A method for removing residual glycolide from polyglycolic acid and the resulting low glycolide residual polyglycolic acid

Abstract

The application discloses a method for removing residual glycolide in polyglycolic acid and low-glycolide-residual polyglycolic acid obtained by the method. The method comprises the following steps: uniformly mixing polyglycolic acid with a nitrogen nitrogen bidentate ligand, and then performing devolatilization treatment to obtain low-glycolide-residual polyglycolic acid. The devolatilization treatment time is shorter, only 1-30 min, and the residual glycolide content of the polyglycolic acid obtained by the preparation method is lower, and can reach less than 0.1%.

Description

Technical Field

[0001] This invention relates to the field of polyglycolic acid resin preparation technology, specifically to a method for removing residual glycolide from polyglycolic acid and the resulting polyglycolic acid with low glycolide residue. Background Technology

[0002] Polyglycolic acid (PGA) is an aliphatic polyester with high barrier properties, high mechanical properties, and biodegradability, and is widely used in the medical, packaging, and oilfield extraction fields. High molecular weight PGA is generally obtained through the ring-opening polymerization of glycolide, but the reaction involves ring chain equilibrium, and the conversion rate of glycolide cannot reach 100%. Glycolide remaining in PGA can affect its processing stability and service performance. Therefore, it is necessary to remove unreacted glycolide after the polymerization reaction reaches a certain extent; this process is called demonolysis, demonolysis, or devolatilization. Taking patents CN102219889A and CN1930211A as examples, PGA is granulated and then passed through a hot drying gas to remove residual glycolide with the gas. However, this process takes several hours and is not economical.

[0003] Therefore, how to efficiently remove glycolide monomers from polyglycolic acid remains a problem that needs to be solved. Summary of the Invention

[0004] To address the problems in the prior art, this invention provides a method for removing residual glycolide from polyglycolic acid (PGA) and the resulting PGA with low residual glycolide. This invention introduces a nitrogen-nitrogen bidentate ligand that chelates with the active site of the catalyst, thereby deactivating the catalyst, reducing depolymerization reactions, and improving the PGA devolatilization effect.

[0005] One of the objectives of this invention is to provide a method for removing residual glycolide from polyglycolic acid.

[0006] The method includes:

[0007] Polyglycolic acid was mixed evenly with a nitrogen-nitrogen bidentate ligand and then subjected to devolatilization treatment to obtain polyglycolic acid with low glycolide residue.

[0008] In a preferred embodiment of the present invention,

[0009] The structural formula of the nitrogen-nitrogen bidentate ligand is:

[0010]

[0011] R1 and R2 are, respectively, one or more of the following: monosubstituted or polysubstituted H at any position on the ring, and alkyl groups containing 1 to 10 carbon atoms.

[0012] In a preferred embodiment of the present invention,

[0013] The structural formula of the nitrogen-nitrogen bidentate ligand is:

[0014]

[0015] R1 and R2 are each independently selected from H or alkyl groups containing 1 to 10 carbon atoms, preferably from H or alkyl groups containing 1 to 4 carbon atoms, and more preferably from H or alkyl groups containing 1 to 3 carbon atoms.

[0016] In a preferred embodiment of the present invention,

[0017] The content of the nitrogen-nitrogen bidentate ligand in the mixture of polyglycolic acid and the nitrogen-nitrogen bidentate ligand is 0.001 to 0.5 wt%, preferably 0.005 to 0.3 wt%, and more preferably 0.03 to 0.3 wt%.

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

[0019] The temperature of the devolatilization treatment is 200–235°C, preferably 210–230°C; and / or,

[0020] The devolatilization treatment time is 1–30 min, preferably 1–20 min, more preferably 10–20 min; and / or,

[0021] The pressure of the devolatilization treatment is 0.01 to 5 kPa, preferably 0.01 to 3 kPa, and more preferably 0.01 to 1 kPa.

[0022] In a preferred embodiment of the present invention,

[0023] The devolatilization process is carried out in a devolatilizer, which is preferably at least one of agitated devolatilizer, roller devolatilizer, screw devolatilizer, thin film evaporation devolatilizer, and drop strip devolatilizer.

[0024] In a preferred embodiment of the present invention,

[0025] The polyglycolic acid is obtained by ring-opening polymerization of glycolide, preferably by ring-opening polymerization of glycolide in the presence of a catalyst and a molecular weight regulator.

[0026] In a preferred embodiment of the present invention,

[0027] In the ring-opening polymerization reaction of the glycolide, the acid value of the glycolide is 0.1–20 mol / t, and the water content is 10–500 ppm; and / or,

[0028] The catalyst is at least one selected from the following: stannous octoate, tetraphenyltin, tetrabutyl stannate, stannous chloride, stannous chloride, zinc oxide, diethylzinc, zinc acetate dihydrate, tin lactate, ferric lactate, antimony trioxide, and titanium dioxide; and / or,

[0029] The molecular weight regulator is a hydroxyl-containing compound, preferably at least one selected from water, ethanol, propylene glycol, hexanediol, decanediol, n-butanol, dodecanol, tetradecyl alcohol, and glycerol; and / or,

[0030] The concentration of the catalyst in the mixture of glycolide, catalyst, and molecular weight regulator ranges from 5 to 500 ppm, preferably from 10 to 300 ppm; and / or,

[0031] The content of the molecular weight regulator in the mixture of glycolide, catalyst and molecular weight regulator is 0.01 to 0.1 wt%, preferably 0.01 to 0.08 wt%.

[0032] In a preferred embodiment of the present invention,

[0033] The reaction temperature of the ring-opening polymerization reaction is 120–240°C, preferably 150–230°C, and more preferably 200–230°C; and / or,

[0034] The reaction time for the ring-opening polymerization reaction is 5 to 700 min, preferably 8 to 600 min, and more preferably 10 to 80 min.

[0035] In a preferred embodiment of the present invention,

[0036] The residual glycolic acid contains 2-10 wt% glycolide, and / or...

[0037] The glycolide content in the low-glycolic acid with low residual glycolide is 0.01-1 wt%, preferably 0.01-0.5 wt%.

[0038] A second objective of this invention is to provide a method for obtaining low-residual glycolic acid with low glycolide content, which is one of the objectives of this invention.

[0039] In a preferred embodiment of the present invention,

[0040] The glycolide content in the low-glycolic acid with low residual glycolide is 0.01-1 wt%, preferably 0.01-0.5 wt%.

[0041] The present invention can adopt the following specific technical solutions:

[0042] The method for removing residual glycolide from polyglycolic acid preferably includes the following steps:

[0043] (1) Polyglycolic acid is obtained by adding glycolide, catalyst and molecular weight regulator into a reactor for polymerization reaction;

[0044] (2) Polyglycolic acid and nitrogen-nitrogen bidentate ligands are mixed evenly and then devolatilized in a devolatilizer to obtain polyglycolic acid with low glycolide residue.

[0045] The mixing temperature in step (2) is the same as the temperature of the devolatilization treatment. The mixing can be carried out using conventional mixing equipment in the prior art. In this invention, mixing equipment in the form of a batch reactor, an extruder, a static mixer, etc. is preferred.

[0046] Because polyglycolic acid (PGA) obtained from the ring-opening polymerization of glycolide still contains a catalyst, existing techniques for the devolatilization process of PGA can lead to a reverse reaction in which PGA reacts to form glycolide again under the action of the contained catalyst. Therefore, the glycolide content in the final devolatilized PGA cannot be reduced to an ideal level. This invention incorporates a nitrogen-nitrogen bidentate ligand that inhibits catalyst activity during the devolatilization process. This ligand chelates with the active site of the catalyst, inhibiting the reverse formation of glycolide from PGA, thus improving the devolatilization effect and reducing the residual glycolide content in the resulting PGA to a more ideal level.

[0047] Compared with existing technologies, the devolatilization process of this invention has a shorter processing time, only 1 to 30 minutes, and the method for removing residual glycolide from polyglycolic acid (PGA) yields PGA with a lower residual glycolide content, reaching less than 0.1%. Commercially available PGA typically contains 0.5% to 1% residual glycolide, representing a significant improvement over this method. Since the residual glycolide content after devolatilization is related to the catalyst activity and the temperature, pressure, and time in the system, under the same conditions of catalyst activity and system temperature, pressure, and time, the method of this invention achieves a more significant reduction in glycolide content compared to devolatilization without the addition of a bidentate ligand or with the addition of other metal passivating agents. Furthermore, the bidentate ligand used in this invention has a significant cost advantage compared to metal passivating agents such as phosphites and hydrazides. Detailed Implementation

[0048] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0049] The raw materials used in the embodiments and comparative examples of this invention are all conventional commercially available raw materials.

[0050] The nitrogen-nitrogen bidentate ligands used in the examples and comparative examples were purchased from the manufacturer Innochem.

[0051] The method for testing the residual glycolide content in polyglycolic acid in the embodiments and comparative examples of the present invention is as follows: Polyglycolic acid is mixed with dimethyl sulfoxide, heated to dissolve, and then cooled to room temperature. The supernatant is taken and quantitatively analyzed in a gas chromatograph (Agilent Technologies, model 7890B) to obtain the residual glycolide content in polyglycolic acid.

[0052] Example 1

[0053] 100g of glycolide with an acid value of 5mol / t and a water content of 100ppm, stannous octoate (the concentration of stannous octoate in the mixture of glycolide, stannous octoate, and water is 50ppm), and water (the content of water as a molecular weight regulator in the mixture of glycolide, stannous octoate, and water is 0.02wt%) were added to a reactor for polymerization (temperature 210℃, time 45min) to obtain polyglycolic acid with a residual glycolide content of 6.2wt%. After being mixed evenly with a nitrogen-nitrogen bidentate ligand, it was devolatilized in a stirred devolatilizer at a temperature of 220℃, a pressure of 0.03kPa, and a time of 15min. The resulting low-glycolic acid with a residual glycolide content of 0.1wt% was obtained.

[0054] The content of the aforementioned bidentate ligand in a mixture of polyglycolic acid with a residual glycolide content of 6.2 wt% and the bidentate ligand is 0.05 wt%. The structure of the bidentate ligand is as follows:

[0055] Where R1 = H, R2 = H.

[0056] Example 2

[0057] 100g of glycolide with an acid value of 9mol / t and a water content of 10ppm, tetraphenyltin (the concentration of tetraphenyltin in the mixture of glycolide, tetraphenyltin and dodecyl alcohol is 10ppm) and dodecyl alcohol (the content of dodecyl alcohol in the mixture of glycolide, tetraphenyltin and dodecyl alcohol is 0.1wt%) were added to a reactor for polymerization (temperature 212℃, time 65min) to obtain polyglycolic acid with a residual glycolide content of 2.0wt%. After being mixed evenly with a nitrogen-nitrogen bidentate ligand, it was devolatilized in a roll devolatilizer at a temperature of 230℃, a pressure of 0.01kPa, and a time of 10min. The resulting low-glycolic acid with a residual glycolide content of 0.05wt% was obtained.

[0058] The content of the aforementioned bidentate ligand in a mixture of polyglycolic acid with a residual glycolide content of 2.0 wt% and the bidentate ligand is 0.03 wt%. The structure of the bidentate ligand is as follows:

[0059] Where R1 = methyl and R2 = H.

[0060] Example 3

[0061] 100g of glycolide with an acid value of 20mol / t and a water content of 200ppm, tetrabutyl stannate (the concentration of tetrabutyl stannate in the mixture of glycolide, tetrabutyl stannate, and water is 100ppm), and water (the content of water as a molecular weight regulator in the mixture of glycolide, tetrabutyl stannate, and water is 0.01wt%) were added to a reactor for polymerization (temperature 215℃, time 25min) to obtain polyglycolic acid with a residual glycolide content of 3.8wt%. After being mixed evenly with a nitrogen-nitrogen bidentate ligand, it was devolatilized in a screw devolatilizer at a temperature of 210℃, a pressure of 0.02kPa, and a time of 13min. The resulting low-glycolic acid with a residual glycolide content of 0.01wt% was obtained.

[0062] The content of the aforementioned bidentate ligand in a mixture of polyglycolic acid with a residual glycolide content of 3.8 wt% and the bidentate ligand is 0.1 wt%. The structure of the bidentate ligand is as follows:

[0063] Where R1 = methyl and R2 = methyl.

[0064] Example 4

[0065] 100g of glycolide with an acid value of 0.1mol / t and a water content of 300ppm, tin chloride (concentration of tin chloride in the mixture of glycolide, tin chloride and dodecyl alcohol is 80ppm) and dodecyl alcohol (content of dodecyl alcohol in the mixture of glycolide, tin chloride and dodecyl alcohol is 0.05wt%) were added to a reactor for polymerization (temperature 208℃, time 30min) to obtain polyglycolic acid with a residual glycolide content of 8.2wt%. After being mixed evenly with a nitrogen-nitrogen bidentate ligand, it was devolatilized in a thin-film evaporation devolatilizer at a temperature of 200℃, a pressure of 0.05kPa and a time of 18min. The resulting low-glycolic acid with a residual glycolide content of 0.04wt% was obtained.

[0066] The content of the aforementioned bidentate ligand in a mixture of polyglycolic acid with a residual glycolide content of 8.2 wt% and the bidentate ligand is 0.06 wt%. The structure of the bidentate ligand is as follows:

[0067] Where R1 = methyl, R2 = ethyl.

[0068] Example 5

[0069] 100g of glycolide with an acid value of 15.1mol / t and a water content of 500ppm, along with diethylzinc (concentration of 300ppm in the mixture of glycolide, diethylzinc, and tetradecyl alcohol) and tetradecyl alcohol (content of 0.03wt% in the mixture of glycolide, diethylzinc, and tetradecyl alcohol), were added to a reactor for polymerization (temperature 218℃, time 12min) to obtain polyglycolic acid with a residual glycolide content of 10wt%. After being uniformly mixed with a nitrogen-nitrogen bidentate ligand, the mixture was subjected to devolatilization treatment in a thin-film evaporator at a temperature of 235℃, a pressure of 0.1kPa, and a time of 20min, resulting in low-glycolic acid residual polyglycolic acid with a residual glycolide content of 0.1wt%.

[0070] The aforementioned bidentate ligand contains 0.2 wt% of a mixture of polyglycolic acid with a residual glycolide content of 10 wt% and the bidentate ligand. The structure of the bidentate ligand is as follows:

[0071] Where R1 = H, R2 = methyl.

[0072] Example 6

[0073] 100g of glycolide with an acid value of 2.3mol / t and a water content of 150ppm, tin lactate (the concentration of tin lactate in the mixture of glycolide, tin lactate, and hexanediol is 150ppm), and hexanediol (the content of hexanediol in the mixture of glycolide, tin lactate, and hexanediol is 0.08wt%) were added to a reactor for polymerization (temperature 225℃, time 23min) to obtain polyglycolic acid with a residual glycolide content of 5.1wt%. After being mixed evenly with a nitrogen-nitrogen bidentate ligand, it was subjected to devolatilization treatment in a strip devolatilization device at a temperature of 225℃, a pressure of 1.3kPa, and a time of 20min. The resulting low-glycolic acid with a residual glycolide content of 0.4wt% was obtained.

[0074] The content of the aforementioned bidentate ligand in a mixture of polyglycolic acid with a residual glycolide content of 5.1 wt% and the bidentate ligand is 0.15 wt%. The structure of the bidentate ligand is as follows:

[0075] Where R1 = n-butyl, R2 = n-butyl.

[0076] Example 7

[0077] 100g of glycolide with an acid value of 6.6mol / t and a water content of 100ppm, ferric lactate (200ppm concentration in the mixture of glycolide, ferric lactate, and decanediol), and decanediol (0.06wt% content in the mixture of glycolide, ferric lactate, and decanediol) were added to a reactor for polymerization (temperature 214℃, time 20min) to obtain polyglycolic acid with a residual glycolide content of 3.3wt%. After being mixed evenly with a nitrogen-nitrogen bidentate ligand, the mixture was subjected to devolatilization treatment in a screw devolatilizer at a temperature of 215℃, a pressure of 2.5kPa, and a time of 25min. The resulting low-glycolic acid with a residual glycolide content of 0.8wt% was obtained.

[0078] The content of the aforementioned bidentate ligand in a mixture of polyglycolic acid with a residual glycolide content of 3.3 wt% and the bidentate ligand is 0.25 wt%. The structure of the bidentate ligand is as follows:

[0079] Where R1 = isopropyl and R2 = methyl.

[0080] Example 8

[0081] 100g of glycolide with an acid value of 10.8mol / t and a water content of 230ppm, stannous octoate (concentration of stannous octoate in the mixture of glycolide, stannous octoate and glycerol is 500ppm) and glycerol (content of glycerol in the mixture of glycolide, stannous octoate and glycerol is 0.05wt%) were added to a reactor for polymerization (temperature 210℃, time 10min) to obtain polyglycolic acid with a residual glycolide content of 7.1wt%. After being mixed evenly with a nitrogen-nitrogen bidentate ligand, it was devolatilized in a thin-film evaporation devolatilizer at a temperature of 210℃, a pressure of 3.5kPa and a time of 22min. The resulting low-glycolic acid with a residual glycolide content of 0.5wt% was obtained.

[0082] The content of the aforementioned bidentate ligand in a mixture of polyglycolic acid with a residual glycolide content of 7.1 wt% and the bidentate ligand is 0.5 wt%. The structure of the bidentate ligand is as follows:

[0083] Where R1 = tert-butyl and R2 = tert-butyl.

[0084] Example 9

[0085] 100g of glycolide with an acid value of 3.6mol / t and a water content of 120ppm, stannous chloride (the concentration of stannous chloride in the mixture of glycolide, stannous chloride and ethanol is 40ppm) and ethanol (the content of ethanol in the mixture of glycolide, stannous chloride and ethanol is 0.01wt%) were added to a reactor for polymerization (temperature 215℃, time 55min) to obtain polyglycolic acid with a residual glycolide content of 2.0wt%. After being mixed evenly with a nitrogen-nitrogen bidentate ligand, it was subjected to devolatilization treatment in a strip devolatilizer at a temperature of 220℃, a pressure of 5kPa and a time of 28min. The resulting low-glycolic acid with a residual glycolide content of 1wt% was obtained.

[0086] The content of the aforementioned bidentate ligand in a mixture of polyglycolic acid with a residual glycolide content of 2.0 wt% and the bidentate ligand is 0.05 wt%. The structure of the bidentate ligand is as follows:

[0087] Where R1 = ethyl, R2 = ethyl.

[0088] Comparative Example 1 (without nitrogen-nitrogen bidentate ligands)

[0089] 100g of glycolide with an acid value of 5mol / t and a water content of 100ppm, stannous octoate (stannous octoate concentration of 50ppm in the mixture of glycolide, stannous octoate and water), and water (molecular weight regulator water content of 0.02wt% in the mixture of glycolide, stannous octoate and water) were added to a reactor for polymerization (temperature 210℃, time 45min) to obtain polyglycolic acid with a residual glycolide content of 6.2wt%. The polyglycolic acid was then subjected to devolatilization treatment in a stirred devolatilizer at a temperature of 220℃, a pressure of 0.03kPa, and a time of 15min, resulting in polyglycolic acid with a residual glycolide content of 4.5wt%.

[0090] Comparative Example 2 (with other metal passivating agents added)

[0091] 100g of glycolide with an acid value of 5mol / t and a water content of 100ppm, stannous octoate (50ppm concentration in the mixture of glycolide, stannous octoate, and water), and water (0.02wt% molecular weight regulator water in the mixture of glycolide, stannous octoate, and water) were added to a reactor for polymerization (temperature 210℃, time 45min) to obtain polyglycolic acid with a residual glycolide content of 6.2wt%. After being mixed with dibutyl phosphate (0.05wt% dibutyl phosphate in the mixture of polyglycolic acid and dibutyl phosphate), the mixture was subjected to devolatilization in a stirred devolatilizer at a temperature of 220℃, a pressure of 0.03kPa, and a time of 15min, resulting in polyglycolic acid with a residual glycolide content of 1.5wt%.

[0092] As shown in Examples 1-9, the method of the present invention for removing residual glycolide from polyglycolic acid (PGA) significantly reduces the residual glycolide content in the final PGA to 0.01–1 wt% due to the addition of a nitrogen-nitrogen bidentate ligand during the devolatilization process. Examples 1 and Comparative Examples 1-2 also demonstrate that the residual glycolide content in PGA after devolatilization is related to the activity of the catalyst in the system, as well as the system temperature, pressure, and time. Therefore, under the same conditions of catalyst activity and system temperature, pressure, and time, the method of the present invention achieves a more significant reduction in glycolide content compared to methods without the addition of a nitrogen-nitrogen bidentate ligand or with the addition of other metal passivating agents during the devolatilization process.

Claims

1. A method for removing residual glycolide from polyglycolic acid, comprising: Polyglycolic acid was mixed evenly with a nitrogen-nitrogen bidentate ligand and then subjected to a devolatilization treatment to obtain polyglycolic acid with low glycolide residue; the structural formula of the nitrogen-nitrogen bidentate ligand is as follows: R1 and R2 are, respectively, one or more of the following: monosubstituted or polysubstituted H at any position on the ring, and alkyl groups containing 1 to 10 carbon atoms.

2. The method as described in claim 1, characterized in that: The structural formula of the nitrogen-nitrogen bidentate ligand is: ， R1 and R2 are each independently selected from H or alkyl groups containing 1 to 10 carbon atoms.

3. The method as described in claim 2, characterized in that: The structural formula of the nitrogen-nitrogen bidentate ligand is: ， R1 and R2 are each independently selected from H or alkyl groups containing 1 to 4 carbon atoms.

4. The method as described in claim 1, characterized in that: The content of the nitrogen-nitrogen bidentate ligand in the mixture of polyglycolic acid and nitrogen-nitrogen bidentate ligand is 0.001~0.5wt%.

5. The method as described in claim 4, characterized in that: The content of the nitrogen-nitrogen bidentate ligand in the mixture of polyglycolic acid and nitrogen-nitrogen bidentate ligand is 0.005~0.3wt%.

6. The method as described in claim 1, characterized in that: The temperature of the devolatilization treatment is 200~235℃; and / or, The devolatilization treatment time is 1~30 min; and / or, The pressure for the devolatilization treatment is 0.01~5 kPa.

7. The method as described in claim 6, characterized in that: The temperature of the devolatilization treatment is 210~230℃; and / or, The devolatilization treatment time is 1-20 min; and / or, The pressure for the devolatilization process is 0.01~3 kPa.

8. The method as described in claim 1, characterized in that: The devolatilization process is carried out inside the devolatilizer.

9. The method as described in claim 8, characterized in that: The devolatilizer is at least one of the following: agitated devolatilizer, roller devolatilizer, screw devolatilizer, thin film evaporation devolatilizer, and drop strip devolatilizer.

10. The method as described in claim 1, characterized in that: The polyglycolic acid is obtained by ring-opening polymerization of glycolide.

11. The method as described in claim 10, characterized in that: The polyglycolic acid is obtained by ring-opening polymerization of glycolide in the presence of a catalyst and a molecular weight regulator.

12. The method as described in claim 11, characterized in that: In the ring-opening polymerization reaction of the glycolide, the acid value of the glycolide is 0.1~20 mol / t, and the water content is 10~500 ppm; and / or, The catalyst is at least one selected from the following: stannous octoate, tetraphenyltin, tetrabutyl stannate, stannous chloride, stannous chloride, zinc oxide, diethylzinc, zinc acetate dihydrate, tin lactate, ferric lactate, antimony trioxide, and titanium dioxide; and / or, The molecular weight regulator is a hydroxyl-containing compound; and / or, The concentration of the catalyst in the mixture of glycolide, catalyst, and molecular weight regulator ranges from 5 to 500 ppm; and / or, The molecular weight regulator is present in a mixture of glycolide, catalyst, and molecular weight regulator at a concentration of 0.01 to 0.1 wt%.

13. The method as described in claim 12, characterized in that: The molecular weight regulator is at least one selected from water, ethanol, propylene glycol, hexanediol, decanediol, n-butanol, dodecanol, tetradecyl alcohol, and glycerol; and / or, The concentration of the catalyst in the mixture of glycolide, catalyst, and molecular weight regulator ranges from 10 to 300 ppm; and / or, The molecular weight regulator is present in a mixture of glycolide, catalyst, and molecular weight regulator at a concentration of 0.01 to 0.08 wt%.

14. The method as described in claim 10, characterized in that: The ring-opening polymerization reaction is carried out at a temperature of 120~240℃; and / or, The reaction time for the ring-opening polymerization reaction is 5 to 700 minutes.

15. The method as described in claim 14, characterized in that: The reaction temperature for the ring-opening polymerization reaction is 150~230℃; and / or, The reaction time for the ring-opening polymerization reaction is 8 to 600 minutes.

16. The method according to any one of claims 1-15, characterized in that: The residual glycolic acid contains 2-10 wt% glycolide, and / or, The glycolide content in the low-glycolic acid with residual glycolide is 0.01~1 wt%.

17. The method as described in claim 16, characterized in that: The glycolide content in the low-glycolic acid residual polyglycolic acid is 0.01~0.5wt%.

18. A low-glycolic acid residual polyglycolic acid obtained by the method of any one of claims 1-17.

19. The low-glycolic acid residual polyglycolic acid as described in claim 18, characterized in that: The glycolide content in the low-glycolic acid with residual glycolide is 0.01~1 wt%.

20. The low-glycolic acid residual polyglycolic acid as described in claim 19, characterized in that: The glycolide content in the low-glycolic acid residual polyglycolic acid is 0.01~0.5wt%.

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