Preparation method of schiff base catalyst and preparation method of polyglycolic acid

Abstract

The application provides a preparation method of a Schiff base catalyst and a preparation method of polyglycolic acid. The method comprises the following steps: reacting a diamine monomer with excessive salicylaldehyde monomer to obtain a mixture of a Schiff base compound and salicylaldehyde monomers; further adding an amino alcohol monomer to react with the excessive salicylaldehyde monomers to generate alcohol substances, the alcohol substances can initiate glycolide polymerization; subsequently, reacting the mixture comprising the Schiff base compound and the alcohol substances with a metal compound to obtain a mixture of a Schiff base catalyst and alcohol substances. Compared with the existing technology, the preparation of the Schiff base compound and the Schiff base catalyst is completed in a "one-pot", without the need for multi-step purification treatment, the use of a large amount of organic solvents is avoided, the production process is greatly simplified, and the production cost is effectively reduced.

Description

Technical Field

[0001] This invention belongs to the field of Schiff base catalyst preparation technology, specifically relating to a method for preparing a Schiff base catalyst 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, high 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 has 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, but their use as catalysts for the preparation of polyglycolic acid is rarely reported. Furthermore, current Schiff base compounds typically require purification and other post-treatment before reacting with metal compounds to obtain Schiff base metal compounds (i.e., Schiff base catalysts). However, these post-treatment processes are cumbersome, and purification usually requires large amounts of organic solvents, increasing economic costs and polluting the environment. Moreover, the yield of the final Schiff base catalyst is only around 80% at most. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a method for preparing Schiff base catalysts and a method for preparing polyglycolic acid. This preparation method employs a one-pot process to prepare Schiff base catalysts. After obtaining the Schiff base compound, no purification treatment is required, greatly simplifying the production process, reducing the use of organic solvents, and lowering production costs.

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

[0007] In a first aspect, the present invention provides a method for preparing a Schiff base catalyst, comprising the following steps:

[0008] S1: Reaction of diamine monomers with excess salicylaldehyde monomers yields a mixture of Schiff base compounds and excess salicylaldehyde monomers.

[0009] The molar ratio of the diamine monomer to the salicylaldehyde monomer is 1:(2.4-10);

[0010] S2: React the mixture obtained in step S1 with amino alcohol monomers to obtain a mixture of Schiff base compounds and alcohols;

[0011] S3: React the mixture obtained in step S2 with a metal compound to obtain a mixture of Schiff base catalyst and alcohol.

[0012] Preferably, the molar ratio of salicylaldehyde monomers to amino alcohol monomers in the mixture obtained in step S1 is 1:(1.2-10).

[0013] Preferably, the molar ratio of Schiff base compound to metal compound in the mixture obtained in step S2 is 1:(1 to 1.5).

[0014] Preferably, the reaction in step S1 is carried out in the presence of a solvent.

[0015] Preferably, the solvent is selected from any one or more of methanol, ethanol, isopropanol, butanol, pentanol, hexanol, heptanol, octanol, benzene, toluene, tetrahydrofuran, dichloromethane, or trichloromethane.

[0016] Preferably, the concentrations of the diamine monomer and the salicylaldehyde monomer in the solvent are each independently 5 to 50 wt%.

[0017] Preferably, the reaction in step S1 is carried out at a temperature of 20–100°C for a time of 2–48 hours.

[0018] Preferably, the reaction in step S2 is carried out at a temperature of 20–100°C for a time of 2–48 hours.

[0019] Preferably, the reaction in step S3 is carried out at a temperature of 20–120°C for a time of 2–96 h.

[0020] Preferably, the diamine monomer is selected from any one or more of ethylenediamine, 1,3-propanediamine, 1,2-propanediamine, 2,2'-dimethylpropanediamine, 1,2-butanediamine, 2,3-butanediamine, 1,2-cyclohexanediamine, o-phenylenediamine, 4-nitro-o-phenylenediamine, 2-methyl-1,3-propanediamine, 4-bromo-o-phenylenediamine, 4,5-dichloro-o-phenylenediamine, 4,5-dibromo-o-phenylenediamine, 4,5-difluoro-o-phenylenediamine, 4-fluoro-o-phenylenediamine, or 4-methoxy-o-phenylenediamine.

[0021] Preferably, the salicylaldehyde monomer is selected from 3-bromosalicylic acid aldehyde, 4-bromosalicylic acid aldehyde, 3,5-dibromosalicylic acid aldehyde, 5-fluorosalicylic acid aldehyde, 3-chlorosalicylic acid aldehyde, 4-chlorosalicylic acid aldehyde, 5-chlorosalicylic acid aldehyde, 6-chlorosalicylic acid aldehyde, 4,6-dimethoxysalicylic acid aldehyde, 3,5-dichlorosalicylic acid aldehyde, 4,5-dichlorosalicylic acid aldehyde, 4,6-dichlorosalicylic acid aldehyde, 5,6-dichlorosalicylic acid aldehyde, 5-iodosalicylic acid aldehyde, 3-bromo-5-chlorosalicylic acid aldehyde, 3,5-di-tert-butylsalicylic acid aldehyde, 4-fluorosalicylic acid aldehyde, 6-fluorosalicylic acid aldehyde, 4-methylsalicylic acid aldehyde, 5-methylsalicylic acid aldehyde, 5 - Nitrosalicylic acid, 5-(trifluoromethoxy)salicylic acid, 5-bromo-3-nitrosalicylic acid, 3-bromo-5-nitrosalicylic acid, 4-methoxysalicylic acid, 3-methoxysalicylic acid, 5-fluoro-3-methylsalicylic acid, 3-methylsalicylic acid, 3-tert-butylsalicylic acid, 3,5-diiodosalicylic acid, 3-chloromethyl-5-nitrosalicylic acid, 3,6-dimethylsalicylic acid, 3-chloro-5-fluorosalicylic acid, 3-ethoxysalicylic acid, 4-ethylsalicylic acid, 5-bromo-3-fluorosalicylic acid, or 5-bromo-3-methoxysalicylic acid.

[0022] 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.

[0023] Preferably, the metal compound is selected from any one or more of zinc isopropoxide, zinc chloride, aluminum ethoxylate, aluminum isopropoxide, indium isopropoxide, indium chloride, dibutyltin dichloride, stannous chloride, ferric ethoxylate, ferric isopropoxide, ferric trichloride, yttrium isopropoxide, yttrium chloride, titanium isopropoxide, tetrabutyl titanate, cobalt acetate, manganese acetate, chromium acetate, zirconium acetate, zirconium n-butoxide, hafnium isopropoxide, hafnium n-butoxide, cerium acetate, cerium n-butoxide, or nickel acetate.

[0024] Secondly, the present invention provides a method for preparing polyglycolic acid, comprising the following steps:

[0025] 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;

[0026] The catalyst is a Schiff base catalyst prepared according to the above preparation method, and the initiator is an alcohol substance prepared according to the above preparation method.

[0027] Preferably, the epoxy compound is selected from any one or more of allyl glycidyl ether, styrene oxide, isopropyl glycidyl ether, tert-butyl glycidyl ether, octyl glycidyl ether, phenyl glycidyl ether, 2-toluene glycidyl ether, benzyl glycidyl ether, propylene oxide, butane oxide, 1,2-epoxycyclopentane, 1,2-epoxycyclohexane, 1,2-epoxyoctane, 1,2-epoxydodecane, 1,2-epoxytetradecane, or 1,2-epoxyhexadecane.

[0028] Preferably, the molar ratio of the epoxy compound to glycolide is (0-10):(90-100).

[0029] Preferably, the total mass ratio of the catalyst and initiator to the mass ratio of glycolide is 1:(50-5000).

[0030] Preferably, the reaction temperature is 120–240°C and the reaction time is 1–24 h.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] This invention provides a method for preparing Schiff base catalysts and polyglycolic acid. The method involves reacting a diamine monomer with an excess of salicylaldehyde monomer to obtain a mixture of Schiff base compounds and salicylaldehyde monomers. Further, an amino alcohol monomer is added to react with the excess salicylaldehyde monomers to generate an alcohol, which can initiate glycolide polymerization. Subsequently, the mixture including the Schiff base compound and the alcohol is reacted with a metal compound to obtain a mixture of a Schiff base metal compound (i.e., a Schiff base catalyst) and the alcohol. Compared to existing technologies that require multi-step purification of Schiff base compounds, the preparation of Schiff base compounds and Schiff base catalysts in this invention is completed in a single process, eliminating the need for multi-step purification, avoiding the use of large amounts of organic solvents, greatly simplifying the production process, increasing the yield of Schiff base catalysts to over 90%, and effectively reducing production costs.

[0033] This invention uses the Schiff base catalyst obtained above as a catalyst and alcohol as an initiator to prepare polyglycolic acid by ring-opening polymerization of glycolide. Gel permeation chromatography analysis revealed that the prepared polyglycolic acid has a high number average molecular weight of over 60,000 g / mol and a high yield of over 93.5%. Detailed Implementation

[0034] 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.

[0035] To address the problems of cumbersome post-processing and purification steps for Schiff base compounds in existing technologies, requiring large amounts of organic solvents and resulting in high costs, as well as the low yield of the final Schiff base catalysts, this invention provides a method for preparing Schiff base catalysts, comprising the following steps:

[0036] S1: Reaction of diamine monomers with excess salicylaldehyde monomers yields a mixture of Schiff base compounds and excess salicylaldehyde monomers.

[0037] S2: React the mixture obtained in step S1 with amino alcohol monomers to obtain a mixture of Schiff base compounds and alcohols;

[0038] S3: React the mixture obtained in step S2 with a metal compound to obtain a mixture of Schiff base catalyst and alcohol.

[0039] According to the present invention, a diamine monomer is first reacted with an excess of a salicylaldehyde monomer to obtain a mixture of a Schiff base compound and the excess salicylaldehyde monomer. The diamine monomer is selected from any one or more of ethylenediamine, 1,3-propanediamine, 1,2-propanediamine, 2,2'-dimethylpropanediamine, 1,2-butanediamine, 2,3-butanediamine, 1,2-cyclohexanediamine, o-phenylenediamine, 4-nitro-o-phenylenediamine, 2-methyl-1,3-propanediamine, 4-bromo-o-phenylenediamine, 4,5-dichloro-o-phenylenediamine, 4,5-dibromo-o-phenylenediamine, 4,5-difluoro-o-phenylenediamine, 4-fluoro-o-phenylenediamine, or 4-methoxy-o-phenylenediamine, preferably 1,2'-propanediamine, 1,3'-propanediamine, 1,2'-propanediamine, 1,2'-propanediamine, 1,2'-but ... 1,2'-Propanediamine, 2,2'-Dimethylpropanediamine, 1,2-Butanediamine, 2,3-Butanediamine, 1,2-Cyclohexanediamine, or o-phenylenediamine; wherein the salicylaldehyde monomer is selected from 3-bromosalicylicalaldehyde, 4-bromosalicylicalaldehyde, 3,5-dibromosalicylicalaldehyde, 5-fluorosalicylicalaldehyde, 3-chlorosalicylicalaldehyde, 4-chlorosalicylicalaldehyde, 5-chlorosalicylicalaldehyde, 6-chlorosalicylicalaldehyde, 4,6-dimethoxysalicylicalaldehyde, 3,5-dichlorosalicylicalaldehyde, 4,5-dichlorosalicylicalaldehyde, 4,6-dichlorosalicylicalaldehyde, 5,6-dichlorosalicylicalaldehyde, etc. Salicylaldehyde, 5-iodosalicylaldehyde, 3-bromo-5-chlorosalicylaldehyde, 3,5-di-tert-butylsalicylaldehyde, 4-fluorosalicylaldehyde, 6-fluorosalicylaldehyde, 4-methylsalicylaldehyde, 5-methylsalicylaldehyde, 5-nitrosalicylaldehyde, 5-(trifluoromethoxy)salicylaldehyde, 5-bromo-3-nitrosalicylaldehyde, 3-bromo-5-nitrosalicylaldehyde, 4-methoxysalicylaldehyde, 3-methoxysalicylaldehyde, 5-fluoro-3-methylsalicylaldehyde, 3-methylsalicylaldehyde, 3-tert-butylsalicylaldehyde, 3,5-diiodosalicylaldehyde, 3-chlorosalicylaldehyde The diamine monomer is selected from one or more of the following: 5-nitrosalicylaldehyde, 3,6-dimethylsalicylaldehyde, 3-chloro-5-fluorosalicylaldehyde, 3-ethoxysalicylaldehyde, 4-ethylsalicylaldehyde, 5-bromo-3-fluorosalicylaldehyde, or 5-bromo-3-methoxysalicylaldehyde, preferably one or more of the following: 3-bromosalicylaldehyde, 3,5-dibromosalicylaldehyde, 4,6-dimethoxysalicylaldehyde, 4,5-dichlorosalicylaldehyde, 4-methylsalicylaldehyde, 4-methoxysalicylaldehyde, 3-tert-butylsalicylaldehyde, or 3,6-dimethylsalicylaldehyde. In the above reaction, the salicylaldehyde monomer is in excess. Preferably, the molar ratio of the diamine monomer to the salicylaldehyde monomer is 1:(2.4–10), more preferably 1:(4–6), to ensure a more complete reaction between the diamine monomer and the salicylaldehyde monomer, yielding a higher yield of the Schiff base compound. In this invention, the reaction in step S1 is preferably carried out in the presence of a solvent, which is selected from any one or more of methanol, ethanol, isopropanol, butanol, pentanol, hexanol, heptanol, octanol, benzene, toluene, tetrahydrofuran, dichloromethane or trichloromethane.The concentrations of the diamine monomer and the salicylaldehyde monomer in the solvent are each independently 5–50 wt%, such as 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, or 50 wt%. The reaction temperature is preferably 20–100°C, more preferably 40–80°C; the reaction time is preferably 2–48 h, more preferably 10–24 h.

[0040] In some embodiments of the present invention, the diamine monomer solution is preferably added to the salicylaldehyde monomer solution at a rate of less than 5 mL / min, preferably 2 mL / min, and after mixing and stirring, the mixture is reacted at 20–100°C for 2–48 h. The solvents in the diamine monomer solution and the salicylaldehyde monomer solution can be the same or different, but are preferably the same.

[0041] Because the salicylaldehyde monomers in step S1 are in excess, the product obtained is a mixture of Schiff base compound and excess salicylaldehyde monomers. However, this invention differs from the prior art in that the excess salicylaldehyde monomers are removed through cumbersome post-processing. Instead, an amino alcohol monomer is introduced in step S2 and reacted with the mixture obtained in step S1. This step mainly involves the amino alcohol monomer reacting with the excess salicylaldehyde monomers to generate alcohols that can initiate glycolide polymerization, ultimately yielding a mixture of Schiff base compound and alcohols. 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. This invention does not have any particular restrictions on the source of the amino alcohol monomers; commercially available products are acceptable. In this invention, the molar ratio of salicylaldehyde monomer to amino alcohol monomer in the mixture obtained in step S1 is preferably 1:(1.2-10), more preferably 1:(3-6). In some embodiments of this invention, the amino alcohol monomer preferably participates in the reaction in solution form. The solvent in the solution is selected within the same range as the solvent in the diamine monomer solution and the salicylaldehyde monomer solution, and may be the same as or different from the solvent in the diamine monomer solution and the salicylaldehyde monomer solution, preferably the same. The concentration of the amino alcohol monomer in the amino alcohol monomer solution is 10-50 wt%, preferably 20-30 wt%. In some embodiments of this invention, the mixture obtained in step S1 is preferably reacted with the amino alcohol monomer solution at 20-100°C, more preferably at 40-80°C for 2-48 h, more preferably for 10-24 h, to obtain a mixture of Schiff base compound and alcohol. The reaction is preferably carried out under stirring conditions.

[0042] Then, according to the present invention, the mixture obtained in step S2 is reacted with a metal compound to obtain a mixture of Schiff base catalyst and alcohol. The metal compound is selected from any one or more of zinc isopropoxide, zinc chloride, aluminum isopropoxide, aluminum ethoxylate, indium isopropoxide, indium chloride, dibutyltin dichloride, stannous chloride, ferric ethoxylate, ferric isopropoxylate, ferric trichloride, yttrium isopropoxide, yttrium chloride, titanium isopropoxide, tetrabutyl titanate, cobalt acetate, manganese acetate, chromium acetate, zirconium acetate, zirconium n-butoxide, hafnium isopropoxide, hafnium n-butoxide, cerium acetate, cerium n-butoxide, or nickel acetate, preferably any one or more of zinc isopropoxide, aluminum isopropoxide, aluminum ethoxylate, stannous chloride, ferric ethoxylate, ferric isopropoxylate, or cobalt acetate. The present invention does not have any particular limitation on the source of the above metal compound; commercially available products are acceptable. In this invention, the molar ratio of Schiff base compound to metal compound in the mixture obtained in step S2 is preferably 1:(1-1.5), more preferably 1:1. In some embodiments of this invention, the metal compound preferably participates in the reaction in solution form. The solvent in the solution is selected within the same range as the solvent in the solutions of diamine monomers, salicylaldehyde monomers, and amino alcohol monomers. It can be the same as or different from the solvent in the solutions of diamine monomers, salicylaldehyde monomers, and amino alcohol monomers, but preferably the same. The concentration of the metal compound in the metal compound solution is 5-50 wt%, preferably 20-30 wt%. In some embodiments of this invention, the mixture obtained in step S2 is preferably reacted with the metal compound solution at 20-120°C, more preferably at 50-100°C for 2-96 h, more preferably for 24-72 h, to obtain a mixture of Schiff base catalyst and alcohol. The reaction is preferably carried out under stirring conditions.

[0043] In some preferred embodiments of the present invention, after the reaction in step S3 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 Schiff base catalyst and alcohol is obtained.

[0044] The method provided by this invention involves reacting a diamine monomer with an excess of a salicylaldehyde monomer to obtain a mixture of Schiff base compounds and salicylaldehyde monomers. Further, an amino alcohol monomer is added to react with the remaining salicylaldehyde monomers to generate an alcohol, which can initiate glycolide polymerization. Subsequently, the mixture including the Schiff base compound and the alcohol is reacted with a metal compound to obtain a mixture of a Schiff base catalyst and the alcohol. Compared to existing technologies that require multiple purification steps for the Schiff base compound, the preparation of the Schiff base compound and the Schiff base catalyst in this invention is completed in a single process, eliminating the need for multiple purification steps, avoiding the use of large amounts of organic solvents, greatly simplifying the production process, and effectively reducing production costs.

[0045] Calculations show that the Schiff base catalyst prepared by the above method has a high yield, exceeding 90%.

[0046] The present invention also provides the application of a mixture of Schiff base catalyst and alcohol prepared by the above preparation method in the polymerization of glycolide to prepare polyglycolic acid.

[0047] Based on the above applications, the present invention also provides a method for preparing polyglycolic acid, comprising the following steps:

[0048] In an inert atmosphere, glycolide and optionally an epoxide are reacted in the presence of a catalyst and an initiator to yield polyglycolic acid.

[0049] Wherein, the catalyst is a 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 epoxy compound is selected from any one or more of allyl glycidyl ether, styrene oxide, isopropyl glycidyl ether, tert-butyl glycidyl ether, octyl glycidyl ether, phenyl glycidyl ether, 2-tolyl glycidyl ether, benzyl glycidyl ether, propylene oxide, epoxide, 1,2-epoxidecyclopentane, 1,2-epoxidecyclohexane, 1,2-epoxideoctane, 1,2-epoxidedodecane, 1,2-epoxidetetradecane, or 1,2-epoxidehexadecane, preferably any one or more of styrene oxide, isopropyl glycidyl ether, tert-butyl glycidyl ether, octyl glycidyl ether, phenyl glycidyl ether, benzyl glycidyl ether, or 1,2-epoxidecyclohexane.

[0050] 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 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. It should be noted that whether the amount of epoxide compound added is 0 depends on the metal element in the metal compound. 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, zirconium, hafnium, cerium, yttrium, or titanium, the amount of epoxide compound added is not 0. The total mass ratio of the catalyst and initiator to glycolide is 1:(50-5000), preferably 1:(100-2500), and more preferably 1:(200-1000). In this invention, glycolide and the epoxide are preferably reacted at 120-240°C, more preferably at 150-200°C for 1-24 hours, and even more preferably for 5-12 hours. The reaction is preferably carried out under stirring conditions.

[0051] In some embodiments of the present invention, it is preferable to repeatedly evacuate and purge the reaction flask with nitrogen or argon, then add glycolide, catalyst, and initiator to the reaction flask in sequence, mix and stir, and rapidly heat to the target temperature for reaction. After the reaction is completed, it is preferable to heat to 225-240°C, evacuate to remove unreacted monomers from the system, and apply a vacuum of 100 Pa to obtain the target product - polyglycolic acid. This step, through depressurization in the molten state, can remove unreacted glycolide, thereby achieving purification of the target product polyglycolic acid.

[0052] Calculations showed that the polyglycolic acid prepared using the above method had a high yield, exceeding 93.5%. Furthermore, gel permeation chromatography analysis revealed that the prepared polyglycolic acid had a high number-average molecular weight, exceeding 60,000 g / mol.

[0053] It should be noted that the point values ​​listed above in this invention are merely for illustrative purposes and are not limited thereto. Other point values ​​within the numerical range are also applicable, and will not be elaborated upon here.

[0054] To further illustrate the present invention, detailed descriptions are provided below through the following examples. All experimental materials used in the following examples are 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 consisted of 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 general correction.

[0055] Preparation Example 1

[0056] This preparation example provides a mixture of Schiff base aluminum catalyst and alcohol, which is prepared by the following method:

[0057] 0.1 mol of ethylenediamine was dissolved in 40 mL of toluene and added at a rate of 2 mL / min to 500 mL of toluene solution containing 0.3 mol of 3,5-di-tert-butylsalicylaldehyde. The mixture was stirred and heated to 40 °C. After 10 h, 50 mL of toluene solution containing 0.15 mol of aminoethanol was added, and the reaction was continued at 50 °C for 8 h to obtain a mixture of Schiff base compound and alcohol. 100 mL of toluene solution containing 0.1 mol of aluminum isopropoxide was added, and the mixture was heated to 80 °C. After 72 h, toluene was removed by vacuum at a vacuum degree of 500 Pa. When no more liquid distilled off, 84.8 g of a mixture of aluminum Schiff base catalyst and alcohol was obtained.

[0058] The theoretical mass of the Schiff base aluminum catalyst was calculated to be 61.6 g, and the theoretical mass of the alcohol was 32.6 g.

[0059] 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 56 g, and the yield was calculated to be 90.9% by dividing the actual mass of the Schiff base aluminum catalyst by the theoretical mass. The actual mass of the alcohol was 28.8 g, and the yield was calculated to be 88.3% by dividing the actual mass of the alcohol by the theoretical mass.

[0060] Preparation Example 2

[0061] This preparation example provides a mixture of Schiff base iron catalyst and alcohol, which is prepared by the following method:

[0062] 0.1 mol of cyclohexanediamine was dissolved in 50 mL of toluene and added at a rate of 2 mL / min to 550 mL of toluene solution containing 0.25 mol of 3-bromosalicylic acid. The mixture was stirred and heated to 50 °C. After 9 h, 20 mL of toluene solution containing 0.1 mol of aminoethanol was added, and the reaction was continued at 60 °C for 6 h to obtain a mixture of Schiff base compound and alcohol. 200 mL of toluene solution containing 0.1 mol of isopropoxy iron was added, and the mixture was heated to 85 °C. After 36 h, toluene was removed by vacuum at a vacuum degree of 500 Pa. When no more liquid distilled off, 72.3 g of a mixture of Schiff base iron catalyst and alcohol was obtained.

[0063] The theoretical mass of the Schiff base iron catalyst was calculated to be 63.1 g, and the theoretical mass of the alcohol was 16.3 g.

[0064] 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 57.7 g, and the yield was calculated to be 91.4% by dividing the actual mass of the Schiff base iron catalyst by the theoretical mass. The actual mass of the alcohol was 14.6 g, and the yield was calculated to be 89.6% by dividing the actual mass of the alcohol by the theoretical mass.

[0065] Preparation Example 3

[0066] This preparation example provides a mixture of a Schiff base cobalt catalyst and an alcohol, which is prepared by the following method:

[0067] 0.1 mol of 4-methoxy-o-phenylenediamine was dissolved in 60 mL of toluene and added at a rate of 2 mL / min to 600 mL of toluene solution containing 0.35 mol of 3,5-dibromosalicylic acid. The mixture was stirred and heated to 60 °C. After 8 h, 60 mL of toluene solution containing 0.2 mol of aminopropanol was added, and the reaction was continued at 65 °C for 5 h to obtain a mixture of Schiff base compound and alcohol. 100 mL of toluene solution containing 0.1 mol of cobalt acetate was added, and the mixture was heated to 90 °C. After 60 h, toluene was removed by vacuum at a vacuum degree of 500 Pa. When no more liquid distilled off, 122.5 g of a mixture of Schiff base cobalt catalyst and alcohol was obtained.

[0068] The theoretical mass of the Schiff base cobalt catalyst was calculated to be 75.5g, and the theoretical mass of the alcohol was 56.8g.

[0069] 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 70.2 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 52.3 g, and the yield was 92.1% by dividing the actual mass of the alcohol by the theoretical mass.

[0070] Preparation Example 4

[0071] This preparation example provides a mixture of Schiff base aluminum catalyst and alcohol, which is prepared by the following method:

[0072] 0.1 mol of 1,3-propanediamine was dissolved in 45 mL of ethanol and added at a rate of 2 mL / min to 350 mL of ethanol solution containing 0.27 mol of 4,6-dimethoxysalicylaldehyde. The mixture was stirred and heated to 45 °C. After 12 h, 30 mL of ethanol solution containing 0.1 mol of aminopropanol was added, and the reaction was continued at 55 °C for 10 h to obtain a mixture of Schiff base compound and alcohol. 100 mL of ethanol solution containing 0.1 mol of ethoxyaluminum was added, and the temperature was raised to 80 °C. After 16 h, the ethanol was removed by vacuum at a vacuum degree of 500 Pa. When no more liquid distilled off, 66.2 g of a mixture of Schiff base aluminum catalyst and alcohol was obtained.

[0073] The theoretical mass of the Schiff base aluminum catalyst was calculated to be 51g, and the theoretical mass of the alcohol was 20.2g.

[0074] 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 47.7 g, and the yield was 93.5% by dividing the actual mass of the Schiff base aluminum catalyst by the theoretical mass. The actual mass of the alcohol was 18.5 g, and the yield was 91.6% by dividing the actual mass of the alcohol by the theoretical mass.

[0075] Preparation Example 5

[0076] This preparation example provides a mixture of Schiff base iron catalyst and alcohol, which is prepared by the following method:

[0077] 0.1 mol of 1,2-butanediamine was dissolved in 65 mL of ethanol and added at a rate of 2 mL / min to 400 mL of ethanol solution containing 0.29 mol of 4,5-dichlorosalicylaldehyde. The mixture was stirred and heated to 55 °C. After 14 h, 50 mL of ethanol solution containing 0.15 mol of aminobutanol was added, and the reaction was continued at 60 °C for 9 h to obtain a mixture of Schiff base compound and alcohol. 120 mL of ethanol solution containing 0.1 mol of ethoxy iron was added, and the temperature was raised to 80 °C. After 20 h, the ethanol was removed by vacuum at a vacuum degree of 500 Pa. When no more liquid distilled off, 79.1 g of a mixture of Schiff base iron catalyst and alcohol was obtained.

[0078] The theoretical mass of the Schiff base iron catalyst was calculated to be 57.1 g, and the theoretical mass of the alcohol was 30.6 g.

[0079] 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 51.9 g, and the yield was calculated to be 90.9% by dividing the actual mass of the Schiff base iron catalyst by the theoretical mass. The actual mass of the alcohol was 27.2 g, and the yield was calculated to be 88.9% by dividing the actual mass of the alcohol by the theoretical mass.

[0080] Preparation Example 6

[0081] This preparation example provides a mixture of Schiff base iron catalyst and alcohol, which is prepared by the following method:

[0082] 0.1 mol o-phenylenediamine was dissolved in 70 mL of toluene and added at a rate of 2 mL / min to 350 mL of toluene solution containing 0.31 mol 4-methylsalicylaldehyde. The mixture was stirred and heated to 65 °C. After 8 h, 100 mL of toluene solution containing 0.15 mol aminopentanol was added, and the reaction was continued at 70 °C for 4 h to obtain a mixture of Schiff base compound and alcohol. 200 mL of toluene solution containing 0.1 mol ethoxy iron was added, and the temperature was raised to 90 °C. After 55 h, toluene was removed by vacuum at a vacuum degree of 500 Pa. When no more liquid distilled off, 73.3 g of a mixture of Schiff base iron catalyst and alcohol was obtained.

[0083] The theoretical mass of the Schiff base iron catalyst was calculated to be 48.1 g, and the theoretical mass of the alcohol was 30.4 g.

[0084] 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 45.2 g, and the yield was calculated to be 94% by dividing the actual mass of the Schiff base iron catalyst by the theoretical mass. The actual mass of the alcohol was 28.1 g, and the yield was calculated to be 92.4% by dividing the actual mass of the alcohol by the theoretical mass.

[0085] Preparation Example 7

[0086] This preparation example provides a mixture of a Schiff base cobalt catalyst and an alcohol, which is prepared by the following method:

[0087] 0.1 mol of 2,2'-dimethylpropanediamine was dissolved in 90 mL of isopropanol and added at a rate of 3 mL / min to 550 mL of isopropanol solution containing 0.33 mol of 3-nitrosalicylic acid. The mixture was stirred and heated to 70 °C. After 6 h, 150 mL of isopropanol solution containing 0.2 mol of aminohexanol was added, and the reaction was continued at 75 °C for 3 h to obtain a mixture of Schiff base compound and alcohol. 180 mL of isopropanol solution containing 0.1 mol of cobalt acetate was added, and the temperature was raised to 80 °C. After 24 h, isopropanol was removed by vacuum at a vacuum degree of 500 Pa. When no more liquid distilled off, 85.6 g of a mixture of Schiff base cobalt catalyst and alcohol was obtained.

[0088] The theoretical mass of the Schiff base cobalt catalyst was calculated to be 49.5g, and the theoretical mass of the alcohol was 45.1g.

[0089] 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 45.1 g, and the yield was 91.1% by dividing the actual mass of the cobalt Schiff base catalyst by the theoretical mass. The actual mass of the alcohol was 40.5 g, and the yield was 89.8% by dividing the actual mass of the alcohol by the theoretical mass.

[0090] Preparation Example 8

[0091] This preparation example provides a mixture of Schiff base iron catalyst and alcohol, which is prepared by the following method:

[0092] 0.1 mol of 4,5-dichloro-o-phenylenediamine was dissolved in 150 mL of isopropanol and added at a rate of 3 mL / min to 450 mL of isopropanol solution containing 0.32 mol of 4-methoxysalicylaldehyde. The mixture was stirred and heated to 65 °C. After 4 h, 130 mL of isopropanol solution containing 0.15 mol of aminohexanol was added, and the reaction was continued at 60 °C for 10 h to obtain a Schiff base compound and alcohol mixture solution. 160 mL of isopropanol solution containing 0.1 mol of isopropoxy iron was added, and the temperature was raised to 80 °C. After 50 h, isopropanol was removed by vacuum at a vacuum degree of 500 Pa. When no more liquid distilled off, 87.3 g of a mixture of Schiff base iron catalyst and alcohol was obtained.

[0093] The theoretical mass of the Schiff base iron catalyst was calculated to be 59.8g, and the theoretical mass of the alcohol was 35.8g.

[0094] The obtained products were analyzed using nuclear magnetic resonance (400 MHz, CDCl3). The actual mass of the Schiff base iron catalyst was calculated to be 54.7 g, and the yield was 91.5% by dividing the actual mass of the Schiff base iron catalyst by the theoretical mass. The actual mass of the alcohol was 32.6 g, and the yield was 91.1% by dividing the actual mass of the alcohol by the theoretical mass.

[0095] Preparation Example 9

[0096] This preparation example provides a mixture of Schiff base aluminum catalyst and alcohol, which is prepared by the following method:

[0097] 0.1 mol of cyclohexanediamine was dissolved in 80 mL of isopropanol and added at a rate of 2 mL / min to 600 mL of isopropanol solution containing 0.28 mol of 3-tert-butylsalicylaldehyde. The mixture was stirred and heated to 55 °C. After 11 h, 80 mL of isopropanol solution containing 0.1 mol of aminooctanol was added, and the reaction was continued at 65 °C for 4 h to obtain a Schiff base compound and alcohol mixture solution. 160 mL of isopropanol solution containing 0.1 mol of aluminum isopropoxide was added, and the temperature was raised to 80 °C. After 45 h, isopropanol was removed by vacuum at a vacuum degree of 500 Pa. When no more liquid distilled off, 76.5 g of a mixture of aluminum Schiff base catalyst and alcohol was obtained.

[0098] The theoretical mass of the Schiff base aluminum catalyst was calculated to be 55.6 g, and the theoretical mass of the alcohol was 28.7 g.

[0099] 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 50.9 g, and the yield was calculated to be 91.5% by dividing the actual mass of the Schiff base aluminum catalyst by the theoretical mass. The actual mass of the alcohol was 25.6 g, and the yield was calculated to be 89.2% by dividing the actual mass of the alcohol by the theoretical mass.

[0100] Preparation Example 10

[0101] This preparation example provides a mixture of Schiff base aluminum catalyst and alcohol, which is prepared by the following method:

[0102] 0.1 mol o-phenylenediamine was dissolved in 70 mL of toluene and added at a rate of 2 mL / min to 350 mL of toluene solution containing 0.26 mol 3,6-dimethylsalicylaldehyde. The mixture was stirred and heated to 50 °C. After 13 h, 70 mL of toluene solution containing 0.1 mol aminooctanol was added, and the reaction was continued at 70 °C for 5 h to obtain a mixture of Schiff base compound and alcohol. 100 mL of toluene solution containing 0.1 mol ethoxyaluminum was added, and the mixture was heated to 85 °C. After 40 h, toluene was removed by vacuum at a vacuum degree of 500 Pa. When no more liquid distilled off, 65.5 g of a mixture of Schiff base aluminum catalyst and alcohol was obtained.

[0103] The theoretical mass of the Schiff base aluminum catalyst was calculated to be 48g, and the theoretical mass of the alcohol was 23.5g.

[0104] 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 44.2 g, and the yield was 92.1% by dividing the actual mass of the Schiff base aluminum catalyst by the theoretical mass. The actual mass of the alcohol was 21.3 g, and the yield was 90.6% by dividing the actual mass of the alcohol by the theoretical mass.

[0105] Comparative Preparation Example 1

[0106] This comparative preparation example provides a Schiff base aluminum catalyst, the preparation method of which is as follows:

[0107] 0.1 mol of ethylenediamine was dissolved in 40 mL of toluene and added at a rate of 2 mL / min to 500 mL of toluene solution containing 0.3 mol of 3,5-di-tert-butylsalicylaldehyde. The mixture was stirred and heated to 40 °C. After 10 h, it was cooled to room temperature and distilled. The obtained solid was washed with methanol and recrystallized from acetone to obtain Schiff base crystals, which were dried under vacuum. The obtained Schiff base compound was then dissolved in 50 mL of toluene and mixed with 100 mL of toluene solution containing 0.1 mol of aluminum isopropoxide. The mixture was heated to 80 °C and heated for 72 h. Toluene was removed under vacuum at a vacuum degree of 500 Pa. When no more liquid distilled off, 38.8 g of aluminum Schiff base catalyst was obtained. The theoretical mass of aluminum Schiff base catalyst was calculated to be 61.6 g, and the yield was 63%.

[0108] Comparison of Preparation Example 1 and Preparation Examples 1-10 shows that the method provided in this application is not only simpler in terms of steps and does not require purification, but also yields a higher Schiff base metal catalyst.

[0109] Example 1

[0110] This embodiment provides a polyglycolic acid, the preparation method of which is as follows:

[0111] The reaction flask was repeatedly evacuated and purged with nitrogen. 1 mol (116 g) of glycolide and 0.47 g of the mixture obtained in Preparation Example 1 were added to the reaction flask in sequence. The mixture was stirred and the temperature was rapidly raised to 180 °C. After 8 h, the temperature was raised to 230 °C, and the unreacted monomers in the system were removed by evacuation. The pressure was 100 Pa, and 110.4 g of polyglycolic acid was obtained, with a yield of 95.2%.

[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 92000 g / mol.

[0113] Example 2

[0114] This embodiment provides a polyglycolic acid, the preparation method of which is as follows:

[0115] The reaction flask was repeatedly evacuated and purged with nitrogen. 1 mol (116 g) of glycolide, 0.02 mol (2.4 g) of styrene oxide, and 0.79 g of the mixture obtained in Preparation Example 2 were added to the reaction flask in sequence. The mixture was stirred and the temperature was rapidly raised to 185 °C. After 7 h, the temperature was raised to 225 °C, and the unreacted monomers in the system were removed by evacuation at a pressure of 100 Pa. 110 g of polyglycolic acid was obtained, with a yield of 94.8%.

[0116] 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 63,000 g / mol.

[0117] Example 3

[0118] This embodiment provides a polyglycolic acid, the preparation method of which is as follows:

[0119] The reaction flask was repeatedly evacuated and purged with nitrogen. 1.5 mol (174 g) of glycolide, 0.01 mol (1.5 g) of phenyl glycidyl ether and 1.32 g of the mixture obtained in Preparation Example 3 were added to the reaction flask in sequence. The mixture was stirred and the temperature was rapidly raised to 190 °C. After 6 h, the temperature was raised to 225 °C, and the unreacted monomers in the system were removed by evacuation. The pressure was 100 Pa, and polyglycolic acid was obtained with a yield of 111 g and a yield of 94.5%.

[0120] 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 65000 g / mol.

[0121] Example 4

[0122] This embodiment provides a polyglycolic acid, the preparation method of which is as follows:

[0123] The reaction flask was repeatedly evacuated and purged with nitrogen. 2 mol (232 g) of glycolide and 0.71 g of the mixture obtained in Preparation Example 4 were added to the reaction flask in sequence. The mixture was stirred and the temperature was rapidly raised to 165 °C. After 15 h, the temperature was raised to 230 °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%.

[0124] 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 105,000 g / mol.

[0125] Example 5

[0126] This embodiment provides a polyglycolic acid, the preparation method of which is as follows:

[0127] 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 0.88 g of the mixture obtained in Preparation Example 5 were added to the reaction flask sequentially. The mixture was stirred and the temperature was rapidly raised to 160 °C. After 18 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. 217.8 g of polyglycolic acid was obtained, with a yield of 93.9%.

[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 101000 g / mol.

[0129] Example 6

[0130] This embodiment provides a polyglycolic acid, the preparation method of which is as follows:

[0131] The reaction flask was repeatedly evacuated and purged with nitrogen. 2 mol (232 g) of glycolide, 0.01 mol (1.3 g) of tert-butyl glycidyl ether (130) and 0.79 g of the mixture obtained in Preparation Example 6 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. 221.8 g of polyglycolic acid was obtained, with a yield of 95.6%.

[0132] 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.

[0133] Example 7

[0134] This embodiment provides a polyglycolic acid, the preparation method of which is as follows:

[0135] The reaction flask was repeatedly evacuated and purged with nitrogen. 2 mol (232 g) of glycolide, 1.86 g (0.01 mol) of octyl glycidyl ether, and 0.95 g of the mixture obtained in Preparation Example 7 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 230 °C, and the unreacted monomers in the system were removed by evacuation at a pressure of 100 Pa. 112.4 g of polyglycolic acid was obtained, with a yield of 95.4%.

[0136] 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 78,000 g / mol.

[0137] Example 8

[0138] This embodiment provides a polyglycolic acid, the preparation method of which is as follows:

[0139] The reaction flask was repeatedly evacuated and purged with nitrogen. 2 mol (232 g) of glycolide, 0.02 mol (3.28 g) of benzyl glycidyl ether, and 0.96 g of the mixture obtained in Preparation Example 8 were added to the reaction flask sequentially. 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 at a pressure of 100 Pa. 219.4 g of polyglycolic acid was obtained, with a yield of 94.6%.

[0140] 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.

[0141] Example 9

[0142] This embodiment provides a polyglycolic acid, the preparation method of which is as follows:

[0143] The reaction flask was repeatedly evacuated and purged with nitrogen. 2 mol (232 g) of glycolide and 0.84 g of the mixture obtained in Preparation Example 9 were added to the reaction flask in sequence. The mixture was stirred and the temperature was rapidly raised to 200 °C. After 2 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 g of polyglycolic acid was obtained, with a yield of 94%.

[0144] 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 96,000 g / mol.

[0145] Example 10

[0146] This embodiment provides a polyglycolic acid, the preparation method of which is as follows:

[0147] The reaction flask was repeatedly evacuated and purged with nitrogen. 2 mol (232 g) of glycolide and 0.72 g of the mixture obtained in Preparation Example 10 were added to the reaction flask in sequence. The mixture was stirred and the temperature was rapidly raised to 180 °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, and 220.4 g of polyglycolic acid was obtained, with a yield of 95%.

[0148] 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 116000 g / mol.

[0149] 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 method for preparing a Schiff base catalyst, characterized in that, Includes the following steps: S1: Reaction of diamine monomers with excess salicylaldehyde monomers yields a mixture of Schiff base compounds and excess salicylaldehyde monomers. The molar ratio of the diamine monomer to the salicylaldehyde monomer is 1:(2.4-10); S2: React the mixture obtained in step S1 with amino alcohol monomers to obtain a mixture of Schiff base compounds and alcohols; S3: React the mixture obtained in step S2 with a metal compound to obtain a mixture of Schiff base catalyst and alcohol.

2. The preparation method according to claim 1, characterized in that, The molar ratio of salicylaldehyde monomers to amino alcohol monomers in the mixture obtained in step S1 is 1:(1.2~10); The molar ratio of Schiff base compound to metal compound in the mixture obtained in step S2 is 1:(1 to 1.5).

3. The preparation method according to claim 1, characterized in that, The reaction described in step S1 is carried out in the presence of a solvent.

4. The preparation method according to claim 3, characterized in that, The solvent is selected from any one or more of methanol, ethanol, isopropanol, butanol, pentanol, hexanol, heptanol, octanol, benzene, toluene, tetrahydrofuran, dichloromethane, or trichloromethane; The concentrations of the diamine monomers and salicylaldehyde monomers in the solvent are each independently 5–50 wt%.

5. The preparation method according to claim 1, characterized in that, The reaction in step S1 is carried out at a temperature of 20–100°C for a time of 2–48 hours. The reaction in step S2 is carried out at a temperature of 20–100°C for a time of 2–48 hours. The reaction in step S3 is carried out at a temperature of 20–120°C for a time of 2–96 hours.

6. The preparation method according to claim 1, characterized in that, The diamine monomer is selected from any one or more of ethylenediamine, 1,3-propanediamine, 1,2-propanediamine, 2,2'-dimethylpropanediamine, 1,2-butanediamine, 2,3-butanediamine, 1,2-cyclohexanediamine, o-phenylenediamine, 4-nitro-o-phenylenediamine, 2-methyl-1,3-propanediamine, 4-bromo-o-phenylenediamine, 4,5-dichloro-o-phenylenediamine, 4,5-dibromo-o-phenylenediamine, 4,5-difluoro-o-phenylenediamine, 4-fluoro-o-phenylenediamine, or 4-methoxy-o-phenylenediamine; The salicylaldehyde monomers are selected from 3-bromosalicylaldehyde, 4-bromosalicylaldehyde, 3,5-dibromosalicylaldehyde, 5-fluorosalicylaldehyde, 3-chlorosalicylaldehyde, 4-chlorosalicylaldehyde, 5-chlorosalicylaldehyde, 6-chlorosalicylaldehyde, 4,6-dimethoxysalicylaldehyde, 3,5-dichlorosalicylaldehyde, 4,5-dichlorosalicylaldehyde, 4,6-dichlorosalicylaldehyde, 5,6-dichlorosalicylaldehyde, 5-iodosalicylaldehyde, 3-bromo-5-chlorosalicylaldehyde, 3,5-di-tert-butylsalicylaldehyde, 4-fluorosalicylaldehyde, 6-fluorosalicylaldehyde, 4-methylsalicylaldehyde, 5-methylsalicylaldehyde, 5-nitrate... The following are any one or more of the following: 5-(trifluoromethoxy)salicylaldehyde, 5-bromo-3-nitrosalicylaldehyde, 3-bromo-5-nitrosalicylaldehyde, 4-methoxysalicylaldehyde, 3-methoxysalicylaldehyde, 5-fluoro-3-methylsalicylaldehyde, 3-methylsalicylaldehyde, 3-tert-butylsalicylaldehyde, 3,5-diiodosalicylaldehyde, 3-chloromethyl-5-nitrosalicylaldehyde, 3,6-dimethylsalicylaldehyde, 3-chloro-5-fluorosalicylaldehyde, 3-ethoxysalicylaldehyde, 4-ethylsalicylaldehyde, 5-bromo-3-fluorosalicylaldehyde, or 5-bromo-3-methoxysalicylaldehyde; 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. The metal compound is selected from any one or more of the following: zinc isopropoxide, zinc chloride, aluminum ethoxylate, aluminum isopropoxide, indium isopropoxide, indium chloride, dibutyltin dichloride, stannous chloride, ferric ethoxylate, ferric isopropoxide, ferric trichloride, yttrium isopropoxide, yttrium chloride, titanium isopropoxide, tetrabutyl titanate, cobalt acetate, manganese acetate, chromium acetate, zirconium acetate, zirconium n-butoxide, hafnium isopropoxide, hafnium n-butoxide, cerium acetate, cerium n-butoxide, or nickel acetate.

7. A method for preparing polyglycolic acid, characterized in that, 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 Schiff base catalyst prepared by the preparation method according to any one of claims 1 to 6; The initiator is an alcoholic substance prepared by any one of claims 1 to 6.

8. The preparation method according to claim 7, characterized in that, The epoxy compound is selected from any one or more of allyl glycidyl ether, styrene oxide, isopropyl glycidyl ether, tert-butyl glycidyl ether, octyl glycidyl ether, phenyl glycidyl ether, 2-toluene glycidyl ether, benzyl glycidyl ether, propylene oxide, butane oxide, 1,2-epoxycyclopentane, 1,2-epoxycyclohexane, 1,2-epoxyoctane, 1,2-epoxydodecane, 1,2-epoxytetradecane, or 1,2-epoxyhexadecane.

9. The preparation method according to claim 7, 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:(50-5000).

10. The preparation method according to claim 7, characterized in that, The reaction is carried out at a temperature of 120–240°C for a time of 1–24 hours.