WO2015080675A1

WO2015080675A1 - Molecular weight enhancing agent of polyester comprising amidoalkylidene malonate, a process of enhancing molecular weight and polyester obtained from said molecular weight enhancing agent

Info

Publication number: WO2015080675A1
Application number: PCT/TH2014/000052
Authority: WO
Inventors: Takul LOSIRIWAT; Anupat POTISATITYUENYONG
Original assignee: Ptt Global Chemical Public Company Limited
Priority date: 2013-11-29
Filing date: 2014-11-28
Publication date: 2015-06-04
Also published as: DE212014000222U1

Abstract

The present invention relates to a molecular weight enhancing agent of polyester comprising amido alkylidene malonate, a process for enhancing molecular weight and polyester obtained from the molecular weight enhancing agent. The molecular weight enhancing agent contains alkylidene malonate group having amido electron withdrawing group in the structure at alpha-carbon position. The molecular weight enhancing agent has high reactivity and can be used at low temperature, thus is suitable for polyester, especially, low melting point polyester and reduces energy consumption during the process.

Description

TITLE OF THE INVENTION

MOLECULAR WEIGHT ENHANCING AGENT OF POLYESTER COMPRISING AMIDOALKYLIDENE MALONATE, A PROCESS FOR ENHANCING MOLECULAR WEIGHT AND POLYESTER OBTAINED FROM SAID MOLECULAR WEIGHT ENHANCING AGENT

SUMMARY OF THE INVENTION

This invention relates to a molecular weight enhancing agent of polyester comprising amidoalkylidene malonate, a process for enhancing molecular weight and polyester obtained from said molecular weight enhancing agent wherein the molecular weight enhancing agent contains alkylidene malonate group having amido electron withdrawing group at alpha-carbon position as shown in the structure (I), or tautomer thereof,

wherein

Q represents a hydrocarbon unit selected from aliphatic hydrocarbon, alicyclic hydrocarbon, aromatic hydrocarbon or, optionally, heteroatom-containing hydrocarbon, X represents oxygen or sulfur,

B represents alkylidene malonate group as shown in the structure (a) or tautomer thereof,

wherein Rl and R2 each independently represents an aliphatic hydrocarbon, or Rl and R2 are connected together to form an alicyclic hydrocarbon, or, optionally, containing heteroatom, wherein Rl and R2 have a total number of carbon atoms of not more than 8, and

n represents an integer number from 2 to 10. FIELD OF THE INVENTION

Chemistry relates to a molecular weight enhancing agent, a process for enhancing molecular weight and polymer obtained from said molecular weight enhancing agent.

BACKGROUND OF THE INVENTION

It is understood that physical and mechanical properties of polymers depend on molecular weight of the polymer. Typically, high molecular weight polymers possess better physical and mechanical properties than that of low molecular weight polymers. Thus, it is desirable to produce polymers with high molecular weight.

Polymerization using polycondensation reaction or step-growth polymerization, including the production of polyesters using said reaction is generally reversible reaction which is resulting in low molecular weight polymers. If a high molecular weight polymer is desired, processes of heating and removing co-products such as water or alcohol obtained from the reaction are required. However, such processes need a proper control of the reaction condition as excessive heat or reaction time may cause the disintegration of the polymer chain thus resulting in lower molecular weight than desired. This is the limitation of the method, thus, there are methods to increase the molecular weight of polyesters by reacting polyesters in molten state with chain extender or crosslinker at suitable temperature and time.

The molecular weight enhancing agents those can be applied to polyesters are commercially available in various types. These agents contain different functional groups, such as epoxide group, carboxylic acid anhydride group, carbodiimide group, oxazoline group, oxazolinone group, carbonyl bis-lactam group, diisocyanate group and blocked isocyanate group, that can react with polyesters.

Diisocyanates and polyisocyanates are known in the production of polyesters. Such groups can effectively increase the molecular weight of polyesters. Generally, advantage of isocyanate group that it can react at low temperature, thus energy consumption is reduced during the process, especially when compared to other functional groups such as epoxide and anhydride, which require higher temperature to initiate the reaction. However, the high toxicity of isocyanate group is a concerned issue especially to the respiratory and immune system and also contains the risk of developing cancer. The blocked isocyanate group is the chain extender that is designed to solve the above problems. The objective is to increase safety during transporting and handling processes since the molecular structure of the blocked isocyanate group only releases free isocyanate group when the temperature reaches the deblocking temperature. There are literatures disclosing the use of various types of chemicals as blocking groups in the blocked isocyanate wherein each of them has a certain range of required temperature for deblocking. Even though the blocked isocyanates were safe to transport but free isocyanates produced from heat during the molecular weight enhancing process are still volatile substances. They exhibit the same toxicity as that of normal isocyanate group in all aspects. Thus, the use of blocked isocyanate group cannot solve the health risks issues faced by the frontline workers.

US Patent 4065440 disclosed the use of isopropylidene malonate group to increase molecular weight of polyesters. The isopropylidene malonate has starting reaction temperature with polyesters ranging from 140 to 230 °C which is unsuitable for the use with low melting point polyesters such as bio-based polyesters.

Dumas, Acc. Chem. Res., 2010, 43 (3), pp 440^54 disclosed the use of alkylidene malonate group as blocking group for isocyanate, in which alkylidene malonate group will be broken down to give reactive ketene group which are highly active, unlike other blocked isocyanates, it does not break down to release free isocyanate group during the heating process. It is also outstanding in terms of the synthesis process that does not require additional heat during the reaction, that is, the reaction can be carried out at room temperature and normal atmospheric pressure. Moreover, the cleavage of blocking group to form the reactive ketene occurs in relatively low temperature in the range of approximately 1 10-140 °C comparing to the release of a free isocyanate group in conventional blocked isocyanates such as caprolactam-blocking group in which the release occurs at about 170 °C, while alcohol-blocking group exhibits release at about 185 °C or above, or even when compared with the chain extender consisting of other functional groups such as epoxide group, wherein the reaction occurs at temperature around 170 °C or carboxylic acid anhydride wherein the reaction occurs at about 180 °C.

Isopropylidene malonate is used as blocking group in the production of the blocked isocyanate, for example, as a component for producing film and polyurethane lacquer for product coating as disclosed in US4507427A. However, there is no report of the use of such chemical structure for the purpose of increasing the molecular weight of polyesters. In addition, the commonly used chain extenders and crosslinkers generally have high sensitivity to moisture, since their chemical structures actively react with nucleophiles such as hydroxyl group which is also a component of water. Therefore, moisture must be avoided during storage to prevent the deactivation of the reactive groups. The functional groups including epoxide group, carboxylic anhydride group and carbodiimide group are easily broken down when exposed to moisture.

Although certain chain extenders do not react with water, they still have difficulties during storage e.g. the blocked isocyanate that uses caprolactam as a blocking group has hygroscopic properties and will become sticky in poor storage condition. In contrast, the molecular weight enhancing agent that use isopropylidene malonate as protecting group does not react with water despite a prolonged exposure period as it does not have hygroscopic property.

Therefore, there is a demand for the molecular weight enhancing agent that is highly reactive, not sensitive to moisture, and can be used at low temperature which is suitable for polyesters, preferably low melting point polyesters such as bio-based polyesters, which tend to break down easily when being used at high temperature during the process for enhancing the molecular weight.

DETAILED DESCRIPTION OF THE INVENTION

Definition

Technical or scientific terms used herein will be understood by those skilled in the art, unless stated otherwise.

Equipment, apparatus, methods, or chemicals mentioned herein means equipment, apparatus, methods, or chemicals commonly operated or used by those skilled in the art, unless explicitly stated that they are equipment, apparatus, methods or chemicals specifically use in this invention.

The use of the singular or plural nouns with the term "comprising" in the claims or in specification refers to "one" and also "one or more", "at least one" and "one or more than one".

In this application, the term "about" is used to indicate that any value presented herein may potentially vary or deviate. Such variation or deviation may result from errors of apparatus, methods used in calculation or from individual operator implementing the apparatus or methods. These include variations or deviations caused by the changes of physical properties such as molecular weight.

"Molecular weight enhancing agent" refers to the chain extenders, crosslinkers or a mixture of the above-mentioned. The chain extenders and crosslinkers for the polyesters contain functional groups that can react with hydroxyl functional group (OH) and carboxylic acid group (COOH) in polyesters. As used herein, the chain extenders are defined by the number of functional groups that can react with polyesters, which is two, which results in the linkage of the polymer chain without significantly changing the rheological property. While the crosslinkers are defined by the number of functional groups that can react with polyesters of three or more functional groups that will affect the microstructure of the polymer, by introducing the additional branching to the structure of the original polymer.

"Hydrocarbon with heteroatom" means derivatives of hydrocarbons in which carbon or hydrogen atoms are substituted by one or more heteroatoms in the structure.

"Heteroatom" means non-carbon atoms, including but not limited to, tetrels, for example, silicon, germanium, tin and lead; pniktogens, for example, nitrogen, phosphorus, arsenic, antimony and bismuth; chalcogens, for example, oxygen, sulfur, selenium, and tellurium; halogens, for example, fluorine, chlorine, bromine and iodine.

"phr" represents the ratio of the molecular weight enhancing agent that is added to the polyesters per one hundred parts of polyesters. Unless stated otherwise, phr is calculated by weight.

"Inert solvent" means solvent that does not react with polyester and with molecular weight enhancing agent, especially the solvent that can dissolve the molecular weight enhancing agent. The example of inert solvent includes the solvents from the ether group, for example, diethyl ether, methyl tertiary-butyl ether (MTBE), tetrahydrofuran (THF) and 1 ,4-dioxane; solvents from the ketone group, for example, acetone, methyl ethyl ketone (MEK), or cyclohexanone; solvents from the aromatic hydrocarbon group, for example, benzene, toluene, various xylene isomers or various cresol isomers; and other organic solvents, for example, dimethyl sulfoxide (DMSO), dimethyl formamide (DMF) and N- methylpyrrolidone (NMP).

One objective of this invention is to provide a molecular weight enhancing agent for polyester that is highly reactive. One objective of this invention is to provide the molecular weight enhancing agent for polyester that can be used at temperature lower than conventional process and is suitable for bio-based polyester typically having low melting point, and reduce energy consumption.

One objective of the invention is to provide the molecular weight enhancing agent comprising amidoalkylidene malonate group, which does not breakdown to give free isocyanate and thus reduces the chance of releasing chemicals that may be harmful to the health of operators and workers when compared with the molecular weight enhancing agent from the conventional isocyanates and the blocked isocyanate groups.

The following details describe the specification of the invention, and are not intended to limit the scope of the invention in any way.

This invention provides the molecular weight enhancing agent of polyester comprising amidoalkylidene malonate, a process for enhancing molecular weight, and the use of said molecular weight enhancing agent, wherein the molecular weight enhancing agent contains alkylidene malonate group having amido electron withdrawing group at the alpha-carbon position as shown in the structure (I), or tautomer thereof,

wherein

wherein Rl and R2 each independently represents an aliphatic hydrocarbon, or Rl and R2 are connected together to form an alicyclic hydrocarbon, or, optionally, containing heteroatom wherein Rl and R2 have a total number of carbon atoms of not more than 8, and

n represents an integer number of from 2 to 10.

Preferably, Q comprises 2 to 21 carbon atoms and more preferably Q comprises 4 to 15 carbon atoms.

In one embodiment, Q is an aliphatic hydrocarbon group selected from tetramethylene, hexamethylene, isophoronediyl groups, oligomer or pre-polymer obtained from aliphatic isocyanates.

In one embodiment, Q is an alicyclic hydrocarbon selected from

dicyclohexylmethanediyl or cyclohexanediyl.

In one embodiment, Q is an aromatic hydrocarbon selected from tolylene, xylylene, diphenylmethanediyl, m-phenylenediyl, p-phenylenediyl, naphthylene groups, oligomer or pre-polymer obtained from aromatic isocyanates.

Preferably, B in the structure (I) is isopropylidene malonate, isobutylidene malonate or cyclohexylidene malonate.

From the structure (I), it can be seen that the amido electron withdrawing group in the structure attached to the carbon atom at the alpha position, between the two carbonyl functional groups in the structure (position 5) provides the electronic effect, which affects electrophilicity and increase the reactivity of the formed ketene. The electrophilicity of the formed ketene group can be theoretically calculated using computer simulation.

The study of thermal properties of the molecular weight enhancing agent provided by this invention using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) found that the molecular weight enhancing agent provided by this invention will be broken down to ketene group having structure associated with its chemical precursor. The initial temperature of the breakdown process is in the range of about 1 10 °C to 170 °C. Such breakdown temperature is lower than the breakdown temperature of molecular weight enhancing agent containing isopropylidene malonate group without carboxamido group, in which the breakdown temperature is around 140 °C to 230 °C.

The molecular weight enhancing agent according to the invention may be used in solid form such as powder or granule, or in liquid form such as preparing as a solution in an inert solvent. The process for enhancing molecular weight of polyester comprises the steps of adding molecular weight enhancing agent into polyester and heating polyester wherein the molecular weight enhancing agent contains alkylidene malonate group having amido electron withdrawing group in the structure at alpha-carbon position as shown in the structure (I), or tautomer thereof as described above.

Preferably, the temperature of molecular weight enhancing process of polyesters according to this invention is in the range of about 1 10 °C to 170 °C and more preferably in the range of about 120 °C to 150 °C.

In one embodiment, the polyesters are bio-based polyesters, preferably, the polyesters having a melting point of lower than 170°C and more preferably in the range of about 50 °C to 160 °C.

More preferably, said polyester is aliphatic homopolyester, aliphatic copolyester, aliphatic-aromatic copolyester or a mixture thereof.

Most preferably, said polyester is aliphatic homopolyester selected from polylactide, polyglycolide; aliphatic copolyester selected from poly(lactic-co-glycolic acid), poly(caprolactone-co-glycolic acid), polybutylene succinate, poly(butylene succinate-co-adipate), polyhydroxybutyrate, or poly(caprolactone-co-lactic acid); aliphatic-aromatic polyester selected from polybutylene terephthalate, poly(butylene- adipate-co-terephthalate), poly(butylene succinate-co-terephthalate) or a mixture thereof.

In one embodiment, the step of adding molecular weight enhancing agent into polyester may be done before the heating step, for example, the addition is done along with polyester granules in the extrusion step or molecular weight enhancing agent may be added while heating polyester, for example, the addition of molecular weight enhancing agent into reactor is done in post-polymerization step.

The amount of molecular weight enhancing agent used may be adjusted according to the proportion of the amount of hydroxyl group (OH) and carboxylic acid group (COOH) contained in polyester. The usage amount is in the range of from 0.1 to 15 phr, particularly is in the range of from 1 to 10 phr.

The following is the preparation of molecular weight enhancing agent provided by this invention.

The synthesis of molecular weight enhancing agent according to this invention may be carried out using the following steps: adding 1 part by mole of diisocyanate or polyisocyanate precursor into inert solvent followed by 0.95 to 1.5 parts by mole of alkylidene malonate at temperature less than 80 °C, stirring the mixture for 30 minutes

adding 2 to 15 parts by mole of basic catalyst

- stirring the mixture until the reaction is completed

pouring the resulting mixture into the acid with concentration of 10-20% of 5- 10 times volume of the mixture, then stirring the mixture for 10 to 60 minutes

separating the resulting solid product and wash it with water until the pH of the washed water is in the range of 5.5 to 7

- drying the obtained solid in vacuum.

The molecular weight enhancing agent according to the invention may be used in solid form such as powder or granule or may be used in liquid form, for example, to prepare the solution in the inert solvent.

The following is the list of molecular weight enhancing agent according to this invention with reference to Q in structure formula (I):

IPMD is the molecular weight enhancing agent according to the invention having Q as isophoronediyl;

HMMD is the molecular weight enhancing agent according to the invention having Q as hexamethylene;

- BMMD is the molecular weight enhancing agent according to the invention having Q as tetramethylene;

TMD is the molecular weight enhancing agent according to the invention having Q as tolylene;

XMD is the molecular weight enhancing agent according to the invention having Q as xylylene; and

CHMMD, is the molecular weight enhancing agent according to the invention which is oligomer obtained from isocyanate having Q as hexamethylene.

The other molecular weight enhancing agents according to the invention, which are not listed above, may be called using the same principle.

The following is property tests of the polyester obtained from the molecular weight enhancing agent according to the invention wherein the equipment and methods used in the test are the equipment and methods that are commonly used and they are not intended to limit the scope of the invention.

Analyzing equipment used in the study of the completeness and the temperature profile of the reaction both in synthesis, and in finding the forming of ketene group are Bruker Fourier transform infrared spectrometer (FT-IR) of model Vertex70/Hyp2000 using the attenuated total reflectance (ATR) method; Netzsch Differential scanning calorimeter (DSC) of model DSC204F1 , and Netzsch Thermogravimetric analyzer of model TG209F1.

Molecular weight of the polyester used in this invention is determined by the size separation using Waters gel permeation chromatography (GPC) of model Alliance GPC 2000 with Styragel column HT 6,5,4,3 at 40 °C using tetrahydrofuran (THF) as eluent with a flow rate of 1 ml/minute and the resulting molecular weight is compared with the standard graph of polystyrene molecular weight obtained from Polymer Laboratory of type S-M-10, which covers molecular weight in the range of 580 to 3,000,000. Addition of molecular weight enhancing agent

75 g of polybutylene adipate-co-terephthalate (PBAT) was molten using mechanical stirrer. Temperature was maintained at 140 °C under nitrogen atmosphere, then 1 phr of molecular weight enhancing agent HMMD was each added portionwise, every 15 minutes. The sample was taken to be analyzed for molecular weight both before and after the addition of HMMD. The result is that molecular weight of polymer correlated with the amount of molecular weight enhancing agent added. The result is shown in Table 1

Table 1: The properties of polyester obtained from the molecular enhancing process using the different amount of molecular weight enhancing agents

Reaction time

75 g of polybutylene adipate-co-terephtalate-co-isophthalate (PBATI) was molten by mechanical stirrer. Temperature was maintained at 165 °C under nitrogen atmosphere, then 5 phr of molecular weight enhancing agent HMMD was added into inert solvent (dioxane). The sample was taken at different intervals. The result is that the completion of molecular weight enhancing reaction took less than 15 minutes. After that the obtained values were significantly unchanged as shown in Table 2.

Table 2: The properties of polyester obtained from the molecular weight enhancing process according to the present invention at different reaction times

Reactivity

To demonstrate the reactivity of the molecular weight enhancement according to the present invention, other molecular weight enhancing agents in isocyanate group such as isophorone diisocyanate (IPDI) and hexamethylene diisocyanate (HDI) and molecular weight enhancing agents in isopropylidene malonate group with no amido electron withdrawing group such as FMD and CypMD having a structure shown in the below figure, were used in the comparison. The comparative molecular weight enhancing agent was added in the same amount as the molecular weight enhancing agent of this invention based on mole of the reactive group.

CypMD

50 g of polybutylene adipate-co-terephthalate (PBAT) and molecular weight enhancing agent were mixed using Hakke® twin-screw micro compounder of model Minilab II. Temperature was maintained in the range of 130-150 °C in every zones and motor speed of the screw was 50 round-per-minute. The result was shown in Table 3. Table 3: The properties of polyesters obtained from the molecular weight enhancing process using different molecular weight enhancing agents

6mmol (+36.55) (+40.05) (+42.81)

150 °C 83876 78016 83098

Mw (Da)

(+55.37) (+44.52) (+53.93)

PDI - 2.05 1.86 1.95

Mn (Da) - 39177 391 13 38810

FMD

Comparative 72713 72964 72377

6mmol Mw (Da) - example 2c (+34.70) (+35.16) (+34.07)

150 °C

PDI - 1.86 1.87 1.86 From Table 3 when compared Control with Example Al and A2, it can be seen that the molecular weight enhancing agent according to the invention with amido-electron withdrawing group can significantly increase the molecular weight of polybutylene adipate-co-terephthalate.

Moreover, when compared Example Al, A2 with Comparative example la and lb, it is found that the molecular weight enhancing agent according to the invention, IPMD and HMMD have higher reactivity than isocyanate IPDI and HDL

In the comparison of Example B l with Comparative example lc and Id, at molecular weight enhancing temperature of 130 °C and Example CI with Comparative example 2c at molecular weight enhancing temperature of 150 °C, it was found that the molecular weight enhancing agent IPMD significantly increases the molecular weight of polybutylene adipate-co-terephthalate compared to the molecular weight enhancing agent FMD and CypMD. Therefore, it can be seen that the amido electron withdrawing group in the structure enhances the effectiveness or reactivity of isopropylidene molecular weight enhancing agent. Applications with various polyesters

Another objective of the invention is to show that the molecular weight enhancing agent used in this invention can be used with various polyesters. These polyesters are intended to be examples selected to illustrate polyesters defined and do not limit the scope of the invention. Moreover, mixtures of polyesters with different types of polymers such as polycarbonate or mixtures of polyesters and other compatible materials such as flour starch or other additives, can be applied as well.

The examples of polyesters are polybutylene adipate (PBA), polyhexamethylene adipate (PHA), polybutylene adipate-co-terephthalate (PBAT), polybutylene adipate-co- terephtalate-co-isophthalate (PBATI) or polybutylene-co-glyceryladipate-co-terephtalate (PBGAT).

Table 4: The properties of polyesters obtained from the molecular weight enhancing process according to the invention

BEST MODE OF THE INVENTION

Best mode of the invention is as disclosed in the detailed description.

Claims

1. A molecular weight enhancing agent for enhancing molecular weight of polyester comprising alkylidene malonate group having amido electron withdrawing group at alpha-carbon position as shown in the structure (I), or its tautomer thereof,

wherein

Q represents a hydrocarbon unit selected from aliphatic hydrocarbon, alicyclic hydrocarbon, aromatic hydrocarbon or, optionally, heteroatom-containing hydrocarbon,

X represents oxygen or sulfur,

n represents an integer number of from 2 to 10.

2. The molecular weight enhancing agent according to claim 1, wherein Q comprises 2 to 21 carbon atoms.

3. The molecular weight enhancing agent according to claim 1 or 2, wherein Q comprises 4 to 15 carbon atoms.

4. The molecular weight enhancing agent according to any one of claims 1 to 3, wherein Q is aliphatic hydrocarbon group selected from tetramethylene, hexamethylene, isophoronediyl, oligomer or pre-polymer obtained from isocyanate comprising said aliphatic hydrocarbon group.

5. The molecular weight enhancing agent according to any one of claims 1 to 3, wherein Q is alicyclic hydrocarbon selected from dicyclohexylmethanediyl or cyclohexanediyl.

6. The molecular weight enhancing agent according to any one of claims 1 to 3, wherein Q is aromatic hydrocarbon group selected from tolylene, xylylene, diphenylmethanediyl, m-phenylenediyl, p-phenylenediyl, naphthylene group, oligomer or pre-polymer obtained from isocyanate comprising said aromatic hydrocarbon group.

7. The molecular weight enhancing agent according to any one of the preceding claims, wherein B is isopropylidene malonate, isobutylidene malonate or cyclohexylidene malonate.

8. The molecular weight enhancing agent according to any one of the preceding claims, wherein the said molecular weight enhancing agent has the breakdown temperature yielding ketene group in the range of 1 10-170 °C.

9. A process for enhancing molecular weight of polyester comprises the steps of adding the molecular weight enhancing agent into polyester and heating the polyester wherein the molecular weight enhancing agent comprises alkylidene malonate group having amido electron withdrawing group at alpha-carbon position as shown in the structure (I), or tautomer thereof,

wherein

n represents an integer number of from 2 to 10.

10. The process for enhancing molecular weight of polyester according to claim 9 wherein Q comprises 2 to 21 carbon atoms.

1 1. The process for enhancing molecular weight of polyester according to claim 9 or 10 wherein Q comprises 4 to 15 carbon atoms.

12. The process for enhancing molecular weight of polyester according to any one of claims 9 to 1 1 wherein Q is aliphatic hydrocarbon group selected from tetramethylene, hexamethylene, isophoronediyl groups, oligomer or pre-polymer obtained from isocyanate comprising said aliphatic hydrocarbon group.

13. The process for enhancing molecular weight of polyester according to any one of claims 9 to 1 1 wherein Q is alicyclic hydrocarbon selected from dicyclohexylmethanediyl or cyclohexanediyl.

14. The process for enhancing molecular weight of polyester according to any one of claims 9 to 1 1 wherein Q is aromatic hydrocarbon group selected from tolylene, xylylene, diphenylmethanediyl, m-phenylenediyl, p-phenylenediyl, naphthylene groups, oligomer or pre-polymer obtained from isocyanate comprising said aromatic hydrocarbon group.

15. The process for enhancing molecular weight of polyester according to any one of claims 9 to 14 wherein B is isopropylidene malonate, isobutylidene malonate or cyclohexilidene malonate.

16. The process for enhancing molecular weight of polyester according to any one of claims 9 to 15 wherein the temperature of the process is in the range of 1 10 °C to 170 °C.

17. The process for enhancing molecular weight of polyester according to claim 16 wherein the temperature of the process is in the range of 120 °C to 150 °C.

18. The process for enhancing molecular weight of polyester according to any one of claims 9 to 15 wherein the polyester is bio-based polyester.

19. The process for enhancing molecular weight of polyester according to claim 18 wherein the melting point of polyester is lower than 170 °C.

20. The process for enhancing molecular weight of polyester according to claim 18 or 19 wherein the melting point of polyester is in the range of 50-160 °C.

21. The process for enhancing molecular weight of polyester according to any one of claims 18 to 20 wherein the polyester is aliphatic homopolyester, aliphatic copolyester, aliphatic-aromatic copolyester or a mixture thereof.

22. The process for enhancing molecular weight of polyester according to claim 21 wherein aliphatic homopolyester is selected from polylactide or polyglycolide.

23. The process for enhancing molecular weight of polyester according to claim 21 wherein aliphatic copolyester is selected from poly(lactic-co-glycolic acid), poly(caprolactone-co-glycolic acid), polybutylene succinate, poly(butylene succinate-co- adipate), polyhydroxybutyrate, or poly(caprolactone-co-lactic acid).

24. The process for enhancing molecular weight of polyester according to claim 21 wherein aliphatic-aromatic polyester is selected from polybutylene terephthalate, poly(butylene-adipate-co-terephthalate) or poly(butylene succinate-co-terephthalate).

25. The process for enhancing molecular weight of polyester according to any one of claims 9 to 24 wherein adding of the molecular weight enhancing agent into polyester is done before or during heating of the polyester.

26. A polyester resin comprises at least one polyester and at least one molecular weight enhancing agent, wherein the molecular weight enhancing agent comprises alkylidene malonate group having amido electron withdrawing group at alpha-carbon position as shown in the structure (I), or tautomer thereof,

wherein Q represents a hydrocarbon unit selected from aliphatic hydrocarbon, alicyclic hydrocarbon, aromatic hydrocarbon or, optionally, heteroatom-containing hydrocarbon, X represents oxygen or sulfur,

n represents an integer number of from 2 to 10.

27. The polyester resin according to claim 26 wherein Q comprises 2 to 21 carbon atoms.

28. The polyester resin according to claim 26 or 27 wherein Q comprises 4 to 15 carbon atoms.

29. The polyester resin according to any one of claims 26 to 28 wherein Q is aliphatic hydrocarbon group selected from tetramethylene, hexamethylene, isophoronediyl groups, oligomer or pre-polymer obtained from isocyanate comprising said aliphatic hydrocarbon group.

30. The polyester resin according to any one of claims 26 to 28 wherein Q is alicyclic hydrocarbon selected from dicyclohexylmefhanediyl or cyclohexanediyl.

31. The polyester resin according to any one of claims 26 to 28 wherein Q is aromatic hydrocarbon group selected from tolylene, xylylene, diphenylmethanediyl, m- phenylenediyl, p-phenylenediyl, naphthylene groups, oligomer or pre-polymer obtained from isocyanate comprising said aromatic hydrocarbon group.

32. The polyester resin according to any one of claims 26 to 31 wherein B is isopropylidene malonate, isobutylidene malonate or cyclohexylidene malonate.

33. The polyester resin according to any one of claims 26 to 32 wherein the temperature of the process is in the range of 1 10 °C to 170 °C.

34. The polyester resin according to claim 33 wherein the temperature of the process is in the range of 120 °C to 150 °C.

35. The polyester resin according to any one of claims 26 to 32 wherein the polyester is bio-based polyester.

36. The polyester resin according to claim 35 wherein the melting point of polyester is lower than 170 °C.

37. The polyester resin according to claim 35 or 36 wherein the melting point of polyester is in the range of 50 to 160 °C.

38. The polyester resin according to any one of claims 35 to 37 wherein the polyester is aliphatic homopolyester, aliphatic copolyester, aliphatic-aromatic copolyester or a mixture thereof.

39. The polyester resin according to claim 38 wherein the aliphatic homopolyester is selected from polylactide or polyglycolide.

40. The polyester resin according to claim 38 wherein the aliphatic copolyester is selected from poly(lactic-co-glycolic acid), poly(caprolactone-co-glycolic acid), polybutylene succinate, poly(butylene succinate-co-adipate), polyhydroxybutyrate or poly(caprolactone-co-lactic acid).

41. The polyester resin according to claim 38 wherein the aliphatic-aromatic polyester is selected from polybutylene terephthalate, poly(butylene-adipate-co- terephthalate) or poly(butylene succinate-co-terephthalate).