CN112094407A - Biguanide group covalent organic framework material and preparation method and application thereof - Google Patents

Abstract

The invention discloses a biguanide-based covalent organic framework material and a preparation method and application thereof. The biguanide-based covalent organic framework material has a two-dimensional organic framework, and its unique biguanide structure can be directly used as lactic acid to be directly polycondensed into polylactic acid and Catalyst for the bulk ring-opening polymerization of lactide into polylactic acid. By introducing biguanide into the covalent organic framework material, the present invention achieves excellent catalytic effect on the direct polycondensation of lactic acid into polylactic acid and the bulk ring-opening polymerization of lactide into polylactic acid, and the polymerization degree of the polymer can be controlled and synthesized according to requirements , the molecular weight distribution index PDI is narrow, the catalyst and the product are easy to separate, and there is no catalyst residue in the product, and the synthesized polylactic acid has high biosafety; at the same time, this covalent organic framework material constructed from biguanide can be reused, greatly The application cost is reduced, and the application can be widely promoted.

Description

A kind of biguanide-based covalent organic framework material and preparation method and application thereof

technical field

The invention relates to a biguanide-based covalent organic framework material, a preparation method and application thereof, and belongs to the technical field of guanidine heterogeneous catalysts.

Background technique

With the rapid development of the field of biomedicine at home and abroad, the demand for medical degradable materials with excellent biocompatibility and safety has increased dramatically, especially in drug carriers and tissue repair materials. Polylactic acid has attracted extensive attention due to its good biocompatibility and degradability, and it has many important applications in the field of biomedicine. Previously, the commercial production of polylactic acid was mainly synthesized by the stannous octoate ring-opening polymerization method, but the tin-containing catalyst could not be completely removed from the polymer after the polymerization reaction. Therefore, it is particularly necessary to develop tin-free, non-toxic and easy-to-separate catalysts.

Covalent Organic Frameworks (COFs) are porous compounds with periodic structures linked by organic building blocks through covalent bonds. Completely different from covalent polymers linked by irreversible condensation, COFs display highly ordered crystal structures through reversible reactions. Compared with traditional crystalline porous solids, such as zeolites and metal-organic frameworks (MOFs), COFs have precise pre-engineered structures and tailored functions that enable function-specific structural and chemical control. Different compositions, porosity, pore sizes, etc. can be designed as required to achieve specific uses.

Generally, the synthesis methods of COFs include solvothermal method, ionothermal method, microwave irradiation method and mechanical grinding method. The most common preparation method of COFs is the solvothermal method, that is, the reaction monomer, solvent and catalyst are added to the system, and the reaction is carried out after deoxygenation through a freeze-pump cycle operation. In a closed reaction system, by controlling the type of solvent, solvent ratio or reaction pressure. , making it thermodynamically stable products in a relatively slow process. There are many shortcomings in traditional homogeneous catalysis, such as the difficulty in separating the reaction product from the catalyst, and the difficulty in reusing the catalyst, resulting in great waste. The use of COFs catalyst can effectively solve the above problems. Since COFs are structurally stable and insoluble in solvents, they can be used as a small-space nanoreactor. After the reaction, it can be easily separated from the reaction mixture and can be used repeatedly.

Guanidine is a nitrogen-containing organic compound and an organic strong base. Its basicity is comparable to that of inorganic strong bases, and its basicity is similar to that of sodium hydroxide. Guanidine catalysts with various structures (bicyclic, monocyclic and acyclic) The emergence of the type) has enabled many basic organic transformations to be efficiently realized. However, due to the high polarity of guanidine compounds, it is difficult to separate and purify them, and there are also many limitations in the synthesis method. Therefore, the introduction of guanidine compounds into covalent organic framework materials as heterogeneous catalysts can be utilized through simple recycling and greatly reduce purification costs and production costs. In the modification of biguanide, it has been reported that it was introduced into functional guanidine ionic liquids, and metformin was immobilized on _SiO2 and introduced into amino-functionalized mesoporous molecular sieves, etc., but the overall catalytic recovery efficiency was not high. In addition, guanidine is also applied in the research of synthesizing polylactic acid. For example, the invention of Chinese Patent Publication No. CN 102875779 B reports the process method of bicyclic guanidine catalyzed polycondensation of lactic acid into medical biodegradable polylactic acid, and Chinese Patent Publication No. CN 104892916 The invention of B reports a process for the controlled synthesis of polylactic acid by organic guanidine-non-toxic alcohol catalyzed active ring-opening polymerization of lactide, but these processes still do not ideally improve the catalytic efficiency and recycling rate. Therefore, combining the advantages of covalent organic framework materials to synthesize new heterogeneous catalysts of guanidine compounds and achieve good catalytic activity for recycling and reuse still has great research and utilization value.

SUMMARY OF THE INVENTION

The object of the present invention is to solve the problem of the existing guanidine catalysts in the application of catalyzing the direct polycondensation of lactic acid into polylactic acid and the ring-opening polymerization of lactide into polylactic acid due to the difficulty of guanidine compound synthesis and the complexity of separation and purification. limitation issue. By introducing biguanide into the covalent organic framework material, the present invention achieves excellent catalytic effect on the direct polycondensation of lactic acid into polylactic acid and the bulk ring-opening polymerization of lactide into polylactic acid, and the degree of polymerization of the polymer can be controlled according to requirements. , the molecular weight distribution index PDI is narrow, the catalyst and the product are easy to separate, and there is no catalyst residue in the product, the synthesized polylactic acid has high biosafety; at the same time, this covalent organic framework material constructed from biguanide can be reused, greatly Reduced application costs.

For realizing the above-mentioned purpose of the invention, the present invention adopts following technical scheme:

A first aspect of the present invention provides a biguanide-based covalent organic framework material. The biguanide-based covalent organic framework material is abbreviated as COF-JNU, and its characteristic structure is shown in formula 1:

结构；“L₂”为

结构中的一种。In formula 1, "L ₁ " is

structure; "L ₂ " is

one of the structures.

A second aspect of the present invention provides a method for preparing a biguanide-based covalent organic framework material COF-JNU, comprising the steps of: mixing aromatic amine and 1,4-benzenedicyanoguanidine or sodium dicyanamide in a molar ratio 2:3, in water or an organic solvent, using hydrochloric acid as a catalyst, under nitrogen protection at 90 to 100 ° C for 24 to 48 hours, and after the reaction is completed, centrifugation, washing and drying are performed to obtain the biguanide-based covalent organic framework material. COF-JNU.

Further, the aromatic amine is melamine, 1,3,5-triaminobenzene, 2,4,6-tris(4-aminophenyl)-1,3,5-triazine or 1,3,5 - A kind of tris(4-aminophenyl)benzene.

Further, the organic solvent is one or more of dimethyl sulfoxide, N,N-dimethylformamide and dioxane used in combination.

Further, the added amount of the hydrochloric acid is 2-3 times the equivalent of the aromatic amine.

The third aspect of the present invention provides the application of a biguanide-based covalent organic framework material COF-JNU in the direct polycondensation of lactic acid into polylactic acid. The biguanide-based covalent organic framework material COF-JNU is added in two steps to react The system carries out a catalytic reaction, and its catalytic reaction equation is shown in the following formula 2:

Wherein, the first step reaction is the synthesis of oligomeric lactic acid OLLA, that is, a predetermined amount of L-lactic acid and COF-JNU (relative to the quality of L-lactic acid is 0.5%), placed in a sealed reactor of 30torr under nitrogen protection, 135 The viscous liquid mixture of oligomeric lactic acid OLLA is obtained by reacting at ℃ for 2 to 3 hours; the second step is the synthesis of polylactic acid PLLA, that is, the viscous liquid mixture of oligomeric lactic acid OLLA obtained in the first step is continuously heated to 175 ℃ , at the same time, the pressure in the reactor was reduced to 10torr, and the reaction was carried out for 0.5 to 4 hours. After the reaction was completed, it was cooled to room temperature. The reaction solution was dissolved in acetone, and the catalyst COF-JNU was recovered by filtration. The filtrate was poured into water, and centrifuged after standing. The precipitate was dried under vacuum at room temperature to obtain a white solid, which was polylactic acid PLLA. Using the biguanide-based covalent organic framework material COF-JNU of the present invention, the yield rate of the catalytic reaction for the direct polycondensation of lactic acid into polylactic acid is over 94%, the Mn is in the range of 1×10 ⁴ to 4.5×10 ⁴ , and the PDI is 1.10 ~1.30.

The fourth aspect of the present invention provides the application of a biguanide-based covalent organic framework material COF-JNU in the bulk ring-opening polymerization of lactide to form polylactic acid. The biguanide-based covalent organic framework material COF-JNU directly Add lactide bulk ring-opening polymerization into polylactic acid reaction system and carry out catalytic reaction, and its catalytic reaction equation is shown in the following formula 3:

The specific steps are as follows: the monomer L-lactide and COF-JNU (relative to the mass of L-lactide are 0.5%), placed in a reaction kettle under nitrogen protection, and reacted at 130 ° C for 0.5 to 4 hours. After cooling to room temperature, the reaction solution was dissolved in acetone, and the catalyst COF-JNU was recovered by filtration. The filtrate was poured into water, and the precipitate was separated by centrifugation after standing, and vacuum-dried at room temperature to obtain a white solid, which was polylactic acid PLLA. Using the biguanide-based covalent organic framework material COF-JNU of the present invention, the yield rate of the catalytic reaction for the bulk ring-opening polymerization of lactide into polylactic acid is over 95%, and the range of Mn is 1×10 ⁴ to 5×10 ⁴ , PDI is 1.10 ~ 1.30.

Further, the described covalent organic framework material COF-JNU constructed from biguanides, after catalyzing the direct polycondensation of lactic acid into polylactic acid and the bulk ring-opening polymerization of lactide into polylactic acid, the reaction solution is simply treated. The catalyst can be recovered by filtration, and after washing and drying, it can be used for the next round of heterogeneous catalytic reaction.

Compared with the prior art, the present invention has the following advantages and beneficial effects:

(1) The biguanide-based covalent organic framework material COF-JNU of the present invention has better thermal stability, catalytic activity, and recycling performance;

(2) The biguanide-based covalent organic framework material COF-JNU of the present invention can be prepared under a variety of single or mixed solvent conditions, the synthesis method is universal, the synthesis method is simple, and the structure is controllable;

(3) The biguanide-based covalent organic framework material COF-JNU of the present invention has high catalytic efficiency in the application of catalyzing the direct polycondensation of lactic acid into polylactic acid and the bulk ring-opening polymerization of lactide into polylactic acid, and the degree of polymer polymerization It can be synthesized in a controlled manner according to demand, and the molecular weight distribution index PDI is narrow;

(4) The biguanide-based covalent organic framework material COF-JNU of the present invention is easy to separate the catalyst and the product in the application of catalyzing the direct polycondensation of lactic acid into polylactic acid and the bulk ring-opening polymerization of lactide into polylactic acid, and there is no catalyst residue in the product , the synthetic polylactic acid is highly biosafe.

Description of drawings

Fig. 1 is the infrared spectrogram of COF-JNU-01 of the embodiment of the present invention 1;

Fig. 2 is the transmission electron microscope picture of COF-JNU-01 of the 200nm scale of the embodiment of the present invention 1;

Fig. 3 is the transmission electron microscope picture of COF-JNU-01 of the 500nm scale of Example 1 of the present invention;

Fig. 4 is the thermogravimetric analysis diagram of COF-JNU-01 of the embodiment of the present invention 1;

5 is a nitrogen adsorption-desorption curve diagram of COF-JNU-01 of Example 1 of the present invention.

Detailed ways

The present invention will be further described below with reference to the accompanying drawings and preferred embodiments. This embodiment is implemented on the premise of the technical solution of the present invention, and provides detailed implementation methods and processes, but the protection scope of the present invention is not limited to the following Examples, the experimental methods without specific conditions in the following examples are usually based on conventional conditions or conditions suggested by the manufacturer.

The reagents used in the examples of the present invention and the comparative examples are shown in Table 1 below, but are not limited thereto:

Table 1

Reagent name molecular formula CAS number supplier purity Sodium Dicyanamide C₂N₃Na 1934-75-4 Shanghai Aladdin Biochemical Technology Co., Ltd. 96% Hydrochloric acid (HCl aqueous solution) / 7647-01-0 Sinopharm Group Chemical Reagent Co., Ltd. 36～38% Ethanol C₂H₆O 64-17-5 Shanghai Titan Technology Co., Ltd. 99.5% melamine C₃H₆N₆ 108-78-1 Shanghai Titan Technology Co., Ltd. 99% p-phenylenediamine C₆H₈N₂ 106-50-3 Shanghai Aladdin Biochemical Technology Co., Ltd. 99% 4-Aminoacetophenone C₈H₉NO 99-92-3 Shanghai Titan Technology Co., Ltd. 99% p-toluenesulfonic acid monohydrate TsOH·H₂O 6192-52-5 Sinopharm Group Chemical Reagent Co., Ltd. 99% Ethyl acetate C₄H₈O₂ 141-78-6 Shanghai Titan Technology Co., Ltd. 99.5% Anhydrous sodium sulfate Na₂SO₄ 15124-09-1 Sinopharm Group Chemical Reagent Co., Ltd. 98% nitrogen N₂ 7727-37-9 Wuxi Taihu Gas Co., Ltd. 99.2% 4-Aminobenzonitrile C₇H₆N₂ 873-74-5 Shanghai Aladdin Biochemical Technology Co., Ltd. 98% 1,3,5-Triaminobenzene C₆H₉N₃ 108-72-5 Shanghai Bide Pharmaceutical Technology Co., Ltd. 95% Chloroform CHCl₃ 67-66-3 Sinopharm Group Chemical Reagent Co., Ltd. 99.7% Trifluoromethanesulfonic acid CF₃SO₃H 1493-13-6 Shanghai Titan Technology Co., Ltd. 99% sodium hydroxide NaOH 1310-73-2 Sinopharm Group Chemical Reagent Co., Ltd. 97% L-lactic acid C₃H₆O₃ 79-33-4 Shanghai Bide Pharmaceutical Technology Co., Ltd. 95% acetone C₃H₆O 67-64-1 Sinopharm Group Chemical Reagent Co., Ltd. 99.5% L-lactide C₆H₈O₄ 4511-42-6 Shanghai Bide Pharmaceutical Technology Co., Ltd. 99%

Example 1

A preparation method of a biguanide-based covalent organic framework material (COF-JNU-01), comprising the following steps:

Weigh melamine (0.42g, 0.33mmol), sodium dicyanamide (0.045g, 0.5mmol) and 20mL of water into the Shrek tube, add HCl aqueous solution (0.08mL) dropwise while stirring, and under nitrogen protection after the dropwise addition 100 ℃ reaction 36h. After the reaction, it was left to stand overnight, and after centrifugation, it was washed three times with ethanol and water, respectively. After vacuum drying, a yellow powder can be obtained, which is the covalent organic framework material COF-JNU-01.

The present invention characterizes the above-synthesized biguanide-based covalent organic framework material COF-JNU-01.

Among them, Figure 1 shows the infrared spectrum of COF-JNU-01, indicating the successful synthesis of COF-JNU-01.

Figures 2 and 3 are the TEM images of COF-JNU-01 with 200nm and 500nm scales, respectively, showing that COF-JNU-01 is flake-like and is a micron-scale organic framework material, forming a large specific surface area, which is conducive to improving the catalysis reactivity.

Figure 4 is a thermogravimetric analysis diagram of COF-JNU-01, which shows that COF-JNU-01 has better thermal stability, thereby ensuring that the heterogeneous catalyst of the present invention has good stability in the application process.

Figure 5 is the nitrogen adsorption-desorption curve of COF-JNU-01, which shows that COF-JNU-01 has a higher specific surface area.

Example 2

A preparation method of a biguanide-based covalent organic framework material (COF-JNU-02), comprising the following steps:

(1) Synthesis of monomer 1,4-benzenedicyanoguanidine

P-phenylenediamine (1.30 g, 12 mmol) was weighed into a boiling aqueous solution of sodium dicyanamide (0.49 g, 5.5 mmol), stirred for 10 minutes, and then added with 1 M HCl aqueous solution (25 mL), and refluxed for 3 hours. After the reaction is completed, the solvent is spun off, the residue is treated with hot ethanol, and filtered while hot to obtain a light gray solid, which is the monomer 1,4-benzenedicyanoguanidine.

(2) Synthesis of monomer 1,3,5-tris(4-aminophenyl)benzene

4-Aminoacetophenone (2.7g, 20mmol) was weighed into the reaction flask, heated to 130°C and then gradually melted, TsOH·H ₂ O (0.54g, 0.15eq) was added in batches, and then the temperature was raised to 145°C and reacted for 16h . After the reaction, ethyl acetate was added to dissolve the reactant, and then water was added for extraction. Anhydrous sodium sulfate is added to the organic phase to dry, and a yellow powder can be obtained after column chromatography, which is the monomer 1,3,5-tris(4-aminophenyl)benzene.

(3) Synthesis of covalent organic framework material COF-JNU-02

Weigh the monomers 1,3,5-tris(4-aminophenyl)benzene (0.117g, 0.33mol), 1,4-benzenedicyanoguanidine (0.121g, 0.5mmol), and 20mL of water and add them to history In the Lake tube, HCl aqueous solution (0.08 mL) was added dropwise while stirring, and the reaction was performed at 100° C. for 36 h under nitrogen protection after the dropwise addition. After the reaction, it was left to stand overnight, and after centrifugation, it was washed three times with ethanol and water, respectively. After vacuum drying, a yellow powder can be obtained, which is the covalent organic framework material COF-JNU-02.

Example 3

A preparation method of a biguanide-based covalent organic framework material (COF-JNU-03), comprising the following steps:

(1) Synthesis of monomer 2,4,6-tris(4-aminophenyl)-1,3,5-triazine

Weigh 4-aminobenzonitrile (3.08g, 26mmol) into the reaction flask, then add 20mL of chloroform as a solvent, very slowly add trifluoromethanesulfonic acid (8mL, 88.8mmol) dropwise in an ice bath, and react during dropwise addition The liquid became viscous, nitrogen protection was completed after the dropwise addition. After stirring for 1 h, the mixture was moved to room temperature and stirred for 24 h. After the reaction, 40 mL of distilled water was weighed and added to the reaction solution, and then 2M NaOH solution was slowly added to adjust the pH of the filtrate to neutral. The crude product was washed five times with distilled water, and a pale yellow powder was obtained by column chromatography, which was the monomer 2,4,6-tris(4-aminophenyl)-1,3,5-triazine.

(2) Synthesis of covalent organic framework material COF-JNU-03

Weigh 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (0.118g, 0.33mmol), sodium dicyanamide (0.045g, 0,5mmol) and 20mL of water into In the Shrek tube, HCl aqueous solution (0.08 mL) was added dropwise while stirring, and after the dropwise addition was completed, the reaction was carried out at 100° C. for 36 h under nitrogen protection. After the reaction, it was left to stand overnight, and after centrifugation, it was washed three times with ethanol and water, respectively. After vacuum drying, a yellow powder can be obtained, which is the covalent organic framework material COF-JNU-03.

Example 4

A preparation method of biguanide-based covalent organic framework material COF-JNU-04, comprising the following steps:

Weigh 1,3,5-triaminobenzene (0.41g, 0.33mmol), 1,4-benzenedicyanoguanidine (0.121g, 0.5mmol (the preparation method is the same as in step (1) of Example 2)) and 20mL of water Add it to the Shrek tube, add HCl aqueous solution (0.08mL) dropwise during stirring, and react at 100°C for 36h under nitrogen protection after the dropwise addition. After the reaction is completed, let it stand overnight, and wash with ethanol and water three times after centrifugation. The yellow powder is obtained, which is the covalent organic framework material COF-JNU-04.

The products obtained in Examples 2 to 4 were measured by infrared spectroscopy, transmission electron microscopy, thermogravimetric analysis and nitrogen adsorption-desorption with the method of Example 1, and obtained technical effects similar to those in Example 1, and all had good performance. Dispersibility, high specific surface area and excellent thermal stability.

Example 5

The biguanide-based covalent organic framework material COF-JNU of the present invention exhibits excellent catalytic activity in the application of catalyzing the direct polycondensation of lactic acid into polylactic acid and its convenient separation and recovery performance. The application of the biguanide-based covalent organic framework material COF-JNU-01 synthesized in Example 1 in the reaction of catalyzing the direct polycondensation of lactic acid into polylactic acid is described as follows.

(1) Synthesis of oligomeric lactic acid OLLA

Weigh L-lactic acid (2g) and COF-JNU-01 (0.1g), place them in a sealed reactor of 30torr under nitrogen protection, and react at 135°C for 2h, and then a viscous liquid mixture of oligomeric lactic acid OLLA can be obtained.

(2) Synthesis of polylactic acid PLLA

The viscous liquid mixture of the oligomeric lactic acid OLLA obtained in step (1) was continued to be heated to 175° C., while the pressure in the reaction kettle was gradually reduced to 10 torr, and the reaction was performed for 2 h. After the reaction was completed, it was cooled to room temperature. The reaction solution was dissolved in acetone, and the catalyst COF-JNU-01 in the filter cake was filtered and recovered for the next cycle of catalysis, and the filtrate was poured into water. The solid, namely polylactic acid PLLA, had a yield of 95.1%, Mn=2.1×10 ⁴ , and PDI=1.12.

Example 6

The biguanide-based covalent organic framework material COF-JNU of the present invention exhibits excellent catalytic activity in the application of catalyzing the bulk ring-opening polymerization of lactide into polylactic acid, and its convenient separation and recovery performance. The application of the biguanide-based covalent organic framework material COF-JNU-01 synthesized in Example 1 in the reaction of catalyzing the bulk ring-opening polymerization of lactide into polylactic acid is described as follows.

The monomer L-lactide (1 g) and COF-JNU-01 (0.05 g) were placed in a reaction kettle under nitrogen protection, and reacted at 130 ° C for 3 h, and cooled to room temperature after the reaction. The reaction solution was dissolved in acetone, the catalyst COF-JNU-01 in the filter cake was filtered and recovered for the next cycle of catalysis, the filtrate was poured into water, the precipitate was centrifuged after standing, and the white solid was obtained by vacuum drying at room temperature. It is polylactic acid PLLA, its yield is 96.2%, Mn=3.2×10 ⁴ , PDI=1.13.

Comparative Example 1

Using bicyclic guanidine as a catalyst, with reference to the invention patent of Patent Publication No. CN 102875779 B, the method provided by Example 2 in the invention patent "Bicyclic guanidine catalyzed polycondensation of lactic acid into medical biodegradable polylactic acid" prepares polylactic acid PLLA, and the specific steps are:

80 g of L-lactic acid (mass content 90%) was charged into the reaction kettle, and the operation of vacuuming and filling with argon was repeated three times. Heated to 110°C under 200torr, and dehydrated for 1h. Then the reactor was depressurized to 100torr and the reaction was continued for 1h at 130°C. Then, the pressure of the reactor was reduced to 30 torr and the reaction was continued at 150° C. for 1 h to obtain oligomeric lactic acid OLLA.

240 mg of catalyst bicyclic guanidine was added to the reaction kettle, the pressure of the reaction kettle was reduced to 10 torr, and the temperature was raised to 190 °C for 16 h. After the reaction was stopped, the reaction kettle was cooled to room temperature, the polymer was dissolved in acetone, then poured into ethanol at 0°C, filtered under reduced pressure, and the solid was dried at 50°C under vacuum for 36 hours to obtain a white solid, which is polylactic acid PLLA , the yield was 73.1%, Mn=2.3×10 ⁴ , PDI=1.70.

Comparative Example 2

Taking guanine acetate as a catalyst and ethanol as an initiator, according to the invention patent "Organic Guanidine-Nontoxic Alcohol Catalyzed Active Ring-Opening Polymerization of Lactide to Synthesize Polylactic Acid" in the patent publication number CN 104892916 B. The method that embodiment 4 provides prepares polylactic acid PLLA, and the concrete steps are:

The monomer LLA 100g, the catalyst guanine acetate 0.098g and the initiator ethanol 0.230g were added to the polymerization reactor, and the air in the polymerization reactor was driven out by three "vacuum-exchange nitrogen" cycle operations, and the pressure in the reactor was kept constant at 0.6 After torr, the reactor was sealed, heated to 96°C in 30min under stirring, and then reacted at 115±1°C for 80min to obtain a white solid, namely polylactic acid PLLA, the yield was 83.7%, Mn=2.0×10 ⁴ , PDI = 1.18.

By comparing the yield, Mn and PDI values of the polylactic acid PLLA prepared by the methods of Comparative Example 1 and Example 5, Comparative Example 2 and Example 6, it can be seen that the catalytic activity of the biguanide-based covalent organic framework material COF-JNU of the present invention is It is more excellent, and the polymer polymerization degree can be controlled and synthesized according to the demand, and the molecular weight distribution index PDI is narrower. In addition, the biguanide-based covalent organic framework material COF-JNU of the present invention is easy to separate from the product, and there is no catalyst residue in the product. The polylactic acid is highly biosafe.

The above descriptions are only preferred embodiments of the present invention, but the protection scope of the present invention is not limited thereto. All equivalent changes, simplifications and modifications made according to the scope of the patent application of the present invention that do not violate the principles involved in the present invention shall fall within the scope of the present invention.

Claims (10)

1. a biguanide-based covalent organic framework material, is characterized in that, the characteristic structure of described biguanide-based covalent organic framework material COF-JNU is as shown in formula 1:

In formula 1, "L ₁ " is

structure; "L ₂ " is

one of the structures. 2. the preparation method of a kind of biguanide-based covalent organic framework material according to claim 1, is characterized in that, comprises the steps: aromatic amine and 1,4-phenylenedicyanoguanidine or sodium dicyanamide are molar The ratio of 2:3, in water or organic solvent, using hydrochloric acid as a catalyst, under nitrogen protection at 90 ~ 100 ° C for 24 ~ 48 hours, after the reaction is completed, centrifugation, washing and drying to obtain the biguanide-based covalent organic framework Material COF-JNU. 3. The preparation method of a biguanide-based covalent organic framework material according to claim 2, wherein the aromatic amine is melamine, 1,3,5-triaminobenzene, 2,4,6- One of tris(4-aminophenyl)-1,3,5-triazine or 1,3,5-tris(4-aminophenyl)benzene. 4. The preparation method of a biguanide-based covalent organic framework material according to claim 2, wherein the organic solvent is dimethyl sulfoxide, N,N-dimethylformamide, dioxygen One or more of the six rings are used in combination. 5 . The method for preparing a biguanide-based covalent organic framework material according to claim 2 , wherein the addition amount of the hydrochloric acid is 2-3 times the equivalent of the aromatic amine. 6 . 6. The application of a biguanide-based covalent organic framework material according to claim 1 in the direct polycondensation of lactic acid into polylactic acid. 7. the application of a kind of biguanide-based covalent organic framework material according to claim 6 in the direct polycondensation of lactic acid into polylactic acid, it is characterized in that, described biguanide-based covalent organic framework material COF-JNU is added in two steps The reaction system carries out a catalytic reaction, and its catalytic reaction equation is shown in the following formula 2:

Wherein, the first step is the synthesis of oligomeric lactic acid OLLA; the second step is the synthesis of polylactic acid PLLA. 8. the application of a kind of biguanide-based covalent organic framework material in the direct polycondensation of lactic acid into polylactic acid according to claim 7, is characterized in that, described first step reaction step comprises: the L-lactic acid of predetermined amount and COF-JNU (0.5% relative to L-lactic acid quality), placed in a sealed reaction kettle of 30torr under nitrogen protection, and reacted at 135°C for 2～3h to obtain the viscous liquid mixture of the oligomeric lactic acid OLLA; The second reaction step includes: continuing to heat the viscous liquid mixture of oligomeric lactic acid OLLA obtained in the first step to 175°C, while reducing the pressure in the reactor to 10torr, reacting for 0.5-4h, and cooling to room temperature after the reaction is completed , the reaction solution was dissolved in acetone, the catalyst COF-JNU was recovered by filtration, the filtrate was poured into water, the precipitate was centrifuged after standing, and the white solid was obtained by vacuum drying at room temperature, namely the polylactic acid PLLA. 9. The application of a biguanide-based covalent organic framework material according to claim 1 in the bulk ring-opening polymerization of lactide into polylactic acid. 10. The application of a biguanide-based covalent organic framework material according to claim 9 in the bulk ring-opening polymerization of lactide into polylactic acid, wherein the biguanide-based covalent organic framework material COF-JNU Directly add lactide bulk ring-opening polymerization into polylactic acid reaction system and carry out catalytic reaction, and its catalytic reaction equation is shown in the following formula 3:

The specific steps are as follows: the monomer L-lactide and COF-JNU (relative to the mass of L-lactide are 0.5%), placed in a reaction kettle under nitrogen protection, and reacted at 130 ° C for 0.5 to 4 hours. After cooling to room temperature, the reaction solution was dissolved in acetone, and the catalyst COF-JNU was recovered by filtration. The filtrate was poured into water, and the precipitate was separated by centrifugation after standing, and vacuum-dried at room temperature to obtain a white solid, which was polylactic acid PLLA.

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