A macrocyclic schiff base molybdenum complex and a preparation method and application thereof
By preparing a macrocyclic Schiff base molybdenum complex as a catalyst, the problems of catalyst biotoxicity and reaction rate in the ring-opening polymerization of ε-caprolactone were solved, and the efficient preparation of high molecular weight polycaprolactone was achieved, which is suitable for industrial production.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- QUZHOU RES INST OF ZHEJIANG UNIV
- Filing Date
- 2024-06-13
- Publication Date
- 2026-05-29
AI Technical Summary
In the existing technology, the catalysts for the ring-opening polymerization of ε-caprolactone have strong biotoxicity and poor reaction rates, making it difficult to obtain high molecular weight polycaprolactone.
Using macrocyclic Schiff base molybdenum complexes as catalysts, these compounds are prepared via condensation and coordination reactions and used in the ring-opening polymerization of ε-caprolactone and lactide to improve monomer conversion and molecular weight.
The macrocyclic Schiff base molybdenum complex significantly improved the reaction rate and monomer conversion, reduced the heavy metal ion content, and produced polycaprolactone with a high molecular weight, making it suitable for industrial production.
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Figure CN118702738B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of catalytic technology for the preparation of biodegradable plastics by ring-opening polymerization of cyclic esters, and in particular to a macrocyclic Schiff base molybdenum complex, its preparation method, and its application. Background Technology
[0002] The widespread use of polymer materials has brought great convenience to our daily lives, but it has also brought serious environmental problems, such as white pollution. Furthermore, with the depletion of non-renewable resources such as fossil fuels and natural gas, there is an urgent need for renewable and biodegradable polymer materials to replace traditional ones. Biodegradable polymer materials can be degraded into environmentally harmless H2O and CO2 in a short time through microbial or chemical decomposition. Due to their environmental friendliness and excellent physicochemical properties, they are widely used in agriculture, biomedicine, disposable products, electronic products, textiles, and other fields.
[0003] Poly(ε-caprolactone) (PCL), as a biodegradable polymer, possesses excellent mechanical properties, biodegradability, and compatibility with other polymers. Among numerous polymer materials, PCL is an ideal material for applications in the biomedical and pharmaceutical fields due to its superior performance. In existing technologies, PCL is synthesized through the self-condensation polymerization of 6-hydroxyhexanoic acid and the ring-opening polymerization of ε-caprolactone. While the self-condensation polymerization of 6-hydroxyhexanoic acid is a linear monomer condensation polymerization, and although this method is simple to operate, it requires high reaction temperatures and long reaction times, and the water generated during the reaction inhibits the reaction, making it impossible to obtain high molecular weight polymers.
[0004] The ring-opening polymerization of ε-caprolactones requires a catalyst, which plays a crucial role in controlling the polymerization process and regulating the structure of the resulting polycaprolactone, thus affecting the performance and application prospects of the polymer. Ring-opening polymerization of ε-caprolactones includes three mechanisms: cationic polymerization, anionic polymerization, and coordination-intercalation polymerization. Among these, coordination-intercalation polymerization has become a research hotspot due to its ability to produce polymers with controllable structures and molecular weights. Using catalysts can make the ring-opening polymerization reaction milder, with fewer side reactions and controllable polymer molecular weights; however, the performance of the catalyst changes with variations in the metal central atom and ligands. Therefore, selecting a suitable coordination catalyst for the ring-opening polymerization of cyclic esters is crucial for improving production efficiency and product quality.
[0005] In the prior art, the paper "Study on Coordination Polymer Catalysts for the Ring-Opening Polymerization of ε-Caprolactone" (Nanjing University of Science and Technology, Tian Feng, March 2021) mentions that aluminum complexes containing Schiff base ligands and their derivatives can be used to catalyze the ring-opening polymerization of cyclic esters. Gallium, indium, and bismuth are also frequently used as complex centers, exhibiting good activity for the ring-opening polymerization of caprolactone. Furthermore, among transition metal complexes capable of catalyzing the ring-opening polymerization of caprolactone, relevant research mainly focuses on metals such as iron, nickel, copper, zinc, titanium, and zirconium. CN116813898A discloses a cyclic lactone ring-opening polymerization catalyst, wherein the catalyst is a metal complex with an N,N'-bis(3,5-di-tert-butylsalicylene)-1,2-cyclohexanediamine structure, which is used for the ring-opening polymerization of ε-caprolactone. Currently, stannous octoate is commonly used as a catalyst in industrial processes for catalyzing ring-opening polymerization to produce biodegradable polyesters. Such heavy metal catalysts have strong biotoxicity and poor polymerization rates.
[0006] Therefore, a non-toxic, harmless, and environmentally friendly catalyst is needed for the ring-opening polymerization of cyclic esters, which can improve the conversion rate and reaction rate of ε-caprolactone during the reaction, resulting in polycaprolactone with a higher molecular weight. Summary of the Invention
[0007] To address the aforementioned limitations of the prior art, the present invention aims to provide a macrocyclic Schiff base molybdenum complex, its preparation method, and its applications. The present invention prepares a Schiff base ligand through a condensation reaction, and then performs a coordination reaction between the Schiff base ligand and a molybdenum source to obtain the macrocyclic Schiff base molybdenum complex. Due to its unique structure, the macrocyclic Schiff base molybdenum complex prepared by the present invention can be used as a catalyst in the ring-opening polymerization of caprolactone and the polymerization of caprolactone and lactide to increase the molecular weight of the polymer and improve the monomer conversion rate.
[0008] To achieve the above objectives, the present invention adopts the following technical solution:
[0009] In a first aspect, the present invention provides a macrocyclic Schiff base molybdenum complex, the chemical structural formula of which is shown in formula (I):
[0010]
[0011] In the formula, the substituent R is -tBu or -Me, and the substituent X is -CH2CH2- or -O-.
[0012] A second aspect of the present invention provides a method for preparing a macrocyclic Schiff base molybdenum complex, comprising the following steps:
[0013] (1) After mixing monomer A, monomer B and toluene evenly, a condensation reaction was carried out. The reaction product was filtered and washed to obtain Schiff base ligand.
[0014] (2) Schiff base ligands and molybdenum source were used as reactants and toluene as reaction solvent. After coordination reaction, toluene was removed and recrystallized to obtain macrocyclic Schiff base molybdenum complex.
[0015] Preferably, in step (1), monomer A is 2,2'-ethylenediphenylamine or 4,4'-diaminodiphenyl ether; monomer B is 4-tert-butyl-2,6-dicarboxyphenol or 4-methyl-2,6-dicarboxyphenol.
[0016] Preferably, in step (1), the molar ratio of monomer A to monomer B is 1:(1-1.2); the total mass of monomer A and monomer B is in the mass ratio of toluene to 1:(40-100).
[0017] Preferably, in step (1), the condensation reaction is carried out at a temperature of 120-140℃ and a reaction time of 4-8h.
[0018] Preferably, in step (1), the solvent used in the washing process is one or more of acetone, cyclohexane, dichloromethane or acetonitrile.
[0019] Preferably, in step (2), the molybdenum source is one of molybdenum acetylacetonate, molybdenum pentachloride, molybdenum tetrachloride oxychloride, or molybdenum hexacarbonyl.
[0020] Preferably, in step (2), the molar ratio of Schiff base ligand to molybdenum source is 1:(1-2), and the mass ratio of Schiff base ligand to reaction solvent is 1:(40-100).
[0021] Preferably, in step (2), the coordination reaction is carried out at a temperature of 120°C and a reaction time of 12-24 h.
[0022] Preferably, in step (2), acetonitrile, N,N-dimethylformamide or acetone is used for recrystallization.
[0023] A third aspect of the invention provides the use of macrocyclic Schiff base molybdenum complexes in either 1) or 2) below:
[0024] 1) Catalyzes the ring-opening polymerization of caprolactone;
[0025] 2) Catalyzes the polymerization of caprolactone and lactide.
[0026] Preferably, the preparation process of the ring-opening polymerization of caprolactone catalyzed by macrocyclic Schiff base molybdenum complex includes the following steps:
[0027] After ε-caprolactone is completely dehydrated, a macrocyclic Schiff base molybdenum complex is added as a catalyst and benzyl alcohol as an initiator. After ring-opening polymerization, polycaprolactone is obtained.
[0028] More preferably, the molar ratio of the catalyst to ε-caprolactone is 1:(250-1000); and the molar ratio of the initiator to the catalyst is (1-1.5):1.
[0029] A further preferred method is to completely dehydrate ε-caprolactone by placing it under vacuum for 2 hours.
[0030] More preferably, during the ring-opening polymerization reaction, the reaction temperature is 120-150℃, the vacuum degree is 20-50Pa, and the reaction time is 2-4h.
[0031] Preferably, the preparation process of the polymerization reaction of caprolactone and lactide catalyzed by macrocyclic Schiff base molybdenum complex includes the following steps:
[0032] ε-caprolactone and lactide are used as reactants, and a macrocyclic Schiff base molybdenum complex is used as a catalyst. After the reactants are dehydrated, they are polymerized with the catalyst to obtain the final product.
[0033] More preferably, the molar ratio of ε-caprolactone to lactide is 1:(1-1.5); the molar ratio of the total amount of ε-caprolactone and lactide to the amount of catalyst is (250-1000):1.
[0034] A further preferred method is to dehydrate the mixed ε-caprolactone and lactide under vacuum for 2 hours.
[0035] More preferably, during the polymerization reaction, the reaction temperature is 120-150℃, the vacuum degree is 20-50Pa, and the reaction time is 2-4h.
[0036] The beneficial effects of this invention are:
[0037] The macrocyclic Schiff base molybdenum complex used in this invention has a unique structure and exhibits good dispersibility in the polymerization reaction system. Furthermore, the macrocyclic Schiff base prepared by this invention, when used in the ring-opening polymerization of cyclic esters to prepare biodegradable bio-copolyesters, can significantly reduce reaction time and increase the polymerization rate, achieving a rate increase of more than three times compared to existing industrial-grade tin-based catalysts. Specifically, at a reaction temperature of 150°C, caprolactone conversion can reach over 99% within 1 hour. Therefore, the macrocyclic Schiff base molybdenum complex prepared by this invention, when used to catalyze ring-opening polymerization reactions, can not only significantly increase the reaction rate and monomer conversion, reduce the content of toxic heavy metal ions in the polymer, but also increase the molecular weight of polycaprolactone.
[0038] The preparation process of the macrocyclic Schiff base molybdenum complex designed in this invention is simple, environmentally friendly, and suitable for industrial mass production. Attached Figure Description
[0039] Figure 1 X-ray photoelectron spectroscopy characterization of the macrocyclic Schiff base molybdenum complex prepared in Example 1;
[0040] Figure 2 The macrocyclic Schiff base molybdenum complex prepared in Example 1 13 C10 HMR solid-state NMR;
[0041] Figure 3 Infrared spectrum of the macrocyclic Schiff base molybdenum complex prepared in Example 1;
[0042] Figure 4 Example 2: Polycaprolactone prepared 1 H NMR characterization image;
[0043] Figure 5 Gel permeation chromatography characterization of polycaprolactone obtained in Example 2;
[0044] Figure 6 Example 3: Polylactide-caprolactone prepared 1 1H NMR characterization image. Detailed Implementation
[0045] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.
[0046] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.
[0047] The experimental materials used in the embodiments of this invention are all conventional experimental materials in the art and can be purchased through commercial channels.
[0048] Example 1: Preparation of macrocyclic Schiff base molybdenum complexes
[0049] (1) 2,2'-Ethylene diphenylamine and 4-tert-butyl-2,6-dicarboxyphenol were used as reactants and mixed in a molar ratio of 1:1. Toluene was then added. The total mass ratio of 2,2'-ethylenediphenylamine and 4-tert-butyl-2,6-dicarboxyphenol to toluene was 1:80. The mixture was stirred at 130°C for 4 hours to carry out the condensation reaction. The toluene was refluxed and the water generated in the reaction was removed. After the reaction was completed, the mixture was filtered and the precipitate was washed with acetone to obtain an orange-red solid, which was the Schiff base ligand.
[0050] (2) Schiff base ligand and molybdenum acetylacetonate were used as reactants and toluene as the reaction solvent. The molar ratio of Schiff base ligand to molybdenum acetylacetonate was 1:1.2 and the mass ratio of Schiff base ligand to reaction solvent was 1:80. The complexation reaction was carried out at 120°C for 12 h with stirring. After removing the toluene solvent, the complex was recrystallized with acetonitrile to obtain the macrocyclic Schiff base molybdenum complex.
[0051] The chemical formula of the macrocyclic Schiff base molybdenum complex obtained by this invention is shown below:
[0052] It is abbreviated as [MoO2(LH2)].
[0053] The macrocyclic Schiff base molybdenum complex prepared in this embodiment was characterized, specifically as follows: Figure 1-3 As shown.
[0054] like Figure 1 As shown, the detection of the N1s peak with a binding energy of 398.6 eV indicates that nitrogen exists in the molecule in the C=N form; the XPS spectrum of Mo shows that Mo 3d 3 / 2 and Mo3d 5 / 2 The values were 235.7 eV and 232.6 eV, respectively, proving that most of the Mo in the complex exists in the hexavalent form (based on C1s 284.8 eV).
[0055] like Figure 2 As shown, the peaks in the 24.62-34.82 ppm range correspond to the tert-butyl carbon peak of the ligand and, in a small portion, the methyl carbon peak of the recrystallization solvent acetonitrile; the peak at 163.41 ppm corresponds to the absorption peak of the carbon-nitrogen double bond in the Schiff base macrocycle. Additionally, carbon peaks on the benzene ring also appear in the 105-170 ppm range.
[0056] like Figure 3 As shown, 2957cm -1 The peak is attributed to the skeletal stretching vibration of C—H on the benzene ring, at 1625 cm⁻¹. -1 These are the peaks of the -CN- stretching vibration in Schiff bases. When -CN is coordinated with molybdenum, the peaks are at 938 and 906 cm⁻¹. －1 The presence of the characteristic absorption peak [MoO2(LH2)] indicates that the Schiff base ligand coordinates with molybdenum to form a complex.
[0057] Example 2: Ring-opening polymerization of ε-caprolactone catalyzed by macrocyclic Schiff base molybdenum complex
[0058] ε-caprolactone was added to a three-necked flask equipped with a stirrer, a vacuum device, and a temperature control device. The mixture was dehydrated under vacuum for 2 hours to ensure complete dehydration. Then, the macrocyclic Schiff base molybdenum complex prepared in Example 1 was added to the three-necked flask as a catalyst. The molar ratio of the macrocyclic Schiff base molybdenum complex to ε-caprolactone was 1:500, and the molar ratio of the initiator benzyl alcohol to the catalyst was 1:1. The ring-opening polymerization reaction was carried out at 150°C and atmospheric pressure for 3 hours, followed by a 1-hour reaction under a vacuum of 30 Pa. The reaction system was then poured into 200 mL of a cold methanol-acetic acid mixture (methanol to acetic acid mass ratio of 200:1) to obtain polycaprolactone.
[0059] The polycaprolactone obtained in this embodiment was structurally characterized, and the results are as follows: Figures 4-5 As shown.
[0060] Depend on Figure 4 It can be seen that the conversion rate of caprolactone monomer is higher than 99%, which shows that using the macrocyclic Schiff base molybdenum complex prepared in this invention as a catalyst can improve the monomer conversion rate of caprolactone ring-opening polymerization.
[0061] Depend on Figure 5 It can be seen that the number-average molecular weight of PCL obtained after 2 hours of reaction is 55931 and the weight-average molecular weight is 95008. This shows that using the macrocyclic Schiff base molybdenum complex prepared in this invention as a catalyst can increase the molecular weight of polycaprolactone obtained by ring-opening polymerization.
[0062] Example 3: Polymerization of lactide and ε-caprolactone catalyzed by macrocyclic Schiff base molybdenum complexes
[0063] 4.4 g of ε-caprolactone was added to a 100 mL three-necked flask equipped with a stirrer, vacuum device, and temperature control. The mixture was dehydrated under vacuum for 2 hours to ensure complete dehydration of the ε-caprolactone monomer. Then, the macrocyclic Schiff base molybdenum complex prepared in Example 1 was added to the three-necked flask as a catalyst and benzyl alcohol as an initiator. The molar ratio of catalyst to ε-caprolactone was 1:500, and the molar ratio of initiator to catalyst was 1:1. The reaction was carried out at a reaction temperature of 140 °C under normal pressure to catalyze the reaction of ε-caprolactone. Polymerization was carried out for 1 hour. After the reaction was completed, 5.6 g of dried lactide was added, and the reaction was continued at normal pressure for 1 hour, followed by a vacuum reaction at 30 Pa for 1 hour. After the reaction was completed, the reaction system was poured into 200 mL of a cold mixed solution of methanol and acetic acid (methanol to acetic acid mass ratio of 200:1) to obtain a copolymer of caprolactone and lactide. The conversion rate of caprolactone in the copolymer composition was 67%, the conversion rate of lactide was 99%, the number average molecular weight was 32353, and the molecular weight distribution PDI was 1.97.
[0064] Depend on Figure 6It can be seen that the conversion rate of lactide monomer is higher than 99%, while the conversion rate of caprolactone is about 70%.
[0065] Example 4: Ring-opening copolymerization of ε-caprolactone and γ-lactide catalyzed by macrocyclic Schiff base molybdenum complex
[0066] 4.4 g of ε-caprolactone and 5.6 g of lactide were mixed and added to a 100 mL three-necked flask equipped with a stirrer, vacuum device, and temperature control. The mixture was dehydrated under vacuum for 2 hours to ensure complete dehydration of both ε-caprolactone and γ-lactide. Then, the macrocyclic Schiff base molybdenum complex prepared in Example 1 was added to the three-necked flask as a catalyst, with a molar ratio of macrocyclic Schiff base molybdenum complex to ε-caprolactone of 500:1. Ring-opening polymerization was carried out at 150 °C and 30 Pa vacuum for 2 hours. The reaction system was then poured into 100 mL of a cold methanol-acetic acid mixture (methanol to acetic acid mass ratio of 200:1) to obtain the copolymer of caprolactone and lactide. The copolymer composition showed a caprolactone conversion rate of 67%, a lactide conversion rate of 62%, a polymer number-average molecular weight of 24782, and a molecular weight distribution (PDI) of 1.52.
[0067] Example 5: Cyclic Schiff base molybdenum complex-catalyzed ring-opening copolymerization of ε-caprolactone and lactide
[0068] 4.4 g of ε-caprolactone was weighed and added to a 100 mL three-necked flask equipped with a stirrer, vacuum device, and temperature control device. The monomer was completely dehydrated under vacuum for 2 hours. Then, the macrocyclic Schiff base molybdenum complex prepared in Example 1 was added as a catalyst, with a catalyst-to-ε-caprolactone molar ratio of 250:1. The polymerization reaction of caprolactone was catalyzed at 140 °C and a vacuum of 30 Pa. After 1 hour of polymerization, 5.6 g of dried lactide was added, and the reaction was continued at atmospheric pressure for 2 hours, followed by a vacuum reaction for 1 hour. The reaction system was then poured into 100 mL of a cold methanol-acetic acid mixture (methanol-acetic acid mass ratio of 200:1) to obtain the copolymer of caprolactone and lactide. The copolymer composition showed a caprolactone conversion rate of 87% and a lactide conversion rate of 95%, with a polymer number-average molecular weight of 38264 and a molecular weight distribution (PDI) of 1.87.
[0069] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.
Claims
1. An application of a macrocyclic Schiff base molybdenum complex in either 1) or 2) below: 1) Catalyzing the ring-opening polymerization of caprolactone; 2) Catalyzes the polymerization reaction of caprolactone and lactide; The structural formula of the macrocyclic Schiff base molybdenum complex is shown in formula (I). Formula (I); In the formula, the substituent R is - t Bu or -Me, with substituent X being -CH2CH2- or -O-; Its preparation method is as follows: (1) After mixing monomer A, monomer B and toluene evenly, a condensation reaction is carried out. The reaction product is filtered and washed to obtain Schiff base ligand. The monomer A is 2,2'-ethylenediphenylamine or 4,4'-diaminodiphenyl ether, and the monomer B is 4-tert-butyl-2,6-dicarboxyphenol or 4-methyl-2,6-dicarboxyphenol; (2) Schiff base ligands and molybdenum source were used as reactants and toluene as reaction solvent. After coordination reaction, toluene was removed and recrystallized to obtain macrocyclic Schiff base molybdenum complex. The molybdenum source is one of molybdenum acetylacetonate, molybdenum pentachloride, molybdenum tetrachloride oxychloride, or molybdenum hexacarbonyl; the molar ratio of Schiff base ligand to molybdenum source is 1:(1-2), and the mass ratio of Schiff base ligand to reaction solvent is 1:(40-100); in the coordination reaction, the reaction temperature is 100-130℃, and the reaction time is 12-24 h.
2. The application as described in claim 1, characterized in that, In step (1), the molar ratio of monomer A to monomer B is 1:(1-1.2); the total mass ratio of monomer A and monomer B to toluene is 1:(40-100); in the condensation reaction, the reaction temperature is 120-140℃ and the reaction time is 4-8h.
3. The application as described in claim 1, characterized in that, The specific steps for catalyzing the ring-opening polymerization of caprolactone are as follows: After ε-caprolactone is completely dehydrated, a macrocyclic Schiff base molybdenum complex is added as a catalyst and benzyl alcohol as an initiator. After ring-opening polymerization, polycaprolactone is obtained.
4. The application as described in claim 3, characterized in that, The molar ratio of the catalyst to ε-caprolactone is 1:(250-1000); the molar ratio of the initiator to the catalyst is (1-1.5):
1.
5. The application as described in claim 1, characterized in that, The specific steps of the polymerization reaction of caprolactone and lactide are as follows: ε-caprolactone and lactide are used as reactants, and a macrocyclic Schiff base molybdenum complex is used as a catalyst. After the reactants are dehydrated, they are polymerized with the catalyst to obtain the final product.
6. The application as described in claim 5, characterized in that, The molar ratio of ε-caprolactone to lactide is 1:(1-1.5); the molar ratio of the total amount of ε-caprolactone and lactide to the amount of catalyst is (250-1000):1; during the polymerization reaction, the reaction temperature is 120-150 ℃, the vacuum degree is 20-50 Pa, and the reaction time is 2-3 h.