A process for the preparation of a polyglycolic acid with low yellowness value and the polyglycolic acid obtained

Abstract

The application discloses a preparation method of low-yellow-value polyglycolic acid and the obtained polyglycolic acid. The preparation method of the low-yellow-value polyglycolic acid comprises the step of mixing and reacting components including glycolide and a reaction aid; the mixing and reacting adopts at least four gradient temperature increasing modes; the temperature of the second section is increased by 0-9 DEG C than that of the first section, preferably by 5-9 DEG C; the temperature of the last section is increased by 1-5 DEG C than that of the previous adjacent section, preferably by 2-5 DEG C; and the temperature of the other adjacent section is increased by 16-40 DEG C than that of the previous adjacent section, preferably by 16-35 DEG C. The specific gradient temperature increasing process can reduce the occurrence of side reactions such as depolymerization reaction, aromatization reaction and monomer cracking reaction in the reaction process, and the yellow value of the polyglycolic acid product is reduced, and the color phase of the product is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of polyglycolic acid preparation, in particular to a preparation method of low-yellow-value polyglycolic acid and the obtained polyglycolic acid. BACKGROUND

[0002] Polyglycolic acid (PGA) is a biodegradable polymer with excellent gas barrier properties, excellent mechanical processing properties, and outstanding biodegradation performance, and is widely used in medical materials (surgical sutures and drug release capsules), packaging materials (in-bottle membranes), film materials (mulch films), and engineering plastics (oil field) and the like.

[0003] The synthesis of PGA is generally obtained by ring-opening polymerization of glycolide. According to different processes and formulations, the yellow value of the obtained PGA is not the same. Some downstream products have higher requirements for the yellow value of the raw materials, such as medical materials and packaging materials. The existing technology, for example, patent CN112469763A, has a yellow value of 40-90, which is difficult to meet the needs of specific products.

[0004] Therefore, there is an urgent need for a process for preparing low-yellow-value polyglycolic acid. SUMMARY

[0005] To solve the problems in the prior art, the present application provides a preparation method of low-yellow-value polyglycolic acid and the obtained polyglycolic acid. The present application uses a specific gradient temperature rising process, so that the active center generation section, the reaction initiation section, the deep polymerization section, and the reaction equilibrium section can be carried out in the optimal temperature range, which can reduce the occurrence of side reactions such as depolymerization reaction, aromatization reaction, and monomer cracking reaction during the reaction, which is manifested as the reduction of the yellow value of the polyglycolic acid product and the improvement of the product color.

[0006] One of the purposes of the present application is to provide a preparation method of low-yellow-value polyglycolic acid, which comprises the step of mixing and reacting components comprising glycolide and reaction aids; the mixing and reacting adopts at least 4-stage gradient temperature rising; the temperature of the second stage is increased by 0-9℃, preferably 5-9℃, than that of the first stage; the temperature of the last stage is increased by 1-5℃, preferably 2-5℃, than that of the previous adjacent stage; the temperature of the next stage of the other adjacent stages is increased by 16-40℃, preferably 16-35℃, than that of the previous adjacent stage.

[0007] In a preferred embodiment of the present application,

[0008] The mixing and reacting adopts 4-9-stage gradient temperature rising, preferably 5-9-stage gradient temperature rising, for example, 5-stage, 6-stage, 7-stage, 8-stage, or 9-stage gradient temperature rising; and / or,

[0009] The residence time at each temperature is 0-60 minutes, preferably 0-30 minutes, more preferably 2-30 minutes.

[0010] In a preferred embodiment of the present application,

[0011] The mixed reaction is carried out at 100-240°C, preferably at 120-240°C; preferably,

[0012] The first temperature range is between 125-155°C; the last temperature range is between 225-235°C.

[0013] In a preferred embodiment of the present application,

[0014] The mixed reaction is carried out in at least one of a static mixer, an extruder, a horizontal double shaft reactor, a twin rotor reactor, preferably in a static mixer, which is a conventional static mixer in the art.

[0015] In a preferred embodiment of the present application,

[0016] The glycolide is in a molten state; preferably, the molten glycolide enters the reactor at a temperature range of 80-155°C; more preferably,

[0017] The acid value of the glycolide is 0.1-50 mol / t, preferably 0.2-25 mol / t; and / or, the water content of the glycolide is 10-1000 ppm, preferably 20-500 ppm.

[0018] In a preferred embodiment of the present application,

[0019] The reaction aid includes a catalyst and an initiator.

[0020] In a preferred embodiment of the present application,

[0021] The catalyst is selected from at least one of stannous octoate, tetraphenyl tin, tetrabutyl tin, stannous chloride, stannous chloride dihydrate, tin chloride, stannous acetylacetonate, tin lactate, tin ethoxide, zinc oxide, zinc acetylacetonate, diethyl zinc, zinc acetate dihydrate, iron lactate, antimony trioxide; and / or,

[0022] The amount of the catalyst is 0.0005%-0.05%, preferably 0.001%-0.03%, based on the total weight of the glycolide and the reaction aid being 100%.

[0023] In a preferred embodiment of the present application,

[0024] The initiator contains at least one hydroxyl group, preferably at least one of water, a fatty alcohol, more preferably at least one of water, methanol, ethanol, propanol, butanol, pentanol, decanol, dodecanol, tetradecanol, and hexadecanol; and / or,

[0025] The amount of the initiator is 0-1%, preferably 0-0.5%, more preferably 0.05-0.5%, based on 100% of the total weight of glycolide and the reaction aid.

[0026] Other conventional reaction aids, such as antioxidants, can also be included in the present application, and the antioxidants are at least one of phosphate compounds, phosphite compounds, hindered phenols, etc., and the amount of the antioxidants is also a conventional amount, which can be added by a person skilled in the art according to the actual situation.

[0027] In a preferred embodiment of the present application,

[0028] The preparation method further comprises a step of devolatilizing the glycolide polyglycolic acid mixture obtained after the reaction; preferably, the devolatilization is performed at an absolute pressure of ≤400 Pa, and / or a temperature of 225-240°C, and / or a time of 2-60 minutes.

[0029] The preparation method of the low-yellow-value polyglycolic acid of the present application can adopt the following specific technical solutions:

[0030] (1) The molten glycolide and the aid are respectively introduced into a static mixer for mixing and polymerization reaction to obtain a glycolide polyglycolic acid mixture; the static mixer adopts at least 4 stages of gradient temperature increase; the temperature range of the first stage is between 125-155°C; the temperature range of the last stage is between 225-235°C; the temperature of the second stage is increased by 0-9°C compared with that of the first stage; the temperature of the last stage is increased by 1-5°C compared with that of the previous adjacent stage; the temperature of the other adjacent stages is increased by 16-40°C between the previous adjacent stage and the next adjacent stage.

[0031] (2) The glycolide polyglycolic acid mixture is introduced into a devolatilizer for removal of unreacted glycolide to obtain a low-yellow-value polyglycolic acid.

[0032] The second object of the present application is to provide a polyglycolic acid obtained by the preparation method of the first object of the present application.

[0033] In a preferred embodiment of the present application,

[0034] The yellow value of the polyglycolic acid is less than 40.

[0035] The present application has the following beneficial effects:

[0036] The present application considers that the ring-opening polymerization reaction of glycolide comprises multiple stages, including active center generation section, reaction initiation section, deep polymerization section, reaction equilibrium section, etc., therefore, by adopting specific gradient temperature rising process, each stage is in the preferred temperature range, which can reduce the occurrence of depolymerization reaction, aromatization reaction, monomer cracking reaction and other side reactions in the reaction process, which is manifested as the reduction of the yellowness value of the polyglycolic acid product and the improvement of the product color phase. DETAILED DESCRIPTION

[0037] The present application will be described in detail below in combination with specific examples, it is necessary to point out here that the following examples are only used to further illustrate the present application, and cannot be understood as limiting the protection scope of the present application, some non-essential improvements and adjustments of the present application made by the person skilled in the art according to the content of the present application still belong to the protection scope of the present application.

[0038] The raw materials used in the examples are all conventional commercially available raw materials.

[0039] Determination of the yellowness value of polyglycolic acid: the yellowness value of polyglycolic acid particles was measured by a HunterLab Scan XE yellowness index instrument by reflection method.

[0040]

Example 1

[0041] The molten glycolide with an acid value of 1 mol / t, a water content of 300 ppm and a temperature of 100℃ was mixed with a catalyst stannous octoate and an initiator n-butanol in a static mixer respectively to carry out mixing and polymerization reaction, and a glycolide polyglycolic acid mixture was obtained. The static mixer adopted a 7-stage gradient temperature rising mode, which were 130℃, 135℃, 155℃, 185℃, 205℃, 225℃ and 227℃ respectively; the temperature residence time of each stage was 5 minutes, 5 minutes, 10 minutes, 20 minutes, 40 minutes, 20 minutes and 5 minutes respectively. Based on the total weight of glycolide, catalyst and initiator being 100%, the catalyst content was 0.002%, and the initiator content was 0.5%. The glycolide polyglycolic acid mixture entered a roller type devolatilizer to remove unreacted glycolide, the devolatilizer pressure was 100 Pa, the temperature was 230℃, and the time was 20 minutes, and polyglycolic acid with a yellowness value of 35 was obtained.

[0042]

Example 2

[0043] The molten glycolide with an acid value of 10 mol / t, a water content of 100 ppm, and a temperature of 100°C is fed into a static mixer with a catalyst diethyl zinc and an initiator dodecanol respectively for mixing and polymerization reaction to obtain a glycolide polyglycolic acid mixture. The static mixer adopts an 8-stage gradient heating mode, which is 126°C, 135°C, 155°C, 174°C, 190°C, 206°C, 225°C, and 230°C respectively. The temperature residence time of each stage is 5 minutes, 5 minutes, 5 minutes, 10 minutes, 15 minutes, 20 minutes, 5 minutes, and 5 minutes respectively. Based on the total weight of the glycolide, the catalyst, and the initiator being 100%, the catalyst content is 0.02%, and the initiator content is 0.1%. The glycolide polyglycolic acid mixture is fed into a roller-type devolatilizer for removal of unreacted glycolide. The devolatilizer pressure is 400 Pa, the temperature is 232°C, and the time is 10 minutes to obtain a polyglycolic acid with a yellowness value of 30.

[0044] [Example 3]

[0045] The molten glycolide with an acid value of 2 mol / t, a water content of 190 ppm, and a temperature of 100°C is fed into a horizontal double-shaft reactor with a catalyst stannous octoate and an initiator water respectively for mixing and polymerization reaction to obtain a glycolide polyglycolic acid mixture. The horizontal double-shaft reactor adopts a 5-stage gradient heating mode, which is 140°C, 145°C, 180°C, 220°C, and 225°C respectively. The temperature residence time of each stage is 5 minutes, 5 minutes, 15 minutes, 40 minutes, and 5 minutes respectively. Based on the total weight of the glycolide, the catalyst, and the initiator being 100%, the catalyst content is 0.006%, and the initiator content is 0.8%. The glycolide polyglycolic acid mixture is fed into a roller-type devolatilizer for removal of unreacted glycolide. The devolatilizer pressure is 50 Pa, the temperature is 228°C, and the time is 8 minutes to obtain a polyglycolic acid with a yellowness value of 32.

[0046] [Example 4]

[0047] The molten glycolide with an acid value of 4 mol / t, a water content of 250 ppm and a temperature of 100℃ is respectively introduced into a double-rotor reactor with a catalyst stannous chloride and an initiator decanol for mixing and polymerization reaction to obtain a glycolide polyglycolic acid mixture. The double-rotor reactor adopts a 9-stage gradient heating mode, i.e. 125, 126, 142, 158, 174, 190, 206, 222, 227℃ respectively; the temperature residence time of each stage is 5 minutes, 5 minutes, 5 minutes, 5 minutes, 5 minutes, 10 minutes, 15 minutes, 10 minutes, 5 minutes respectively. Based on the total weight of the glycolide, the catalyst and the initiator being 100%, the catalyst content is 0.008% and the initiator content is 0.25%. The glycolide polyglycolic acid mixture is introduced into a roller-type devolatilizer for removal of unreacted glycolide, the devolatilizer pressure is 20 Pa, the temperature is 232℃, and the time is 5 minutes, to obtain a polyglycolic acid with a yellowness value of 38.

[0048] [Comparative Example 1]

[0049] The molten glycolide with an acid value of 10 mol / t, a water content of 100 ppm and a temperature of 100℃ is respectively introduced into a static mixer with a catalyst diethyl zinc and an initiator dodecanol for mixing and polymerization reaction to obtain a glycolide polyglycolic acid mixture. The static mixer adopts a fixed temperature for each stage, i.e. 225℃, and the reaction time is 70 minutes. Based on the total weight of the glycolide, the catalyst and the initiator being 100%, the catalyst content is 0.02% and the initiator content is 0.1%. The glycolide polyglycolic acid mixture is introduced into a roller-type devolatilizer for removal of unreacted glycolide, the devolatilizer pressure is 400 Pa, the temperature is 232℃, and the time is 10 minutes, to obtain a polyglycolic acid with a yellowness value of 60.

[0050] [Comparative Example 2] (The temperature of the second stage is increased by 10℃ than that of the first stage)

[0051] The molten glycolide with an acid value of 1 mol / t, a water content of 300 ppm and a temperature of 100℃ is respectively introduced into a static mixer with a catalyst stannous octoate and an initiator n-butanol for mixing and polymerization reaction to obtain a glycolide polyglycolic acid mixture. The static mixer adopts a 7-stage gradient heating mode, i.e. 130℃, 140℃, 160℃, 185℃, 205℃, 225℃, 227℃ respectively; the temperature residence time of each stage is 5 minutes, 5 minutes, 10 minutes, 20 minutes, 40 minutes, 20 minutes, 5 minutes respectively. Based on the total weight of the glycolide, the catalyst and the initiator being 100%, the catalyst content is 0.002% and the initiator content is 0.5%. The glycolide polyglycolic acid mixture is introduced into a roller-type devolatilizer for removal of unreacted glycolide, the devolatilizer pressure is 100 Pa, the temperature is 230℃, and the time is 20 minutes, to obtain a polyglycolic acid with a yellowness value of 44.

[0052] [Comparative Example 3] (the temperature of the last segment is increased by 10°C compared to the immediately preceding segment)

[0053] Glycolide with an acid value of 1 mol / t, a water content of 300 ppm, and a temperature of 100°C in a molten state was mixed and polymerized with a catalyst stannous octoate and an initiator n-butanol in a static mixer to obtain a glycolide polyglycolic acid mixture. The static mixer used a 7-segment gradient temperature increase, 130°C, 135°C, 155°C, 185°C, 205°C, 225°C, and 235°C, respectively. The temperature residence time of each segment was 5 minutes, 5 minutes, 10 minutes, 20 minutes, 40 minutes, 20 minutes, and 5 minutes, respectively. Based on the total weight of the glycolide, the catalyst, and the initiator being 100%, the catalyst content was 0.002%, and the initiator content was 0.5%. The glycolide polyglycolic acid mixture was introduced into a roller-type devolatilizer to remove unreacted glycolide, the devolatilizer pressure was 100 Pa, the temperature was 230°C, and the time was 20 minutes, to obtain a polyglycolic acid with a yellowness value of 48.

[0054] [Comparative Example 4] (the temperature of the last segment is increased by less than 16°C compared to the immediately preceding segment)

[0055] Glycolide with an acid value of 1 mol / t, a water content of 300 ppm, and a temperature of 100°C in a molten state was mixed and polymerized with a catalyst stannous octoate and an initiator n-butanol in a static mixer to obtain a glycolide polyglycolic acid mixture. The static mixer used a 7-segment gradient temperature increase, 130°C, 135°C, 155°C, 185°C, 205°C, 225°C, and 235°C, respectively. The temperature residence time of each segment was 5 minutes, 5 minutes, 10 minutes, 20 minutes, 40 minutes, 20 minutes, and 5 minutes, respectively. Based on the total weight of the glycolide, the catalyst, and the initiator being 100%, the catalyst content was 0.002%, and the initiator content was 0.5%. The glycolide polyglycolic acid mixture was introduced into a roller-type devolatilizer to remove unreacted glycolide, the devolatilizer pressure was 100 Pa, the temperature was 230°C, and the time was 20 minutes, to obtain a polyglycolic acid with a yellowness value of 48.

[0056] [Comparative Example 5] (the temperature of the last segment is increased by more than 40°C compared to the immediately preceding segment)

[0057] The molten glycolide with an acid value of 1 mol / t, a water content of 300 ppm and a temperature of 100℃ is respectively introduced into static mixers with a catalyst stannous octoate and an initiator n-butanol for mixing and polymerization reaction, to obtain a glycolide polyglycolic acid mixture. The static mixers adopt a 5-stage gradient heating mode, i.e. 130℃, 135℃, 180℃, 225℃ and 227℃, and the temperature residence time of each stage is 5 minutes, 15 minutes, 30 minutes, 50 minutes and 5 minutes respectively. Based on the total weight of the glycolide, the catalyst and the initiator being 100%, the catalyst content is 0.002% and the initiator content is 0.5%. The glycolide polyglycolic acid mixture is introduced into a roller-type devolatilizer for removal of unreacted glycolide, the devolatilizer pressure is 100 Pa, the temperature is 230℃ and the time is 20 minutes, to obtain a polyglycolic acid with a yellowness value of 51.

[0058] As can be seen from Example 2 and Comparative Example 1, under the same reaction raw materials, total reaction time and devolatilization conditions, the yellowness value of the polyglycolic acid obtained in Comparative Example 1 is obviously worse than that in Example 2, because the polymerization reaction in Comparative Example 1 is carried out at a fixed temperature.

[0059] As can be seen from Example 1 and Comparative Example 2, under the same reaction raw materials, reaction time and devolatilization conditions, the yellowness value of the polyglycolic acid obtained in Comparative Example 2 is obviously higher than that in Example 1, because the temperature of the second stage of the multi-stage gradient heating reaction in Comparative Example 2 is increased by 10℃ than that of the first stage, which is not within the range of 0-9℃ in the present application.

[0060] As can be seen from Example 1 and Comparative Example 3, under the same reaction raw materials, reaction time and devolatilization conditions, the yellowness value of the polyglycolic acid obtained in Comparative Example 3 is also obviously higher than that in Example 1, because the temperature of the last stage of the multi-stage gradient heating reaction in Comparative Example 3 is increased by 10℃ than that of the previous adjacent stage, which is not within the range of 1-5℃ in the present application.

[0061] As can be seen from Example 1 and Comparative Examples 4-5, under the same reaction raw materials, total reaction time and devolatilization conditions, the yellowness value of the polyglycolic acid obtained in Comparative Examples 4-5 is obviously higher than that in Example 1, because the temperature of the last stage of the multi-stage gradient heating reaction in Comparative Example 4 is increased by less than 16℃ than that of the previous adjacent stage, and the temperature of the last stage of the multi-stage gradient heating reaction in Comparative Example 5 is increased by more than 40℃ than that of the previous adjacent stage, which are not within the range of 16-40℃ in the present application.

[0062] Therefore, in this invention, only when the gradient heating method satisfies the following conditions: the temperature of the second stage is 0-9°C higher than that of the first stage; the temperature of the last stage is 1-5°C higher than that of the previous adjacent stage; and the temperature of the latter stage of other adjacent stages is 16-40°C higher than that of the previous adjacent stage, can the occurrence of side reactions such as depolymerization, aromatization, and monomer cracking during the reaction process be effectively reduced. This is manifested as a decrease in the yellowness value of the polyglycolic acid product and an increase in the product hue. Preferably, the yellowness value of the obtained polyglycolic acid is all below 40.

[0063] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

[0064] All publications, patent applications, patents, and other references mentioned in this specification are incorporated herein by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the meanings commonly understood by those skilled in the art. In case of conflict, the definitions in this specification shall prevail.

[0065] When this specification uses the prefixes “known to those skilled in the art,” “prior art,” or similar terms to derive materials, substances, methods, steps, apparatus, or components, the objects derived from such prefixes cover those commonly used in the art at the time of this application, but also include those that are not currently commonly used but will become generally recognized in the art as suitable for similar purposes.

[0066] The endpoints and any values ​​of the ranges disclosed in this application are not limited to the precise ranges or values; such ranges or values ​​should be understood to include values ​​close to them. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. In principle, various technical solutions can be combined with each other to obtain new technical solutions, which should also be considered as specifically disclosed herein.

[0067] In the context of this specification, except where expressly stated otherwise, any matters or issues not mentioned shall apply directly to those known in the art without any modification.

[0068] Moreover, any implementation described herein can be freely combined with one or more other implementations described herein, and the resulting technical solutions or technical ideas are considered to be part of the original disclosure or original description of the present application, and should not be considered as new content that has not been disclosed or anticipated herein, unless the combination is considered to be obviously unreasonable by those skilled in the art.

Claims

1. A method for preparing a low-yellow-value polyglycolic acid, comprising the step of mixing and reacting components including glycolide and a reaction aid; the mixing and reacting is performed in at least 5 stages of temperature gradient; the temperature of the second stage is increased by 0-9℃ compared to the first stage; the temperature of the last stage is increased by 1-5℃ compared to the previous adjacent stage; the temperature of the next stage of other adjacent stages is increased by 16-40℃ compared to the previous adjacent stage.

2. The method according to claim 1, wherein: the temperature of the second stage is increased by 5-9℃ compared to the first stage.

3. The method according to claim 1, wherein: the temperature of the last stage is increased by 2-5℃ compared to the previous adjacent stage.

4. The method according to claim 1, wherein: the temperature of the next stage of other adjacent stages is increased by 16-35℃ compared to the previous adjacent stage.

5. The method according to claim 1, wherein: the mixing and reacting is performed in 5-9 stages of temperature gradient; and / or, the residence time of each stage is 0-60 minutes.

6. The method according to claim 5, wherein: the residence time of each stage is 0-30 minutes.

7. The method according to any one of claims 1-6, wherein: the mixing and reacting is performed at 100-240℃.

8. The method according to claim 7, wherein: the temperature of the first stage is in the range of 125-155℃; and the temperature of the last stage is in the range of 225-235℃.

9. The method according to claim 1, wherein: the mixing and reacting is performed in at least one of a static mixer, an extruder, a horizontal twin-screw reactor, and a twin-rotor reactor.

10. The method according to claim 9, wherein: the mixing and reacting is performed in a static mixer.

11. The method according to claim 1, wherein: the glycolide is in a molten state.

12. The method according to claim 11, wherein: the molten glycolide is introduced into the reactor at a temperature in the range of 80-155℃.

13. The method according to claim 12, wherein: the glycolide has an acid value of 0.1-50 mol / t; and / or, the glycolide has a water content of 10-1000 ppm.

14. The method according to claim 13, wherein: the glycolide has an acid value of 0.2-25 mol / t; and / or, the glycolide has a water content of 20-500 ppm.

15. The method according to claim 1, wherein: the reaction aid comprises a catalyst and an initiator.

16. The method according to claim 15, wherein: the catalyst is selected from at least one of stannous octoate, tetraphenyl tin, tetrabutyl tin chloride, stannous chloride, stannous chloride dihydrate, tin chloride, stannous acetylacetone, tin lactate, tin ethoxide, zinc oxide, zinc acetylacetone, diethyl zinc, zinc acetate dihydrate, iron lactate, and antimony trioxide; and / or, the catalyst is used in an amount of 0.0005%-0.05% based on 100% of the total weight of the glycolide and the reaction aid. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 17. The preparation method according to claim 16, wherein: the amount of the catalyst is 0.001% to 0.03% based on 100% of the total weight of glycolide and the reaction aid.

18. The preparation method according to claim 15, wherein: the initiator contains at least one hydroxyl group; and / or, the amount of the initiator is 0 to 1% based on 100% of the total weight of glycolide and the reaction aid.

19. The preparation method according to claim 18, wherein: the initiator is at least one of fatty alcohols; and / or, the amount of the initiator is 0 to 0.5% based on 100% of the total weight of glycolide and the reaction aid.

20. The preparation method according to claim 19, wherein: the initiator is at least one of methanol, ethanol, propanol, butanol, pentanol, decanol, dodecanol, tetradecanol, and hexadecanol.

21. The preparation method according to claim 15, wherein: the initiator is water.

22. The preparation method according to claim 1, further comprising: a step of de-volatilizing the glycolide polyglycolic acid mixture obtained after the reaction.

23. The preparation method according to claim 22, wherein: the de-volatilization is performed at an absolute pressure of 400 Pa or less, and / or a temperature of 225 to 240°C, and / or a time of 2 to 60 minutes. ​ ​ ​ ​ ​ ​ ​ ​ ​