Process for producing polyesters containing 2,5-furandicarboxylate units

Abstract

A process for producing a polyester comprising 2,5-furandicarboxylate units, the process comprising: a) providing or producing a starting composition comprising 2,5-furandicarboxylic acid, an aliphatic diol, and an inhibitor for inhibiting ether formation between aliphatic diol molecules, b) subjecting the starting composition to esterification conditions to produce an ester composition, and c) contacting the ester composition with a germanium-containing catalyst under polycondensation conditions to produce a polyester comprising 2,5-furandicarboxylate units, wherein the inhibitor is selected from the group consisting of amines and lithium hydroxide.

Description

[0001] The present invention relates to a process for producing polyesters containing 2,5-furandicarboxylate units, polyesters containing 2,5-furandicarboxylate units, catalyst systems for use in such processes, and uses of the respective catalyst systems. Also disclosed are the use of lithium hydroxide to increase the polymerization rate during solid-phase polymerization and / or melt-state polymerization, and the use of an inert gas atmosphere to enhance the color properties during crystallization and / or solid-phase polymerization of polyesters containing 2,5-furandicarboxylate units.

[0002] 2,5-Furandicarboxylic acid (FDCA) is known in the art as a promising building block for replacing petroleum-based monomers in the production of high-performance polymers. In recent years, FDCA and polyethylene furanoate (PEF), a plant-based polyester, have attracted considerable attention. PEF is a recyclable plastic with superior performance characteristics compared to the plastics widely used today. These materials could significantly reduce dependence on petroleum-based polymers and plastics while allowing for more sustainable management of global resources. Comprehensive research is underway to develop technologies for commercially viable production of FDCA and PEF.

[0003] FDCA is typically obtained by oxidizing molecules with a furan moiety, such as 5-hydroxymethylfurfural (5-HMF) and the corresponding 5-HMF esters or 5-HMF ethers, which are typically obtained from plant sugars, for example by dehydration of sugars. Various oxidation processes are known from the prior art, including, for example, enzyme-catalyzed or metal-catalyzed processes, such as those described in WO 2010 / 132740 and WO 2011 / 043660.

[0004] While much of the research effort in the early days of this technology was directed toward the efficient production of FDCA monomer, researchers soon realized that achieving an efficient process for producing high-performance polyesters from FDCA was at least as challenging. While FDCA is often considered a structural and functional analog of terephthalic acid (TA), which is used to produce the widely used polyester polyethylene terephthalate (PET), it became apparent that several established technologies known in the PET industry could not be readily adapted to produce high-performance polyesters from FDCA that meet the relevant industry requirements. A comprehensive prior art is available regarding processes for producing polyesters from FDCA that focus on different aspects of the technology (e.g., EP 3116932, EP 3116934, WO 2013 / 1209989, and US 2010 / 0174044).

[0005] Several of the aforementioned difficulties are due to the different chemical properties of the monomers TA and FDCA. One very important aspect of this difference is the starting materials used in the processes for producing the respective polyesters. PET is produced on an industrial scale from the free diacid (i.e., by esterification and polycondensation) and dialkyl esters of TA (i.e., by transesterification and polycondensation), whereas the present process uses FDCA, the free diacid, as the starting material for esterification and subsequent polycondensation.

[0006] Compared to TA and its dialkyl esters, as well as the dialkyl esters of FDCA, FDCA is more susceptible to the detrimental effect known as decarboxylation. Decarboxylation is a chemical reaction of carboxylic acids that removes a carboxyl group and releases carbon dioxide, producing, for example, the monoacid furancarboxylic acid (FCA). Elevated temperatures and / or reduced pressures favor decarboxylation. Consequently, decarboxylation of FDCA has been found to be particularly severe during polycondensation processes, which typically employ high temperatures. Decarboxylation is undesirable for the production of high-performance polyesters with high molecular weights, as the FCA and its monoesters formed during esterification with diols act as chain terminators during polycondensation, thereby reducing the maximum molecular weight of the polyester that can be obtained. Accordingly, while decarboxylation is not generally reported as a problem in the architecture of TA / PET technology, reducing it during the production of polyesters containing 2,5-furandicarboxylate units from FDCA is highly advantageous.

[0007] The main object of the present invention is to provide an improved process for producing polyesters comprising 2,5-furandicarboxylate units from furandicarboxylic acid, wherein the process is capable of providing polyesters comprising 2,5-furandicarboxylate units having a low number of decarboxylated end groups and preferably a high molecular weight.

[0008] In order to obtain polyesters having good mechanical properties, it was an object of the present invention to provide a process which reduces the formation of ethers of aliphatic diols which, when introduced into the polyester produced, would have a negative impact on its properties.

[0009] Due to the expected potential of polyesters comprising 2,5-furandicarboxylate units as more eco-friendly alternatives compared to petroleum-based polyesters, a further object was to provide a process that can be operated using compounds that are considered to be more eco-friendly compared to the prior art.

[0010] Since polyesters comprising 2,5-furandicarboxylate are considered promising for some packaging applications where consumers desire transparent materials, such as for bottles, it is a further object of the present invention to provide a process for producing polyesters having good optical properties.

[0011] Furthermore, it was an object to provide a process for producing polyesters comprising 2,5-furandicarboxylate units which can be obtained in a subsequent solid phase polymerization to a high molecular weight within a relatively short reaction time (eg shorter than in prior art processes).

[0012] Another object is to provide polyesters containing 2,5-furandicarboxylate units having improved properties, in particular a high molecular weight and a low number of decarboxylated end groups and preferably a low number of ethers of aliphatic diols incorporated into the polyester. The respective polyesters therefore preferably exhibit a favorable number of carboxylic acid and hydroxyl end groups in order to be suitable for further processing, for example by solid-phase polymerization or certain reactive compounding steps.

[0013] Another object of the present invention is to provide a catalyst system for the respective process, and the use of said catalyst system for reducing the degree of decarboxylation during polycondensation.

[0014] Prior art processes for producing polyesters of diacids typically involve at least two distinct steps, namely, esterification and polycondensation, with some processes also including additional intermediate steps, such as pre-polycondensation and / or subsequent processing steps, such as pelletization, crystallization, and / or solid-phase polymerization of the resulting resin. During the esterification process, the diacid reacts with a diol under esterification conditions to produce a mixture comprising monomeric diesters and monoesters of the diacid and diol, such as hydroxyalkyl esters, depending on the concentration of the starting materials, as well as water, residual free diacid, and low-molecular-weight oligomers of these compounds.

[0015] It is known in the art that diols (particularly aliphatic diols) can form ethers with other diol molecules, thereby producing higher molecular weight diols with ether functionality. A prominent example known from TA / PET technology is the formation of diethylene glycol (DEG) from monoethylene glycol (MEG). These ether compounds can be introduced into the final polyester and are known to have an adverse effect on the physicochemical properties of the resulting polyester. Inhibitors can inhibit the ether formation between diol compounds during the esterification step, wherein in TA / PET technology, these compounds are often labeled as DEG inhibitors, indicating that they are intended to reduce the formation of DEG.

[0016] The composition obtained in the esterification step is subsequently subjected to polycondensation conditions at elevated temperature and reduced pressure in order to obtain the final polyester.The polycondensation is generally carried out in the presence of a polycondensation catalyst, which is generally a metal compound.

[0017] Optionally, a pre-polycondensation step may be used between the esterification step and the polycondensation step. The pre-polycondensation step is typically conducted at a pressure lower than that used in the esterification and can be used to remove the most volatile components (such as free glycols and other low molecular weight compounds) before further reducing the pressure to begin the polycondensation process.

[0018] Several inhibitors and polycondensation catalysts are known from the prior art. Examples of the respective compounds disclosed in the architecture for PET production are described in KR20130100697.

[0019] For the present process, a combination of an inhibitor and a polycondensation catalyst is used to produce polyester and is hereinafter referred to as a catalyst system. The inhibitor is primarily used in the esterification step and the polycondensation catalyst is used in the polycondensation step, with the simultaneous use of both compounds in both steps being optional.

[0020] Well-known catalyst systems for the preparation of polyesters, including processes for PEF production, are those comprising antimony compounds as polycondensation catalysts and ammonium compounds (especially tetraethylammonium hydroxide) or alkaline phosphates (especially sodium dihydrogen phosphate or disodium hydrogen phosphate) as inhibitors, as disclosed, for example, in WO 2015 / 137807.

[0021] In experiments described by Yosra Chebbi et al., “Solid-State Polymerization of Poly(Ethylene Furanoate) Biobased Polyester, III: Extended Strudy on Effect of Catalyst Type on Molecular Weight Increase,” Polymers, 2019, 11, 438, a germanium-containing catalyst was used to polymerize 2,5-dimethylfuran dicarboxylate and ethylene glycol at a diester / diol molar ratio of 1 / 2. Among various metal-based catalysts, germanium oxide catalysts were found to have the highest activation energy and yield low-molecular-weight PEFs.

[0022] WO 2015 / 142181 , US 2018 / 265629 and US 2017 / 0015781 include germanium in a long list of metals that can be used as a basis for polymerization catalysts.

[0023] It has now surprisingly been found that, in a process for producing polyesters comprising 2,5-furandicarboxylate units, decarboxylation can be reduced by using a catalyst system comprising a very specific group of polycondensation catalysts and a very specific group of inhibitors, namely a germanium compound as polycondensation catalyst and an inhibitor selected from the group consisting of amines and lithium hydroxide.

[0024] Below, the subject matter of the present invention will be discussed in more detail, wherein preferred embodiments of the present invention are disclosed. Particularly preferred is the combination of two or more preferred embodiments to obtain particularly preferred embodiments. Accordingly, particularly preferred is a process according to the present invention that defines two or more features of preferred embodiments of the present invention.

[0025] Each process and polyester according to the invention is described.Preferred embodiments are where the process produces a specific and / or preferred polyester as described in more detail below.

[0026] Hereinafter, weight average molecular weight and number average molecular weight are determined as disclosed in the experimental section below. In summary, weight average molecular weight and number average molecular weight are determined by using gel permeation chromatography (GPC) using hexafluoroisopropanol and 0.05 M potassium trifluoroacetate as eluents and calibrated using polymethyl methacrylate standards.

[0027] The present process for producing a polyester comprising 2,5-furandicarboxylate units comprises: a) providing or producing a starting composition comprising 2,5-furandicarboxylic acid, an aliphatic diol, and an inhibitor for inhibiting ether formation between aliphatic diol molecules, b) subjecting the starting composition to esterification conditions to produce an ester composition, preferably including the inhibitor, and c) contacting the ester composition with a germanium-containing catalyst under polycondensation conditions to produce a polyester comprising 2,5-furandicarboxylate units, wherein the inhibitor is selected from the group consisting of amines and lithium hydroxide.

[0028] The starting composition can be produced or provided, for example, purchased from a separate supplier. The starting composition comprises 2,5-furandicarboxylic acid, i.e., the free diacid. Processes starting with dialkyl esters of FDCA are not easily decarboxylated. Decarboxylation of FDCA produces 2-furancarboxylic acid, which acts as a chain terminator in the polycondensation and limits the maximum achievable molecular weight of the polyester. Therefore, it is particularly preferred to carefully limit the concentration of 2-furancarboxylic acid in the starting composition. The starting composition preferably comprises 500 ppm or less, preferably 400 ppm or less, and more preferably 300 ppm or less, of 2-furancarboxylic acid by weight, relative to the weight of the starting composition.

[0029] The starting composition further comprises an aliphatic diol.The process is very flexible in the type of aliphatic diol used, without limiting its beneficial effect on decarboxylation.

[0030] The starting composition also includes an inhibitor for inhibiting ether formation between aliphatic diol molecules. The effects of ether formation are known for various aliphatic diols, and an inhibitor capable of reducing ether formation for a given diol can be safely assumed to also at least reduce the amount of ether formation for other diols. In particular, ether formation has been found to be more problematic for reactions using FDCA as a starting material than for TA.

[0031] The starting composition prepared in step a) is subjected to esterification conditions to produce an ester composition including an inhibitor. The esterification of a diol compound with an acid compound is a reaction well known to those skilled in the art and is typically carried out at elevated temperatures. The chemical composition of the ester composition may vary based on the molar ratio of the starting materials used in the starting composition. However, for commonly used molar ratios, the ester composition tends to include monoesters of the diacid and diol compound, diesters of the diacid and diol compound, small amounts of unreacted FDCA and low molecular weight oligomers of the respective compounds, and potentially unreacted aliphatic diol compound.

[0032] Depending on the inhibitor and the reaction conditions, the ester composition at the end of the esterification typically comprises the inhibitor and / or its reaction products and / or its decomposition products, respectively. In order to achieve the desired effect of inhibiting ether formation in the process of the present invention, the inhibitor will be present during the esterification and will therefore also be contained in the ester composition as an inhibitor and / or its reaction products and / or its decomposition products. However, for some embodiments, it may be advantageous to remove the inhibitor and / or its reaction products and / or its decomposition products after step b) but before polycondensation. However, it is preferred that the inhibitor and / or its reaction products and / or its decomposition products are also present during polycondensation. In fact, the catalyst system of the present invention is specifically selected to allow the presence of the polycondensation catalyst (i.e., the germanium compound) during the esterification and the presence of the inhibitor (i.e., the amine or lithium hydroxide) in both steps.

[0033] The ester composition obtained in step b) is contacted with a germanium-containing catalyst under polycondensation conditions, wherein further intermediate steps may be carried out between step b) and step c), for example a pre-polycondensation step as described above. This polycondensation serves to produce a polyester comprising 2,5-furandicarboxylate units by forming further ester moieties between the compounds of the ester composition by means of esterification and transesterification, wherein, for example, water and / or aliphatic diols are released during the condensation process and are generally removed from the reaction due to the elevated temperatures and reduced pressures used during the polycondensation.

[0034] Both the esterification reaction and the polycondensation can be carried out in one or more steps and can be suitably operated as a batch, semi-continuous or continuous process. The esterification process is preferably carried out until the esterification reaction has proceeded to the point where 80% or more, preferably 85% or more, most preferably 90% or more of the acid groups have been converted to ester moieties before the polycondensation begins.

[0035] The polycondensation is carried out in the presence of a germanium-containing catalyst. Many different germanium-containing compounds are suitable as germanium-containing catalysts.

[0036] In the process of the present invention, the inhibitor is selected from the group consisting of amines and lithium hydroxide. The inventors have found that in principle all amines, such as primary amines, secondary amines or tertiary amines can be used in the process of the present invention.

[0037] Those skilled in the art will appreciate that the amounts of inhibitor and polycondensation catalyst may vary within typical ranges known for catalyst systems and depend primarily on the type of compound used and the amount of FDCA used in the starting material. Therefore, those skilled in the art can readily determine the appropriate amounts of these compounds for their particular purpose.

[0038] The process of the present invention overcomes the shortcomings of prior art processes and provides a process for producing polyesters comprising 2,5-furandicarboxylate units from 2,5-furandicarboxylic acid, wherein decarboxylation is reduced and the process provides polyesters comprising 2,5-furandicarboxylate units that have high molecular weight, good processability in subsequent solid-phase polymerization, i.e., exhibit good molecular weight gain during solid-phase polymerization, and a low number of decarboxylated end groups. Furthermore, the formation of ethers of aliphatic diols, which can adversely affect the properties of the produced polyester, is reduced. Furthermore, the process of the present invention allows the production of polyesters exhibiting excellent optical properties.

[0039] As a beneficial effect, the process of the present invention uses compounds that are considered to be more eco-friendly, particularly compared to the antimony compounds used in prior art processes.

[0040] Preferred is a process according to the invention wherein the aliphatic diol comprises 2 to 8 carbon atoms, preferably 2 to 6 carbon atoms, wherein the aliphatic diol preferably has carbon atoms only in the main chain. Preferably, the aliphatic diol does not comprise COC linkages.

[0041] Relatively short and mostly linear glycols are considered to show a particularly strong tendency to ether formation under conditions commonly used for esterification. Some aliphatic glycols themselves already contain ether groups in the main chain, i.e., COC connections. For example, DEG is a glycol with an internal ether group. Although such compounds are sometimes used intentionally in the prior art, it is generally found that the use of respective glycols can produce polyesters with less favorable physical-chemical properties. Although it would still be beneficial to reduce the formation of even longer oligomers (e.g., by ether formation between two diethylene glycol molecules), it is naturally most preferred to avoid the presence of respective glycols together with ether functionality.

[0042] Furthermore, alkylene glycols are generally readily available in large quantities and are easy to handle and process. At the same time, the resulting polyesters have been shown to exhibit excellent mechanical properties, particularly when ethylene glycol and / or butanediol are used.

[0043] Therefore, the process according to the present invention is preferred, wherein the polyester comprising 2,5-furandicarboxylate units is a polyalkylene furanoate, preferably selected from the group consisting of poly(ethylene 2,5-furandicarboxylate), poly(propylene 2,5-furandicarboxylate), poly(butylene 2,5-furandicarboxylate), poly(pentylene 2,5-furandicarboxylate) and copolymers thereof, more preferably selected from the group consisting of poly(ethylene 2,5-furandicarboxylate) and poly(butylene 2,5-furandicarboxylate), most preferably poly(ethylene 2,5-furandicarboxylate).

[0044] Despite the advantages described above for aliphatic diols without internal ether groups, for certain applications it may be advantageous to use diols with ether moieties. This is particularly true for heteroalicyclic compounds, such as isosorbide, which are known to produce polyesters with promising properties for specific applications.

[0045] In view of this, the process according to the present invention is preferred, wherein the aliphatic diol is selected from the group consisting of acyclic diols and alicyclic diols, preferably selected from the group consisting of alkylene glycols and alicyclic diols, more preferably selected from the group consisting of alkylene glycols, cyclohexanedimethanol and isosorbide, most preferably alkylene glycol, and particularly preferably ethylene glycol.

[0046] It has been discussed in the prior art that the molar ratio of aliphatic diol to FDCA can affect the molecular weight that can be obtained by such a process, as well as the rate at which the molecular weight increases during the subsequent solid phase polymerization process. For the specific process of the present invention using a germanium compound and a specific inhibitor, the inventors have identified a molar ratio that has been found to be particularly beneficial.

[0047] Therefore, preference is given to a process according to the invention wherein the molar ratio of the aliphatic diol to the 2,5-furandicarboxylic acid in the starting composition is in the range of 1.01 to 1.80, preferably 1.05 to 1.70, more preferably 1.07 to 1.60, most preferably 1.10 to 1.30. Preferably, the ester composition comprises a 2,5-furandicarboxylic acid mono-hydroxyalkyl ester and a 2,5-furandicarboxylic acid di-hydroxyalkyl ester, wherein the ester is obtained by 1 The total ratio of hydroxyl end groups measured by H-NMR to carboxylic acid end groups measured by titration is in the range of 1.01 to 4.6, preferably 1.05 to 2.00, more preferably 1.07 to 1.80, most preferably 1.10 to 1.30, wherein the ... 1The amount of hydroxyl end groups measured by H-NMR is preferably in the range of 300 eq / t to 2400 eq / t, more preferably 500 eq / t to 2000 eq / t, most preferably 600 eq / t to 1800 eq / t, and the amount of carboxylic acid end groups measured by titration is preferably in the range of 300 eq / t to 1200 eq / t, more preferably 500 eq / t to 1000 eq / t, most preferably 600 eq / t to 900 eq / t. Preferably, 2,5-furandicarboxylic acid and the aliphatic diol constitute 90% or more, preferably 95% or more, most preferably 98% or more by weight of the starting composition subjected to esterification, relative to the weight of the starting composition.

[0048] Preferably, the polyester produced by the present process consists of poly(ethylene 2,5-furandicarboxylate).

[0049] As described above, the optimal conditions for carrying out the esterification and polycondensation were determined in order to find the best process parameters in combination with the specific polycondensation catalyst and the specific inhibitor of the process of the present invention, thereby further minimizing decarboxylation while optimizing the yield and quality of the polyester obtainable.

[0050] It was found that the esterification of the present process is preferably carried out at a temperature in the range of 180°C to 260°C, preferably 185°C to 240°C, more preferably 190°C to 230°C. The polycondensation is preferably carried out at a temperature in the range of 240°C to 300°C, preferably 260°C to 290°C, more preferably 265°C to 285°C. Preferably, the esterification is carried out at a pressure in the range of 40 kPa to 400 kPa, preferably 50 kPa to 150 kPa, more preferably 60 kPa to 110 kPa. Preferably, the polycondensation is carried out at a reduced pressure in the range of 0.05 kPa to 100 kPa, preferably 0.05 kPa to 10 kPa, more preferably 0.1 kPa to 1 kPa.

[0051] The preferred process parameters described above are particularly applicable to those processes wherein 2,5-furandicarboxylic acid and aliphatic diol constitute 90% or more, preferably 95% or more, most preferably 98% or more by weight of the starting composition.

[0052] Although the actual reaction time depends on the starting materials used and their amounts, the esterification is generally carried out for a time t in the range of 30 min to 480 min, preferably 60 min to 360 min, more preferably 120 min to 300 min, most preferably 180 min to 240 min, and the polycondensation is generally carried out for a time t in the range of 10 min to 260 min, preferably 30 min to 190 min, more preferably 60 min to 120 min.

[0053] As indicated above, the process according to the invention is preferred in which the esterification is carried out in the presence of a germanium compound.

[0054] The above-described process is particularly preferred because the catalyst system can be conveniently applied together with the starting composition, i.e., the polycondensation catalyst and inhibitor can be added simultaneously, eliminating the need for a further process step, which would otherwise be required if the polycondensation catalyst had to be added later. This advantageous effect of the process of the present invention is possible because a germanium compound is used as the polycondensation catalyst, whereas other polycondensation catalysts have been found to be deactivated if present during the esterification process. The possibility of adding the polycondensation catalyst during the esterification process offers further advantages, particularly when using a germanium compound having a relatively low solubility, as the time available to completely dissolve the catalyst prior to polycondensation is increased.

[0055] Germanium can be present in the catalyst system as a metal or a cation. Preferred is a process according to the invention wherein the germanium-containing catalyst is selected from the group consisting of germanium oxides and germanium salts, preferably from the group consisting of organic germanium salts and germanium oxides. In this context, organic germanium salts include salts of germanium cations with at least one hydrocarbon anion. Most preferably, the germanium-containing catalyst consists of germanium oxide.

[0056] The inhibitor is preferably selected from the group consisting of primary amines, secondary amines, tertiary amines and lithium hydroxide, preferably selected from the group consisting of primary amines, tertiary amines and lithium hydroxide, more preferably selected from the group consisting of 2-(diethylamino)ethanol (Et2NEtOH), N,N-dimethyldodecylamine (Me2NDodec), 3-aminocrotonic acid ester with butanediol (ACAEBD) and lithium hydroxide, most preferably selected from the group consisting of 2-(diethylamino)ethanol and N,N-dimethyldodecylamine. As discussed below, it may be preferred that the inhibitor is lithium hydroxide.

[0057] As shown above, the process of the present invention can flexibly select the type of germanium-containing catalyst and inhibitor, as long as the inhibitor is an amine and / or lithium hydroxide. However, in the process of the present invention, it is found that specific compounds show particularly excellent performance and low decarboxylation. About germanium-containing catalysts, germanium oxide is preferred because of its performance and its adaptability (resilience) to the process parameters commonly adopted during esterification and / or polycondensation. Among the potential inhibitors, it is particularly found that the decarboxylation of primary amines, tertiary amines and lithium hydroxide is well reduced, among which 3-aminobutyl crotonate (ACAEBD), Et2NEtOH and Me2NDodec are identified as particularly suitable amines. These three amines were intentionally selected to explore the applicability of a large group of amines, although each experiment requires effort. Similarly, the degree of steric hindrance also changes by acting with ACAEBD as a larger difunctional amine.

[0058] Can preferably use primary amine, secondary amine and / or tertiary amine as inhibitor, especially if need good optical properties.In these cases, with primary amine, especially Et2NEtOH and Me2NDodec obtain particularly good result.

[0059] As indicated above, the concentration range of the polycondensation catalyst and / or inhibitor can be selected by those skilled in the art for their particular process. However, the inventors have determined that the optimal concentration range for the germanium-containing catalyst and inhibitor is particularly suitable when the starting composition comprises 90% or more, preferably 95% or more, and most preferably 98% or more by weight of FDCA and aliphatic diol.

[0060] Therefore, preferred is a process according to the invention in which the concentration of the germanium-containing catalyst in step c) is preferably in the range of 10 ppm to 1000 ppm by weight, preferably 30 ppm to 500 ppm, more preferably 50 ppm to 300 ppm, and most preferably 70 ppm to 150 ppm, calculated as metal per se, relative to the weight of the starting composition. Preferably, the amount of germanium-containing catalyst in step c) is in the range of 0.005% to 0.1%, preferably 0.005% to 0.05%, and more preferably 0.01% to 0.04% by weight, relative to the weight of 2,5-furandicarboxylic acid in the starting composition. Preferably, the molar ratio of the germanium-containing catalyst to FDCA in the starting composition is in the range of 0.0001 to 0.01, preferably 0.0002 to 0.001.

[0061] Preferably, the inhibitor concentration in the starting composition is in the range of 5 ppm to 1300 ppm, preferably 20 ppm to 700 ppm, more preferably 30 ppm to 450 ppm by weight, relative to the weight of the starting composition, wherein preferably, the amine concentration in the starting composition is in the range of 60 ppm to 400 ppm, preferably 80 ppm to 350 ppm, more preferably 120 ppm to 300 ppm by weight, relative to the weight of the starting composition, and / or the lithium hydroxide concentration in the starting composition is in the range of 5 ppm to 200 ppm, preferably 10 ppm to 100 ppm, more preferably 20 ppm to 60 ppm by weight, relative to the weight of the starting composition. Preferably, the inhibitor concentration in the starting composition is less than 0.1 mol%, preferably less than 0.05 mol%, preferably less than 0.03 mol%, relative to the amount of 2,5-furandicarboxylic acid in the starting composition. Preferably, the molar ratio of inhibitor to FDCA in the starting composition is in the range of 0.0001 to 0.001, preferably 0.00015 to 0.0004.

[0062] More specifically, preferably the concentration of 2-(diethylamino)ethanol (Et2NEtOH) in the starting composition is in the range of 5 ppm to 670 ppm by weight, preferably 30 ppm to 340 ppm, more preferably 60 ppm to 200 ppm, relative to the weight of the starting composition, and / or wherein the concentration of N,N-dimethyldodecamine (Me2NDodec) and / or 3-aminocrotonic acid butanediol ester in the starting composition is in the range of 5 ppm to 1300 ppm by weight, preferably 60 ppm to 700 ppm, more preferably 120 ppm to 450 ppm by weight, relative to the weight of the starting composition.

[0063] Although other polycondensation catalysts or other inhibitors may be used or added, it is preferred to use only germanium-containing compounds as polycondensation catalysts and only amines and / or lithium hydroxide as inhibitors. Therefore, the process according to the present invention is preferred in which the polycondensation catalyst consists of a germanium compound and the inhibitor consists of an inhibitor selected from the group consisting of amines and lithium hydroxide. Preferably, the concentration of the antimony compound in the starting composition is in the range of 0 to 50 ppm by weight, preferably 0 to 20 ppm, and more preferably less than 5 ppm, relative to the weight of the starting composition. The combined concentration of the ammonium compound and sodium in the starting composition is preferably in the range of 0 to 50 ppm by weight, preferably 0 to 20 ppm, and more preferably less than 5 ppm, relative to the weight of the starting composition.

[0064] Preferred is a process according to the invention wherein by using TCE-d2 1 The amount of decarboxylated end groups in the polyester comprising 2,5-furandicarboxylate units after polycondensation, as determined by H-NMR, is less than 7 eq / t, preferably less than 6 eq / t, most preferably less than 5 eq / t. Full details of the measurement are given below.

[0065] Preferably, after polycondensation, relative to the 1 The weight of polyalkylene furanoate, determined by H-NMR, the ether of aliphatic diol incorporated into the polyester comprising 2,5-furandicarboxylate units is less than 3% by weight, preferably less than 2.5%. Full details of the measurement are given below.

[0066] It is preferred that the high performance polyester has less than 7 eq / t (ie 7 equivalents per metric ton (corresponding to mol / t) of decarboxylated end groups. Similarly, it is preferred that the amount of ether of aliphatic diol incorporated into the polyester is less than the values ​​indicated above.

[0067] Those skilled in the art are familiar with suitable methods for determining end groups in polyesters, including titration, infrared and proton-NMR ( 1H-NMR) method. In many cases, different methods are used to quantify the four main end groups, namely carboxylic acid end groups, hydroxyl end groups, ester end groups and end groups obtained after decarboxylation. AT Jackson and DF Robertson have published a method for the determination of end groups in PET in "Molecular Characterization and Analysis of Polymers" (JM Halmers in RJ Meier (ed.), B. Barcelo (ed.), "Comprehensive Analytical Chemistry", Vol. 53, (2008) Elsevier, pp. 183-193). 1 H-NMR method. For polyesters containing 2,5-furandicarboxylate units, a similar approach can be followed. In this context, the measurement of the end groups can be performed at room temperature without excessive risk of precipitation of the polyester from solution. This method using deuterated 1,1,2,2-tetrachloroethane (TCE-d2) 1 The H-NMR method is well suited for determining the amount of decarboxylated end groups (DEC) and can also be used to determine the content of aliphatic diol ethers incorporated into polyesters. Peak assignments were set using the TCE peak with a chemical shift of 6.04 ppm. The furan peak with a chemical shift of 7.28 ppm was integrated, and the integral value was set to 2.000, representing two protons on the furan ring. The chemical shift of the decarboxylated end group was found to be 7.64-7.67 ppm, representing one proton. The DEG content was determined by integrating the shifts of the protons adjacent to the ether functionality, for example, the shift of DEG from 3.82 to 3.92 ppm, representing four protons. The amount of hydroxyl end groups (HEG) was determined by the two methylene protons of the hydroxyl end group at 4.0 ppm. In the present invention's architecture, the method described above was used to determine the content of DEC, DEG, and other ethers, as well as HEG, while the amount of carboxylic acid end groups (CEG) was determined using titration, as described in the experimental section below. The shifts for DEG are illustrative using monoethylene glycol as the diol. One skilled in the art can readily determine the corresponding shifts for other ethers produced from other diols. The decarboxylation shifts mentioned are relatively insensitive to the choice of diol, as is the acid titration method for determining CEG.

[0068] Preference is given to a process according to the invention, wherein the polyester comprising 2,5-furandicarboxylate units after polycondensation preferably has a number average molecular weight of 20 kg / mol or more, preferably 25 kg / mol or more, preferably 30 kg / mol or more.

[0069] While the polyester obtained after polycondensation can be used directly for specific applications, in some cases it may be beneficial to add further processing steps. These steps may include crystallizing the polyester to obtain a crystalline polyester and subjecting the crystalline polyester to solid-phase polymerization to increase the molecular weight. Therefore, it may be preferred that the process further comprises the steps of: d) crystallizing the polyester comprising 2,5-furandicarboxylate units obtained in step c) to obtain a crystalline or semi-crystalline polyester comprising 2,5-furandicarboxylate units, and e) subjecting the crystalline polyester comprising 2,5-furandicarboxylate units produced in step d) to solid-phase polymerization to increase the molecular weight.

[0070] The general concept of these two steps is known from TA / PET technology. However, the inventors have identified specific process parameters that have been found to be particularly beneficial for the process of the present invention, namely the use of a specific polycondensation catalyst and a specific inhibitor, especially when both compounds are still present in the crystalline polyester, as is usually the case.

[0071] Within this range, the process according to the present invention is preferred, wherein the solid-phase polymerization is carried out at an elevated temperature in the range of Tm-80°C to Tm-20°C, preferably Tm-60°C to Tm-25°C, more preferably Tm-60°C to Tm-30°C, where Tm is the melting point (in °C) of the polyester comprising 2,5-furandicarboxylate units, and wherein the solid-phase polymerization is preferably carried out at an elevated temperature in the range of 160°C to 240°C, more preferably 170°C to 220°C, and most preferably 180°C to 210°C. The melting point of the polymer is readily determined by DSC and measured at the peak of the endothermic peak. ISO 11357-3 describes such melting determinations. Crystallization is preferably carried out at an elevated temperature in the range of 100°C to 200°C, preferably 120°C to 180°C, and more preferably 140°C to 160°C. Crystallization is preferably carried out for a time t in the range of 0.5 h to 48 h, preferably 1 h to 6 h, wherein step d) is carried out directly after step c) without cooling the polyester comprising 2,5-furandicarboxylate units to below 50° C. Crystallization is preferably carried out at or near ambient pressure, or less preferably at a reduced pressure of less than 100 kPa or less than 10 kPa. Solid-phase polymerization is preferably carried out under an inert gas atmosphere, preferably nitrogen, helium, neon or argon.

[0072] The crystalline or semi-crystalline polyester obtained in step d) is preferably pelletized to obtain a pellet size of 20 to 180 pellets per gram, preferably 40 to 140 pellets per gram.

[0073] The optimal time for selecting crystallization can be selected based on the crystallization enthalpy dHcryst of the polyester. When the polyester obtained in step c) is heated to produce a semi-crystalline or crystalline polyester, the amount of decarboxylation end groups does not change. However, the degree of crystallinity changes significantly. This can be determined by means of differential scanning calorimetry (DSC). When heated at a suitable rate, the degree of crystallinity is usually measured as the enthalpy of melting a semi-crystalline polymer. The degree of crystallinity is expressed in units of J / g and is the net enthalpy of the melting peak (endotherm) after correcting for any crystallization (exotherm) occurring at high temperatures. The process according to the present invention is preferred, wherein crystallization is carried out for a time t such that the net enthalpy dHcryst of the polyester comprising 2,5-furandicarboxylic acid ester is greater than 20 J / g, preferably greater than 25 J / g, more preferably greater than 30 J / g, as measured by DSC using a heating rate of 10 dC / min.

[0074] Solid-state polymerization can lead to a significant increase in the number-average molecular weight and weight-average molecular weight of the resulting polyester. However, the optical properties are adversely affected by the crystallization and solid-state polymerization steps.

[0075] It has now been discovered that optical properties can be enhanced if not only the solid-state polymerization, but also the crystallization step itself, is carried out in an atmosphere with reduced oxygen concentration, preferably under an inert gas atmosphere. It has been found that by adopting this strategy, optical properties can be improved by a factor of approximately 2.5 to 4. Reduced oxygen concentration atmosphere means an atmosphere with a reduced oxygen concentration compared to air at ambient pressure, preferably with an oxygen partial pressure of less than 1 kPa, more preferably less than 0.1 kPa, most preferably less than 0.01 kPa, and even more preferably less than 0.001 kPa.

[0076] The crystallization of the process of the present invention is preferably carried out in an atmosphere with a reduced oxygen concentration, preferably under an inert gas atmosphere, preferably under a nitrogen, helium, neon or argon atmosphere, most preferably under a nitrogen atmosphere. It has been found that polyesters comprising 2,5-furandicarboxylate units can be produced after solid-state polymerization, which have an absorbance of 0.06 or less, preferably 0.04 or less, more preferably 0.02 or less, measured at 400 nm in a 30 mg / mL solution in a 8:2 (vol / vol) mixture of dichloromethane:hexafluoroisopropanol using an optical path length of 2.5 cm.

[0077] Surprisingly, it has been found that the rate of molecular weight increase during solid-state polymerization can be significantly increased if lithium hydroxide is used as an inhibitor. Polyesters with very high molecular weight can be obtained in very short solid-state polymerization times. This results in a significant increase in process output.

[0078] Polyesters containing 2,5-furandicarboxylate units can be prepared having a number average molecular weight of 30 kg / mol or more, preferably 45 kg / mol or more, more preferably 60 kg / mol or more. Polyesters containing 2,5-furandicarboxylate units can have a weight average molecular weight of 90 kg / mol or more, preferably 100 kg / mol or more, more preferably 180 kg / mol or more.

[0079] It has been further discovered that the process allows the addition of typical stabilizers known in the prior art. Therefore, the process starting composition can further contain a stabilizer. Stabilizers include phosphorus-containing compounds, particularly phosphite-containing compounds, phosphate-containing compounds, and phosphonate-containing compounds, preferably phosphoric acid, and hindered phenol compounds.

[0080] The present invention also relates to a catalyst system for the process according to the invention, comprising a germanium compound (preferably germanium oxide) as a polycondensation catalyst and one or more inhibitors selected from the group consisting of Et2NetOH, Me2Ndodec, 3-aminocrotonate butanediol (ACAEBD), and lithium hydroxide. The invention also relates to the use of such a catalyst system according to the invention for reducing decarboxylation during the esterification and polycondensation of 2,5-furandicarboxylic acid and an aliphatic diol to produce a polyester comprising 2,5-furandicarboxylate units, preferably in the process according to the invention.

[0081] The present invention further relates to polyesters comprising 2,5-furandicarboxylate units, preferably polyalkylene furanoates, which after polycondensation have a weight average molecular weight of 40 kg / mol or more, preferably 45 kg / mol or more, more preferably 60 kg / mol or more, wherein 1 The amount of decarboxylated end groups in the polyester, determined by H-NMR, is less than 7 eq / t, preferably less than 6 eq / t, most preferably less than 5 eq / t, wherein the polyester comprising 2,5-furandicarboxylate units preferably comprises less than 5 ppm by weight of antimony compounds and less than 5 ppm by weight of ammonium compounds, wherein the polyester comprising 2,5-furandicarboxylate units is most preferably produced by the process according to the invention.

[0082] Surprisingly, it has been found that the use of lithium hydroxide as an additive in the esterification and / or polycondensation process increases the average molecular weight growth per unit time in the subsequent solid phase polymerization and / or melt polymerization of polyesters comprising 2,5-furandicarboxylate units.

[0083] Surprisingly, it was found that the use of an inert gas atmosphere during the crystallization of polyesters comprising 2,5-furandicarboxylate units having a weight average molecular weight of 40 kg / mol or more enhances the color properties and / or reduces the absorbance at 400 nm.

[0084] The present invention will be further illustrated by the following examples. Example

[0085] Abbreviations and measurements:

[0086] DEC represents the decarboxylation end group equivalent per metric ton of polymer obtained (in eq / t), and cDEG represents the amount of diethylene glycol incorporated into the polyester (in weight percentage relative to the weight of the polyester). In this context, the value of decarboxylation end groups (DEC), the amount of hydroxyl end groups, and the amount of diethylene glycol in the polyester are determined by using TCE-d2 as described above. 1 H-NMR was obtained.

[0087] In a typical experiment, approximately 10 mg of polyester was weighed and placed in an 8 ml glass vial. 0.7 ml of TCE-d2 was added to the vial and the polyester was dissolved at room temperature while stirring the mixture in the vial. 1 The dissolved mixture was analyzed by H-NMR while setting the peak of TCE-d2 at 6.04 ppm.

[0088] A_400 is the absorbance of a 30 mg / mL polyester solution in a 8:2 (vol / vol) mixture of dichloromethane:hexafluoroisopropanol in a 2.5 cm diameter round vial measured at 400 nm. The measurement data for the 2.5 cm diameter vial can be converted to the typical 1 cm equivalent path length by dividing the measurement data by 2.5.

[0089] The amount of carboxylic acid end groups (CEG) in eq / t was measured by titration based on ASTM D7409, i.e., a solution of 0.4 to 1.2 g of a polymer sample dissolved in 50 mL of o-cresol was titrated with 0.01 M potassium hydroxide in ethanol to its equivalence point using bromocresol green as an indicator.

[0090] The weight average molecular weight and number average molecular weight were determined by using gel permeation chromatography (GPC). GPC measurements were performed at 35°C using two PSS PFG linear M (7 μm, 8×300 mm) columns with pre-columns. Hexafluoroisopropanol containing 0.05 M potassium trifluoroacetate was used as the eluent. The flow rate was set to 1.0 mL / min, the injection volume was 50 μL, and the run time was 50 minutes. Calibration was performed using polymethyl methacrylate standards.

[0091] In the experiments, the concentrations in ppm are given relative to the theoretical maximum weight of polymer that can be obtained from the respective starting composition, calculated by multiplying the number of moles of FDCA in the starting composition by the molecular weight of the corresponding theoretical polymer repeating unit (i.e. FDCA + aliphatic diol - 2*H2O).

[0092] The FDCA used in the experiments included less than 500 ppm of FCA.

[0093] Experiment A:

[0094] The starting composition comprising ethylene glycol and 2,5-furandicarboxylic acid in a molar ratio of 1.13 and the inhibitor in the amount shown in Table 1 was subjected to a temperature of 200° C. and atmospheric pressure for 20 minutes and subsequently to a temperature of 220° C. and atmospheric pressure for 180 minutes. In the ester composition obtained, 1 The hydroxyl end groups were measured by H-NMR and were found to be 1544 eq / t. The carboxylic acid end groups were measured by titration and were found to be 984 eq / t. After esterification, a Sb polycondensation catalyst was added as a metal oxide to 0.65 ml of ethylene glycol. The polycondensation was carried out at 260° C. for 75 min. The type and amount of the polycondensation catalyst are indicated in Table 1, and the results obtained for the polymer after melt polymerization (i.e., polycondensation) are listed in Table 2.

[0095] Table 1

[0096]

[0097] Table 2

[0098]

[0099] The experimental data given above show that, with the processes of the prior art, it is possible to obtain polymers containing a small amount of diethylene glycol and good optical properties, as indicated by the A_400 value which should be as low as possible. However, it can be seen that the comparative experiment Comparative Example 1, which is very similar to the prior art using an antimony catalyst and tetraethylammonium hydroxide (TEAOH), produces a polymer containing a large number of decarboxylated end groups.

[0100] Experiment B:

[0101] 20 g of 2,5-furandicarboxylic acid was mixed with ethylene glycol in the molar ratios shown below. Unless otherwise specified, an inhibitor was added in the amounts shown in Table 3 before the composition was subjected to a temperature of 220°C for 210 minutes. After esterification, a polycondensation catalyst was added. Polycondensation was carried out at 260°C for 75 minutes. The types and amounts of polycondensation catalysts and inhibitors are indicated in Table 3, and the results obtained for the polymers after melt polymerization (i.e., after polycondensation) are listed in Table 4.

[0102] Table 3

[0103]

[0104] a) Polycondensation was carried out at 265°C

[0105] b) After esterification, add 15ppm H3PO4 as a stabilizer

[0106] c) Esterification lasts only 180 minutes

[0107] d) Polycondensation was carried out at 270°C

[0108] Table 4

[0109]

[0110] The experimental results are summarized in Tables 3 and 4. Comparative Experiments Comparative Examples 6 to 18 all employed non-germanium polycondensation catalysts and typical inhibitors (e.g., sodium dihydrogen phosphate, disodium hydrogen phosphate, tetraethylammonium hydroxide) as well as the specific inhibitors of the present invention (i.e., amines and lithium hydroxide). The resulting polyesters exhibited significant decarboxylation, i.e., 7 eq / t or greater.

[0111] The experiments according to Examples 1 to 7 of the present invention used the polycondensation catalyst and inhibitor of the present invention. The obtained polyester had a decarboxylation rate of 4 eq / t to 5 eq / t.

[0112] As a beneficial side effect, good molecular weights and good optical properties as indicated by the A_400 values ​​can be obtained. In particular, it is noted that significantly lower A_400 values ​​are obtained if the amines Et2NEtOH or Me2NDodec are combined with the germanium compound.

[0113] The resin obtained after polycondensation as described above was crystallized at 150°C in an air or nitrogen atmosphere at atmospheric pressure, and then solid-phase polymerized at 200°C in a nitrogen atmosphere at reduced pressure for 24 hours. The average diameter of the particles subjected to solid-phase polymerization was 1.4 to 2.0 mm. The results are summarized in Table 5.

[0114] Table 5

[0115]

[0116] The data show that similar molecular weights can be achieved with the process of the present invention compared to prior art processes.

[0117] If crystallization is performed in an atmosphere with a reduced oxygen concentration (eg, under an inert gas atmosphere), the optical characteristics represented by the A_400 value can be enhanced.

[0118] Experiment C:

[0119] Scale-up experiments were conducted using either 1.5 kg or 30 kg of a starting composition comprising ethylene glycol and 2,5-furandicarboxylic acid. Before the composition was subjected to esterification conditions, an inhibitor was added in an amount equivalent to 0.026 mol% of the amount of 2,5-furandicarboxylic acid. In the ester compositions obtained in Comparative Example 24 and Example 9, the inhibitor was added in an amount equivalent to 0.026 mol% of the amount of 2,5-furandicarboxylic acid. 1 The ratios of hydroxyl end groups measured by H-NMR to carboxylic acid end groups measured by titration ranged from 1161 eq / t to 954 eq / t and from 1398 eq / t to 816 eq / t, respectively. After esterification, the polycondensation catalyst was added as a metal oxide in 0.65 mL of ethylene glycol. The types and amounts of the polycondensation catalyst and inhibitor are indicated in Table 6, and the process parameters are disclosed in Table 7. The results obtained for the polymers after melt polymerization are listed in Table 8.

[0120] Table 6

[0121]

[0122] b) After esterification, add 15ppm H3PO4 as a stabilizer

[0123] Table 7

[0124]

[0125] Table 8

[0126]

[0127] The experimental results summarized above show that polyesters with reduced amounts of decarboxylation end groups can be obtained by the process of the invention. For certain combinations of catalyst and inhibitor according to the invention, low decarboxylation is observed in addition to good optical properties and comparable molecular weight.

[0128] The resin obtained as described above was crystallized at 150°C in an air or nitrogen atmosphere at atmospheric pressure, and then solid-phase polymerized at 200°C in a nitrogen atmosphere at reduced pressure for 24 hours. The average diameter of the particles subjected to solid-phase polymerization was 1.4 to 2.0 mm. The results are summarized in Table 9.

[0129] Table 9

[0130]

[0131] Examples 8 and 9 show that, for the experiments, particularly good molecular weights were achieved after only 24 hours of solid-state polymerization.

[0132] Furthermore, the experimental data in Table 9 show that the optical properties of the polyester can be improved if crystallization is carried out in an atmosphere with reduced oxygen concentration (e.g., under an inert gas atmosphere). Furthermore, these experiments demonstrate that the use of lithium hydroxide as an inhibitor in combination with a germanium-containing catalyst results in a significant increase in molecular weight during solid phase polymerization.

[0133] Although the polycondensation reaction of Experimental Example 9 was carried out for only about half the time used in Comparative Example 25, Example 9 and Comparative Example 25 obtained almost the same molecular weight after the polycondensation reaction. After 24 hours of solid phase polymerization, the resin obtained in Example 9 showed M w The relative increase was approximately +167%, while Comparative Example 25 only showed a relative increase of approximately +65%.

Claims

1. A process for producing a polyester comprising 2,5-furandicarboxylate units, the process comprising: a) providing or producing a starting composition comprising 2,5-furandicarboxylic acid, an aliphatic diol and an inhibitor for inhibiting ether formation between the aliphatic diol molecules, b) subjecting the starting composition to esterification conditions to produce an ester composition, and c) contacting the ester composition with a germanium-containing catalyst under polycondensation conditions to produce a polyester comprising 2,5-furandicarboxylate units, The inhibitor is selected from the group consisting of amines and lithium hydroxide.

2. The process according to claim 1, wherein the aliphatic diol comprises 2 to 8 carbon atoms.

3. The process according to claim 1 or 2, wherein the molar ratio of the aliphatic diol to 2,5-furandicarboxylic acid of the starting composition is in the range of 1.01 to 1.

80.

4. The process of claim 1 or 2, wherein the esterification conditions comprise a temperature in the range of 180°C to 260°C and wherein the polycondensation conditions comprise a temperature in the range of 240°C to 300°C.

5. The process of claim 1 or 2, wherein the starting composition is subjected to esterification conditions in the presence of the germanium-containing catalyst.

6. The process according to claim 1 or 2, wherein the germanium-containing catalyst is added to the esterification and / or polycondensation as a germanium salt or germanium oxide or a mixture thereof.

7. The process according to claim 1 or 2, wherein the inhibitor is selected from the group consisting of 2-(diethylamino)ethanol, N,N-dimethyldodecylamine, 3-aminocrotonate and lithium hydroxide.

8. The process according to claim 1 or 2, wherein 1 The amount of decarboxylation terminal groups in the polyester comprising 2,5-furandicarboxylate units after polycondensation, as determined by H-NMR, is less than 7 eq / t.

9. The process according to claim 1 or 2, further comprising the steps of: d) crystallizing the polyester comprising 2,5-furandicarboxylate units obtained in step c) to obtain a crystalline polyester comprising 2,5-furandicarboxylate units, and e) subjecting the crystalline polyester comprising 2,5-furandicarboxylate units produced in step d) to solid phase polymerization to increase the molecular weight.

10. The process according to claim 9, wherein the solid phase polymerization is carried out at an elevated temperature in the range of Tm-80°C to Tm-20°C, wherein Tm is the melting point of the polyester comprising 2,5-furandicarboxylate units in °C as determined according to ISO 11357-3.

11. The process of claim 9, wherein the crystallization is performed under an atmosphere with reduced oxygen concentration.

12. A catalyst system for use in a process according to any one of claims 1 to 11, comprising a germanium compound as a polycondensation catalyst and one or more inhibitors selected from the group consisting of 2-(diethylamino)ethanol, N,N-dimethyldodecylamine, 3-aminocrotonate and lithium hydroxide.

13. Use of the catalyst system according to claim 12 in a process according to any one of claims 1 to 11.

14. A polyester comprising 2,5-furandicarboxylate units, obtained according to the process of any one of claims 1 to 11, wherein the polyester has a weight average molecular weight of 40 kg / mol or more after polycondensation, as determined by gel permeation chromatography using hexafluoroisopropanol and 0.05 M potassium trifluoroacetate as eluents and calibrated using polymethyl methacrylate standards, wherein the amount of decarboxylation end groups in the polyester is less than 7 eq / t, the amount of decarboxylation end groups being determined by using TCE-d2 1 H-NMR determination.

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