A composite catalyst for ring-opening polymerization of cyclic esters, its preparation method and use

Abstract

The present application relates to a kind of composite catalyst for ring ester ring-opening polymerization and its preparation method and application, the composite catalyst is specifically by hydroxy acid derivative HO-R2-COOH and metal alkoxide M-(O-R1) n Reaction in organic solvent is obtained.The composite catalyst can be used in the preparation of polyester in ring ester ring-opening polymerization reaction.Compared with prior art, the composite catalyst of the present application is simple to prepare, has higher catalytic efficiency at lower metal concentration, and is especially suitable for catalyzing the ring-opening polymerization reaction of glycolide and lactide.

Description

Technical Field

[0001] This invention relates to the field of composite catalyst technology, and in particular to a composite catalyst for the ring-opening polymerization of cyclic esters, its preparation method, and its application. Background Technology

[0002] The environmental problems associated with plastics have driven people to seek more environmentally friendly alternatives to petroleum-derived products. Aliphatic polyesters are high molecular weight polymers containing aliphatic ester bonds in their molecular chains. They have a polyhydroxy fatty acid backbone as the main structure of the molecular chain and can be biodegraded by microorganisms or enzymes in nature (such as in soil or ocean). As a substitute for polyolefins, they are now widely used in various fields, such as food, packaging, and medicine.

[0003] One of the main routes for preparing aliphatic polyesters is through the ring-opening polymerization of cyclic esters. Catalysts such as tin, aluminum, magnesium, zinc, iron, titanium, indium, or rare earth elements are commonly used to catalyze the ring-opening polymerization of glycolide, lactide, or ε-caprolactone. Tin-based catalysts are gradually being used less due to their toxicity, and other catalysts also have problems such as low activity, large dosage, or complex preparation. For example, zinc-based catalysts have attracted much attention because of their strong Lewis acidity and low biotoxicity, but they require a high concentration of metal catalyst during use, which affects the performance of the final product.

[0004] Therefore, there is an urgent need for a composite catalyst that can solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to provide a composite catalyst for the ring-opening polymerization of cyclic esters, its preparation method, and its application in order to solve the above-mentioned problems. The catalyst is prepared by reacting a hydroxy acid derivative HO-R2-COOH with a metal alkoxide M-(O-R1)n. The preparation method is simple, and the composite catalyst obtained has high catalytic efficiency at a low metal concentration.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] The first objective of this invention is to provide a composite catalyst for the ring-opening polymerization of cyclic esters, wherein the composite catalyst is prepared by reacting a hydroxy acid derivative HO-R2-COOH with a metal alkoxide M-(O-R1)n; wherein R2 is a C1-C2 alkyl group substituted with at least one phenyl group, or an unsubstituted or substituted phenylene group, or a diphenylene group, etc.

[0008] Preferably, the hydroxy acid derivative is selected from one of the substances in Table 1.

[0009] Table 1 lists optional hydroxy acid derivatives.

[0010]

[0011] Preferably, M in M-(O-R1)n is selected from one or more transition metal elements.

[0012] More preferably, M in M-(O-R1)n is selected from one or more of Ti, V, Mn, Nb, Ta, Mo, W, etc.;

[0013] Preferably, R1 in M-(O-R1)n is selected from one of the alkyl groups.

[0014] More preferably, R1 in M-(O-R1)n is selected from one of methyl, ethyl, n-propyl, isopropyl, or tert-butyl.

[0015] The second objective of this invention is to provide a method for preparing a composite catalyst for the ring-opening polymerization of cyclic esters. The method for preparing the composite catalyst for the ring-opening polymerization of cyclic esters includes the following steps: reacting the hydroxy acid derivative HO-R2-COOH with the metal alkoxide M-(O-R1)n in an organic solvent at a certain reaction temperature and reaction time.

[0016] Preferably, the reaction temperature is 120-150℃ and the reaction time is 4-12h.

[0017] Preferably, the molar ratio of the hydroxy acid derivative HO-R2-COOH to the metal alkoxide M-(O-R1)n is (0.5~2):1.

[0018] Preferably, the organic solvent is selected from one or more of benzene, toluene, dichloromethane, tetrahydrofuran, ethyl acetate, and diethyl ether. The mass ratio of the total mass of the reactants (the sum of the mass of the hydroxy acid derivative and the mass of the metal alkoxide) to the organic solvent is between 1:(5-30). For example, the mass ratio of the total mass of the reactants to the organic solvent can be 1:10, or 1:20.

[0019] A third objective of this invention is to provide an application of the composite catalyst for the ring-opening polymerization of cyclic esters, wherein the composite catalyst described above is applied to the preparation of polyesters by the ring-opening polymerization of cyclic esters.

[0020] Preferably, the reaction temperature of the ring-opening polymerization is 80-250℃, and the reaction time is 0.5-12h.

[0021] The molar ratio of the cyclic ester to the metal in the composite catalyst can be (200-10000):1. More preferably, the molar ratio of the cyclic ester to the metal in the composite catalyst is (200-1000):1. More preferably, the molar ratio of the cyclic ester to the metal element in the composite catalyst is (200-400):1.

[0022] Preferably, the application of the composite catalyst in the ring-opening polymerization of cyclic esters to prepare polyester includes the following steps: under a nitrogen atmosphere, the cyclic ester, composite catalyst, initiator and solvent are reacted in a reactor. After the reaction is completed, a precipitant is added to precipitate the polymer, and the product is obtained after filtration and vacuum drying.

[0023] Preferably, the cyclic ester is one or more of glycolide, lactide, butylidene lactone, caprolactone, etc.

[0024] More preferably, the cyclic ester is glycolide and / or lactide.

[0025] Preferably, the solvent is a low-carbon alcohol, ethyl acetate, tetrahydrofuran, dichloromethane, or toluene, etc. The amount of solvent used is 2 to 15 times the mass of the cyclic ester.

[0026] Preferably, the precipitant can be one or more selected from methanol, ethanol, acetic acid, phenol, tetrachloroethane, hexafluoroisopropanol, trifluoroacetic acid, or water. The amount of precipitant used is 0.5 to 5 times the amount of solvent.

[0027] Preferably, the initiator can be a cationic polymerization initiator such as a protic acid, Lewis acid, or alkylating agent (e.g., trifluoromethanesulfonic acid, p-toluenesulfonic acid), or an anionic polymerization initiator (e.g., potassium benzoate, potassium phenolate, potassium stearate). The mass of the initiator is 0–1.5% wt% of the mass of the cyclic ester.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] 1. The present invention is simple to prepare by reacting the hydroxy acid derivative HO-R2-COOH with the metal alkoxide M-(O-R1)n. The prepared composite catalyst has high catalytic efficiency at low metal concentrations, and is especially suitable for catalyzing the ring-opening polymerization of glycolide and lactide.

[0030] 2. The composite catalyst of the present invention for the ring-opening polymerization of cyclic esters has low toxicity, high activity, small dosage, and simple preparation. When the molar ratio of cyclic ester to metal in the composite catalyst is 300:1, the monomer conversion rate of cyclic ester is above 92%. Detailed Implementation

[0031] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0032] The applicant believes that during the conceptualization process:

[0033] Generally, some metal alkoxides (e.g., titanium alkoxides) are neutral and do not exhibit obvious acidity or basicity. However, under certain specific conditions, they can act as hydrogen bond acceptors, exhibiting basic characteristics and forming acid-base bifunctional catalysts with hydrogen bond donors. Furthermore, after losing one or two hydrogens, the hydrogen bond donor can coordinate with the metal center in the metal alkoxide, enhancing the activity and stability of the metal. The following shows a schematic diagram of a complex formed by a hydroxy acid derivative losing two hydrogens and a group IVB metal M.

[0034]

[0035] Therefore, a composite catalyst can be prepared based on the coordination of the metal center and the complex and acid-base co-catalysis. Specifically, it can be prepared by reacting the hydroxy acid derivative HO-R2-COOH with the metal alkoxide M-(O-R1)n.

[0036] Any preparation methods, materials, structures, or composition ratios not explicitly described in this technical solution are considered common technical features disclosed in the prior art.

[0037] In the following embodiments of the present invention, all raw materials are commercially available.

[0038] Examples 1-10

[0039] This embodiment provides a method for preparing a composite catalyst for the ring-opening polymerization of cyclic esters, comprising the following steps:

[0040] A certain proportion of hydroxy acid derivatives were reacted with metal alkoxide M-(O-R1)n in an organic solvent. The reaction temperature was 120-150℃ (the reaction process could be carried out under closed pressure or by reflux condensation). The reaction time was 4-12h. After the reaction was completed, the mixture was cooled to room temperature, and then the volatiles were removed by vacuum distillation and dried in an oven. The composite catalysts CAT1-10 in Examples 1-10 were prepared using this method, as shown in Table 2.

[0041] Table 2 shows the reaction conditions for Examples 1-10.

[0042]

[0043]

[0044] (All organic solvents are toluene, with a molar ratio of hydroxy acid derivative to metal alkoxide, and the total mass ratio of reactants to organic solvents is 1:10.)

[0045] Application Examples 1-10

[0046] The composite catalysts prepared in Examples 1-10 above were used in the ring-opening polymerization reaction of cyclic esters, respectively, as described in Examples 1-10, including the following steps:

[0047] Under a nitrogen atmosphere, cyclic esters, composite catalysts, initiators, and solvents are reacted in a reactor at a temperature of 80-250℃ for 0.5-12 hours. After the reaction is complete, a precipitant is added to precipitate the polymer, and the product is obtained after filtration and vacuum drying.

[0048] The monomer conversion rate of the product was tested, including the following steps: Take about 0.5 g of sample and place it in a sealed container. Accurately add 15 mL of hexafluoroisopropanol to dissolve it. After dissolution, transfer the test solution to a 100 mL round-bottom (flat-bottom) flask. Add 15 mL of hexafluoroisopropanol to the sealed container and wash it clean. Transfer it to the flask and accurately add 10 mL of acetone. Shake to precipitate the polymer, shake to dissolve, filter, and collect the filtrate. Take 1 μL each of the above reference solution and test solution and inject them into the gas chromatograph. Record the chromatogram and calculate the content of residual small molecule substances.

[0049] The reaction conditions and monomer conversion test results of the products in Examples 1-10 are shown in Table 3.

[0050] Table 3 shows the reaction conditions and monomer conversion test results of the products in Application Examples 1-10.

[0051]

[0052]

[0053] (Toluene is used as the solvent, ethanol as the precipitant, and p-toluenesulfonic acid as the initiator. The molar ratio is the molar ratio of the cyclic ester to the metal element in the composite catalyst. The amount of solvent is 10 times the mass of the cyclic ester, the amount of precipitant is the same as the amount of solvent, and the mass of initiator is 0.5% wt of the mass of the cyclic ester.)

[0054] As can be seen from Application Examples 2-4 and 7-9 in Table 3, the monomer conversion rate decreases with increasing molar ratio of the cyclic ester to the metal element in the composite catalyst. However, when the molar ratio of the cyclic ester to the metal element in the composite catalyst is 300:1, the decrease in monomer conversion rate is not significant compared to the rate corresponding to a molar ratio of 200:1, but the increase is significant compared to the rate corresponding to a molar ratio of 400:1. Therefore, in practical applications, setting the molar ratio of the cyclic ester to the metal element in the composite catalyst to 300:1 is more suitable. Table 3 shows that when the molar ratio of the cyclic ester to the metal element in the composite catalyst is 300:1, the monomer conversion rate of the cyclic ester is consistently above 92%.

[0055] Furthermore, in the application examples where the molar ratio of the cyclic ester to the metal element in the composite catalyst is 300:1, in the ring-opening polymerization reaction of glycolide, the monomer conversion rate of application example 3 is significantly higher than that of application examples 1 and 5 (both with Ti as the metal element), and in the ring-opening polymerization reaction of lactide, the monomer conversion rate of application example 8 is significantly higher than that of application example 10 (both with Nb as the metal element). Among them, the catalyst CAT3 used in application example 3 is prepared from 3-hydroxy-2-phenylpropionic acid and Ti(OMe)4, and the catalyst CAT8 used in application example 8 is prepared from 2-hydroxymethylbenzoic acid and Nb(OEt)5. It is speculated that after 3-hydroxy-2-phenylpropionic acid and 2-hydroxymethylbenzoic acid lose hydrogen, they can form a more stable complex with the metal center.

[0056] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. The application of a composite catalyst in the ring-opening polymerization of cyclic esters to prepare polyester, characterized in that, The composite catalyst was prepared by reacting 3-hydroxy-2-phenylpropionic acid with Ti(OMe)4. The cyclic ester is glycolide, and the preparation of polyester by ring-opening polymerization of the cyclic ester includes the following steps: under a nitrogen atmosphere, glycolide, composite catalyst, initiator and solvent are reacted in a reactor at a reaction temperature of 220°C for 5 hours. After the reaction is completed, a precipitant is added to precipitate the polymer, and the product is obtained after filtration and vacuum drying. The solvent used is toluene; The precipitant is ethanol; The initiator is p-toluenesulfonic acid, and the mass of the initiator is 0.5% wt of the mass of glycolide; The molar ratio of glycolide to the metal element in the composite catalyst is (200~400):

1.

2. The application according to claim 1, characterized in that, The preparation method of the composite catalyst includes the following steps: reacting the 3-hydroxy-2-phenylpropionic acid with Ti(OMe)4 in an organic solvent at a certain reaction temperature and reaction time to obtain the composite catalyst.

3. The application according to claim 2, characterized in that, The reaction temperature is 120-150℃, and the reaction time is 4-12h; The molar ratio of 3-hydroxy-2-phenylpropionic acid to Ti(OMe)4 is (0.5~2):1.

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