according to claim 3 wherein the polyfunctional acrylates present in the reaction medium of step (E) are or comprise: - pentaerythritol tetraacrylate (PETA).

5. A process according to claim 3 wherein the polyfunctional acrylates present in the reaction medium of step (E) are or comprise: - trimethylolpropane triacrylate (TMPTA).

6. A process according to claim 1 wherein the polyfunctional acrylates of step (E) are in the form of a mixture comprising: (i) at least one polyfunctional acrylate comprising exactly 3, 4 or 5 acrylate functions; and (ii) at least one polyfunctional acrylate comprising a number of acrylate functions other than 3, 4 or 5, with such a proportion between compounds (i) and (ii) that the average number of acrylate functions in the polyfunctional acrylates of the mixture is between 3 and 5, preferably between 3 and 4.

7. A process according to claim 1 wherein the polyfunctional acrylates present in the reaction medium of step (E) are prepolymers from a step (EO), prior to step (E), wherein said prepolymers are prepared by contacting polyfunctional acrylates with a substoichiometric amount of polyamines.

8. A process according to any one of claims 1 to 7 wherein each of the polyamines present in the reaction medium of step (E) comprises exactly 5 or 6 NH bonds present in an amine function.

9. A process according to claim 8 wherein each of the polyamines present in the reaction medium of step (E) comprises exactly 5 NH bonds present in an amine function.

10. Process according to claim 9 wherein the polyamines present in the reaction medium of step (E) are or include: dipropylene triamine (DPTA).

11. The method according to claim 10 wherein step (E) is carried out by bringing into contact: - a premix comprising: the polyamine (or mixture of polyamines); and a blowing agent, and optionally a surfactant; and possibly other additives; and - polyfunctional acrylate (or a mixture of polyfunctional acrylates).

12. The method according to claim 10 wherein step (E) is carried out by bringing into contact: - a premix comprising: the polyfunctional acrylate (or the mixture of polyfunctional acrylates); and a blowing agent, and optionally a surfactant; and possibly other additives; and - the polyamine (or the mixture of polyamines).

13. Material in the form of a rigid or semi-rigid foam, obtained by implementing the process of any one of claims 1 to 10.

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