Photocrosslinkable copolyesters and methods of making the same by copolymerization

Abstract

The present invention relates to a process for the preparation of a photocrosslinkable copolyester, comprising the step of polycondensation of glycerol with dicarboxylic acid monomers and at least one itaconic acid-based crosslinker selected from itaconic acid and / or itaconic anhydride in the presence of a stabilizer. The present invention also relates to the corresponding photocrosslinkable copolyester, to a photocrosslinkable composition comprising the photocrosslinkable copolyester and to the use thereof, in particular for the preparation of products by 3D printing, as well as to the corresponding crosslinked copolyester.

Description

Technical Field

[0001] This invention relates to photocrosslinkable copolyesters, particularly photocrosslinkable copolyesters containing unsaturated bonds. The invention also relates to methods for their preparation and their uses, particularly in crosslinking methods (e.g., 3D printing methods), and the corresponding crosslinked copolyesters. Background Technology

[0002] Biodegradable polyesters, such as polylactic acid (PLA), polyglycolic acid (PGA) and its copolymers, as well as poly(glycerol sebacate) (PGS), are now widely used in the preparation of biomaterials, which can be used as medical biomaterials or as surface coatings.

[0003] These polyesters are typically produced by melt polycondensation of glycerol and diacid under high temperature and reduced pressure for a considerable reaction time.

[0004] However, with the development of 3D printing applications, it is necessary to operate at temperatures close to ambient temperature and atmospheric pressure, and preferably with shorter reaction times. Therefore, new materials and their preparation methods are being sought that can meet the requirements of 3D printing applications while maintaining satisfactory thermomechanical properties.

[0005] Similarly, traditional methods are not suitable for integrating temperature-sensitive organic molecules into biomaterials.

[0006] Therefore, photocrosslinking materials have been developed by copolymerizing glycerol with sebacic acid and unsaturated acids, wherein the unsaturated groups can then undergo photocrosslinking reactions, for example, under ultraviolet light irradiation (see WO2019 / 215441 and WO2021 / 078962 for details).

[0007] Therefore, other authors have turned to itaconic acid (an unsaturated acid) as a comonomer. This comonomer is particularly noteworthy because, unlike derivatives of (meth)acrylic acid, it is non-toxic and readily available from biological sources, enabling the production of photocrosslinkable polymers that can be used in a wide range of applications, including biomedical applications, with a relatively low carbon footprint.

[0008] Rueben et al. (MRS Advances (2018), 3(27), 1551-1556) correspondingly described the synthesis of copolymers of glycerol, sebacic acid and itaconic acid, but the preparation time was particularly long (24 hours).

[0009] Patent application CN114456335 also describes copolymers of polyols, aliphatic diacids, and itaconic acid, particularly copolymers of glycerol, sebacic acid, and itaconic acid. However, the inventors have demonstrated that the polycondensation preparation method in CN114456335 cannot be reproduced. Specifically, under the stated conditions, uncontrolled side reactions (particularly crosslinking reactions) related to the reactivity of the α,β-unsaturated double bonds of itaconic acid are observed. These reactions lead to heterogeneity of the functionalized copolymer and increase the viscosity of the resulting product until it solidifies, making the copolymer unusable in applications such as coatings or 3D printing.

[0010] Therefore, there is a need for photocrosslinkable copolyesters whose preparation methods are simple, reliable, and repeatable, and particularly suitable for industrial-scale production, while avoiding uncontrolled side reactions. Specifically, the crosslinking time is shortened to a point where photocrosslinkable copolyesters can be used in 3D printing methods, especially at ambient temperature and atmospheric pressure. The monomers used are preferably non-toxic and bioavailable to limit the carbon footprint of the resulting copolyester. Furthermore, the processing temperature is typically lower than conventional methods and is advantageously compatible with heat-sensitive organic molecules. Summary of the Invention

[0011] Therefore, in a first aspect of the present invention, a method for preparing a photocrosslinkable copolyester is provided, the method comprising polycondensation of glycerol with a dicarboxylic acid monomer and at least one itaconic acid crosslinking agent in the presence of a stabilizer.

[0012] The stabilizer has the effect of limiting or even eliminating side reactions. The polycondensation yield is correspondingly improved, and the photocrosslinkable copolyester has a viscosity suitable for the intended application (especially 3D printing) and improved purity.

[0013] On the other hand, the present invention relates to a photocrosslinkable copolyester of glycerol and dicarboxylic acid monomers that can be obtained by the method of the present invention, wherein the degree of itaconic acid functionalization is greater than or equal to 0.1 mmol / g, preferably greater than or equal to 0.5 mmol / g, and more preferably greater than or equal to 1 mmol / g.

[0014] On the other hand, the present invention relates to a photocrosslinkable composition comprising the photocrosslinkable copolyester of the present invention and an optional photoinitiator.

[0015] On the other hand, the present invention relates to a method for photocrosslinking the photocrosslinkable composition of the present invention, the method comprising the step of irradiating the photocrosslinkable composition with ultraviolet light.

[0016] On the other hand, the present invention relates to a crosslinked copolyester obtained by crosslinking the photocrosslinkable copolyester of the present invention or the photocrosslinkable composition of the present invention.

[0017] On the other hand, the present invention relates to the use of the photocrosslinkable composition of the present invention for the preparation of products by 3D printing. Invention Details For the purposes of this invention, the term "a" or "an" means "one or more" or "at least one".

[0019] For the purposes of this invention, a numerical range expressed as "between a and b" represents a numerical range within the range strictly greater than a to strictly less than b (i.e., excluding the endpoints a and b), while any numerical range expressed as "a to b" represents a numerical range from a to b (i.e., including the strict endpoints a and b).

[0020] In this specification, the term “about” should be understood to mean that the value may be 10% lower or higher than the indicated value, especially 5%, and particularly 1%.

[0021] The compounds mentioned in this specification may be fossil-derived or bio-based. In the latter case, they may be obtained, in whole or in part, from biomass or from renewable raw materials derived from biomass. Similarly, the compounds mentioned may also be derived from the recycling of used materials, i.e., they may be obtained, in whole or in part, from recycling methods or from raw materials that themselves originated from recycling methods. This particularly relates to monomers, i.e., especially glycerol, dicarboxylic acids, and itaconic acid crosslinking agents.

[0022] Glycerol is a triol with the following formula: .

[0023] For the purposes of this invention, "photocrosslinkable" polymers (including copolyesters) should be understood as polymers whose chemical structure is altered by crosslinking reactions under light irradiation, more specifically, under the influence of ultraviolet light. Generally, these are free radical reactions in the presence of a photoinitiator.

[0024] For the purposes of this invention, "ambient temperature" should be understood to generally refer to a temperature between 15°C and 40°C, preferably between 20°C and 30°C, and especially about 25°C.

[0025] In this article, "atmospheric pressure" should be understood as a pressure of approximately 1 bar.

[0026] 1. A method for preparing photocrosslinkable copolyesters This invention relates to a method for preparing a photocrosslinkable copolyester, the method comprising polycondensation of glycerol with a dicarboxylic acid monomer and at least one itaconic acid crosslinking agent in the presence of a stabilizer.

[0027] The itaconic acid crosslinking agent is selected from itaconic acid and / or itaconic anhydride. The use of itaconic anhydride allows for the restriction of water molecule (H2O) generation during the polycondensation reaction, thereby increasing the overall yield and / or reaction rate of the polycondensation, especially under potentially milder temperature conditions, which can shorten the reaction time.

[0028] Polycondensation is preferably carried out in the absence of inorganic acids (e.g., phosphoric acid).

[0029] The dicarboxylic acid monomer can be aliphatic, aromatic, or aliphatic / aromatic monomers. The dicarboxylic acid monomer cannot be itaconic acid. Aliphatic / aromatic dicarboxylic acid monomers comprise both an aliphatic and an aromatic moiety. The dicarboxylic acid monomer preferably contains 4 to 36 carbon atoms. "Aliphatic" should be understood to refer to straight-chain, branched, and / or cyclic hydrocarbon groups, which can be saturated or unsaturated, but are not aromatic.

[0030] According to a preferred variant of the invention, the dicarboxylic acid monomer is aliphatic, especially saturated, and can be linear or branched, preferably (C3-C4)-3-4-5-6-6-7-8-9 ... 20 Alkyl dicarboxylic acid, more preferably (C8-C 15 )Alkyldicarboxylic acid. (C x -C y Alkyl groups are saturated, straight-chain or branched divalent hydrocarbon groups containing x to y carbon atoms.

[0031] Dicarboxylic acid monomers advantageously include or consist of the general formula [HOOC-(CH2]). n The diacid composition of [-COOH], wherein n is a number in the range of 1 to 30, preferably a number in the range of 5 to 10.

[0032] The dicarboxylic acid monomer may be specifically selected from malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, dodecanoic acid, hexadecanoic acid, octadecanoic acid, or a mixture of two or more of these dicarboxylic acids.

[0033] Preferably, the dicarboxylic acid monomer may be selected from malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, or a mixture of two or more of these dicarboxylic acids.

[0034] According to a variant of the invention, the dicarboxylic acid monomer can be a mixture of at least two dicarboxylic acids. In this case, the dicarboxylic acid monomer preferably includes sebacic acid.

[0035] The dicarboxylic acid monomer preferably includes or is composed of sebacic acid.

[0036] According to a preferred variant of the invention, the dicarboxylic acid monomer, glycerol, and itaconic acid crosslinking agent are the only monomers during the polycondensation process. Most preferably, the sebacic acid monomer, itaconic acid crosslinking agent, and glycerol are the only monomers in the polycondensation process.

[0037] As used herein, "stabilizer" should be understood to mean a compound that can limit (or even eliminate) secondary reactions of the double bonds of the itaconic acid ester functional group (e.g., radical reactions or Michael reactions leading to uncontrolled crosslinking of the polymer). Preferably, the stabilizer does not react with the double bonds in significant yield, or the reaction is reversible. For example, the stabilizer can undergo a Michael addition reaction in a reversible manner. Therefore, it is a nucleophilic compound with low reactivity to crosslinking agents, such as phenol or aniline.

[0038] Phenol should be understood as referring to organic compounds containing the phenol functional group: The phenolic functional group may be substituted or unsubstituted, especially substituted by one or more substituents selected from halogen atoms, -NO2 or C1-C6 alkyl, C1-C6 alkoxy or NH-(C1-C6 alkyl) groups.

[0039] Aniline should be understood as referring to organic compounds containing the aniline functional group. , where R n Represents H or C1-C6 alkyl, which may or may not be substituted, especially by one or more substituents selected from halogen atoms, -NO2 or C1-C6 alkyl, C1-C6 alkoxy or NH-(C1-C6 alkyl) groups.

[0040] According to the first variant, the stabilizer comprises or is composed of the general formula: The compound composition: in X represents O or NR n , where R n Represents H or C1-C6 alkyl, R1 represents H, -CO-aryl, or -CO-heteroaryl. R independently represents H, a halogen atom, -NO2, -OH, C1-C6 alkoxy, -COOH, -COO-(C1-C6 alkyl), NH-(C1-C6 alkyl), -SR2, or C1-C6 alkyl (optionally substituted with an OR2 or SR2 group). R2 independently represents C1-C8 alkyl, and p is a number in the range of 1 to 4, preferably 1 or 2.

[0041] Preferably, p is 1 or 2, and R independently represents H, -OH, -COOH, C1-C6 alkyl (optionally substituted by an SR2 group, wherein R2 represents C1-C8 alkyl) or C1-C6 alkoxy.

[0042] R1 preferentially represents H or -CO-phenyl.

[0043] For the purposes of this invention, "halogen atom" or "halogen" should be understood to mean fluorine, chlorine, bromine or iodine atom.

[0044] For the purposes of this invention, "C1-C6 alkyl" groups should be understood to refer to monovalent saturated straight-chain or branched hydrocarbon chains having 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms. Examples include methyl, ethyl, propyl, isopropyl, butyl, pentyl, or hexyl.

[0045] For the purposes of this invention, the term "C1-C6 alkoxy" should be understood to refer to a C1-C6 alkyl group as defined above, which is attached to the remainder of the molecule by an oxygen atom. Examples include methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, tert-butoxy, n-pentoxy, or n-hexoxy.

[0046] In this document, "aryl" should be understood to refer to an aromatic hydrocarbon group, preferably containing 6 to 10 carbon atoms and comprising one or more fused rings, such as phenyl or naphthyl. Advantageously, the aryl group is phenyl.

[0047] In this article, "heteroaryl" should be understood as an aromatic group containing 5 to 10 ring atoms, one or more (preferably 1 to 4, or even more preferably 1 or 2) of which are heteroatoms, such as sulfur, nitrogen, or oxygen atoms, and the remaining ring atoms are carbon atoms. Examples of heteroaryl groups are: furanyl, thiophene, pyrrole, pyridinyl, imidazolyl, triazolyl, tetrazolyl, oxazolyl, isoxazolyl, thiazolyl, isothiazolyl, pyrazolyl, oxadiazolyl, thiadiazolyl, pyridazinyl, pyrimidinyl, pyrazinyl, triazinyl, quinolinyl, isoquinolinyl, quinoxalinyl, or indoleyl.

[0048] Therefore, stabilizers can be used alone or in mixtures.

[0049] Typically, stabilizers are aniline, phenol, methoxyphenol (especially 4-methoxyphenol or guaiacol), 2,6-dimethoxyphenol, 4,6-bis(octylthiomethyl)-o-cresol and / or 2-hydroxy-4-methoxybenzophenone.

[0050] The amount of stabilizer introduced relative to the total mass of the monomer is advantageously between 0.01% by mass and 5% by mass, preferably between 0.1% and 2%, and more preferably between 0.5% and 1.6%.

[0051] The molar ratio of glycerol to (the sum of itaconic acid crosslinking agents and dicarboxylic acid monomers) is advantageously 1 / 2 to 10 / 1, especially 1 / 1 to 5 / 1, and preferably 1 / 1 to 2 / 1.

[0052] The molar ratio of itaconic acid crosslinking agent to dicarboxylic acid monomer is advantageously 1 / 99 to 99 / 1, preferably 10 / 90 to 90 / 10, and more preferably 20 / 80 to 80 / 20.

[0053] For the purposes of this invention, "condensation polymerization" should be understood as a polymerization reaction in which multiple molecules with different properties combine to form a polymer and eliminate light molecules. This invention relates to the esterification reaction between a triol (glycerol) and a diacid (a dicarboxylic acid monomer and optionally itaconic acid), producing an ester and water molecules. Depending on the molar ratio between the monomers, the condensation polymerization reaction may include two sub-steps: first, an esterification sub-step, in which each newly formed ester bond simultaneously generates a water molecule; subsequently, where appropriate, a transesterification sub-step that does not generate water molecules. When the itaconic acid crosslinking agent is itaconic anhydride, the reaction can be compared to transesterification because no water molecules are generated, at least initially—the free carboxylic acid generated during the ring-opening process of itaconic anhydride subsequently reacts and releases water.

[0054] Itaconic acid crosslinking agents can be added simultaneously with glycerol and dicarboxylic acid monomers, or added in a subsequent step. Therefore, according to the first embodiment, the method includes: a) The step of contacting glycerol with a dicarboxylic acid monomer and at least one itaconic acid crosslinking agent, and b) Polycondensation step in the presence of a stabilizer.

[0055] According to the second implementation scheme, the method includes: a') The step of contacting glycerol with the dicarboxylic acid monomer, b') A first polycondensation step of glycerol with a dicarboxylic acid monomer to obtain a mixture containing poly(glycerol dicarboxylic acid ester), c') the step of contacting the mixture containing poly(glycerol dicarboxylate) with at least one itaconic acid crosslinking agent, and d') Optionally, a second polycondensation step in the presence of a stabilizer to form a photocrosslinkable copolyester.

[0056] Introducing itaconic acid crosslinking agents in step c') instead of step a') can further reduce side reactions.

[0057] According to any variant of the invention, the contact of the monomers, particularly steps a) and a'), is carried out in a reactor. Subsequent steps may be carried out in the same reactor or in different reactors. Those skilled in the art will be able to adjust the type and number of reactors required for the method, taking into account heating and pressure conditions.

[0058] Steps a), b), a'), b'), c') and d') are preferably carried out in an inert atmosphere.

[0059] According to one embodiment, the polycondensation step is carried out in the presence of a catalyst, the catalyst content of which is particularly 20,000 ppm or less, particularly 10,000 ppm or less, 5,000 ppm or less, preferably 3,000 ppm or less, and advantageously 2,000 ppm or less, relative to the total mass of monomers used.

[0060] The duration of polycondensation step b) can be between 1 hour and 24 hours.

[0061] Using a catalyst can shorten the reaction time. 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, and more preferably less than 2 hours.

[0062] The catalyst may specifically comprise or consist of Brønsted acids (e.g., sulfuric acid, p-toluenesulfonic acid) or Lewis acids (e.g., AlCl3, TiCl4, TiOBu4, butylstannic acid, metal trifluoromethanesulfonates or trifluoromethanesulfonates, such as bismuth trifluoromethanesulfonate, etc.) or mixtures thereof. Particularly advantageous catalysts are metal trifluoromethanesulfonates (or trifluoromethanesulfonates) in which the metal is in the oxidation state (III), especially metal salts selected from lanthanum trifluoromethanesulfonate (Ln(TfO)3), yttrium trifluoromethanesulfonate, scandium trifluoromethanesulfonate, bismuth trifluoromethanesulfonate, and iron trifluoromethanesulfonate.

[0063] The catalyst preferably contains or consists of a food-grade catalyst.

[0064] "Food-grade catalyst" should be understood as a catalyst suitable for food contact (for animals and humans) that meets the requirements to ensure that the catalyst does not pose a toxic risk to the polyester produced. Such catalysts particularly comply with the requirements of U.S. Standards 21 CFR 175.300, 21 CFR 177.2420, and / or 21 CFR 175.105, which are in force as of the application date.

[0065] Food-grade catalysts are advantageously tin-based catalysts, preferably selected from organotin compounds containing a carboxyl group (-C(O)OH) or a functional group (-Sn(O)OH). According to specific variants of the invention, the catalyst is selected from alkyltin compounds containing a carboxyl functional group (-C(O)OH) or a functional group (-Sn(O)OH), wherein the alkyl group has 1 to 10 carbon atoms, preferably 1 to 4 carbon atoms. These specific compounds include food-grade monobutyltin oxide (or stannic acid) and food-grade tris(2-ethylhexanoic acid) monobutyltin.

[0066] According to a preferred variant of the invention, the catalyst is food-grade monobutyltin oxide (or stannic acid).

[0067] Examples of catalysts that can be used for the purposes of this invention include monobutyltin oxide sold by PMC Organometallix under the name FASCAT 9100 and tris(2-ethylhexanoic acid) monobutyltin sold under the name FASCAT 9102. Particularly preferred is the monobutyltin oxide catalyst sold by PMC Organometallix under the name FASCAT 9100.

[0068] Therefore, at the end of step a) or in step b), the catalyst is advantageously introduced into the reaction medium in an amount less than or equal to 5000 ppm relative to the total mass of the monomers, preferably greater than or equal to 2500 ppm.

[0069] The polycondensation steps, especially steps b), b') and d'), are advantageously carried out at temperatures from 50°C to 250°C, preferably from 100°C to 200°C, and especially from 120°C to 190°C.

[0070] The reaction time for the first polycondensation (b') is typically between 1 hour and 48 hours, preferably between 2 hours and 26 hours, and more preferably between 2 hours and 24 hours. This step can be advantageously considered complete when the observed molar conversion of the minority monomers (i.e., glycerol, or conversely, the sum of dicarboxylic acid monomers and itaconic acid crosslinking agents) reaches 70%, preferably 80%, or especially 90% or higher. The molar conversion can be determined by measuring the mass of the removed distillate (water), or by sampling from the reaction medium and utilizing… 13 The determination is made by monitoring the disappearance of free minority monomers using 12C NMR or size exclusion chromatography (SEC).

[0071] The reaction time for the second polycondensation step d') is typically between 30 minutes and 12 hours, preferably between 1 hour and 8 hours, especially 2 hours and 6 hours. This step can be advantageously considered complete when the molar conversion of a few monomers is 70%, preferably 80%, or especially 90% or higher. Alternatively, when the second polycondensation step d') is carried out under stirring, the step can be considered complete when the torque of the stirring motor reaches a predetermined target value, which is preferably selected to ensure that the molar mass and viscosity of the polymer are suitable for the application targeted by this invention.

[0072] During the polycondensation step, especially in steps b) or b') and / or d'), the pressure inside the reactor can be constant or variable. The polycondensation step, especially in steps b) or b') and d'), is typically carried out at pressures between 0.0001 and 2 bar.

[0073] As mentioned above, water is a byproduct of polycondensation.

[0074] Therefore, according to a preferred variant of the invention, the polycondensation steps, especially steps b), b'), and / or d'), should be carried out under conditions where water can be removed from the reaction medium (or from the reactor). Removing the generated water during the polycondensation process has several advantages: it can increase the reaction yield and accelerate its reaction kinetics. The water thus recovered is preferably recycled as a solvent for contacting steps a) or a').

[0075] Furthermore, measuring the amount of water removed allows for monitoring the progress of the polycondensation reaction, particularly the completion of the first esterification step.

[0076] To remove water during the polycondensation step, a reactor and appropriate temperature and pressure conditions can be used to distill the water. The polycondensation reaction, especially steps b) or d'), is preferably carried out under reduced pressure, in which case the pressure is typically less than or equal to 30 mbar, especially less than or equal to 20 mbar, and preferably less than or equal to 10 mbar.

[0077] Therefore, according to the first embodiment, the method includes: a) The step of contacting glycerol with a dicarboxylic acid monomer and at least one itaconic acid crosslinking agent and a stabilizer, and b) In the polycondensation step under reduced pressure, the pressure is usually less than or equal to 30 mbar, especially less than or equal to 20 mbar, preferably less than or equal to 10 mbar, preferably at a temperature between 110°C and 200°C, preferably in the range of 120°C to 180°C, especially 130°C.

[0078] According to another embodiment, the method includes: a') The step of contacting glycerol with the dicarboxylic acid monomer, b') A first polycondensation step of glycerol with a dicarboxylic acid monomer under a pressure in the range of 1 bar to 2 bar to obtain a mixture containing poly(glycerol dicarboxylic acid ester). c') the step of contacting the mixture containing poly(glycerol dicarboxylate) with at least one itaconic acid crosslinking agent and a stabilizer, and d') A second polycondensation step under reduced pressure in the presence of a stabilizer, typically at a pressure less than or equal to 30 mbar, particularly less than or equal to 20 mbar, preferably less than or equal to 10 mbar, to form a photocrosslinkable copolyester.

[0079] The polycondensation step d') is preferably carried out between 50°C and 250°C, preferably in the range of 100°C to 200°C, and especially in the range of 120°C to 190°C. In a particular embodiment, the target temperature range for the polycondensation step d') is 110°C to 200°C, preferably 120°C to 180°C. This temperature is preferably achieved using isothermal conditions or a temperature ramp. The temperature ramp may include one or more isothermal stages (also called holding stages), with the ramp gradient typically between +0.1°C / min and +1°C / min.

[0080] Using reduced pressure during the polycondensation step can significantly improve the yield and kinetics of the corresponding polycondensation step.

[0081] According to another variation of the invention, at the end of step c'), before being placed under depressurization, the pressure is preferably reduced to an intermediate pressure between atmospheric pressure and the target depressurization value, optionally achieved through a constant pressure phase. Any method known to those skilled in the art can be used to reduce the pressure, particularly using peristaltic pumps, diaphragm pumps, rotary pumps, etc. This intermediate pressure is less than 1 bar, for example in the range of 50 to 800 mbar.

[0082] The reaction medium is then placed under reduced pressure, preferably under vacuum. In this document, "vacuum" should be understood as a pressure reduced to approximately 1 millibar.

[0083] Steps a) and a') of contacting glycerol with a dicarboxylic acid monomer and optionally at least one itaconic acid crosslinking agent are typically carried out at temperatures ranging from 20°C to 100°C.

[0084] In step a) or a'), the glycerol and dicarboxylic acid monomers can come into contact in water. Therefore, according to a variant of the invention, the contact of the monomers in step a) or a') is carried out by adding water to the mixture of glycerol and dicarboxylic acid monomers. Adding water to the monomer mixture can homogenize the mixture, thereby reducing its overall viscosity. To promote this homogenization, stirring can be performed using known methods.

[0085] According to these variants, the amount of water added to the monomer is between 0% and 100% of the mass of the monomer used, preferably between 5% and 50% of the mass of the monomer used, and more preferably between 10% and 25% of the mass of the monomer used.

[0086] According to other particularly preferred variants of the invention, the homogenization of the reaction mixture following the addition of the dicarboxylic acid monomer and optionally at least one itaconic acid crosslinking agent is improved by introducing the monomer into the mixture comprising glycerol and water to bring the monomer into contact. To facilitate this homogenization, stirring can be performed using known methods.

[0087] According to these preferred variants, prior to step a) or a'), glycerol is mixed with water, with the molar ratio of glycerol to water advantageously ranging from 1 / 10 to 10 / 1.

[0088] The mixing of glycerol and the aqueous solution can be carried out in a reactor at ambient temperature (approximately 23°C at atmospheric pressure), which can be the same reactor as in step a). This premixing step may optionally include heating the glycerol and water, for example, to a temperature in the range of approximately 50°C to 100°C. The medium is then heated for a time sufficient to dissolve or homogenize the glycerol in the water. To promote homogenization of the medium, it can be stirred in a known manner, regardless of whether it is heated.

[0089] Depending on any of these variants, the dicarboxylic acid monomer can be introduced into a mixture containing glycerol and water in liquid or solid form.

[0090] According to a preferred variant of the invention, the dicarboxylic acid monomer is introduced in solid form into a mixture containing glycerol and water, and after contact with the monomer, a step of melting the dicarboxylic acid monomer in an aqueous medium is performed.

[0091] Depending on other variants, especially when dicarboxylic acid monomers are introduced in liquid form at ambient temperature, the reflux step is optional.

[0092] According to one variant, step c') of contacting a mixture containing poly(glycerol dicarboxylate) with at least one itaconic acid crosslinking agent comprises adding at least one itaconic acid crosslinking agent and optionally a stabilizer to a mixture heated to a temperature between 50°C and 250°C, preferably in the range of 100°C to 200°C, and especially 120°C to 190°C. During the contact step c'), the temperature may preferably be in the range of ambient temperature to 130°C.

[0093] The method may further include a post-treatment step of the resulting copolyester to reduce the residual monomer content. This post-treatment step may be a washing step and / or a liquid-liquid extraction step using a water-immiscible organic solvent (preferably dichloromethane), preferably followed by washing with an aqueous phase (especially a neutral aqueous phase) and / or a saline phase (e.g., NaCl) and / or an acidic aqueous phase (e.g., a hydrochloric acid solution, especially 1 N or 2 N). The liquid-liquid extraction and / or washing are performed in a known manner.

[0094] 2. Photocrosslinkable copolyester and its composition The itaconic acid functionalization degree of the photocrosslinkable copolyester obtained by the method of the present invention is greater than or equal to 0.1 mmol / g, preferably greater than or equal to 0.5 mmol / g, and more preferably greater than or equal to 1 mmol / g.

[0095] As used herein, "itaconic acid functionalization degree" should be understood as the content of C=C double bonds in the polymer provided by at least one itaconic acid crosslinking agent, expressed in millimoles of double bonds per gram of polymer. The itaconic acid functionalization degree is typically determined by carbon-13 nuclear magnetic resonance (NMR). 13 Measured by C NMR.

[0096] The degree of itaconic acid functionalization can also be indirectly obtained by determining free itaconic acid using size exclusion chromatography (SEC). The content of free (or residual) itaconic acid is then determined. Assuming that the remaining portion of the itaconic acid used has completely reacted, the degree of itaconic acid functionalization corresponds to the difference between the amount of itaconic acid used in the reaction (or the initial amount) and the amount of free itaconic acid, expressed in millimoles per gram of the resulting polymer.

[0097] For copolymers of glycerol and itaconic acid crosslinking agents, especially those free of other monomers and diacid monomers, with a molar ratio of glycerol to itaconic acid crosslinking agent of 1:1 and a chain length of 100 glycerol / diacid monomers, the theoretical value of the degree of itaconic acid functionalization is 5.23 mmol / g, and experimental measurements confirm that it is between 5 and 6 mmol / g.

[0098] Therefore, the degree of itaconic acid functionalization in photocrosslinkable copolyesters is generally less than or equal to 6 mmol / g, especially less than or equal to 5 mmol / g. Advantageously, the degree of itaconic acid functionalization is generally greater than or equal to 0.1 mmol / g, especially greater than or equal to 0.5 mmol / g, and especially greater than or equal to 1 mmol / g.

[0099] The dicarboxylic acid monomer is advantageously, for example, the dicarboxylic acid monomer described in point 1 above. The dicarboxylic acid monomer preferably comprises or is composed of the formula [HOOC-(CH2] n The compound composition is [-COOH], wherein n is a number in the range of 1 to 30, preferably in the range of 1 to 10. It is advantageously sebacic acid (n=8).

[0100] Photocrosslinkable copolyesters may also have at least one of the following characteristics: Its number-average molar mass (Mn) is greater than or equal to 500 g / mol, especially 1000 g / mol, advantageously greater than or equal to 1500 g / mol, and preferably greater than or equal to 1700 g / mol; Its number-average molar mass (Mn) is less than or equal to 3500 g / mol, preferably less than or equal to 3000 g / mol; Its dispersion (Mw / Mn) is less than or equal to 10, preferably less than or equal to 8, and especially less than or equal to 6; The residual monomer content relative to the total weight of the polymer is less than 15% by weight, preferably less than or equal to 10% by weight; and / or The content of 1,2,3-triacylglycerol units is less than 25 mol% relative to the total number of units in the polymer, preferably less than 20 mol%.

[0101] Number-average molar mass (Mn), weight-average molar mass (Mw), and dispersion (also known as polydispersity, expressed as dispersion). The ratio of Mw to Mn (Mw / Mn) can be determined by SEC analysis in a known manner, particularly as described below. The content of residual monomers and the content of 1,2,3-triacylglycerol units can be determined by SEC analysis in a known manner. 1 H NMR, combined with 2D HSQC / HMBC and, when appropriate 13 The C NMR experiment was performed as follows.

[0102] The present invention also relates to a photocrosslinkable composition comprising: As described in this article, photocrosslinkable copolyesters, and Optional photoinitiator.

[0103] "Photoinitiator" should be understood as a compound that, when exposed to light, especially ultraviolet light, generates free radicals, thereby initiating a photocrosslinking reaction (usually a free radical reaction).

[0104] Using an excessive amount of photoinitiator can actually produce undesirable reactions during the photocrosslinking step. Therefore, it is advantageous that the content of photoinitiator is 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.

[0105] Photoinitiators suitable for photocrosslinking are well known to those skilled in the art. Photoinitiators are particularly selected from the type I photoinitiator family. Type I photoinitiators are unimolecular systems whose reactions proceed via homolytic cleavage of C-C bonds (especially via Norrish type I cleavage). The molecules involved are typically aromatic ketones, which, upon absorbing light, undergo homolytic cleavage (Norrish I-type cleavage) of the bond at the α-position relative to the carbonyl group from the triplet excited state, resulting in the formation of two free radicals capable of initiating free radical polymerization (see, in particular, Ley et al., 14th International French Optical Symposium on Optical Methods and Techniques for Industry [14th International French Optical Symposium on Optical Methods and Techniques for Industry] / 16th French Congress of the Club FLUVISU / SFO (CMOI-FLUVISU 2015), Club CMOI – French Optical Society, Nov. 2015, Pleumeur-Bodou, France. pp.124-129. hal-01583762).

[0106] Type I photoinitiators are specifically precursors of any benzoyl radical. Type II photoinitiators are specifically designed to add a radical precursor (amine) to any hexadecyl radical precursor (inert). These specifically include 2,4,6-trimethylbenzoyl diphenylphosphine ester (TPO-L), diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), or 1-hydroxycyclohexylphenyl ketone (HCHPK).

[0107] The photocrosslinkable composition may also contain one or more standard additives in the prior art, such as fillers. Fillers may be organic or inorganic. Additives may also be selected from stabilizers, compatibilizers, molding agents, active ingredient release modifiers, and antioxidants.

[0108] The composition may also contain plant-targeting active ingredients. Such compositions can be used to coat plants or parts of plants. According to this embodiment, the invention also relates to a plant treatment method comprising applying a photocrosslinkable composition to at least a portion of a plant or to soil.

[0109] Plant-targeted active products specifically include phytostimulants for agricultural use, particularly for stimulating plants of the genus Rubber Tree (e.g., Brazilian rubber tree).

[0110] Phytosanitary products, plant protection products, or herbal medicines refer to one or more substances (of natural or synthetic origin) with chemical or biological properties that are used in agriculture, horticulture, or forestry to protect cultivated plants from pests (animal pests, plant pathogens, parasitic plants, weeds) or to optimize crop yields by promoting the growth of cultivated plants and by treating their growing environment (especially the soil).

[0111] "Biostimulant" should be understood as a substance that can stimulate plant nutrient processes independently of any nutrients it contains, with the aim of improving one or more of the following characteristics of the plant or its rhizosphere: nutrient use efficiency, tolerance to abiotic stress, quality characteristics, and availability of nutrients locked in the soil or rhizosphere (according to EU Regulation 2019 / 1009). Biostimulants can be certain low-risk natural preparations (NPLCs). NPLCs are: - Natural substances (NSBU) used for biostimulant purposes, or - Basic substances.

[0112] The definition of basic substances is found in Article 23 of Regulation (EC) 1107 / 2009. These substances are those with phytosanitary value, but whose primary use is not plant protection (e.g., food).

[0113] The formulations of the present invention preferably contain phytosanitary active ingredients and / or biostimulants, which are selected from stimulants, fertilizers, insecticides, fungicides, nutrients, fungicides, insecticides and growth regulators.

[0114] The formulations of the present invention preferably contain phytosanitary active ingredients and / or biostimulants, which are ethylene precursors, preferably ethephon.

[0115] The compositions of the present invention may be in the form of paste, patch, granules or spray solution, preferably in the form of paste.

[0116] 3. Photocrosslinking methods The present invention also relates to a method for photocrosslinking the photocrosslinkable composition or photocrosslinkable copolyester described herein, the method comprising the step of irradiating the photocrosslinkable composition or photocrosslinkable copolyester with ultraviolet light, preferably in the presence of a photoinitiator.

[0117] The irradiation is advantageously carried out at a temperature in the range of 15°C to 30°C.

[0118] The irradiation is usually carried out at atmospheric pressure.

[0119] Preferably, the wavelength of irradiation is between 250 nm and 500 nm, more preferably in the range of 300 nm to 450 nm, more preferably in the range of 350 nm to 400 nm, and especially 365 nm.

[0120] Irradiation is advantageous at 5 to 25 mW / cm 2 Especially 8 to 20 mW / cm 2 It is performed at a power level.

[0121] Advantageously, the content of photoinitiator is less than or equal to 5% by mass relative to the total mass of the photocrosslinkable composition, more preferably less than or equal to 1% by mass.

[0122] The photoinitiator is as described above.

[0123] The typical irradiation time for photocrosslinkable compositions or photocrosslinkable copolyesters is between 1 second and 5 hours.

[0124] It is preferable to add the photoinitiator to the crosslinkable composition or copolyester at ambient temperature. This avoids any unwanted crosslinking reactions.

[0125] More specifically, the present invention relates to the use of photocrosslinkable compositions for the preparation of products by 3D printing (preferably photocrosslinked 3D printing). Examples of such techniques are stereolithography (SLA) and methods known as digital light processing (DLP), continuous liquid interface fabrication (CLIP), solar polymer printing (DPP), and thin film transfer imaging (FTI).

[0126] 4. Cross-linked copolyesters and their applications The present invention also relates to crosslinked copolyesters obtained by crosslinking (especially thermal crosslinking and / or photocrosslinking) the photocrosslinkable copolyester of the present invention or the photocrosslinkable composition of the present invention.

[0127] According to one variant, the crosslinked copolyester can therefore be obtained by the photocrosslinking method described above.

[0128] According to another variant, crosslinked copolyesters can be obtained by thermal crosslinking, particularly by thermal initiation, optionally in the presence of an initiator, particularly selected from substances that generate free radicals by thermal decomposition, such as peroxides (e.g., cumene hydroperoxide) or azo compounds (e.g., azobisisobutyronitrile (AIBN)), in a dispersed or non-dispersed medium.

[0129] Cross-linked copolyesters advantageously possess the following characteristics: The glass transition temperature Tg is preferably between -100°C and +30°C, between -80°C and +10°C, and especially between -60°C and 0°C, and / or Storage modulus G' greater than or equal to 0.02 MPa at 37°C and 10 Hz.

[0130] The energy storage modulus G' at 37°C and 10 Hz is advantageously less than or equal to 10 MPa.

[0131] Therefore, the photocrosslinkable composition of the present invention or the photocrosslinkable copolyester of the present invention can be used to prepare products by 3D printing.

[0132] Examples of the products mentioned include patches, implants, particles (especially microparticles and large particles), coatings, fibers, and threads that diffuse active ingredients. Attached Figure Description

[0133] Further features, objects and advantages of the present invention will become apparent from the following description, which is purely illustrative and non-limiting, and should be read in conjunction with the accompanying drawings.

[0134] [ Figure 1 [ ] is a schematic diagram of a simplified reaction scheme involved in the synthesis of poly(glycerol-co-sebate-co-itaconate) according to Example 1.

[0135] [ Figure 2 [ ] is a schematic diagram of the storage modulus G* measured, for example, of the copolyester of Example 1, after photocrosslinking, with or without a photoinitiator. Detailed Implementation

[0136] Example The following examples are given by way of illustration, but should not be construed as limiting the invention in any way.

[0137] Materials and methods Structural analysis: NMR Structural analysis was performed using NMR to determine the degree of itaconic acid functionalization and the proportion of unreacted (residual) itaconic anhydride or itaconic acid in the polymer. Spectra were acquired using a Bruker Avance III 600 MHz spectrometer equipped with a 5 mm BBFO Z-grade broadband probe. Quantitative analysis was then conducted. 1 The 1H NMR experiments used a simple 30° pulse sequence with 64 acquisitions and a 3-second repetition delay between each acquisition. Unless otherwise specified, the sample was dissolved in a deuterated solvent, i.e., deuterated acetone (acetone-d). 6 (in) . Combined 1 H NMR spectra and 2D HSQC / HMBC and 13C10 NMR experiments can be used to quantitatively analyze the microstructure of different functionalized PGS (see the attribution table).

[0138] Macroeconomic structural analysis: SEC-RI Size exclusion chromatography (SEC) technology allows for the separation of macromolecules in solution based on their size by using a column packed with porous gel. Macromolecules are separated according to their hydrodynamic volume, with the largest molecules eluting first.

[0139] While the SEC method is not absolute, it provides information on the molar mass distribution in a polymer. Different number-average molar masses (Mn) and weight-average molar masses (Mw) can be determined based on commercially available standards, and the polydispersity index (PDI) can be calculated. = Mw / Mn), also known as dispersion.

[0140] The "macrostructure" of the copolyester was analyzed by size exclusion chromatography (SEC-RI) with a differential refractometer and calibrated using low molecular weight polystyrene (PS) supplemented with a medium molecular weight standard. The sample was dissolved in butylated hydroxytoluene (BHT)-free THF at a concentration of approximately 1 g / L, stirred for two hours, and then injected. The analysis was conducted at 35 °C, with a mobile phase flow rate of 1 mL / min, using an Agilent 2 Mixed E + 2 Mixed 2 column.

[0141] Thermal Analysis: DSC Thermal analysis of the copolyester was performed using differential scanning calorimetry on a DSC3+ calorimeter sold by Mettler Toledo, using a sealed standard aluminum crucible with two small holes of opposite diameter on the crucible lid, a helium flow rate of 40 mL / min, and the following temperature ramp: 1. Maintain the temperature at 25℃ for 2 minutes. 2. Cool down from 25℃ to -100℃ at a rate of 10℃ / minute. 3. Maintain the temperature at -100℃ for 2 minutes. 4. Cool from -100℃ to 100℃ at a rate of 10℃ / minute using a ramp. 5. Cool down from 100℃ to -100℃ at a rate of -30℃ / minute on a ramp. 6. Maintain the temperature at -100℃ for 2 minutes. 7. Increase the temperature from -100℃ to 100℃ at a rate of 10℃ / minute.

[0142] The measurements taken at slope 7 correspond to the Tg of the cross-linked copolyester.

[0143] Structural Analysis: MIR Using wavelengths of 4000 and 650 cm -1 The kinetics of photocrosslinking were monitored using a mid-infrared spectrometer (MIR) (a Vertex 70” model sold by Bruker), equipped with a germanium crystal and MCT detector on a Vertex 70-3 spectrometer. The cumulative scan count (Ns) used was 32. The spectrometer was equipped with a power of 9 mW / cm². 2 A 365 nm ultraviolet LED lamp was used to irradiate the sample at a distance of 5 cm. The intensity of the irradiation was tracked at 1638 cm⁻¹ as the duration of ultraviolet irradiation varied. -1 The disappearance of the C=C band of itaconic acid at 1638 cm⁻¹ (measured at 1638 cm⁻¹) -1 The peak area of ​​the spectral band is used to monitor the crosslinking process.

[0144] Measurement of mechanical properties: Storage modulus G' Mechanical properties were measured on an Anton Paar MCR302 rheometer equipped with a 20 mm diameter planar-planar geometry. Measurements were performed on cylindrical samples 2 mm thick × 2 cm in diameter, which were molded in a metal mold and then subjected to UV-LED light (LED 365 nm, 9 Mw / cm²) at ambient temperature. 2 Crosslinking was performed for 1 hour to obtain the product.

[0145] The sample was subjected to a frequency sweep from 0.1 to 100 Hz at 37 °C under a sinusoidal shear load with a strain of 0.1%. The stresses obtained were measured. The results are expressed as the storage modulus (G') at 37 °C and 10 Hz, in megapascals (MPa).

[0146] The moduli G*, G', and G'' are calculated according to the following formula: in: σ is the measured stress, and ε is the strain applied to the sample; G' is the real part of G*, called the storage modulus, which characterizes the stiffness of a viscoelastic material. G'' characterizes the elastic behavior (the energy stored and fully recovered by the material). i is the "imaginary" unit (i 2 =-1); G'' is the imaginary part of G*, called the loss modulus or dissipation modulus, which characterizes viscous behavior (energy dissipated in the form of heat).

[0147] Example 1: Synthesis of the photocrosslinkable copolyester of the present invention: poly(glycerol-co-sebate-co-itaconate) In the following text, PGS-co-IA represents poly(glycerol-co-sebate-co-itaconic acid ester) obtained with itaconic acid as a crosslinking agent, and PGS-co-ANHYTA represents poly(glycerol-co-sebate-co-itaconic acid ester) obtained with itaconic anhydride as a crosslinking agent.

[0148] Procedures using stabilizers but not catalysts: Under a nitrogen flow, glycerol (1 molar equivalent), sebacic acid (0.5 molar equivalent), itaconic acid or anhydride (0.5 molar equivalent), and 4-methoxyphenol (1.1 to 1.2% by mass of the mixture) were added to a 500 mL jacketed reactor, the top of which was connected to a distillation column, a condenser, and a collector for recovering the distillate. The reactor was then gradually heated to 130 °C under nitrogen with stirring. Once the temperature in the medium reached 130 °C, the reaction was carried out at 130 °C for 24 hours under atmospheric pressure and a nitrogen flow, with continuous removal of moisture. The reaction was stopped when the conversion exceeded 80% (measured by the amount of water produced).

[0149] After cooling to ambient temperature, PGS-co-IA or PGS-co-ANHYTA is recovered as a yellow, viscous solid.

[0150] Procedures using stabilizers and catalysts: Under a nitrogen stream, glycerol (1 molar equivalent), sebacic acid (0.5 molar equivalent), itaconic acid (0.5 molar equivalent), and 4-methoxyphenol (1.5 wt% of the monomer mixture) were added to a 100 mL reactor topped with a distillation column, a condenser, and a collector for recovering the distillate. The reactor was then gradually heated to 140 °C under nitrogen with stirring. Once the medium was homogeneous at 140 °C, bismuth trifluoromethanesulfonate (0.5 wt% of the monomer mixture) was added. The reaction was carried out at 140 °C for 1 hour and 45 minutes under atmospheric pressure and a nitrogen stream, with continuous removal of water. The reaction was terminated by stopping heating.

[0151] After cooling to ambient temperature, PGS-co-IA is recovered as a viscous solid.

[0152] Procedures without stabilizers: Glycerol (1 molar equivalent), sebacic acid (0.5 molar equivalent), and itaconic acid (0.5 molar equivalent) were added to a 500 mL jacketed reactor under a nitrogen flow. The reactor was topped with a distillation column, a condenser, and a collector for recovering the distillate. The reactor was then gradually heated to 130 °C under nitrogen with stirring. Once the temperature in the medium reached 130 °C, the reaction was carried out at atmospheric pressure and a nitrogen flow at 130 °C, with continuous removal of water. After 20 hours of reaction, an insoluble yellow gel (crosslinked PGS) was obtained (an undesirable crosslinking side reaction).

[0153] Crosslinked PGS-co-IA was recovered as a yellow gel insoluble in acetone and THF.

[0154] 13 10⁻⁶ C NMR analysis (acetone d6) [Table 1] *Consider the unsaturated groups of free and grafted itaconic acid or anhydrides. Results of low molecular weight SEC-RI analysis (THF, polystyrene standard) [Table 2] Example 2: Photocrosslinking In the presence or absence of photoinitiators 2,4,6-trimethylbenzoyl diphenylphosphine ester (TPO-L), diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), or 1-hydroxycyclohexylphenyl ketone (HCHPK), under ambient temperature and atmospheric pressure, under ultraviolet light (LED 365 nm, 9 mW / cm²), 2 The photocrosslinkable copolyester of Example 1 was crosslinked by irradiation for 1 hour (distance between lamp and sample surface: 5 cm). A photoinitiator was pre-introduced at a mass percentage of 1% of the total mixture. The photoinitiator was used to compensate for the molar amount of stabilizer present in the functionalized PGS.

[0155] Infrared analysis allows for verification at 1638 cm⁻¹ -1 The C=C band of itaconic acid ester at the location almost completely disappeared, which confirms the effectiveness of the photocrosslinking reaction.

[0156] Figure 2 The rheological measurements of the resulting crosslinked copolyester are shown. These measurements indicate that the stiffness of the crosslinked copolyester is much higher than that of the photocrosslinkable copolyester, further confirming the effectiveness of the photocrosslinking reaction.

[0157] Table 3 lists the measured glass transition temperature (Tg) of copolyesters with and without photoinitiators.

[0158] Results of differential scanning calorimetry (DSC) analysis after photocrosslinking [Table 3] in conclusion The method of this invention is simple, rapid, reliable, and repeatable. Due to the use of a stabilizer, the method also avoids uncontrolled side reactions.

[0159] The photocrosslinkable copolyesters of Example 1 were derived from non-toxic and bio-based monomers and are suitable for product manufacturing in 3D printing methods. Their mechanical and physicochemical properties are on par with prior art photocrosslinkable polymers, but they use itaconic acid ester crosslinking agents, which are non-toxic and 100% bio-based / bio-based reagents.

[0160] References: CN114456335 WO2019 / 215441 WO2021 / 078962 Rueben et al., MRS Advances (2018), 3(27), 1551-1556

Claims

1. A method for preparing a photocrosslinkable copolyester, the method comprising the step of polycondensation of glycerol with a dicarboxylic acid monomer and at least one itaconic acid crosslinking agent selected from itaconic acid and / or itaconic anhydride in the presence of a stabilizer, wherein, The dicarboxylic acid monomer is preferably an aliphatic monomer.

2. The method according to claim 1, wherein, The dicarboxylic acid monomer comprises or is composed of the general formula [HOOC-(CH2]). n The compound composition is [-COOH], wherein n is a number in the range of 1 to 30, preferably in the range of 5 to 10, and advantageously sebacic acid (n=8).

3. The method according to claim 1 or 2, wherein, The molar ratio of the itaconic acid crosslinking agent to the dicarboxylic acid monomer ranges from 1 / 99 to 99 / 1, preferably from 10 / 90 to 90 / 10, and advantageously from 20 / 80 to 80 / 20.

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

5. The method according to any one of claims 1 to 4, wherein, The polycondensation is carried out in the presence of a catalyst, the content of which is particularly 20,000 ppm or less, especially 10,000 ppm or less, 5,000 ppm or less, preferably 3,000 ppm or less, and advantageously 2,000 ppm or less, relative to the total mass of the monomers used.

6. The method according to any one of claims 1 to 5, wherein the method comprises: a) The step of contacting glycerol with a dicarboxylic acid monomer and at least one itaconic acid crosslinking agent, and b) Polycondensation step in the presence of a stabilizer.

7. The method according to any one of claims 1 to 5, wherein the method comprises: a') The step of contacting glycerol with the dicarboxylic acid monomer, b') A first polycondensation step of glycerol with a dicarboxylic acid monomer to obtain a mixture containing poly(glycerol dicarboxylic acid ester), c') the step of contacting the mixture containing poly(glycerol dicarboxylate) with at least one itaconic acid crosslinking agent, and d') Optionally, a second polycondensation step in the presence of a stabilizer to form a photocrosslinkable copolyester.

8. The method according to claim 7, wherein, The second polycondensation step (d') is carried out under reduced pressure, typically less than or equal to 30 mbar, especially less than or equal to 20 mbar, and preferably less than or equal to 10 mbar.

9. The method according to any one of claims 6 to 8, wherein, The contact step a) or a') is carried out by adding water to a mixture of glycerol and dicarboxylic acid monomers and optionally itaconic acid crosslinking agents.

10. A photocrosslinkable copolyester of glycerol and a dicarboxylic acid monomer, wherein the degree of itaconic acid functionalization is 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, wherein the photocrosslinkable copolyester can be obtained by the method according to any one of the preceding claims.

11. The photocrosslinkable copolyester according to claim 10, further comprising at least one of the following characteristics: - Its number-average molar mass (Mn) is greater than or equal to 500 g / mol, especially 1000 g / mol, advantageously greater than or equal to 1500 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 dispersion (Mw / Mn) is less than 10, preferably less than or equal to 8, and especially less than or equal to 6; - The residual monomer content is less than or equal to 15% by weight of the polymer; and / or - The content of 1,2,3-triacylglycerol units is less than 25 mol% relative to the total number of units in the polymer, preferably less than or equal to 20 mol%.

12. A photocrosslinkable composition comprising: The photocrosslinkable copolyester according to claim 10 or 11, and Optional photoinitiator, advantageously, the content of the photoinitiator is less than or equal to 5% by mass relative to the total mass of the composition.

13. A method for photocrosslinking the photocrosslinkable composition according to claim 12, the method comprising the step of irradiating the photocrosslinkable composition with ultraviolet light.

14. A crosslinked copolyester obtained by crosslinking a photocrosslinkable copolyester according to claim 10 or 11 or a photocrosslinkable composition according to claim 12.

15. The crosslinked copolyester according to claim 14, which can be obtained by the method according to claim 13.

16. The crosslinked copolyester according to claim 14 or 15, characterized in that, The crosslinked copolyester has: - A glass transition temperature Tg between -100°C and +30°C, preferably between -80°C and +10°C, especially between -60°C and 0°C, and / or - Storage modulus G' greater than or equal to 0.02 MPa at 37°C and 10 Hz.

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

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