Method for producing polyester (co)polymer

Abstract

The present invention relates to a process for the preparation of a (co)polyester comprising the esterification, in the presence of a catalyst, of at least one monomer selected from hydroxycarboxylic acids to form an oligomer, followed by polycondensation to form a (co)polymer comprising monomer units derived from said at least one monomer, said at least one monomer being selected from α- and / or β-hydroxycarboxylic acids, in which a monohydric alcohol, in which the hydroxy group is the only reactive functional group, is also added in an amount of 5-150% by weight relative to the total weight of the monomers, said alcohol having a boiling point of 175° C. or more at ambient pressure and an acid dissociation constant (pKa) of 12.0 or less and 7.0 or more.

Description

[Technical field]

[0001] The present invention relates to a process for the preparation of polyester (co)polymers, further to novel polyester (co)polymers, compositions containing polyester (co)polymers, and articles comprising said polyester (co)polymers. [Background technology]

[0002] Poly(glycolic acid) (PGA), poly(lactic acid) (PLA) and their copolymers poly(lactide-co-glycolide) (PLGA) are linear aliphatic polyesters that have attracted great interest in the continuing transition to more sustainable plastic alternatives. This interest is based on their biodegradability and the fact that these polymers can be made from sustainable sources. PLA and PGA are bioabsorbable and their degradation rates, physical, mechanical and other properties can be tailored by using these copolymers or by varying the molecular weight. PGA is primarily used in biomedical applications due to its biocompatibility and degradability. Although PGA exhibits excellent barrier properties, it has high crystallinity, thermal instability and limited solubility, which hinder its processability and limit its use in a wider range of applications (such as packaging). On the other hand, PLA is a material that has become popular because it can be economically produced from renewable resources and has industrial compostability. PLA is used as medical implants in the form of anchors, screws, plates, pins, rods, and meshes because it can degrade into harmless lactic acid. PLA can also be used in other applications, such as degradable packaging materials, either through casting, injection molding, or spinning. It is useful in the production of bulk packaging, compost bags, food packaging, and disposable tableware. Although PLA is not yet a commercialized polymer, in 2010 it was the second most consumed bioplastic in the world. PLA is the most widely used plastic filament material in 3D printing, but the widespread application of PLA is hindered by a number of physical and processing weaknesses. Examples include poor barrier properties, insufficient strength, and limited degradability. For example, in environments where the requirements are not met, it degrades very slowly, similar to non-bioplastics.

[0003] When glycolic acid (GA) is copolymerized with lactic acid (LA), the material properties of the resulting copolymer can be tailored, avoiding the aforementioned problems to some extent. Currently, these polyesters and copolyesters are commercially produced via ring-opening melt polymerization (ROP) of glycolide and / or lactide, the cyclic dimers of glycolic acid and lactic acid, respectively. PLGA copolymers with high glycolide content (prepared by ROP) reportedly demonstrate high performance as a barrier against moisture and oxygen (see Murcia Valderrama M et al., ACS Appl. Polym. Mat. 2020, 2, 2706). This, together with its degradability and easier processability than PGA, suggests the potential of PLGA copolymers, for example, in the packaging industry. Although high molecular weights, which are for example related to favorable mechanical properties, can be achieved by this ROP synthesis strategy, the intermediate steps involved in the overall process lead to costly production, especially considering the even higher cost of glycolide compared to lactide.

[0004] Direct polycondensation of GA and / or LA monomers is considered a more cost-effective route for homo- and copolymerization of these acids. Both acids contain hydroxyl and carboxyl groups, so they can be directly converted (by esterification) to polyesters. Unfortunately, this method requires two equilibrium reactions that affect and limit the molecular weight of the resulting polymer. One reaction is related to the dehydration equilibrium for esterification, and the other reaction is related to the ring-chain equilibrium with depolymerization to glycolide or lactide, respectively. As the reaction proceeds and oligomers are formed, high temperatures and high vacuum are required for the removal of water. Under these conditions, the depolymerization reaction prevails, resulting in the formation of the monomers glycolide and lactide.

[0005] The above-mentioned shortcomings limit the possibility of producing polyesters with sufficiently high molecular weight, so this method is not currently used to produce polyesters such as PGA or PLGA, or even poly(mandelic acid) (PMA), on a commercial scale. Nevertheless, there is an increasing demand for more sustainable polymers, and as a result, there is a need for inexpensive production routes, especially for polymers containing GA and LA. Therefore, direct polycondensation approaches are still being explored as alternatives for producing these polyesters on an industrial scale.

[0006] Several studies have been reported on exploring synthetic routes for the production of PGA. However, only a few studies have been published on the preparation of high molecular weight PLGA copolymers. In fact, most of the studies on the polycondensation of PLGA or PGA copolymers have focused on the production of low molecular weight products (M less than 14 kDa). n ) have been reported. Although such copolymers may be useful in biomedical applications, e.g., drug delivery systems, they are not suitable for a wide range of applications where properties such as mechanical strength are also relevant. There remains a need for suitable, cheaper and potentially economical synthetic routes for the commercial production of high molecular weight products. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] US2011282020A1 [Patent Document 2] WO2013 / 062408A1 [Patent Document 3] WO2010 / 010282A1 [Non-patent literature]

[0008] [Non-Patent Document 1] Murcia Valderrama M et al., ACS Appl. Polym. Mat. 2020, 2, 2706 Summary of the Invention [Problem to be solved by the invention]

[0009] It would be advantageous to provide an efficient, preferably cheaper and potentially more economical, method for producing polyester (co)polymers comprising hydroxycarboxylic acids, in particular α-hydroxycarboxylic acids such as GA, LA, mandelic acid, etc., which would be of great interest in the market since the (new) high molecular weight (co)polyesters produced would have improved properties, such as better biodegradability, mechanical properties, thermal properties, barrier properties and alkali resistance, and could be applied in a wide range of applications. [Means for solving the problem]

[0010] The present invention therefore provides a process for the preparation of a (co)polyester comprising the esterification, in the presence of a catalyst, of at least one monomer selected from hydroxycarboxylic acids to form an oligomer, followed by polycondensation to form a (co)polymer comprising monomer units derived from said at least one monomer, said at least one monomer being selected from α- and / or β-hydroxycarboxylic acids, in which a monohydric alcohol, in which the hydroxy group is the only reactive functional group, is also added in an amount of 2.5 to 150% by weight, relative to the total weight of the monomers, said alcohol having a boiling point at ambient pressure of ≥ 175°C and an acid dissociation constant (pKa) of ≤ 12.0 and ≥ 7.0.

[0011] Advantageously, it has been found that the monohydric alcohols used in the process according to the invention facilitate the polymerization reaction in such a way that the complex and expensive ring-opening melt polymerization techniques (e.g. using cyclic dimer glycolide and / or lactide) as commonly used in the prior art processes are not required, especially for the preparation of the relevant polyester (co)polymers (PLA, PGA, PLGA, etc.) of high number average molecular weight (Mn), generally above 15000 g / mol. By using the process according to the invention it is possible to prepare the desired polyester (co)polymers directly from the relevant hydroxycarboxylic acids.

[0012] The present invention provides advantageous methods for the preparation of both existing and, in particular, new polyester (co)polymers, which can be advantageously used in a wide range of (industrial) applications, such as films, fibers, injection (blow) molded parts and packaging materials.

[0013] Additionally, the present invention provides a composition comprising any one of the novel polyester (co)polymers described above, and additionally one or more additives and / or one or more additional polymers.

[0014] The present invention further provides an article comprising a polyester (co)polymer according to the present invention or a composition comprising said polyester (co)polymer and one or more additives and / or additional polymers. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The present invention relates to a polymerization method for producing polyester (co)polymers (i.e. polymers or copolymers). A "polyester" is understood herein as a polymer comprising several monomer units linked via ester functional groups in the main chain. An ester functional group can be formed by reacting a hydroxyl group (-OH) with a carboxyl / carboxylic acid group (-C(=O)OH). A polyester copolymer is understood herein as a polyester in which several types of monomer units are linked in the same polymer backbone.

[0016] By "monomer unit" is herein understood a unit contained in a polyester copolymer and obtainable after polymerization of the monomers, i.e. a "monomer unit" is a building block which a single monomer or monomeric compound contributes to the structure of the polymer, i.e., herein a unit of at least one hydroxycarboxylic acid. By "monomer" or "monomer compound" is herein understood at least one starting hydroxycarboxylic acid which is polymerized.

[0017] In the present process, at least one monomer is selected from α- and / or β-hydroxycarboxylic acids, particularly preferred are the α-hydroxycarboxylic acids lactic acid and glycolic acid. Preferred β-hydroxycarboxylic acids are 3-hydroxybutanoic acid, 3-hydroxypentanoic acid, 3-hydroxyhexanoic acid, 3-hydroxyoctanoic acid, 3-hydroxydecanoic acid, and 3-hydroxydodecanoic acid. In addition to the at least one monomer selected from α- and / or β-hydroxycarboxylic acids, optionally one or more additional monomers can be used in the present process. Any further monomers herein are selected from a more comprehensive group of hydroxycarboxylic acids, including other α- and / or β-hydroxycarboxylic acids, such as, for example, mandelic acid, 3-hydroxypropionic acid, 2-, 3- and 4-hydroxybutyric acid, hydroxycaproic acid, hydroxyvaleric acid, hydroxyhexanoic acid, hydroxyheptanoic acid, hydroxyoctanoic acid, hydroxynonanoic acid, hydroxymethylfuran carboxylic acid or hydroxybenzoic acid, or mixtures of these hydroxycarboxylic acids.

[0018] A particularly preferred process according to the invention is one in which one monomer is lactic acid and the other monomer is glycolic acid, in particular 5-25 mol % lactic acid and 75-95 mol % glycolic acid, especially 10 mol % lactic acid and 90 mol % glycolic acid together giving a total of 100 mol %.

[0019] The process of the present invention comprises a step of adding a monohydric alcohol in the process, the hydroxyl group of the monohydric alcohol being the only reactive functional group, the boiling point of the monohydric alcohol at ambient pressure being equal to or higher than 175°C and up to a maximum of 300°C, and the acid dissociation constant (pKa) being equal to or lower than 12.0 and equal to or higher than 7.0. The amount of monohydric alcohol used is 2.5-150% by weight, preferably 5-150% by weight, more preferably 50-140% by weight, particularly 60-135% by weight, especially 70-130% by weight, based on the total weight of the monomers. In particular, the monohydric alcohol is an optionally substituted phenol, such as phenol, 4-alkylphenol, 4-alkoxyphenol, 2-alkylphenol, 2-alkoxyphenol, etc., or any mixture thereof, more preferably 4-methylphenol and / or 2-alkoxyphenol (particularly 2-methoxyphenol).

[0020] For certain special polyesters, a special combination of a specific monohydric alcohol and a special catalyst is preferably used. For example, it has been found that in producing PLA, a polycondensation route starting from L-lactic acid in the presence of SnOct2 as a catalyst and assisted by a small amount of phenol gives better results than other specific combinations. Thus, in producing PLA, when the monohydric alcohol is phenol, especially in combination with SnOct2 as a catalyst, the amount of monohydric alcohol used is preferably 2.5-30% by weight, more preferably 5-20% by weight, based on the total weight of the monomers.

[0021] The addition of the monohydric alcohol may be carried out before the reaction begins, for example, preferably by initially mixing the monomers with the monohydric alcohol, although the monohydric alcohol may be added at a later stage during the reaction, or both at the beginning and during the reaction, if desired. Preferably, the monohydric alcohol is added before or during the esterification step. The monohydric alcohol can act as a reactive diluent in the reaction mixture, which may be desirable or deemed necessary under certain circumstances.

[0022] If deemed necessary, for example if the reaction mixture is very viscous and dilution is deemed expedient or necessary, a solvent may also be advantageously added to the reaction mixture, said solvent being selected from liquid chemicals not carrying reactive substituents, such as diphenyl ether, dimethoxybenzene, etc. Thus, in an embodiment, in the process of the invention, a solvent is further added at the start of the process or during the course of the esterification.

[0023] As the process of the invention proceeds, the monohydric alcohol present in the reaction mixture is discharged from the reactor. The discharged material can advantageously be separated and purified and recycled. Thus, another embodiment of the invention relates to the above-described polymerization process, additionally comprising the steps of separating the monohydric alcohol (e.g., by distillation), optionally followed by purifying the separated material to recover purified monohydric alcohol, and preferably recycling said purified monohydric alcohol to the process.

[0024] The amount of each of the different monomer units in the polyester copolymer can be determined by proton nuclear magnetic resonance ( 1 The amount of each of the different monomer units in the polyester copolymer can be determined by 1 H NMR. A person skilled in the art will easily find the analytical conditions for determining the amount of each of the different monomer units in the polyester copolymer.

[0025] The polyester copolymers according to the present invention may be random copolymers, or in some cases may have a more chunky microstructure.

[0026] The number average molecular weight (Mn) of the polyester copolymer can vary and can depend, for example, on the type and amount of monomer added, the catalyst, the reaction time, and the reaction temperature and pressure.

[0027] The polyester copolymers according to the invention preferably have a number average molecular weight of 15000 g / mol or more, more preferably 20000 g / mol or more up to 200000 g / mol.

[0028] Weight average molecular weight (Mw) and number average molecular weight (Mn) can be determined by gel permeation chromatography (GPC) using poly(methyl methacrylate) standards as the reference material for calculation and hexafluoro-2-propanol as the eluent at 35° C. Total molecular weight is determined as described in the Analytical Methods section of the Examples herein.

[0029] The polyester (co)polymers according to the invention have a polydispersity index (PDI) ranging from ≧1.7 to ≦2.5, preferably from 1.9 to 2.3. PDI is the ratio of weight average molecular weight (Mw) to number average molecular weight (Mn), i.e. Mw / Mn, and indicates the distribution in chain lengths of the polymer. A high Mw is generally related to the viscosity of the polymer in the molten state and is therefore important for processability.

[0030] The glass transition temperature of the polyester copolymers can be measured by conventional methods, in particular by differential scanning calorimetry (DSC) under a nitrogen atmosphere at a heating rate of 10° C. / min. All glass transition temperatures herein are determined as described in the Analytical Methods section of the Examples.

[0031] Preferably, the polyester copolymer is generally obtained and / or derived, partially or completely (through its monomers), from one or more sustainable sources, preferably from sustainable biomass materials and / or carbon monoxide and / or carbon dioxide. More preferably, the polyester copolymer is entirely obtained and / or derived from such one or more sustainable sources. Preferably, the polyester copolymer is obtained and / or derived, partially or completely, from sources other than coal, gas or petroleum.

[0032] The process for making the polyester copolymer may include melt polymerization, and, in the case of semi-crystalline polymers, optionally solid state polymerization. For example, the process may include melt mixing the monomers in the presence of a metal-containing catalyst (also referred to herein as melt polymerization).

[0033] The polyester copolymer according to the invention can be produced, for example, by a method for producing a polyester copolymer, which comprises melt mixing the monomers in the presence of a metal-containing catalyst at a temperature ranging from 150° C. or more, more preferably 180° C. or more, up to 230° C. or less, more preferably 220° C. or less. The monohydric alcohol is added at a suitable stage of the method, as described herein above. The melt mixing can optionally be carried out in a reactor. Thus, optionally, the melt mixing can be preceded by an introduction stage in which the monomers are introduced into the reactor, and optionally, the melt mixing can be followed by a recovery stage in which the polyester copolymer is recovered from the reactor.

[0034] The process for making polyester copolymers may also include a combination of melt and solid state polymerization, where the polyester copolymer product of a melt polymerization step is subsequently subjected to a solid state polymerization step.

[0035] The process according to the invention may be carried out in the presence of one or more additives, such as ether inhibitors and stabilizers, such as light, UV and heat stabilizers, liquefaction agents, flame retardants and antistatic agents. The additives may be added at the beginning of the process or during or after the polymerization reaction. Other additives include primary and / or secondary antioxidants. Primary antioxidants may be, for example, sterically hindered phenols, such as the compounds Hostanox® 0 3, Hostanox® 0 10, Hostanox® 0 16, Ultranox® 210, Ultranox® 276, Dovernox® 10, Dovernox® 76, Dovernox® 3114, Irganox® 1010 or Irganox® 1076. The secondary antioxidant may be, for example, a compound containing trivalent phosphorus, such as Ultranox® 626, Doverphos® S-9228 or Sandostab® P-EPQ.

[0036] The process according to the invention may comprise several stages. Optionally, the process according to the invention may comprise a transesterification stage and a polycondensation stage, the transesterification stage being carried out prior to the polycondensation stage. Optionally, the transesterification stage may be preceded by an introduction stage in which the hydroxycarboxylic acid monomer and optionally additional monomers are introduced into the reactor. Optionally, the polycondensation stage may be followed by a recovery stage in which the polyester copolymer is recovered from the reactor.

[0037] The process according to the invention can be carried out in batch, semi-batch or continuous mode. The transesterification and polycondensation steps can be conveniently carried out in one and the same reactor, but can also be carried out in two separate reactors, for example the transesterification step is carried out in a first transesterification reactor and the polycondensation step is carried out in a second polycondensation reactor.

[0038] Thus, the method according to the invention may suitably - introducing a hydroxycarboxylic acid monomer and optionally additional monomer into the reactor, optionally together with an amount of monohydric alcohol; - an esterification (transesterification) stage in which the monomers are reacted in an esterification (transesterification) reaction, optionally with the addition of an amount of monohydric alcohol, and in an optional pre-polycondensation reaction, thereby producing oligomers; - a polycondensation step in which the oligomers are further reacted in a polycondensation reaction, thereby producing a polyester copolymer; and - recovering the polyester copolymer from the reactor. Includes.

[0039] In any introduction stage, all relevant reagents / components (monohydric alcohol, catalyst, monomers) can be introduced into the reactor simultaneously, for example in the form of a feed mixture or divided into separate portions. The monomers can be introduced into the reactor in the molten phase, but they can also be melted and mixed after introduction into the reactor.

[0040] The optional esterification (transesterification) step is generally carried out over a reaction time which varies depending on the temperature selected, but which preferably ranges from 0.5 hours or more, more preferably 1.0 hours or more, to 16.0 hours or less, more preferably 12.0 hours or less. During the transesterification step, the temperature may be increased in steps or gradually.

[0041] The polycondensation step may optionally be carried out at the same or higher temperature at which the transesterification step is carried out. The transesterification step may, for example, be carried out at a temperature in the range of 150° C. or more, more preferably 180° C. or more, even more preferably 190° C. or more to 230° C. or less. A polycondensation step may optionally follow the transesterification step, which may, for example, be carried out at a temperature in the range of 195° C. or more, more preferably 200° C. or more to 275° C. or less, more preferably 255° C. or less, most preferably 235° C. or less.

[0042] The optional polycondensation step is preferably carried out for a reaction time ranging from 0.5 hours or more, more preferably 1.0 hours or more, to 8.0 hours or less, more preferably 6.0 hours or less. During the polycondensation step, the temperature may be increased stepwise or gradually.

[0043] The polycondensation step may be followed by a recovery step in which the polyester copolymer described above is recovered from the reactor. The polyester may be recovered, for example, by extraction from the reactor in the form of threads of molten polymer. The threads may be converted into granules using conventional granulation techniques.

[0044] The esterification / transesterification step is preferably carried out under an inert gas atmosphere, optionally under ambient pressure or at a slightly higher pressure, for example up to 5 bar. Preferably, the polycondensation step is carried out under reduced pressure. The polycondensation step can be carried out at a pressure ranging, for example, from 0.01 mbar (corresponding to 1 Pascal) or more, more preferably from 0.1 mbar (corresponding to 10 Pascal) or more to 10.0 mbar (corresponding to 1.0 kPascal), more preferably from 5.0 mbar (corresponding to 500 Pascal) or less, in particular below 1 mbar.

[0045] The process according to the invention is optionally carried out in the presence of a (metal-containing) catalyst. For example, an acid such as p-toluenesulfonic acid may be used as a catalyst. The metal-containing catalyst may, for example, comprise a derivative of tin (Sn), titanium (Ti), zirconium (Zr), germanium (Ge), antimony (Sb), bismuth (Bi), hafnium (Hf), ytterbium (Yb), magnesium (Mg), cerium (Ce), zinc (Zn), cobalt (Co), iron (Fe), manganese (Mn), calcium (Ca), strontium (Sr), sodium (Na), lead (Pb), potassium (K), aluminum (Al), and / or lithium (Li). Examples of suitable metal-containing catalysts include salts, such as acetates and oxides (including glycol adducts and Ti alkoxides) of Li, Ca, Mg, Mn, Zn, Pb, Sb, Sn, Ge, Yb, and Ti. Examples of such compounds may be, for example, those described in paragraphs

[0026] to

[0029] of US2011282020A1 and page 5 of WO2013 / 062408A1. Preferably, the metal-containing catalyst is a tin-containing catalyst, such as a tin(IV)-containing or tin(II)-containing catalyst. More preferably, the metal-containing catalyst is an alkyltin(IV) salt and / or an alkyltin(II) salt. Examples include alkyltin(IV) salts, alkyltin(II) salts, dialkyltin(IV) salts, dialkyltin(II) salts, trialkyltin(IV) salts, trialkyltin(II) salts, or mixtures of one or more of these. These tin(IV) and / or tin(II) catalysts may be used together with alternative or additional metal-containing catalysts. Examples of alternative or additional metal-containing catalysts that may be used include titanium (IV) alkoxides or chelates, zirconium (IV) chelates or zirconium (IV) salts (e.g., alkoxides); hafnium (IV) chelates or hafnium (IV) salts (e.g., alkoxides); yttrium (III) alkoxides or chelates; lanthanum (III) alkoxides or chelates; scandium (III) alkoxides or chelates; cerium (III) alkoxides or chelates.Preferred catalysts are selected from butyl stannoic acid, tin(II) 2-ethylhexanoate, tin(II) chloride, titanium butoxide, and any combination thereof. Preferably, the catalyst is selected from butyl stannoic acid, tin(II) chloride, and tin(II) 2-ethylhexanoate. An exemplary metal-containing catalyst is, in particular, butyl stannoic acid (also known as n-butyltin hydroxide oxide).

[0046] In a preferred method, the amount of catalyst used is selected from 0.01 to 0.1 molar equivalents relative to said at least one monomer. The catalyst may be added at the start of the reaction or in portions during the reaction, for example, in a preferred embodiment, one portion may be added before the esterification step and one portion may be added at the start of the polycondensation step.

[0047] The process according to the invention may further comprise a step of carrying out polymerization in the solid state after the above-mentioned recovery step (i.e. recovering the polyester copolymer from the reactor). That is, the above-mentioned recovered polyester copolymer may be further polymerized in the solid state, thereby increasing the chain length. Such polymerization in the solid state is also called solid state polymerization (SSP). Such solid state polymerization advantageously further increases the number average molecular weight of the polyester copolymer. This may further advantageously enhance the mechanical and rheological properties of the polyester copolymer before injection blow molding or extrusion. Solid state polymerization preferably comprises a step of heating the polyester copolymer in the substantial or complete absence of oxygen and water, for example by purging with a vacuum or an inert gas.

[0048] Advantageously, the method according to the invention therefore comprises the steps of: - melt polymerization, where the monomers mentioned above are polymerized in the melt to produce a polyester (co)polymer melt product; - optional pelletization to convert the polyester (co)polymer melt product into pellets and optional drying of the pellets under vacuum or with the aid of purging with an inert gas; - solid-state polymerization of the polyester (co)polymer melt product, optionally in the form of pellets, at a temperature above the Tg of the polyester (co)polymer melt product and below the melting temperature of the polyester (co)polymer melt product. may include.

[0049] In the present invention, the solid-state polymerization may be carried out at a temperature ranging from 150° C. or more to 220° C. or less, as appropriate. The solid-state polymerization may be carried out under ambient pressure (i.e., atmospheric pressure of 1.0 bar, equivalent to 0.1 megapascals) with purging with an inert gas stream (e.g., nitrogen or argon, etc.), or under vacuum, e.g., at a pressure of 100 mbar (equivalent to 0.01 megapascals) or less. The solid-state polymerization may be carried out for a period of time ranging from 2 hours or more to 60 hours or less, as appropriate. The duration of the solid-state polymerization may be adjusted to achieve the desired final number average molecular weight for the polyester copolymer.

[0050] A preferred and advantageous embodiment of the process of the invention comprises (a) an esterification step comprising heating in a reactor, in the presence of a catalyst, at least one monomer selected from lactic acid and glycolic acid, in the presence of a monohydric alcohol in an amount of 5-150% by weight relative to the total weight of the monomers, to a temperature of 180-200° C. for a period of 6-12 hours, followed by (b) a polycondensation step comprising continuing stirring for a period of 1-3 hours and gradually reducing the pressure to a vacuum of less than 5 mbar, in particular less than 1 mbar, while removing the condensation product (water), and, optionally, at the same time, during step (b), further increasing the temperature by 10-30° C. up to a maximum of 210° C. to facilitate the removal of the monohydric alcohol and residual condensation products from the reactor.

[0051] In a further advantageous embodiment, there is provided a polyester (co)polymer, preferably obtained or obtainable by the process according to the present disclosure, having a number average molecular weight of at least 15,000 Daltons, measured by gel permeation chromatography, and a polydispersity index ranging from at least 1.7 to at most 2.5. Particularly preferred are polyester (co)polymers consisting of at least 80% of monomer units derived from α- and / or β-hydroxycarboxylic acids.

[0052] The polyester (co)polymers obtained or obtainable by the method according to the present disclosure may have advantageous properties such as improved water and oxygen permeability compared to, for example, polylactic acid (PLA) and / or polyethylene terephthalate (PET).

[0053] The polyester (co)polymer obtained or obtainable by the process of the present disclosure may, if appropriate, be combined with additives and / or other (co)polymers, and therefore the present invention further provides a composition comprising said polyester copolymer and additionally one or more additives and / or one or more additional other (co)polymers.

[0054] Such compositions may, for example, contain nucleating agents as additives. These nucleating agents may be organic or inorganic in nature. Examples of nucleating agents include talc, calcium silicate, sodium benzoate, calcium titanate, boron nitride, zinc salts, porphyrins, chlorins and phlorins.

[0055] The composition according to the invention may also comprise, as additives, nanometric (i.e. having nanometric particles) or non-nanometric, functionalized or non-functionalized, organic or inorganic fillers or fibers. These may be silica, zeolites, glass fibers or beads, clays, mica, titanates, silicates, graphite, calcium carbonate, carbon nanotubes, wood fibers, carbon fibers, polymer fibers, proteins, cellulose fibers, lignocellulosic fibers, and nondestructured granular starch. These fillers or fibers may allow for an improvement in hardness, stiffness or permeability to water or gas. The composition may comprise between 0.1% and 75% by weight, for example between 0.5% and 50% by weight, of fillers and / or fibers, relative to the total weight of the composition. The composition may also be of composite type, i.e. it may comprise a large amount of these fillers and / or fibers.

[0056] The composition may also contain, as additives, opacifiers, dyes and pigments, which may be selected from cobalt acetate and the following compounds: HS-325 Sandoplast® Red BB, also known as Solvent Red 195, a compound carrying an azo function, HS-510 Sandoplast® Blue 2B, an anthraquinone, Polysynthren® Blue R and Clariant® RSB Violet.

[0057] The composition may also contain, as additives, processing aids to reduce the pressure in the processing equipment. Release agents may also be used which allow the polyester to be molded with less adhesion to the equipment for shaping, such as the dies or rollers of a calendering machine. These agents may be selected from fatty acid esters and amides, metal salts, soaps, paraffin or hydrocarbon waxes. Specific examples of these agents are zinc stearate, calcium stearate, aluminum stearate, stearic acid amide, erucic acid amide, behenic acid amide, beeswax or candelilla wax.

[0058] The composition may also include other additives, such as stabilizers as described herein above.

[0059] In addition, the composition may contain one or more additional polymers other than the one or more polyester copolymers according to the invention. Such additional polymers may be selected from the group consisting of polyamides, polystyrene, styrene copolymers, styrene / acrylonitrile copolymers, styrene / acrylonitrile / butadiene copolymers, polymethyl methacrylate, acrylic copolymers, poly(ether / imide), polyphenylene oxides, such as poly(2,6-dimethylphenylene oxide), polyphenylene sulfides, poly(ester / carbonates), polycarbonates, polysulfones, polysulfone ethers, polyether ketones and blends of these polymers. The composition may also contain, as additional polymers, polymers that allow the improvement of the impact resistance of the polymer, in particular functional polyolefins, such as functionalized polymers and copolymers of ethylene or propylene, core / shell copolymers or block copolymers. The composition according to the invention can also contain as additional polymers polymers of natural origin, such as starch, cellulose, chitosan, alginate, proteins, such as gluten, pea protein, casein, collagen, gelatin or lignin, which can or cannot be physically or chemically modified. Starch can be used in destructured or plasticized form. In the latter case, the plasticizer can be water or a polyol, in particular glycerol, polyglycerol, isosorbide, sorbitan, sorbitol, mannitol or even urea. In particular, the method described in document WO2010 / 010282A1 can be used to prepare the composition.

[0060] These compositions can be produced, if appropriate, by conventional methods for converting thermoplastics. These conventional methods may include at least one stage of melting or softening blending the polymers and one stage of recovering the composition. Such blending can be carried out, for example, in an internal blade or rotor mixer, an external mixer, or a single-screw or co-rotating or counter-rotating twin-screw extruder. However, it is preferred that this blending is carried out by extrusion, in particular by using a co-rotating extruder. The blending of the constituents of the composition can be carried out, if appropriate, at a temperature in the range of 220 to 300° C., preferably under an inert atmosphere. In the case of an extruder, the various constituents of the composition can be introduced, if appropriate, by means of an introduction hopper located along the extruder.

[0061] The present invention also relates to an article comprising a polyester copolymer according to the invention or a composition comprising a polyester copolymer according to the invention and one or more additives and / or additional polymers.

[0062] The polyester copolymers may be conveniently used to manufacture articles such as films, fibers, injection molded parts and packaging materials, for example for receptacle or coated paper applications. The use of polyester copolymers is particularly advantageous when cold resistance is required for such films, fibers, injection molded parts or packaging materials. The articles may be fibers, for example for use in the textile industry. These fibers may be woven or even nonwoven to form fabrics. As already mentioned, the articles may be films or sheets. These films or sheets may be produced by calendering, cast film extrusion or film blown extrusion techniques. These films may be used to produce labels or insulators. The articles may be produced from the polyester copolymers or compositions comprising the polyester copolymers and one or more additives and / or additional polymers using conventional conversion techniques. The articles may also be containers for transporting gases, liquids and / or solids. The containers may be flasks, bottles, for example sparkling or still water bottles, juice bottles, carbonated drink bottles, carboys, alcoholic drink bottles, medicine bottles or cosmetic bottles, dishes, etc. These containers can be of any size. The articles can be manufactured as appropriate by, for example, extrusion blow molding, thermoforming, or injection blow molding.

[0063] The polyester copolymers can also be used for paper coating in powder, solution or melt form, for example in rod / dispersion coating, spray coating and / or extrusion / blow coating techniques.

[0064] The present invention therefore also advantageously provides a method for producing an article comprising the use of one or more polyester copolymers according to the invention, preferably comprising the steps of: 1) providing a polyester copolymer obtainable by the method of the present invention; 2) melting said polyester copolymer and optionally one or more additives and / or one or more additional polymers, thereby producing a polymer melt; and 3) extrusion blow molding, thermoforming and / or injection blow molding the polymer melt to obtain an article.

[0065] The article may also be manufactured by a process that includes the step of applying a layer of polyester in the molten state to a layer based on an organic polymer, metal or adhesive composition in the solid state, which may be carried out by pressing, overmolding, lamination, extrusion lamination, coating or extrusion coating.

[0066] The present invention is further illustrated by the following non-limiting examples. EXAMPLES

[0067] List of abbreviations DSC = Differential Scanning Calorimetry DMSO-d6 = deuterated dimethyl sulfoxide GA = glycolic acid GPC = gel permeation chromatography HFIP-d2 = deuterated hexafluoroisopropanol LA=Lactic acid MA = monohydric alcohol Mn=number average molecular weight 4-MP = 4-methylphenol Mw=mass average molecular weight PGA = Polyglycolic Acid PLA = Polylactic acid PLGA = poly(lactide-co-glycolide) copolymer PDI=Mw / Mn=polydispersity index TCE-d2 = 1,2-dideutero-1,1,2,2-tetrachloroethane Tg = glass transition temperature

[0068] Materials and Analytical Techniques All chemicals were used without further purification. Glycolic acid (99%) and L-lactic acid (L-LA) (90% aqueous solution), phenol (99%), 4-methylphenol (99%), 1,4-dimethoxybenzene and 2-methoxyphenol (guaiacol) were purchased from Acros Organics. Butylstannoic acid (BuSnO(OH)) (97%), tin(II) 2-ethylhexanoate (Sn(Oct)2), tin(II) chloride (SnCl2), p-toluenesulfonic acid (pTSA), titanium butoxide Ti(OBu)4, and ytterbium(III) trifluoromethanesulfonate [Yb(OTf)3] were purchased from Sigma Aldrich. Deuterated dimethylsulfoxide (DMSO-d6) and hexafluoroisopropanol (HFIP-d2) were also obtained from Sigma Aldrich. All chemicals were used without further purification.

[0069] on a Bruker AMX 400 (1H, 400.13MHz) using DMSO-d6 as the solvent. 1 The reaction progress and structure of all PLA samples and copolymers and homopolymers with initial compositions of 90 mol% and 80 mol% GA (100% GA) were followed by H NMR spectroscopy. The final products containing 100 mol% and 90 mol% GA were no longer soluble in this solvent. Although they are soluble in HFIP-d2, it is expensive, so only a representative sample was analyzed. The degree of racemization of some PLA samples was measured in DMSO-d6 on a Bruker Avance 500. 13 C NMR was recorded.

[0070] Molecular weight distributions were determined by gel permeation chromatography (GPC). Measurements were performed on a Merck-Hitachi LaChrom HPLC system equipped with two PL gel 5 μm MIXED-C (300 × 7.5 mm) columns using hexafluoroisopropanol as the mobile phase and poly(methyl methacrylate) (PMMA) as the calibration standard. Reported molecular weights were calculated with the software package Wyatt Astra 6.1.

[0071] Thermal transitions were measured using a Mettler Toledo differential scanning calorimeter DSC 3+ STAR. e was determined using the system. For PLGA copolymers, approximately 5 mg of each sample was introduced into a sealed aluminum pan (40 μm) and heated from room temperature to 200 °C (10 °C min -1 ). The sample was held at that temperature for 2 minutes and then cooled at the same rate to 25° C. Another heating scan was recorded under the same conditions. For PGA homopolymer, a similar method with two heating and cooling scans was applied from room temperature to 240° C. The reported glass transition temperatures T g and melting temperature T m was obtained from the second scan. The thermal stability of some of the most representative samples was determined using a TGA / DSC 3+ STARe system from Mettler Toledo. For this purpose, about 10 mg of copolymer was introduced into a sealed aluminum sample vessel (40 μm). It was then run at a flow rate of 50 mL.min -1 The sample was heated from room temperature up to 400°C (10°C.min -1 ). For PLA samples, typically, approximately 5 mg of sample was placed in a sealed 40 μm aluminum crucible under nitrogen atmosphere (50 mL min -1 ) and all samples were heated for 10℃ min -1 The sample was heated from room temperature to 180° C. at 100° C. and then cooled at the same rate to 25° C. The same program was repeated once more and the thermal transitions were obtained from the resulting curves.

[0072] Example 1 Synthesis of PLGA10 / 90 and PLGA20 / 80 from polycondensation of GA and LA using 2-methylphenol The reaction between lactic acid (LA) and glycolic acid (GA) monomers in the presence of 4-methylphenol (4-MP) can result in the formation of GA-GA, LA-GA and / or LA-LA oligomers through interactions between their hydroxyl and carboxyl end groups, with the formation of water as a by-product. At the same time, both acids can react with 4-MP through its -OH group. The formed oligomers containing acid groups at the ends of the chains can also react with the hydroxy groups of the free 4-MP in the reaction mixture. Thus, the esterification reaction can proceed until no acid end groups remain in the reaction medium, so that all GA-GA, LA-GA or LA-LA oligomers can be bound to 4-MP, forming phenolic esters. The subsequent step consists of transesterification of the formed phenolic esters, with exchange between the ester and the terminal hydroxyl group. Since this reaction is reversible, 4-MP is distilled out of the system and the equilibrium moves towards molecular weight increase.

[0073] In a typical experiment, 90 or 80 mol% GA and 10 or 20 mol% LA were used, respectively, with a total monomer charge of 20 grams per batch, in the presence of 0.1 mol% BuSnO(OH) as catalyst. The reactions were carried out in the presence of 4-MP. For comparison, experiments without 4-MP (thus a typical melt polycondensation) and with non-reactive 1,4-dimethoxybenzene were carried out, respectively. First, the effect of 4-MP addition on the molecular weight was tested. For this purpose, the amount of 4-MP (if used) was varied up to 100 mol% with respect to the total monomer charge. Note: Both L and racemic LA were tested and no differences were observed at LA contents below 20%. Procedure: GA and LA monomers, 4-MP or 1,4-dimethoxybenzene, and the catalyst were introduced into a three-necked reactor equipped with a mechanical stirrer (105 rpm) and an inlet and outlet for nitrogen. The esterification stage was carried out under a nitrogen atmosphere (30 mL min -1 ) and ambient pressure at 190° C. (oil bath temperature) for about 9 hours. The temperature was then increased to 200° C. and the pressure was gradually reduced over 2 hours until it reached 1 mbar to remove 4-MP. The same procedure was carried out for comparative melt polycondensation examples, thus without the addition of 4-MP or with the addition of 1,4-dimethoxybenzene. Finally, the product was collected and analyzed ( 1 H NMR, GPC, thermal properties).

[0074] The results are shown in Table 1 (Table 1A and Table 1B).

[0075] [Table 1A]

[0076] [Table 1B]

[0077] Example 2 Synthesis of PLGA10 / 90 from polycondensation of GA and LA using 2-methoxyphenol The naturally occurring organic compound 2-methoxyphenol, also known as guaiacol, which has a wide range of applications, is also used in PLGA. 10 / 90 The general procedure was carried out in a similar manner as described in Example 1. It was found that the esterification reaction between GA and / or LA in the presence of 2-methoxyphenol worked best at temperatures above 200° C. (oil bath temperature). Below 200° C., the reactivity between 2-methoxyphenol and both acids is very low. The amount of 2-methoxyphenol was set at 75 mol % (120 wt %) of the total monomer charge. In Table 2, a summary of the reaction conditions (temperature and time) is presented together with the glass transition temperature (Tg), number average molecular weight (Mn) and polydispersity index (PDI) obtained for the experiments carried out using 2-methoxyphenol.

[0078] [Table 2]

[0079] Example 3 Synthesis of polyglycolic acid (PGA) from polycondensation of glycolic acid (GA). PGA was synthesized using a strategy similar to that described in Example 1. BuSnO(OH) was used as the catalyst. However, the solubility of PGA is very low in both solvents, limiting the analytical possibilities. In a typical experiment, 20 grams of GA was added to a three-necked reactor equipped with a mechanical stirrer under a nitrogen atmosphere. Reaction conditions were varied, e.g., different amounts of 4-MP, reaction temperatures and times were tested and adjusted according to the results obtained for each experiment. A reference sample without 4-MP and a sample with 1,4-dimethoxybenzene were also prepared.

[0080] The results are shown in Table 3.

[0081] [Table 3]

[0082] Barrier property measurement Then, the copolymer PLGA prepared as described in Example 1 10 / 90 and PLGA 20 / 80The films were obtained by compression molding using a hot press (Carver AutoFour / 3015-NE, H). The polymer samples were first dried under vacuum at 40°C for 12 hours, and then sandwiched between two PTFE films (0.14 mm thick) and two aluminum plates (each 3 mm thick). The compression temperature was 100°C for 12 hours, and 150°C for 12 hours. 20 / 80 and PLGA 10 / 90 For the samples, pressures were set at 180°C and 195°C, respectively. The sandwich was kept at 0.5 ton for 1 minute, followed by 1 ton and 3 ton for 30 seconds each. The resulting film was rapidly cooled by contacting the PTFE sandwich with two cold aluminum plates. The thickness of the samples was measured at 12 different points using an electronic micrometer and then averaged. The oxygen and water permeability of films from both types of copolymers with thicknesses of 100-130 μm were measured with a Totalperm (Permtech srl) instrument. The system was calibrated according to the ASTM F1927-14 standard for oxygen and the ASTM E96 / E96M-15 standard for water, using standard PET films provided by Permtech (Italy). Before the measurements, the films were conditioned for about 20 hours and then tested for both examples at 30°C and 70% relative humidity (RH).

[0083] result: The water permeability (WP) and oxygen permeability (OP) of the films of the two PLGA copolymers were measured at 30° C. and 70% RH.

[0084] WP: PLGA 20 / 80 -7 is 0.68gr.mm.m -2 .day -1 .bar -1 It was found that the water permeability was PLGA 10 / 90 -25 is 0.31gr.mm.m. -2 .day -1 .bar -1 It was found that the water permeability was

[0085] Both copolymers act as a barrier against moisture, similar to PLA (2.5gr.mm.m -2 .day -1 .bar -1 ) and non-oriented PET (0.83gr.mm.m -2 .day -1 .bar -1 The improvement compared to PLA is significant for both copolymers, but the difference with PET is only for PLGA. 20 / 80 -7 is less, and PLGA 10 / 90 At -25 it's a bit too big.

[0086] OP: The measured oxygen permeability for both PLGA copolymers was 1 mm.cm 3 .m -2 .day -1 .bar -1 It was less than.

[0087] Both copolymers act as a barrier to oxygen, similar to PLA (14.15 mm.cm 3 .m -2 .day -1 .bar -1 ) and PET (4.52 mm.cm 3 .m -2 .day -1 .bar -1 ) show significantly better performance than either

[0088] Example 4 Synthesis of polylactic acid (PLA) from polycondensation of lactic acid (LA) First, the effect of the addition of monohydric alcohol for the polycondensation of L-LA was tested using variable amounts of phenol. The polymerization setup consisted of a 250 mL three-neck glass reactor equipped with a mechanical stirrer, an inlet for nitrogen and a condenser. In a typical synthesis, the lactic acid solution, 0.1 mol% of BuSnO(OH) catalyst and the required amount of monohydric alcohol (mol % with respect to the total monomer dose) were added to the reactor conditioned in an oil bath at 190 °C. The reaction mixture was constantly stirred under nitrogen flow and atmospheric pressure for up to 23 h. The temperature was then increased to 200 °C and the pressure was gradually reduced (at intervals of 15 min) from 400 to 1 mbar and maintained at 1 mbar pressure for 30 min. The products were collected and crushed for analysis. Comparative experiments without monohydric alcohol and with 1,4-dimethoxybenzene (non-reactive solvent) were performed. Additional experiments were later performed to test the effect of other catalysts at varying reaction temperatures on the resulting PLA molecular weight.

[0089] Table 4 presents a summary of the reaction conditions along with the resulting molecular weight distributions and glass transition temperatures of the PLA samples synthesized in this example. The structure of all samples was found to be amorphous. The molecular weights increased significantly when the reaction was carried out with up to about 10 wt% phenol compared to experiments carried out in the absence of monohydric alcohol. n In particular, the maximum M obtained using phenol (10 wt%) was n Equivalent to M n A three to four times larger amount of the solvent 1,4-dimethoxybenzene (38 wt%) was required to reach Furthermore, when comparing the three catalysts using 10 mol% phenol, it was observed that SnOct2 showed overall better performance than BuSnO(OH) over the range of reaction temperatures tested.

[0090] [Table 4]

[0091] Conclusion: Optimization of existing polymerization routes or development of new cheap and scalable methods is important to face the ongoing plastics transition, where PLA will continue to occupy a stable position. A polycondensation route starting from L-lactic acid and assisted by small amounts of phenol (up to 10 wt%) was found herein to increase the molecular weight of PLA. The latter was improved by about a factor of two compared to a typical polycondensation under comparable conditions. Using SnOct2 as a catalyst, M n reached 18.2 kDa and PDI 2.4, respectively. Similar molecular weight improvements could be achieved using non-reactive solvents, but this required the use of 3-4 times the amount compared to phenol.

Claims

1. 1. A process for preparing a (co)polyester, comprising esterifying at least one monomer selected from hydroxycarboxylic acids in the presence of a catalyst to form an oligomer, followed by polycondensation to form a (co)polymer comprising monomer units derived from said at least one monomer, the at least one monomer is selected from α- and / or β-hydroxycarboxylic acids; a monohydric alcohol in which a hydroxy group is the only reactive functional group is further added in an amount of 2.5 to 150% by weight based on the total weight of the monomers; The method of claim 1, wherein the monohydric alcohol has a boiling point at ambient pressure of 175°C or greater and an acid dissociation constant (pKa) of 12.0 or less and 7.0 or greater.

2. 10. The method of claim 1, wherein the monohydric alcohol is an optionally substituted phenol.

3. 3. The method according to claim 1, wherein the at least one monomer selected from α- and / or β-hydroxycarboxylic acids is selected from lactic acid and glycolic acid.

4. 10. The method of claim 1, wherein one monomer is lactic acid and the other monomer is glycolic acid.

5. 10. The method of claim 1, wherein the catalyst is selected from butylstannoic acid, tin(II) 2-ethylhexanoate, tin(II) chloride, titanium butoxide, and any combination thereof.

6. 6. The process of claim 5, wherein the amount of catalyst used is selected from 0.01 to 0.1 molar equivalents relative to the at least one monomer.

7. 10. The process of claim 1, wherein a solvent is further added at the beginning of the process or during the course of the esterification.

8. 2. A polyester (co)polymer obtainable or obtainable by the process of claim 1, having a number average molecular weight of 15,000 Daltons or more, measured by gel permeation chromatography, and a polydispersity index ranging from 1.7 to 2.

5.

9. 9. The polyester (co)polymer according to claim 8, consisting of at least 80% of monomer units derived from α- and / or β-hydroxycarboxylic acids.

10. A composition comprising a polyester (co)polymer according to claim 8 or 9 and additionally one or more additives and / or one or more additional (co)polymers.

11. 10. An article comprising a polyester (co)polymer according to claim 8 or 9 and one or more additives and / or additional polymers.