A process for ring-opening polymerization of glycolide using an initiator

Abstract

The present invention relates to a process for the ring-opening polymerization of glycolide using a novel initiator. A polymerization system is composed of glycolide, a catalyst, and an initiator. The initiator contains hydrophilic and hydrophobic groups and heteroatoms such as sulfur and nitrogen. While metal ions in traditional catalysts catalyze polymerization, they will complex with the oxygen atoms of ester bonds to catalyze the cleavage of the ester bonds of polyglycolide (PGA), resulting in a decrease in the molecular weight of PGA and an increase in the chromaticity of the product. The heteroatoms contained in the novel initiator of the present invention have a strong complexing ability with metals, can form a relatively stable coordination complex with the catalyst, prevent the cleavage of PGA, and reduce the chromaticity of the product. In addition, the addition of this novel initiator introduces some flexible chain segments, lowers the freezing point of PGA, and enables the polymerization temperature to be reduced. Compared with the prior art, the present invention has the advantages of high product molecular weight, relatively uniform molecular weight distribution, large operation flexibility in the polymerization reaction time, and wide temperature control window, and is suitable for industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer material synthesis, and particularly to a process for ring-opening polymerization of glycolide using a novel initiator. Background Art

[0002] Although traditional polymer materials such as PP, PE, PS, etc. have brought a lot of convenience to life, due to imperfect recycling and their difficulty in degrading in the earth environment itself, serious "white pollution" has been caused. Therefore, developing degradable and environmentally friendly polymer materials to replace traditional non-degradable polymer materials has become an important research direction. Polyglycolide (abbreviated as PGA) is a completely biodegradable material that is harmless to the environment. It can be hydrolyzed in organisms and can also be metabolized by microorganisms in the natural environment, and finally decomposed into water and carbon dioxide. It has been widely used in the field of biomedical materials. At present, the synthesis process of polyglycolide has become increasingly mature. However, while the metal ions in traditional catalysts catalyze the polymerization, they will complex with the oxygen atoms of the ester bonds to catalyze the cleavage of the ester bonds of polyglycolide (abbreviated as PGA), resulting in a darker color of the obtained product, a smaller molecular weight of PGA, insufficient melt strength and tensile strength, and a slower degradation rate, which is not very suitable for the conventional applications of plastic products and the popularization of biomaterials. In addition, the polyglycolide production synthesis process has high energy consumption, low production efficiency, and high cost, and it is difficult to replace the existing market of traditional plastics. Therefore, conducting systematic research on the polymerization process of polyglycolide, exploring and improving the synthesis process of polyglycolide, is of great significance for the future industrial promotion and commercialization of polyglycolide in the degradable plastic market.

[0003] There are two processes for the preparation of polyglycolide. One is to directly dehydrate and polycondense glycolic acid. The polyglycolide obtained by this process has a low molecular weight and is difficult to be used for processing and forming materials. The other is to heat and decompose the polycondensation polymer of glycolic acid to obtain cyclic glycolide, and use ring-opening polymerization of glycolide to obtain polyglycolide with a molecular weight of tens of thousands to hundreds of thousands. Patent CN101616907A reports a process for preparing polyglycolide with a weight average molecular weight Mw greater than 200,000 by ring-opening polymerization of glycolide. However, a large amount of high-boiling solvents are used in this polymerization process, increasing the energy consumption of the preparation process and the cost of solvent recovery and utilization. Patent CN111087580A (Pujing Chemical Industry) obtains polyglycolic acid with a relatively high molecular weight by adding a dehydrating agent to polyglycolic acid with a weight average molecular weight lower than 20,000. The molecular weight of polyglycolic acid is increased from 14,000 to 70,000 by this process, but the molecular weight does not reach more than one hundred thousand, the raw material cost increases and the process is complex. Summary of the Invention

[0004] In view of the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a process for the ring-opening polymerization of glycolide using a novel initiator to solve the problems in the prior art.

[0005] The present invention is achieved by the following technical solutions:

[0006] On the one hand, the present invention provides a process for the ring-opening polymerization of glycolide, which process at least includes the following steps:

[0007] (1) Pre-polymerize the glycolide monomer, catalyst and initiator at a certain temperature and pressure to provide a PGA prepolymer; wherein, the initiator includes at least one of a hydrophilic functional group, a hydrophobic functional group and a heteroatom;

[0008] (2) Polymerize the PGA prepolymer provided in step (1) under reduced pressure to provide a PGA oligomer;

[0009] (3) Further polymerize the PGA oligomer provided in step (2) under further reduced pressure to obtain a PGA polymer.

[0010] On the other hand, the present invention provides a system for the ring-opening polymerization process of glycolide, which includes a reaction kettle, a first-stage reactor, a second-stage reactor and a third-stage reactor connected in sequence along the raw material logistics direction.

[0011] On the other hand, the present invention provides a polyglycolide prepared by using the ring-opening polymerization process of glycolide as described in the present invention.

[0012] On the other hand, the present invention provides the use of the polyglycolide as described in the present invention in the field of biodegradable plastics.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0014] In the process for the ring-opening polymerization of glycolide using a novel initiator of the present invention, the heteroatom contained in the initiator has a strong complexing ability with metals, can form a relatively stable coordination complex with the catalyst, prevent the breakage of PGA, and thus reduce the product chromaticity. At the same time, the addition of this novel initiator introduces some flexible chain segments, reduces the freezing point of PGA, and enables the polymerization temperature to be reduced. Therefore, the present invention is of great significance for obtaining polyglycolide with high molecular weight and uniform distribution, reducing the polymerization temperature, and reducing energy consumption. In addition, the process of the present invention has the advantages of a large operation flexibility of the polymerization reaction time and a wide temperature control window, and is suitable for industrial production. Detailed Embodiments

[0015] Hereinafter, the embodiments of the process for the ring-opening polymerization of glycolide using a novel initiator are specifically and publicly described in detail.

[0016] The "range" disclosed in this application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can include or exclude the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 - 120 and 80 - 110 are listed for a specific parameter, ranges of 60 - 110 and 80 - 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5. In this application, unless otherwise specified, the numerical range "a - b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" are fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0017] If there is no special instruction, all embodiments and optional embodiments of this application can be combined with each other to form a new technical solution.

[0018] If there is no special instruction, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0019] If there is no special instruction, all steps of this application can be carried out in sequence or randomly, preferably in sequence. For example, the process includes steps (1) and (2), which means that the process can include steps (1) and (2) carried out in sequence, or can also include steps (2) and (1) carried out in sequence. For example, it is mentioned that the process may further include step (3), which means that step (3) can be added to the process in any order. For example, the process can include steps (1), (2), and (3), or can also include steps (1), (3), and (2), or can also include steps (3), (2), and (1), etc.

[0020] If there is no special instruction, the "including" and "comprising" mentioned in this application mean open-ended or can also be closed-ended. For example, the "including" and "comprising" can mean that other components not listed can also be included or comprised, or can also mean that only the listed components are included or comprised.

[0021] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or present) and B is false (or absent); A is false (or absent) while B is true (or present); or both A and B are true (or present).

[0022] The applicant of the present invention unexpectedly found through a large number of experiments that in a polymerization system composed of glycolide, a catalyst, and an initiator, the monomer glycolide can undergo ring-opening polymerization under the action of the catalyst and an initiator containing a flexible chain segment and special performance characteristic functional groups (hydrophilic and hydrophobic groups -OH, -COOR, -CH2OCH2-, etc.) to generate a high-molecular-weight PGA with a weight-average molecular weight of 100,000 to 380,000. Based on this, the present invention was completed. Specifically:

[0023] On the one hand, the present invention provides a glycolide ring-opening polymerization process, and the process at least includes the following steps:

[0024] (1) Pre-polymerize the glycolide monomer, the catalyst, and the initiator under certain temperature and pressure to provide a PGA prepolymer; wherein, the initiator includes at least one of a hydrophilic functional group, a hydrophobic functional group, and a heteroatom;

[0025] (2) Polymerize the PGA prepolymer provided in step (1) under reduced pressure to provide a PGA oligomer;

[0026] (3) Further polymerize the PGA oligomer provided in step (2) under further reduced pressure to obtain a PGA polymer.

[0027] In the glycolide ring-opening polymerization process provided by the present invention, in step (1), the glycolide monomer, the catalyst, and the initiator are pre-polymerized under certain temperature and pressure to provide a PGA prepolymer. In a specific embodiment, generally, the glycolide monomer, the catalyst, and the initiator can be first melted to form a liquid phase. Specifically, they can be melted under stirring in a high-pressure reaction kettle. The temperature in the high-pressure reaction kettle can be, for example, 100 - 130 °C, and the stirring time can be, for example, 30 - 60 min. The melted liquid phase can be transferred to the first-stage reactor for pre-polymerization reaction to generate a PGA prepolymer.

[0028] In step (1) of the present invention, the initiator generally contains a flexible chain segment and special performance characteristic functional groups. Among them, the hydrophilic functional group in the initiator can be selected from one or more of -OH, -CH2OCH2-, -CHO, -COOH, -COO-, etc. The hydrophobic functional group is selected from one or more of -CH3, -C6H5, -CH3F, etc.; the heteroatom is selected from sulfur and / or nitrogen, etc.

[0029] In a specific embodiment, the initiator comprises a compound having the following general formula:

[0030]

[0031] wherein X, R1, and R2 are each independently selected from O, CRa1R a2 or SiR b1 R b2 ; R a1 , R a2 , R b1 R b2 are each independently selected from hydrogen, deuterium, a substituted or unsubstituted C1-C30 straight-chain or branched-chain alkyl group, a substituted or unsubstituted C6-C40 aryl group, or a substituted or unsubstituted C3-C40 heteroaryl group. In some embodiments, R a1 R a2 R b1 R b2 are each independently selected from a substituted or unsubstituted C1-C5 straight-chain or branched-chain alkyl group, a substituted or unsubstituted C5-C10 straight-chain or branched-chain alkyl group, a substituted or unsubstituted C10-C15 straight-chain or branched-chain alkyl group, a substituted or unsubstituted C15-C20 straight-chain or branched-chain alkyl group, a substituted or unsubstituted C20-C25 straight-chain or branched-chain alkyl group, a substituted or unsubstituted C25-C30 straight-chain or branched-chain alkyl group, etc. Preferably, X, R1, and R2 are each independently selected from O, -CH(CH3)-, -CH2-.

[0032] R3 is selected from deuterium, a halogen, a cyano group, a substituted or unsubstituted C1-C30 straight-chain or branched-chain alkyl group, a C1-C30 alkoxy group, a substituted or unsubstituted C6-C40 aryl group, or a substituted or unsubstituted C3-C40 heteroaryl group. In some embodiments, R3 is selected from a substituted or unsubstituted C1-C5 straight-chain or branched-chain alkyl group, a substituted or unsubstituted C5-C10 straight-chain or branched-chain alkyl group, a substituted or unsubstituted C10-C15 straight-chain or branched-chain alkyl group, a substituted or unsubstituted C15-C20 straight-chain or branched-chain alkyl group, a substituted or unsubstituted C20-C25 straight-chain or branched-chain alkyl group, a substituted or unsubstituted C25-C30 straight-chain or branched-chain alkyl group, etc. Preferably, R3 is selected from -CHCl2.

[0033] n1 is an integer selected from 0 to 10; more specifically, n1 can be selected from 0 to 5, 5 to 10, 0 to 3, 3 to 5, 5 to 8, 8 to 10, etc., and can also be selected from 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, etc.

[0034] n2 is an integer selected from 0 to 5; n2 can be selected from 0 to 3, 3 to 5, etc., and can also be selected from 0, 1, 2, 3, 4, 5, etc.

[0035] n3 is selected from integers from 0 to 5; n3 can be selected from 0 to 3, 3 to 5, etc., or can also be selected from 0, 1, 2, 3, 4, 5, etc.

[0036] In step (1) of the present invention, the catalyst is selected from metal oxides and metal salts. Preferably, the metal oxide is selected from one or a combination of more than one of antimony trioxide, germanium dioxide, titanium dioxide, zinc oxide, and tin oxide. The metal salts are selected from one or a combination of more than one of zinc acetate, stannous octoate, calcium acetate, zinc acetate dihydrate, stannous chloride, and stannous chloride dihydrate.

[0037] In step (1) of the present invention, the mass of the catalyst can be 0.01 to 2.0 wt%, 0.01 to 0.05 wt%, 0.05 to 1.0 wt%, 1.0 to 1.5 wt%, or 1.5 to 2.0 wt%, etc. of the mass of the glycolide monomer.

[0038] In step (1) of the present invention, the mass of the initiator is 0.01 to 2.0 wt%, 0.01 to 0.05 wt%, 0.05 to 1.0 wt%, 1.0 to 1.5 wt%, or 1.5 to 2.0 wt%, etc. of the mass of the glycolide monomer.

[0039] In step (1) of the present invention, the purity of the glycolide monomer is greater than 99%.

[0040] In step (1) of the present invention, the pressure of the prepolymerization reaction can be 100 - 500 kPa, 100 - 200 kPa, 200 - 300 kPa, 300 - 400 kPa, or 400 - 500 kPa, etc.

[0041] In step (1) of the present invention, the temperature of the prepolymerization reaction can be 100 - 220 °C, 100 - 160 °C, 160 - 200 °C, or 200 - 220 °C, etc. The temperature of the prepolymerization reaction is preferably 100 - 160 °C.

[0042] In step (1) of the present invention, the time of the prepolymerization reaction can be 1 - 12 h, 1 - 6 h, 6 - 12 h, 1 - 4 h, 4 - 8 h, or 8 - 12 h, etc. The time of the prepolymerization reaction is preferably 1 - 6 h.

[0043] In step (1) of the present invention, the weight - average molecular weight of the PGA prepolymer can be 1000 - 10000, 1000 - 5000, 5000 - 10000, 1000 - 3000, 3000 - 5000, 5000 - 8000, or 8000 - 10000, etc.

[0044] In step (1) of the present invention, it should be noted that during the prepolymerization process, the main purpose is to remove small-molecule water or methanol. The lower the absolute pressure, the more effective the removal of small-molecule substances. The residence time and the small-molecule removal effect show a volcanic curve trend. In a specific embodiment, under the conditions of an absolute pressure of 100 kPa and a reaction temperature of 160 °C, when the residence time is 1 - 6 h, the weight-average molecular weight of the PGA prepolymer increases from 2500 to 8300. When the residence time is further extended to 12 h, the weight-average molecular weight decreases to 1800.

[0045] In the process of ring-opening polymerization of glycolide provided by the present invention, in step (2), the PGA oligomer provided in step (1) is polymerized under reduced pressure to provide a PGA oligomer.

[0046] In step (2) of the present invention, the provided PGA prepolymer needs to be further polymerized under reduced pressure. The PGA prepolymer provided in step (1) can be reduced in pressure to, for example, 10 - 30 kPa, 10 - 20 kPa, 20 - 30 kPa, 10 - 15 kPa, 15 - 20 kPa, 20 - 25 kPa, or 25 - 30 kPa, etc.

[0047] In step (2) of the present invention, during the further polymerization of the PGA prepolymer, the temperature of the polymerization reaction can be 110 - 220 °C, 110 - 120 °C, 120 - 220 °C, 110 - 160 °C, or 160 - 220 °C, etc. The temperature of the polymerization reaction is preferably 110 - 200 °C.

[0048] In step (2) of the present invention, during the further polymerization of the PGA prepolymer, the time of the polymerization reaction can be 1 - 10 h, 1 - 5 h, 5 - 10 h, etc. The time of the polymerization reaction is preferably 1 - 5 h.

[0049] In step (2) of the present invention, the molecular weight of the PGA oligomer obtained after polymerization is 10000 - 150000, 10000 - 50000, 50000 - 100000, 100000 - 150000, 10000 - 30000, 30000 - 50000, 50000 - 80000, 80000 - 100000, 100000 - 120000, or 120000 - 150000, etc.

[0050] In step (2) of the present invention, in a specific embodiment, the PGA prepolymer obtained in step (1) is transferred to the second reactor, the pressure is reduced to 10 - 30 kPa, and polymerization is carried out at 110 - 220 °C for 1 - 10 h to obtain a low molecular weight PGA oligomer with a weight average molecular weight of ten thousand to over one hundred thousand. The molecular weight of the PGA oligomer can be, for example, 10,000 - 150,000, and more specifically, it can be 10,000 - 50,000, 50,000 - 100,000, 100,000 - 150,000, 10,000 - 30,000, 30,000 - 50,000, 50,000 - 80,000, 80,000 - 100,000, 100,000 - 120,000, or 120,000 - 150,000, etc.

[0051] In the ring - opening polymerization process of glycolide provided by the present invention, in step (3), the PGA oligomer provided in step (2) is further polymerized after further reducing the pressure to obtain a PGA polymer.

[0052] In step (3) of the present invention, in the further polymerization reaction of the PGA oligomer, it is necessary to further reduce the pressure of the PGA oligomer provided in step (2) to 1 - 2 kPa, 1 - 1.5 kPa, or 1.5 - 2 kPa, etc.

[0053] In step (3) of the present invention, in the further polymerization reaction of the PGA oligomer, the temperature of the polymerization reaction can be, for example, 120 - 220 °C, 120 - 130 °C, 130 - 200 °C, 200 - 220 °C, etc. The temperature of the polymerization reaction is preferably 130 - 200 °C.

[0054] In step (3) of the present invention, in the further polymerization reaction of the PGA oligomer, the time of the polymerization reaction can be, for example, 0.5 - 10 h, 0.5 - 2 h, 2 - 5 h, 5 - 8 h, or 8 - 10 h, etc. The time of the polymerization reaction is preferably 0.5 - 2 h.

[0055] In step (3) of the present invention, in step (3), the molecular weight of the PGA polymer is 10,000 - 380,000, 10,000 - 300,000, 300,000 - 380,000, 10,000 - 100,000, 100,000 - 200,000, 200,000 - 300,000, etc.

[0056] In step (3) of the present invention, the further polymerization reaction of the PGA oligomer is carried out in the third reactor. In a specific embodiment, the oligomer obtained in step (2) is transferred to the third reactor, the pressure is reduced to 1 - 2 kPa, and polymerization is carried out at 120 - 220 °C for 0.5 - 10 h to obtain a PGA polymer with a weight average molecular weight of 10,000 - 380,000.

[0057] In the glycolide ring-opening polymerization process provided by the present invention, to improve the efficiency, the pre-polymerization reaction temperature should not be lower than the standard boiling point of the lowest-boiling component in the composition. However, to prevent the thermal depolymerization of polyglycolide, the temperatures of the three-stage polymerization should not be too high.

[0058] After the reaction is completed, a small amount of the sample is taken for quenching, and then its molecular weight is measured by GPC and the intrinsic viscosity is measured by an Ubbelohde viscometer. The other samples are taken out for treatment (granulation, strand drawing, etc.), and then tested through the required properties (crystallization properties, hydrolysis resistance, antioxidant properties, tensile strength, melt index, etc.).

[0059] The second aspect of the present invention provides a system for the glycolide ring-opening polymerization process, including a reaction kettle, a first-stage reactor, a second-stage reactor, and a third-stage reactor that are connected in sequence along the raw material flow direction.

[0060] Specifically, in the polymerization system for glycolide ring-opening polymerization, the polymerization system includes a reaction kettle (high-pressure reaction kettle) for storing raw materials and three-stage reactors connected in sequence by pipelines along the raw material flow direction, namely the first-stage reactor used in step (1), the second-stage reactor used in step (2), and the third-stage reactor used in step (3). The reaction kettle and the polymerization reactor should include at least one feed stream and at least one discharge stream; the liquid melt is discharged from the bottom of the reaction kettle and fed into the reactor from the bottom. The first-stage reactor, the second-stage reactor, and the third-stage reactor are all commonly used polymerization reactors in the prior art.

[0061] The third aspect of the present invention provides polyglycolide, which is prepared by using the glycolide ring-opening polymerization process described in the first aspect of the present invention.

[0062] The fourth aspect of the present invention provides the use of the polyglycolide described in the third aspect of the present invention in the field of degradable plastics.

[0063] The mechanism of the present invention is described as follows:

[0064] Polyglycolide belongs to a biodegradable polymer. While increasing the polymerization reaction rate, it is necessary to avoid the degradation of the polymer during the reaction. On this basis, further increase the molecular weight of the product and ensure a uniform molecular weight distribution. The initiator is a substance that generates the active center of the free radical polymerization reaction. It is not only an important factor affecting the polymerization reaction rate but also an important factor affecting the relative molecular weight of the polymer. The present invention has discovered a novel initiator containing special performance characteristic functional groups (hydrophilic and hydrophobic groups -OH, -COOH, COO-, -CH2(O)CH2-, etc.) and heteroatoms such as sulfur and nitrogen. This initiator can form a stable coordination complex with the catalyst, avoid the breakage of PGA, and lower the freezing point of PGA, resulting in a lower polymerization temperature. While effectively increasing the polymerization reaction rate and energy consumption, it promotes the rapid increase of the polymerization molecular weight, obtaining PGA with a higher molecular weight and a uniform distribution.

[0065] Advantages of the present invention:

[0066] (1) The polyglycolide prepared by the present invention has a good surface color and a relatively high weight-average molecular weight, and is very suitable for use as a food packaging material and a medical material.

[0067] (2) The initiator used in the present invention lowers the freezing point of PGA, resulting in a lower polymerization temperature and thus reducing energy consumption.

[0068] (3) For the ring-opening polymerization process of glycolide described in the present invention, the polymerization reaction time has a large operating flexibility and the temperature control window is wide, which is suitable for industrial production.

[0069] The following further illustrates the beneficial effects of the present invention in conjunction with examples.

[0070] In order to make the invention purpose, technical solution and beneficial technical effects of the present invention clearer, the present invention will be further described in detail below in conjunction with examples. However, it should be understood that the examples of the present invention are only for explaining the present invention and not for limiting the present invention, and the examples of the present invention are not limited to the examples given in the specification. For the examples where specific experimental conditions or operating conditions are not indicated, they are prepared according to conventional conditions or according to the conditions recommended by the material suppliers.

[0071] In addition, it should be understood that one or more process steps mentioned in the present invention do not exclude the existence of other process steps before and after the combined steps or the insertion of other process steps between these explicitly mentioned steps, unless otherwise specified; it should also be understood that the combined connection relationship between one or more devices / apparatuses mentioned in the present invention does not exclude the existence of other devices / apparatuses before and after the combined devices / apparatuses or the insertion of other devices / apparatuses between these two explicitly mentioned devices / apparatuses, unless otherwise specified. Moreover, unless otherwise specified, the numbers of each process step are only convenient tools for identifying each process step, rather than limiting the arrangement order of each process step or the scope in which the present invention can be implemented. The change or adjustment of their relative relationship, without substantial change in the technical content, should also be regarded as the scope in which the present invention can be implemented.

[0072] In the following examples, the reagents, materials, and instruments used can be obtained commercially without special instructions.

[0073] The following tests on physical and chemical properties, etc. are as follows:

[0074] A. Weight-average molecular weight and its distribution

[0075] (1) Dissolve the sample in a hexafluoroisopropanol solution to prepare a solution with a mass fraction of 0.1% - 0.3%;

[0076] (2) Filter with a polytetrafluoroethylene filter membrane with a pore size of 0.4 μm;

[0077] (3) Take 20 μL and add it to the GPC injector, and use 5 standard polymethyl methacrylates with different molecular weights for molecular weight calibration.

[0078] B. Intrinsic viscosity

[0079] Weigh about 0.125 g of the sample, dissolve it in 25 ml of hexafluoroisopropanol, dissolve it in a constant temperature water bath at 25 °C, use an Ubbelohde viscometer to measure and calculate the intrinsic viscosity [η], and measure it 3 times on average under the condition of 25 °C. The difference in the efflux time for each measurement should not exceed 0.2 s.

[0080] C. Melt index

[0081] Test according to the method of GB / T 3682.2 - 2018, the test temperature is 230 °C, and the weight of the weight is 2.16 kg.

[0082] D. Yellowness

[0083] The yellowness index is measured by a yellowness index instrument.

[0084] F. Freezing point

[0085] The freezing point was determined by differential scanning calorimetry (DSC).

[0086] An appropriate amount of PGA was weighed, placed in a crucible, covered with a lid, and placed in a DSC. An empty crucible was used as a reference. Nitrogen was filled at a certain flow rate, and then the temperature was raised to the melting temperature at a rate of 10 °C / min, held for 2 min, and then cooled at a certain cooling rate until all of the PGA solidified.

[0087] The raw material glycolide monomer needs to be vacuum dried overnight under the conditions of an absolute pressure of 1 - 20 KPa and a temperature of 40 - 50 °C.

[0088] There is no special limitation on the catalyst, and it can be selected from metal oxides and metal salts; preferably, the metal oxide is selected from one or a combination of antimony trioxide, germanium dioxide, titanium dioxide, zinc oxide, and tin oxide; the metal salts are selected from one or a combination of zinc acetate, stannous octanoate, calcium acetate, zinc acetate dihydrate, stannous chloride, and stannous chloride dihydrate; and its dosage is 0.01 - 2.0 wt% of the mass of the raw material monomers.

[0089] Example 1

[0090] 1000 g of glycolide monomer, 2 g of stannous octanoate, and 2.5 g of the compound represented by the following formula (1) were added to a reaction kettle, heated to 90 °C at normal pressure to completely melt the reactants, and then the melt was transported to a prepolymerization reactor with an absolute pressure of 200 KPa and a temperature of 150 °C, and left for 2.5 h for prepolymerization reaction; then the obtained prepolymer was transported to a reactor with an absolute pressure of 20 KPa and a temperature of 180 °C, and left for 2 h for polymerization to obtain a PGA oligomer; the PGA oligomer was continuously transported to a polymerization reactor with an absolute pressure of 2 KPa and a temperature of 200 °C and left for 1 h for final polymerization reaction to finally obtain a PGA polymer.

[0091] The measurement results of the product polyglycolide polymer are as follows:

[0092] ① The weight - average molecular weight (Mw) is 350,000;

[0093] ② The ratio of weight - average molecular weight to number - average molecular weight (Mw / Mn) is 1.1;

[0094] ③ The intrinsic viscosity is 2.2 dL / g;

[0095] ④ The melt index is 5.1 g / min;

[0096] ⑤ The freezing point is 160 °C;

[0097] ⑥ The yellowness index is 26.

[0098] Chemical formula 1

[0099]

[0100] Example 2

[0101] The difference between this example and Example 1 lies in the different polymerization reaction temperatures. Specifically, 1000 g of glycolide monomer, 2 g of stannous octoate, and 2.5 g of the compound described in the above formula (1) are added to the reaction kettle. Under normal pressure, it is heated to 90 °C to completely melt the reactants, and then the melt is transported to a prepolymerization reactor with an absolute pressure of 200 KPa and a temperature of 160 °C, and stays for 2.5 h for prepolymerization reaction; then the obtained prepolymer is transported to a reactor with an absolute pressure of 20 KPa and a temperature of 200 °C, and stays for 2 h for polymerization to obtain a PGA oligomer; the PGA oligomer is continuously transported to a polymerization reactor with an absolute pressure of 2 KPa and a temperature of 200 °C and stays for 1 h for final polymerization reaction to finally obtain a PGA polymer.

[0102] The measurement results of the product polyglycolide polymer are as follows:

[0103] ① The weight-average molecular weight (Mw) is 330,000;

[0104] ② The ratio of weight-average molecular weight to number-average molecular weight (Mw / Mn) is 1.2;

[0105] ③ The intrinsic viscosity is 2.01 dL / g;

[0106] ④ The melt index is 5.6 g / min

[0107] ⑤ The freezing point is 160 °C;

[0108] ⑥ The yellowness index is 25.

[0109] Example 3

[0110] 1000 g of glycolide monomer, 2 g of stannous octoate, and 2.5 g of the compound described in the above formula (1) are added to the reaction kettle. Under normal pressure, it is heated to 90 °C to completely melt the reactants, and then the melt is transported to a prepolymerization reactor with an absolute pressure of 200 KPa and a temperature of 160 °C, and stays for 2.5 h for prepolymerization reaction; then the obtained prepolymer is transported to a reactor with an absolute pressure of 20 KPa and a temperature of 200 °C, and stays for 2 h for polymerization to obtain a PGA oligomer; the PGA oligomer is continuously transported to a polymerization reactor with an absolute pressure of 2 KPa and a temperature of 215 °C and stays for 1 h for final polymerization reaction to finally obtain a PGA polymer.

[0111] The measurement results of the product polyglycolide polymer are as follows:

[0112] ① The average molecular weight (Mw) is 360,000;

[0113] ② The ratio of weight-average molecular weight to number-average molecular weight (Mw / Mn) is 1.31;

[0114] ③ The intrinsic viscosity is 2.3 dL / g;

[0115] ④ The melt index is 5 g / min;

[0116] ⑤ The freezing point is 158 °C;

[0117] ⑥ The yellowness index is 28.

[0118] Example 4

[0119] Add 1000 g of glycolide monomer, 2 g of stannous octoate, and 2.5 g of the compound described in the above formula (1) to the reaction kettle. Heat to 90 °C under normal pressure to completely melt the reactants, and then transfer the melt to a prepolymerization reactor with an absolute pressure of 200 KPa and a temperature of 150 °C, and stay for 2.5 h for prepolymerization reaction; then transfer the obtained prepolymer to a reactor with an absolute pressure of 20 KPa and a temperature of 180 °C, and stay for 2 h for polymerization to obtain a PGA oligomer; continue to transfer the PGA oligomer to a polymerization reactor with an absolute pressure of 2 KPa and a temperature of 215 °C and stay for 1 h for final polymerization reaction to finally obtain a PGA polymer.

[0120] The measurement results of the product polyglycolide polymer are as follows:

[0121] ① The weight-average molecular weight (Mw) is 310,000;

[0122] ② The ratio of weight-average molecular weight to number-average molecular weight (Mw / Mn) is 1.5;

[0123] ③ The intrinsic viscosity is 1.89 dL / g;

[0124] ④ The melt index is 7.2 g / min;

[0125] ⑤ The freezing point is 166 °C;

[0126] ⑥ The yellowness index is 23.

[0127] Example 5

[0128] Add 1000 g of glycolide monomer, 2 g of stannous octoate, and 2.5 g of the compound described in the above formula (1) into the reaction kettle. Heat it to 90 °C under normal pressure to completely melt the reactants, and then transfer the melt to a prepolymerization reactor with an absolute pressure of 200 KPa and a temperature of 130 °C, and stay for 2.5 h for prepolymerization reaction; then transfer the obtained prepolymer to a reactor with an absolute pressure of 20 KPa and a temperature of 180 °C, and stay for 2 h for polymerization to obtain a PGA oligomer; continue to transfer the PGA oligomer to a polymerization reactor with an absolute pressure of 2 KPa and a temperature of 200 °C and stay for 1 h for final polymerization reaction to finally obtain a PGA polymer.

[0129] The measurement results of the product polyglycolide polymer are as follows:

[0130] ① The number-average molecular weight (Mw) is 280,000;

[0131] ② The ratio of weight-average molecular weight to number-average molecular weight (Mw / Mn) is 1.63;

[0132] ③ The intrinsic viscosity is 1.73 dL / g;

[0133] ④ The melt index is 10 g / min;

[0134] ⑤ The freezing point is 177 °C;

[0135] ⑥ The yellowness index is 20.

[0136] Example 6

[0137] The difference between this example and Example 1 is the residence time. Specifically, add 1000 g of glycolide monomer, 2 g of stannous octoate, and 2.5 g of the compound described in the above formula (1) into the reaction kettle. Heat it to 90 °C under normal pressure to completely melt the reactants, and then transfer the melt to a prepolymerization reactor with an absolute pressure of 200 KPa and a temperature of 150 °C, and stay for 6 h for prepolymerization reaction; then transfer the obtained prepolymer to a reactor with an absolute pressure of 20 KPa and a temperature of 180 °C, and stay for 5 h for polymerization to obtain a PGA oligomer; continue to transfer the PGA oligomer to a polymerization reactor with an absolute pressure of 2 KPa and a temperature of 200 °C and stay for 2 h for final polymerization reaction to finally obtain a PGA polymer.

[0138] The measurement results of the product polyglycolide polymer are as follows:

[0139] ① The number-average molecular weight (Mw) is 365,000;

[0140] ② The ratio of weight-average molecular weight to number-average molecular weight (Mw / Mn) is 1.3;

[0141] ③ The intrinsic viscosity is 2.35 dL / g;

[0142] ④The melt index is 4.5 g / min;

[0143] ⑤The freezing point is 158 °C;

[0144] ⑥The yellowness index is 28.

[0145] Example 7

[0146] Add 1000 g of glycolide monomer, 2 g of stannous octoate, and 2.5 g of the compound described in the above formula (1) to the reaction kettle. Heat to 90 °C under normal pressure to completely melt the reactants, and then transport the melt to a prepolymerization reactor with an absolute pressure of 200 KPa and a temperature of 150 °C. Stay for 3 h to carry out the prepolymerization reaction; then transport the obtained prepolymer to a reactor with an absolute pressure of 20 KPa and a temperature of 180 °C. Stay for 3 h to carry out the polymerization to obtain a PGA oligomer; continue to transport the PGA oligomer to a polymerization reactor with an absolute pressure of 2 KPa and a temperature of 200 °C and stay for 1.5 h to carry out the final polymerization reaction to finally obtain a PGA polymer.

[0147] The measurement results of the product polyglycolide polymer are as follows:

[0148] ①The number-average molecular weight (Mw) is 350,000;

[0149] ②The ratio of weight-average molecular weight to number-average molecular weight (Mw / Mn) is 1.23;

[0150] ③The inherent viscosity is 2.3 dL / g;

[0151] ④The melt index is 5.8 g / min;

[0152] ⑤The freezing point is 160 °C;

[0153] ⑥The yellowness index is 27.

[0154] Example 8

[0155] Add 1000 g of glycolide monomer, 2 g of stannous octoate, and 2.5 g of the compound described in the above formula (1) to the reaction kettle. Heat to 90 °C under normal pressure to completely melt the reactants, and then transport the melt to a prepolymerization reactor with an absolute pressure of 200 KPa and a temperature of 150 °C. Stay for 2.5 h to carry out the prepolymerization reaction; then transport the obtained prepolymer to a reactor with an absolute pressure of 20 KPa and a temperature of 180 °C. Stay for 2.5 h to carry out the polymerization to obtain a PGA oligomer; continue to transport the PGA oligomer to a polymerization reactor with an absolute pressure of 2 KPa and a temperature of 200 °C and stay for 1.5 h to carry out the final polymerization reaction to finally obtain a PGA polymer.

[0156] The measurement results of the product polyglycolide polymer are as follows:

[0157] ① The weight-average molecular weight (Mw) is 352,000;

[0158] ② The ratio of weight-average molecular weight to number-average molecular weight (Mw / Mn) is 1.17;

[0159] ③ The inherent viscosity is 2.32 dL / g;

[0160] ④ The melt index is 6 g / min;

[0161] ⑤ The freezing point is 160 °C;

[0162] ⑥ The yellowness index is 27.

[0163] Example 9

[0164] Add 1000 g of glycolide monomer, 2 g of stannous octoate, and 2.5 g of the compound described in the above formula (1) to the reaction kettle. Heat to 90 °C under normal pressure to completely melt the reactants, and then transfer the melt to a prepolymerization reactor with an absolute pressure of 200 KPa and a temperature of 150 °C, and stay for 2 h for prepolymerization reaction; then transfer the obtained prepolymer to a reactor with an absolute pressure of 20 KPa and a temperature of 180 °C, and stay for 2 h for polymerization to obtain a PGA oligomer; continue to transfer the PGA oligomer to a polymerization reactor with an absolute pressure of 2 KPa and a temperature of 200 °C and stay for 1.5 h for final polymerization reaction to finally obtain a PGA polymer.

[0165] The measurement results of the product polyglycolide polymer are as follows:

[0166] ① The weight-average molecular weight (Mw) is 380,000;

[0167] ② The ratio of weight-average molecular weight to number-average molecular weight (Mw / Mn) is 1.12;

[0168] ③ The inherent viscosity is 2.65 dL / g;

[0169] ④ The melt index is 4.6 g / min;

[0170] ⑤ The freezing point is 156 °C;

[0171] ⑥ The yellowness index is 30.

[0172] Example 10

[0173] Add 1000 g of glycolide monomer, 2 g of stannous octoate, and 2.5 g of the compound described in the above formula (1) to the reactor. Heat the reactants to 90 °C under atmospheric pressure until they are completely melted. Then, transfer the melt to a prepolymerization reactor with an absolute pressure of 200 KPa and a temperature of 150 °C, and keep it there for 1.5 h for prepolymerization reaction. Next, transfer the obtained prepolymer to a reactor with an absolute pressure of 20 KPa and a temperature of 180 °C, and keep it there for 1.5 h for polymerization to obtain a PGA oligomer. Continuously transfer the PGA oligomer to a polymerization reactor with an absolute pressure of 2 KPa and a temperature of 200 °C, and keep it there for 1 h for final polymerization reaction to finally obtain a PGA polymer.

[0174] The measurement results of the product polyglycolide polymer are as follows:

[0175] ① The weight-average molecular weight (Mw) is 380,000;

[0176] ② The ratio of weight-average molecular weight to number-average molecular weight (Mw / Mn) is 1.35;

[0177] ③ The intrinsic viscosity is 3.0 dL / g;

[0178] ④ The melt index is 3.5 g / min;

[0179] ⑤ The freezing point is 157 °C;

[0180] ⑥ The yellowness index is 30.

[0181] Example 11

[0182] Add 1000 g of glycolide monomer, 2 g of stannous octoate, and 2.5 g of the compound described in the above formula (1) to the reactor. Heat the reactants to 90 °C under atmospheric pressure until they are completely melted. Then, transfer the melt to a prepolymerization reactor with an absolute pressure of 200 KPa and a temperature of 150 °C, and keep it there for 1 h for prepolymerization reaction. Next, transfer the obtained prepolymer to a reactor with an absolute pressure of 20 KPa and a temperature of 180 °C, and keep it there for 1 h for polymerization to obtain a PGA oligomer. Continuously transfer the PGA oligomer to a polymerization reactor with an absolute pressure of 2 KPa and a temperature of 200 °C, and keep it there for 0.5 h for final polymerization reaction to finally obtain a PGA polymer.

[0183] The measurement results of the product polyglycolide polymer are as follows:

[0184] ① The weight-average molecular weight (Mw) is 310,000;

[0185] ② The ratio of weight-average molecular weight to number-average molecular weight (Mw / Mn) is 1.42;

[0186] ③ The intrinsic viscosity is 1.98 dL / g;

[0187] ④The melt index is 7.5 g / min;

[0188] ⑤The freezing point is 170 °C;

[0189] ⑥The yellowness index is 23.

[0190] Comparative Example 1

[0191] Add 1000 g of glycolide monomer and 2 g of stannous octoate to the reactor, heat to 90 °C under atmospheric pressure to completely melt the reactants, and then transfer the melt to a prepolymerization reactor with an absolute pressure of 200 KPa and a temperature of 150 °C, and stay for 2.5 h for prepolymerization reaction; then transfer the obtained prepolymer to a reactor with an absolute pressure of 20 KPa and a temperature of 180 °C, and stay for 2 h for polymerization to obtain a PGA oligomer; continue to transfer the PGA oligomer to a polymerization reactor with an absolute pressure of 2 KPa and a temperature of 200 °C and stay for 1 h for final polymerization reaction to finally obtain a PGA polymer.

[0192] The measurement results of the product polyglycolide polymer are as follows:

[0193] ①The weight-average molecular weight (Mw) is 12000;

[0194] ②The ratio of weight-average molecular weight to number-average molecular weight (Mw / Mn) is 2.05;

[0195] ③The intrinsic viscosity is 0.38 dL / g;

[0196] ④The melt index is 50 g / min;

[0197] ⑤The freezing point is 220 °C;

[0198] ⑥The yellowness index is 10.

[0199] Comparative Example 2

[0200] Add 1000 g of glycolide monomer, 2 g of stannous octoate and 2.5 g of lauryl alcohol to the reactor, heat to 90 °C under atmospheric pressure to completely melt the reactants, and then transfer the melt to a prepolymerization reactor with an absolute pressure of 200 KPa and a temperature of 150 °C, and stay for 2.5 h for prepolymerization reaction; then transfer the obtained prepolymer to a reactor with an absolute pressure of 20 KPa and a temperature of 180 °C, and stay for 2 h for polymerization to obtain a PGA oligomer; continue to transfer the PGA oligomer to a polymerization reactor with an absolute pressure of 2 KPa and a temperature of 200 °C and stay for 1 h for final polymerization reaction to finally obtain a PGA polymer.

[0201] The measurement results of the product polyglycolide polymer are as follows:

[0202] ①The weight-average molecular weight (Mw) is 130000;

[0203] ② The ratio of weight-average molecular weight to number-average molecular weight (Mw / Mn) is 1.9;

[0204] ③ The intrinsic viscosity is 0.81 dL / g;

[0205] ④ The melt index is 45 g / min.

[0206] ⑤ The freezing point is 200 °C;

[0207] ⑥ The yellowness index is 15.

[0208] Comparative Example 3

[0209] Add 1000 g of glycolide monomer, 2 g of stannous octoate, and 2.5 g of 1,4-butanediol to the reaction kettle, heat to 90 °C at atmospheric pressure to completely melt the reactants, and then transfer the melt to a prepolymerization reactor with an absolute pressure of 200 KPa and a temperature of 150 °C, and stay for 2.5 h for prepolymerization reaction; then transfer the obtained prepolymer to a reactor with an absolute pressure of 20 KPa and a temperature of 180 °C, and stay for 2 h for polymerization to obtain a PGA oligomer; continue to transfer the PGA oligomer to a polymerization reactor with an absolute pressure of 2 KPa and a temperature of 200 °C and stay for 1 h for final polymerization reaction to finally obtain a PGA polymer.

[0210] ① The weight-average molecular weight (Mw) is 15000;

[0211] ② The ratio of weight-average molecular weight to number-average molecular weight (Mw / Mn) is 1.6;

[0212] ③ The intrinsic viscosity is 0.52 dL / g;

[0213] ④ The melt index is 45 g / min;

[0214] ⑤ The freezing point is 200 °C;

[0215] ⑥ The yellowness index is 15.

[0216] Comparative Example 4

[0217] Add 1000 g of glycolide monomer, 2 g of stannous octoate, and 2.5 g of isopropanol to the reaction kettle, heat to 90 °C at atmospheric pressure to completely melt the reactants, and then transfer the melt to a prepolymerization reactor with an absolute pressure of 200 KPa and a temperature of 150 °C, and stay for 2.5 h for prepolymerization reaction; then transfer the obtained prepolymer to a reactor with an absolute pressure of 20 KPa and a temperature of 180 °C, and stay for 2 h for polymerization to obtain a PGA oligomer; continue to transfer the PGA oligomer to a polymerization reactor with an absolute pressure of 2 KPa and a temperature of 200 °C and stay for 1 h for final polymerization reaction to finally obtain a PGA polymer.

[0218] ① The weight-average molecular weight (Mw) is 13,000;

[0219] ② The ratio of weight-average molecular weight to number-average molecular weight (Mw / Mn) is 2.6;

[0220] ③ The intrinsic viscosity is 0.45 dL / g;

[0221] ④ The melt index is 56 g / min.

[0222] ⑤ The freezing point is 220 °C;

[0223] ⑥ The yellowness index is 15.

[0224] The above description of the embodiments is to enable those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative efforts. Therefore, the present invention is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A process for the ring-opening polymerization of glycolide, the process at least comprising the following steps: (1) Pre-polymerize glycolide monomer, catalyst and initiator at a certain temperature and pressure to provide a PGA prepolymer; (2) Polymerize the PGA prepolymer provided in step (1) under reduced pressure to provide a PGA oligomer; (3) Further polymerize the PGA oligomer provided in step (2) under further reduced pressure to obtain a PGA polymer; The initiator includes a compound having the following general formula: wherein, X, R1, and R2 are each independently selected from O, CR a1 R a2 ; R a1 、R a2 、R b1 、R b2 are each independently selected from any one of hydrogen, deuterium, substituted or unsubstituted C1-C30 straight-chain or branched-chain alkyl; R3 is selected from any one of deuterium, halogen, substituted or unsubstituted C1-C30 straight-chain or branched-chain alkyl groups; n1 is selected from integers from 1 to 10; n2 is selected from integers from 1 to 5; n3 is selected from integers from 1 to 5.

2. The process for the ring-opening polymerization of glycolide according to claim 1, characterized in that, In step (1), it includes first melting the glycolide monomer, catalyst and initiator to form a liquid phase, and then carrying out the pre-polymerization reaction of the liquid phase in a first-stage reactor.

3. The process for ring-opening polymerization of glycolide according to claim 1, wherein, In step (1), it further includes any one or more of the following features: A1) In step (1), the catalyst is selected from metal oxides and metal salts; A2) In step (1), the mass of the catalyst is 0.01-2.0 wt% of the mass of the glycolide monomer; A3) In step (1), the mass of the initiator is 0.01-2.0 wt% of the mass of the glycolide monomer; A4) In step (1), the purity of the glycolide monomer is greater than 99%; A5) In step (1), the pressure of the pre-polymerization reaction is 100-500 kPa; A6) In step (1), the temperature of the pre-polymerization reaction is 100-220 °C; A7) In step (1), the time of the pre-polymerization reaction is 1-12 h; A8) In step (1), the weight-average molecular weight of the PGA prepolymer is 1000-10000.

4. The process for ring-opening polymerization of glycolide according to claim 3, wherein The metal oxides are selected from one or more combinations of antimony trioxide, germanium dioxide, titanium dioxide, zinc oxide, tin oxide; the metal salts are selected from one or more combinations of zinc acetate, stannous octanoate, calcium acetate, zinc acetate dihydrate, stannous chloride, stannous chloride dihydrate.

5. The process for ring-opening polymerization of glycolide according to claim 3, wherein, In step (1), the temperature of the pre-polymerization reaction is 100-160 °C.

6. The process for ring-opening polymerization of glycolide according to claim 3, wherein In step (1), the time of the pre-polymerization reaction is 1-6 h.

7. The process for the ring-opening polymerization of glycolide according to claim 1, characterized in that, In step (2), it further includes any one or more of the following features: B1) In step (2), the PGA oligomer provided in step (1) is depressurized to 10-30 kPa; B2) In step (2), the temperature of the polymerization reaction is 110-220 °C; B3) In step (2), the time of the polymerization reaction is 1-10 h; B4) In step (2), the molecular weight of the PGA oligomer is 10000-150000; B5) In step (2), the polymerization reaction of the PGA prepolymer is carried out in a second-stage reactor.

8. The process for ring-opening polymerization of glycolide according to claim 7, wherein In step (2), the temperature of the polymerization reaction is 110-200 °C.

9. The process for the ring-opening polymerization of glycolide according to claim 7, wherein, In step (2), the time of the polymerization reaction is 1-5 h.

10. The process for the ring-opening polymerization of glycolide according to claim 1, wherein In step (3), it further includes any one or more of the following features: C1) In step (3), further reduce the pressure of the PGA oligomer provided in step (2) to 1 - 2 kPa; C2) In step (3), the temperature of the polymerization reaction is 120 - 220 °C; C3) In step (3), the time of the polymerization reaction is 0.5 - 10 h; C4) In step (3), the further polymerization reaction of the PGA oligomer is carried out in a third-stage reactor; C5) In step (3), the molecular weight of the PGA polymer is 10,000 - 380,000.

11. The process for ring-opening polymerization of glycolide according to claim 10, characterized in that, In step (3), the temperature of the polymerization reaction is 130 - 200 °C.

12. The process for the ring-opening polymerization of glycolide according to claim 10, wherein, In step (3), the time of the polymerization reaction is 0.5 - 2 h.

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