Method for synthesising a glycerol polyester and glycerol polyester obtained thereby

Abstract

The invention relates to a method for preparing a glycerol polyester and a carboxylic diacid by polycondensation, which method comprises (a) a step of bringing into contact the monomers comprising at least the glycerol and a dicarboxylic acid, at a temperature below 100°C under an inert atmosphere, in a glycerol / dicarboxylic acid molar ratio ranging from 0.5 / 1 to 10 / 1; (b) an esterification step performed under an inert atmosphere at a temperature above 25°C, wherein the method comprises the use of a catalyst in an amount ranging from 0.01 wt% to 3 wt% relative to the weight of the monomers, the catalyst being a metal triflate (or trifluoromethylsulfonate), the metal being chosen from among scandium, yttrium, lanthanides, bismuth, gallium, indium, tin, thallium, aluminium, iron, copper, zinc, cadmium, titanium, zirconium, niobium, ruthenium, silver, tungsten, platinum and hafnium.

Description

[0001] Title of the invention: Process for the synthesis of a glycerol polyester and glycerol polyester obtained

[0002] Technical field

[0003] The field of the present invention is that of the synthesis of aliphatic polyesters, in particular glycerol polyester, obtained by esterification of hydroxyl groups of a polyol and carboxyl groups of a diacid by a polycondensation reaction.

[0004] State of the art

[0005] A conventional method for synthesizing a polymer of glycerol and a diacid is carried out in a molten medium at high temperature with long reaction times and consists of an esterification step followed by a polycondensation carried out at very low pressure. Such a method is for example described in EP1448656A1. The monomers constituting such a polymer have different affinities. Thus, glycerol is typically not very soluble with dicarboxylic acids. This poor affinity between monomers has the consequence of making the reaction difficult to control and reproduce due to difficult homogenization of the reaction medium. This leads to the production of polymers with uncontrolled macrostructural and microstructural properties, which result in limited physicochemical properties that do not always meet application needs.

[0006] US2020 / 0247945 A1 also describes a very low pressure bulk synthesis (solvent-free) of a glycerol polymer and a diacid, in particular polyglycerol sebacate (PGS). The kinetics are accelerated by a heterogeneous catalysis process, in the presence of solid calcined sulfated titanium. The polycondensation takes place at a pressure of 300 mTorr to 600 mTorr (0.4 to 0.8 mbar) in a heterogeneous medium in the presence of a quantity of the solid catalyst ranging from 1.5 to 2 mol% relative to the monomers. Since the catalyst remains in the solid state in the polycondensation medium, it is necessary to separate it from the polymer obtained at the end of the reaction. In addition, this process is energy-intensive since it requires high calcination temperatures, as well as extremely low pressure for esterification. These types of conditions also require expensive specific installations.Furthermore, this document does not provide any information on the exact microstructure and macrostructure of the resulting polyesters.

[0007] Other processes for the mass synthesis of glycerol polyesters and dicarboxylic acids have been described using other metal catalysts, in particular for the production of polyglycerol sebacate (PGS). Some metal catalysts used in these synthesis processes nevertheless have a toxicological profile which is not always compatible with the use of these polyesters to prepare biomaterials which requires syntheses in a very controlled toxicity environment.

[0008] The article in Polymer 55 (2014) 5065-5072 describes the synthesis of a polymer of glycerol and a dicarboxylic acid, adipic acid, in a bulk medium in the presence of dibutyltin oxide, which has an acute toxicity level. The resulting polymers are hyperbranched with relatively low molar masses, even after 1.5 hours of reaction. As shown in this article, the glycerol monomer involved in the preparation of glycerol polyesters is trifunctional. In other words, during polymerization, the esterification reaction can take place on the three alcohol functions of glycerol. This leads to the creation of crosslinking points or branching points in the polymer by the creation of units (1,2,3-triacylglyceride) and therefore leads to branched polyester structures.When the connection points are not controlled and undergone, we can quickly obtain a gelled product and therefore a product which flows with difficulty, causing risks of blockage and material breakage, and which is complicated to shape.

[0009] The reference Chem. Sci ., 2017, 8, 7106 7111, describes the production of PGS with an improved branching rate, thanks to the use of a boronic acid catalyst with better selectivity for the reaction of the primary alcohol functions of glycerol. This gain is nevertheless obtained by using sebacate dichloride, which leads to constraints with regard to Health, Safety and Environment (HSE) rules and reduces the industrial feasibility of such a process.

[0010] There is a continuing need to develop efficient synthesis processes for biocompatible glycerol and dicarboxylic acid polymers, especially PGS, with reduced reaction times, as well as milder pressure and temperature conditions in an acceptable toxicity environment for better industrial compatibility.

[0011] In this research, one must not lose sight of the need to control the structure of the polymer obtained, in particular by ensuring the maintenance of a controlled branching rate. It must also be taken into account that shortening reaction times for greater process efficiency can result in lower molar masses and the generation of a certain quantity of residual monomers. These can complicate the control of the thermomechanical properties of the polymer obtained.

[0012] It has been shown in WO2015184313A1 that a process for synthesizing a biocompatible glycerol polyester by the polycondensation of a diacid and glycerol, in the presence of water, allows the control of the polymerization reaction that occurs. Therefore, the development of efficient and less energy-intensive synthesis processes for a polymer of glycerol and a dicarboxylic acid, in particular PGS, must be compatible with the use of a solvent, such as water.

[0013] Technical problem

[0014] The objective of the invention is to provide an efficient and less energy-intensive process for the synthesis of a polymer of glycerol and a dicarboxylic acid, in particular PGS, compatible with the use of a solvent, which meets all the constraints defined above and which overcomes the problems encountered with prior processes. In particular, the objective of the invention is to provide an efficient and industrially more affordable process for the synthesis of a polymer of glycerol and a dicarboxylic acid, in particular PGS, having a number-average molecular weight of at least 1000g / mol with reduced reaction times and mild pressure and temperature conditions in a non-toxic environment, while controlling the structure of the polymer obtained, in particular by maintaining a controlled level of (1,2,3-triacylglyceride) units and minimizing the amount of residual monomers, in particular below 5% by mass.

[0015] Statement of the invention

[0016] Continuing its efforts, the Applicant has developed a process for synthesizing a polymer of glycerol and a dicarboxylic acid with accelerated kinetics which overcomes the synthesis difficulties described above and which offers an acceptable toxicological environment. In particular, the Applicant has developed a synthesis process which makes it possible to obtain, with significantly accelerated kinetics, even at atmospheric pressure, a polymer of glycerol and a dicarboxylic acid having a number-average molar mass of at least 1000 g / mol, or even reaching values ​​of at least 3000 g / mol, with a low residual monomer content, less than 5% by mass relative to the polymer, while controlling the content of (1,2,3-triacylglyceride) units.

[0017] One advantage of this process is that it allows for accelerated kinetics at atmospheric pressure. Another advantage of this process is that it takes place in a homogeneous medium and does not require a phase separation step at the end of the reaction. Another advantage of this process is that it is compatible with the use of a solvent such as water.

[0018] Thus, the subject of the invention is a process for preparing a polymer of glycerol and a dicarboxylic acid by polycondensation which comprises

[0019] (a) bringing into contact the monomers comprising at least glycerol and a dicarboxylic acid at a temperature below 100°C, according to a glycerol / dicarboxylic acid molar ratio varying from 0.5 / 1 to 10 / 1,

[0020] (b) esterification under an inert atmosphere at a temperature above 25°C, which process comprises the use of a catalyst in an amount varying in a range from 0.01% by mass to 3% by mass relative to the mass of monomers, said catalyst being a metal triflate (or trifluoromethyl sulfonate), the metal being chosen from scandium, yttrium, lanthanides, bismuth, gallium, indium, tin, thallium, aluminum, iron, copper, zinc, cadmium, titanium, zirconium, niobium, ruthenium, silver, tungsten, platinum and hafnium.

[0021] Summary of the invention

[0022] The invention, described in more detail below, relates to at least one of the embodiments listed in the following points:

[0023] 1. A process for preparing a polyester of glycerol and a dicarboxylic acid by polycondensation which comprises

[0024] (a) bringing into contact the monomers comprising at least glycerol and a dicarboxylic acid, at a temperature below 100°C, according to a glycerol / dicarboxylic acid molar ratio varying from 0.5 / 1 to 10 / 1,

[0025] (b) esterification under an inert atmosphere at a temperature above 25°C and at atmospheric pressure, which process comprises the use of a catalyst in an amount in a range from 0.01% by mass to 3% by mass relative to the mass of monomers, said catalyst being a metal triflate (or trifluoromethyl sulfonate), the metal being chosen from scandium, yttrium, lanthanides, bismuth, gallium, indium, tin, thallium, aluminum, iron, copper, zinc, cadmium, titanium, zirconium, niobium, ruthenium, silver, tungsten, platinum and hafnium.2. Process according to the preceding embodiment in which the dicarboxylic acid is aliphatic and comprises 3 to 36 carbon atoms.

[0026] 3. Process according to any one of the preceding embodiments in which the dicarboxylic acid has the formula [HOOC-(CH2)n-COOH], in which n is a number ranging from 1 to 30, preferably a number ranging from 1 to 10.

[0027] 4. Process according to any one of the preceding embodiments in which the dicarboxylic acid is 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.

[0028] 5. A method according to any one of the preceding embodiments wherein the dicarboxylic acid comprises sebacic acid.

[0029] 6. Method according to any one of the preceding embodiments in which the dicarboxylic acid is sebacic acid.

[0030] 7. Method according to any one of the preceding embodiments in which the dicarboxylic acid is in liquid form.

[0031] 8. Process according to any one of embodiments 1 to 6 in which the dicarboxylic acid is in solid form.

[0032] 9. Process according to the preceding embodiment in which the contacting of the monomers of step (a) is followed by a step of melting the diacid monomer in the mixture of monomers.

[0033] 10. Process according to any one of the preceding embodiments in which the contacting of the monomers of step (a) is carried out in the presence of water or an organic solvent, polar or apolar, preferably in the presence of water.

[0034] 11. Process according to any one of the preceding embodiments in which, at the end of the contacting of the monomers from step (a), the reaction medium is brought to reflux.

[0035] 12. Process according to any one of the preceding embodiments in which the catalyst is used in an amount varying in a range from 0.05% to 1% by mass relative to the mass of monomers, preferably from 0.1% to 1% by mass relative to the mass of monomers. 13. Process according to any one of the preceding embodiments in which the catalyst is scandium triflate, bismuth triflate or iron triflate, preferably bismuth triflate or iron triflate.

[0036] 14. Process according to any one of the preceding embodiments in which esterification step (b) is carried out at atmospheric pressure.

[0037] 15. Method according to any one of the preceding embodiments in which the catalyst is introduced:

[0038] - during step (a) with monomers, at room temperature

[0039] - at the end of step (a), preferably when a temperature greater than or equal to 25°C is reached.

[0040] 16. Process according to any one of the preceding embodiments, which process comprises a step of removing water, preferably by distillation, which follows or is concomitant with the esterification step (b).

[0041] 17. Method according to any one of the preceding embodiments, which method comprises, at the end of step (b), a step (c) of placing the medium under vacuum at a pressure of less than 10 mbar at a temperature of more than 25°C.

[0042] 18. Method according to any one of the preceding embodiments which method comprises at the end of step (b),

[0043] - a step (c) of placing the medium under vacuum at a pressure lower than 10 mbar at a temperature higher than 25°C and

[0044] - a step (d) of maintaining the vacuum and a temperature above 25°C, to carry out polycondensation.

[0045] 19. Method according to the preceding embodiment in which the catalyst is introduced

[0046] - during step (a) with monomers, at room temperature

[0047] - at the end of step (a), preferably when a temperature greater than or equal to 25°C is reached;

[0048] - at the end of esterification step (b), before placing under vacuum to continue with polycondensation.

[0049] 20. Method according to embodiment 18 or 19 which method comprises a step of removing water, preferably by distillation, which follows or is concomitant with the polycondensation step (d).

[0050] 21. Polyester of glycerol and a dicarboxylic acid, capable of being obtained by the process defined in any one of the preceding embodiments.

[0051] 22. Polyester of glycerol and a dicarboxylic acid according to embodiment 21, characterized in that said polyester is poly(glycerol sebacate).

[0052] 23. Method for crosslinking a glycerol polyester and a dicarboxylic acid obtained by the method defined in any one of embodiments 1 to 20, which method comprises a step of cooking the glycerol polyester and a dicarboxylic acid at the end of the method defined in any one of embodiments 1 to 20.

[0053] Definitions

[0054] In this document, unless expressly stated otherwise, all percentages (%) indicated are percentages (%) by weight.

[0055] On the other hand, any interval of values ​​designated by the expression "between a and b" represents the range of values ​​from more than a to less than b (i.e., excluding the limits a and b), while any interval of values ​​designated by the expression "from a to b" means the range of values ​​from a to b (i.e., including the strict limits a and b). In this document, when an interval of values ​​is designated by the expression "from a to b", the interval represented by the expression "between a and b" is also and preferably designated.

[0056] 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. Similarly, the compounds mentioned may also come from the recycling of materials already in use, 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 particularly concerns monomers.

[0057] Detailed description of the invention

[0058] The process according to the invention for preparing a polyester of glycerol and a dicarboxylic acid by polycondensation comprises the steps:

[0059] (a) bringing into contact the monomers comprising at least glycerol and a dicarboxylic acid, corresponding to a temperature below 100°C, according to a glycerol / dicarboxylic acid molar ratio varying from 0.5 / 1 to 10 / 1,

[0060] (b) esterification under an inert atmosphere at a temperature above 25°C, which process comprises the use of a catalyst in an amount varying in a range from 0.01% by mass to 3% by mass relative to the mass of monomers, said catalyst being a metal triflate (or trifluoromethyl sulfonate), the metal being scandium, yttrium, lanthanides, bismuth, gallium, indium, tin, thallium, aluminum, iron, copper, zinc, cadmium, titanium, zirconium, niobium, ruthenium, silver, tungsten, platinum and hafnium.

[0061] According to step (a) of the process of the invention, the glycerol and dicarboxylic acid monomers are brought into contact.

[0062] The dicarboxylic acid monomer according to the invention may be aliphatic, aromatic or aliphatic / aromatic. In the latter case, the diacid comprises an aliphatic part and an aromatic part. It preferably comprises from 3 to 36 carbon atoms. Aliphatic means linear, cyclic or branched aliphatic, whether saturated or unsaturated. According to preferred variants of the invention, the dicarboxylic acid monomer is aliphatic comprising 3 to 36 carbon atoms.

[0063] According to these variants, the dicarboxylic acid monomer may preferably correspond to the formula [HOOC-(CH2)n-COOH], in which n is a number ranging from 1 to 30, preferably a number ranging from 1 to 10.

[0064] Preferably, according to these variants of the invention, 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.

[0065] According to variants of the invention, the dicarboxylic acid monomer may be a mixture of at least two different dicarboxylic acids. Preferably then, the dicarboxylic acid monomer comprises sebacic acid.

[0066] According to preferred variants of the invention, the dicarboxylic acid monomer is sebacic acid.

[0067] According to preferred variants of the invention, the dicarboxylic acid monomer and glycerol are the only monomers. Very preferably then, the sebacic acid monomer and glycerol are the only monomers.

[0068] According to any of the variants of the invention, the contacting of the monomers is carried out in a container or reactor. The following reactions can take place in the same reactor. Given the heating and pressure conditions, a person skilled in the art will be able to adapt the type of container or reactor necessary for the process.

[0069] The dicarboxylic acid monomer can be used in liquid or solid form.

[0070] According to the invention, the monomers are brought into contact at a temperature below 100°C. Advantageously, particularly when the dicarboxylic acid monomer is introduced in solid form, the contacting of the monomers is followed by a step of melting the diacid monomer, in order to homogenize the medium. Alternatively, the addition of water or an organic solvent to the monomer mixture allows homogenization of the mixture and thus reduces its overall viscosity. In order to promote this homogenization, stirring is carried out in a known manner.

[0071] Thus, according to variants of the invention, the contacting of the monomers of step (a) is carried out in the presence of an organic solvent or water, preferably in the presence of water.

[0072] According to these variants, an organic solvent, more preferably polar and aprotic or water is optionally added to the monomers in an amount by mass of between 0% by mass and 1000% by mass of the mass of the monomers involved, preferably ranging from 5% by mass to 500% by mass of the mass of the monomers involved, more preferably ranging from 10% by mass to 50% by mass of the mass of the monomers involved. For the case where the solvent is a polar organic solvent, it is preferably aprotic, chosen by a person skilled in the art as allowing the monomers and the polymer produced to be solubilized and with a boiling point sufficiently high to carry out the reaction under the required conditions, such as for example tetrahydrofuran, dichloromethane, acetone, acetonitrile.

[0073] According to an advantageous implementation of the invention, after bringing the monomers of step (a) into contact, the reaction medium is brought to reflux by heating it. The reflux of the medium allows, for example, the melting of the dicarboxylic acid monomer when it is introduced in solid form. The reflux of the reaction medium can be carried out by heating the medium to a temperature varying from approximately 50 to 180°C for a sufficient time to obtain the melting and intimate mixing of the monomers. During this temperature increase step which makes it possible to obtain a homogeneous medium, care is taken to condense the vapors well in the reactor, for example by configuring the column in total reflux, according to methods well known to those skilled in the art.

[0074] In other variants, for example when the dicarboxylic acid is introduced as a liquid at room temperature, the reflux step is optional.

[0075] Those skilled in the art will understand that in certain embodiments, it may be advantageous, especially in the presence of a solvent such as water or an organic solvent, in particular a solvent whose boiling point is below 200°C at atmospheric pressure, to put the reaction medium under pressure to reach temperatures of up to 200°C, or more in order to shorten the reflux time and / or for the case where the diacid monomer only melts at high temperatures. This places the reaction medium at a temperature above the boiling point at atmospheric pressure, which depends on the ingredients that constitute it.

[0076] According to step (a) of the process of the invention, the glycerol and dicarboxylic acid monomers are brought into contact with a glycerol / diacid molar ratio of between 0.5 / 1 and 10 / 1, preferably ranging from 0.9 / 1 to 2.0 / 1, more preferably from 1.0 / 1 to 1.5 / 1.

[0077] The monomers are then in liquid form and mixed homogeneously, allowing subsequent esterification and polycondensation reactions to take place in a controlled manner.

[0078] The glycerol and dicarboxylic acid monomers react with each other according to step (b) of the process of the invention, under an inert atmosphere at a temperature above 25°C, preferably ranging from 80°C to 200°C, more preferably from 100°C to 180°C, more preferably from 100°C to 160°C, by applying an isotherm or by applying a temperature ramp of between +0.1°C / min to +1°C / min in one go or in several ramps interspersed with periods of temperature maintenance until the target temperature is reached.

[0079] The esterification reaction time is defined until the conversion to monomers is greater than 50%, preferably greater than 60%, more preferably greater than 70%, preferably greater than 80%, more preferably greater than 90%, typically between 1h and 48h depending on the conditions applied, preferably between 2h and 26h, preferably between 2h30 and 24h. The conversion is determined by measuring the mass of distillate produced, namely here water produced, or by NMR 13 C by measuring free glycerol or by SEC by measuring free sebacic acid or free glycerol. Preferably, the conversion is determined by measuring the mass of distillate produced, in particular water produced. These different measurement methods are known to those skilled in the art.

[0080] A reaction under an inert atmosphere is known to mean a reaction in an inert gas such as nitrogen, carbon dioxide, a rare gas or a mixture thereof.

[0081] This esterification step (b) is preferably carried out at atmospheric pressure. Conducting at atmospheric pressure makes it possible, in particular, to easily and simply evacuate, without any specific elaborate device, the water formed during the esterification of the acid functions.

[0082] Thus, according to advantageous variants of the invention, concomitantly with step (b), the water produced as a by-product of the esterification reaction is removed, for example by distillation or any other method known for removing water. According to the variants which involve the use of water as a solvent in step (a), the removal of the water formed in step (b), for example by distillation, can be carried out following the step of removing the water initially added in step (a). Thus, at this stage of the process according to these variants, part of the water removed is the water added to carry out step (a), while the other part of the water is the by-product of the reaction of the monomers with each other. By measuring the quantity of water removed, it is possible to determine when the water from step (a) has been completely removed. It is thus possible to determine the start of step (b).

[0083] An essential element of the invention consists of the use of a catalyst in an amount varying in a range from 0.01% by mass to 3% by mass, said catalyst being a metal triflate (or trifluoromethyl sulfonate), the metal being chosen from scandium, yttrium, lanthanides, bismuth, gallium, indium, tin, thallium, aluminum, iron, copper, zinc, cadmium, titanium, zirconium, niobium, ruthenium, silver, tungsten, platinum and hafnium. Preferably, the catalyst is scandium triflate, bismuth triflate or iron triflate, preferably bismuth triflate or iron triflate. In the case of iron triflate, iron III triflate will be preferred.The inventors have in fact demonstrated that these catalysts are selective with respect to the primary alcohol functions of glycerol, generating weakly branched chains with a significantly increased molar mass compared to those obtained without using a catalyst.

[0084] The introduction of the catalyst into the process can be carried out at any stage of the process. Thus, it can be introduced: during step (a), preferably in an inert medium with monomers, at room temperature at the end of step (a), preferably when the reaction medium reaches the reaction temperature greater than or equal to 25°C and the medium is homogeneous The catalyst can be introduced directly in solid form, in dissolved form or in suspension in a liquid or in liquid form. When the catalyst is introduced in solid form, it is mixed with the reaction medium and dissolved in a known manner, for example with stirring. The catalyst is soluble in the reaction medium at atmospheric pressure, so that step (b) takes place in a homogeneous medium.

[0085] The catalyst according to the invention is introduced in an amount varying in a range from 0.01% by mass to 3% by mass, preferably from 0.05% by mass to 1% by mass, more preferably from 0.1% to 1% by mass relative to the mass of monomers.

[0086] At the end of these steps of the process according to the invention, the polyester produced can be recovered in a known manner, stored if necessary, and possibly treated for subsequent use.

[0087] According to variants of the invention, at the end of step (b), the process can continue with a step (c) by which the reaction medium is then placed under vacuum.

[0088] Here, the term "vacuum" means lowering the pressure to a value less than or equal to 100 mbara, preferably less than 50 mbara, more preferably less than 10 mbara. According to one embodiment, the pressure is in a range from 5 mbara to 10 mbara.

[0089] According to these variants, at the end of step (b), prior to the vacuuming of step (c), the pressure can be gradually reduced, possibly in stages, to an intermediate pressure between atmospheric pressure and vacuum. Any method known to those skilled in the art can be used to lower the pressure according to a ramp or manually, in particular using a diaphragm pump, a rotary pump, etc. Such an intermediate pressure is less than 1 bara and varies, for example, from 800 mbara to 50 mbara.

[0090] According to these variants again, the introduction of the catalyst can also be done directly at the end of step (b) before reducing the pressure to an intermediate pressure, or during the reduction, for example upon reaching a plateau, or just before the evacuation of step (c), or even after the evacuation of step (c).

[0091] At the end of step (c) and the possible introduction of the catalyst into the reaction medium, the process of the invention can optionally continue with a step (d) of polycondensation at a temperature above 25°C, preferably varying from 80°C to 250°C, more preferably from 80°C to 200°C, more preferably from 100°C to 180°C, possibly following a ramp of between +0.1°C / min and 1°C / min. Once the target temperature is reached, the pressure is gradually decreased to near vacuum.

[0092] The polycondensation can then be carried out concomitantly with step (b), or instantly in a time necessary for the installation of the vacuum at the end of step (b), or even for a period of up to 10 hours under vacuum during step (d). According to any of the variants of the invention, the end of the polycondensation is determined by means of the torque of the stirring motor which reaches a target value guaranteeing a targeted molar mass via a targeted viscosity index and / or by SEC measurement of a sample taken. The polycondensation duration is for example from 1h to 8h, or even from 2h to 6h.

[0093] According to variants of the invention, concomitantly with optional step (d), the water produced by the polycondensation reaction is removed, for example, by distillation or any other known method for removing water. According to advantageous variants of the invention, concomitantly with step (b) and step (d), the water produced by the esterification and polycondensation reactions is removed, for example, by distillation or any other known method for removing water. According to these variants, the removal of water, for example, by distillation, may be continuous from the step of removing the water initially added in the case where step (a) is carried out in the presence of water. When the removal of water is carried out by distillation, this may occur in conjunction with stirring and / or purging of the contents of the container by reaction under an inert gas.

[0094] At the end of these steps of the process according to the invention, the polyester produced can be recovered in a known manner, stored if necessary, and possibly treated for subsequent use.

[0095] At the end of these steps of the process according to the invention, the polyester of glycerol and a dicarboxylic acid obtained can also be cooked so as to form a thermoset polyester. The reaction medium of the polycondensation process according to the invention is a homogeneous medium in which the metal triflate catalyst is dissolved. Crosslinking subsequent to the synthesis of the polyester of glycerol and a dicarboxylic acid can thus advantageously be carried out in the presence of the metal triflate catalyst, which does not need to be separated from the polyester obtained at the end of the polycondensation. Crosslinking of the polyester manufactured according to the process of the invention can be carried out by recovering the polyester obtained from the polycondensation, introducing it into equipment suitable for crosslinking, and maintaining it at a sufficient temperature and for a sufficient time in order to obtain a thermoset product.

[0096] The polyester of glycerol and a dicarboxylic acid, capable of being obtained by the process according to the invention defined above according to any one of its variants, is also the subject of the invention.

[0097] The implementation of the process of the invention in all its variants and aspects, preferred or not, makes it possible to obtain a polyester of glycerol and a dicarboxylic acid, in particular a poly(glycerol sebacate) or PGS which very advantageously has the following physicochemical characteristics: a residual monomer content of less than 5% by weight of the weight of the polymer, a number-average molar mass Mn greater than or equal to 1000 g / mol, a controlled content of (1,2,3-triacylglyceride) units, preferably less than 20 mol% relative to all the units of the polymer.According to certain embodiments, the method according to the invention makes it possible to obtain a poly(glycerol sebacate) or PGS having the following physicochemical characteristics: a residual monomer content of less than 5% by weight of the weight of the polymer, a number-average molar mass Mn greater than or equal to 2000 g / mol, or even greater than or equal to 3000 g / mol, a controlled content of (1,2,3-triacylglyceride) units, preferably less than 20 mol% relative to all the units of the polymer.

[0098] The physicochemical characteristics of the polyester obtained with the process of the invention suggest interesting homogeneous and reproducible properties, due to the low level of residual monomers, and in particular improved processing properties due to the controlled level of unit (1,2,3-triacylglyceride) and therefore the control of the branching level. Indeed, the branching level is expressed as the molar ratio of the level of unit (1,2,3-triacylglyceride) to the sum of the levels of all the acylglyceride functions of the polymer.

[0099] The residual monomer content is determined according to the method described in the examples.

[0100] The macrostructure (Mn, Mw) of the polyester of glycerol and a dicarboxylic acid is determined by SEC according to the method described in the examples.

[0101] The microstructure of the polyester of glycerol and a dicarboxylic acid is determined by C NMR 13according to the method described in the examples.

[0102] The above-mentioned characteristics of the present invention, as well as others, will be better understood upon reading the following description of several exemplary embodiments of the invention, given for illustrative and non-limiting purposes.

[0103] EXAMPLES OF CARRYING OUT THE INVENTION

[0104] 1- Synthesis of polyglycerol sebacate):

[0105] The reactions are carried out in a 100 mL glass reactor stirred by a magnetic bar, topped with a small glass column and a condenser connected to a distillate recovery vessel. The reactor is connected to a ramp allowing nitrogen flushing or vacuuming of the reactor. A quantity of glycerol, a quantity of dicarboxylic acid - here sebacic acid - and optionally a solvent - here water, are introduced at room temperature and under nitrogen flow (0.1 L / min) in step (a). The products are used as is, without further purification, apart from inerting under nitrogen for 15 min before introduction into the reactor. The molar ratios between the monomers and the solvent concentration are specified in Table 1.

[0106] The nitrogen flow is maintained throughout step (b), under atmospheric pressure, with a stirring speed increased to 400 rpm and a heating setpoint set at a target temperature for a defined time specified in Table 1. If necessary, the catalyst is introduced into the reaction medium in a concentration defined at 0.5% w / w at this stage of the process and expressed relative to the total mass of monomers used. The water distilled during this step is recovered in the graduated recovery vessel. It is thus possible to measure the quantity of water produced and thus calculate the conversion. The reaction is carried out up to 80% conversion before moving on to the next step.

[0107] Then, a gradual vacuum is optionally applied to the reactor contents in step (c). The pressure is slowly reduced over about 15 minutes to a target value of less than 10 mbar. Once the pressure in the reaction vessel is stabilized, the medium is left to react at a target temperature and for a number of hours defined in Table 1 during step (d).

[0108] The produced PGS is transferred from the reactor vessel to a container after the facility has been depressurized and allowed to cool to room temperature. The product is then transferred to a freezer for storage, where it is frozen for at least approximately 24 hours before analysis.

[0109] 2- Measurement methods used:

[0110] 2-1 Determination of the microstructure of PGS polymers:

[0111] The microstructure of polymers is determined by NMR analysis 1H, supplemented by NMR analysis 13 C when the resolution of the NMR spectra of the X H does not allow the attribution and quantification of all species. Measurements are carried out using a BRUKER 500MHz NMR spectrometer at frequencies of 500.43 MHz for proton observation and 125.83 MHz for carbon observation.

[0112] 2-2 Determination of the macrostructure of PGS polymers and the level of residual monomers:

[0113] 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.

[0114] Although not an absolute method, SEC allows us to understand the distribution of molar masses of a polymer. From commercial standard products, the different number-average (Mn) and weight-average (Mw) molar masses can be determined.

[0115] Size exclusion chromatography analyses were performed using a Viscotek apparatus (Malvem Instruments) equipped with 4 columns, a guard column and 3 detectors (differential refractometer and viscometer, and light scattering). 1 mL of a sample solution with a concentration of 1 mg mL' 1 in THF was filtered through a 0.45 µm PTFE membrane. 100 pL of this solution was eluted in THF using a flow rate of 1 mL.min' 1at a temperature of 35 °C. OmniSEC software was used for data acquisition and analysis. Number-average molar masses (A n) were calculated using a calibration curve from standard polystyrenes (A p : 1,306 to 2,520,000 g mol-1) from Polymer Standard Service (Mainz). The technique used is size exclusion chromatography (SEC) with a column set optimized for the separation of low-mass species.

[0116] The samples were dissolved at a concentration of 1 g / L in unstabilized THF and then stirred for 2 h before being injected. The analytical conditions used in the study are described in the following table:

[0117] The calibration used for Moore's calculation is a PS calibration, covering a range from 2,520,000 to 162 g.mol' 1 .

[0118] The calibration used is a mixed low weight and medium weight PS calibration from PSS Standards.

[0119] The mass range is from 162 to 66,000 g.mol' 1 . Calibration allows the determination of Mn values ​​(g.mol' 1 ), Mw (g.mol' 1 ), D (Mw / Mn) in PS equivalent:

[0120] The macrostructure calculation takes into account zones 1 and 2, with residual monomers not being considered as part of the polymer.

[0121] The determination of sebacic acid and glycerol levels is carried out by external calibration.

[0122] A standard range using samples of sebacic acid and glycerol at different concentrations was carried out.

[0123] 3- Results:

[0124] Table 1a below gives the operating conditions of the synthesis process, Table 1b gives the results of the measurements carried out on the PGS obtained at the end of these syntheses. Tests: a. Synthesis of PGS carried out without catalyst or with too high a catalyst concentration (not in accordance with the invention):

[0125] Table the

[0126] *Bismuth Inflate catalyst

[0127] Table lb

[0128] According to the processes of examples 2 and 3, carried out without catalyst and in bulk (without solvent) on

[0129] 5 total durations of 4h and 6h respectively - in accordance with the prior art, a PGS is obtained whose Mn reaches a value lower than 1000 g / mol with a residual monomer content higher than 5% by weight of the weight of the polymer obtained. It takes 24h of synthesis without catalyst and in the presence of water to reach an Mn higher than 1000 g / mol with a residual monomer content lower than 5% by weight of the weight of the polymer obtained, as indicated in example 1. Finally, when too high a catalyst concentration is used (1.5% mol or 6% by weight relative to the monomers, i.e. 60,000 ppm), the reaction medium quickly takes on a yellow / orange color, with the formation of gel, which shows poor control of the reaction (example 4). The gel obtained cannot be analyzed because it is not soluble in the analytical solvents. 5 b. PGS syntheses carried out in the presence of the catalyst (in accordance with the invention):

[0130] Table 2a below gives the operating conditions of the synthesis process, Table 2b gives the results of the measurements carried out on the PGS obtained at the end of these syntheses.

[0131] The catalysts used are bismuth triflate (Bi(OTf)3), scandium triflate (Sc(OTf)3) and iron triflate (Fe(OTf)3) with a catalyst concentration expressed as 0 ppm relative to the total mass of monomers. Table 2a

[0132] Table 2b Comparison of examples 1 (non-compliant) and examples 9, 12, 18 and 19 (compliant with the invention):

[0133] According to the process carried out with the bismuth triflate catalyst in the presence of water, in accordance with the invention, a PGS is obtained whose Mn reaches a value greater than 3000 g / mol with a residual monomer content less than 5% by weight of the weight of the polymer obtained with a total duration of 3h to 3hl 5 under atmospheric pressure with 0.5%w / w and 0.1%w / w of catalyst (examples 9, 18 and 19) or with an additional step under reduced pressure (example 12): the acceleration of the reaction kinetics in view of that of example 1 is therefore very significant.

[0134] Comparison of examples 1 (non-compliant) and examples 16 and 17 (compliant with the invention):

[0135] According to the process carried out with iron triflate catalyst in the presence of water, in accordance with the invention, a PGS is obtained whose Mn reaches a value greater than 2600 g / mol with a residual monomer content less than 5% by weight of the weight of the polymer obtained with a total duration of 2h or 3h under atmospheric pressure with 0.4%w / w and 0.1%w / w of catalyst: the acceleration of the reaction kinetics in view of that of example 1 is therefore very significant.

[0136] Comparison of examples 5, 6 and 7 carried out with 0.5%w / w of Bismuth triflate under atmospheric pressure (compliant) with example 2 (non-compliant):

[0137] It is observed that the process carried out without bulk catalyst and with reaction times of the same order of magnitude, the molar masses are very significantly lower with high residual monomer levels.

[0138] Comparison of examples 8 and 10 (compliant) with example 3 (non-compliant):

[0139] We observe in the same way as previously that the process carried out without bulk catalyst and with reaction times of the same order of magnitude, the molar masses are very significantly lower with high residual monomer levels.

[0140] It is observed that examples 11, 12, 13, 14 and 15 (compliant) carried out with lower catalyst concentrations show molar masses of the polymers obtained which are very significantly higher, with low residual monomer levels, than the examples carried out without catalyst with similar reaction times (non-compliant examples 2 and 3).

[0141] Finally, we observe that non-compliant example 4, carried out with a catalyst concentration of 6% w / w, gives a yellow / orange gel that cannot be analyzed, symptomatic of an uncontrolled reaction.

Claims

CLAIMS 1. A process for preparing a polyester of glycerol and a dicarboxylic acid by polycondensation which comprises (a) bringing into contact the monomers comprising at least glycerol and a dicarboxylic acid, at a temperature below 100°C, according to a glycerol / dicarboxylic acid molar ratio varying from 0.5 / 1 to 10 / 1, (b) esterification under an inert atmosphere at a temperature above 25°C, which process comprises the use of a catalyst in an amount in a range from 0.01% by mass to 3% by mass relative to the mass of monomers, said catalyst being a metal triflate (or trifluoromethyl sulfonate), the metal being chosen from scandium, yttrium, lanthanides, bismuth, gallium, indium, tin, thallium, aluminum, iron, copper, zinc, cadmium, titanium, zirconium, niobium, ruthenium, silver, tungsten, platinum and hafnium.

2. Process according to the preceding claim in which the dicarboxylic acid has the formula [HOOC-(CH2)n-COOH], in which n is a number ranging from 1 to 30, preferably a number ranging from 1 to 10.

3. A method according to any one of the preceding claims wherein the dicarboxylic acid is sebacic acid.

4. Process according to any one of the preceding claims in which the glycerol / dicarboxylic acid molar ratio varies from 0.9 / 1 to 2.0 / 1, preferably from 1.0 / 1 to 1.5 / 1.

5. Process according to any one of the preceding claims in which the contacting of the monomers of step (a) is carried out in the presence of water or an organic, polar or apolar solvent, preferably in the presence of water.

6. Process according to any one of the preceding claims, in which the catalyst is used in an amount varying in a range from 0.05% to 1% by mass relative to the mass of monomers, more preferably in a range from 0.1% to 1% by mass relative to the mass of monomers.

7. A process according to any one of the preceding claims wherein the catalyst is scandium triflate, bismuth triflate or iron triflate, preferably bismuth triflate or iron triflate.

8. Process according to any one of the preceding claims in which step (b) of esterification under an inert atmosphere at a temperature above 25°, is carried out until reaching a monomer conversion greater than 50%, preferably greater than 60%, more preferably greater than 70% determined by measuring the mass of distillate produced.

9. Process according to any one of the preceding claims in which the esterification step (b) is carried out at atmospheric pressure.

10. Method according to any one of the preceding claims, which method comprises, at the end of step (b), a step (c) of placing the medium under vacuum at a pressure of less than 10 mbar at a temperature of more than 25°C.

11. Method according to any one of the preceding claims, which method comprises at the end of step (b), - a step (c) of placing the medium under vacuum at a pressure lower than 10 mbar at a temperature higher than 25°C and - a step (d) of maintaining the vacuum and a temperature above 25°C to carry out polycondensation.

12. Process according to any one of the preceding claims in which the catalyst is introduced: during step (a) with monomers, at room temperature at the end of step (a), preferably when a temperature greater than or equal to 25°C is reached; optionally at the end of esterification step (b), for the case where this is followed by placing under vacuum to continue with the polycondensation.

13. Process according to any one of the preceding claims, which process comprises at least one step of removing water, preferably by distillation, which follows or is concomitant with the esterification step (b).

14. Process according to any one of claims 11 to 13, which process comprises at least one step of removing water, preferably by distillation, which follows or is concomitant with the polycondensation step (d).

15. Process for crosslinking a glycerol polyester and a dicarboxylic acid obtained by the process defined in any one of claims 1 to 14, which process comprises a step of cooking the glycerol polyester and a dicarboxylic acid at the end of the process defined in any one of claims 1 to 14.

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