A bidentate schiff base catalyst, a preparation method thereof and a preparation method of polyglycolic acid

Abstract

The application provides a double-center Schiff base catalyst, a preparation method of the double-center Schiff base catalyst and a preparation method of polyglycolic acid. The double-center Schiff base catalyst has a structure shown in formula I or formula II, and two active sites exist in the structure. The catalytic activity can be improved through the synergistic coordination between the double metal centers. In the preparation method of the double-center Schiff base catalyst, the preparation of a Schiff base compound and the preparation of the catalyst are completed in a 'one-pot', the purification process of the Schiff base compound is reduced, the production process is greatly simplified, the use of organic solvents is reduced, the yield of the catalyst is improved, and the production cost is reduced. The double-center Schiff base catalyst is used for catalyzing the ring-opening polymerization of glycolide to generate polyglycolic acid. According to gel permeation chromatography analysis, the number average molecular weight of the prepared polyglycolic acid is above 85000 g / mol, and the yield is above 93%.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation technology, specifically relating to a dual-center Schiff base catalyst and its preparation method, and a method for preparing polyglycolic acid. Background Technology

[0002] Polyglycolic acid (PEG) is a synthetic polymer material with good biodegradability and biocompatibility. It possesses excellent processing properties, high mechanical strength and modulus, high solvent resistance, and high gas barrier properties, making it suitable for preparing medical polymer materials (such as surgical sutures and artificial skin). PEG can be decomposed into environmentally friendly compounds by water, microorganisms, and enzymes, and it shows broad application prospects as a biodegradable plastic in packaging materials and degradable films.

[0003] Currently, ring-opening polymerization of glycolide is a feasible process route for preparing high-molecular-weight polyglycolic acid. In the ring-opening polymerization of glycolide, stannous octoate, which has a much higher catalytic activity than other metal catalysts, is generally used as the catalyst. In the commercial production of polyglycolic acid, a faster polymerization rate can improve production efficiency and reduce production costs. Currently, there are two main strategies to increase the polymerization rate: (1) increase the polymerization temperature; however, if only the polymerization temperature is increased, the reaction equilibrium will be disrupted, the depolymerization rate of the product will be increased, the molecular chain growth of the polymer will be severely affected, and this strategy will increase side reactions, leading to an increase in the yellowness index of the product; (2) increase the amount of metal catalyst; however, in the ring-opening polymerization of glycolide, if an excessive amount of catalyst is added to the reaction system, the residual metal compounds in the product will reduce its thermal stability.

[0004] Therefore, a catalyst with high catalytic activity is needed to improve the production efficiency of polyglycolic acid. In recent years, Schiff base catalysts have been widely used due to their high catalytic activity. Currently, there are some reports on the synthesis of Schiff base catalysts. For example, patent CN105131045A discloses a salicylaldehyde Schiff base ligand nickel metal complex and its preparation method. However, the preparation of this complex requires multiple steps, making the production process cumbersome. It also requires the use of organic solvents, causing serious environmental pollution, and the yield of the obtained Schiff base complex is only 47%. Furthermore, there are few reports on the use of Schiff base catalysts for the catalytic preparation of polyglycolic acid. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a dual-center Schiff base catalyst and its preparation method, as well as a method for preparing polyglycolic acid. The dual-center Schiff base catalyst exhibits high catalytic activity, and the preparation method is simple, with a yield exceeding 90%.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a dual-center Schiff base catalyst having the structure shown in Formula I or Formula II:

[0008]

[0009] Wherein, R is the group remaining after removing the glycidyl ether from the diglycidyl ether, and the diglycidyl ether is selected from any one or more of ethylene glycol diglycidyl ether, butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, 1,2-cyclohexanediol diglycidyl ether, resorcinol diglycidyl ether, bisphenol A diglycidyl ether, or bisphenol F diglycidyl ether;

[0010] R1 and R2 are independently selected from hydrogen, halogen, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C1-C6 alkoxy or nitro groups;

[0011] R3 is the group remaining after removing two amino groups and one carboxyl group from a diaminocarboxylic acid, wherein the diaminocarboxylic acid is selected from any one of 2,3-diaminopropionic acid, 2,4-diaminobutyric acid, 2,3-diaminobutyric acid, 2,5-diaminovaleric acid, 3,4-diaminobenzoic acid, or 2,3-diaminobenzoic acid; that is, R3 is selected from...

[0012]

[0013] The R4 is selected from halogens, substituted or unsubstituted C1-C6 alkoxy or ester groups;

[0014] M1 is selected from any one of zinc, cobalt, nickel or tin;

[0015] M2 is selected from any one of aluminum, indium, chromium, iron, manganese, cerium, or yttrium.

[0016] Preferably, R1 and R2 are independently selected from hydrogen, halogen, -CH3, -CH2Cl, -CH2CH3, -CH(CH3)2, -OCH(CH3)2, -C(CH3)3, -OCH3, -OCH2CH3, -OCF3 or -NO2.

[0017] Preferably, the R4 is selected from -OCH3, -OCH2CH3, -OCH(CH3)2, -Cl or -OOCCH3.

[0018] Preferably, the dual-center Schiff base catalyst is selected from any one of the following formulas 1 to 10:

[0019]

[0020]

[0021]

[0022] Secondly, the present invention provides a method for preparing the above-mentioned dual-center Schiff base catalyst, comprising the following steps:

[0023] S1: Reaction of diglycidyl ether and diaminocarboxylic acid yields a tetraamine compound;

[0024] S2: React the tetraamine compound with an excess of the salicylaldehyde monomer shown in formula A to obtain a mixture of Schiff base compound and excess salicylaldehyde monomer.

[0025] The molar ratio of the tetraamine compound to the salicylaldehyde monomer is 1:(4.5-10);

[0026] S3: React the mixture obtained in step S2 with amino alcohol monomers to obtain a mixture of Schiff base compounds and alcohols;

[0027] S4: React the mixture obtained in step S3 with a metal compound to obtain a mixture of a two-center Schiff base catalyst and an alcohol.

[0028] The general formula of the metal compound is M1(R4)2 or M2(R4)3;

[0029] The structural formula of the salicylaldehyde monomer represented by formula A is shown below:

[0030]

[0031] Preferably, the diaminocarboxylic acid is selected from any one or more of 2,3-diaminopropionic acid, 2,4-diaminobutyric acid, 2,3-diaminobutyric acid, 2,5-diaminovaleric acid, 3,4-diaminobenzoic acid, or 2,3-diaminobenzoic acid.

[0032] Preferably, the amino alcohol monomer is selected from any one or more of 2-amino-1-ethanol, 3-amino-1-propanol, 4-amino-1-butanol, 3-amino-1-butanol, 5-amino-1-pentanol, 6-amino-1-hexanol, or 8-amino-1-octanol.

[0033] Preferably, the molar ratio of the diglycidyl ether to the diaminocarboxylic acid is 1:(2-3).

[0034] Preferably, the molar ratio of excess salicylaldehyde monomer to amino alcohol monomer in the mixture obtained in step S2 is 1:(1.1~10).

[0035] Preferably, the molar ratio of Schiff base compound to metal compound in the mixture obtained in step S3 is 1:(2-3).

[0036] Preferably, the reaction temperature in step S1 is 140–220°C, and the reaction time is 1–24 h.

[0037] Preferably, the temperature of each reaction in steps S2 and S3 is 20–100°C, and the time is 2–48 h.

[0038] Preferably, the reaction temperature in step S4 is 30–120°C, and the reaction time is 2–48 h.

[0039] Thirdly, the present invention provides a method for preparing polyglycolic acid, comprising the following steps:

[0040] In an inert atmosphere, glycolide and an optional epoxy compound are reacted in the presence of a catalyst and an initiator to obtain polyglycolic acid;

[0041] The catalyst is the dual-center Schiff base catalyst involved in the above technical solution; the initiator is the alcohol involved in the above technical solution.

[0042] Preferably, the molar ratio of the epoxy compound to glycolide is (0-10):(90-100).

[0043] Preferably, the total mass ratio of the catalyst and initiator to the mass of glycolide is 1:(25-2500).

[0044] Preferably, the reaction temperature is 120–240°C and the reaction time is 2–24 hours.

[0045] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0046] This invention provides a bicentric Schiff base catalyst with the structure shown in Formula I or Formula II. It can be seen that the catalyst structure contains two active sites. Through the synergistic coordination between the bimetallic centers, the catalytic activity of the original single-center catalyst can be improved. This invention uses it as a catalyst for the ring-opening polymerization of glycolide to produce polyglycolic acid. Gel permeation chromatography analysis shows that the prepared polyglycolic acid has a high number-average molecular weight, exceeding 85,000 g / mol, and a high yield, exceeding 93%.

[0047] Furthermore, in the preparation method of the above-mentioned dual-center Schiff base catalyst provided by the present invention, a tetraamine compound with excellent solubility is obtained through the addition reaction of diglycidyl ether and diaminocarboxylic acid. Compared with the prior art, this synthesis method is simple, the process is greatly shortened, and no solvent is required, thus reducing production costs. Then, in the reaction with salicylaldehyde monomers, due to the excellent solubility of the tetraamine compound of the present invention, the concentration of the reaction components can be increased, the use of organic solvents can be reduced, which is beneficial to industrialization. Compared with the prior art, the salicylaldehyde monomer added in the present invention is an excess monomer, and the prepared Schiff base compound does not require purification. By adding an amino alcohol and reacting with the excess salicylaldehyde monomer, a product containing hydroxyl groups (i.e., an alcohol) is obtained, which can be directly used as an initiator for glycolide polymerization. In summary, in the present invention, the preparation of the Schiff base compound and the preparation of the dual-center Schiff base catalyst are completed in a "one-pot" process, reducing the purification process of the Schiff base compound, greatly simplifying the production process, reducing the use of organic solvents, increasing the yield of the dual-center Schiff base catalyst to over 90%, and reducing production costs. Detailed Implementation

[0048] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0049] To address the problem of the lack of effective methods to improve the production efficiency of polyglycolic acid in existing technologies, this invention provides a dual-center Schiff base catalyst having the structure shown in Formula I or Formula II:

[0050]

[0051] Wherein, R is the group remaining after removing the glycidyl ether from the diglycidyl ether, and the diglycidyl ether is selected from any one or more of ethylene glycol diglycidyl ether, butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, 1,2-cyclohexanediol diglycidyl ether, resorcinol diglycidyl ether, bisphenol A diglycidyl ether, or bisphenol F diglycidyl ether;

[0052] R1 and R2 are independently selected from hydrogen, halogen, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C1-C6 alkoxy or nitro groups;

[0053] R3 is the group remaining after removing two amino groups and one carboxyl group from a diaminocarboxylic acid, wherein the diaminocarboxylic acid is selected from any one of 2,3-diaminopropionic acid, 2,4-diaminobutyric acid, 2,3-diaminobutyric acid, 2,5-diaminovaleric acid, 3,4-diaminobenzoic acid, or 2,3-diaminobenzoic acid; that is, R3 is selected from...

[0054]

[0055] The R4 is selected from halogens (F, Cl, Br, I), substituted or unsubstituted C1-C6 alkoxy or ester groups;

[0056] M1 is selected from any one of zinc, cobalt, nickel or tin;

[0057] M2 is selected from any one of aluminum, indium, chromium, iron, manganese, cerium, or yttrium.

[0058] In some embodiments of the invention, the dual-center Schiff base catalyst has the structure shown in Formula I or Formula II, wherein R1 and R2 are independently preferably selected from hydrogen, halogen, -CH3, -CH2Cl, -CH2CH3, -CH(CH3)2, -OCH(CH3)2, -C(CH3)3, -OCH3, -OCH2CH3, -OCF3, or -NO2; and R3 is selected from... The R4 is preferably selected from -OCH3, -OCH2CH3, -OCH(CH3)2, -Cl or -OOCCH3.

[0059] In this invention, the substituted group in the above-mentioned "substituted or unsubstituted" can be selected from either halogen or methyl.

[0060] In some specific embodiments of the present invention, the dual-center Schiff base catalyst is selected from any one of the following formulas 1 to 10:

[0061]

[0062]

[0063]

[0064] This invention also provides a method for preparing the above-mentioned dual-center Schiff base catalyst, comprising the following steps:

[0065] S1: Reaction of diglycidyl ether and diaminocarboxylic acid yields a tetraamine compound;

[0066] S2: React the tetraamine compound with an excess of the salicylaldehyde monomer shown in formula A to obtain a mixture of Schiff base compound and excess salicylaldehyde monomer.

[0067] The molar ratio of the tetraamine compound to the salicylaldehyde monomer is 1:(4.5-10);

[0068] S3: React the mixture obtained in step S2 with amino alcohol monomers to obtain a mixture of Schiff base compounds and alcohols;

[0069] S4: React the mixture obtained in step S3 with a metal compound to obtain a mixture of a two-center Schiff base catalyst and an alcohol.

[0070] The general formula of the metal compound is M1(R4)2 or M2(R4)3;

[0071] The structural formula of the salicylaldehyde monomer represented by formula A is shown below:

[0072]

[0073] According to the present invention, diglycidyl ether and diaminocarboxylic acid are first reacted to obtain a tetraamine compound. The selection of the diglycidyl ether is as described in the relevant content of the above technical solution and will not be repeated here. The diaminocarboxylic acid is selected from any one or more of 2,3-diaminopropionic acid, 2,4-diaminobutyric acid, 2,3-diaminobutyric acid, 2,5-diaminovaleric acid, 3,4-diaminobenzoic acid, or 2,3-diaminobenzoic acid. In some embodiments of the present invention, the diglycidyl ether and diaminocarboxylic acid are preferably reacted at a molar ratio of 1:(2-3), more preferably 1:2.5, at 140-220°C for 1-24 h, and more preferably at 150-200°C for 5-12 h. In this reaction step, the diglycidyl ether and diaminocarboxylic acid undergo an addition reaction to obtain the tetraamine compound, and the reaction is preferably carried out under stirring conditions.

[0074] After obtaining the tetraamine compound, according to the present invention, it is preferable to react the tetraamine compound with an excess of the salicylaldehyde monomer shown in Formula A above to obtain a mixture of Schiff base compound and excess salicylaldehyde monomer. In this reaction step, the tetraamine compound undergoes an addition reaction with the excess salicylaldehyde monomer, and due to the excess salicylaldehyde monomer, a mixture of Schiff base compound and excess salicylaldehyde monomer is finally obtained. In some embodiments of the present invention, the salicylaldehyde monomer may specifically be selected from 3-bromosalicylicalaldehyde, 3,5-dibromosalicylicalaldehyde, 5-fluorosalicylicalaldehyde, 3-chlorosalicylicalaldehyde, 5-chlorosalicylicalaldehyde, 3,5-dichlorosalicylicalaldehyde, 5-iodosalicylicalaldehyde, 3-bromo-5-chlorosalicylicalaldehyde, 3,5-di-tert-butylsalicylicalaldehyde, 5-methylsalicylicalaldehyde, 5-nitrosalicylicalaldehyde, 5-(trifluoromethoxy)salicylicalaldehyde, 5 The tetraamine compound is selected from any one or more of the following: 3-bromo-3-nitrosalicylaldehyde, 3-bromo-5-nitrosalicylaldehyde, 3-methoxysalicylaldehyde, 5-fluoro-3-methylsalicylaldehyde, 3-methylsalicylaldehyde, 3-tert-butylsalicylaldehyde, 3,5-diiodosalicylaldehyde, 3-chloromethyl-5-nitrosalicylaldehyde, 3-chloro-5-fluorosalicylaldehyde, 3-ethoxysalicylaldehyde, 5-bromo-3-fluorosalicylaldehyde, or 5-bromo-3-methoxysalicylaldehyde. In some embodiments of the present invention, the reaction of the tetraamine compound with the salicylaldehyde monomer is preferably carried out in the presence of a solvent, which is an organic solvent well known to those skilled in the art, specifically selected from any one or more of ethanol, isopropanol, butanol, pentanol, hexanol, heptanol, octanol, benzene, toluene, tetrahydrofuran, dichloromethane, or trichloromethane. In some embodiments of the present invention, the reaction is preferably carried out at 20–100°C for 2–48 h, more preferably at 40–70°C for 5–30 h, with the molar ratio of the tetraamine compound to an excess of the salicylaldehyde monomer represented by Formula A being 1:(4.5–10), more preferably 1:(5–8). The reaction is preferably carried out under stirring conditions.

[0075] Because the salicylaldehyde monomer is in excess in step S2, the product obtained is a mixture of Schiff base compound and excess salicylaldehyde monomer. However, this invention differs from existing technologies by not removing the excess salicylaldehyde monomer through cumbersome post-processing. Instead, in step S3, an amino alcohol monomer is introduced and reacted with the mixture obtained in step S2. This step primarily involves the amino alcohol monomer reacting with the excess salicylaldehyde monomer to generate an alcohol that can initiate the ring-opening polymerization of glycolide, ultimately yielding a mixture of Schiff base compound and alcohol. The amino alcohol monomer is selected from any one or more of 2-amino-1-ethanol, 3-amino-1-propanol, 4-amino-1-butanol, 3-amino-1-butanol, 5-amino-1-pentanol, 6-amino-1-hexanol, or 8-amino-1-octanol. In some embodiments of the present invention, the reaction of the mixture obtained in step S3 with the amino alcohol monomer is preferably carried out in the presence of a solvent selected from any one or more of methanol, ethanol, isopropanol, butanol, pentanol, hexanol, heptanol, octanol, benzene, toluene, tetrahydrofuran, dichloromethane, or trichloromethane. The solvent may be the same as or different from the solvent used in step S2, but is preferably the same. In some embodiments of the present invention, the reaction is preferably carried out at 20–100°C for 2–48 h, more preferably at 40–70°C for 5–30 h, with a molar ratio of excess salicylaldehyde monomer to amino alcohol monomer of 1:(1.1–10), more preferably 1:(3–5). The reaction is preferably carried out under stirring conditions.

[0076] Then, according to the present invention, the mixture obtained in step S3 is preferably reacted with a metal compound to obtain a mixture of a two-center Schiff base catalyst and an alcohol. The general formula of the metal compound may be M1(R4)2 or M2(R4)3. In some embodiments of the present invention, the metal compound may be selected from any one or more of aluminum isopropoxide, aluminum ethoxylate, dibutyltin dichloride, stannous chloride, indium isopropoxide, indium chloride, zinc isopropoxide, zinc chloride, ferric ethoxylate, ferric isopropoxide, ferric chloride, cobalt acetate, nickel acetate, manganese acetate, chromium acetate, cerium acetate, cerium n-butoxide, yttrium isopropoxide, and yttrium chloride. The present invention does not impose any particular limitation on the source of the above metal compound; commercially available products are acceptable. In some embodiments of the present invention, the reaction of the mixture obtained in step S3 with the metal compound is also preferably carried out in the presence of a solvent, which may be selected from any one or more of methanol, ethanol, isopropanol, butanol, pentanol, hexanol, heptanol, octanol, benzene, toluene, tetrahydrofuran, dichloromethane, or trichloromethane. The solvent may be the same as or different from the solvent used in steps S2 and S3, but is preferably the same. In some embodiments of the present invention, the reaction is preferably carried out at 30–120°C for 2–48 h, more preferably at 40–80°C for 5–30 h, with a molar ratio of Schiff base compound to metal compound of 1:(2–3), more preferably 1:2.5. The reaction is preferably carried out under stirring conditions.

[0077] In some preferred embodiments of the present invention, after the reaction in step S4 is completed, the solvent is preferably removed by vacuuming. The vacuum degree during vacuuming is preferably 500 Pa. Vacuuming is stopped when no more liquid distills out, and finally a dry mixture of dual-center Schiff base catalyst and alcohol is obtained.

[0078] In the preparation method of the above-mentioned dual-center Schiff base catalyst provided by the present invention, a tetraamine compound with excellent solubility is obtained through the addition reaction of diglycidyl ether and diaminocarboxylic acid. Compared with the prior art, this synthesis method is simple, the process is greatly shortened, and no solvent is required, thus reducing production costs. Then, in the reaction with salicylaldehyde monomers, due to the excellent solubility of the tetraamine compound of the present invention, the concentration of the reaction components can be increased, reducing the use of organic solvents and facilitating industrialization. Compared with the prior art, the salicylaldehyde monomer added in the present invention is an excess monomer, and the prepared Schiff base compound does not require purification. By adding an amino alcohol and reacting with the excess salicylaldehyde monomer, a product containing hydroxyl groups (i.e., an alcohol) is obtained, which can be directly used as an initiator for glycolide polymerization. In summary, in the present invention, the preparation of the Schiff base compound and the preparation of the dual-center Schiff base catalyst are completed in a "one-pot" process, reducing the purification process of the Schiff base compound, greatly simplifying the production process, reducing the use of organic solvents, and lowering production costs.

[0079] Calculations show that the yield of the dual-center Schiff base catalyst obtained by the above preparation method is high, exceeding 90%.

[0080] The present invention also provides the application of a mixture of a dual-center Schiff base catalyst prepared by the above preparation method and an alcohol in the ring-opening polymerization of glycolide to prepare polyglycolic acid.

[0081] This invention also provides a method for preparing polyglycolic acid, comprising the following steps:

[0082] In an inert atmosphere, glycolide and an optional epoxy compound are reacted in the presence of a catalyst and an initiator to obtain polyglycolic acid.

[0083] The catalyst is a dual-center Schiff base catalyst prepared according to the above preparation method, and the initiator is an alcohol substance prepared according to the above preparation method. The epoxide compound is selected from any one or more of the following: propylene oxide, butane oxide, 1,2-epoxycyclopentane, 1,2-epoxycyclohexane, 1,2-epoxyoctane, 1,2-epoxydodecane, 1,2-epoxytetradecane, 1,2-epoxyhexadecane, allyl glycidyl ether, styrene oxide, isopropyl glycidyl ether, tert-butyl glycidyl ether, octyl glycidyl, phenyl glycidyl ether, 2-toluene glycidyl ether, or benzyl glycidyl ether.

[0084] This invention does not impose any particular limitation on the inert atmosphere; nitrogen or argon atmospheres, well-known to those skilled in the art, can be used. In some embodiments of this invention, the total mass ratio of the catalyst and initiator to the glycolide is 1:(25-2500), preferably 1:(50-2000), and more preferably 1:(100-1000). It should be noted that the term "optional epoxide compound" refers to whether or not an epoxide compound may be added. Its addition depends on the metal element in the catalyst. For example, when the metal element is aluminum, tin, or indium, the amount of epoxide compound added is 0; when the metal element is zinc, iron, cobalt, nickel, manganese, chromium, cerium, or yttrium, the amount of epoxide compound added is not 0. In this invention, the preferred molar ratio of the epoxide compound to glycolide is (0-10):(90-100), where (0-10) can be 0, specifically 0:100, 1:99, 2:98, 3:97, 4:96, 5:95, 6:94, 7:93, 8:92, 9:91, or 10:90, etc. In some embodiments of this invention, the glycolide and optionally the epoxide compound are preferably reacted at 120-240°C for 2-24 hours in the presence of a catalyst and an initiator, more preferably at 150-200°C for 5-12 hours, according to the above ratio. The reaction is preferably carried out under stirring.

[0085] In some embodiments of the present invention, it is preferable that after the reaction is completed, the temperature is raised to 230-240°C, and the unreacted monomers in the system are removed by vacuuming at a pressure of 100 Pa to obtain polyglycolic acid.

[0086] Calculations showed that the polyglycolic acid prepared using the above method had a high yield, exceeding 93%. Furthermore, gel permeation chromatography analysis revealed that the prepared polyglycolic acid had a high number-average molecular weight, exceeding 85,000 g / mol.

[0087] It should be noted that the point values ​​listed above in this invention are merely illustrative and not limited to these values. Other point values ​​within the range are also applicable and will not be elaborated upon here. To further illustrate this invention, the following examples provide a detailed description. The experimental materials used in the following examples of this invention are all commercially available products. The number-average molecular weight of polyglycolic acid in the following examples was determined by gel permeation chromatography (GPC) using a Waters 410 HPLC pump. The mobile phase was a solution of hexafluoroisopropanol containing 5 mM sodium trifluoroacetate, the temperature was 35°C, the flow rate was 1 mL / min, and a monodisperse polystyrene standard was used for universal correction.

[0088] Example 1

[0089] This embodiment provides a polyglycolic acid, the preparation method of which is as follows:

[0090] S1: Add 0.1 mol (20.2 g) of butanediol diglycidyl ether and 0.2 mol (20.8 g) of 2,3-diaminopropionic acid to a 2 L round-bottom flask, mix and stir, and heat to 140 °C. After 6 h, cool to 50 °C, add 400 mL of toluene and stir to dissolve. Then add the solution at a rate of 5 mL / min to 800 mL of toluene solution containing 0.6 mol (140 g) of 3,5-di-tert-butylsalicylaldehyde, and mix and stir at 50 °C for 8 h. Then, 100 mL of a toluene solution containing 0.3 mol (18.3 g) of aminoethanol was added, and the reaction was continued at 45 °C for 12 h to obtain a Schiff base compound and alcohol mixture solution. This solution was then mixed with 500 mL of a toluene solution containing 0.2 mol (40.8 g) of aluminum isopropoxide, and the temperature was raised to 90 °C. After 24 h, the toluene was removed by vacuum at a vacuum degree of 500 Pa. When no more liquid was distilled off, 197.7 g of the Schiff aluminum catalyst and alcohol mixture shown in Formula 1 was obtained.

[0091] The theoretical mass of the Schiff base aluminum catalyst was calculated to be 151.4 g, and the theoretical mass of the alcohol was 65.1 g.

[0092] The obtained products were analyzed using nuclear magnetic resonance (400 MHz, CDCl3). Based on the characteristic chemical shifts of the Schiff aluminum catalyst and the alcohol, the actual mass of the Schiff aluminum catalyst was 139.4 g, and the yield was calculated to be 92% by dividing the actual mass of the catalyst by the theoretical mass. The actual mass of the alcohol was 58.3 g, and the yield was calculated to be 89.7% by dividing the actual mass of the alcohol by the theoretical mass.

[0093] S2: The reaction flask was repeatedly evacuated and purged with nitrogen. 2 mol (232 g) of glycolide and 1.08 g of the mixture obtained in step S1 were added to the reaction flask in sequence. The mixture was stirred and the temperature was rapidly raised to 170 °C. After 12 h, the temperature was raised to 230 °C and the unreacted monomers in the system were removed by evacuation. The pressure was 100 Pa. 218.1 g of polyglycolic acid was obtained, with a yield of 94%.

[0094] The polyglycolic acid obtained in this invention was analyzed by gel permeation chromatography, and the number average molecular weight of polyglycolic acid was determined to be 95,000 g / mol.

[0095] Example 2

[0096] This embodiment provides a polyglycolic acid, the preparation method of which is as follows:

[0097] S1: Add 0.12 mol (20.9 g) of ethylene glycol diglycidyl ether and 0.24 mol (25 g) of 2,3-diaminopropionic acid to a 2 L round-bottom flask, mix and stir, and heat to 145 °C. After 5.5 h, cool to 45 °C, add 250 mL of toluene to dissolve, and then add at a rate of 3 mL / min to 750 mL of toluene solution containing 0.6 mol (167.4 g) of 3,5-dibromosalicylic acid. Mix and stir at 40 °C for 10 h, and then add 0.2 mol (12.2 g) of aminoethanol. A 50 mL toluene solution was added and reacted at 45 °C for 8 h to obtain a Schiff base compound and alcohol mixture solution. This solution was then mixed with a 300 mL toluene solution containing 0.24 mol (49 g) aluminum isopropoxide. The mixture was heated to 85 °C and reacted for 36 h. Toluene was removed by vacuum at a vacuum degree of 500 Pa. When no more liquid distilled off, 222.7 g of the Schiff base aluminum catalyst and alcohol mixture shown in Formula 2 was obtained. The theoretical mass of the Schiff base aluminum catalyst was calculated to be 200.4 g, and the theoretical mass of the alcohol was 45.7 g.

[0098] The obtained products were analyzed using nuclear magnetic resonance (400 MHz, CDCl3). The actual mass of the Schiff base aluminum catalyst was calculated to be 182.4 g, and the yield was 91% by dividing the actual mass of the Schiff base aluminum catalyst by the theoretical mass. The actual mass of the alcohol was 40.3 g, and the yield was 88.2% by dividing the actual mass of the alcohol by the theoretical mass.

[0099] S2: The reaction flask was repeatedly evacuated and purged with nitrogen. 2 mol (232 g) of glycolide and 2.46 g of the mixture obtained in step S1 were added to the reaction flask in sequence. The mixture was stirred and the temperature was rapidly raised to 175 °C. After 10 h, the temperature was raised to 235 °C and the unreacted monomers in the system were removed by evacuation. The pressure was 100 Pa. 217.2 g of polyglycolic acid was obtained, with a yield of 93.6%.

[0100] The polyglycolic acid obtained in this invention was analyzed by gel permeation chromatography, and the number average molecular weight of polyglycolic acid was determined to be 93,000 g / mol.

[0101] Example 3

[0102] S1: Add 0.14 mol (32.2 g) of 1,6-hexanediol diglycidyl ether and 0.28 mol (33 g) of 2,4-diaminobutyric acid to a 3 L round-bottom flask, mix and stir, and heat to 150 °C. After 5 h, cool to 30 °C, add 450 mL of toluene and stir to dissolve. Then add the solution at a rate of 5 mL / min to 900 mL of toluene containing 0.65 mol (130.7 g) of 3-bromosalicylic acid. Mix and stir at 45 °C for 12 hours. After h, 60 mL of a toluene solution containing 0.15 mol (11.3 g) aminopropanol was added, and the reaction was continued at 40 °C for 10 h to obtain a Schiff base compound and alcohol mixture solution. Then, it was mixed with 600 mL of a toluene solution containing 0.28 mol (66.3 g) tin acetate, heated to 85 °C, and after 48 h, the toluene was removed by vacuum at a vacuum degree of 500 Pa. When no more liquid was distilled off, 218.4 g of the Schiff base tin catalyst and alcohol mixture shown in Formula 3 was obtained.

[0103] The theoretical mass of the Schiff base tin catalyst was calculated to be 210.6 g, and the theoretical mass of the alcohol was 29.4 g.

[0104] The obtained products were analyzed using nuclear magnetic resonance (400 MHz, CDCl3). Based on the characteristic chemical shifts of the Schiff base tin catalyst and the alcohol, the actual mass of the Schiff base tin catalyst was 192.7 g, and the yield was calculated to be 91.1% by dividing the actual mass of the Schiff base tin catalyst by the theoretical mass. The actual mass of the alcohol was 25.7 g, and the yield was calculated to be 87.4% by dividing the actual mass of the alcohol by the theoretical mass.

[0105] S2: The reaction flask was repeatedly evacuated and purged with nitrogen. 2 mol (232 g) of glycolide and 2.4 g of the mixture obtained in step S1 were added to the reaction flask in sequence. The mixture was stirred and the temperature was rapidly raised to 180 °C. After 9 h, the temperature was raised to 240 °C and the unreacted monomers in the system were removed by evacuation. The pressure was 100 Pa. 219.2 g of polyglycolic acid was obtained, with a yield of 94.5%.

[0106] The polyglycolic acid obtained in this invention was analyzed by gel permeation chromatography, and the number average molecular weight of polyglycolic acid was determined to be 92000 g / mol.

[0107] Example 4

[0108] S1: Add 0.12 mol (24.2 g) of butanediol diglycidyl ether and 0.24 mol (28.3 g) of 2,4-diaminobutyric acid to a 3 L round-bottom flask, mix and stir, and heat to 155 °C. After 4.5 h, cool to 35 °C, add 300 mL of toluene to dissolve, and then add at a rate of 8 mL / min to 850 mL of toluene solution containing 0.55 mol (135.3 g) of 3-bromo-5-nitrosalicylic acid. Mix and stir at 35 °C. After stirring for 15 hours, 70 mL of a toluene solution containing 0.2 mol (15 g) aminopropanol was added, and the reaction was continued at 45 °C for 8 hours to obtain a Schiff base compound and alcohol mixture solution. Then, it was mixed with 350 mL of a toluene solution containing 0.24 mol (45.8 g) ethoxy iron, heated to 85 °C, and after 36 hours, the toluene was removed by vacuum at a vacuum degree of 500 Pa. When no more liquid was distilled off, 204.5 g of the Schiff base iron catalyst and alcohol mixture shown in Formula 4 was obtained.

[0109] The theoretical mass of the Schiff base iron catalyst was calculated to be 194.8 g, and the theoretical mass of the alcohol was 32.2 g.

[0110] The obtained products were analyzed using nuclear magnetic resonance (400 MHz, CDCl3). Based on the characteristic chemical shifts of the Schiff base iron catalyst and the alcohol, the actual mass of the Schiff base iron catalyst was 176.3 g, and the yield was calculated to be 90.5% by dividing the actual mass of the Schiff base iron catalyst by the theoretical mass. The actual mass of the alcohol was 28.2 g, and the yield was calculated to be 87.6% by dividing the actual mass of the alcohol by the theoretical mass.

[0111] S2: The reaction flask was repeatedly evacuated and purged with nitrogen. 2 mol (232 g) of glycolide, 0.02 mol (2.32 g) of isopropyl glycidyl ether and 2.27 g of the mixture obtained in step S1 were added to the reaction flask in sequence. The mixture was stirred and the temperature was rapidly raised to 185 °C. After 8 h, the temperature was raised to 235 °C, and the unreacted monomers in the system were removed by evacuation at a pressure of 100 Pa. 216.5 g of polyglycolic acid was obtained, with a yield of 93.3%.

[0112] The polyglycolic acid obtained in this invention was analyzed by gel permeation chromatography, and the number average molecular weight of polyglycolic acid was determined to be 102000 g / mol.

[0113] Example 5

[0114] S1: Add 0.14 mol (30.2 g) neopentyl glycol diglycidyl ether and 0.28 mol (33 g) 2,3-diaminobutyric acid to a 3 L round-bottom flask, mix and stir, and heat to 180 °C. After 2 h, cool to 30 °C, add 500 mL of toluene and stir to dissolve. Then add the solution at a rate of 6 mL / min to 700 mL of toluene solution containing 0.7 mol (133.7 g) 3,5-dichlorosalicylaldehyde. Mix and stir at 40 °C for 1 hour. After 8 hours, 55 mL of a toluene solution containing 0.2 mol (17.8 g) of aminobutanol was added, and the reaction was continued at 50 °C for 7 hours to obtain a Schiff base compound and alcohol mixture solution. This solution was then mixed with 400 mL of a toluene solution containing 0.28 mol (51.2 g) of zinc acetate, and the temperature was raised to 60 °C. After 20 hours, the toluene was removed by vacuum at a vacuum degree of 500 Pa. When no more liquid was distilled off, 211.5 g of the Schiff base zinc catalyst and alcohol mixture shown in Formula 5 was obtained.

[0115] The theoretical mass of the Schiff base zinc catalyst was calculated to be 188.4 g, and the theoretical mass of the alcohol was 44.5 g.

[0116] The obtained products were analyzed using nuclear magnetic resonance (400 MHz, CDCl3). Based on the characteristic chemical shifts of the Schiff base zinc catalyst and the alcohol, the actual mass of the Schiff base zinc catalyst was 172 g, and the yield was calculated to be 91.3% by dividing the actual mass of the Schiff base zinc catalyst by the theoretical mass. The actual mass of the alcohol was 39.5 g, and the yield was calculated to be 88.8% by dividing the actual mass of the alcohol by the theoretical mass.

[0117] S2: The reaction flask was repeatedly evacuated and purged with nitrogen. 2 mol (232 g) of glycolide, 0.02 mol (2.6 g) of tert-butyl glycidyl ether and 2.33 g of the mixture obtained in step S1 were added to the reaction flask in sequence. The mixture was stirred and the temperature was rapidly raised to 180 °C. After 7 h, the temperature was raised to 240 °C, and the unreacted monomers in the system were removed by evacuation at a pressure of 100 Pa. 216 g of polyglycolic acid was obtained, with a yield of 93.1%.

[0118] The polyglycolic acid obtained in this invention was analyzed by gel permeation chromatography, and the number average molecular weight of polyglycolic acid was determined to be 94,000 g / mol.

[0119] Example 6

[0120] S1: 0.1 mol (22.2 g) resorcinol diglycidyl ether and 0.2 mol (23.6 g) 2,3-diaminobutyric acid were added to a 3 L round-bottom flask, mixed and stirred, and heated to 185 °C. After 1.5 h, the mixture was cooled to 35 °C, and 550 mL of toluene was added and stirred to dissolve. Then, the solution was added at a rate of 5 mL / min to 650 mL of toluene solution containing 0.5 mol (68 g) 3-methylsalicylaldehyde. The mixture was stirred at 45 °C for 16 h, and then 0.15 mol (13.4 g) aminobutyric acid was added. An 80 mL toluene solution of an alcohol was reacted at 55 °C for 6 h to obtain a Schiff base compound and alcohol mixture solution. This solution was then mixed with a 450 mL toluene solution of 0.2 mol (40.8 g) aluminum isopropoxide. The mixture was heated to 85 °C and reacted for 24 h. Toluene was removed under vacuum at a vacuum degree of 500 Pa. When no more liquid distilled off, 132.3 g of the Schiff base aluminum catalyst and alcohol mixture (as shown in Formula 6) was obtained. The theoretical mass of the Schiff base aluminum catalyst was calculated to be 117.4 g, and the theoretical mass of the alcohol was 27 g.

[0121] The obtained products were analyzed using nuclear magnetic resonance (400 MHz, CDCl3). Based on the characteristic chemical shifts of the Schiff base aluminum catalyst and the alcohol, the actual mass of the Schiff base aluminum catalyst was 108.2 g, and the yield was calculated to be 92.2% by dividing the actual mass of the Schiff base aluminum catalyst by the theoretical mass. The actual mass of the alcohol was 24.1 g, and the yield was calculated to be 89.3% by dividing the actual mass of the alcohol by the theoretical mass.

[0122] S2: The reaction flask was repeatedly evacuated and purged with nitrogen. 2 mol (232 g) of glycolide and 1.5 g of the mixture obtained in step S1 were added to the reaction flask in sequence. The mixture was stirred and the temperature was rapidly raised to 185 °C. After 6 h, the temperature was raised to 235 °C and the unreacted monomers in the system were removed by evacuation. The pressure was 100 Pa. 219.9 g of polyglycolic acid was obtained, with a yield of 94.8%.

[0123] The polyglycolic acid obtained in this invention was analyzed by gel permeation chromatography, and the number average molecular weight of polyglycolic acid was found to be 90,000 g / mol.

[0124] Example 7

[0125] S1: 0.13 mol (29.9 g) of 1,2-cyclohexanediol diglycidyl ether and 0.26 mol (34.3 g) of 2,5-diaminopentanoic acid were added to a 3 L round-bottom flask, mixed and stirred, and heated to 160 °C. After 4 h, the mixture was cooled to 40 °C, and 600 mL of toluene was added and stirred to dissolve. Then, the solution was added at a rate of 10 mL / min to 950 mL of toluene solution containing 0.6 mol (73.2 g) of salicylaldehyde. The mixture was stirred at 50 °C for 12 h, and then 0.2 mol (20.6 g) of aminopentanol was added. A 120 mL toluene solution was added and reacted at 60 °C for 5 h to obtain a Schiff base compound and alcohol mixture solution. This solution was then mixed with 180 mL toluene solution containing 0.26 mol (42.1 g) aluminum ethoxylate. The mixture was heated to 85 °C and reacted for 8 h. Toluene was removed under vacuum at a vacuum degree of 500 Pa. When no more liquid distilled off, 162.2 g of the Schiff base aluminum catalyst and alcohol mixture shown in Formula 7 was obtained. The theoretical mass of the Schiff base aluminum catalyst was calculated to be 146.3 g, and the theoretical mass of the alcohol was 30.4 g.

[0126] The obtained products were analyzed using nuclear magnetic resonance (400 MHz, CDCl3). Based on the characteristic chemical shifts of the Schiff base aluminum catalyst and the alcohol, the actual mass of the Schiff base aluminum catalyst was 135.3 g, and the yield was calculated to be 92.5% by dividing the actual mass of the Schiff base aluminum catalyst by the theoretical mass. The actual mass of the alcohol was 26.9 g, and the yield was calculated to be 88.5% by dividing the actual mass of the alcohol by the theoretical mass.

[0127] S2: The reaction flask was repeatedly evacuated and purged with nitrogen. 2 mol (232 g) of glycolide and 1.77 g of the mixture obtained in step S1 were added to the reaction flask in sequence. The mixture was stirred and the temperature was rapidly raised to 190 °C. After 5 h, the temperature was raised to 230 °C and the unreacted monomers in the system were removed by evacuation. The pressure was 100 Pa. 220.4 g of polyglycolic acid was obtained, with a yield of 95%.

[0128] The polyglycolic acid obtained in this invention was analyzed by gel permeation chromatography, and the number average molecular weight of polyglycolic acid was determined to be 92000 g / mol.

[0129] Example 8

[0130] S1: 0.16 mol (36.8 g) of 1,6-hexanediol diglycidyl ether and 0.32 mol (42.2 g) of 2,5-diaminovalerate were added to a 3 L round-bottom flask, mixed and stirred, and heated to 165 °C. After 3.5 h, the mixture was cooled to 45 °C, and 650 mL of toluene was added and stirred to dissolve. Then, the solution was added at a rate of 6 mL / min to 600 mL of toluene solution containing 0.75 mol (114 g) of 3-methoxysalicylaldehyde. The mixture was stirred at 55 °C for 10 h, and then 0.25 mol (25.8 g) of the solution was added. A 150 mL toluene solution of aminopentanol was reacted at 65 °C for 4 h to obtain a Schiff base compound and alcohol mixture solution. This solution was then mixed with a 250 mL toluene solution of 0.32 mol (56.6 g) cobalt acetate. The mixture was heated to 90 °C and subjected to vacuum at 500 Pa for 18 h. When no more liquid distilled off, 220.1 g of the Schiff base cobalt catalyst and alcohol mixture (as shown in Formula 8) was obtained. The theoretical mass of the Schiff base cobalt catalyst was calculated to be 195.2 g, and the theoretical mass of the alcohol was 42.5 g.

[0131] The obtained products were analyzed using nuclear magnetic resonance (400 MHz, CDCl3). The actual mass of the cobalt Schiff base catalyst was calculated to be 181.5 g, and the yield was 93% by dividing the actual mass of the cobalt Schiff base catalyst by the theoretical mass. The actual mass of the alcohol was 38.6 g, and the yield was 90.8% by dividing the actual mass of the alcohol by the theoretical mass.

[0132] S2: The reaction flask was repeatedly evacuated and purged with nitrogen. 2 mol (232 g) of glycolide, 0.01 mol (1.5 g) of phenyl glycidyl ether (150) and 2.38 g of the mixture obtained in step S1 were added to the reaction flask in sequence. The mixture was stirred and the temperature was rapidly raised to 195 °C. After 4 h, the temperature was raised to 235 °C, and the unreacted monomers in the system were removed by evacuation. The pressure was 100 Pa, and 218.8 g of polyglycolic acid was obtained, with a yield of 94.3%.

[0133] The polyglycolic acid obtained in this invention was analyzed by gel permeation chromatography, and the number average molecular weight of polyglycolic acid was found to be 90,000 g / mol.

[0134] Example 9

[0135] S1: 0.11 mol (24.4 g) of resorcinol diglycidyl ether and 0.22 mol (33.4 g) of 2,3-diaminobenzoic acid were added to a 3 L round-bottom flask, mixed and stirred, and heated to 205 °C. After 1 h, the temperature was lowered to 45 °C, and 350 mL of toluene was added and stirred to dissolve. Then, the solution was added at a rate of 5 mL / min to 680 mL of toluene solution containing 0.55 mol (97.9 g) of 3-tert-butylsalicylaldehyde. The mixture was stirred at 60 °C for 8 h, and then 0.2 mol (23.4 g) of aminohexanol was added to 20 mL of toluene solution. A 0 mL toluene solution was reacted at 55 °C for 10 h to obtain a Schiff base compound and alcohol mixture solution. This solution was then mixed with a 250 mL toluene / 100 mL ethanol solution containing 0.22 mol (35.6 g) aluminum ethoxylate. The mixture was heated to 80 °C and reacted for 5 h. Toluene was then removed under vacuum at a vacuum degree of 500 Pa. When no more liquid distilled off, 179.7 g of the Schiff base aluminum catalyst and alcohol mixture (as shown in Formula 9) was obtained. The theoretical mass of the Schiff base aluminum catalyst was calculated to be 151.9 g, and the theoretical mass of the alcohol was 43 g.

[0136] The obtained products were analyzed using nuclear magnetic resonance (400 MHz, CDCl3). The actual mass of the Schiff base aluminum catalyst was calculated to be 141 g, and the yield was 92.8% by dividing the actual mass of the Schiff base aluminum catalyst by the theoretical mass. The actual mass of the alcohol was 38.7 g, and the yield was 90% by dividing the actual mass of the alcohol by the theoretical mass.

[0137] S2: The reaction flask was repeatedly evacuated and purged with nitrogen. 2 mol (232 g) of glycolide and 1.95 g of the mixture obtained in step S1 were added to the reaction flask in sequence. The mixture was stirred and the temperature was rapidly raised to 190 °C. After 3 h, the temperature was raised to 230 °C and the unreacted monomers in the system were removed by evacuation. The pressure was 100 Pa. 217.6 g of polyglycolic acid was obtained, with a yield of 93.8%.

[0138] The polyglycolic acid obtained in this invention was analyzed by gel permeation chromatography, and the number average molecular weight of polyglycolic acid was determined to be 89,000 g / mol.

[0139] Example 10

[0140] S1: 0.15 mol (32.4 g) neopentyl glycol diglycidyl ether and 0.3 mol (45.6 g) 2,3-diaminobenzoic acid were added to a 3 L round-bottom flask, mixed and stirred, and heated to 210 °C. After 1 h, the mixture was cooled to 50 °C, and 700 mL of toluene was added to dissolve it. Then, it was added at a rate of 7 mL / min to 750 mL of toluene solution containing 0.7 mol (98 g) 5-fluorosalicylaldehyde. After mixing and stirring at 55 °C for 6 h, 0.25 mol (15.3 g) aminoethanol was added to 90 mL of toluene solution. A 10 mL toluene solution was reacted at 50 °C for 12 h to obtain a Schiff base compound and alcohol mixture solution. This solution was then mixed with 0.3 mol (69.9 g) of iron isopropoxy in 700 mL of toluene solution. The mixture was heated to 90 °C and reacted for 7 h. Toluene was removed by vacuum at a vacuum degree of 500 Pa. When no more liquid distilled off, 207.7 g of the Schiff base iron catalyst and alcohol mixture shown in Formula 10 was obtained. The theoretical mass of the Schiff base iron catalyst was calculated to be 196.5 g, and the theoretical mass of the alcohol was 29.3 g.

[0141] The obtained products were analyzed using nuclear magnetic resonance (400 MHz, CDCl3). Based on the characteristic chemical shifts of the Schiff base iron catalyst and the alcohol, the actual mass of the Schiff base iron catalyst was 182 g, and the yield was calculated to be 92.6% by dividing the actual mass of the Schiff base iron catalyst by the theoretical mass. The actual mass of the alcohol was 25.7 g, and the yield was calculated to be 87.7% by dividing the actual mass of the alcohol by the theoretical mass.

[0142] S2: The reaction flask was repeatedly evacuated and purged with nitrogen. 2 mol (232 g) of glycolide, 3 g (0.02 mol) of phenyl glycidyl ether and 2.26 g of the mixture obtained in step S1 were added to the reaction flask in sequence. The mixture was stirred and the temperature was rapidly raised to 185 °C. After 6 h, the temperature was raised to 235 °C, and the unreacted monomers in the system were removed by evacuation at a pressure of 100 Pa. Polyglycolic acid was obtained with a yield of 216.9 g and a yield of 93.5%.

[0143] The polyglycolic acid obtained in this invention was analyzed by gel permeation chromatography, and the number average molecular weight of polyglycolic acid was determined to be 87,000 g / mol.

[0144] Comparative Example 1

[0145] This comparative example provides a polyglycolic acid, the preparation method of which is as follows:

[0146] The reaction flask was repeatedly evacuated and purged with nitrogen. 2 mol (232 g) of glycolide, 0.76 g of aluminum isopropoxide, and 0.002 mol of benzyl alcohol were added to the reaction flask in sequence, mixed and stirred, and the temperature was rapidly raised to 170 °C. After 12 h, the temperature was raised to 230 °C, and the unreacted monomers in the system were removed by evacuation at a pressure of 100 Pa. 213.4 g of polyglycolic acid was obtained, with a yield of 92%.

[0147] The polyglycolic acid obtained in this invention was analyzed by gel permeation chromatography, and the number average molecular weight of polyglycolic acid was determined to be 82000 g / mol.

[0148] Comparative Example 2

[0149] This comparative example provides a polyglycolic acid, the preparation method of which is as follows:

[0150] The reaction flask was repeatedly evacuated and purged with nitrogen. 2 mol (232 g) of glycolide, 0.76 g of stannous octoate, and 0.002 mol of benzyl alcohol were added to the reaction flask sequentially. The mixture was stirred and the temperature was rapidly raised to 170 °C. After 12 h, the temperature was raised to 230 °C, and the unreacted monomers were removed by evacuation at a pressure of 100 Pa. 215.3 g of polyglycolic acid was obtained, with a yield of 92.8%.

[0151] The polyglycolic acid obtained in this invention was analyzed by gel permeation chromatography, and the number average molecular weight of polyglycolic acid was determined to be 86000 g / mol.

[0152] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A bidentate Schiff base catalyst characterized in that, It has the structure shown in Formula I or Formula II: Wherein, R is the group remaining after removing the glycidyl ether from the diglycidyl ether, and the diglycidyl ether is selected from any one or more of ethylene glycol diglycidyl ether, butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, 1,2-cyclohexanediol diglycidyl ether, resorcinol diglycidyl ether, bisphenol A diglycidyl ether, or bisphenol F diglycidyl ether; R1 and R2 are independently selected from hydrogen, halogen, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C1-C6 alkoxy or nitro groups; R3 is the group remaining after removing two amino groups and one carboxyl group from a diaminocarboxylic acid, wherein the diaminocarboxylic acid is selected from any one of 2,3-diaminopropionic acid, 2,4-diaminobutyric acid, 2,3-diaminobutyric acid, 2,5-diaminovaleric acid, 3,4-diaminobenzoic acid, or 2,3-diaminobenzoic acid. The R4 is selected from halogens, substituted or unsubstituted C1-C6 alkoxy or ester groups; M1 is selected from any one of zinc, cobalt, nickel or tin; M2 is selected from any one of aluminum, indium, chromium, iron, manganese, cerium, or yttrium.

2. The double-centered Schiff base catalyst according to claim 1, characterized in that, R1 and R2 are independently selected from hydrogen, halogen, -CH3, -CH2Cl, -CH2CH3, -CH(CH3)2, -OCH(CH3)2, -C(CH3)3, -OCH3, -OCH2CH3, -OCF3 or -NO2; The R4 is selected from -OCH3, -OCH2CH3, -OCH(CH3)2, -Cl or -OOCCH3.

3. The double-centered Schiff base catalyst according to claim 1, characterized in that, The dual-center Schiff base catalyst is selected from any one of the following formulas 1 to 10:

4. A process for the preparation of the double-centered Schiff base catalyst as claimed in any one of claims 1 to 3, characterized in that, Includes the following steps: S1: Reaction of diglycidyl ether and diaminocarboxylic acid yields a tetraamine compound; S2: React the tetraamine compound with an excess of the salicylaldehyde monomer shown in formula A to obtain a mixture of Schiff base compound and excess salicylaldehyde monomer. The molar ratio of the tetraamine compound to the salicylaldehyde monomer is 1:(4.5-10); S3: React the mixture obtained in step S2 with amino alcohol monomers to obtain a mixture of Schiff base compounds and alcohols; S4: React the mixture obtained in step S3 with a metal compound to obtain a mixture of a two-center Schiff base catalyst and an alcohol. The general formula of the metal compound is M1(R4)2 or M2(R4)3; The structural formula of the salicylaldehyde monomer represented by formula A is shown below:

5. The preparation method according to claim 4, characterized in that, The diaminocarboxylic acid is selected from any one or more of 2,3-diaminopropionic acid, 2,4-diaminobutyric acid, 2,3-diaminobutyric acid, 2,5-diaminovaleric acid, 3,4-diaminobenzoic acid, or 2,3-diaminobenzoic acid. The amino alcohol monomers are selected from any one or more of 2-amino-1-ethanol, 3-amino-1-propanol, 4-amino-1-butanol, 3-amino-1-butanol, 5-amino-1-pentanol, 6-amino-1-hexanol, or 8-amino-1-octanol.

6. The preparation method according to claim 4, characterized in that, The molar ratio of the diglycidyl ether to the diaminocarboxylic acid is 1:(2-3); The molar ratio of excess salicylaldehyde monomers to amino alcohol monomers in the mixture obtained in step S2 is 1:(1.1~10); The molar ratio of Schiff base compound to metal compound in the mixture obtained in step S3 is 1:(2-3).

7. The preparation method according to claim 4, characterized in that, The reaction temperature in step S1 is 140–220°C, and the reaction time is 1–24 h. The temperature of each reaction in steps S2 and S3 is independently 20–100°C, and the time is independently 2–48 h. The reaction temperature in step S4 is 30–120°C, and the reaction time is 2–48 h.

8. A method for the preparation of polyglycolic acid, characterized by, Includes the following steps: In an inert atmosphere, glycolide and an optional epoxy compound are reacted in the presence of a catalyst and an initiator to obtain polyglycolic acid; The catalyst is a dual-center Schiff base catalyst according to any one of claims 1 to 3 or a dual-center Schiff base catalyst prepared by the preparation method according to any one of claims 4 to 7. The initiator is an alcoholic substance prepared by any one of claims 4 to 7.

9. The preparation method according to claim 8, characterized in that, The molar ratio of the epoxy compound to glycolide is (0-10):(90-100); The total mass ratio of the catalyst and initiator to the mass of glycolide is 1:(25-2500).

10. The preparation method according to claim 8, characterized in that, The reaction is carried out at a temperature of 120–240°C for a time of 2–24 hours.

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