Synthesis and purification method of glycolide

Abstract

The invention belongs to the technical field of synthetic chemistry, and particularly relates to a synthesis and purification method of glycolide. The invention provides a synthesis and purification method of glycolide. The synthesis and purification method comprises the steps of polymerization reaction, crude product evaporation, primary purification and secondary purification. According to the technical scheme provided by the invention, the method for preparing glycolide by taking methyl glycolate as a raw material is provided, the raw material does not contain carboxyl, and the content of an acid value in a product can be correspondingly reduced; meanwhile, during ring-opening polymerization, the molecular weight of the synthesized glycolide is not influenced by polymerization inhibition generated by reactive hydrogen on carboxyl; furthermore, according to the technical scheme provided by the invention, the yield of the glycolide can reach 84% or above through experimental determination, and the purity and the acid value of the obtained glycolide can meet the use requirements. The synthesis and purification method of glycolide provided by the invention solves the technical defect of low glycolide purification yield in the prior art.

Description

Technical Field

[0001] The present application belongs to the technical field of synthetic chemistry, and in particular relates to a method for synthesizing and purifying glycolide. Background Art

[0002] Glycolide is a cyclic ester generated by the demethanolization of two molecules of methyl glycolate, and is also an intermediate for the synthesis of polyglycolic acid. The synthesis of polyglycolic acid by glycolide ring-opening polymerization is currently the most mature industrial method. The molecular weight of the polyglycolic acid obtained by this method is controllable, that is, high molecular weight polyglycolic acid can be obtained relatively easily. High molecular weight polyglycolic acid has excellent properties, such as biodegradability, gas barrier properties, mechanical properties and heat resistance, etc., and plays a very important role in high-end application fields such as medicine. The difficulty in synthesizing high molecular weight polyglycolic acid by glycolide ring-opening polymerization is whether the purity of glycolide can meet the polymerization requirements. The purification of glycolide is an indispensable step to obtain high molecular weight polyglycolic acid.

[0003] In the prior art, the purification of glycolide is mostly aimed at reducing the acid value content in the glycolide system. For example, according to the contents disclosed in Chinese patent CN 107868075 A and Chinese patent CN 116082291 A, recrystallization and multiple washing operations are required during the purification process, which affects the glycolide yield to a certain extent.

[0004] Therefore, developing a method for synthesizing and purifying glycolide to solve the technical defect of low glycolide purification yield in the prior art has become an urgent problem to be solved by those skilled in the art. Summary of the invention

[0005] Based on this, it is necessary to provide a method for synthesizing and purifying glycolide in view of the technical defect of low glycolide purification yield in the existing technology.

[0006] The present application provides a method for synthesizing and purifying glycolide, and the method for synthesizing and purifying glycolide is as follows:

[0007] Step 1, polymerization reaction: methyl glycolate is mixed with a catalyst, and a polymerization reaction is carried out after stepwise heating, and the polymerization reaction is followed by post-treatment to obtain methyl glycolate oligomers;

[0008] Step 2, distilling off the crude product: the methyl glycolate oligomer is depolymerized under heating conditions, and the distilled glycolide is received in a container filled with a solvent to obtain a glycolide solution;

[0009] Step 3, first purification: distilling the glycolide solution distilled out in step 2 to obtain first purified solid-phase glycolide;

[0010] Step 4, second purification: the solid-phase glycolide obtained in the first purification in step 3 is mixed with a good solvent, heated and stirred, and then cooled, and the filter cake is collected by suction filtration and vacuum dried to obtain purified glycolide;

[0011] In step 1, the catalyst is: stannous chloride and / or stannous octoate.

[0012] In one embodiment, in step 2, the solvent is selected from any one or more of n-propanol, isopropanol, n-butanol, isobutanol, tert-butanol and n-pentanol;

[0013] and / or,

[0014] Calculated by mass, the feed ratio of the solvent to the methyl glycolate oligomer is (0.5-1):1.

[0015] In one embodiment, in step 4, the good solvent is selected from any one or more of ethyl acetate, tetrahydrofuran and dichloromethane.

[0016] In one embodiment, in step 1, the stepwise heating method is: heating to 120-160°C at a rate of 5-20°C / min, maintaining for 15-150min, and then continuing to heat to 170-200°C at a rate of 1-5°C / min;

[0017] and / or,

[0018] In step 1, the polymerization reaction time is 2 to 8 hours.

[0019] In one embodiment, in step 1, the stepwise heating method is: heating to 130-150°C at a rate of 8-15°C / min, maintaining for 30-90min, and then heating to 180-190°C at a rate of 3-5°C / min;

[0020] and / or,

[0021] In step 1, the polymerization reaction time is 3 to 6 hours.

[0022] In one embodiment, in step 2, the depolymerization temperature is 230-260° C., the depolymerization heating time is 1-4 h, and the evaporation operation is performed under vacuum conditions.

[0023] In one embodiment, in step 2, the depolymerization temperature is 240-250° C., and the heating time for depolymerization is 2-4 h.

[0024] In one embodiment, in step 1, the amount of the catalyst added is 0.01 wt% to 1 wt% by mass.

[0025] In one of the embodiments, in step 1, the amount of the catalyst added is 0.05 wt% to 0.5 wt% by weight.

[0026] In one embodiment, in step 3, the distillation is carried out in an inert gas protective atmosphere, the distillation temperature is 80-100° C., and the distillation time is 0.5-5 h;

[0027] In step three, the inert gas is selected from any one or more of nitrogen, argon and helium.

[0028] In one embodiment, in step 3, the distillation is carried out in an inert gas protective atmosphere, the distillation temperature is 85-95° C., and the distillation time is 1-4 h;

[0029] In step three, the inert gas is selected from any one or more of nitrogen, argon and helium.

[0030] In one embodiment, in step 4, the heating and stirring temperature is 50-70° C., the heating and stirring time is 1-3 hours, and the heating and stirring is carried out in an inert gas protective atmosphere.

[0031] In one embodiment, in step 4, the heating and stirring temperature is 60-70° C., the heating and stirring time is 2-3 hours, and the heating and stirring is carried out in an inert gas protective atmosphere.

[0032] In one embodiment, in step 4, the cooling time is 6 to 10 hours, the cooling temperature is room temperature, and the vacuum drying time is 8 to 12 hours.

[0033] In one embodiment, in step 4, the inert gas is selected from any one or more of nitrogen, argon and helium.

[0034] In summary, the present application provides a method for synthesizing and purifying glycolide, which includes: polymerization reaction, crude product distillation, first purification and second purification. In the gold technical solution provided by the present application, a method for preparing glycolide using methyl glycolate as raw material is provided, the raw material does not contain carboxyl groups, and the acid value content in the product can be reduced accordingly; at the same time, during the ring-opening polymerization, the active hydrogen on the carboxyl group will not produce inhibition to affect the molecular weight of the synthesized glycolide; further, according to experimental measurements, the technical solution provided by the present application, the glycolide yield can reach more than 84%, and the purity and acid value of the obtained glycolide can meet the use requirements. The present application provides a method for synthesizing and purifying glycolide, which solves the technical defect of low glycolide purification yield in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0036] Figure 1 In the technical solution provided in the embodiment of the present application, a schematic flow chart of a method for synthesizing and purifying glycolide. DETAILED DESCRIPTION

[0037] The embodiments of the present application provide a method for synthesizing and purifying glycolide, which is used to solve the technical defect of low glycolide purification yield in the prior art, and has become a problem to be solved urgently by those skilled in the art.

[0038] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are described in detail below in conjunction with the accompanying drawings and examples. In the following description, many specific details are set forth to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present application, so the present application is not limited by the specific embodiments disclosed below.

[0039] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0040] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of this application, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0041] In this application, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0042] In the present application, unless otherwise clearly specified and limited, a first feature being “above” or “below” a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being “above”, “above”, and “above” a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being “below”, “below”, and “below” a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0043] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it may be directly on the other element or there may be a central element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. The terms "vertical", "horizontal", "upper", "lower", "left", "right" and similar expressions used herein are for illustrative purposes only and are not intended to be the only implementation method.

[0044] The following will be combined Figure 1 , a specific example of the preparation of a synthetic purification method of glycolide provided in this application is carried out.

[0045] In the following examples of the present application, the test method for the glycolide acid value of the product is as follows:

[0046] The test was performed using a Swiss Metrohm 877 potentiometric titrator: the electrode was a non-aqueous glass electrode, the titrant was a 0.01 mol / L potassium methoxide solution in anhydrous methanol, and the solvent was a mixture of dichloromethane and anhydrous methanol in a volume ratio of 4:1.

[0047] Example 1

[0048] Add 200g of methyl glycolate and 0.2g of stannous chloride catalyst into a straight four-necked flask, mix, heat to 150°C at a rate of 5°C / min, maintain for 60min, continue to heat to 180°C at a rate of 5°C / min, vacuumize to reduce the pressure of the reaction system to below 5kPa, and continue the polymerization reaction for 3h to obtain a pale yellow or yellow crude product of methyl glycolate oligomer. The obtained crude product of methyl glycolate oligomer is crushed, and then washed with toluene, filtered and dried in sequence to obtain methyl glycolate oligomer.

[0049] The glycolate oligomer obtained above was heated to a molten state at 250°C, and the pressure was reduced to 2 kPa, and the reaction was carried out for 2 hours for depolymerization. During the depolymerization process, the distilled glycolide was received in a receiving flask filled with isopropanol solvent. During the receiving process, a light yellow liquid first appeared in the receiving flask, and then a solidified light yellow solid gradually appeared on the wall of the receiving flask. At this time, the receiving flask was heated and stirred until the solid on the wall of the flask was completely dissolved. After continuous stirring for 2 hours, it was allowed to stand until the solution in the flask was separated into layers, wherein the upper layer was a glycolide solution.

[0050] The glycolide solution obtained above was distilled at 85° C. for 2 h in a nitrogen atmosphere to remove the organic solvent isopropanol, thereby obtaining the first purified solid-phase glycolide.

[0051] The solid phase glycolide obtained by the first purification was mixed with 500 ml of good solvent ethyl acetate in a flask, heated to 60-70°C until the solid was completely dissolved, and stirred for 3 hours. The entire heating and stirring process was carried out in an inert gas nitrogen atmosphere. After stirring, the flask was quickly placed in a water bath at room temperature to cool for 10 hours, and the filter cake was collected by suction filtration. The solid on the filter cake was vacuum dried for 12 hours to obtain purified glycolide.

[0052] The glycolide finally obtained in this embodiment was tested by the above-mentioned method for testing the acid value content, and its acid value content was 9.36×10 -9 mol / g, the yield was 84.6% and the purity was 99.9%.

[0053] Example 2

[0054] Add 200g of methyl glycolate and 1g of stannous octoate catalyst into a straight four-necked flask, mix, heat to 130°C at a rate of 15°C / min, maintain for 90min, continue to heat to 170°C at a rate of 3°C / min, vacuumize to reduce the pressure of the reaction system to below 5kPa, and continue the polymerization reaction for 6h to obtain a pale yellow or yellow crude product of methyl glycolate oligomer. The obtained crude product of methyl glycolate oligomer is crushed, and then washed with toluene, filtered and dried in sequence to obtain methyl glycolate oligomer.

[0055] The glycolate oligomer obtained above was heated to a molten state at 230°C, and the pressure was reduced to 1 kPa, and the reaction was carried out for 1 hour for depolymerization. During the depolymerization process, the distilled glycolide was received in a receiving flask filled with a solvent of n-butanol. During the receiving process, a light yellow liquid first appeared in the receiving flask, and then a solidified light yellow solid gradually appeared on the wall of the receiving flask. At this time, the receiving flask was heated and stirred until the solid on the wall of the flask was completely dissolved, and the stirring was continued for 2 hours and then allowed to stand until the solution in the flask was separated into layers, wherein the upper layer was a glycolide solution.

[0056] The glycolide solution obtained above was distilled at 95° C. for 1.5 h in a nitrogen atmosphere to remove the organic solvent isopropanol, thereby obtaining the first purified solid-phase glycolide.

[0057] The solid phase glycolide obtained by the first purification was mixed with 500 ml of good solvent ethyl acetate in a flask, heated to 60-70°C until the solid was completely dissolved, and stirred for 1 hour. The entire heating and stirring process was carried out in an inert gas nitrogen atmosphere. After stirring, the flask was quickly placed in a water bath at room temperature to cool for 10 hours, and the filter cake was collected by suction filtration. The solid on the filter cake was vacuum dried for 12 hours to obtain purified glycolide.

[0058] The above method for testing the acid value content was used to test the glycolide finally obtained in this embodiment, and the acid value content was 8.18×10 -9 mol / g, the yield was 84.1% and the purity was 99.9%.

[0059] Example 3

[0060] 200g of methyl glycolate and 1.5g of stannous octoate catalyst were added to a straight four-necked flask, and after mixing, the temperature was raised to 140°C at a rate of 20°C / min and maintained for 90min, and then the temperature was further raised to 180°C at a rate of 1°C / min, and the pressure of the reaction system was reduced to below 5kPa by vacuum, and the polymerization reaction was continued for 4h to obtain a pale yellow or yellow crude product of methyl glycolate oligomer. The crude product of methyl glycolate oligomer was crushed, and then washed with toluene, filtered and dried in sequence to obtain methyl glycolate oligomer.

[0061] The glycolate oligomer obtained above was heated to a molten state at 250°C, and the pressure was reduced to 1 kPa, and the reaction was carried out for 2 hours for depolymerization. During the depolymerization process, the distilled glycolide was received in a receiving flask filled with a solvent of n-butanol. During the receiving process, a light yellow liquid first appeared in the receiving flask, and then a solidified light yellow solid gradually appeared on the wall of the receiving flask. At this time, the receiving flask was heated and stirred until the solid on the wall of the flask was completely dissolved, and the stirring was continued for 2 hours and then allowed to stand until the solution in the flask was separated into layers, wherein the upper layer was a glycolide solution.

[0062] The glycolide solution obtained above was distilled at 100° C. for 1 h in a nitrogen atmosphere to remove the organic solvent tert-butyl alcohol, thereby obtaining the first purified solid-phase glycolide.

[0063] The solid phase glycolide obtained by the first purification was mixed with 500 ml of good solvent ethyl acetate in a flask, heated to 70°C until the solid was completely dissolved, and stirred for 1 hour. The entire heating and stirring process was carried out in an inert gas nitrogen atmosphere. After stirring, the flask was quickly placed in a water bath at room temperature to cool for 10 hours, and the filter cake was collected by suction filtration. The solid on the filter cake was vacuum dried for 12 hours to obtain purified glycolide.

[0064] The above method for testing the acid value content was used to test the glycolide finally obtained in this embodiment, and the acid value content was 8.09×10 -9 mol / g, the yield was 85.3% and the purity was 99.9%.

[0065] Comparative Example 1

[0066] 200 g of methyl glycolate and 0.2 g of stannous chloride catalyst were added to a straight four-necked flask, and after mixing, the temperature was raised to 150°C at a rate of 25°C / min and maintained for 60 min, and then the temperature was further raised to 180°C at a rate of 10°C / min, and the pressure of the reaction system was reduced to below 5 kPa by vacuum, and the polymerization reaction was continued for 3 hours to obtain a pale yellow or yellow crude product of methyl glycolate oligomer. The obtained crude product of methyl glycolate oligomer was crushed, and then washed with toluene, filtered and dried in sequence to obtain methyl glycolate oligomer.

[0067] The glycolate oligomer obtained above was heated to a molten state at 250°C, and the pressure was reduced to 2 kPa, and the reaction was carried out for 2 hours for depolymerization. During the depolymerization process, the distilled glycolide was received in a receiving flask filled with isopropanol solvent. During the receiving process, a light yellow liquid first appeared in the receiving flask, and then a solidified light yellow solid gradually appeared on the wall of the receiving flask. At this time, the receiving flask was heated and stirred until the solid on the wall of the flask was completely dissolved. After continuous stirring for 2 hours, it was allowed to stand until the solution in the flask was separated into layers, wherein the upper layer was a glycolide solution.

[0068] The glycolide solution obtained above was distilled at 85° C. for 2 h in a nitrogen atmosphere to remove the organic solvent isopropanol, thereby obtaining the first purified solid-phase glycolide.

[0069] The solid phase glycolide obtained by the first purification was mixed with 500 ml of good solvent ethyl acetate in a flask, heated to 60°C until the solid was completely dissolved, and stirred for 3 hours. The entire heating and stirring process was carried out in an inert gas nitrogen atmosphere. After stirring, the flask was quickly placed in a water bath at room temperature to cool for 10 hours, and the filter cake was collected by suction filtration. The solid on the filter cake was vacuum dried for 12 hours to obtain purified glycolide.

[0070] The above method for testing the acid value content was used to test the glycolide finally obtained in this embodiment, and the acid value content was 10.18×10 -9 mol / g, the yield was 81.6% and the purity was 99.9%.

[0071] Comparative Example 2

[0072] Add 200 g of methyl glycolate and a certain amount of catalyst stannous octoate into a straight four-necked flask, heat to 130 °C at 30 °C / min, raise the temperature to 170 °C after a period of time, then evacuate the system pressure to below 5 kPa, continue the reaction for 2 h to 6 h, and obtain light yellow or yellow methyl glycolate oligomers.

[0073] Then it was heated to 250°C, and the pressure was reduced to 1 kPa and the reaction was carried out for 2 hours. As the reaction proceeded, a light yellow liquid first appeared in the receiving flask, and then a solidified light yellow solid substance gradually appeared on the wall of the receiving flask. Ethyl acetate was added to the receiving flask, and the substance in the receiving flask was heated to completely dissolve, then kept warm for 30 minutes and then cooled to 5°C for crystallization purification. After filtration, it was melted and crystallized for secondary purification. The glycolide was heated to 95°C for melting, and then cooled to 75°C for crystallization at 0.5°C / min, and then heated to 850°C for sweating, and the sweating liquid was removed. Finally, the temperature was raised to melt and collect the glycolide product to obtain a white glycolide product.

[0074] The purified glycolide was tested using the above-mentioned method for testing the acid value content, and the acid value content was 7.06×10 -9 mol / g, the yield is 79.2% and the purity is 99.9%.

[0075] Comparative Example 3

[0076] Add 200 g of methyl glycolate and a certain amount of catalyst stannous octoate into a straight four-necked flask, heat to 130°C, and after a period of time, increase the temperature to 170°C, then evacuate the system pressure to below 5 kPa, and continue the reaction for 2 h to 6 h to obtain light yellow or yellow methyl glycolate oligomers.

[0077] Then it was heated to 250°C, and the pressure was reduced to 1 kPa and the reaction was carried out for 2 hours. As the reaction proceeded, a light yellow liquid first appeared in the receiving flask, and then a solidified light yellow solid substance gradually appeared on the wall of the receiving flask. Ethyl acetate was added to the receiving flask, and the substance in the receiving flask was completely dissolved after heating. The temperature was kept for 30 minutes and then cooled to 5°C for crystallization and purification. After filtering, it was washed three times with methanol and then dissolved in ethyl acetate for secondary cooling and crystallization purification to obtain purified glycolide.

[0078] The purified glycolide was tested using the above-mentioned method for testing the acid value content, and the acid value content was 7.32×10 -9 mol / g, the yield is 77.9% and the purity is 99.4%.

[0079] The technical solution provided in this application has the following advantages:

[0080] First, in the process of synthesizing glycolide, the method of preparing glycolide using methyl glycolate as raw material does not contain carboxyl groups, and the acid value content in the product can be reduced accordingly;

[0081] Second, during the ring-opening polymerization, the active hydrogen on the carboxyl group will not inhibit the polymerization and affect the molecular weight of the synthesized glycolide;

[0082] Third, during the purification process, there is no need for multiple washings, which reduces the loss of glycolide and provides a higher glycolide yield. Furthermore, through experimental measurements, the technical solution provided in this application can achieve a glycolide yield of more than 84%, and the purity and acid value of the obtained glycolide can meet usage requirements.

[0083] In summary, the present application provides a method for synthesizing and purifying glycolide, which includes: polymerization reaction, crude product distillation, first purification and second purification. In the gold technical solution provided by the present application, a method for preparing glycolide using methyl glycolate as raw material is provided, the raw material does not contain carboxyl groups, and the acid value content in the product can be reduced accordingly; at the same time, during the ring-opening polymerization, the active hydrogen on the carboxyl group will not produce inhibition to affect the molecular weight of the synthesized glycolide; further, according to experimental measurements, the technical solution provided by the present application, the glycolide yield can reach more than 84%, and the purity and acid value of the obtained glycolide can meet the use requirements. The present application provides a method for synthesizing and purifying glycolide, which solves the technical defect of low glycolide purification yield in the prior art.

[0084] The technical features of the above-mentioned embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification. At the same time, other implementation methods can be derived from the above-mentioned embodiments, so that structural and logical replacements and changes can be made without departing from the scope of this disclosure.

[0085] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be construed as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent application shall be subject to the attached claims.

Claims

1. A method for synthesizing and purifying glycolide, characterized in that: The synthesis and purification method is: Step 1, polymerization reaction: methyl glycolate is mixed with a catalyst, and a polymerization reaction is carried out after stepwise heating, and the polymerization reaction is followed by post-treatment to obtain methyl glycolate oligomers; Step 2, distilling off the crude product: the methyl glycolate oligomer is depolymerized under heating conditions, and the distilled glycolide is received in a container filled with a solvent to obtain a glycolide solution; Step 3, first purification: distilling the glycolide solution distilled out in step 2 to obtain first purified solid-phase glycolide; Step 4, second purification: the solid-phase glycolide obtained in the first purification in step 3 is mixed with a good solvent, heated and stirred, and then cooled, and the filter cake is collected by suction filtration and vacuum dried to obtain purified glycolide; In step 1, the catalyst is: stannous chloride and / or stannous octoate.

2. The synthesis and purification method according to claim 1, characterized in that: In step 2, the solvent is selected from any one or more of n-propanol, isopropanol, n-butanol, isobutanol, tert-butanol and n-pentanol; and / or, Calculated by mass, the feed ratio of the solvent to the methyl glycolate oligomer is (0.5-1):

1.

3. The synthesis and purification method according to claim 1 or 2, characterized in that: In step 4, the good solvent is selected from any one or more of ethyl acetate, tetrahydrofuran and dichloromethane.

4. The synthesis and purification method according to any one of claims 1 to 3, characterized in that: In step 1, the stepwise heating method is: heating to 120-160°C at a rate of 5-20°C / min, maintaining for 15-150min, and then heating to 170-200°C at a rate of 1-5°C / min; and / or, In step 1, the polymerization reaction time is 2 to 8 hours.

5. The synthesis and purification method according to any one of claims 1 to 3, characterized in that: In step 2, the depolymerization temperature is 230-260° C., the depolymerization heating time is 1-4 hours, and the evaporation operation is performed under vacuum conditions.

6. The synthesis and purification method according to any one of claims 1 to 3, characterized in that: In step 1, the amount of the catalyst added is 0.01wt% to 1wt%.

7. The synthesis and purification method according to any one of claims 1 to 3, characterized in that: In step 3, the distillation is carried out in an inert gas protective atmosphere, the distillation temperature is 80-100° C., and the distillation time is 0.5-5 h; In step three, the inert gas is selected from any one or more of nitrogen, argon and helium.

8. The synthesis and purification method according to any one of claims 1 to 3, characterized in that: In step 4, the heating and stirring temperature is 50-70° C., the heating and stirring time is 1-3 hours, and the heating and stirring is carried out in an inert gas protective atmosphere.

9. The synthesis and purification method according to claim 8, characterized in that: In step 4, the cooling time is 6 to 10 hours, the cooling temperature is room temperature, and the vacuum drying time is 8 to 12 hours.

10. The synthesis and purification method according to claim 8 or 9, characterized in that: In step 4, the inert gas is selected from any one or more of nitrogen, argon and helium.

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