Synthesis process for bio-based superabsorbent polymers (SAPs)

Abstract

The present invention relates to the field of superabsorbent polymers (SAP) and more particularly to a process for the synthesis of a bio-based superabsorbent polymer (SAP) having a water absorption capacity of a material (WAC) greater than 50, said process comprising in particular a step of polymerization of itaconic acid followed by a step of post-crosslinking of the polymer obtained.

Description

Title of the invention: Process for the synthesis of bio-sourced super absorbent polymers (SAP) Technical field

[0001] The invention relates to the field of super absorbent polymers and more particularly relates to a process for synthesizing a biosourced super absorbent polymer (SAP) having a water absorption capacity of a material (WAC) greater than or equal to 50, said process comprising in particular a step of polymerization of itaconic acid followed by a step of post-crosslinking of the poly(itaconate) obtained. State of the art

[0002] Super absorbent polymers (SAPs) are polymers with high water absorption and water retention capacity relative to their mass. These are therefore particularly useful in many applications requiring the absorption or retention of water. For example, in the field of agriculture, SAPs can retain water in the soil and improve plant irrigation. In the field of hygiene products, SAPs can absorb large quantities of liquid, which is particularly useful for products such as diapers. Finally, SAPs also find numerous outlets in the industrial field, for example in the design of sealing cables, but also for controlling humidity in packaging. Given the remarkable properties of SAPs, many applications are therefore conceivable.

[0003] Three types of SAP can be cited, namely SAPs of natural, semi-synthetic and synthetic origin. SAPs of natural origin are exclusively composed of natural polymers, for example cellulose or chitosan. Semi-synthetic SAPs are based on natural polymers mixed with synthetic SAPs. Finally, synthetic SAPs are derived from petroleum-based monomers such as acrylic acid or acrylamide. However, the latter can be particularly toxic and therefore not suitable for certain applications. In addition, synthetic SAPs are not biodegradable and therefore not compostable. Finally, being derived from the petrochemical industry, their production is very expensive in terms of natural resources and not very ecological.

[0004] There is therefore a need for new super absorbent polymers of natural origin having a water absorption capacity (WAC) of at least 50. Among the bio-sourced, non-toxic monomers, itaconic acid is of great interest given its properties.

[0005] It is already known from the prior art, for example patent FR 3029525, methods synthesis of SAP from itaconic acid. However, there is no known synthesis process from itaconic acid that makes it possible to obtain an SAP with a high water absorption capacity (WAC), namely a WAC greater than or equal to 50. Indeed, the low molar masses of itaconic acid homopolymers and the low yields for obtaining poly(itaconates) do not make it possible to obtain an SAP with the desired properties.

[0006] Although the prior art teaches us the addition of so-called internal crosslinker during the polymerization step, for example polyethylene glycol diacrylate or bis-acrylamide, but also the addition of activators, such as N,N-Dimethylethanolamine, making it possible in particular to increase the molar masses of itaconic acid homopolymers. Biosourced SAPs having a WAC greater than or equal to 50 are not known.

[0007] To meet this need, the invention proposes a process for synthesizing an SAP from itaconic acid comprising, in addition to the polymerization step, a post-crosslinking step to obtain a biosourced SAP having the desired properties, namely a high WAC, greater than or equal to 50. Summary of the invention

[0008] Thus, the invention relates to a process for synthesizing a bio-sourced super absorbent polymer (SAP) having a WAC of at least 50, said process comprising the following steps: a. homopolymerization of itaconic acid or copolymerization of itaconic acid and at least one monomer chosen from a monomeric or oligomeric water-soluble monomer, said monomer being monofunctional or polyfunctional, with at least one base in water, b. post-crosslinking of the homopolymer or copolymer obtained in the previous step with at least one crosslinker carrying at least two groups reactive with the acid functions of the homopolymer or copolymer obtained in the previous step.

[0009] This first step of polymerization of itaconic acid thus makes it possible to obtain polymers (or poly(acid)) comprising numerous carboxylic acid groups of particular interest during the post-crosslinking step. The post-crosslinking step then comprises the addition of at least one crosslinking agent with the itaconic acid polymers obtained during the polymerization step, the latter carrying groups capable of reacting with said carboxylic acid groups, allowing the synthesis of SAPs having the desired properties.

[0010] The homopolymerization or copolymerization step advantageously comprises the addition of an initiator and an activator, said activator making it possible to activate the primer so that it decomposes more quickly.

[0011] According to a particularly preferred subject, the initiator is potassium persulfate or ammonium persulfate, and the activator is MMA^W'-tetramethylcthylcthylcncdiaminc, also called TMEDA.

[0012] To improve and optimize the synthesis and the desired final properties of SAP, the activator / initiator molar ratio is preferably between 0.1:1 and 1:1.

[0013] The polymerization step may therefore be a homopolymerization of itaconic acid, that is to say a polymerization with only itaconic acid. Alternatively, the polymerization step may be a copolymerization of itaconic acid and at least one other monomer distinct from itaconic acid. Preferably, the co-monomer is chosen from a monomeric or oligomeric water-soluble monomer, which may be monofunctional or polyfunctional.

[0014] When this polymerization step comprises the addition of a co-monomer, this is advantageously a biosourced monomeric carboxylated vinyl monomer or a biosourced oligomeric carboxylated vinyl monomer.

[0015] More preferably, the monomeric carboxylated vinyl monomer is the monomer of formula Ia or Ib, hereinafter respectively represented [Chem 1] and [Chem 2].

[0016] [Chem.l] CH2=CH--R

[0017] [Chem.2] R'--CH=CH--R

[0018] Particularly preferably, the monomeric carboxylated vinyl monomer is selected from acrylic acid, methacrylic acid, crotonic acid, muconic acid, sorbic acid, α-Aceto acrylic, citraconic acid, mesaconic acid, aconitic acid, vinyl sulfonic acid, vinyl phosphoric acid, vinyl amine, and allyl amine.

[0019] According to another object, the co-monomer is a polyfunctional oligomeric carboxylated vinyl monomer, this is then advantageously a monomer of formula IIa or IIb, hereinafter respectively represented [Chem 3] and [Chem 4].

[0020] [Chem.3] HOX HO, ¥ ¥ 0'!

[0021] [Chem.4]

[0022] More preferably, the polyfunctional oligomeric carboxylated vinyl monomer is chosen from polyitaconate, polycitraconate, and polymesaconate, even more preferably polyitaconate.

[0023] This step of polymerization of itaconic acid further comprises the addition of a base, this being preferentially chosen from NaOH, KOH, NH40H as well as their combination.

[0024] Preferably, the itaconic acid monomer has a mass concentration of between 30% and 150%.

[0025] Once the polymerization is complete, these itaconic acid or poly(itaconate) polymers obtained are then crosslinked by an additional post-crosslinking step to increase the water retention capacity (WAC) of the super absorbent polymer.

[0026] For this purpose, post-crosslinking is carried out by means of at least one crosslinker. Preferably, to optimize the reaction, the crosslinker is present between 0.5 and 20 mol% relative to the itaconic acid, more preferably between 1 and 10 mol%.

[0027] According to a preferred object, the crosslinking agent comprises at least one reactive group, this being chosen from the epoxy, vinyl ether, [3-hydroxyalkylamide, hydroxy ethyl] group

[0028]

[0029]

[0030]

[0031]

[0032]

[0033]

[0034]

[0035]

[0036]

[0037]

[0038]

[0039] amide, and oxazoline. More preferably, the epoxy group is the compound of formula Ilia or Illb, hereinafter respectively represented [Chem 5] and [Chem 6]. [Chem. 5] [Chem. 6] Particularly preferably, the crosslinker used is a polyglycerol poly-glycidyl ether, also known as DENACOL®, for example DENACOL® EX-521 or DENACOL® EX-314. The crosslinking step may also comprise the addition of at least one biopolymer carrying acid functions, preferably carboxylic acid groups, this having the effect of modulating the physicochemical properties of the SAPs. More preferably, this biopolymer is chosen from alginates, hyaluronic acid, glycosaminoglycans (GAG), proteoglycans, glycoproteins, pectins, and oxidized celluloses. According to a variant of the invention, the process may comprise an additional precipitation step after step a) of polymerization, to obtain the itaconic acid polymers in powder form. In this context, the precipitant is preferably a solvent chosen from acetone, ethanol, and l-methoxy-2-propanol. Other features and advantages will emerge from the detailed description of the invention and the examples which follow. Detailed description of the invention Definition For the purposes of the invention, the term “itaconic acid” means the molecule represented by the following formula [Chem 7]. [Chem. 7] For the purposes of the invention, the term "poly(acid)" means a polymer obtained by polymerization of an acid, for example itaconic acid.

[0040] For the purposes of the invention, the term "activator" means a molecule having at least two amine functions. It may preferably be N,N,N',N' -tetramethylethylenediamine or TMEDA, of formula [Chem 8].

[0041] [Chem. 8] ch3

[0042] For the purposes of the invention, the term “initiator” means a chemical molecule capable of generating radicals by thermal, photochemical or redox activation, for example potassium persulfate or ammonium persulfate.

[0043] By "crosslinker" in the sense of the invention, we mean a chemical molecule capable of crosslinking, that is to say of forming a three-dimensional network by the creation of chemical bonds between the macromolecular chains. Preferably, the crosslinker carries a reactive group with acid functions, more preferably the crosslinker is a polyglycerol polyglycidyl ether, for example DENACOL®, such as DENACOL® EX-521 or DENACOL® EX-314.

[0044] By "biosourced" within the meaning of the invention, we mean a molecule (or a set of molecules) obtained by extraction from biomass (for example: cellulose) or obtained by reactions applied to biomass (for example: glycerol from the esterification of triglycerides).

[0045] Method according to the invention

[0046] The present invention therefore relates to a process for synthesizing a biosourced super absorbent polymer (SAP) having a WAC of at least 50 comprising the following steps: a. Homopolymerization of itaconic acid or copolymerization of itaconic acid and at least one monomer chosen from a water-soluble monomeric or oligomeric, monofunctional or polyfunctional monomer, with at least one base in water, b. Post-crosslinking of the homopolymer or copolymer obtained in the previous step with a crosslinker carrying at least two groups reactive with the acid functions of the homopolymer or copolymer obtained in the previous step.

[0047] The first step therefore consists of polymerizing or copolymerizing itaconic acid, in water, partially or totally with various bases, said bases being preferentially chosen from NaOH, KOH, NH4OH, and their combination.

[0048] According to an object of the invention, the polymerization is a copolymerization. In this context, the comonomer is not itaconic acid, preferably the comonomer is then an unsaturated, biosourced comonomer copolymerizable with itaconic acid. Preferably, said comonomer carries acid groups to ensure both its hydrophilic and crosslinkable character during the post-crosslinking step.

[0049] These comonomers can be used together or separately. Preferably, the comonomer is chosen from a monomeric or oligomeric, monofunctional or polyfunctional water-soluble monomer, and their combination.

[0050] Several types of comonomers can thus be used; they can be monofunctional or polyfunctional monomeric, or monofunctional or polyfunctional oligomeric. According to a particularly preferred subject of the invention, the comonomer is a biosourced monofunctional carboxylated vinyl monomer or a biosourced polyfunctional carboxylated vinyl monomer. More preferably, the comonomer is a monofunctional carboxylated vinyl monomer, even more preferably a monomer of formula [Chem 1] or [Chem 2] represented below.

[0051] [Chem.l] CH2=CH--R

[0052] [Chem.2] R'--CH=CH--R

[0053] The groups R and R' represented above may be identical or different and are hydrophilic or water-dilutable groups carrying heteroelements such as O, N, S, P.

[0054] Even more preferably, the co-monomer is a monofunctional carboxylated vinyl monomer chosen from one of the co-monomers listed in Table 1 below.

[0055] [Tableauxl] Name STRUCTURE Acrylic acid OH Ï 0 Methacrylic acid ,QH Crotonic acid ,OH z TQ Muconic acid o HO ï Sorbic acid G . .. ... À PH a-Aceto acrylic / G Citaronic acid Ch. -GH UT HO-CU. Mesaconic acid O s À. ..OH HU - f 0 Aconitic acid HU „0 HO. n '9 f 0 V 0 1 A il KH HO- ■-■■■■ -PW ^;Loh Cts- TrW&' Vinyl Sulfonic acid A Pli Vinyl phosphoric acid 'JH G Vinyl amine N'“Kj FL With Rt and. R2 ~ H; H Alkyi Allyl amine s'—

[0056] According to another object of the invention, the co-monomer may be a monomer polyfunctional carboxylated vinyl. They can be of the poly(itaconate) type below represented [Chem 3] or of the polyisomer type of itaconate, for example polyci- traconate or polymesaconate, or of the polymuconic type represented below [Chem 4].

[0057] [Chem.3] Hb

[0059] Group A being a biosourced polyester or polyether oligomer with n between 0 and 100, more preferably between 2 and 20.

[0060] By way of example, the polyester may be obtained by non-stoichiometric polycondensation of a diacid and an excess diol making it possible to obtain an oligoester comprising at least one hydroxyl group, or of a diacid and an excess di-epoxy making it possible to obtain an oligoester comprising at least one epoxy group. The functionalization of these oligoesters may be carried out, according to the knowledge of a person skilled in the art, for example by the so-called “one pot” method, by adding either itaconic anhydride (for hydroxy oligoesters) or itaconic acid (for epoxy oligoesters).

[0061] Polyether diols or polyether polyols may also be used, such as polyglycerol, for example prepared by polyetherification of bio-sourced diol (such as butane diol). These hydroxy-terminated polyethers may be functionalized with itaconic anhydride.

[0062] Epoxy terminated polyethers can also be used such as polyglycidyl ether of glycerol, sorbitol, diglycidyl ether of 1,3-propane, 1,4-butane, isorbide, after functionalization with itaconic acid.

[0063] Thus, the polymerization step of the process according to the invention is either a homopolymerization, that is to say a polymerization with itaconic acid alone, or a copolymerization, that is to say the polymerization of itaconic acid in the presence of comonomers. The itaconic acid, after solubilization in basic water, is polymerized in water, at a mass concentration between 30 and 150% by mass.

[0064] This polymerization step is preferably carried out in the presence of an initiator and an activator. Said initiator is advantageously chosen from potassium persulfate and ammonium persulfate, more preferably between 0.5 and 5 mol% relative to the monomer. The activator is preferably N,N,N',N'-tetramethylethylenediamine (TMEDA).

[0065] According to another preferred object, the activator:initiator molar ratio is between 0.1:1 and 1:1.

[0066] The polymerization step is also preferably carried out at a temperature between 20°C and 100°C for a duration between 30 minutes and 7 hours.

[0067] When the polymerization is a co-polymerization, variable quantities of comonomers of formula [Chem 1] or [Chem2] and / or of formula [Chem 3] or [Chem4] can be used, these are preferably between 0 and 20 mol%.

[0068] According to a particularly preferred embodiment, the initiator is ammonium persulfate and the activator is N,N,N',N'-tetramethylethylenediamine (TMEDA) of formula [Chem 8].

[0069] For example, rhomopolymerization as well as copolymerization are preferably carried out in the presence of ammonium persulfate at 1.3 mol%, TMEDA at a ratio of 0.5:1 at 60°C for 3.5 hours.

[0070] According to a variant of the invention, the process may further comprise a precipitation step after the polymerization step. Thus, at the end of the polymerization, the polymer obtained is then preferentially precipitated in a solvent, such as acetone, ethanol or l-Methoxy-2-propanol to obtain the polymer in powder form.

[0071] Once the polymerization step is complete, with or without a precipitation step, the polymer obtained is intended to be crosslinked to obtain an SAP having the desired properties.

[0072] When the process according to the invention comprises an additional precipitation step, making it possible to obtain a polymer in powder form, the post-crosslinking step comprises a first additional step of solubilization in aqueous media of the polymer in powder form. Conversely, the post-crosslinking is carried out directly from the polymer obtained at the end of the polymerization step a).

[0073] The second step of the process according to the invention therefore aims to crosslink the polymers obtained during the first step (or poly(acid)) in the presence or absence of biopolymers also carrying acid functions. Thus, according to an object of the invention, the crosslinking step advantageously comprises the addition of at least one biopolymer carrying acid functions.

[0074] The biopolymers used can be of different types, either they are biopolymers directly carrying acid functions, for example alginates, hyaluronic acid, Glycosaminoglycans (GAG), proteoglycans, glycoproteins, or pectins, or they are modified biopolymers, known to those skilled in the art, carrying acid groups such as oxidized cellulose.

[0075] Thus, preferably, the biopolymer is chosen from alginates, hyaluronic acid, glycosaminoglycans (GAG), proteoglycans, glycoproteins, pectins, and oxidized celluloses.

[0076] These biopolymers carrying acid functions will also participate in the post-crosslinking of the itaconic polyacid, itself carrying acid groups. The use of these biopolymers carrying acid functions makes it possible in particular to modulate the physicochemical properties of the SAPs, to increase the final WAC, and therefore to diversify their applications.

[0077] Indeed, post-crosslinking requires compounds carrying groups reacting with the acid functions of the polymer obtained during the first step; such compounds are preferably crosslinkers.

[0078] Thus, according to a particularly preferred object of the invention, the reactive group carried by the crosslinking agent is chosen from the epoxy, vinyl ether, hydroxy ethyl amide, and oxazoline group.

[0079] Given his general knowledge, the person skilled in the art knows how to choose the crosslinking agent comprising or not these groups according to the particular reactivities sought and the post-crosslinking conditions (temperature etc.)

[0080] However, according to a particularly preferred object, the crosslinker comprises as reactive group an epoxy group, given its reactivity with acid functions at medium temperature and their cost.

[0081] More preferably, the epoxy group is the compound of formula Ilia or Illb, with x greater than or equal to 2, hereinafter respectively represented [Chem 5] and [Chem 6].

[0082] [Chem.5]

[0083] [Chem.6]

[0084] By way of example, the synthesis of biosourced oligodiepoxys or polyepoxys (V) is carried out according to the non-stoichiometric polycondensation process of a 100% biosourced monomeric di- or polyepoxy (IIIA) or of an oligomeric di- or polyepoxy (IIIB) with either biosourced monomeric di- or polyacids (IVA) or oligomeric di- or polyacids (IVB), represented below.

[0085] [Chem.9] / R ......p.. CG3H j ( (Va ) K [ 77---4-------F (H h) p4__ C0 ., h ^ (IVg) \ HAS / \ / xx with x- 2 Excess . (V)

[0086] The compound of formula Ilia may be, for example, a di or polyglycidyl ether of glycerol, sorbitol, a diglycidyl ether of butane diol, propane diol, in de isosorbide.

[0087] The biosourced polyacid of formula (IVa) is very preferably a poly(itaconate) obtained from itaconic acid.

[0088] The compound of formula (V) can be obtained according to Flory's law, by playing on the excess of monomeric (Ilia) or oligomeric (Illb) diepoxy compared to the oligomeric di- or poly acids (IVa, IVb). The following reaction illustrates the reaction between a monomeric diepoxy and a monomeric diacid, which makes it possible to vary the distance between the two epoxy groups and therefore the physicochemical characteristics of the SAPs obtained.

[0089] [Chem. 10] rs

[0090] Even more preferably, the crosslinker used is DENACOL of formula [Chem 11].

[0091] [Chem. 11] V ' pn OH m S 4-0

[0092] The crosslinker is preferably present between 0.5 and 20 mol% relative to the itaconic acid, more preferably between 1 and 10 mol%.

[0093] The post-crosslinking step may also comprise the addition of a catalyst, this being present between 0 and 5 mol% relative to the crosslinking agent. The catalysts used may be water-soluble tertiary amines; or in basic media may be, for example, NaOH or KOH with a pH > 7. When a catalyst is added, the medium is preferably brought to 60°C for 30 min with stirring before extending the post-crosslinking in a closed container in the oven at 60°C.

[0094] A super absorbent polymer having a WAC of at least 50 is then obtained.

[0095] The absorbent efficiency of the super absorbent polymers synthesized according to the process of the invention can be evaluated by the water absorption capacity of a material or WAC (Water Absorption Capacity).

[0096] The WAC is therefore the water absorption capacity of a material, this is expressed in grams of water per gram of sample. The determination of WAC is carried out according to different standards depending on the nature of the material tested (textile, construction material, plastic). The standard relating to plastics is the NF EN ISO 62 / ASTM D570 standard.

[0097] In particular, the method concerning super absorbent polymers consists of introducing a known mass (ml) of dry polymer into 500 times the volume of water of ml and leaving the polymer to absorb the water for 24 hours. Then the gel obtained is filtered and then weighed (m2).

[0098] The WAC is calculated according to the formula below.

[0099] [Math.l] WAC = ^-mi

[0100] The invention is now illustrated by non-limiting examples of the method according to the invention and by results. Examples

[0101] Example 1 - Homopolymerization of itaconic acid

[0102] A solution is prepared with 150mL of distilled water and 46.15g of sodium hydroxide. This is prepared in an ice bath to avoid excessive heat. Itaconic acid (150g) is then added to the sodium hydroxide solution for neutralization. This step is also carried out in an ice bath. The resulting mixture is introduced into a reactor and placed under nitrogen bubbling for 30min, the time to raise the temperature to 60°C. Potassium persulfate K2S2O8 (4.05g, solid) and TMEDA (1.74g, liquid) are introduced into the reactor to initiate polymerization. Stirring is set at 250 rpm. After 3h30 of synthesis, the medium is very viscous, and mechanical stirring is no longer effective.225mL of water are then introduced to facilitate the removal of the reactor and a temperature of 60°C with stirring at 250rpm is maintained while observing the decrease in viscosity to allow dropwise precipitation in the ethanol for a water / ethanol ratio of 1 / 10.

[0103] The polymer obtained is then dried in an oven. The molar mass obtained is 37000 g.mol-1.

[0104] Example 2 - Copolymerization of itaconic acid

[0105] A solution is prepared with 10 mL of distilled water and 2.801 g of sodium hydroxide. This is prepared in an ice bath to avoid excessive heat. Itaconic acid (9.110 g; 0.070 moles) is then added to the sodium hydroxide solution for neutralization. This step is also carried out in an ice bath. The resulting mixture is introduced into a reactor, acrylic acid (0.890 g; 0.012 moles) is added and placed under nitrogen bubbling for 30 min, the time to raise the temperature to 80°C. Potassium persulfate K2S208 (0.270 g, solid) and TMEDA (0.124 g, liquid) are introduced into a flask to initiate polymerization. After 3 hours of synthesis, the medium is very viscous, and stirring is no longer effective. 15mL of water are then introduced to facilitate the removal of the flask and a temperature of 60°C with stirring is maintained for the time to observe the decrease in viscosity to allow dropwise precipitation in ethanol for a water / ethanol ratio of 1 / 10.

[0106] The polymer obtained is then dried in an oven. The molar mass obtained is 18000 g.mol-1.

[0107] Example 3 - Post-crosslinking of the homopolymer obtained according to example 1

[0108] 5 g of a poly(itaconate) homopolymer according to Example 1 are introduced into a 50 mL flask. 10 mL of distilled water is then added to the flask. The mixture is dissolved for 1 hour under magnetic stirring at 60°C. The DENACOL® EX-314 crosslinking agent is introduced into the flask at a level of 0.246 g, stirring and the temperature are maintained for 30 min to ensure good homogeneity of the mixture. Then, the reaction mixture is poured into silicone molds which are placed in a crystallizing dish equipped with a beaker filled with distilled water. The crystallizing dish is wrapped in aluminum film and placed in an oven for 48 hours at 60°C. The gels thus obtained are lyophilized for 12 hours to eliminate traces of residual water.

[0109] The SAP then obtained has a WAC of 93.

[0110] Example 4 - Post-crosslinking of the copolymer obtained according to Example 2

[0111] 5 g of a sodium poly(itaconate) homopolymer with a molar mass 18,000 g.mol-1 are introduced into a 50 mL flask. 10 mL of distilled water are then added to the flask. The whole is solubilized for 1 h under magnetic stirring at 60°C. The crosslinking agent DENACOL EX-314 is introduced into the flask at a level of 0.493 g, stirring is maintained for 30 min to ensure good homogeneity of the mixture. Then, the reaction mixture is taken into syringes which are placed in an oven for a period of 15 h at 60°C.

[0112] The SAP then obtained has a WAC of 72.

Claims

Claims

1. A process for synthesizing a bio-based super absorbent polymer (SAP), said SAP having a water absorption capacity (WAC) of at least 50, said process comprising the following steps: a. Homopolymerization of itaconic acid or copolymerization of itaconic acid and at least one monomer selected from a monomeric or oligomeric water-soluble monomer, said monomer being monofunctional or polyfunctional, with at least one base in water, b. Post-crosslinking of the homopolymer or copolymer obtained in the preceding step with at least one crosslinker carrying at least two groups reactive with the acid functions of the homopolymer or copolymer obtained in the preceding step.

2. Synthesis process according to the preceding claim, characterized in that the homopolymerization or copolymerization step also comprises the addition of an initiator and an activator.

3. Synthesis process according to the preceding claim, characterized in that the initiator is potassium persulfate or ammonium persulfate, and the activator is N,N,N',N' -tetramethylethylenediamine.

4. Synthesis process according to claim 2 or 3, characterized in that the activator / initiator molar ratio is between 0.1:1 and 1:

1.

5. Synthesis process according to one of the preceding claims, characterized in that the reactive group carried by the crosslinker is chosen from the epoxy, vinyl ether, hydroxy ethyl amide, and oxazoline group.

6. Synthesis process according to the preceding claim, characterized in that the epoxy group is the compound of formula: "y | 'or \ X

7. ; o 4 Synthesis process according to one of the preceding claims, characterized the crosslinker is polyglycerol polyglycidyl ether.

8. Synthesis process according to one of the preceding claims, characterized in that the crosslinker is present between 0.5 and 20 mol% relative to the itaconic acid, preferably between 1 and 10 mol%.

9. Synthesis process according to one of the preceding claims, characterized in that the crosslinking step also comprises the addition of at least one biopolymer carrying acid functions.

10. Synthesis process according to the preceding claim, characterized in that the biopolymer is chosen from alginates, hyaluronic acid, glycosaminoglycans (GAG), proteoglycans, glycoproteins, pectins, oxidized celluloses.

11. Synthesis process according to one of the preceding claims, characterized, the co-monomer of step a) is a biosourced monomeric carboxylated vinyl monomer or a biosourced oligomeric carboxylated vinyl monomer.

12. Synthesis process according to the preceding claim, characterized in that the monomeric carboxylated vinyl monomer is the monomer of formula: CH2=CH---R, or R'--CH=CH--R

13. Synthesis process according to one of claims 11 or 12, characterized in that the monomeric carboxylated vinyl monomer is chosen from acrylic acid, methacrylic acid, crotonic acid, muconic acid, sorbic acid, α-Aceto acrylic, citraconic acid, mesaconic acid, aconitic acid, vinyl sulfonic acid, vinyl phosphoric acid, vinyl amine, and allyl amine.

14. Synthesis process according to claim 11, characterized in that the oligomeric carboxylated vinyl monomer is the monomer of formula: Or

15.

16.

17. Synthesis process according to claim 11 or 14, characterized in that the oligomeric carboxylated vinyl monomer is chosen from polyitaconate, polycitraconate, and polymesaconate. Synthesis process according to one of the preceding claims, characterized in that the base of step a) is chosen from NaOH, KOH, NH4OH and their combination. Synthesis process according to one of the preceding claims, characterized in that the mass concentration of itaconic acid is between 30% and 150%.