Heteropolyacid metal MOF heterogeneous catalyst containing copper, silicon and tungsten and preparation method of heteropolyacid metal MOF heterogeneous catalyst

Abstract

The invention belongs to the technical field of heterogeneous catalysts for synthesis of polycaprolactone-polyethylene glycol segmented copolymers, and particularly relates to a copper-silicon-tungsten-containing heteropoly acid metal MOF heterogeneous catalyst and a preparation method thereof. The polyacid type metal-organic framework heterogeneous catalyst can effectively catalyze epsilon-caprolactone and PEG to carry out ring-opening copolymerization so as to prepare a related technology of the PCL-PEG segmented copolymer, and the related technology is not reported yet. Aiming at the problems, the invention provides the copper-silicon-tungsten-containing heteropolyacid metal MOF heterogeneous catalyst, the chemical formula of the copper-silicon-tungsten-containing heteropolyacid metal MOF heterogeneous catalyst is [Cu2 (L) 3 (SiW12O40) (H2O) 4] n, and the catalyst is a heterogeneous catalyst, not only inherits the characteristics of high specific surface area and adjustable structure of an MOF material, but also has excellent catalytic activity and acidity of heteropolyacid, provides more active sites for catalytic reaction, and has a good application prospect. Compared with a traditional homogeneous catalyst, the catalyst has the advantage that the catalyst can be easily separated from and recycled from a reaction system.

Description

Technical Field

[0001] This invention belongs to the technical field of heterogeneous catalysts for the synthesis of polycaprolactone-polyethylene glycol block copolymers, specifically relating to a copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst and its preparation method. Background Technology

[0002] Polycaprolactone (PCL) is considered an ideal biomedical material due to its excellent biodegradability, compatibility, and flexible molecular chain structure. However, its strong hydrophobicity and slow degradation rate limit its direct application as a drug-controlled release carrier. To overcome these limitations, it is often copolymerized with hydrophilic and biofriendly polyethylene glycol (PEG) to construct PCL-PEG block copolymers. These materials can have their physicochemical properties systematically controlled, significantly expanding their application potential in drug delivery systems such as nanoparticles, and are currently a research hotspot in the field of biomaterials.

[0003] Currently, the synthesis of PCL-PEG copolymers mainly relies on the ring-opening copolymerization reaction of ε-caprolactone initiated by PEG, and metal-based homogeneous catalysts such as stannous octoate are commonly used. However, such catalytic systems have significant drawbacks: on the one hand, they are sensitive to water and oxygen, have poor stability, and often lead to low monomer conversion rates, increased side reactions, and a wider molecular weight distribution of the products, which is not conducive to precise synthesis; on the other hand, the catalyst is prone to remain in the product, and the potential biotoxicity risks posed by the metal components (such as tin) have raised serious safety concerns in pharmaceutical applications, restricting the clinical translation of such materials.

[0004] In recent years, heterogeneous catalysts such as polyoxometalate (polyacid)-based coordination polymers and metal-organic frameworks have demonstrated high activity and selectivity in the ring-opening homopolymerization of cyclic esters such as ε-caprolactone and lactide, providing new directions for the development of green catalytic systems. However, it must be pointed out that ring-opening block copolymerization is far more complex in mechanism and control than homopolymerization. Its success depends heavily on the precise matching of the catalyst's reaction rates to various monomers, its ability to regulate the sequence structure, and its compatibility with macromolecular initiators (such as PEG). Currently, there are no reports in the published literature of heterogeneous catalysts with polyacid-based metal-organic frameworks effectively catalyzing the ring-opening copolymerization of ε-caprolactone and PEG to prepare PCL-PEG block copolymers. This reflects that catalytic systems suitable for homopolymerization may not be directly applicable to the more complex block copolymerization process.

[0005] Therefore, developing novel heterogeneous catalytic systems that are highly efficient, biocompatible, and capable of precisely controlling the copolymerization sequence and molecular weight is crucial for synthesizing high-quality PCL-PEG copolymers and promoting their advanced medical applications. Addressing the core issues of residual toxicity in existing homogeneous catalysts and the lack of copolymerization catalytic systems, this study designs and prepares novel polyacid-based metal-organic framework heterogeneous catalysts to achieve efficient and controllable ring-opening copolymerization of ε-caprolactone and polyethylene glycol. This has significant scientific research value and clear industrial application potential. Summary of the Invention

[0006] A problem existing in the prior art is that no relevant technology has been reported regarding the effective catalysis of ring-opening copolymerization of ε-caprolactone and PEG with heterogeneous catalysts of polyacid metal-organic frameworks to prepare PCL-PEG block copolymers. To address this problem, this invention provides a copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst with the chemical formula [Cu2(L)3(SiW]3]. 12 O 40 (H2O)4] n In the chemical formula, L represents the organic ligand, which is 2,3,5,6-tetrafluoro-bis(1,2,4-triazol-1-methyl)benzene; H₂O is the solvent; Cu is the metal central ion; and SiW 12 O 40 It is a heteropolyacid anion, where n represents the repeating structural unit Cu2(L)3(SiW) 12 O 40 The infinite extension of )(H2O)4.

[0007] Preferably, the secondary structural units of the copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst satisfy the following conditions: the crystal belongs to the triclinic crystal system, and the space group is [missing information]. .

[0008] Preferably, the cell parameters of the copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst are a=11.662(2) Å, b=13.171(2) Å, c=13.668(2) Å, α=65.9(1)°, β=76.9(1)°, γ=69.5(1)°, cell volume is 1783.4(2) Å3, and Z=1.

[0009] The preparation method of the copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst includes the following steps:

[0010] Copper salt, silicotungstic acid, 2,3,5,6-tetrafluoro-bis(1,2,4-triazol-1-methyl)benzene, and deionized water were mixed evenly, and the pH of the reaction system was adjusted to be acidic (pH=1.0~2.0). The copper-containing silicotungstic heteropolyacid metal MOF heterogeneous catalyst was obtained by self-assembly through solvothermal reaction.

[0011] Preferably, the solvothermal reaction involves placing the reaction system at 140-200°C for 6-96 hours. After the reaction is completed, the reaction system is cooled to room temperature, and solid-liquid separation is performed to collect the solid product, thereby obtaining the target catalyst.

[0012] Preferably, the copper salt includes one or more of copper nitrate, copper acetate, copper chloride, copper sulfate, and their hydrates.

[0013] Preferably, the ratio of 2,3,5,6-tetrafluoro-bis(1,2,4-triazol-1-methyl)benzene to deionized water is 1 mmol: 30~120 mL.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0015] (1) This invention constructs a novel metal-organic framework (MOF) heterogeneous catalyst by ingeniously combining catalytically active copper ions, structurally rigid fluorinated organic ligands, and highly stable, strongly acidic silicotungsten heteropolyacid anions. This structure achieves the integration and synergy of multiple component functions, inheriting not only the characteristics of high specific surface area and tunable structure of MOF materials, but also the excellent catalytic activity and acidity of heteropolyacids, providing more active sites for catalytic reactions and significantly improving catalytic performance;

[0016] (2) The catalyst is a solid heterogeneous system, which has the advantage of being easy to separate and recover from the reaction system compared with traditional homogeneous catalysts. This greatly simplifies the post-processing, reduces production costs, and facilitates the recycling of the catalyst, meeting the requirements of green chemistry and sustainable chemical production;

[0017] (3) The catalyst was used in the ring-opening copolymerization of caprolactone and polyethylene glycol, exhibiting excellent catalytic activity. It can efficiently initiate the polymerization reaction with extremely low catalyst dosage. Its heterogeneous characteristics help to obtain polycaprolactone-polyethylene glycol block copolymers with narrower molecular weight distribution and more regular structures;

[0018] (4) The prepared polycaprolactone-polyethylene glycol block copolymer (PCL-PEG) is an important type of biodegradable polymer material with extremely high application value in biomedical fields such as drug sustained-release carriers and tissue engineering scaffolds. The catalytic system provided by this invention offers a new technical route for the efficient and green synthesis of this functional polymer. Attached Figure Description

[0019] Figure 1 : is the ¹H NMR spectrum of 2,3,5,6-tetrafluoro-bis(1,2,4-triazol-1-methyl)benzene.

[0020] Figure 2: This is the infrared spectrum of the copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst obtained in Example 1.

[0021] Figure 3 : This is a coordination environment diagram of the copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst obtained in Example 1 of the present invention.

[0022] Figure 4 : This is a two-dimensional layered structure diagram of the copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst obtained in Example 1 of the present invention.

[0023] Figure 5 : This is the PXRD spectrum of the copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst obtained in Example 1.

[0024] Figure 6 : This is the TG curve of the copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst obtained in Example 1.

[0025] Figure 7 : This is a graph showing the molecular weight and molecular weight distribution of the polycaprolactone-polyethylene glycol copolymer obtained by application 1.

[0026] Figure 8 : is the ¹H NMR spectrum of the polycaprolactone-polyethylene glycol copolymer obtained by application 1. Detailed Implementation

[0027] The present invention will be described in detail below with reference to embodiments. However, it should be understood that the following embodiments are merely illustrative examples of implementation of the present invention and are not intended to limit the scope of the present invention.

[0028] The 2,3,5,6-tetrafluoro-bis(1,2,4-triazol-1-methyl)benzene used in the following embodiments of the present invention is prepared by the following method:

[0029] (1) Tetrafluoro-terephthalic acid (10.50 g, 0.05 mol) was added to a 250 mL round-bottom flask, followed by 120 mL of dichloromethane. After stirring until clear, thionyl chloride (23.79 g, 0.20 mol) was added, and stirring continued until clear. The mixture was then refluxed at 40-45 °C for 1 hour. After the reaction was completed, the reaction solution was rotary evaporated to obtain approximately 11.30 g of a white solid, namely the intermediate 2,3,5,6-tetrafluoro-1,4-di(chloromethyl)benzene, with a yield of approximately 99.59%.

[0030] (2) Subsequently, triazole (6.91 g, 0.10 mol) and anhydrous potassium carbonate (20.0 g) were added to a 500 mL four-necked flask, followed by 120 mL of acetone. The mixture was stirred for 30 minutes. All the white solid obtained in step (1) was dissolved in 180 mL of acetone and added dropwise to the reaction system of step (2) while stirring. After the addition was complete, the mixture was refluxed and stirred at 57-60 °C for 12 hours. After the reaction was completed, the reaction mixture was separated by vacuum filtration. The filter cake was washed with water, filtered, and dried to obtain the first part of the product. The filtrate was evaporated by rotary evaporation, washed with water, and dried to obtain the second part of the product. The two parts of the product were combined to obtain approximately 9.91 g of white solid (i.e., the target product 2,3,5,6-tetrafluoro-bis(1,2,4-triazole-1-methyl)benzene), with a total yield of approximately 64.2%.

[0031] The obtained 2,3,5,6-tetrafluoro-bis(1,2,4-triazol-1-methyl)benzene was characterized by the following NMR spectrometry:

[0032] Instruction manual attached Figure 1 This is the ¹H NMR spectrum of 2,3,5,6-tetrafluoro-bis(1,2,4-triazole-1-methyl)benzene. The spectrum shows two characteristic signals at δ = 8.73 (single peak, 1H) and 7.97 (single peak, 1H), both attributed to hydrogen atoms in different chemical environments on the triazole ring of 2,3,5,6-tetrafluoro-bis(1,2,4-triazole-1-methyl)benzene. The signal at δ = 5.60 (single peak, 2H) is attributed to hydrogen atoms on the methylene group of 2,3,5,6-tetrafluoro-bis(1,2,4-triazole-1-methyl)benzene. The testing conditions were: ¹H NMR (500 MHz, DMSO-d6), acquired using an AVANCE NEO 500 MHz NMR spectrometer from Bruker GmbH, Germany.

[0033] Example 1

[0034] A method for preparing a copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst is as follows:

[0035] Copper nitrate trihydrate (24.2 mg, 0.1 mmol), 2,3,5,6-tetrafluoro-bis(1,2,4-triazol-1-methyl)benzene (47.0 mg, 0.15 mmol), and silicotungstic acid hexahydrate (143.5 mg, 0.7 mmol) were added to 6 mL of deionized water. After stirring at room temperature for 20 minutes, the pH of the reaction system was adjusted to 1.5 with hydrochloric acid at a concentration of 0.1 mol / L. The reaction system was then transferred to a 25 mL polytetrafluoroethylene autoclave and subjected to a solvothermal reaction at 180 °C for 72 hours. The reaction system was then slowly cooled to room temperature to obtain blue blocky crystals (i.e., the target product: a copper-containing silicotungstic heteropolyacid metal MOF heterogeneous catalyst) in 80% yield (84.4 mg, based on silicotungstic acid hexahydrate).

[0036] The copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst obtained in Example 1 was characterized as follows:

[0037] (1) Infrared testing:

[0038] Instruction manual attached Figure 2 This is the infrared spectrum of the copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst obtained in Example 1. The image shows the 3000-3500 cm⁻¹ region. –1 The broad absorption peaks within the range are attributed to the stretching vibrations of OH groups in the coordinated water molecules of the copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst; 1128–1637 cm⁻¹ –1 and 1131-1637 cm –1 The absorption peak is attributed to the skeletal vibration of the organic ligand, 667‒1032 cm⁻¹ –1 The absorption peak at that point is due to the vibrations of ν(W=O) and ν(Si–O–Si). The test conditions were KBr pellet method, and the instrument was a Nicolet iS 10 infrared spectrometer from Thermo Fisher Scientific.

[0039] (2) Crystal structure determination:

[0040] The crystal structure of the copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst obtained in Example 1 was determined using a Bruker Apex II CCD diffractometer at 293(2) K. Diffraction points were collected in ω-scan mode using graphite-monochromated MoKα rays (λ=0.71073 Å). The collected data were restored using the SAINT program and semi-empirical absorption correction was performed using the SADABS method. The structural analysis and refinement were performed using the SHELXS and SHELXL programs of the SHELXTL program, respectively. The coordinates and anisotropic parameters of all non-hydrogen atoms were obtained by correcting F2 using the full matrix least squares method. During the structural refinement process, all hydrogen atoms were theoretically fixed on the parent atom and given isotropic displacement parameters that were slightly larger than the parent atom displacement parameters (C–H, 1.2 or O–H, 1.5 times). Detailed crystal measurement data are shown in Table 1. (Instrument model: Bruker SMART APEX II, Bruker GmbH, Germany).

[0041] Table 1 , The crystal structures in Table 1 show that the asymmetric unit of the copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst contains one Cu II ion and half a [SiW] ion. 12 O 40 The 4-coordinated Cu II anion consists of a hemi-2,3,5,6-tetrafluoro-bis(1,2,4-triazol-1-methyl)benzene ligand and two coordinated water molecules. The hexacoordinated Cu II ion adopts a twisted octahedral configuration, with a [SiW] ion... 12 O 40 The Cu–N ion is coordinated with an oxygen atom (O3), two oxygen atoms (O1 and O2) from coordinated water, and three nitrogen atoms (N1, N4#1, and N7) from the 2,3,5,6-tetrafluoro-bis(1,2,4-triazol-1-methyl)benzene ligand. The Cu-O bond length is 2.000(1)–2.590(13) Å, and the Cu–N bond length is 1.979(15)–2.004(13) Å. See attached instruction manual. Figure 3 This is a coordination environment diagram of the copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst obtained in Example 1 of the present invention.

[0042] As per the instruction manual Figure 4 As shown, a flexible 2,3,5,6-tetrafluoro-bis(1,2,4-triazol-1-methyl)benzene organic ligand bridges adjacent Cu II ions in cis and trans configurations to form a one-dimensional ladder-shaped double chain along the c-axis, with Cu…Cu distances of 15.0 Å and 13.7 Å. The adjacent ladders are further connected via [SiW... 12 O 40 Four ions are linked to form a two-dimensional grid along the bc plane. (See attached instruction manual.) Figure 4This is a two-dimensional layered structure diagram of the copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst obtained in Example 1 of the present invention.

[0043] (3) Characterization of phase purity:

[0044] Instruction manual attached Figure 5 This is the X-ray powder diffraction (PXRD) pattern of the copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst obtained in Example 1. The figure shows a series of sharp characteristic diffraction peaks at 2θ≈3~10, which are in high agreement with the theoretical spectrum obtained through single-crystal structure simulation. This result confirms that the copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst possesses high crystallinity and phase purity, providing a structural guarantee for its reliable application in the catalytic ring-opening copolymerization of ε-caprolactone and polyethylene glycol to prepare polycaprolactone-polyethylene glycol block copolymers. The tests were performed using a Rigaku D / Max-2500 diffractometer (Japan).

[0045] (4) Thermal stability characterization:

[0046] Instruction manual attached Figure 6 The thermogravimetric (TG) curves of the copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst obtained in Example 1 are shown. The results indicate that the coordination polymer framework possesses high thermal stability, showing no significant decomposition before 285 °C, suggesting that it can maintain structural stability at higher temperatures. The tests were performed using a NETZSCH TG 209 F3 thermogravimetric analyzer (Germany).

[0047] Example 2 is the same as Example 1, except that copper acetate monohydrate is used instead of copper nitrate trihydrate in Example 1 in Example 2. The yield of the copper-containing silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst obtained in Example 2 is 63%.

[0048] Example 3 is the same as Example 1, except that copper chloride is used in Example 3 instead of copper nitrate trihydrate in Example 1. The yield of the copper-containing silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst obtained in Example 3 is 52%.

[0049] Example 4 is the same as Example 1, except that the pH of the solvothermal reaction in Example 4 is 1.0. The yield of the copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst obtained in Example 4 is 42%.

[0050] Example 5 is the same as Example 1, except that the pH of the solvothermal reaction in Example 5 is 2.0. The yield of the copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst obtained in Example 5 is 59%.

[0051] Example 6 is the same as Example 1, except that the solvothermal reaction temperature in Example 6 is 140°C. The yield of the copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst obtained in Example 6 is 47%.

[0052] Example 7 is the same as Example 1, except that the solvothermal reaction temperature in Example 7 is 200°C. The yield of the copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst obtained in Example 7 is 75%.

[0053] Example 8 is the same as Example 1, except that the solvothermal reaction time in Example 8 is 6 hours. The yield of the copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst obtained in Example 8 is 43%.

[0054] Example 9 is the same as Example 1, except that the solvothermal reaction time in Example 9 is 96 hours. The yield of the copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst obtained in Example 8 is 81%.

[0055] Example 10 is the same as Example 1, except that 4.5 ml of deionized water was used in Example 10. The yield of the copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst obtained in Example 10 was 65%.

[0056] Example 11 is the same as Example 1, except that 18 ml of deionized water was used in Example 11. The yield of the copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst obtained in Example 11 was 77%.

[0057] Example 12 is the same as Example 1, except that the amount of silicotungstic acid hexahydrate in Example 12 is 20.5 mg (the molar ratio of copper salt to silicotungstic acid is 1:1). The yield of the copper-containing silicotungstic heteropolyacid metal MOF heterogeneous catalyst obtained in Example 12 is 40%.

[0058] Example 13 is the same as Example 1, except that the amount of silicotungstic acid hexahydrate in Example 13 is 164.0 mg (the molar ratio of copper salt to silicotungstic acid is 1:8). The yield of the copper-containing silicotungstic heteropolyacid metal MOF heterogeneous catalyst obtained in Example 13 is 63%.

[0059] Example 14 is the same as Example 1, except that the amount of copper nitrate trihydrate in Example 14 is 36.3 mg (the molar ratio of copper salt to 2,3,5,6-tetrafluoro-bis(1,2,4-triazol-1-methyl)benzene ligand is 1:1). The yield of the copper-containing silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst obtained in Example 14 is 59%.

[0060] Example 15 is the same as Example 1, except that the amount of copper nitrate trihydrate in Example 15 is 7.2 mg (the molar ratio of copper salt to 2,3,5,6-tetrafluoro-bis(1,2,4-triazol-1-methyl)benzene ligand is 1:5). The yield of the copper-containing silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst obtained in Example 15 is 61%.

[0061] Comparative Example 1 is the same as Example 1, except that the same molar amount of silver nitrate trihydrate was used in Comparative Example 1 instead of copper nitrate trihydrate in Example 1. The solvothermal reaction of Comparative Example 1 yielded a white amorphous powder, which could not be analyzed by X-ray single crystal.

[0062] Comparative Example 2 is the same as Example 1, except that the same molar amount of zinc nitrate trihydrate was used in Comparative Example 2 to replace the copper nitrate trihydrate in Example 1. The solvothermal reaction of Comparative Example 2 yielded a white amorphous powder with an unknown structure, which could not be analyzed by X-ray single crystal.

[0063] Comparative Example 3 is the same as Example 1, except that the same volume of N,N-dimethylformamide was used in Comparative Example 3 instead of deionized water, the solvent in the solvothermal reaction of Example 1. The solvothermal reaction of Comparative Example 3 yielded a clear green solution; no crystalline sample was obtained, making X-ray single-crystal analysis impossible.

[0064] Comparative Example 4 is the same as Example 1, except that the same volume of anhydrous methanol was used in Comparative Example 4 instead of deionized water, the solvent in the solvothermal reaction of Example 1. The solvothermal reaction of Comparative Example 4 yielded a blue amorphous powder with an unknown structure, which could not be analyzed by X-ray single crystal.

[0065] Specific applications

[0066] Application 1

[0067] The preparation method of polycaprolactone-polyethylene glycol block copolymer is as follows:

[0068] (1) The copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst obtained in Example 1 was used as a catalyst for the ring-opening copolymerization of ε-caprolactone and polyethylene glycol to prepare polycaprolactone-polyethylene glycol copolymer. The specific reaction steps are as follows:

[0069] 3424.80 mg ε-caprolactone (CAS No.: 502-44-3) (30.00 mmol), 3000.00 mg polyethylene glycol 10000 (0.30 mmol), and 6.45 mg copper-containing silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst (0.006 mmol) were added to a Schlenk reaction tube, and the ring-opening copolymerization reaction was carried out at 160 °C with magnetic stirring for 12 hours. After the reaction was completed, the mixture was cooled to room temperature, dissolved in dichloromethane, and petroleum ether was added to the filtrate to precipitate the copolymer. The copolymer was then dried under vacuum at 40 °C for 12 hours to obtain a white polycaprolactone-polyethylene glycol copolymer, denoted as PCEC-1, with a number-average molecular weight of 32623 and a molecular weight distribution index of 1.07. The relevant test results are shown in Table 2.

[0070] The polycaprolactone-polyethylene glycol block copolymer obtained by application 1 was characterized as follows:

[0071] (1) Molecular weight and molecular weight distribution index test:

[0072] The molecular weight and distribution of polycaprolactone-polyethylene glycol copolymer were determined by gel permeation chromatography (GPC). The determination conditions were as follows: polystyrene as standard, tetrahydrofuran as mobile phase, RID-10A differential refractive index detector, flow rate 0.6 mL / min, run time 40 min, injection volume 20 μL, column temperature 30 °C. The tests were performed using a Shimadzu LC-20AD gel permeation chromatograph (SJM).

[0073] Instruction manual attached Figure 7 The figure shows the molecular weight and molecular weight distribution of the polycaprolactone-polyethylene glycol copolymer obtained by application 1. As can be seen from the figure, the number-average molecular weight of PCEC-1 is 32626, the weight-average molecular weight is 30488, and the molecular weight distribution is relatively narrow, only 1.07. This strongly demonstrates that the copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst is a highly efficient and controllable "quasi-active" polymerization system. It not only has high catalytic efficiency, but more importantly, it achieves precise molecular-level control over the polymerization process, enabling the preparation of polymers with highly uniform molecular weight. This is usually the goal pursued by homogeneous metal-organic catalysts, but the copper-silicon-tungsten heteropolyacid metal MOF achieves this in a heterogeneous form, which is an important manifestation of its potential as a new generation of high-performance catalysts.

[0074] The polycaprolactone-polyethylene glycol copolymer obtained by application 1 was characterized by ¹H NMR as follows:

[0075] Instruction manual attached Figure 8The figure shows the 1H NMR spectrum of the polycaprolactone-polyethylene glycol copolymer obtained by application 1. As can be seen from the figure, the characteristic proton peaks of polycaprolactone in the polycaprolactone-polyethylene glycol copolymer, the triplet at δ=4.06 ppm (t, 2H, J = 6.0 Hz) belongs to the methylene proton (−O−CH−) directly connected to the ester group in the polycaprolactone backbone; the triplet at δ=2.30 ppm (t, 2H, J = 6.0 Hz) belongs to the methylene (−C−CH−) adjacent to the carbonyl group; the multiplets at δ=1.60-1.70 ppm (m, 4H) and δ=1.38 ppm (m, 2H) belong to the remaining methylene protons in the chain. The test conditions were: ¹H NMR (500 MHz, DMSO-d6), acquired using an AVANCE NEO 500 MHz nuclear magnetic resonance spectrometer from Bruker GmbH, Germany.

[0076] Application 2 is the same as Application 1, except that the ring-opening copolymerization reaction temperature in Application 2 is 120℃ and the reaction time is 72 hours. The relevant test results of the polycaprolactone-polyethylene glycol copolymer (denoted as PCEC-2) obtained by Application 2 are shown in Table 2.

[0077] Application 3 is the same as Application 1, except that the ring-opening copolymerization reaction temperature in Application 3 is 180℃ and the reaction time is 6 hours. The relevant test results of the polycaprolactone-polyethylene glycol copolymer (denoted as PCEC-3) obtained by Application 3 are shown in Table 2.

[0078] Application 4 is the same as Application 1, except that the amount of ε-caprolactone used in the ring-opening copolymerization reaction in Application 4 is 1712.4 mg (15 mmol). The relevant test results of the polycaprolactone-polyethylene glycol copolymer (denoted as PCEC-4) obtained in Application 4 are shown in Table 2.

[0079] Application 5 is the same as Application 1, except that the amount of ε-caprolactone used in the ring-opening copolymerization reaction in Application 5 is 6849.6 mg (60 mmol). The relevant test results of the polycaprolactone-polyethylene glycol copolymer (denoted as PCEC-5) obtained by Application 5 are shown in Table 2.

[0080] Application 6 is similar to Application 1, except that the amount of copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst used in the ring-opening copolymerization reaction of Application 6 is 1.29 mg (0.0012 mmol). The relevant test results of the polycaprolactone-polyethylene glycol copolymer (denoted as PCEC-6) obtained by Application 6 are shown in Table 2.

[0081] Application 7 is the same as Application 1, except that the amount of copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst used in the ring-opening copolymerization reaction of Application 7 is 12.9 mg (0.012 mmol). The relevant test results of the polycaprolactone-polyethylene glycol copolymer (denoted as PCEC-7) obtained by Application 7 are shown in Table 2.

[0082] Comparative Application 1 is the same as Application 1, except that the catalyst used in the ring-opening copolymerization reaction in Comparative Application 1 is copper nitrate trihydrate, and the molar amount of copper nitrate trihydrate is the same as the molar amount of the copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst in Application 1. The relevant test results of the polycaprolactone-polyethylene glycol copolymer (denoted as PCEC-8) obtained in Comparative Application 1 are shown in Table 2.

[0083] Comparative Application 2 is the same as Application 1, except that the catalyst used in the ring-opening copolymerization reaction in Comparative Application 2 is 2,3,5,6-tetrafluoro-bis(1,2,4-triazole-1-methyl)benzene. The molar amount of 2,3,5,6-tetrafluoro-bis(1,2,4-triazole-1-methyl)benzene is the same as the molar amount of the copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst in Application 1. The relevant test results of the polycaprolactone-polyethylene glycol copolymer (denoted as PCEC-9) obtained in Comparative Application 2 are shown in Table 2.

[0084] Comparative Application 3 is the same as Application 1, except that the catalyst used in the ring-opening copolymerization reaction in Comparative Application 3 is stannous octoate, and the molar amount of stannous octoate is the same as the molar amount of the copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst in Application 1. The relevant test results of the polycaprolactone-polyethylene glycol copolymer (denoted as PCEC-10) obtained in Comparative Application 3 are shown in Table 2.

[0085] Comparative Application 4 is the same as Application 1, except that the catalyst used in the ring-opening copolymerization reaction in Comparative Application 4 is zinc lactate, and the molar amount of zinc lactate is the same as that of the copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst in Application 1. The relevant test results of the polycaprolactone-polyethylene glycol copolymer (denoted as PCEC-11) obtained in Comparative Application 4 are shown in Table 2.

[0086] Comparative Application 5 and Application 1 are similar, except that the catalyst used in the ring-opening copolymerization reaction in Comparative Application 5 is {[Co3(Fbtx)5(V2W]}. 18 O 62 (H2O)2]·26H2O} n(According to the literature N. Shen, T. Tian, ​​J. Chang, K.-L.Huang, Z.-H. Zhang, X. Feng, J. Gu, S.-C. Chen, M.-Y. He, Q. Chen, Anunprecedented cobalt(II)-containing Wells-Dawson-type tungstovanadate-basedmetal-organic framework as an efficient catalyst for ring-openingpolymerization of ε–caprolactone, synthesized by the method reported in CrystEngComm, 2020, 22, 3556-3663), {[Co3(Fbtx)5(V2W 18 O 62 (H2O)2]·26H2O} n The molar amount of the catalyst is the same as that of the copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst in Application 1. The relevant test results of the polycaprolactone-polyethylene glycol copolymer (denoted as PCEC-12) obtained in Application 5 are shown in Table 2.

[0087] Comparative Application 6 is the same as Application 1, except that the catalyst used for the ring-opening copolymerization of caprolactone and polyethylene glycol in Comparative Application 6 is [Mo2O4(μ2-OH)2(Htrz)] (synthesized according to Example 1 described in Chinese Invention Patent CN114015070A). The molar amount of [Mo2O4(μ2-OH)2(Htrz)] is the same as the molar amount of the copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst in Application 1. The relevant test results of the polycaprolactone-polyethylene glycol copolymer (denoted as PCEC-13) obtained in Comparative Application 6 are shown in Table 2.

[0088] Table 2 , Analysis of the test data in Table 2 shows that the molecular weight of the polycaprolactone-polyethylene glycol copolymer increases with increasing synthesis conditions (reaction time, reaction temperature, raw material molar ratio, and catalyst molar amount). The molecular weight of the polycaprolactone-polyethylene glycol copolymer is also related to the catalyst; among various catalysts, the copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst exhibits the best catalytic effect. The polycaprolactone-polyethylene glycol copolymer obtained by application 1 has the highest number-average molecular weight and the smallest molecular weight distribution, significantly superior to using copper salts or organic ligands alone as catalysts. When traditional stannous octoate or zinc lactate are used as catalysts for ring-opening copolymerization, the resulting copolymers have small molecular weights and wide molecular weight distributions. The test results from Applications 5 and 6 show that although heteropolyacid MOFs and isopolymolybdate MOFs can be used as heterogeneous catalysts for the ring-opening block copolymerization of ε-caprolactone, their catalytic activity is significantly lower than that of the copper-containing silicon-tungsten heteropolyacid metal MOFs involved in this invention. Furthermore, their ability to control the copolymerization reactivity ratio is limited, resulting in a wider molecular weight distribution of the obtained copolymers and a lower molecular weight of the polyester products. This indicates that catalysts suitable for the ε-caprolactone homopolymerization system may not be effectively applicable to the ring-opening block copolymerization reaction.

[0089] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst, characterized in that, The chemical formula is [Cu2(L)3(SiW] 12 O 40 (H2O)4] n In the chemical formula, L represents the organic ligand, which is 2,3,5,6-tetrafluoro-bis(1,2,4-triazol-1-methyl)benzene; H₂O is the solvent; Cu is the metal central ion; and SiW 12 O 40 It is a heteropolyacid anion, where n represents the repeating structural unit Cu2(L)3(SiW) 12 O 40 The infinite extension of )(H2O)4.

2. The copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst according to claim 1, characterized in that, The secondary structure units of the copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst satisfy the following conditions: the crystal belongs to the triclinic crystal system, and the space group is [missing information]. .

3. The copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst according to claim 2, characterized in that, The cell parameters of the copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst are a=11.662(2) Å, b=13.171(2) Å, c=13.668(2) Å, α=65.9(1)°, β=76.9(1)°, γ=69.5(1)°, cell volume is 1783.4(2) Å3, and Z=1.

4. A copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst according to any one of claims 1-3, characterized in that, The preparation method includes the following steps: Copper salt, silicotungstic acid, 2,3,5,6-tetrafluoro-bis(1,2,4-triazol-1-methyl)benzene, and deionized water were mixed evenly, and the pH of the reaction system was adjusted to be acidic. The copper-containing silicotungstic heteropolyacid metal MOF heterogeneous catalyst was obtained by self-assembly through solvothermal reaction.

5. The copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst according to claim 4, characterized in that, pH=1.0~2.

0.

6. The copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst according to claim 4, characterized in that, The solvothermal reaction involves placing the reaction system at 140-200℃ for 6-96 hours. After the reaction is completed, the reaction system is cooled to room temperature, and solid-liquid separation is performed to collect the solid product, thus obtaining the target catalyst.

7. The copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst according to claim 4, characterized in that, Copper salts include one or more of copper nitrate, copper acetate, copper chloride, copper sulfate, and their hydrates.

8. The copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst according to claim 4, characterized in that, The ratio of 2,3,5,6-tetrafluoro-bis(1,2,4-triazol-1-methyl)benzene to deionized water is 1 mmol: 30~120 mL.

9. A polycaprolactone-polyethylene glycol block copolymer, characterized in that, Using caprolactone and polyethylene glycol as block copolymer monomers, and a copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst as described in any one of claims 1-3 as a catalyst, caprolactone and polyethylene glycol undergo a ring-opening copolymerization reaction.

10. A polycaprolactone-polyethylene glycol block copolymer, characterized in that, The amount of copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst used is determined based on the molar ratio of the copper-silicon-tungsten heteropolyacid metal MOF heterogeneous catalyst to caprolactone being 1:1000~1:10000.

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