WO2017023175A1

WO2017023175A1 - Poly( alkylene furandicarboxylate)-comprising polyester

Info

Publication number: WO2017023175A1
Application number: PCT/NL2016/050570
Authority: WO
Inventors: Hajime Nakajima; Jesper Gabriël VAN BERKEL; Jeffrey John Kolstad
Original assignee: Furanix Technologies B.V.
Priority date: 2015-08-04
Filing date: 2016-08-04
Publication date: 2017-02-09
Also published as: NL2015266B1

Abstract

A polyester is provided that comprises a poly(alkylene furandicarboxylate) and a chain extending agent, wherein the chain extending agent has been selected from an oligomeric or polymeric compound having two or more functional groups, wherein the functional groups have suitably been selected from carbodiimide and epoxide groups. The polyester may be prepared by adding a poly(alkylene furandicarboxylate) and the chain extending agent to a heat processing device to form a blend and by subjecting the blend to melt compounding.

Description

Poly(alkylene furandicarboxylate)-comprising polyester

The present invention relates to a polyester that comprises poly(alkylene

furandicarboxylate).

Poly(alkylene furandicarboxylate) has been developed as a polyester with

advantageous properties. As monomers use is made of an alkylene glycol and furan- dicarboxylic acid, in particular 2,5-furandicarboxylic acid. 2,5-Furandicarboxylic acid (2,5- FDCA) is a diacid that can be produced from natural sources such as carbohydrates. Routes for its preparation using air oxidation of 2,5-disubstituted furans such as 5-hydroxymethyl furfural or ethers thereof with catalysts comprising Co and Mn have been disclosed in e.g. WO2010/132740, WO201 1/043660 and WO201 1/043661 .

US 2551731 describes the preparation of polyesters and polyester-amides by reacting glycols with dicarboxylic acids of which at least one contains a heterocyclic ring, such as 2,5- FDCA. Under melt polymerization conditions, using sodium and magnesium methoxide as a catalyst, 2,5-FDCA or 2,5-FDCA dimethyl ester and 1.6 equivalents of ethylene glycol were reacted in an esterification step or transesterification step, respectively, at ambient pressure between 160 and 220 °C, after which a polycondensation was carried out between 190 and 220 °C under a few mm Hg pressure. The product had a reported melting point of 205-210 °C and readily yielded filaments from the melt.

In WO 2013/120989 a continuous process for the preparation of poly(ethylene furandicarboxylate) is described wherein 2,5-FDCA or a diester thereof is mixed with ethylene glycol at elevated temperature to give a paste or a homogeneous solution, the paste or solution is converted to an esterification product of 2,5-FDCA and ethylene glycol, the esterification product is polycondensed under reduced pressure, wherein the

polycondensation is performed in two stages. In an example the polycondensation product was reported to have an intrinsic viscosity of 1.05 dL/g.

In WO 2010/077133 a process for preparing furandicarboxylate-containing polyesters is described wherein the diester of 2,5-FDCA is transesterified with a diol, and the ester composition thus obtained is subjected to polycondensation. The polycondensate may then be subjected to solid state polymerization.

WO 2013/062408 discloses a process, wherein the dimethyl ester of 2,5-FDCA is transesterified with ethylene glycol, or bis(2-hydroxyethyl)-2,5-furandicarboxylate is used as starting material. The transesterification product or this starting material is then subjected to polycondensation and after a drying/crystallization step the polycondensate is subjected to solid state polymerization to enhance the molecular weight of the polycondensate. The product may be used as water bottles, fibers or films. KR 20140003167 describes a polyester polymer which is manufactured by using a biomass originated furandicarboxylate ester compound with ethylene glycol. The polyesters thus produced yield b* values in the range of 6 to 10. In comparative examples also furan- dicarboxylic acid has been used. These polyesters have more color and have b* values in the range 25 to 34.

In US 2012/0207956 polyesters are described, having a 2,5-furandicarboxylate moiety within the polymer backbone and having a degree of polymerization of 185 to 600. These polymers are made in a three step process involving the esterification of the 2,5-FDCA or the transesterification of the diester thereof with a diol, and a second step involving

polycondensation, followed by solid state polymerization as third step. In examples the degree of polymerization is not attained for poly(ethylene furandicarboxylate) and

poly(propylene furandicarboxylate). These examples illustrate the difficulty of obtaining poly(alkylene furandicarboxylates) with a satisfactory molecular weight.

US 2015/064383 discloses a copolymer comprising poly(ethylene furandicarboxylate) and a chain architecture modifying agent having a reactive functionality of at least two. By "chain architecture modifying agent" is understood a compound with functional groups capable of additional reactions with the terminal groups of a polyester resin, e.g. hydroxyl or carboxyl groups. These functional groups react with the terminal groups, resulting in chain extension or branching. According to this application US 2015/064383 the copolymers thus obtained have an increased number (Mn) or weight average molecular weight (Mw), which may be from about 10% to about 100% more than the molecular weight of unmodified poly(ethylene furandicarboxylate). Examples of suitable chain architecture modifying agents are mentioned in the application, which include pyromellitic dianhydride, pentaerythritol, electron deficient alkene compounds, such as e.g. maleates, acrylates, maleimides, imide- substituted alkenes, a multianhydride, a multioxazoline, a multiepoxide or a multilactone. In examples a bismaleimide, pyromellitic dianhydride, and pentaerythritol were used. In none of the examples an increase of molecular weight was determined.

It has now been found that some chain extending agents involve an increase of molecular weight whereas others fail to do so. It was found that the effective chain extending agents were oligomeric and polymeric compounds.

Accordingly, the present invention provides a polyester comprising poly(alkylene furandicarboxylate) and a chain extending agent, wherein the chain extending agent has been selected from an oligomeric or polymeric compound having two or more functional groups.

Surprisingly, it was found that the use of monomeric, individual tetrafunctional compounds such as pyromellitc dianhydride did not result in any increase of molecular weight. However, when the functional groups were incorporated into an oligomer wherein at least one unit was repeated the functional groups enabled the increase of molecular weight.

The functional groups are selected such that they can react with a terminal group of the poly(alkylene furandicarboxylate). Such terminal groups include carboxylic acid end groups, hydroxyl end groups, alkyl ester groups, which occur when the polyalkylene furandicarboxylate has been manufactured from an ester of FDCA and a diol, and furoic acid end groups, which result from the decarboxylation of a carboxylic acid end group or carboxylic acid ester end group. It is evident that the chain extending effect is most prominent when the functional groups in the chain extending agent molecule are capable of reacting with a carboxylic acid group and/or a hydroxyl group. It has been found that very good results are obtainable when the functional groups have been selected from carbodiimide and epoxide groups. The carbodiimide groups tend to react with the carboxylic acid end groups and the epoxide groups react with both the hydroxyl group and the carboxylic end groups.

The oligomeric or polymeric backbone of the chain extending agent may be built up with a variety of monomers. Such monomers include aliphatic olefins, such as ethylene, propylene, butylene, but also aromatic olefins can be used, such as styrene or a-methyl styrene. It is advantageous when the oligomeric or polymeric backbone also includes carboxylate groups, in particular acrylate or methacrylate groups. Suitably a portion of the acrylate or methacrylate groups may be esterified by means of an alkyl group, typically an alkyl group with 1 to 6 carbon atoms. Alternatively, the acrylate or methacrylate group is ionic with an appropriate cation. Another portion of the acrylate or methacrylate moieties is suitably esterified with glycidyl so that the epoxy functionality is introduced into the oligomer or polymer. Preferably, the chain extending agent comprises an oligomeric or polymeric backbone of styrene units or ethylene units, acrylate and/or methacrylate units and epoxide functional groups. The epoxide functionality is suitably introduced by means of glycidyl moieties that are esterified with the carboxylic function of a portion of the acrylate or methacrylate groups. Such chain extending agents are commercially available under the trademarks Joncryl (ex BASF) or Lotader (ex Arkema).

Carbodiimides that are comprised in the chain extending agents used in the present invention are suitably represented by formula (I)

wherein is selected from an organic group, preferably comprising an isocyanate or capped isocyanate group, R_3, is an isocyanate or capped isocyanate group, and R₂ represents an alphatic, alicyclic or aromatic group and n represents an integer in the range of 2 to 1000, preferably from 5 to 200.

Preferred groups R₂ are divalent moieties of optionally substituted aromatic groups, such as 2,8-diisopropylbenzene, naphthalene, 3,5-diethyltoluene, 4,4^,-rnethylenebis(2,8- diethylenephenyl), 4,4' -methylenebisC2-ethyh6-methylpbenyl), 4,4' -rnethylenebis(2,8- diisopropylphenyl), 4,4' -methylenebis(2-etbyl-5-methylcyclohexyl), 2,4,8-triisoprapylbenzene, or a divalent group derived from cycloalkanes, such as cyclohexane, methylcyclohexane and the like, or derived from optionally substituted alkanes, such as n-hexane or

dicydohexylmethane. Preferred R₂ groups include the 1 ,3-(2,4,8-triisopropyl)pbenylene, tetramethylxylylene and 1 ,3~bis(1-rnethylethylene)benzene groups.

Preferred terminal groups R₁ and R₃ are isocyanates, which are characterized by a free NCO group, and capped isocyanates, the NCO groups of which have been subject to an addition reaction with reactive molecules such as secondary amines, oximes, lactams, esters or hydroxyl compounds such as phenols or alcohols or polyois, and the NCO groups of which can by way of example be liberated again by heating. Polymeric biobased carbodiimides are described in US patent application No. 2013/274508 wherein the free NCO groups are capped with a biobased polyol. The carbodiimides have a functionality of greater than 1 and a hydroxy carboxylic ester moiety having 2 to 24 carbon atoms.

The oligorneric or polymeric carbodiimides to be used according to the invention include commercially available products, examples being the Stabaxol P® and BioAdimide® products from Rhein Chemie GmbH having a molecular weight of at least 3000 and a carbodiimide content of 12 - 14 %wt.

The amount of chain extending agent that may be added to the poly(alkylene furandicarboxylate) may vary within wide ranges. According to US2015/0064383 the amount of chain architecture modifying agent that may be added to polyethylene furandicarboxylate may vary from about 0.010 to about 1.0 %wt. However, the chain architecture modifying agents that are employed in the production of the copolyesters in US2015/0064383 tend to be low molecular weight chemical compounds. The amount of the oligorneric or polymeric chain extending agents conform the present invention are suitably present in the polyester in an amount in the range of 0.01 to 2.5% wt, preferably in the range of 0.05 to 2.0 %wt, based on the polyester.

The poly(alkylene furandicarboxylate) typically comprises 2,5-FDCA as diacid building block and an alkylene glycol, or a mixture of alkylene glycols, as diol building blocks. The alkylene glycol may be selected from the group consisting of C₂-C₁₀ alkylene glycol, suitably from the group consisting of C₂-C₆ alkylene glycols, more preferably from the group consisting of C₂-C₄ alkylene glycol. Most preferably, the alkylene glycol is ethylene glycol. The amount of alkylene glycol is suitably in the range of 100 to 95 mol%, based on the molar amount of diacid building blocks. If the amount of alkylene glycol is less than 100 mol%, the remaining diol building blocks may comprise dialkylene glycol, such as diethylene glycol, trialkylene glycol, isosorbide, erythritol or mixtures thereof. Preferably, the poly(alkylene furan dicarboxylate) comprises substantially 100% alkylene glycol as diol building blocks. Suitably, the diacid building blocks of the polyester consists for at least 95 mol% of 2,5-FDCA, i.e. 2,5- furandicarboxylic acid. The remaining 5 mol% may comprise other diacids, such as terephthalic acid, isophthalic acid, azelaic acid, adipic acid, sebacic acid, succinic acid, 1 ,4- dicyclohexane dicarboxylic acid, maleic acid and mixtures thereof. Preferably, the

poly(alkylene furandicarboxylate) comprises a poly(alkylene 2,5-furandicarboxylate). The poly(alkylene 2,5-furandicarboxylate) suitably comprises only 100% FDCA as diacid building blocks. Since the diol preferably comprises ethylene glycol, the poly(alkylene

furandicarboxylate) is preferably poly(ethylene 2,5-furandicarboxylate).

The poly(aSkylene furandicarboxylate), such as polyietbylene 2,5-furandicarboxylate} may have a relatively high molecular weight. The molecular weight may be expressed in terms of intrinsic viscosity. First the relative viscosity is determined in a 60/40 w/w

mixture of phenol and tetrachloroethane at 30 °C and a concentration (c) of 0.4 g/dL. This procedure is similar to the ASTM D4603 standard for the determination of the inherent viscosity for poly(ethylene terephthalate). The intrinsic viscosity is then calculated using the Billmyer equation:

Intrinsic viscosity

The polyethylene furandicarboxylate has typically been subjected to solid state polymerization, also known as solid stating. Due to solid stating the molecular weight is increased such as to 0.65 to 1.2 dL/g, preferably to an intrinsic viscosity of at least 0.75 dL/g, more preferably in the range of 0.75 dL/g to 1 .2 dL/g.

The molecular weight may also be determined via Gel Permeation Chromatography, using polystyrene as standard. The number average molecular weight of the poly(alkylene furandicarboxylate) may then suitably be in the range of 20,000 to 150,000, as determined by GPC, using polystyrene as standard.

As indicated above, the poly(alkylene furandicarboxylate) can contain C₂-C₁₀ alkylene groups, suitably C₂-C₆ alkylene groups, more preferably C₂-C₄ alkylene groups. Most preferably, the poly(alkylene furandicarboxylate) is poly(ethylene 2,5-furandicarboxylate). It has been found that the end groups of the polyester chains have an influence of the effectiveness of the chain extending agent. The end groups can be selected from the group consisting of a carboxylic end group, a hydroxyl end group, an alkyl ester end group and a furoic acid end group. The Salter may be obtained owing to decarboxylation in the

polymerization process. It has been found advantageous that the poly(alkylene

furandicarboxylate) has a carboxylic end group (CEG) content in the range of 0 to 122 meq/kg, preferably from 1 to 70 meq/kg. Since chain extending agents that comprise carbodiimide and epoxy groups are particularly effective when the poly(alkylene

furandicarboxylate) has a CEG content in the range of 10 to 40 meq/kg, poly(alkylene furandicarboxylate)s having such preferred CEG contents are very suitable. The carboxylic acid end groups are determined by using the titration method according to ASTM D7409, adapted for poly(ethylene 2,5-furandicarboxylate). A thus modified method thereof involves the titration of a 4% w/v solution of poly(ethylene 2,5- furandicarboxylate) in ortho-cresol with 0.01 M KOH in ethanol as titrant to its equivalence point, using 0.5 mg of bromocresol green (2,6-dibromo-4-[7-(3,5-dibromo-4-hydroxy-2- methyl-phenyl)-9,9-dioxo-8-oxa-9A6-thiabicyclo[4.3.0]nona-1 ,3,5-trien-7-yl]-3-methyl-phenol) in 0.1 ml ethanol as indicator.

In addition the poly(alkylene furandicarboxylate) has a hydroxyl end group (HEG) content in the range of 10 to 100 meq/kg. Chain extenders with epoxy groups and

carbodiimide groups have been found to be very effective when the poly(alkylene

furandicarboxylate) has a HEG content in the range of 10 to 50 meq/kg. Such poly(alkylene furandicarboxylate)s are therefore preferred.

In general there are a number of methods to determine the end groups in polyesters. Such methods include titration, infrared and nuclear magnetic resonance (NMR) methods. Often the separate methods are used to quantify the four main end groups: carboxylic acid end groups, hydroxyl end groups, alkyl ester groups, such as the methyl ester end groups (for polyesters from the dialkyl ester of a dicarboxylic acid) and the end groups that are obtained after decarboxylation.A. Jackson and D.F. Robertson have published an ¹H-NMR method for end group determination in "Molecular Characterization and Analysis of Polymers" (J.M. Chalmers en R.J. Meier (eds.), Vol. 53 of "Comprehensive Analytical Chemistry", by B. Barcelo (ed.), (2008) Elsevier, on pages 171 -203. In this method the hydroxyl end group is determined in polyethylene terephthalate (PET) by using a selection of harsh solvents such as 3-chlorophenol, 1 ,1 , 1 ,3,3,3-hexafluoro-2-propanol, trichloroacetic acid or trifluoroacetic acid. It is preferred to use deuterated 1 ,1 ,2,2-tetrachloroethane (TCE-d2) as solvent without any derivatization of the polyester. A similar method can be carried out for polyesters that comprise furandicarboxylate moieties and ethylene glycol residues. The measurement of the end groups for the latter polyesters can be performed at room temperature without an undue risk of precipitation of the polyester from the solution. This ¹H-NMR method using TCE-d2 is very suitable to determine the hydroxyl end groups (HEG) and the furoic acid end groups, also known as decarboxylation end groups (DecarbEG). Peak assignments are set using the TCE peak at a chemical shift of 6.04 ppm. The furan peak at a chemical shift of 7.28 ppm is integrated and the integral is set at 2.000 for the two protons on the furan ring. The HEG is determined from the two methylene protons of the hydroxyl end group at 4.0 ppm. The content of DEG is determined from the integral of the shifts at 3.82 to 3.92 ppm, representing four protons. The decarboxylated end groups are found at a shift of 7.64-7.67 ppm, representing one proton. When the polyester also comprises methyl ester end groups, the methyl signal will occur at about 3.97 ppm, representing 3 protons. The poly(alkylene furandicarboxylate) is typically a semi-crystalline polyester. Polymer crystallinity can be determined with Differential Scanning Calorimetry (DSC) by quantifying the heat associated with melting of the polymer. The heat can be reported as the percentage of crystallinity by normalizing the melting heat to that of a 100% crystalline sample. However, those samples are rare. Therefore, the crystallinity is often expressed as net enthalpy in terms of number of Joules per gram which number is derived from the DSC technique. The enthalpy of melting and crystallization can be determined in accordance with ISO 1 1357-3. The poly(alkylene furandicarboxylate) in the composition according to the invention suitably has a crystallinity of at least 25 J/g, preferably at least 40 J/g, measured by DSC. The crystallinity will then advantageously be in the range of 40 to 90 J/g.

The melting point of a polymer is easily determined by DSC and measured at the top of the endothermic peak. The IS01 1357-3 standard describes such a melting point determination. In accordance with this determination, the poly(alkylene furandicarboxylate) suitably has a melting point of at least 200 °C. In highly crystalline polyester the melting point may exceed 230°C and may be as high as 245 °C. It suitably has a melting point of at least 200 °C, preferably at least 215 °C.

Acetaldehyde may be formed during the polycondensation process in the preparation of poly(ethylene 2,5-furandicarboxylate). Its content in polyester compositions can be determined using known methods. A suitable method is described in ASTM F 2013; this is described for polyethylene terephthalate, but can also be used for the polyester composition of the present invention. Applicants have found that polyester compositions can have acetaldehyde values of 18 mg/kg, or higher, prior to the additional steps of solid state polymerization. Applicants have also found that a suitable solid state polymerization process can reduce the levels of acetaldehyde. Such a suitable solid state polymerization process comprises heating a semi-crystalline starting polyester comprising ethylene 2,5- furandicarboxylate units, and having a melting point Tm, at a temperature in the range of (Tm-40°C) to Tm to obtain a solid stated polyester, wherein the semi-crystalline starting polyester has an intrinsic viscosity of at least 0.45 dL/g, and an amount of carboxylic acid end groups in the range of 15 to 122 meq/kg. It was found that the solid stated poly(ethylene furandicarboxylate) thus obtained had a reduced acetaldehyde level, e.g. to less than 1 mg/kg (ppm) and preferably to less than 0.5 mg/kg, calculated as acetaldehyde per kg poly(ethylene 2,5-furandicarboxylate).

As is taught in US 6569479 acetaldehyde is naturally formed during processing of any polyester containing ethylene glycol linkages. The compound is formed via a two-step reaction: the first step is cleavage of a polymer chain, generating a vinyl end group and a carboxylic acid end group. The second step is reaction of the vinyl end group with a hydroxyethyl end group, reforming the polymer chain and releasing acetaldehyde. When the polymer is used in a container for beverages, the aeetaidehyde may migrate from the container sidewa!i into the beverage over time. During the lifetime of a typical container, several hundred ppb of aeetaidehyde can migrate from the container sidewall into the beverage. For sensitive products, such as water, these levels of acetaidehyde are significantly above the taste threshold. In US 4340721 it is shown that when polyethylene terephthala^e contains more than 1 ppm aeetaidehyde, the polymer is unsuitable for use as material for beverage containers. Therefore there is a great desire to limit the amount of aeetaidehyde in polyesters comprising ethylene furandicarboxylate units also to a level below 1 ppm (mg aeetaidehyde per kg polyester). The composition according to the invention preferably contains poly{ethylene furandicarboxylate) having an aeetaidehyde content of at most 1 mg/kg, preferably at most 0.5 mg/kg.

The polyester according to the invention can be easily manufactured by melt compounding. Accordingly the present invention provides a method for the preparation of a polyester as described above, wherein a poly(alkylene furandicarboxylate) and a chain extending agent selected from an oligomeric or polymeric compound having two or more functional groups are added to a heat processing device to form a blend and the blend is subjected to melt compounding. Conveniently, a suitable heat processing device is an extruder, so that the melt compounding preferably is achieved in an extruder. The extrusion is suitably conducted at a temperature above the melting point of the poly(alkylene furandicarboxylate), Since the melting temperature of the poly(alkylene furandicarboxylate) is typically above 200 °C and can be as high as 215 °C, the temperature in the heat processing equipment is preferably at least 200 °C, more preferably at least 220 °C. In order to avoid thermal degradation of the polyester, the temperature is suitably not exceeding 350 °C, preferably at most 300 °C. A most preferred temperature range is from 225 to 275 °C.

The blending of the chain extending agent and the poly(alkylene furandicarboxylate) may be accomplished in any known manner. It is feasible to combine the chain extending agent per se with poly(alkylene furandicarboxylate). It is also feasible to prepare a masterbatch of chain extending agent in a polymer, e.g. a poly(alkylene furandicarboxylate) and add the masterbatch to a batch of poly(alkylene furandicarboxylate). In this way it is easier to add the appropriate amount of chain extending agent to the batch of poly(alkylene furandicarboxylate). The concentration of chain extending agent in such a masterbatch may vary. It is preferred to prepare masterbatches with a concentration of chain extending agent in the range of 2.5 to 50 %wt, based on the masterbatch.

The invention is further illustrated by means of the following Examples.

EXAMPLES

Four different types of chain extending agents were used in a series of experiments. Agent 1 was a copolymer of styrene, alkylacrylate and glycidyl acrylate, having a molecular weight of about 6800. The epoxy equivalent weight is about 285 g/mol, boiling down to about 7 epoxy equivalents per mol.

Agent 2 is a carbodiimide polymer, based on benzene-2,4-diisocyanato-1 ,3,5-tris(1- methylethyl) units, available under the trade mark BioAdimide 500 XT from RheinChemie GmbH. It has a carbodiimide content of about 13.0% and a melting range of 70 to 80 °C

Agent 3 is pyromellitic dianhydride.

Agent 4 is a bisoxazoline, viz. 1 ,3-bis(2-oxazolinyl)-benzene.

Two different poly(ethylene 2,5-furandicarboxylate) resins were used. PEF-1 was a resin with a number average molecular weight Mn of 33300, a carboxylic acid end group content (CEG) of 3 meq/kg, and a hydroxyl end group content (HEG) of 87 meq/kg.

PEF-2 was a resin with an Mn of 34200, a CEG of 27.0 meq/kg and a HEG of 32.0 meq/kg.

EXAMPLE 1

Polyester resin PEF-1 and some of the chain extending agents were extruded in an extruder at 255 °C at a screw rotation of 50 rpm for 1 minute. The amounts of the agents could be varied. The Mn before extrusion was 33300. The Mn after the extrusion was measured via GPC (gel permeation chromatography), using polystyrene as standard. The results are shown in Table 1. The table also shows the amount of chain extending agent, expressed as %wt based on the amount of polyester resin. For comparison purposes also the PEF resin without any additive was subjected to the extrusion for 1 minute.

Table 1

Experiment 2 is according to the present invention. Experiments 3-5 are in conformity of the teachings of US 2015/064383. The results show that Experiment No. 2 yields the best results.

EXAMPLE 2

Resin PEF-2 was used in a series of experiments wherein the chain extending agents were also employed in different amounts. The extrusion was again carried out at 255 °C, but now for 10 min. The results are shown in Table 2. Table 2

Experiment Nos. 7 to 9 are according to the invention. Agent 1 is already effective at very low concentrations. At higher concentrations, the carbodiimide agent, i.e. Agent 2 is very effective. The agent that is recommended in US 2015/064383, viz. Agent 3, performs poorly, both in low concentrations and in high concentrations.

EXAMPLE 3

Resin PEF-2 was blended with some chain extending agents in varying amounts. The blends were prepared by extrusion at 255 °C for 40 sec. The resulting blends were subjected to compression molding. Compression molding bowties with a thickness of 1.5 mm and a diameter of 3.0 cm were obtained. From the bowties the elongation at break and ultimate tensile strength were determined. The results are shown in Table 3.

Table 3

Experiments 13-16 have been conducted with polyesters according to the present invention. The results show that the elongation at break is maintained at a satisfactory level, and that the ultimate tensile strength is significantly improved by the chain extending agents 1 and 2. Contrary to these findings it appeared that Agent 3, according to US 2015/0064383, had a negative effect on the elongation at break and on the ultimate tensile strength.

Claims

1. Polyester comprising poly(alkylene furandicarboxylate) and a chain extending agent, wherein the chain extending agent has been selected from an oligomeric or polymeric compound having two or more functional groups.

2. Polyester according to claim 1 , wherein the functional groups have been selected from carbodiimide and epoxide groups.

3. Polyester according to claim 1 or 2, wherein the chain extending agent comprises an oligomeric or polymeric backbone of styrene units or ethylene units, acrylate and/or methacrylate units and epoxide functional groups.

4. Polyester according to any one of claims 1 to 3, wherein the chain extending agent comprises a carbodiimide of formula (I)

(I)

wherein and R₃ are independently selected from an organic group, preferably an isocyanate or capped isocyanate group, and R₂ represents an alphatic, alicyclic or aromatic group and n represents an integer in the range of 2 to 1000.

5. Polyester according to any one of claims 1 to 4, wherein the polyester comprises the chain extending agent in an amount in the range of 0.01 to 2.5% wt, preferably in the range of 0.05 to 2.0 %wt, based on the polyester.

6. Polyester according to any one of claims 1 to 5, wherein the poly(alkylene furandicarboxylate) has a number average molecular weight of 20,000 to 150,000, determined with GPC using polystyrene as standard.

7. Polyester according to any one of claims 1 to 6, wherein the poly(alkylene furandicarboxylate) has a carboxylic end group content in the range of 0 to 122 meq/kg, preferably from 1 to 70 meq/kg.

8. Polyester according to any one of claims 1 to 7, wherein the poly(alkylene furandicarboxylate) has a hydroxyl end group content in the range of 10 to 100 meq/kg.

9. Polyester according to any one of claims 1 to 8, which has a crystallinity of at least 40 J/g, measured by Differential Scanning Calorimetry (DSC).

10. Polyester according to any one of claims 1 to 9, which has a melting point of at least 215 °C.

1 1. Polyester according to any one of claims 1 to 10, wherein the poly(alkylene furandicarboxylate) is a poly(ethylene 2,5-furandicarboxylate).

12. Composition comprising the poly( ethylene 2,5-furandicarboxylate) according to claim 1 1 , which has an acetaldehyde content of at most 1 mg/kg, preferably at most 0.5 mg/kg.

13. Method for the preparation of a polyester according to any one of claims 1 to 8, wherein a poly(alkylene furandicarboxylate) and a chain extending agent selected from an oligomeric or polymeric compound having two or more functional groups are added to a heat processing device to form a blend and the blend is subjected to melt compounding.

14. Method according to claim 13, wherein the melt compounding is achieved in an extruder.

15. Method according to claim 13 or 14, wherein the blend is subjected to extrusion at a temperature in the range of 200 to 350 °C.