WO2014204296A1

WO2014204296A1 - Semi-crystalline polyester

Info

Publication number: WO2014204296A1
Application number: PCT/NL2014/000019
Authority: WO
Inventors: Daniël STEPHAN VAN ES; Thiyagarajan SHANMUGAM; Johannes RUTGER IDSARD KNOOP
Original assignee: Stichting Dutch Polymer Institute
Priority date: 2013-06-21
Filing date: 2014-06-23
Publication date: 2014-12-24
Also published as: NL1040265C2

Abstract

The invention relates to a semi-crystalline polyester comprising dicarboxyiic acid residues and diol residues, wherein the dicarboxyiic acid residues comprise 2,4-furandicarboxylic acid residues and wherein the diol residues comprise aliphatic diol residues. Such polyester may be prepared by polymerizing in the melt a mixture comprising (1) 2,4-furandicarboxylic acid and/or an ester-forming derivative thereof, (2) an aliphatic diol and/or an ester-forming derivative thereof, and (3) a catalyst.

Description

Semi-crystalline polyester

The invention relates to a semi-crystalline polyester, to a process for preparing such polyester and to a semi-crystalline polyester obtained by such method.

Now that raw materials of fossil origin become increasingly scarce and expensive, there is a strong desire for a structural transition from fossil- based feedstocks to sustainable, bio-based raw materials. An example is the use of bio-based monomers in engineering plastics such as polyesters.

Diacids that are conventionally used in these plastics are usually derived from fossil feedstocks, such as terephthalic acid for the production of

poly(ethylene-terephthalate) and poly(butylene-terephthalate), usually referred to as PET and PBT, respectively. It is contemplated that the high performance of such plastics as engineering plastics amongst other relies on the high rigidity of the terephthalate residues. In the production of polyesters, many efforts have therefore been made to substitute the conventional terephthalates with rigid bio-based alternatives, with the aim to obtain materials having properties that are similar or improved compared to those of the materials of fossil origin.

A well-known bio-based substitute for terephthalic acid (ester) is 2,5- furandicarboxylic acid (ester), as is described in e.g. J. Renew. Mater., Vol 1 , No. 1 , January 2013, 61-72. Polyesters comprising 2,5-furandicarboxylic acid residues, such as poly(ethylene-2,5-furandicarboxylate) (known as 2,5-PEF) and poly(butylene-2,5-furandicarboxylate) (known as 2,5-PBF) have been shown to be useful alternatives for conventional terephthalate-based polyesters. There remains however an increasing need for more bio-based diacids, which would enable the development of a greater variety of bio-based engineering plastics.

It is therefore an object of the present invention to provide a bio- based polyester that may serve as an alternative to known polyesters. Such an alternative may for example comprise bio-based residues that have an improved availability via biological pathways and/or that have improved material properties. It is in particular an object to provide a bio-based polyester that has a high thermal stability, more in particular one that is higher than that of known polyesters. It is a further object to provide a bio-based polyester that has no or a low colour.

It is also an object of the present invention to provide a process for preparing a bio-based polyester that is faster, less complicated and/or more energy-efficient than processes for bio-based polyesters known in the art.

Therefore, the invention relates to a polyester comprising dicarboxylic acid residues and diol residues, wherein the dicarboxylic acid residues comprise 2,4 furandicarboxylic acid residues and wherein the diol residues comprise aliphatic diol residues. A polyester of the invention is preferably a semi-crystalline polyester.

For the purpose of the invention, by a dicarboxylic acid residue is meant a residue derived from a dicarboxylic acid. Analogously, by a diol residue is meant a residue derived from a diol, and so on. Thus, in an alternative wording, the invention relates to a polyester comprising residues derived from a dicarboxylic acid and residues derived from a diol, wherein the residues derived from a dicarboxylic acid comprise residues derived from 2,4-furandicarboxylic acid and wherein the residues derived from a diol comprise residues derived from an aliphatic diol. For the sake of clarity and for the purpose of the present invention, however, the more concise wordings of dicarboxylic acid residue and diol residue are used, respectively.

The polyester typically comprises a chain comprising at least one segment wherein a 2,4-furandicarboxylic acid residue is linked to an aliphatic diol residue via an ester linkage. Usually, however, does such chain comprise a much higher amount of such ester linkages. A chain may for example comprise 100 or more, 500 or more, or 1000 or more of such ester linkages. A chain may in particular consist of a plurality of alternating 2,4- furandicarboxylic acid residues and aliphatic diol residues. The degree of polymerization of a chain of a polymer of the invention may be 100 or more, 500 or more, or 1000 or more.

A polyester of the invention may comprise other dicarboxylic acid residues than 2,4-furandicarboxylic acid residues. The amount of 2,4- furandicarboxylic acid residues in the polyester may be 99 mol% or more, 95 mol% or more, 90 mol% or more, 80 mol% or more, 70

mol% or more or 60 mol% or more of the total amount of dicarboxylic acid residues. Usually, the 2,4-furandicarboxylic acid residues constitute 50 mol% or more of the total amount of dicarboxylic acid residues. The dicarboxylic acid residues may - in addition to the 2,4-furandicarboxylic acid residues - thus comprise one or more further residues, for example residues selected from the group of 2,5-furandicarboxylic acid residues, 3,4-furandicarboxylic acid residues, 2,3-furandicarboxylic acid residues, terephthalic acid residues, isophthalic acid residues, phthalic acid residues, succinic acid residues and adipic acid residues. The amount of further dicarboxylic acid residues may be 1 mol% or more, 5 mol% or more, 10 mol% or more, 20 mol% or more, 30 mol% or more or 40 mol% more.

A polyester of the invention may comprise one type of aliphatic diol residue, but may also comprise two or more different types of diol residues, at least one of which is an aliphatic diol residue. It may for example also comprise aromatic diol residues. The amount of aliphatic diol residues may be at least 60 mol%, at least 70 mol%, at least 80 mol%, at least 90 mol% or at least 95 mol% of the total amount of diol residues. Usually, the aliphatic diol residues constitute 50 mol% or more of the total amount of diol residues.

An aliphatic diol residue may in particular be selected from the group of ethylene glycol, 1 ,2-propandiol, 1 ,3-propanediol, 1 ,2-butanediol, 1 ,3- butanediol, 1 ,4-butanediol, 2,3-butanediol, 1 ,5-pentanediol, 1 ,4-pentanediol, 2,4-pentanediol 1 ,6-hexanediol, 1 ,5-hexanediol, 1 ,4-hexanediol, 2,5- hexanediol,3,4-hexanediol, cyclobutane-1 ,2-dimethanol, cyclobutane-1 ,3- dimethanol, cyclopentane- ,2-dimethanol, cyclopentane-1 ,3-dimethanol, cyclohexane-1 ,2-dimethanol, cyclohexane-1 ,3-dimethanol, cyclohexane-1 ,4- dimethanol and 2,2 bis(4-hydroxycyclohexyl)propane.

A polyester of the invention may further comprise monohydroxy monocarboxylic acid residues, such as alpha, beta or gamma hydroxy acids, more in particular monohydroxy monocarboxylic acid residues selected from the group of hydrobenzoic acids (including the ortho-, meta- and para- isomers), lactic acid, glycolic acid and gamma-hydroxybutyric acid. The amount of monohydroxy monocarboxylic acid residues may be 1 mol% or more, 2 mol% or more, 5 mol% or more, 20 mol% or more or 35 mol% or more, relative to the total amount of residues in the polyester. Usually, up to 50 mol% of the total amount of residues are monohydroxy monocarboxylic acid residues.

An end-group of a chain of a polyester of the invention may be a carboxy group (connected to the furan moiety), a hydroxyl group, or an alkyl ester of a carboxy group (which carboxy group is connected to the furan ring). The type of end-group depends on the applied stoichiometry of the

polymerization reaction and on the functionalization of the terminal carboxy group of a terminal 2,4-furandicarboxylic acid residue.

The average molar mass Mn of a polymer of the invention is usually 4.000 g/mol or more, 8.000 g/mol or more or 16.000 g/mol or more.

Preferably, it is 20.000 g/mol or more.

By "semi-crystalline" is meant a material which has a mixture of crystalline domains and amorphous domains. The degree of crystallinity is usually between 1 % and 95% or between 2 and 90%.

With an aliphatic diol residue is meant that the diol residue does not contain aromatic groups. The aliphatic diol residue is in particular a residue wherein the two oxygen atoms (i.e. those originating from the diol hydroxyl groups but in the polyester being part of an ester group) are for example separated by a -(CH2)n- group, where n is 2 or more. They may also be separated by a -(CHR)2- group, where is R is a hydrocarbyl group, e.g. a methyl group or an ethyl group. They may also be separated by a -(CHR¹)- (CH2)n-(CHR²)- group, where n is 1 one or more and R¹ and R² are a hydrocarbyl group, e.g. a methyl group or an ethyl group. R and R² may be different hydrocarbyl groups that are chosen independently from each other.

The link between the two oxygen atoms in the aliphatic diol residue is in particular selected from the group of -(CH2)2- (i.e. ethylene), -(CH2)3- (i.e. ,3-propylene), -(CH2>4- {i.e. ,4-butylene) and -(CHCH3HCH3CH)- (i.e. 2,3-butylene). Thus, the diol from which the residue is derived is in these cases ethylene glycol, ,3-propylene glycol, 1 ,4-butylene glycol and 2,3- butylene glycol. The melting point of a polyester according to the invention usually depends on the average molar mass Mn. Thus, by varying the Mn of polyesters of the invention, the melting point can be influenced. Usually, polyesters of the invention have a melting temperature of 160°or lower, 150°or lower, 140°or lower or 130°or lower.

A polyester according to the invention is usually opaque in its solid state.

It was surprisingly found that the melting points of the polyesters of the invention are much lower than those of the 2,5-furandicarboxylic acid analogues. In addition, the polyesters of the invention have a higher thermal stability than the corresponding polyesters derived from 2,5-furandicarboxylic acid (see Table 2).

The invention further relates to a process for preparing a polymer of the invention, comprising forming a mixture comprising

- 2,4-furandicarboxylic acid and/or an ester-forming derivative thereof;

- an aliphatic diol and/or an ester-forming derivative thereof; and

- a catalyst,

followed by performing a melt polymerization by exposing the mixture to a temperature of at least 100 °C, yielding a semi-crystalline polyester.

Usually, once formed, the mixture is exposed to elevated

temperatures, e.g. up to 150 °C, up to 175 °C, up to 200 °C, up to 215 °C or up to 225 °C. The best results are obtained when the temperature of the mixture is increased step-wise to up to 215 °C.

Usually, the molar ratio of 2,4-furandicarboxylic acid and/or an ester- forming derivative thereof to aliphatic diol and/or an ester-forming derivative thereof is in the range of 1 :1.5 to 1 :2.5. Thus there is usually an excess of the diol relative to the diacid.

The amount of 2,4-furandicarboxylic acid and/or an ester-forming derivative thereof and aliphatic diol and/or an ester-forming derivative thereof in the mixture may be at least 60 mol%, at least 70 mol%, at least 80 mol%, at least 90 mol% or at least 95 mol% of the monomers present in the mixture.

Usually, the 2,4-furandicarboxylic acid (ester) monomers and the aliphatic diol (ester) monomers together constitute 50 mol% or more of the total amount of monomers in the mixture.

The polyester obtained with a process of the invention is usually colourless. In the event that it is coloured, for example slightly yellow, it may easily be obtained as a colourless solid after purification. Purification may for example be performed by dissolving the polyester in a chlorinated solvent such as chloroform followed by precipitation in an alcohol such as methanol.

It is surprising that with 2,4-furandicarboxylic acid colourless polyesters can be obtained, in particular when during the synthesis

temperatures of up to 200 °C or 215 °C are applied. This is because - in contrast to the 2,5-furandicarboxylic acid isomer - there is an alpha-hydrogen atom on the 5-position of the furan ring (i.e. at the carbon next to the oxygen). Such hydrogen atom is much more reactive than the other hydrogens on the furan ring (on the 3- and 4-positions), and is known to make the

2,4-furandicarboxylic acid monomer more susceptible to degradation and accompanying colouration, especially when it is exposed to elevated temperatures above 200 °C. In a method of the present invention, however, the polyester product appears to be colourless or almost colourless, which is an advantage for the application the polyester in bottles for e.g. soda.

The catalyst may be selected from the group of titanium

tetraalkoxides (e.g. Ti(/-OPr)₄, Ti(OEt)₄, or Ti(OMe)₄, Ti(/-OBu)4))^',

dibutyltinoxide (DBTO), dibutyltinlaurate (DBTL), stannous oxide and tinoctanoate.

By an ester-forming derivative of a diol or a carboxylic acid is meant a derivative that is capable of being transformed into an ester. This is also meant to include a monomeric ester from which a polyester is formed. In the latter case, a transesterification reaction takes place.

An ester-forming derivative of a diol may be an ester, for example an acetate ester. An ester-forming derivative of a carboxylic acid may be its diacid chloride or its diester such as a dimethyl ester or a diethyl ester.

The invention further relates to a polymer obtainable by the process of the invention. EXAMPLES

Synthesis: In a typical experiment, polymerizations were conducted in 100 ml_ three-neck round-bottom flasks equipped with a mechanical overhead stirrer, nitrogen inlet and water-condenser. 2,4-furandicarboxylic acid dimethylester (1.5 g, 8.14 mmol) and diol (16.2 mmol) were charged into the reaction flask. The set-up was placed under vacuum and purged with nitrogen gas, and this cycle was repeated for three times.

The polymerization method involves two stages. During the first stage, the reaction was carried out under nitrogen gas to form oligomers. The reaction mixture was heated in the silicone-oil bath at 115 °C for 15 min. After observing the complete melt of the mixtures, the catalyst Ti(OiPr)₄ (0.10 mmol) in 1 ml_ of toluene was added into the flask under the continuous flow of nitrogen gas. The temperature was now increased to 160 °C and stirred for 12 h, and finally to 200 - 215 °C for 1 -2 h to complete the first stage of pre- polymerisation reaction. The methanol and toluene were collected in the cooling flask.

During the second stage of the polymerization to obtain high molar mass polyesters, high vacuum of 0.02 mbar was applied gradually to the polymerisation set-up at 210 - 215 °C for 2 h. After completion of the reaction, the reaction mixture was cooled down to room temperature under nitrogen atmosphere. The polymer was purified by dissolving in 10 mL of chloroform/TFA mixture (6:1 ) and precipitated in 100 mL of methanol to yield a white powder. The yields were in the range of 80 - 90 %. The structural and thermal properties of the obtained polyesters were measured and are given in the tables below (Table 1 & 2).

Table 1. Molar masses of polyesters based on 2,4-furandicarboxylic acid dimethyl ester (2,4-FDCA-Me, white rows) and 2,5-furandicarboxylic acid dimethyl ester (2,5-FDCA-Me, grey rows) with the diols ,2-ethanediol (1 ,2- EDO), 1 ,3-propanediol (1 ,3-PDO), 1 ,4-butanediol (1 ,4-BDO) and 2,3- butanediol (2,3-BDO).

The molar masses of the polymers were determined by GPC, using HFIP as solvent.

Table 2. Thermal properties of polyesters based on

2.4- furandicarboxylic acid dimethyl ester (2,4-FDCA-Me, white rows) and

2.5- furandicarboxylic acid dimethyl ester (2,5-FDCA-Me, grey rows) with the diols 1 ,2-ethanediol (1 ,2-EDO), 1 ,3-propanediol (1 ,3-PDO), 1 ,4-butanediol

(1 ,4-BDO) and 2,3- butanediol (2,3-BDO).

TGA samples were heated from 30 °C to 600 °C at a heating rate of 10 °C/min under a nitrogen flow of 60 mL/min.

The DSC measurement followed the standard heating and cooling rate of 10 °C/min. Not observed up to 230 °C.

Claims

1. Semi-crystalline polyester comprising dicarboxylic acid residues and diol

residues, wherein the dicarboxylic acid residues comprise

2,4-furandicarboxylic acid residues and wherein the diol residues comprise aliphatic diol residues.

2. Semi-crystalline polyester according to claim 1 , wherein the 2,4- furandicarboxylic acid residues constitute 50 mol% or more of the total amount of dicarboxylic acid residues.

3. Semi-crystalline polyester according to claim 1 or 2, wherein the aliphatic diol residues constitute 50 mol% or more of the total amount of diol residues.

4. Semi-crystalline polyester according to any one of claims 1-3, wherein the dicarboxylic acid residues further comprise one or more residues selected from the group of 2,5-furandicarboxylic acid residues, 3,4-furandicarboxylic acid residues, 2,3-furandicarboxylic acid residues, terephthalic acid residues, isophthalic acid residues, phthalic acid residues, succinic acid residues and adipic acid residues.

5. Semi-crystalline polyester according to any one of claims 1-4, wherein the diol residues comprise two or more different types of aliphatic diol residues.

6. Semi-crystalline polyester according to any one of claims 1-5, further

comprising monohydroxy monocarboxylic acid residues.

7. Semi-crystalline polyester according to any one of claims 1-6, wherein up to 50 mol% of the total amount of residues are monohydroxy monocarboxylic acid residues.

8. Semi-crystalline polyester according to claim 7, wherein the monohydroxy

monocarboxylic acid residue is selected from the group of ortho- hydroxybenzoic acid, meta-hydroxybenzoic acid, para-hydroxybenzoic acid, lactic acid, glycolic acid and gamma-hydroxybutyric acid.

9. Semi-crystalline polyester according to any one of claims 1-8, wherein the aliphatic diol residue is selected from the group of ethylene glycol, 1 ,2- propanediol, 1 ,3-propanediol, ,2-butanediol, ,3-butanediol, 1 ,4-butanediol, 2,3-butanediol, 1 ,5-pentanediol, 1 ,4-pentanediol, 2,4-pentanediol 1 ,6- hexanediol, 1 ,5-hexanediol, 1 ,4-hexanediol, 2,5-hexanediol, 3,4-hexanediol, cyciobutane-1 ,2-dimethanol, cyclobutane-1 ,3-dimethanol, cyclopentane-1 ,2- dimethanol, cyclopentane-1 ,3-dimethanol, cyclohexane-1 ,2-dimethanol, cyclohexane-1 ,3-dimethanol, cyclohexane-1 , 4-dimethanol and

2,2-bis(4-hydroxycyclohexyl)propane.

0. Semi-crystalline polyester according to any one of claims 1-9, having a melting temperature of 160°or lower.

1 . Process for preparing a polyester according to any one of claims 1-10,

comprising forming a mixture comprising

- 2,4-furandicarboxylic acid and/or an ester-forming derivative thereof;

- an aliphatic diol and/or an ester-forming derivative thereof; and

- a catalyst,

followed by performing a melt polymerization by exposing the mixture to a temperature of at least 00 °C, yielding a semi-crystalline polyester, and thereafter optionally followed by performing a solid state post condensation.

12. Process according to claim 11 , wherein the molar ratio of 2,4-furandicarboxylic acid and/or an ester-forming derivative thereof to aliphatic diol and/or an ester- forming derivative thereof is in the range of 1 :1.5 to 1 :2.5.

13. Process according to claim 1 or 12, wherein the amount of 2,4- furandicarboxylic acid and/or an ester-forming derivative thereof and aliphatic diol and/or an ester-forming derivative thereof in the mixture is at least 95 mol% of the monomers present in the mixture.

14. Process according to any one of claims 1-13, wherein the catalyst is

selected from the group of titanium tetraalkoxides, dibutyltinoxide (DBTO), dibutyltinlaurate (DBTL), stannous oxide and tinoctanoate.

15. Semi-crystalline polyester obtainable by the process of any of claims 1 1-14.