A bio-based polyester containing acetal structure and preparation method thereof

Abstract

The invention discloses a bio-based polyester containing an acetal structure and a preparation method thereof. The bio-based polyester is prepared by using 5-hydroxymethylfurfural and trimethylolpropane as raw materials, synthesizing 5-ethyl-2-(5-hydroxymethyl-2-furan)-1,3-dioxane-5-methanol through an acetalization reaction, and then bulk polymerization is carried out with a dibasic acid using dibutyltin oxide as a catalyst under nitrogen protection to obtain the bio-based polyester. The preparation method disclosed in the present invention has low-cost and widely available synthetic raw materials, is environmentally friendly, simple to operate, and is conducive to industrial production. It provides an economical and green alternative process path for the existing process method for preparing polyester using non-renewable resources. The prepared bio-based polyester has a high glass transition temperature, excellent thermal stability and ultraviolet shielding performance, and is an ideal alternative product for non-renewable polyester materials.

Description

Technical Field

[0001] The present invention relates to the field of polymer materials, and in particular to a bio-based polyester containing an acetal structure and a preparation method thereof. Background Art

[0002] Polyesters are macromolecular polymers formed by the reaction of polyols and polyacids. Due to their strong impact resistance, excellent dimensional stability, heat resistance, and oxygen barrier properties, they are widely used in aerospace, machinery manufacturing, various packaging materials, agricultural films, biomedicine, and other daily life fields. However, most polyester materials are derived from non-renewable petrochemical resources such as petroleum. Large-scale production of these materials leads to the accumulation of waste plastics, resource depletion, and environmental damage. To address these issues, the demand for polyesters derived from sustainable resources is increasingly urgent. Therefore, synthesizing biomass monomers from sustainable resources and preparing related bio-based polyester materials are particularly important for reducing dependence on non-renewable resources at the source. Researchers are committed to the development of bio-based polyester materials, but the number of available varieties is limited, the glass transition temperature of polyesters is low, and their thermal stability and UV shielding properties need to be further improved. For example, polylactic acid (PLA), a bio-based polyester, has a glass transition temperature of only 55°C, making it unusable at high temperatures and unable to shield UV rays above 300nm.

[0003] 5-Hydroxymethylfurfural (HMF) is a bio-based raw material obtained by hydrolyzing sugars such as glucose or fructose in biomass under the action of an acid catalyst. The aldehyde and hydroxyl groups in its structure give it good reactivity and can be converted into various high-value-added compounds through chemical reactions.

[0004] Currently, the catalytic conversion of 5-hydroxymethylfurfural can be used to synthesize a variety of bio-based monomers and further produce bio-based polyesters. However, the resulting polyesters typically suffer from low molecular weight and easy cross-linking, resulting in low glass transition temperatures and poor thermal stability. Effectively utilizing 5-hydroxymethylfurfural to produce high-performance polyester materials, while overcoming these shortcomings, such as low glass transition temperatures, poor thermal stability, and poor UV shielding, has become an urgent challenge. The development of high-performance polyester materials based on 5-hydroxymethylfurfural could provide an economical and green alternative to existing polyester production methods that utilize non-renewable resources. Summary of the Invention

[0005] In view of this, the present invention provides a bio-based polyester containing an acetal structure to solve the problems of low glass transition temperature, poor thermal stability and UV shielding performance of the various bio-based monomers currently synthesized based on 5-hydroxymethylfurfural and further obtaining bio-based polyesters.

[0006] In addition, the present invention also provides a method for preparing the bio-based polyester, which provides an economical and green alternative process path for the existing process of preparing polyester using non-renewable resources.

[0007] In the first aspect, the bio-based polyester containing an acetal structure has the following general structural formula:

[0008]

[0009] Wherein: n is a natural number, ranging from 42 to 107; R1 is the part of the dibasic acid other than the carboxyl group.

[0010] In the present disclosure and possible embodiments, the dibasic acid is selected from at least one of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, terephthalic acid, dimethyl terephthalate, phthalic acid, dimethyl phthalate, 2,5-furandicarboxylic acid, dimethyl 2,5-furandicarboxylate, N,N'-trans-1,4-cyclohexane-bis(pyrrolidone-4-carboxylic acid) and N,N'-trans-1,4-cyclohexane-bis(pyrrolidone-4-carboxylic acid methyl ester).

[0011] In the present disclosure and possible embodiments, the value range of n is 60-95.

[0012] In the present disclosure and possible embodiments, the value range of n is 80-90.

[0013] In a second aspect, the method for preparing the bio-based polyester containing an acetal structure according to the first aspect comprises:

[0014] It is prepared by bulk polymerization of 5-ethyl-2-(5-hydroxymethyl-2-furan)-1,3-dioxane-5-methanol and dibasic acid.

[0015] In the present disclosure and possible embodiments, the bulk polymerization method includes:

[0016] The 5-ethyl-2-(5-hydroxymethyl-2-furan)-1,3-dioxane-5-methanol, the dibasic acid and the catalyst are sequentially subjected to esterification reaction, pre-polycondensation and polycondensation reaction under closed reaction conditions to complete the bulk polymerization.

[0017] In the present disclosure and possible embodiments, the molar ratio of the 5-ethyl-2-(5-hydroxymethyl-2-furan)-1,3-dioxane-5-methanol to the dibasic acid is 1-2:1; and / or,

[0018] The catalyst is dibutyltin oxide.

[0019] In the present disclosure and possible embodiments, the amount of the catalyst added is 0.05% to 0.4% of the molar amount of 5-ethyl-2-(5-hydroxymethyl-2-furan)-1,3-dioxane-5-methanol; and / or,

[0020] The esterification reaction temperature is 160-190° C. and the reaction time is 8-12 hours; and / or,

[0021] The vacuum degree of the pre-polycondensation reaction is 5kPa-16kPa, the reaction temperature is 170-200°C, and the reaction time is not less than 0.5h; and / or,

[0022] The polycondensation reaction is carried out under a vacuum degree of less than or equal to 60 Pa, the polycondensation reaction temperature is 170-220° C., and the polycondensation reaction time is 2-5 hours; and / or,

[0023] The esterification reaction is carried out under the protection of nitrogen.

[0024] In the present disclosure and possible embodiments, the method for preparing 5-ethyl-2-(5-hydroxymethyl-2-furan)-1,3-dioxane-5-methanol comprises:

[0025] 5-Hydroxymethylfurfural and trimethylolpropane are dissolved in a solvent, and under acidic conditions and stirring, the 5-Hydroxymethylfurfural and the trimethylolpropane undergo an acetalization reaction, and the reaction product is post-treated to obtain the 5-ethyl-2-(5-hydroxymethyl-2-furan)-1,3-dioxane-5-methanol.

[0026] In the present disclosure and possible embodiments, the molar ratio of the 5-hydroxymethylfurfural to the trimethylolpropane is 1:1.05-1.50; and / or,

[0027] The solvent is isopropyl alcohol; and / or,

[0028] The acetalization reaction temperature is 20-35° C., and the reaction time is 12-24 hours; and / or,

[0029] generating the acidic conditions by p-toluenesulfonic acid; and / or,

[0030] The post-processing method comprises:

[0031] After the acetalization reaction is completed, the solvent in the reaction product is removed by evaporation.

[0032] The present invention has the following beneficial effects:

[0033] The disclosed bio-based polyester containing an acetal structure is a bio-based monomer synthesized from 5-hydroxymethylfurfural. 5-Hydroxymethylfurfural is a green, renewable resource with a wide range of sources. Monomers synthesized from this raw material and related polyesters can reduce dependence on petrochemical resources. In addition, the polyester material of the present invention has a relatively high glass transition temperature, excellent thermal stability and ultraviolet shielding properties, and can be used as a green alternative to traditional polyesters. The polyester has good ultraviolet filtering ability in the range of 200 to 600 nm, which makes the polyester prepared based on the bio-based monomer have the potential to be used in fields requiring ultraviolet shielding. At the same time, the bio-based polyester preparation method of the present invention has a simple synthesis process, is easy to operate, is green and environmentally friendly, has a high synthesis yield, and has the possibility of large-scale production, thereby providing an economical and green alternative process path to the existing process method for preparing polyester using non-renewable resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The above and other objects, features and advantages of the present disclosure will become more apparent through the following description of the embodiments of the present disclosure with reference to the accompanying drawings, in which:

[0035] Figure 1 This is the hydrogen nuclear magnetic resonance spectrum of the bio-based polyester in Example 1;

[0036] Figure 2 This is the carbon NMR spectrum of the bio-based polyester of Example 2;

[0037] Figure 3 This is the DSC melting curve of the bio-based polyester of Example 3;

[0038] Figure 4 This is the TGA curve of the bio-based polyester of Example 3;

[0039] Figure 5 This is the UV transmittance curve of the bio-based polyester of Example 4;

[0040] Figure 6 This is the DSC melting curve of the bio-based polyester in Example 5. DETAILED DESCRIPTION

[0041] The present disclosure is described below based on embodiments, but it is worth noting that the present disclosure is not limited to these embodiments. In the detailed description of the present disclosure below, some specific details are described in detail. However, for the parts not described in detail, those skilled in the art can also fully understand the present disclosure.

[0042] In the embodiments of the present disclosure, unless otherwise specified, all raw materials are basically purchased from commercial sources or prepared by conventional methods in the art.

[0043] In the embodiments of the present disclosure, nuclear magnetic resonance spectroscopy 1H-NMR was measured at room temperature using a Bruker AscendTM instrument, 400 MHz, DMSO-d6; thermogravimetric analysis was performed using a CDR-34P comprehensive thermal analyzer from Shanghai Instrument and Electronics Corporation in a nitrogen atmosphere at a heating rate of 10°C / min within the temperature range of 30-600°C; thermal transition analysis was performed using a TA Q2000 differential scanning calorimeter at a heating rate of 10°C / min within a nitrogen atmosphere within the temperature range of 0-200°C; and ultraviolet transmittance was measured using a UV-8000 ultraviolet-visible spectrophotometer from Shanghai Yuanxi Instrument Co., Ltd. over a full wavelength scan range of 200-800 nm.

[0044] In each embodiment of the present disclosure, 5-ethyl-2-(5-hydroxymethyl-2-furan)-1,3-dioxane-5-methanol is used, and its structural formula is:

[0045]

[0046] In each embodiment of the present disclosure, the method for preparing 5-ethyl-2-(5-hydroxymethyl-2-furan)-1,3-dioxane-5-methanol is as follows: based on 5-hydroxymethylfurfural, 5-hydroxymethylfurfural and trimethylolpropane are reacted through acetalization to obtain 5-hydroxymethylfurfural; in each embodiment, the molar ratio of 5-hydroxymethylfurfural to trimethylolpropane is 1:1.05-1.50; the specific steps of the preparation method are:

[0047] 5-Hydroxymethylfurfural and trimethylolpropane are dissolved in a solvent, and an acetalization reaction is carried out between 5-Hydroxymethylfurfural and trimethylolpropane under acidic and stirring conditions. The reaction product is post-treated to obtain the 5-ethyl-2-(5-hydroxymethyl-2-furan)-1,3-dioxane-5-methanol.

[0048] In each embodiment of the present disclosure, the solvent is isopropanol; the acidic condition is provided by p-toluenesulfonic acid; the reaction temperature is 20-35°C, and the reaction time is 12-24 hours; and the post-treatment is to evaporate the excess solvent in the reaction product after the reaction is completed to obtain a bio-based monomer containing an acetal structure.

[0049] Example 1

[0050] 5-ethyl-2-(5-hydroxymethyl-2-furan)-1,3-dioxane-5-methanol is prepared from 5-hydroxymethylfurfural and trimethylolpropane. The specific process is as follows:

[0051] 10.09 g of 5-hydroxymethylfurfural (0.080 mol), 12.88 g of trimethylolpropane (0.096 mol), and 0.34 g of p-toluenesulfonic acid (0.18 mmol) were weighed and dissolved in 50 mL of isopropanol solution. The mixture was then stirred at 25° C. for 15 h to allow the mixture to undergo an acetalization reaction. After the reaction was completed, the reaction product was evaporated until all the isopropanol solvent was evaporated to obtain the 5-ethyl-2-(5-hydroxymethyl-2-furan)-1,3-dioxane-5-methanol monomer of Example 1 as a yellow powder.

[0052] In Example 1 of the present disclosure, the chemical structure of the monomer 5-ethyl-2-(5-hydroxymethyl-2-furan)-1,3-dioxane-5-methanol was determined by nuclear magnetic resonance.

[0053] Figure 1 It is a product of 5-ethyl-2-(5-hydroxymethyl-2-furan)-1,3-dioxane-5-methanol prepared from 5-hydroxymethylfurfural and trimethylolpropane. 1 H-NMR. As can be seen from the figure, the peaks at δ6.23ppm(d) and δ6.32ppm(c) are attributed to the -C=CH- proton peak on the furan ring structure, the peak at δ5.45ppm(e) corresponds to the -CH- proton peak on the acetal structure, the peaks at δ5.23ppm(a) and δ4.63ppm(i) correspond to the -OH structural proton peaks, the peaks at δ3.89ppm(f) and δ3.56ppm(g) correspond to the -CH2- structural proton peaks on the acetal ring unit, δ3.63ppm(h) and δ4.35ppm(b) correspond to the -CH2- proton peaks connected to the two hydroxyl groups, respectively, and δ0.77ppm(k) and δ1.14ppm(j) are the -C2H5 proton peaks connected to the acetal ring.

[0054] Through the above 1 H-NMR analysis proved that the synthesis of 5-ethyl-2-(5-hydroxymethyl-2-furan)-1,3-dioxane-5-methanol was successful.

[0055] Example 2

[0056] Bio-based polyester is prepared from 5-ethyl-2-(5-hydroxymethyl-2-furan)-1,3-dioxane-5-methanol and succinic acid. The specific process is as follows:

[0057] 1) Weigh 5.73 g of 5-ethyl-2-(5-hydroxymethyl-2-furan)-1,3-dioxane-5-methanol and 2.81 g of succinic acid in a 1:1 alcohol-acid molar ratio and place them in an airtight round-bottom flask. Add 0.048 g of dibutyltin oxide as a catalyst and, under a nitrogen atmosphere, allow esterification of 5-ethyl-2-(5-hydroxymethyl-2-furan)-1,3-dioxane-5-methanol with succinic acid at 160°C for 9 h.

[0058] 2) After the esterification reaction is completed, the temperature of the reaction system is adjusted to 180° C., the nitrogen protection is removed, and the reaction system is pre-polycondensed for 0.5 h under a vacuum condition of 16 kPa;

[0059] 3) After the pre-polycondensation is completed, the reaction system is subjected to polycondensation for 2 hours under a high vacuum degree of 60 Pa to obtain the bio-based polyester of Example 2.

[0060] Figure 2 The bio-based polyester of Example 2 was prepared from 5-ethyl-2-(5-hydroxymethyl-2-furan)-1,3-dioxane-5-methanol and succinic acid. 1 H-NMR, such as Figure 2 It can be seen that the peak at δ2.64ppm(j) is attributed to the two -CH2- proton peaks of succinic acid. Figure 1 The nuclear magnetic resonance analysis of the 5-ethyl-2-(5-hydroxymethyl-2-furan)-1,3-dioxane-5-methanol monomer and the disappearance of the two -OH proton peak signals at δ4.63ppm and δ5.23ppm prove that the synthesis of the bio-based polyester in this Example 2 is successful.

[0061] Example 3

[0062] 1. Preparation of bio-based polyester:

[0063] Bio-based polyester is prepared from 5-ethyl-2-(5-hydroxymethyl-2-furan)-1,3-dioxane-5-methanol and dimethyl terephthalate. The specific process is as follows:

[0064] 1) Weigh 5.78 g of 5-ethyl-2-(5-hydroxymethyl-2-furan)-1,3-dioxane-5-methanol and 4.66 g of dimethyl terephthalate in a 1:1 molar ratio of alcohol to acid, place the mixture in an airtight round-bottom flask, add 0.058 g of dibutyltin oxide, and under a nitrogen atmosphere, set the reaction temperature to 180° C. At this temperature, 5-ethyl-2-(5-hydroxymethyl-2-furan)-1,3-dioxane-5-methanol and dimethyl terephthalate are subjected to an esterification reaction for 9 hours;

[0065] 2) After the esterification reaction is completed, the reaction temperature is adjusted to 200° C., the nitrogen protection is removed, and the reaction system is pre-polycondensed for 0.5 h under a vacuum degree of 16 kPa;

[0066] 3) After the pre-polycondensation is completed, the reaction system is subjected to polycondensation for 2 hours under a high vacuum degree of 60 Pa to obtain the bio-based polyester of Example 3.

[0067] 2. Performance testing:

[0068] 1)DSC test:

[0069] ① Take 5-10 mg of the bio-based polyester prepared in Example 3 and place it in a differential scanning calorimeter to measure the melting curve;

[0070] ② Set the "heating-isothermal-cooling-isothermal-heating" program with a temperature test range of 0 to 200°C and a heating and cooling rate of 10°C / min to obtain the melting curve.

[0071] Figure 3 This is the DSC test melting curve of the bio-based polyester of Example 3. It can be observed from the figure that the glass transition temperature of the polyester is 120°C, which is higher than the glass transition temperature of polylactic acid 55°C.

[0072] 2) TGA test:

[0073] ① Weigh 5-10 mg of the bio-based polyester prepared in Example 3 and place it in a comprehensive thermal analyzer to measure the TGA curve;

[0074] ② Set the test program with a test temperature range of 30-600°C and a heating and cooling rate of 10°C / min, and obtain TGA data under a nitrogen atmosphere.

[0075] Figure 4 This is the TGA curve of the bio-based polyester of Example 3. It can be seen from the figure that the T d,5％ =287℃.

[0076] Example 4

[0077] 1. Preparation of bio-based polyester:

[0078] Bio-based polyester is prepared from 5-ethyl-2-(5-hydroxymethyl-2-furan)-1,3-dioxane-5-methanol and dimethyl 2,5-furandicarboxylate. The specific process is as follows:

[0079] 1) 6.03 g of 5-ethyl-2-(5-hydroxymethyl-2-furan)-1,3-dioxane-5-methanol and 4.60 g of dimethyl 2,5-furandicarboxylate were weighed in a 1:1 alcohol-acid molar ratio and placed in an airtight round-bottom flask. 0.059 g of dibutyltin oxide catalyst was added. Under a nitrogen atmosphere, the reaction temperature was set to 170° C. At this temperature, 5-ethyl-2-(5-hydroxymethyl-2-furan)-1,3-dioxane-5-methanol and dimethyl 2,5-furandicarboxylate were subjected to an esterification reaction for 9.5 hours;

[0080] 2) After the esterification reaction is completed, the reaction temperature is adjusted to 180° C., the nitrogen protection is removed, and the reaction system is pre-polycondensed for 0.5 h under a vacuum degree of 16 kPa;

[0081] 3) After the pre-polycondensation is completed, the reaction system is subjected to polycondensation for 2 hours under a high vacuum degree of 60 Pa to obtain the bio-based polyester of Example 4.

[0082] 2. Performance testing:

[0083] Specifically, the ultraviolet transmittance of the bio-based polyester of Example 4 was tested:

[0084] 1) Taking an appropriate amount of the bio-based polyester prepared in Example 4, melting it at 110° C. to prepare a film required for testing;

[0085] 2) Set the wavelength scanning range to 200-800 nm and perform the UV transmittance test at room temperature.

[0086] Figure 5 This is the UV transmittance curve of the bio-based polyester of Example 4. As can be seen from the figure, the bio-based polyester has good UV shielding performance in the wavelength range of 200 to 600 nm, which is better than the UV shielding ability of polylactic acid.

[0087] Example 5

[0088] 1. Preparation of bio-based polyester:

[0089] Bio-based polyester was prepared from 5-ethyl-2-(5-hydroxymethyl-2-furyl)-1,3-dioxane-5-methanol and N,N'-trans-1,4-cyclohexane-bis(pyrrolidone-4-carboxylic acid methyl ester) by the following process:

[0090] 1) 4.34 g of 5-ethyl-2-(5-hydroxymethyl-2-furan)-1,3-dioxane-5-methanol and 6.60 g of N,N'-trans-1,4-cyclohexane-bis(pyrrolidone-4-carboxylic acid methyl ester) were weighed in a 1:1 alcohol-acid molar ratio and placed in an airtight round-bottom flask. 0.061 g of dibutyltin oxide catalyst was added. Under a nitrogen atmosphere, the reaction temperature was set to 180°C. At this temperature, 5-ethyl-2-(5-hydroxymethyl-2-furan)-1,3-dioxane-5-methanol and N,N'-trans-1,4-cyclohexane-bis(pyrrolidone-4-carboxylic acid methyl ester were subjected to an esterification reaction for 9.2 hours.

[0091] 2) After the esterification reaction is completed, the reaction temperature is adjusted to 200° C., the nitrogen protection is removed, and the reaction system is pre-polycondensed for 0.5 h under a vacuum degree of 16 kPa;

[0092] 3) After the pre-polycondensation is completed, the reaction system is subjected to polycondensation for 2 hours under a high vacuum degree of 60 Pa to obtain the bio-based polyester of Example 5.

[0093] 2. Performance testing:

[0094] Specifically, the bio-based polyester of Example 5 was subjected to DSC test:

[0095] 1) 5-10 mg of the bio-based polyester prepared in Example 5 was placed in a differential scanning calorimeter to measure the melting curve;

[0096] 2) Set the "heating-isothermal-cooling-isothermal-heating" program with a temperature test range of 0 to 200°C and a heating and cooling rate of 10°C / min to obtain a melting curve.

[0097] Figure 6 This is the DSC test melting curve of the bio-based polyester of Example 5. It can be observed from the figure that the glass transition temperature of the polyester is 126°C, which is higher than the glass transition temperature of polylactic acid by 55°C.

[0098] The above-described embodiments are merely examples of implementation methods of the present disclosure, and their descriptions are relatively specific and detailed. However, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art may make various modifications, equivalent substitutions, and improvements without departing from the scope of the present disclosure, and these modifications are all within the scope of protection of the present disclosure. Therefore, the scope of protection of the present invention shall be based on the appended claims.

Claims

1. A bio-based polyester containing an acetal structure, characterized in that: Its general structural formula is as follows: Wherein: n is a natural number, ranging from 42 to 107; R1 is the part of the dibasic acid other than the carboxyl group.

2. The bio-based polyester containing acetal structure according to claim 1, characterized in that: The dibasic acid is selected from at least one of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, terephthalic acid, dimethyl terephthalate, phthalic acid, dimethyl phthalate, 2,5-furandicarboxylic acid, dimethyl 2,5-furandicarboxylate, N,N'-trans-1,4-cyclohexane-bis(pyrrolidone-4-carboxylic acid) and N,N'-trans-1,4-cyclohexane-bis(pyrrolidone-4-carboxylic acid methyl ester).

3. The bio-based polyester containing acetal structure according to claim 1 or 2, characterized in that: The value range of n is 60-95.

4. The bio-based polyester containing acetal structure according to claim 3, characterized in that: The value range of n is 80-90.

5. The method for preparing the bio-based polyester containing acetal structure according to any one of claims 1 to 4, characterized in that: include: It is prepared by bulk polymerization of 5-ethyl-2-(5-hydroxymethyl-2-furan)-1,3-dioxane-5-methanol and dibasic acid.

6. The method for preparing a bio-based polyester containing an acetal structure according to claim 5, characterized in that: The bulk polymerization method comprises: The 5-ethyl-2-(5-hydroxymethyl-2-furan)-1,3-dioxane-5-methanol, the dibasic acid and the catalyst are sequentially subjected to esterification reaction, pre-polycondensation and polycondensation reaction under closed reaction conditions to complete the bulk polymerization.

7. The method for preparing a bio-based polyester containing an acetal structure according to claim 6, wherein: The molar ratio of the 5-ethyl-2-(5-hydroxymethyl-2-furan)-1,3-dioxane-5-methanol to the dibasic acid is 1-2:1; and / or, The catalyst is dibutyltin oxide.

8. The method for preparing a bio-based polyester containing an acetal structure according to claim 7, characterized in that: The amount of the catalyst added is 0.05% to 0.4% of the molar amount of 5-ethyl-2-(5-hydroxymethyl-2-furan)-1,3-dioxane-5-methanol; and / or, The esterification reaction temperature is 160-190° C. and the reaction time is 8-12 hours; and / or, The vacuum degree of the pre-polycondensation reaction is 5kPa-16kPa, the reaction temperature is 170-200°C, and the reaction time is not less than 0.5h; and / or, The polycondensation reaction is carried out under a vacuum degree of less than or equal to 60 Pa, the polycondensation reaction temperature is 170-220° C., and the polycondensation reaction time is 2-5 hours; and / or, The esterification reaction is carried out under the protection of nitrogen.

9. The method for preparing a bio-based polyester containing an acetal structure according to claim 8, characterized in that: The preparation method of 5-ethyl-2-(5-hydroxymethyl-2-furan)-1,3-dioxane-5-methanol comprises: 5-Hydroxymethylfurfural and trimethylolpropane are dissolved in a solvent, and under acidic conditions and stirring, the 5-Hydroxymethylfurfural and the trimethylolpropane undergo an acetalization reaction, and the reaction product is post-treated to obtain the 5-ethyl-2-(5-hydroxymethyl-2-furan)-1,3-dioxane-5-methanol.

10. The method for preparing a bio-based polyester containing an acetal structure according to claim 9, characterized in that: The molar ratio of the 5-hydroxymethylfurfural to the trimethylolpropane is 1:1.05-1.50; and / or, The solvent is isopropyl alcohol; and / or, The acetalization reaction temperature is 20-35° C., and the reaction time is 12-24 hours; and / or, generating said acidic conditions by p-toluenesulfonic acid; and / or, The post-processing method comprises: After the acetalization reaction is completed, the solvent in the reaction product is removed by evaporation.

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