Photocrosslinkable copolyesters and method for obtaining same by copolymerisation

Abstract

The present invention relates to a method for preparing a photocrosslinkable copolyester, comprising a step of polycondensation of glycerol with a dicarboxylic acid monomer and at least one itaconic crosslinking agent chosen from itaconic acid and / or itaconic anhydride, in the presence of a stabilising agent. The invention also relates to the corresponding photocrosslinkable copolyester, to photocrosslinkable compositions comprising same, and to the use thereof in particular for the preparation of products by 3D printing, and to the corresponding crosslinked copolyester.

Description

[0001] DESCRIPTION

[0002] TITLE: PHOTOCROSSLINKABLE COPOLYESTERS AND PROCESS FOR OBTAINING THEM BY COPOLYMERIZATION

[0003] FIELD OF THE INVENTION

[0004] The present invention relates to photocrosslinkable copolyesters, comprising in particular unsaturated bonds. The present invention also relates to their preparation process and their use, in particular in crosslinking processes such as 3D printing processes, and to the corresponding crosslinked copolyesters.

[0005] STATE OF THE ART

[0006] Biodegradable polyesters, such as polylactic acid (PLA), polyglycolic acid (PGA) and their copolymers, poly(glycerol sebacate) (PGS), are now ubiquitous in the preparation of biomaterials useful both as medical biomaterials and as surface coatings.

[0007] Conventionally, these polyesters are prepared by melt polycondensation of glycerol and a diacid, at high temperature and under reduced pressure, with fairly long reaction times.

[0008] However, with the development of 3D printing application techniques, which require working at near-ambient temperature, under atmospheric pressure, and preferably with short reaction times, new materials have been sought whose preparation processes would be compatible with the requirements of 3D printing application, while retaining satisfactory thermo-mechanical properties.

[0009] Similarly, conventional processes are not compatible with the integration of temperature-sensitive organic molecules into biomaterials.

[0010] Photocrosslinkable materials have thus been developed, obtained by copolymerization of glycerol with sebacic acid and unsaturated acids, the unsaturations being able to be subsequently subjected to a photocrosslinking reaction, for example under UV irradiation (see in particular WO2019 / 215441 and WO2021 / 078962).

[0011] Other authors have therefore turned to the use of itaconic acid (unsaturated acid) as a comonomer. This comonomer is particularly interesting because, unlike (meth)acrylic acid derivatives, it is not toxic and is easily biosourced, which allows the production of photocrosslinkable polymers that can be used for a wide range of applications, including biomedical ones, with a relatively low carbon footprint.

[0012] Thus, Rueben et al. (MRS Advances (2018), 3(27), 1551-1556) describe the synthesis of copolymers of glycerol, sebacic acid and itaconic acid, but with particularly long preparation times (24h). Patent application CN114456335 also describes copolymers of polyols, aliphatic diacids and itaconic acid, and in particular copolymers of glycerol, sebacic acid and itaconic acid. However, the inventors demonstrated that the preparation process by polycondensation of CN114456335 was not reproducible.Indeed, under the conditions described, uncontrolled parasitic reactions (in particular crosslinking reactions) linked to the reactivity of the established a,p-double bonds of itaconic acid are observed, reactions which induce heterogeneity of the functional copolymer, and which increase the viscosity of the product obtained until it solidifies, which makes it impossible to use in applications as a coating or in a 3D printing process for example.

[0013] There is therefore a need for photocrosslinkable copolyesters whose preparation process is simple, reliable and reproducible to implement, and in particular suitable for industrial scale, avoiding the occurrence of uncontrolled parasitic reactions. In particular, crosslinking times are reduced, so that photocrosslinkable copolyesters can be used in 3D printing processes, in particular at room temperature and atmospheric pressure. The monomers used will preferably be non-toxic and bio-sourced, in order to limit the carbon footprint of the copolyesters obtained. In addition, the processing temperatures are generally lower than in conventional processes, and advantageously compatible with organic molecules sensitive to high temperatures.

[0014] BRIEF STATEMENT OF THE INVENTION

[0015] To this end, according to a first aspect of the invention, a process for preparing a photocrosslinkable copolyester is proposed, comprising the polycondensation of glycerol with a dicarboxylic acid monomer and at least one itaconic crosslinking agent, in the presence of a stabilizing agent.

[0016] The stabilizing agent has the effect of limiting or even eliminating the occurrence of parasitic reactions. Polycondensation yields are therefore improved, the photocrosslinkable copolyester has a viscosity suitable for the intended applications (particularly in 3D printing), and improved purity.

[0017] According to another aspect, the invention relates to a photocrosslinkable copolyester of glycerol and of a dicarboxylic acid monomer with an itaconic functionalization rate greater than or equal to 0.1 mmol / g, preferably greater than or equal to 0.5 mmol / g, more preferably greater than or equal to 1 mmol / g, capable of being obtained by the process of the invention.

[0018] According to another aspect, the invention relates to a photocrosslinkable composition comprising a photocrosslinkable copolyester according to the invention, and optionally, a photoinitiator. According to another aspect, the invention relates to a method for photocrosslinking the photocrosslinkable composition of the invention, comprising a step of UV irradiation of the photocrosslinkable composition.

[0019] According to another aspect, the invention relates to a crosslinked copolyester obtained by crosslinking the photocrosslinkable copolyester according to the invention or a photocrosslinkable composition according to the invention.

[0020] According to another aspect, the invention relates to the use of a photocrosslinkable composition according to the invention for the preparation of products by 3D printing.

[0021] DETAILED DESCRIPTION OF THE INVENTION

[0022] For the purposes of the present invention, the term “a” or “an” means “one or more” or “at least one”.

[0023] For the purposes of the present invention, a range of values ​​designated by the expression "between a and b" represents the range of values ​​from strictly greater than a to strictly less than b (i.e. excluding the limits a and b), while any range of values ​​designated by the expression "from a to b" represents the range of values ​​from a to b, i.e. including the strict limits a and b.

[0024] In this description, the term "approximately" means that the value concerned may be 10% lower or higher, in particular 5%, in particular 1%, than the value indicated. The compounds mentioned in the description may be of fossil or bio-sourced origin. In the latter case, they may be, partially or totally, derived from biomass or obtained from renewable raw materials derived from biomass. In the same way, the compounds mentioned may also come from the recycling of materials already used, that is to say they may be, partially or totally, derived from a recycling process, or obtained from raw materials themselves derived from a recycling process. This concerns in particular monomers, that is to say in particular glycerol, dicarboxylic acid and itaconic crosslinking agent.

[0025] OH

[0026] HO J OH

[0027] Glycerol is a triol with the following formula:

[0028] For the purposes of the present invention, the term “photocrosslinkable” polymer (including a copolyester) means a polymer which, under the influence of light irradiation, and more particularly UV irradiation, undergoes crosslinking reactions, thus modifying its chemical structure. In general, these are radical reactions in the presence of a photoinitiator. For the purposes of the present invention, the term “room temperature” means a temperature generally between 15°C and 40°C, preferably between 20°C and 30°C, in particular approximately 25°C.

[0029] By "atmospheric pressure" we mean a pressure of approximately 1 bar.

[0030] 1. Process for the preparation of a photocrosslinkable copolyester

[0031] The invention relates to a process for preparing a photocrosslinkable copolyester, comprising the polycondensation of glycerol with a dicarboxylic acid monomer and at least one itaconic crosslinking agent, in the presence of a stabilizing agent.

[0032] The itaconic crosslinking agent is chosen from itaconic acid and / or itaconic anhydride. The use of itaconic anhydride makes it possible to limit the production of water molecules (H2O) during the polycondensation reaction, and thus to improve the overall yield of the polycondensation, and / or the reaction rate, in particular under temperature conditions which may be milder, which makes it possible to reduce reaction times.

[0033] Preferably, the polycondensation reaction is carried out in the absence of inorganic acid, such as phosphoric acid.

[0034] The dicarboxylic acid monomer may be aliphatic, aromatic, or aliphatic / aromatic. The dicarboxylic acid monomer cannot be itaconic acid. An aliphatic / aromatic dicarboxylic acid monomer comprises an aliphatic moiety and an aromatic moiety. The dicarboxylic acid monomer preferably comprises from 4 to 36 carbon atoms. "Aliphatic" means a linear, branched, and / or cyclic hydrocarbon group, whether saturated or unsaturated but not aromatic.

[0035] According to preferred variants of the invention, the dicarboxylic acid monomer is aliphatic, in particular saturated, in particular linear or branched, preferably it is a (C3-C2o)alkanediyldicarboxylic acid, more preferably a (C8-Cis)alkanediyldicarboxylic acid. A group (C x -C y )alkanediyl is a divalent, saturated, linear or branched hydrocarbon group comprising from x to y carbon atoms.

[0036] Advantageously, the dicarboxylic acid monomer comprises or consists of a diacid of general formula [HOOC-(CH2)n-COOH] in which n is a number ranging from 1 to 30, preferably a number ranging from 5 to 10.

[0037] In particular, the dicarboxylic acid monomer may be chosen from malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, hexadecanedioic acid, octadecanedioic acid or a mixture of two or more of these dicarboxylic acids. Preferably, the dicarboxylic acid monomer may be chosen from malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid or a mixture of two or more of these dicarboxylic acids.

[0038] According to variants of the invention, the dicarboxylic acid monomer may be a mixture of at least two dicarboxylic acids. Preferably then, the dicarboxylic acid monomer comprises sebacic acid.

[0039] Preferably, the dicarboxylic acid monomer comprises or consists of sebacic acid. According to preferred variants of the invention, the dicarboxylic acid monomer, glycerol and the itaconic crosslinking agent are the only monomers during the polycondensation. Very preferably, the sebacic acid monomer, the itaconic crosslinking agent and glycerol are the only monomers in the polycondensation.

[0040] As used herein, a “stabilizing agent” means a compound that limits (or even eliminates) side reactions of the double bond of the itaconate function, such as, for example, radical reactions leading to uncontrolled crosslinking of the polymer, or Michael reactions. Preferably, the stabilizing agent does not react with the double bond with significant yields, or reacts reversibly. For example, the stabilizing agent will be able to carry out a Michael addition reaction reversibly. It is therefore a nucleophilic compound that is not very reactive towards the crosslinking agent, such as a phenol or an aniline. A phenol means an organic compound comprising a phenol function:

[0041] , substituted or unsubstituted or unsubstituted, in particular by one or more substituents chosen from a halogen atom, -NO2, or a C1-C6 alkyl, C1-C6 alkoxy, NH-C1-C6 alkyl group.

[0042] An aniline is an organic compound comprising an aniline function: with R n representing H or a C1-C6 alkyl group, substituted or unsubstituted, in particular by one or more substituents chosen from a halogen atom, -NO2, or a C1-C6 alkyl, C1-C6 alkoxy, NH-C1-C6 alkyl group.

[0043] According to a first variant, the stabilizing agent comprises or consists of a compound of general formula: in which

[0044] X represents O or NR n with R n representing H or a C 1 -C 6 alkyl group,

[0045] Ri represents H, -CO-aryl or -CO-heteroaryl, R independently represents H, halogen, -NO2, -OH, C1-C6 alkoxy, -COOH, -COO-C1-C6 alkyl, NH-C1-C6 alkyl, -SR2, or C1-C6 alkyl optionally substituted with OR2 or SR2,

[0046] R2 independently represents a C1-C8 alkyl group and p is a number ranging from 1 to 4, preferably 1 or 2.

[0047] Preferably, p is 1 or 2, and R independently represents H, -OH, -COOH, a C1-C6 alkyl group optionally substituted with an SR2 group in which R2 represents a C1-C8 alkyl group, or a C1-C6 alkoxy group.

[0048] Advantageously, Ri represents H or -CO-phenyl.

[0049] For the purposes of the present invention, the term "halogen atom" or "halogen" means fluorine, chlorine, bromine and iodine atoms.

[0050] For the purposes of the present invention, the term “(Ci-Ce)alkyl” group means a saturated, linear or branched monovalent hydrocarbon chain comprising 1 to 6, preferably 1 to 4, carbon atoms. By way of example, mention may be made of methyl, ethyl, propyl, isopropyl, butyl, pentyl or hexyl groups.

[0051] For the purposes of the present invention, the term "(Ci-Ce)alkoxy" group means a (Ci-Ce)alkyl group, as defined above, linked to the rest of the molecule via an oxygen atom. By way of example, mention may be made of the methoxy, ethoxy, n-propoxy, iso-propoxy, n-butoxy, t-butoxy, n-pentoxy, or n-hexoxy groups.

[0052] By "aryl" is meant here an aromatic hydrocarbon group, preferably comprising from 6 to 10 carbon atoms, and comprising one or more fused rings, such as for example a phenyl or naphthyl group. Advantageously, this is phenyl.

[0053] By "heteroaryl" is meant here an aromatic group comprising 5 to 10 cyclic atoms including one or more heteroatoms, advantageously 1 to 4 and even more advantageously 1 or 2, such as for example sulfur, nitrogen or oxygen atoms, the other cyclic atoms being carbon atoms. Examples of heteroaryl groups are furyl, thienyl, pyrrolyl, pyridinyl, imidazolyl, triazolyl, tetrazolyl, oxazolyl, isoxazolyl, thiazolyl, isothiazolyl, pyrazolyl, oxadiazolyl, thiadiazolyl, pyridazinyl, pyrimidinyl, pyrazinyl, triazinyl, quinolyl, isoquinolyl, quinoxalyl or indyl.

[0054] The stabilizing agent can therefore be used alone or in a mixture.

[0055] Typically, these are aniline, phenol, methoxyphenol (especially 4-methoxyphenol or guaiacol), syringol, 4,6-bis(octylthiomethyl)-o-cresol and / or 2-hydroxy-4-methoxybenzophenone.

[0056] The amount of stabilizing agent introduced is advantageously between 0.01% and 5% by mass relative to the total mass of the monomers, preferably ranging from 0.1% to 2%, more preferably from 0.5% to 1.6%. Advantageously, the molar ratio glycerol / (sum of the itaconic crosslinking agent and dicarboxylic acid monomer) is from 1 / 2 to 10 / 1, in particular from 1 / 1 to 5 / 1, preferably from 1 / 1 to 2 / 1.

[0057] Advantageously, the molar ratio of itaconic crosslinking agent / dicarboxylic acid monomer is from 1 / 99 to 99 / 1, preferably from 10 / 90 to 90 / 10, more preferably from 20 / 80 to 80 / 20.

[0058] For the purposes of the present invention, the term "polycondensation" means a polymerization reaction in which several molecules of different natures unite to form a polymer with the elimination of light molecules. In the present invention, esterification reactions between a triol (glycerol) and diacids (the dicarboxylic acid monomer and optionally itaconic acid) are involved, which form esters and water molecules. Depending on the molar ratios between monomers, the polycondensation may comprise two reaction sub-steps: first an esterification sub-step, which produces a water molecule next to each newly formed ester bond, then, if appropriate, a transesterification sub-step without the formation of water molecules.When the itaconic crosslinking agent is itaconic anhydride, the reaction can be likened to a transesterification, since no water molecules are produced, at least at the beginning of the reaction - subsequently, the free carboxylic acid formed during the opening of itaconic anhydride reacts in turn to release water.

[0059] The itaconic crosslinking agent may be added at the same time as the glycerol and the dicarboxylic acid monomer, or in a later step. Thus, according to a first embodiment, the method comprises: a) a step of bringing the glycerol into contact with the dicarboxylic acid monomer and the at least one itaconic crosslinking agent, and b) a polycondensation step in the presence of the stabilizing agent.

[0060] According to a second embodiment, the method comprises: a') a step of bringing the glycerol into contact with the dicarboxylic acid monomer, b') a first step of polycondensation of the glycerol with the dicarboxylic acid monomer to obtain a mixture comprising poly(glycerol dicarboxylate), c') a step of bringing the mixture comprising poly(glycerol dicarboxylate) into contact with the at least one itaconic crosslinking agent, and d') Optionally a second step of polycondensation in the presence of the stabilizing agent, to form the photocrosslinkable copolyester.

[0061] The introduction of the itaconic crosslinking agent in step (c') and not in step (a') makes it possible to further reduce the parasitic reactions. According to any of the variants of the invention, the contacting of the monomers, in particular steps (a) and (a'), is carried out in a reactor. The following steps can take place in the same reactor or in another reactor. Given the heating and pressure conditions, a person skilled in the art will be able to adapt the type and number of reactor(s) necessary for the process.

[0062] Preferably, steps (a), (b), (a'), (b'), (c') and (d') are carried out under an inert atmosphere. According to one embodiment, the polycondensation step(s) are carried out in the presence of a catalyst, in particular at a content of 20,000 ppm or less, in particular 10,000 ppm or less, 5000 ppm or less, preferably 3000 ppm or less, advantageously 2000 ppm or less, relative to the total mass of monomer used.

[0063] Step b) of polycondensation can last between 1 hour and 24 hours.

[0064] Reaction times are shortened when a catalyst is used. In the absence of a catalyst, the duration of step b) is typically 20 to 24 hours, while in the presence of a catalyst, the duration of step b) is typically less than 20 hours, preferably less than 15 hours, preferably less than 2 hours.

[0065] The catalyst may in particular comprise or consist of a Bronstedt acid (such as, for example, sulfuric acid, para-toluene sulfonic acid) or a Lewis acid (such as, for example, AICh, TiCL, TiOBu4, butylstannoic acid, metal salts of trifluoromethanesulfonates (or triflate), such as, for example, bismuth triflate, etc.), or a mixture thereof. Particularly advantageous catalysts are metal salts of metal triflate (or trifluoromethylsulfonate), the metal being of oxidation state (III), and in particular a metal salt chosen from Lanthanide triflates (Ln(TfO)a), yttrium triflate, scandium triflate, bismuth triflate and iron triflate.

[0066] Preferably, the catalyst comprises or consists of a food-grade catalyst. By "food-grade catalyst" is meant a catalyst suitable for food contact (for animals and humans) which meets requirements ensuring that there is no risk of toxicity induced by this catalyst for the polyester produced. Such a catalyst meets in particular the requirements of American standards 21 CFR 175.300, 21 CFR 177.2420 and / or 21 CFR 175.105 in force on the filing date.

[0067] The food grade catalyst is advantageously based on tin, and preferably chosen from organotin compounds comprising a carboxyl function (-C(O)OH) or a (-Sn(O)OH) function. According to particular variants of the invention, the catalyst is chosen from alkyltins comprising a carboxyl function (-C(O)OH) or a (-Sn(O)OH) function, the alkyl group having 1 to 10 carbon atoms, preferably 1 to 4 carbon atoms. Among these particular compounds, mention may be made of food grade monobutyltin oxide (or stannoic acid) and food grade monobutyltin tris(2-ethylhexanoate).

[0068] According to preferred variants of the invention, the catalyst is food grade monobutyltin oxide (or stannoic acid).

[0069] Examples of catalysts useful for the purposes of the invention include monobutyltin oxide marketed under the name FASCAT 9100 and monobutyltin tris(2-ethylhexanoate) marketed under the name FASCAT 9102 by the company PMC Organometallix. Particularly preferred is the catalyst monobutyltin oxide marketed under the name FASCAT 9100 by the company PMC Organometallix.

[0070] Thus, a catalyst will advantageously be introduced into the reaction medium, at the end of step (a) or step b), in an amount less than or equal to 5000 ppm relative to the total mass of the monomers, preferably an amount greater than or equal to 2500 ppm.

[0071] Advantageously, the polycondensation step, and in particular steps (b), (b'), and (d'), are carried out at a temperature of 50°C to 250°C, preferably of 100°C to 200°C, in particular of 120°C to 190°C.

[0072] The reaction time of the first polycondensation (b') is typically between 1 h and 48 h, preferably varies from 2 h to 26 h, preferably from 2 h to 24 h. Advantageously, this step will be considered to be complete when a molar conversion rate of the minority monomer, i.e. glycerol on the one hand, or of the sum of the dicarboxylic acid and itaconic crosslinking monomers on the other hand, of 70%, preferably 80% or in particular 90% or more, is observed. The molar conversion rate can be determined by measuring the mass of distillate (water) removed, or by monitoring the disappearance of the free minority monomer by NMR. 13 C or size exclusion chromatography (SEC) on samples taken from the reaction medium.

[0073] The reaction time of the second polycondensation (d') is typically between 30 minutes and 12 hours, preferably ranging from 1 hour to 8 hours, in particular from 2 hours to 6 hours. Advantageously, this step will be considered to be complete when the molar conversion rate of the minority monomer is 70%, preferably 80% or in particular 90% or more. Alternatively, when the second polycondensation step (d') is carried out with stirring, the step may be considered to be complete when the torque of the stirring motor reaches a predetermined target value, preferably chosen to guarantee a molar mass and a viscosity of the polymer suitable for the applications targeted in the invention.

[0074] During the polycondensation step, and in particular during steps (b) or (b') and / or (d'), the pressure in the reactor may be constant or variable. The polycondensation step, and in particular during steps (b) or (b') and (d'), is typically carried out at a pressure of between 0.0001 and 2 bar. As indicated above, a by-product of the polycondensation reaction is water. Thus, according to a preferred variant of the invention, the polycondensation step, in particular step (b), (b') and / or (d'), will be carried out under conditions that make it possible to remove water from the reaction medium (or from the reactor). Removing water as it is formed during the polycondensation has several advantages: it makes it possible to improve the yield of the reaction and to accelerate its kinetics. Preferably, the water thus recovered will be recycled as a solvent for the contacting step (a) or (a').

[0075] Furthermore, measuring the quantity of water removed also makes it possible to monitor the progress of the polycondensation reaction, and in particular the end of the first esterification sub-step. To remove water during the polycondensation step, a reactor and temperature and pressure conditions suitable for distilling the water may be used. Preferably, the polycondensation reaction, in particular step (b) or (d'), will be carried out under reduced pressure, the pressure typically being less than or equal to 30 mbar, in particular less than or equal to 20 mbar, preferably less than or equal to 10 mbar in this case.

[0076] Thus, according to one embodiment, the method comprises: a) a step of bringing the glycerol into contact with the dicarboxylic acid monomer and the at least one itaconic crosslinking agent, and the stabilizing agent, and b) a step of polycondensation under reduced pressure, the pressure typically being less than or equal to 30 mbar, in particular less than or equal to 20 mbar, preferably less than or equal to 10 mbar, and preferably at a temperature between 110°C and 200°C, preferably ranging from 120°C to 180°C, in particular 130°C.

[0077] According to another embodiment, the method comprises: a') a step of bringing glycerol into contact with dicarboxylic acid monomer, b') a first step of polycondensation of glycerol with the dicarboxylic acid monomer to obtain a mixture comprising poly(glycerol dicarboxylate), at a pressure ranging from 1 to 2 bar, c') a step of bringing the mixture comprising poly(glycerol dicarboxylate) into contact with the at least one itaconic crosslinking agent and the stabilizing agent, and d') a second step of polycondensation in the presence of the stabilizing agent under reduced pressure, the pressure typically being less than or equal to 30 mbar, in particular less than or equal to 20 mbar, preferably less than or equal to 10 mbar, to form the photocrosslinkable copolyester.

[0078] The polycondensation step d') is preferably carried out at a temperature of between 50°C and 250°C, preferably ranging from 100°C to 200°C, in particular from 120°C to 190°C. In a particular embodiment, the target temperature of the polycondensation step d') varies from 110°C to 200°C, preferably from 120°C to 180°C. The temperature is preferably reached by applying an isotherm or a heating ramp. The heating ramp may comprise one or more stages, also called temperature maintenance periods, and the ramp typically has a slope of between +0.1°C / min to +1°C / min.

[0079] Working under reduced pressure during the polycondensation stages in fact makes it possible to improve the yield and kinetics of the corresponding polycondensation stage.

[0080] According to another variant of the invention, at the end of step (c'), prior to placing under reduced pressure, the pressure is preferably reduced to an intermediate pressure between atmospheric pressure and the target reduced pressure, possibly in stages. Any method known to those skilled in the art can be used to lower the pressure, in particular using a peristaltic pump, a membrane pump, a rotary pump, etc. Such an intermediate pressure is less than 1 bar and varies, for example, from 800 mbar to 50 mbar. The reaction medium is then placed under reduced pressure, and preferably under vacuum. Here, "vacuum" means that the pressure is lowered until it reaches a value around 1 mbar.

[0081] Steps (a) and (a') of bringing the glycerol into contact with the dicarboxylic acid monomer and optionally the at least one itaconic crosslinking agent are typically carried out at a temperature varying from 20°C to 100°C.

[0082] In step (a) or (a'), the glycerol and dicarboxylic acid monomers may be brought into contact in water. Thus, according to variants of the invention, the contacting of the monomers of step (a) or (a') is carried out by adding water to the mixture of glycerol and dicarboxylic acid monomer. The addition of water to the monomer mixture allows homogenization of the mixture and thus reduces its overall viscosity. In order to promote this homogenization, stirring may be implemented in a known manner.

[0083] According to these variants, the water is added to the monomers in an amount by mass of between 0% and 100% by mass relative to the mass of the monomers used, preferably ranging from 5% to 50% by mass relative to the mass of the monomers used, more preferably ranging from 10% to 25% by mass relative to the mass of the monomers used.

[0084] According to other particularly preferred variants of the invention, the contacting of the monomers is carried out by introducing the dicarboxylic acid monomer - and optionally the at least one itaconic crosslinking agent - into a mixture comprising glycerol and water, improving the homogenization of the reaction mixture after the addition of the dicarboxylic acid monomer and optionally the at least one itaconic crosslinking agent. In order to promote this homogenization, stirring can be implemented in a known manner.

[0085] According to these preferred variants, prior to step (a) or (a'), the glycerol and water are mixed with a molar ratio of glycerol to water advantageously varying from 1 / 10 to 10 / 1. The mixing of the glycerol and the aqueous solution may take place at room temperature (approximately 23°C at atmospheric pressure) in a reactor, which may be the same as that of step (a). This preliminary mixing step may optionally comprise heating the glycerol and water, for example to a temperature varying from approximately 50°C to 100°C. The medium is then heated for a sufficient time to dissolve or disperse the glycerol homogeneously in the water. In order to promote homogenization of the medium, stirring may be carried out in a known manner, whether or not there is heating.

[0086] According to any of these variants, the dicarboxylic acid monomer can be introduced into the mixture comprising glycerol and water, in liquid form or in solid form.

[0087] According to preferred variants of the invention, the dicarboxylic acid monomer is introduced into a mixture comprising glycerol and water, in solid form and the contacting of the monomers is followed by a step of melting the dicarboxylic acid monomer in the aqueous medium.

[0088] According to other variants, in particular when the dicarboxylic acid monomer is introduced in the form of a liquid at room temperature, the reflux step is optional.

[0089] According to a variant, step (c') of bringing the mixture comprising poly(glycerol dicarboxylate) into contact with the at least one itaconic crosslinking agent comprises the addition of the at least one itaconic crosslinking agent, and optionally the stabilizing agent, to the mixture heated to a temperature of between 50°C and 250°C, preferably ranging from 100°C to 200°C, in particular from 120°C to 190°C. Preferably, during the contacting step c'), the temperature can vary from room temperature to 130°C.

[0090] The process may also comprise a subsequent step of post-treatment of the copolyester obtained, to reduce the residual monomer content. This may be a washing step, and / or a liquid-liquid extraction step, with a water-immiscible organic solvent, preferably dichloromethane, preferably followed by washing with an aqueous phase, in particular a neutral aqueous phase, and / or one loaded with salts (for example NaCl) and / or acid (for example a hydrochloric acid solution, in particular 1 N or 2 N). The liquid-liquid extraction and / or washing are carried out in a known manner.

[0091] 2. Copolvester and photocrosslinkable composition

[0092] The photocrosslinkable copolyester, capable of being obtained by the process according to the invention, has an itaconic functionalization rate greater than or equal to 0.1 mmol / g, preferably greater than or equal to 0.5 mmol / g, more preferably greater than or equal to 1 mmol / g.

[0093] As used herein, the "itaconic functionalization rate" means the rate of C=C double bonds provided by the at least one itaconic crosslinking agent in the polymer, expressed in mmol of double bonds / g of polymer obtained. The itaconic functionalization rate is typically measured by carbon 13 nuclear magnetic resonance (NMR 13 C).

[0094] The itaconic functionalization rate can also be obtained indirectly by measuring the free itaconic acid by size exclusion chromatography (SEC). The rate of free (or residual) itaconic acid is then measured. Assuming that the remainder of the itaconic acid involved has completely reacted, the itaconic functionalization rate corresponds to the difference between the quantity of itaconic acid involved in the reaction (or initial), and the quantity of free itaconic acid, these quantities being expressed in mmol / g of polymer obtained.

[0095] For a copolymer of glycerol and itaconic crosslinking agent without any other monomer, and in particular without any other diacid monomer, with a glycerol: itaconic crosslinking agent molar ratio of 1:1 and a sequence of 100 glycerol / diacid monomers, the theoretical itaconic functionalization rate is 5.23 mmol / g, confirmed by experimental measurements as being between 5 and 6 mmol / g.

[0096] Thus, the photocrosslinkable copolyester has an itaconic functionalization rate typically less than or equal to 6 mmol / g, in particular less than or equal to 5 mmol / g. Advantageously, the itaconic functionalization rate is typically greater than or equal to 0.1 mmol / g, in particular greater than or equal to 0.5 mmol / g, in particular greater than or equal to 1 mmol / g.

[0097] Advantageously, the dicarboxylic acid monomer is such as the dicarboxylic acid monomer described above in point 1. Preferably, it comprises or consists of a compound of formula [HOOC-(CH2)n-COOH], in which n is a number ranging from 1 to 30, preferably a number ranging from 1 to 10. Advantageously, it is sebacic acid (n=8).

[0098] The photocrosslinkable copolyester may also have at least one of the following characteristics:

[0099] • its number-average molar mass (Mn) is greater than or equal to 500 g / mol, in particular 1000 g / mol, advantageously greater than or equal to 1500 g / mol, preferably greater than or equal to 1700 g / mol;

[0100] • its number-average molar mass (Mn) is less than or equal to 3500 g / mol, preferably less than or equal to 3000 g / mol;

[0101] • its dispersity D (Mw / Mn) is less than or equal to 10, preferably less than or equal to 8, in particular less than or equal to 6;

[0102] • a residual monomer content of less than 15%, preferably less than or equal to 10% by weight relative to the total weight of the polymer; and / or

[0103] • a rate of (1,2,3-triacylglyceride) units of less than 25 mol%, preferably less than 20 mol%, relative to all the units of the polymer. The number-average molar mass (Mn), the mass-average molar mass (Mw), and the dispersity (also called polydispersity, dispersity D, which is the Mw / Mn ratio), can be measured in a known manner by SEC analysis, in particular as described below. The rate of residual monomers as well as the rate of (1,2,3-triacylglyceride) units is measured in a known manner by NMR 1 H, where appropriate combined with 2D HSQC / HMBC and NMR experiments 13 C, as described further.

[0104] The invention also relates to a photocrosslinkable composition comprising:

[0105] • a photocrosslinkable copolyester as described herein, and

[0106] • optionally, a photoinitiator.

[0107] A "photoinitiator" is a compound which, when exposed to light, and in particular to UV light, produces a radical which will initiate the photocrosslinking reaction, which is generally radical.

[0108] The use of excessive quantities of photoinitiator can in fact generate undesirable reactions during the photocrosslinking step. Thus, advantageously, the photoinitiator is present at a content less than or equal to 5% by mass, more preferably less than or equal to 1% by mass relative to the total mass of the photocrosslinkable composition.

[0109] Photoinitiators suitable for photocrosslinking are well known to those skilled in the art. The photoinitiators will be chosen in particular from the family of type I photoinitiators. Type I photoinitiators are monomolecular systems which proceed by homolytic cleavage of a CC bond, in particular by Norrish I type cleavage. The molecules involved are generally aromatic ketones which undergo, after absorption of light, a homolytic cleavage of the bond in position a relative to the carbonyl group (Norrish I type cleavage) from their triplet excited state, which leads to the formation of two free radicals capable of initiating a radical polymerization reaction (see in particular Ley et al. I4 èmeInternational French-speaking conference on Optical Methods and Techniques for industry / 16th French congress of the FLUVISU / SFO club (CMOI-FLUVISU 2015), CMOI Club - French Optical Society, Nov 2015, Pleumeur-Bodou, France, pp.124-129. hal-01583762).

[0110] Type I photoinitiators are in particular any precursor of benzoyl radical:

[0111] Type I

[0112] R «Alkyl-R r aci,-3l ïier / oy c Ra ral nc-zpe a .lc Type II photoinitiators are in particular, any precursor of a ketyl radical (inert) and with a radical precursor (an amine).

[0113] Type II

[0114] CH2NHR2

[0115] Inert cetyte radical; Rach::;»l alt yh-airint;

[0116] Examples include 2,4,6-Trimethylbenzoyldi-Phenylphosphinate (TPO L), diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide (TPO), or 1-Hydroxycyclohexyl phenyl ketone (HCHPK).

[0117] The photocrosslinkable composition may further comprise one or more additives conventional in the art, such as fillers. The fillers may be organic or inorganic. The additive may also be chosen from the group consisting of stabilizers, compatibilizing agents, shaping agents, regulators of release of an active ingredient, antioxidants.

[0118] The composition may further comprise an ingredient that is active with respect to plants. Such compositions may be used to coat plants or parts of plants. According to this embodiment, the invention also relates to a method for treating plants comprising the application to at least part of the plants or to the soil of the photocrosslinkable composition.

[0119] As active products for plants, we can also mention in particular plant stimulation agents for agricultural applications, in particular rubber trees, such as Hevea brasiliensi.

[0120] A plant protection product, plant protection product or plant protection product is a substance or mixture of substances of a chemical or biological nature (of natural or synthetic origin) used in agriculture, horticulture or forestry to protect cultivated plants against bioaggressors (animal pests, phytopathogenic agents, parasitic plants, weeds) or to optimize crops by promoting the growth of cultivated plants and treating their environment (particularly soils).

[0121] A "biostimulant" is a substance that stimulates plant nutrition processes independently of the nutrients it contains with the aim of improving one or more of the following characteristics of plants or their rhizosphere: nutrient use efficiency, tolerance to abiotic stress, quality characteristics, availability of nutrients confined in the soil or rhizosphere (in accordance with EU Regulation 2019 / 1009). Biostimulants may be certain natural preparations of low concern (NPCs). NPCs are:

[0122] - Natural substances for biostimulant use (SNUB).

[0123] - Either basic substances.

[0124] Basic substances are defined by Article 23 of Regulation (EC) No 1107 / 2009. These are substances of phytosanitary interest but whose main use is other than plant protection (e.g. foodstuffs).

[0125] Preferably, the formulation according to the invention comprises a phytosanitary active ingredient and / or a biostimulant chosen from the group consisting of stimulants, fertilizers, pesticides, fungicides, nutrients, bactericides, insecticides, growth regulators.

[0126] Preferably, the formulation according to the invention comprises a phytosanitary active ingredient and / or a biostimulant which is a precursor of ethylene, preferably ethephon.

[0127] The composition according to the invention may be in the form of a paste, patch, granules or solution to be propellant, preferably in the form of a paste.

[0128] 3. Photocrosslinking process

[0129] The invention also relates to a method for photocrosslinking the photocrosslinkable composition or a photocrosslinkable copolyester described herein, comprising a step of UV irradiation of the photocrosslinkable composition or the photocrosslinkable copolyester, preferably in the presence of a photoinitiator.

[0130] Advantageously, the irradiation is carried out at a temperature varying from 15°C to 30°C.

[0131] Irradiation is typically conducted at atmospheric pressure.

[0132] Preferably, the irradiation is carried out at a wavelength of between 250 nm and 500 nm, preferably ranging from 300 to 450 nm, more preferably from 350 to 400 nm, in particular 365 nm.

[0133] Advantageously, the irradiation is carried out at a power of 5 to 25 mW / cm 2 , notably from 8 to 20 mW / cm 2 .

[0134] Advantageously, the photoinitiator is present at a content of less than or equal to 5% by mass, more preferably less than or equal to 1% by mass relative to the total mass of the photocrosslinkable composition.

[0135] Photoinitiators are as defined above.

[0136] The photocrosslinkable composition or photocrosslinkable copolyester is generally irradiated for a period of between 1s and 5h.

[0137] Preferably, the photoinitiator is added to the crosslinkable composition or copolyester at room temperature. This avoids any unwanted crosslinking reaction. More particularly, the invention relates to the use of the photocrosslinkable composition for the preparation of products by 3D printing, preferably by 3D printing by photocrosslinking. Examples of such technologies are stereolithography (SLA), printing processes known as "Digital Light Processing" (DLP), "Continuous Liquid Interface Production" (CLIP), "Daylight Polymer Printing" (DPP), or "Film Transfer Imaging" (FTI).

[0138] 4. Crosslinked copolyester and uses

[0139] The invention also relates to a crosslinked copolyester obtained by crosslinking, in particular thermal crosslinking and / or photocrosslinking, of the photocrosslinkable copolyester of the invention or of a photocrosslinkable composition according to the invention.

[0140] According to a variant, the crosslinked copolyester is therefore capable of being obtained by the photocrosslinking process described above.

[0141] According to another variant, the crosslinked copolyester can be obtained by thermal crosslinking, in particular with thermal initiation optionally in the presence of initiators chosen in particular from radical producers by thermal decomposition, such as for example peroxides, such as cumene hydroperoxide, or azos, such as for example azobiisobutyronitrile (AIBN), in a dispersed medium or not.

[0142] The crosslinked copolyester advantageously has:

[0143] • a glass transition temperature Tg of between -100°C and +30°C, preferably from -80°C to +10°C, in particular from -60°C to 0°C, and / or

[0144] • a storage modulus G' at 37°C and 10 Hz greater than or equal to 0.02 MPa. Advantageously, the storage modulus G' at 37°C and 10 Hz is less than or equal to 10 MPa. Thus, the photocrosslinkable composition according to the invention or the photocrosslinkable copolyester according to the invention is useful for the preparation of products by 3D printing.

[0145] The products are, for example, patches diffusing active ingredients, implants, particles (in particular micro- and macroparticles), coatings, fibers and threads, etc.

[0146] DESCRIPTION OF FIGURES

[0147] Other characteristics, aims and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting, and which must be read in conjunction with the attached drawings.

[0148] [Fig. 1] represents a simplified reaction scheme of the reactions involved in the synthesis of poly(glycerol-co-sebacate-co-itaconate) according to example 1. [Fig. 2] represents the storage modules G* as on the copolyesters of example 1 and after photocrosslinking in the presence or absence of photoinitiator.

[0149] EXAMPLES

[0150] The following examples are given for illustrative purposes, but should in no way be considered as limiting the present invention.

[0151] Materials and methods

[0152] Structural analysis: NMR

[0153] Structural analysis as well as determination of the itaconic functionalization rate and the proportion of unreacted (residual) itaconic anhydride or acid present in the polymer are performed by NMR analysis. Spectra are acquired on a BRUKER Avance III 600 MHz spectrometer equipped with a BBFO-zgrad 5mm broadband probe. The NMR experiment 1 Quantitative H, uses a single 30° pulse sequence and a 3-second repetition delay between each of the 64 acquisitions. The samples are solubilized in a deuterated solvent, deuterated acetone (acetone d 6 ) unless otherwise stated. The NMR spectrum 1 H coupled to 2D HSQC / HMBC and NMR experiments 13 C allow the quantification of the microstructure of the different functional PGS (see attribution tables).

[0154] Macrostructure analysis: SEC RI

[0155] The SEC (Size Exclusion Chromatography) technique separates macromolecules in solution according to their size through columns filled with a porous gel. The macromolecules are separated according to their hydrodynamic volume, with the largest being eluted first.

[0156] Although not an absolute method, SEC allows us to understand the molar mass distribution of a polymer. From commercial standard products, the different number-average (Mn) and weight-average (Mw) molar masses can be determined and the polydispersity index (D = Mw / Mn), also called dispersity, calculated.

[0157] The "macrostructure" of the copolyesters is analyzed by size exclusion chromatography with differential refractometer detection (SEC RI), in low-weight polystyrene (PS) calibration extended with medium-weight standards. The samples are dissolved at a concentration of approximately 1g / L in THF without butylated hydroxytoluene (BHT), then stirred for two hours before being injected. The analysis temperature is 35°C, with a mobile phase flow rate of 1mL / minute on 2 Mixed E + 2 Mixed 2 columns marketed by Agilent.

[0158] Thermal analysis: DSC

[0159] The thermal analysis of the copolyesters is carried out by differential scanning calorimetry on a DSC 3+ calorimeter marketed by Mettler Toledo, in standard aluminum crucibles with sealed lids and pierced with two diametrically opposed holes, under a Helium flow rate of 40mL / minute using the following temperature ramp:

[0160] 1. isothermal 25°C for 2 minutes,

[0161] 2. ramp from 25°C to -100°C at 10°C / minute,

[0162] 3. isothermal at -100°C for 2 minutes,

[0163] 4. ramp from -100°C to 100°C at 10°C / minute,

[0164] 5. ramp from 100°C to -100°C to -30°C / minute,

[0165] 6. isothermal at -100°C for 2 minutes,

[0166] 7. from -100°C to 100°C at 10°C / minute.

[0167] The measurement carried out at ramp 7 corresponds to the Tg of the crosslinked copolyester.

[0168] Structural analysis: MIR

[0169] Photocrosslinking kinetic monitoring was performed with a mid-infrared spectrometer (MIR) with wavelengths between 4000 and 650cm' 1, (Vertex 70” model marketed by Brucker) equipped with a germanium crystal on a Vertex 70-3 spectrometer with MCT detector. An accumulation of number of scans (Ns) of 32 is used. The spectrometer was equipped with a 365nm UV LED lamp with a power of 9mW / cm 2 irradiating at a distance of 5cm from the sample. Crosslinking is monitored by following the disappearance of the C=C band of itaconate at 1638cm' 1 as a function of the UV irradiation time (measurement of the peak area of ​​the band at 1638cm' 1 ).

[0170] Measurement of mechanical properties: storage modulus G'

[0171] The mechanical properties are measured on an Anton Paar rheometer model MCR302, equipped with a 20mm diameter plane-plane geometry. The measurements are carried out on a cylindrical sample 2mm thick and 2cm in diameter, obtained by molding in a metal mold then crosslinking for 1 hour under a UV LED lamp (LED 365nm, 9Mw / cm2) at room temperature.

[0172] This sample is subjected to a frequency sweep from 0.1 to 100 Hertz in sinusoidal shear stress at 0.1% strain, at a temperature of 37°C. The resulting stress is measured. The results used are the storage modulus (G') at 37°C and 10Hz, they are expressed in megapascal (MPa).

[0173] The moduli G*, G' and G” are calculated according to the equations below: with: o the measured stress and E the deformation imposed on the sample. • G', the real part of G*, called conservation modulus, which characterizes the rigidity of the viscoelastic material. ” characterizes the elastic behavior (the energy conserved and totally restored by the material);

[0174] • i the “imaginary” unit (i 2 = -1);

[0175] • G”, the imaginary part of G*, called the loss modulus or dissipation modulus, which characterizes the viscous behavior (the energy dissipated in the form of heat).

[0176] Example 1: Synthesis of a photocrosslinkable copolyester according to the invention: poly(glycerol-co-sebacate-co-itaconate)

[0177] In the following we will note PGS-co-IA a poly(glycerol-co-sebacate-co-itaconate) obtained with itaconic acid as crosslinking agent, and PGS-co-ANHYTA a poly(glycerol-co-sebacate-co-itaconate) obtained with itaconic anhydride as crosslinking agent.

[0178] Operating mode with stabilizing agent without catalyst:

[0179] In a 500mL double jacketed reactor topped with a distillation column, a condenser and a distillate recovery trap, under nitrogen flow, glycerol (1 molar equivalent), sebacic acid (0.5 molar equivalents), itaconic acid or anhydride (0.5 molar equivalents) and 4-methoxyphenol (1.1-1.2% ma ssique of the mixture) are added. The reactor is then heated to 130 °C gradually with stirring and under nitrogen. Once the temperature of 130 °C is reached in the medium, the reaction is left for 24 hours under atmospheric pressure and nitrogen flow, at 130 °C, the water is continuously removed. When the conversion exceeds 80% by measuring the quantity of water produced, the reaction is stopped. The PGS-co-IA or PGS-co-ANHYTA is recovered in the form of a yellow viscous solid when cooled to room temperature.

[0180] Operating mode with stabilizing agent and with catalyst:

[0181] In a 100mL reactor topped with a distillation column, a condenser and a distillate recovery trap, under nitrogen flow, glycerol (1 molar equivalent), sebacic acid (0.5 molar equivalents), itaconic acid (0.5 molar equivalents), 4-methoxyphenol (1.5% ma ssique of the monomer mixture) are added. The reactor is then heated to 140 °C gradually with stirring and under nitrogen. Once the medium is homogeneous at 140 °C, Bismuth triflate (0.5% by mass of the monomer mixture) is added. The reaction is left for 1 hour 45 minutes under atmospheric pressure and nitrogen flow, at 140 °C, the water is continuously removed. The reaction is stopped by stopping the heating.

[0182] PGS-co-IA is recovered as a viscous solid when cooled to room temperature.

[0183] Procedure without stabilizing agent: In a 500mL double jacketed reactor topped with a distillation column, a condenser and a distillate recovery trap, under nitrogen flow, glycerol (1 molar equivalent), sebacic acid (0.5 molar equivalents) and itaconic acid (0.5 molar equivalents) are added. The reactor is then gradually heated to 130°C with stirring and under nitrogen. Once the temperature of 130°C is reached in the medium, the reaction is left under atmospheric pressure and nitrogen flow, at 130°C with the water continuously removed. An insoluble yellow gel (crosslinked PGS) is obtained after 20 hours of reaction (undesired parasitic crosslinking).

[0184] Cross-linked PGS-co-IA is recovered as a yellow gel insoluble in acetone and

[0185] *Takes into account the unsaturations of the free and grafted itaconic acid or anhydride Results of analyses by SEC RI low weight, THF, poly(styrene) standard [TABLE 2]

[0186] Example 2: Photocrosslinking

[0187] The photocrosslinkable copolyesters of example 1 are crosslinked under UV lamp (LED 365nm, 9Mw / cm 2) during an exposure time of 1 hour (distance between the lamp and the surface of the sample: 5cm), at room temperature and atmospheric pressure, in the presence or absence of photoinitiator 2,4,6-Trimethylbenzoyldi-Phenylphosphinate (TPO L), or diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide (TPO), or 1-Hydroxycyclohexyl phenyl ketone (HCHPK). The photoinitiator is previously introduced in a mass percentage of 1% by mass relative to the total mixture. A molar compensation of the stabilizing agent present in the functional PGS is carried out with the photoinitiator.

[0188] Infrared analysis validates the almost total disappearance of the C=C band of itaconate at 1638 cm -1 , which confirms the efficiency of the photocrosslinking reaction.

[0189] The rheology measurements carried out on the crosslinked copolyesters thus obtained are reported in Figure 2. It can be seen from these measurements that the crosslinked copolyester is much more rigid than the photocrosslinkable copolyester, further confirming the effectiveness of the photocrosslinking reaction.

[0190] Table 3 reports the measurements of the glass transition temperatures Tg of the copolyesters with and without photocrosslinking. Results of differential scanning calorimetry (DSC) analyses after photocrosslinking [TABLE 3]

[0191] Conclusion

[0192] The method of the invention is simple, rapid, reliable and reproducible to implement. It also makes it possible to avoid the occurrence of uncontrolled parasitic reactions, thanks to the use of a stabilizing agent.

[0193] The photocrosslinkable copolyesters of Example 1 are obtained from non-toxic and bio-sourced monomers, and are suitable for the manufacture of products in 3D printing processes. They have mechanical and physicochemical properties of the same order of magnitude as the photocrosslinkable polymers of the prior art, but using an itaconate crosslinking agent, i.e. non-toxic and 100% bio-sourced / bio-sourced.

[0194] Bibliographic references:

[0195] CN 114456335

[0196] WO2019 / 215441

[0197] WO2021 / 078962

[0198] Rueben et al. MRS Advances (2018), 3(27), 1551-1556

Claims

CLAIMS 1. Process for the preparation of a photocrosslinkable copolyester, comprising a step of polycondensation of glycerol with a dicarboxylic acid monomer and at least one itaconic crosslinking agent chosen from itaconic acid and / or itaconic anhydride, in the presence of a stabilizing agent, the dicarboxylic acid monomer preferably being aliphatic.

2. Method according to claim 1, in which the dicarboxylic acid monomer comprises or consists of a compound of formula [HOOC-(CH2)n-COOH], in which n is a number ranging from 1 to 30, preferably a number ranging from 5 to 10, advantageously sebacic acid (n=8).

3. Method according to claim 1 or 2, in which the molar ratio of itaconic crosslinking agent / dicarboxylic acid monomer is from 1 / 99 to 99 / 1, preferably from 10 / 90 to 90 / 10, advantageously from 20 / 80 to 80 / 20.

4. Process according to any one of claims 1 to 3, in which the polycondensation step is carried out at a temperature of 50°C to 250°C, preferably of 100°C to 200°C, in particular of 120°C to 190°C, and typically in which the polycondensation step is carried out at a pressure of between 0.0001 and 2 bar.

5. Process according to any one of claims 1 to 4, in which the polycondensation is carried out in the presence of a catalyst, in particular at a content of 20,000 ppm or less, in particular 10,000 ppm or less, 5000 ppm or less, preferably 3000 ppm or less, advantageously 2000 ppm or less, relative to the total mass of monomer used.

6. Process according to any one of claims 1 to 5, comprising a) a step of bringing the glycerol into contact with the dicarboxylic acid monomer and the at least one itaconic crosslinking agent, and b) a step of polycondensation in the presence of the stabilizing agent.

7. Process according to any one of claims 1 to 5, comprising a') a step of bringing the glycerol into contact with the dicarboxylic acid monomer, b') a first step of polycondensation of the glycerol with the dicarboxylic acid monomer to obtain a mixture comprising poly(glycerol dicarboxylate), c) a step of bringing the mixture comprising poly(glycerol dicarboxylate) into contact with the at least one itaconic crosslinking agent, and d) optionally a second step of polycondensation in the presence of the stabilizing agent, to form the photocrosslinkable copolyester.

8. Process according to claim 7, in which the second polycondensation step (d') is carried out under reduced pressure, the pressure typically being less than or equal to 30 mbar, in particular less than or equal to 20 mbar, preferably less than or equal to 10 mbar.

9. Method according to any one of claims 6 to 8, in which the contacting step (a) or (a') is carried out by adding water to the mixture of glycerol and dicarboxylic acid monomer, and optionally itaconic crosslinking agent.

10. Photocrosslinkable copolyester of glycerol and a dicarboxylic acid monomer with an itaconic functionalization rate greater than or equal to 0.1 mmol / g, preferably greater than or equal to 0.5 mmol / g, more preferably greater than or equal to 1 mmol / g, capable of being obtained by the process according to any one of the preceding claims.

11. Photocrosslinkable copolyester according to claim 10, further having at least one of the following characteristics: its number-average molar mass (Mn) is greater than or equal to 500 g / mol, in particular 1000 g / mol, advantageously greater than or equal to 11500 g / mol, preferably greater than or equal to 1700 g / mol; its number-average molar mass (Mn) is less than 3500 g / mol, preferably less than or equal to 3000 g / mol; its dispersity D (Mw / Mn) is less than 10, preferably less than or equal to 8, in particular less than or equal to 6; a residual monomer content of less than 15% by weight of the weight of the polymer; and / or a rate of (1,2,3-triacylglyceride) units of less than 25 mol%, preferably less than or equal to 20 mol%, relative to all the units of the polymer.

12. Photocrosslinkable composition comprising • A photocrosslinkable copolyester according to claim 10 or 11, and optionally, a photoinitiator, advantageously at a content less than or equal to 5% by mass relative to the total mass of the composition.

13. Method for photocrosslinking the photocrosslinkable composition of claim 12, comprising a step of UV irradiation of the photocrosslinkable composition.

14. Crosslinked copolyester obtained by crosslinking the photocrosslinkable copolyester of claim 10 or 11 or a photocrosslinkable composition according to claim 12.

15. Crosslinked copolyester according to claim 14, obtainable by the process of claim 13.

16. Crosslinked copolyester according to claim 14 or 15, characterized in that it has: a glass transition temperature Tg of between -100°C and +30°C, preferably from -80°C to +10°C, in particular from -60°C to 0°C, and / or a storage modulus G' at 37°C and at 10 Hz greater than or equal to 0.02 MPa.

17. Use of the photocrosslinkable composition of claim 12 or of the photocrosslinkable copolyester according to claim 10 or 11 for the preparation of products by 3D printing.

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