CN114989403A - Bio-based copolyester based on betulin and preparation method thereof - Google Patents

Abstract

The present invention relates to a bio-based copolyester based on betulin, and the structural formula of the copolyester is shown in formula (1):

In formula (1), x and y are both integers of 1-20, n is an integer of 20-100, R ₁ represents an aliphatic chain unit of aliphatic dicarboxylic acid or its ester product, R ₂ represents aliphatic dibasic aliphatic chain unit of alcohol. The present invention also relates to a preparation method of a bio-based copolyester based on betulin, comprising: aliphatic dicarboxylic acid or its ester product, betulin, aliphatic diol, esterification or transesterification catalyst Mix and react, then add a polycondensation catalyst, a free radical inhibitor, a stabilizer, and an antioxidant, and under vacuum conditions, first react at a first temperature of 160°C-180°C for 1h-3h, and then at a second temperature of 180°C- Continue the reaction at 240° C. for 2h-22h to obtain a bio-based copolyester based on betulin, wherein the second temperature is greater than the first temperature. The copolyester of the present invention has adjustable heat resistance and mechanical properties, and has high transparency.

Description

Bio-based copolyester based on betulin and its preparation method

technical field

The invention relates to the technical field of polymer materials, in particular to a bio-based copolyester based on betulin and a preparation method thereof.

Background technique

Polyester, polyurethane and other polymer materials have a wide range of important applications in agriculture, food packaging, household appliances, medical equipment and many other fields. At present, the vast majority of polymer materials are petroleum-based polymer materials derived from non-renewable fossil resources. Although they are widely used and have excellent performance, they will cause pollution and a large amount of pollution during production, use and after disposal. carbon emission. With the increasingly serious ecological and environmental problems and resource problems, the importance of bio-based polymer materials derived from renewable biomass resources has become increasingly prominent.

SUMMARY OF THE INVENTION

Based on this, it is necessary to address the above problems to provide a betulin-based bio-based copolyester and a preparation method thereof. The betulin-based bio-based copolyester has controllable heat resistance and mechanical properties, and high transparency.

A bio-based copolyester based on betulin, the structural formula of the copolyester is shown in formula (1):

In formula (1), x and y are both integers of 1-20, n is an integer of 20-100, R ₁ represents an aliphatic chain unit of an aliphatic dicarboxylic acid or its ester product, and R ₂ represents an aliphatic dibasic aliphatic chain unit of alcohol.

In one embodiment, the carbon number of the aliphatic dicarboxylic acid or its ester is 4-12;

And/or, the carbon number of the aliphatic diol is 2-6.

In one embodiment, the aliphatic dicarboxylic acid or its ester is selected from succinic acid or its ester, glutaric acid or its ester, adipic acid or its ester, suberic acid or its ester At least one of esters, sebacic acid or its esters, dodecanedioic acid or its esters;

And/or, the aliphatic diol is selected from at least one of ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol kind.

A described preparation method of betulin-based bio-based copolyester, comprising the following steps:

Mixing and reacting aliphatic dicarboxylic acid or its ester product, betulin, aliphatic diol and esterification or transesterification catalyst to obtain a betulin-based polyester prepolymer;

Add polycondensation catalyst, free radical inhibitor, stabilizer and antioxidant to the polyester prepolymer, first react at the first temperature for 1h-3h under vacuum conditions, and then continue to react at the second temperature for 2h- 22h, the bio-based copolyester based on betulin is obtained; wherein, the first temperature is 160°C-180°C, the second temperature is 180°C-240°C, and the second temperature is greater than the first temperature a temperature.

In one embodiment, the molar ratio of the sum of the amounts of the betulin alcohol and the aliphatic diol to the aliphatic dicarboxylic acid or its ester product is 3:1-5:1.

In one embodiment, the molar ratio of the aliphatic dicarboxylic acid or its ester compound to the betulin is 5:1-5:3.

In one embodiment, the esterification or transesterification catalyst is selected from at least one of zinc acetate, isobutyl titanate, tetrabutyl titanate, ethylene glycol antimony and dibutyl tin oxide, and the amount is 0.1%-0.2% of the mole number of the aliphatic dicarboxylic acid or its ester.

In one embodiment, in the step of mixing and reacting aliphatic dicarboxylic acid or its ester compound, betulin alcohol, aliphatic diol and esterification or transesterification catalyst, the reaction temperature is 160°C-220°C ℃, the time is 2h-6h.

In one embodiment, the radical polymerization inhibitor is selected from at least one of hydroquinone, p-methoxyphenol, p-tert-butylcatechol, and p-benzoquinone, and the amount of the aliphatic di- 0.4%-0.6% of the moles of carboxylic acid or its ester.

In one embodiment, the polycondensation catalyst is selected from at least one of antimony trioxide, isobutyl titanate, tetrabutyl titanate, germanium oxide, ethylene glycol antimony, antimony acetate and dibutyl tin oxide The amount is 0.1%-0.2% of the moles of the aliphatic dicarboxylic acid or its ester;

And/or, the stabilizer is selected from phosphorus-based stabilizers, and the dosage is 0.12%-0.15% of the moles of the aliphatic dicarboxylic acid or its ester.

The bio-based copolyester based on betulin of the present invention contains betulin structural units. Since the structure of betulin has a large volume and extremely high rigidity, the rigidity of the molecular chain can be greatly improved, so that the copolyester has Adjustable heat resistance and mechanical properties, and the introduction of the structure of betulin will greatly destroy the regularity of the polymer molecular chain, which can make the copolyester present a completely amorphous state with high transparency. At the same time, because the structure of betulin itself has antibacterial and bacteriostatic activities, the copolyester also has excellent antibacterial properties.

In addition, the present invention adopts a three-step method to prepare the bio-based copolyester based on betulin, that is, esterification/transesterification is performed first to obtain a polyester prepolymer based on betulin, and then the betulin-based polyester prepolymer is prepared under the protection of a free radical inhibitor. , polycondensation of the betulin-based polyester prepolymer at a relatively low temperature of 160°C-180°C to form a low molecular weight prepolymer with a molecular weight of 2000g/mol-10000g/mol. The molecular weight of the low molecular weight prepolymer is The chain already has high rigidity, which greatly increases the activation energy of the oxidation reaction of the carbon-carbon double bond structure. Therefore, when the reaction is carried out at a relatively high temperature of 180℃-240℃, the carbon-carbon double bond structure will not be affected. , and finally a bio-based copolyester based on betulin with tunable heat resistance and mechanical properties and high transparency is obtained.

Description of drawings

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments described in the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without any creative effort.

Fig. 1 is the ¹ H-NMR spectrum of the betulin-based bio-based copolyester prepared in Example 1 of the present invention;

Fig. 2 is the second heating DSC chart of the betulin-based bio-based copolyester prepared in Example 1 of the present invention.

Detailed ways

In order to facilitate understanding of the present invention, the present invention will be described in more detail below. It should be understood, however, that the present invention may be embodied in many different forms and is not limited to the embodiments or examples described herein. Rather, these embodiments or examples are provided so that a thorough and complete understanding of the present disclosure is provided.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terms used herein in the description of the present invention are for the purpose of describing specific embodiments or examples only, and are not intended to limit the present invention. As used herein, optional scope for the term "and/or" includes any one of two or more of the associated listed items, and also includes any and all combinations of the associated listed items, any and all A combination includes a combination of any two of the related listed items, any more of the related listed items, or all of the related listed items.

The structural formula of the betulin-based bio-based copolyester provided by the present invention is shown in formula (1):

In formula (1), x and y are both integers of 1-20, n is an integer of 20-100, R ₁ represents an aliphatic chain unit of an aliphatic dicarboxylic acid or its ester product, and R ₂ represents an aliphatic dibasic aliphatic chain unit of alcohol.

In one embodiment, the carbon number of the aliphatic dicarboxylic acid or its ester product is 4-12, that is, R ₁ represents an aliphatic chain unit with a carbon number of 4-12; Said aliphatic dicarboxylic acid or its ester product is selected from succinic acid or its ester product, glutaric acid or its ester product, adipic acid or its ester product, suberic acid or its ester product, sebacic acid or its ester product At least one of esters, dodecanedioic acid or esters thereof.

In one embodiment, the carbon number of the aliphatic dihydric alcohol is 2-6, that is, R ₂ represents an aliphatic chain unit with a carbon number of 2-6; optionally, the aliphatic dihydric alcohol The alcohol is selected from at least one of ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol.

The bio-based copolyester based on betulin of the present invention contains betulin structural units. Since the structure of betulin has a large volume and extremely high rigidity, the rigidity of the molecular chain can be greatly improved, so that the copolyester has a high rigidity. The heat resistance and mechanical properties can be adjusted according to the structure of betulin alcohol, and the introduction of the structure of betulin alcohol greatly destroys the regularity of the polymer molecular chain, which can make the copolyester present a completely amorphous state with high transparency. .

At the same time, because the structure of betulin itself has antibacterial and bacteriostatic activities, the copolyester also has excellent antibacterial properties.

Although the bio-based copolyester based on betulin has tunable heat resistance and mechanical properties, and high transparency, it has low polycondensation activity due to the secondary hydroxyl group in betulin. Although increasing the reaction temperature can improve the activity of the polycondensation reaction, the carbon-carbon double bond structure of betulin is prone to oxidative crosslinking at high temperatures. Therefore, it is difficult to obtain high molecular weight linear polyesters using conventional two-step melt polycondensation.

For this reason, the present invention also provides a kind of preparation method of described betulin-based bio-based copolyester, comprising the following steps:

S1, mix and react aliphatic dicarboxylic acid or its ester product, betulin, aliphatic diol and esterification or transesterification catalyst to obtain a polyester prepolymer based on betulin;

S2, adding a polycondensation catalyst, a free radical inhibitor, a stabilizer and an antioxidant to the polyester prepolymer, first reacting at the first temperature for 1h-3h under vacuum conditions, and then continuing the reaction at the second temperature 2h-22h, the bio-based copolyester based on betulin is obtained; wherein, the first temperature is 160°C-180°C, the second temperature is 180°C-240°C, and the second temperature is greater than the the first temperature.

The preparation of the bio-based copolyester based on betulin in the present invention adopts a three-step method, that is, esterification/ester exchange reaction is performed first to obtain a polyester prepolymer based on betulin.

Then, under the protection of a radical polymerization inhibitor, the betulin-based polyester prepolymer is polycondensed at a relatively low temperature of 160°C-180°C to form a low molecular weight prepolymer with a molecular weight of 2000g/mol-10000g/mol The molecular chain of the low molecular prepolymer already has high rigidity, which greatly increases the activation energy of the oxidation reaction of the carbon-carbon double bond structure, and it is difficult for free radicals to react with the carbon-carbon double bond structure.

Therefore, when the temperature is raised to a relatively high temperature of 180°C to 240°C, the carbon-carbon double bond structure will not be affected, and a high molecular weight linear polyester is finally obtained, which has adjustable heat resistance and mechanical properties. performance and high transparency.

Specifically, in step S1, the molar ratio of the sum of the consumption of betulin and the aliphatic diol to the aliphatic dicarboxylic acid or its ester is 3:1-5:1, wherein, The molar ratio of the aliphatic dicarboxylic acid or its ester product to the betulin is 5:1-5:3.

In this step, the amount of the esterification or transesterification catalyst is 0.1%-0.2% of the mole number of the aliphatic dicarboxylic acid or its esterification, and the esterification or transesterification catalyst is selected from zinc acetate, At least one of isobutyl titanate, tetrabutyl titanate, ethylene glycol antimony and dibutyl tin oxide.

In this step, the temperature of the reaction is 160°C-220°C, and the time is 2h-6h.

In step S2, the free radical polymerization inhibitor is selected from at least one of hydroquinone, p-methoxyphenol, p-tert-butylcatechol, and p-benzoquinone, and the amount is an aliphatic dicarboxylic acid or its amount. 0.4%-0.6% of the moles of esterified compounds can react with free radicals generated at high temperature to protect the carbon-carbon double bond structure.

In this step, the polycondensation catalyst is selected from at least one of antimony trioxide, isobutyl titanate, tetrabutyl titanate, germanium oxide, ethylene glycol antimony, antimony acetate and dibutyl tin oxide, The dosage is 0.1%-0.2% of the moles of aliphatic dicarboxylic acid or its ester.

In this step, the stabilizer is selected from phosphorus-based stabilizers, specifically selected from trimethyl phosphate, dimethyl phosphate, triphenyl phosphate, diphenyl phosphate, triphenyl phosphite, and diphenyl phosphite At least one of them is used in an amount of 0.12%-0.15% of the moles of the aliphatic dicarboxylic acid or its ester.

In this step, the antioxidant is selected from at least one of Antioxidant-1010, Antioxidant-1076 or Antioxidant-168.

In the preparation method of the present invention, the bio-based copolyester based on betulin can be synthesized through three-step reaction, and its number average molecular weight is as high as 20000 g·mol ^-1 or more.

Hereinafter, the bio-based copolyester based on betulin and its preparation method will be further described by the following specific examples.

Example 1

To a 3L three-necked flask equipped with a heating and stirring device, add 1 mol of dimethyl adipate, 0.4 mol of betulin, 3.6 mol of 1,4-butanediol, and 2 mmol of dibutyltin oxide, and put The reaction was carried out at 180° C. for 4 h to obtain a low molecular weight polyester prepolymer.

Continue to add 1mmol of dibutyltin oxide, 5mmol of p-methoxyphenol, 1.2mmol of trimethyl phosphate, 100mg of antioxidant-1010 to the 3L three-necked flask, and react at 180°C for 2h, then at 230 The reaction was continued at °C for 10 h to obtain a betulin-based bio-based copolyester with a number average molecular weight of 25200 g·mol ^-1 .

The H NMR spectrum of the copolyester obtained in this example is shown in Figure 1, in which the betulin structure accounts for 46 mol% of the molecular mole; the curve obtained by the differential scanning calorimeter test for the second heating scan is as follows As shown in FIG. 2 , the copolyester is a completely amorphous polymer with a glass transition temperature of 62° C. It can be seen from the tensile property test that the copolyester has a breaking strength of 70 MPa and a breaking elongation of 340%.

Example 2

To a 3L three-necked flask equipped with a heating and stirring device, add 1 mol of dimethyl adipate, 0.5 mol of betulin, 4.5 mol of 1,4-butanediol, 2 mmol of tetrabutyl titanate, and at 160 The reaction was carried out at ℃ for 3h to obtain a low molecular weight polyester prepolymer.

Continue to add 1mmol of tetrabutyl titanate, 5mmol of p-benzoquinone, 1.5mmol of triphenyl phosphate, 120mg of antioxidant-1076 to the 3L three-necked flask, and react at 180°C for 2h, then at 220°C The reaction was continued for 15 h to obtain a betulin-based bio-based copolyester having a number average molecular weight of 22400 g·mol ⁻¹ .

Characterized by hydrogen nuclear magnetic resonance spectroscopy, the betulin structure in the copolyester obtained in this example accounts for 65 mol% of the molecular mole fraction; the differential scanning calorimeter test proves that the copolyester is a completely amorphous polymer, The glass transition temperature is 110° C.; the tensile property test shows that the copolyester has a breaking strength of 87 MPa and a breaking elongation of 230%.

Example 3

To a 3L three-necked flask equipped with a heating and stirring device, add 1 mol of dimethyl adipate, 0.2 mol of betulin, 2.8 mol of ethylene glycol, and 1 mmol of zinc acetate, and react at 190 ° C for 6 h to obtain Low molecular weight polyester prepolymer.

Continue to add 1.5mmol of antimony trioxide, 5mmol of hydroquinone, 1.3mmol of diphenyl phosphate, 150mg of antioxidant-168 to the 3L three-necked flask, and react at 160°C for 2h, then at 180°C The reaction was continued for 22 h to obtain a betulin-based bio-based copolyester with a number average molecular weight of 26700 g·mol ⁻¹ .

Characterized by hydrogen nuclear magnetic resonance spectroscopy, the betulin structure in the copolyester obtained in this example accounts for 23 mol% of the molecular mole fraction; the differential scanning calorimeter test proves that the copolyester is a completely amorphous polymer, The glass transition temperature is 85°C; through the tensile properties test, the breaking strength of the copolyester is 79MPa, and the breaking elongation is 270%.

Example 4

To a 3L three-necked flask equipped with a heating and stirring device, add 1 mol of sebacic acid, 0.6 mol of betulin, 4.4 mol of 1,3-propanediol, and 2 mmol of isobutyl titanate, and react at 220 ° C for 2 h , to obtain low molecular weight polyester prepolymers.

Continue to add 1 mmol of isobutyl titanate, 5 mmol of p-methoxyphenol, 1.2 mmol of triphenyl phosphite, and 100 mg of antioxidant-1010 into the 3L three-necked flask, and react at 170 ° C for 2 h, and then in The reaction was continued at 240° C. for 6 h to obtain a betulin-based bio-based copolyester with a number average molecular weight of 27300 g·mol ⁻¹ .

Characterized by hydrogen nuclear magnetic resonance spectroscopy, the betulin structure in the copolyester obtained in this example accounts for 61 mol% of the molecular mole fraction; the differential scanning calorimeter test proves that the copolyester is a completely amorphous polymer, The glass transition temperature is 91° C.; the tensile property test shows that the copolyester has a breaking strength of 83 MPa and a breaking elongation of 170%.

Example 5

To a 3L three-necked flask equipped with a heating and stirring device, add 1mol of sebacic acid, 0.6mol of betulin, 2.4mol of 1,6-hexanediol, and 2mmol of zinc acetate, and react at 180°C for 6h, A low molecular weight polyester prepolymer is obtained.

Continue to add 1mmol of ethylene glycol antimony, 5mmol of p-tert-butylcatechol, 1.4mmol of dimethyl phosphate, 120mg of antioxidant-1076 to the 3L three-necked flask, and react at 180°C for 2h, and then at 230 The reaction was continued for 2 h at ℃ to obtain a betulin-based bio-based copolyester with a number average molecular weight of 22600 g·mol ^-1 .

Characterized by hydrogen nuclear magnetic resonance spectroscopy, the betulin structure in the copolyester obtained in this example accounts for 60 mol% of the molecular mole fraction; the differential scanning calorimeter test proves that the copolyester is a completely amorphous polymer, The glass transition temperature is 78°C; the tensile properties test shows that the copolyester has a breaking strength of 80 MPa and a breaking elongation of 240%.

Example 6

To a 3L three-necked flask equipped with a heating and stirring device, 1 mol of dimethyl succinate, 0.2 mol of betulin, 2.8 mol of 1,5-pentanediol, 2 mmol of zinc acetate were added, and the mixture was heated at 190°C. The reaction was carried out for 3h to obtain a low molecular weight polyester prepolymer.

Continue to add 2mmol of germanium oxide, 5mmol of hydroquinone, 1.3mmol of dimethyl phosphate, 100mg of antioxidant-1010 to the 3L three-necked flask, and react at 180℃ for 2h, and then continue to react at 240℃ 4h, a bio-based copolyester based on betulin with a number average molecular weight of 25200 g·mol ⁻¹ was obtained.

Characterized by hydrogen nuclear magnetic resonance spectroscopy, the betulin structure in the copolyester obtained in this example accounts for 26 mol% of the molecular mole fraction; the differential scanning calorimeter test proves that the copolyester is a completely amorphous polymer, The glass transition temperature is 54°C; the tensile property test shows that the copolyester has a breaking strength of 70 MPa and a breaking elongation of 370%.

Example 7

To a 3L three-necked flask equipped with a heating and stirring device, add 1 mol of dimethyl succinate, 0.6 mol of betulin, 4.4 mol of 1,4-butanediol, 2 mmol of tetrabutyl titanate, and put The reaction was carried out at 180° C. for 4 h to obtain a low molecular weight polyester prepolymer.

1mmol of tetrabutyl titanate, 5mmol of p-methoxyphenol, 1.5mmol of diphenyl phosphite, 100mg of antioxidant-1010 were added to the 3L three-necked flask, and the reaction was carried out at 180°C for 2h, and then in The reaction was continued at 220° C. for 12 h to obtain a betulin-based bio-based copolyester with a number average molecular weight of 26800 g·mol ⁻¹ .

Characterized by hydrogen nuclear magnetic resonance spectroscopy, the betulin structure in the copolyester obtained in this example accounts for 67 mol% of the molecular mole fraction; the differential scanning calorimeter test proves that the copolyester is a completely amorphous polymer, The glass transition temperature is 124°C; the tensile property test shows that the copolyester has a breaking strength of 88 MPa and a breaking elongation of 100%.

Example 8

To a 3L three-necked flask equipped with a heating and stirring device, add 1mol of dodecanedioic acid, 0.5mol of betulin, 4.5mol of ethylene glycol, and 2mmol of zinc acetate, and react at 180°C for 5h to obtain low Molecular weight polyester prepolymer.

Continue to add 1.5mmol of antimony acetate, 5mmol of p-benzoquinone, 1.2mmol of trimethyl phosphate, 100mg of antioxidant-1076 to the 3L three-necked flask, and react at 170℃ for 2h, and then continue to react at 230℃ For 8 h, a betulin-based bio-based copolyester with a number average molecular weight of 25100 g·mol ⁻¹ was obtained.

Characterized by hydrogen nuclear magnetic resonance spectroscopy, the betulin structure in the copolyester obtained in this example accounts for 55 mol% of the molecular mole fraction; the differential scanning calorimeter test proves that the copolyester is a completely amorphous polymer, The glass transition temperature is 70°C; the tensile property test shows that the breaking strength of the copolyester is 75MPa, and the breaking elongation is 280%.

Comparative Example 1

To a 3L three-necked flask equipped with a heating and stirring device, add 1 mol of dimethyl adipate, 0.4 mol of betulin, 3.6 mol of 1,4-butanediol, and 2 mmol of dibutyltin oxide, and put The reaction was carried out at 180° C. for 4 h to obtain a low molecular weight polyester prepolymer.

Continue to add 1mmol of dibutyltin oxide, 1.2mmol of trimethyl phosphate, 100mg of antioxidant-1010 to the 3L three-necked flask, and continue to react at 180°C for 24h to obtain a biobased copolymer based on betulin alcohol ester. However, due to the low reaction temperature in the whole reaction process, the secondary alcohol in betulin has low reactivity at lower temperature, and only low molecular weight oligomers with number average molecular weight below 10000 g·mol ^-1 can be obtained.

Comparative Example 2

To a 3L three-necked flask equipped with a heating and stirring device, add 1 mol of dimethyl adipate, 0.2 mol of betulin, 2.8 mol of ethylene glycol, and 1 mmol of zinc acetate, and react at 190 ° C for 6 h to obtain Low molecular weight polyester prepolymer.

1.5mmol of antimony trioxide, 1.3mmol of diphenyl phosphate and 150mg of antioxidant-168 were added to the 3L three-necked flask, and the reaction was continued at 220°C. After the polycondensation reaction was carried out for 2h, the reaction temperature was high , and no radical inhibitor was added, the product was cross-linked and the reaction failed.

The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity, all possible combinations of the technical features in the above-described embodiments are not described. However, as long as there is no contradiction between the combinations of these technical features, All should be regarded as the scope described in this specification.

The above-mentioned embodiments only represent several embodiments of the present invention, and the descriptions thereof are specific and detailed, but should not be construed as a limitation on the scope of the invention patent. It should be pointed out that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can also be made, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention should be subject to the appended claims.

Claims (10)

1. A betulin-based bio-based copolyester, characterized in that the structural formula of the copolyester is shown as formula (1):

in the formula (1), x and y are integers of 1-20, n is an integer of 20-100, R ₁ A fatty chain unit of an aliphatic dicarboxylic acid or an esterified product thereof, R ₂ Represents an aliphatic chain unit of an aliphatic diol.

2. The betulin-based biobased copolyester according to claim 1, wherein the aliphatic dicarboxylic acid or an esterified product thereof has 4 to 12 carbon atoms;

and/or the aliphatic diol has 2-6 carbon atoms.

3. The betulin-based biobased copolyester according to claim 2, wherein the aliphatic dicarboxylic acid or an esterified product thereof is at least one selected from succinic acid or an esterified product thereof, glutaric acid or an esterified product thereof, adipic acid or an esterified product thereof, suberic acid or an esterified product thereof, sebacic acid or an esterified product thereof, and dodecanedioic acid or an esterified product thereof;

and/or the aliphatic diol is at least one selected from ethylene glycol, 1, 3-propylene glycol, 1, 4-butanediol, 1, 5-pentanediol and 1, 6-hexanediol.

4. A process for the preparation of betulin-based biobased copolyesters according to any one of claims 1 to 3, characterized by the following steps:

mixing and reacting aliphatic dicarboxylic acid or an esterified product thereof, betulin, aliphatic diol and an esterification or ester exchange catalyst to obtain a polyester prepolymer based on the betulin;

adding a polycondensation catalyst, a free radical polymerization inhibitor, a stabilizer and an antioxidant into the polyester prepolymer, reacting for 1h-3h at a first temperature under a vacuum condition, and then continuing to react for 2h-22h at a second temperature to obtain a birch fat alcohol-based bio-based copolyester; wherein the first temperature is 160-180 ℃, the second temperature is 180-240 ℃, and the second temperature is greater than the first temperature.

5. The method for preparing bio-based copolyester based on betulin according to claim 4, wherein the molar ratio of the sum of the amounts of betulin and aliphatic diol to the aliphatic dicarboxylic acid or its esterified product is 3:1-5: 1.

6. The preparation method of betulin-based bio-based copolyester of claim 5, wherein the molar ratio of the aliphatic dicarboxylic acid or the esterified product thereof to the betulin is 5:1-5: 3.

7. The method for preparing bio-based copolyester based on betulin according to claim 4, wherein the esterification or transesterification catalyst is at least one selected from zinc acetate, isobutyl titanate, tetrabutyl titanate, ethylene glycol antimony and dibutyl tin oxide, and is used in an amount of 0.1-0.2% by mole of the aliphatic dicarboxylic acid or its esterified substance.

8. The method for preparing bio-based copolyester based on betulin according to claim 4, wherein the aliphatic dicarboxylic acid or its esterified product, betulin, aliphatic diol, and esterification or transesterification catalyst are mixed and reacted at 160-220 deg.C for 2-6 h.

9. The preparation method of betulin-based bio-based copolyester as claimed in claim 4, wherein the free radical polymerization inhibitor is at least one selected from hydroquinone, p-methoxyphenol, p-tert-butylcatechol, and p-benzoquinone, and is used in an amount of 0.4-0.6% by mole of the aliphatic dicarboxylic acid or its ester.

10. The method for preparing bio-based copolyester based on betulin according to claim 4, wherein the polycondensation catalyst is at least one selected from antimony trioxide, isobutyl titanate, tetrabutyl titanate, germanium oxide, antimony glycol, antimony acetate and dibutyltin oxide, and the amount of the polycondensation catalyst is 0.1-0.2% of the mole number of the aliphatic dicarboxylic acid or the esterified substance thereof;

and/or the stabilizer is selected from phosphorus stabilizers, and the using amount of the stabilizer is 0.12 to 0.15 percent of the mole number of the aliphatic dicarboxylic acid or the ester thereof.

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