A bifunctional porous organic polymer catalyst and a preparation method and application thereof

Abstract

The application provides a bifunctional porous organic polymer catalyst and a preparation method and application thereof, and belongs to the technical field of organic synthesis.Cyclen monomers, hydroxyethyl imidazole onium salt ILs monomers, a crosslinking agent and an initiator are dissolved in DMF, and ultrasonic dispersion is used to fully dissolve them.The mixed solution is transferred to a reaction kettle for reaction, and then cooled to room temperature;solid products are collected by suction filtration, washed with ethyl acetate, and the obtained solid is vacuum dried to obtain an ionic liquid / macrocyclic polyamine bifunctional porous organic polymer.The obtained polymer exhibits excellent catalytic activity, substrate universality and cycle stability as a catalyst under mild conditions.

Description

Technical Field

[0001] This application relates to a bifunctional porous organic polymer catalyst, its preparation method, and its application, belonging to the field of organic synthesis technology. Background Technology

[0002] Converting CO2 into high-value-added cyclic carbonates via cycloaddition reactions with epoxides offers 100% atom economy and is one of the most promising pathways for CO2 resource utilization. However, the inherent thermodynamic stability and kinetic inertness of CO2 molecules make this reaction difficult to carry out without a catalyst. Developing efficient, stable, and easily separable and recoverable catalysts has become a core challenge in this field.

[0003] The cycloaddition reaction between CO2 and epoxides is difficult to carry out even under high temperature and pressure because the reaction requires a very high activation energy. Therefore, a catalyst must be added to lower the activation energy required for the reaction, which also illustrates the important role of catalysts in CO2 fixation reactions. Summary of the Invention

[0004] In view of this, the first objective of this application is to provide a bifunctional porous organic polymer catalyst that integrates multiple active sites, such as secondary amines (hydrogen bond donors / basic sites) of Cyclen units, hydroxyl groups (hydrogen bond donors) and bromide ions (nucleophiles) of imidazolium salt units.

[0005] Specifically, this application is implemented through the following scheme: A bifunctional porous organic polymer catalyst satisfying the general formula: , Where a=1, b=1~3, c=1~3, d=1.

[0006] The second objective of this application is to provide a method for preparing the above-mentioned bifunctional porous organic polymer catalyst, wherein Cyclen monomer, 1-(2-hydroxyethyl)-4-vinylimidazolium bromide, crosslinking agent and initiator are dissolved in an organic solvent and placed in a reaction vessel for polymerization reaction, and the resulting product is the bifunctional porous organic polymer catalyst.

[0007] The structural formula of the Cyclen monomer is: .

[0008] The structural formula of the 1-(2-hydroxyethyl)-4-vinylimidazolium bromide is as follows: .

[0009] Furthermore, as a preferred option: The crosslinking agent is divinylbenzene.

[0010] The initiator is azobisisobutyronitrile.

[0011] The polymerization reaction is carried out at a temperature of 110–130°C.

[0012] The organic solvent is N,N-dimethylformamide, methanol, or ethanol.

[0013] The method for synthesizing the Cyclen monomer is as follows: S1, di-tert-butyl dicarbonate was added dropwise to a mixed solution of 1,4,7,10-tetraazacyclododecane and triethylamine to give 1,4,7-tris(tert-butyloxycarbonyl)-1,4,7,10-tetraazacyclododecane; S2, 1,4,7-tris(tert-butoxycarbonyl)-1,4,7,10-tetraazacyclododecane reacts with 4-chloromethylstyrene under nitrogen protection to give 1-(4-vinylbenzyl)-4,7,10-tris(tert-butoxycarbonyl)-1,4,7,10-tetraazacyclododecane; S3,1-(4-vinylbenzyl)-4,7,10-tris(tert-butoxycarbonyl)-1,4,7,10-tetraazacyclododecane was dissolved in a solvent, cooled in an ice-water bath, and trifluoroacetic acid was slowly added dropwise. The mixture was then heated to room temperature and reacted. The solvent was removed under reduced pressure, toluene was added, and the resulting product was dissolved in water. The pH was adjusted to alkaline, and the mixture was extracted with chloroform. The organic phases were combined, dried, filtered, and the solvent was removed under reduced pressure to obtain the Cyclen monomer.

[0014] The synthesis method of 1-(2-hydroxyethyl)-4-vinylimidazolium bromide is as follows: 4-vinylimidazolium and 2-bromoethanol are evacuated and purged with nitrogen under ice-water bath cooling, and then heated to 30-60℃ under nitrogen protection to obtain 1-(2-hydroxyethyl)-4-vinylimidazolium bromide.

[0015] The third objective of this application is to provide an application of the above-mentioned bifunctional porous organic polymer catalyst in cycloaddition reactions.

[0016] Specifically: A bifunctional porous organic polymer catalyst was added to the reaction system. The reaction system was evacuated and filled with carbon dioxide. Under the carbon dioxide atmosphere, an epoxy substrate was added. Under solvent-free and catalyst-free conditions, the epoxy substrate and CO2 underwent a cycloaddition reaction.

[0017] The substrate for the cycloaddition reaction is any one of styrene oxide, epichlorohydrin, epibromopropane, n-butyl glycidyl ether, isopropyl glycidyl ether, tert-butyl glycidyl ether, glycidyl oxypropyl phenyl ether, glycidyl methacrylate, and 3-glycidyl etheroxypropyltrimethoxysilane.

[0018] Tetraazacyclododecane (Cyclen), a classic macrocyclic polyamine ligand, has uncoordinated secondary amine nitrogen atoms on its ring that can act as basic sites for interaction with CO2 and as hydrogen bond donors to activate epoxides. Unlike tetrasubstituted Cyclens, monosubstituted Cyclens retain three secondary amines, providing an ideal platform for constructing metal-free, multi-active-site synergistic catalytic systems. Based on this, this application provides an ionic liquid / macrocyclic polyamine bifunctional porous organic polymer catalyst (PIL-Cyc-X). Using monosubstituted Cyclen monomers (Cyc-4VB) and hydroxyethyl imidazolium salt ionic liquid monomers (VIm-OH) as functional building blocks, a series of bifunctional POPs catalysts were successfully prepared by solvothermal free radical ternary copolymerization with divinylbenzene as a crosslinking agent. This catalyst integrates multiple active sites, including the secondary amine (hydrogen bond donor / basic site) of the Cyclen unit, the hydroxyl group (hydrogen bond donor) and bromide ion (nucleophile) of the imidazolium salt unit, aiming to achieve highly efficient cycloaddition reactions of CO2 with epoxides under metal-free, solvent-free, and co-catalyst-free conditions. It enables bifunctional synergistic catalysis of "hydrogen bond donor-nucleophile," exhibiting excellent catalytic activity, substrate universality, and cycling stability under mild conditions, achieving a green and efficient heterogeneous CO2 cycloaddition catalysis process. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application.

[0020] Figure 1 This is a schematic diagram of the preparation process of this application.

[0021] Figure 2 Fourier transform infrared spectra of Cyc-4VB, VIM-OH monomers and PIL-Cyc-1 in this application.

[0022] Figure 3 For PIL-Cyc-1 13 CMAS NMR.

[0023] Figure 4 For the morphological characterization of PIL-Cyc-1, parts (a), (b), and (c) in the figure are SEM images under scales of 1, 2, and 5 µm, respectively, and part (d) is an EDS mapping image.

[0024] Figure 5 XPS analysis of PIL-Cyc-1: (a) is the full spectrum, (b) is the C1s spectrum, (c) is the N1s spectrum, (d) is the O1s spectrum, and (e) is the Br 3d spectrum.

[0025] Figure 6 The thermal stability of PIL-Cyc-1.

[0026] Figure 7 CO2-TPD analysis of PIL-Cyc-1 catalyst.

[0027] Figure 8 The figure shows the pore structure properties of PIL-Cyc-1. Part (a) is the nitrogen adsorption / desorption isotherm, and part (b) is the pore size distribution curve.

[0028] Figure 9 The figure shows the adsorption capacity of PIL-Cyc-1 for CO2. Part (a) in the figure is the CO2 adsorption isotherm, and part (b) is the isochoric heat of adsorption of CO2.

[0029] Figure 10 The figure shows the catalytic performance of PIL-Cyc-1. Part (a) shows the effect of reaction temperature on catalytic activity, part (b) shows the effect of reaction time on catalytic activity, and part (c) shows the effect of catalyst dosage on catalytic activity.

[0030] Figure 11 The figure shows the heterogeneous characteristics of the PIL-Cyc-1 catalyst in the reaction system. Part (a) shows the results of the thermal filtration experiment, part (b) shows the recycling performance, part (c) shows the thermogravimetric analysis of the fresh catalyst and the catalyst after five cycles, and part (d) shows the infrared spectral characterization of the fresh catalyst and the catalyst after five cycles.

[0031] Figure 12 The image shows the in-situ infrared spectrum of the PIL-Cyc-1 catalytic epoxide cycloaddition reaction with CO2.

[0032] Figure 13 Atomic-level characterization of the mechanism of the cycloaddition reaction between PIL-Cyc-1 catalyzed epoxy substrates and CO2.

[0033] Figure 14 The mechanism of the PIL-Cyc-1 catalytic oxidation of styrene with CO2 cycloaddition reaction was characterized. Detailed Implementation

[0034] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the technical solutions in the embodiments of this application will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit the technical solutions of this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without creative effort are within the scope of protection of this application.

[0035] Table 1: Reagents and gases used in this embodiment .

[0036] Table 2: Characterization and Testing Instruments in this Embodiment .

[0037] The characterization and testing methods for materials are as follows: (1) Liquid nuclear magnetic resonance spectroscopy (NMR): The proton and carbon spectra of the samples were measured using an AVance-400 (400MHz) NMR spectrometer manufactured by Bruker GmbH, Germany. The samples were dissolved in a suitable deuterated reagent for testing. The instrument was equipped with a 4-mm ZrO2 rotor and a magic angle rotating probe.

[0038] (2) Solid-state nuclear magnetic resonance (SS NMR): solid-state samples 13 The 1C MAS NMR spectrum was acquired using an Infinity-Plus 400 MHz nuclear magnetic resonance spectrometer manufactured by Varian, Inc.

[0039] (3) Fourier Transform Infrared Spectroscopy (FT-IR): Infrared spectral data were measured using a Nicolet 6700 Fourier Transform Infrared Spectrometer from Thermo Fisher Scientific, USA. Samples were prepared using the KBr pellet method, and the wavenumber range was 4000–400 cm⁻¹. -1 .

[0040] (4) X-ray photoelectron spectroscopy (XPS): XPS analysis was performed using a Thermo Scientific K-Alpha spectrometer from Thermo Fisher Scientific. The X-ray source was irradiated with A1 Kα (hv=1486.6 eV) at θ=90°. The binding energy was calibrated using the C 1s peak at 284.8 eV during data analysis.

[0041] (5) Thermogravimetric analysis (TGA): Thermogravimetric analysis data were acquired using a NETZSCH TG 209F3 thermogravimetric analyzer from Germany. The tests were conducted under a nitrogen atmosphere, with a heating rate of 10 °C / min and a temperature range of 25 °C to 600 °C.

[0042] (6) Scanning Electron Microscopy (SEM): The microstructure of the samples was observed using a JEOL JSM-5610LV scanning electron microscope. The samples were sputtered with gold before testing to improve conductivity.

[0043] (7) In-situ FTIR: The test was performed using a Bruker VERTEX 80V infrared spectrometer. Before the test, the sample was pretreated at 80 °C under vacuum for 2 h to remove adsorbed moisture and impurities.

[0044] (8) Carbon dioxide adsorption test: CO2 adsorption isotherms were measured using an ASAP 2020M physical adsorption instrument from Micromeritics, USA. Before the test, the sample was degassed under vacuum at 80 °C for 8 h. CO2 adsorption data at different partial pressures were collected at 273 K and 298 K using the static volumetric method.

[0045] (9) Nitrogen adsorption test: The N2 adsorption / desorption isotherms were also measured using an ASAP 2020M physical adsorption instrument at temperatures of 77 K, 273 K, and 298 K. The specific surface area of ​​the sample was calculated using the BET method within a relative pressure range of P / P0 = 0.05–0.20. Before the test, the sample was degassed under vacuum at 80 °C for 8 h to remove residual solvent and moisture from the pores.

[0046] (10) CO2 / NH3 temperature-programmed desorption (CO2 / NH3-TPD): CO was determined using an AutoChemII 2920 chemisorption analyzer from Micron Instruments, Inc. 2 / NH3 was desorbed using a temperature-programmed process, with desorption curves collected from room temperature to 350 °C.

[0047] (11) Inductively coupled plasma mass spectrometry (ICP-MS): The catalyst sample was pretreated by microwave digestion and the bromine content in the sample was determined by PerkinElmer Agilent 7800 inductively coupled plasma mass spectrometer.

[0048] Example 1

[0049] This embodiment provides a bifunctional porous organic polymer catalyst. The embodiments of this application are described below with reference to the accompanying drawings.

[0050] (a) Synthesis of 1-(4-vinylbenzyl)-1,4,7,10-tetraazacyclododecane (Cyc-4VB) Synthesis of S1, 1,4,7-tris(tert-butoxycarbonyl)-1,4,7,10-tetraazacyclododecane (Cyc-3Boc): Cyclen (1.0 g, 5.80 mmol) and triethylamine (1.81 g, 17.88 mmol) were dissolved in 60 mL of chloroform and stirred at room temperature. Di-tert-butyl dicarbonate (3.59 g, 16.43 mmol) was dissolved in 50 mL of chloroform and slowly added dropwise to the above solution. After the addition was complete, the reaction mixture was stirred at room temperature for 24 hours. After the reaction was complete, the solvent was removed by vacuum distillation, and the crude product was purified by silica gel column chromatography to give Cyc-3Boc as a colorless liquid (2.01 g, yield 73.5%).

[0051] Synthesis of S2, 1-(4-vinylbenzyl)-4,7,10-tris(tert-butoxycarbonyl)-1,4,7,10-tetraazacyclododecane (Cyc-3Boc-4VB): Cyc-3Boc (1.7 g, 3.60 mmol), anhydrous potassium carbonate (0.75 g, 5.4 mmol), potassium iodide (0.60 g, 3.6 mmol), and 4-chloromethylstyrene (0.82 g, 5.40 mmol) were added to 60 mL of acetonitrile and heated to 70 °C with stirring for 3 hours under nitrogen protection. After the reaction was complete, insoluble matter was removed by filtration, the solvent was removed from the filtrate by vacuum distillation, and the crude product was purified by silica gel column chromatography to give Cyc-3Boc-4VB as a colorless liquid (1.78 g, yield 84.2%).

[0052] Synthesis of S3, 1-(4-vinylbenzyl)-1,4,7,10-tetraazacyclododecane (Cyc-4VB): Cyc-3Boc-4VB (1.20 g, 2.04 mmol) was dissolved in 130 mL of dichloromethane and cooled to 0 °C in an ice-water bath. Trifluoroacetic acid (12.78 g, 112.1 mmol) was slowly added dropwise, and the mixture was stirred at room temperature for 6 h after the addition was complete. After the reaction was complete, the solvent was removed under reduced pressure, and 10 mL of toluene was added to the residue and evaporated again to dryness to obtain a yellow oil. The obtained oil was dissolved in water, and the pH was adjusted to alkaline with 1 M NaOH solution. The mixture was extracted five times with chloroform (50 mL each time). The organic phases were combined, dried over anhydrous sodium sulfate, filtered, and the solvent was removed under reduced pressure to obtain Cyc-4VB as a pale yellow oil (0.40 g, yield 90.3%).

[0053] The structure of the target product was determined by 1 H NMR and 13 C NMR confirmed: 1 H NMR (400 MHz, CDCl3): δ 7.38 (d, J =7.9 Hz, 2H), 7.30 (d,J =7.9 Hz, 2H), 6.71 (dd, J =17.6, 10.9 Hz, 1H), 5.74 (d, J =17.6 Hz, 1H), 5.22 (d, J =10.9 Hz, 1H), 3.57 (s, 2H), 2.90–2.70 (m, 16H) ppm; 13 CNMR (400 MHz, CDCl3): δ 136.5, 136.4, 129.5, 126.0, 113.5, 57.8, 51.9, 50.3, 45.7, 44.8, 43.7 ppm.

[0054] (II) Synthesis of ILs monomer 1-(2-hydroxyethyl)-4-vinylimidazolium bromide (VIm-OH) 4-Vinylimidazole (2.80 g, 30 mmol) and 2-bromoethanol (4.05 g, 33 mmol) were added to a 50 mL two-necked round-bottom flask. The mixture was evacuated and purged with nitrogen three times under an ice-water bath. The mixture was then heated to 50 °C and stirred for 48 hours under nitrogen protection. After the reaction was complete, the mixture was cooled to room temperature, and 20 mL of ice-cold diethyl ether was added. The mixture was stirred thoroughly and allowed to stand to separate into layers. The lower viscous liquid layer was separated and washed three times with 10 mL of ice-cold diethyl ether to remove unreacted starting materials. A colorless, viscous liquid product, 1-(2-hydroxyethyl)-4-vinylimidazole ammonium bromide (yield: 90.8%), was obtained.

[0055] The structure of the target product was determined by 1 H NMR: 1 H NMR (400 MHz, DMSO- d 6 ): δ 9.28 (s, 1H, N-CH-N), 8.03 (s, 1H, =CH-), 7.85 (s, 1H, =CH-), 7.22 (dd, J =15.6, 8.7 Hz, 1H, -CH=), 6.02 (dd, J =15.6, 2.4 Hz, 1H, =CH2trans), 5.46 (dd, J =8.7, 2.4 Hz, 1H, =CH2cis), 4.27 (t, J =5.4 Hz, 2H, N-CH2-CH2-OH), 3.69 (t, J=5.4 Hz, 2H, CH2-OH)ppm.

[0056] (III) Synthesis of Ionic Liquid / Macrocyclic Polyamine Bifunctional POP (PIL-Cyc-X) Combination Figure 1 Taking the synthesis of PIL-Cyc-1 as an example, the monosubstituted Cyclen monomer (Cyc-4VB, 0.49 g, 1.7 mmol), the hydroxyethyl imidazolium salt ILs monomer (VIm-OH, 0.75 g, 3.4 mmol), the crosslinking agent divinylbenzene (DVB, 0.22 g, 1.7 mmol), and the initiator azobisisobutyronitrile (AIBN, 0.09 g, 0.5 mmol) were dissolved in 10 mL of N,N-dimethylformamide (DMF) and ultrasonically dispersed for 10 min to ensure complete dissolution. The mixed solution was transferred to a stainless steel reactor lined with polytetrafluoroethylene. The reaction was carried out in an oven at 120 °C for 36 h. After the reaction was completed, the mixture was naturally cooled to room temperature, and the solid product was collected by filtration. The solid product was washed three times with ethyl acetate to remove unreacted monomers. The obtained solid was dried under vacuum at 60 °C for 24 h to obtain the target product PIL-Cyc-1, which was a pale yellow powder (yield: 90.2%). The performance of the above products was tested and analyzed, and the results are as follows:

[0057] (1) FT-IR analysis The structures of Cyc-4VB, VIM-OH monomers, and PIL-Cyc-1 were characterized by Fourier transform infrared spectroscopy, and the results are as follows: Figure 2 As shown: In the spectrum of Cyc-4VB, 3300–3500 cm⁻¹ -1 The broad peak at 1630 cm⁻¹ is attributed to the stretching vibration of the secondary amine NH₄⁺. -1 and 990, 910cm -1 The absorption peaks at these locations are attributed to the vinyl C=C stretching vibration and the out-of-plane bending vibration of the terminal vinyl CH, respectively. In the spectrum of the VIm-OH monomer, the peaks at 3400–3600 cm⁻¹ are... -1 The broad peak is attributed to the OH stretching vibration of the hydroxyethyl group, 1560–1650 cm⁻¹. -1 The multiple peaks in the region represent the skeletal vibrations of the imidazole ring.

[0058] In the spectrum of the terpolymer POP, 1630 cm⁻¹ -1 The characteristic peaks of vinyl groups at 990 and 910 cm⁻¹ weakened. -1 The complete disappearance of the vinyl characteristic peak at 3400–3600 cm⁻¹ indicates that the polymerizable double bonds in the Cyc-4VB and VIM-OH monomers participate in the free radical polymerization reaction. Meanwhile, the peaks at 3400–3600 cm⁻¹... -1The broad peaks at 1600 and 1510 cm⁻¹ still exist, attributable to the stretching vibrations of OH and NH. -1 The benzene ring skeletal vibration peaks at 1560–1650 cm⁻¹ -1 The retention of the imidazole ring vibration peak in the region confirms the successful copolymerization of Cyc-4VB, VIm-OH, and DVB, forming a bifunctional porous organic polymer with multiple active sites.

[0059] (2) 13 CMAS NMR data analysis solid-state 13 The structure of PIL-Cyc-1 was characterized by ¹H NMR, and the results are as follows: Figure 3 As shown: δ The broad peaks in the 30-45 ppm range are attributed to the characteristic vibrational signal peaks of the double-bonded carbon and methylene bridges in polymerization, which were originally in δ The characteristic signal at 110-120 ppm, which is attributed to vinyl terminal carbon, completely disappears. δ The signal in the 50-65 ppm region is attributed to the methylene carbon (N-CH2-CH2-N), benzyl methylene carbon (N-CH2-Ph), and methylene carbon (N-CH2-CH2-OH) in the Cyclen macroring and the hydroxyethyl imidazolium salt unit. δ The broad peak at 120-145 ppm is attributed to the carbon in the benzene ring framework and the unsaturated carbon in the imidazole ring. These results indicate that Cyc-4VB, Vim-OH, and DVB successfully copolymerized to form a bifunctional porous organic polymer with multiple active sites.

[0060] (3) SEM analysis The morphology and elemental distribution of the polymer depolymerization catalyst were characterized using SEM and EDS mapping, and the results are as follows: Figure 4 As shown: From SEM images (see...) Figure 4 As shown in sections (a), (b), and (c), PIL-Cyc-1 exhibits an irregular granular morphology with a relatively uniform particle size distribution. The surface structure of PIL-Cyc-1 is relatively rough, with particles stacked together to form a certain porous structure. EDS elemental mapping analysis revealed that the PIL-Cyc-1 sample contains C, N, O, and Br elements, and these elements are uniformly distributed throughout the material. This demonstrates the successful copolymerization of hydroxyethyl imidazolium salts (ILs) with Cyclen functional monomers and the crosslinking agent DVB, forming a bifunctional porous organic polymer catalyst with multiple active sites.

[0061] (4) XPS analysis The chemical composition of PIL-Cyc-1 was analyzed by XPS, such as... Figure 5 As shown: The full spectrum confirms the presence of C, N, O, and Br elements in the catalyst (see...). Figure 5 (part (a) in the text). Deconvolve the C1s spectrum (see...). Figure 5 In part (b), three distinct characteristic peaks appear at 284.8, 286.3, and 287.2 eV, corresponding to CC / C=C, CN / CO, and C=N, respectively. + In addition, the N1s energy spectrum deconvolve to two characteristic peaks at 398.9 eV and 401.1 eV (see [link to relevant data]). Figure 5 (c) indicates that secondary amines and tertiary amines N and C=N on Cyclen. + The presence of bonds. O1s energy spectrum (see...) Figure 5 The (d) portion of PIL-Cyc-1 shows a singlet at 532.1 eV for the COH bond. These findings confirm the successful synthesis of PIL-Cyc-1, consistent with the expected structure. The Br 3d signal in PIL-Cyc-1 appears at 67.8 eV (3d...). 5 / 2 ) and 68.8 eV (3d 3 / 2 )(See Figure 5 The (e) portion indicates the presence of free halide ions. These results demonstrate that the Cyclen and imidazole moieties were successfully incorporated into the polymer structure.

[0062] (5) Thermogravimetric analysis The thermal stability of PIL-Cyc-1 was investigated using thermogravimetric analysis (TGA). The tests were conducted under a nitrogen atmosphere at a heating rate of 10 °C / min, covering a temperature range of 25–800 °C. The results are as follows: Figure 6 As shown, the thermal decomposition process of PIL-Cyc-1 can be divided into three stages. In the range of room temperature to 100 °C, the sample experienced a slight weight loss of approximately 6 wt%, mainly attributed to the removal of physically adsorbed water and residual solvent. When the temperature rises to the range of 100–300 °C, the sample exhibits a significant thermal stability plateau, with a mass retention rate maintained above 92%, indicating that the covalent backbone of PIL-Cyc-1 and the functional groups of ILs are highly stable within this temperature range. The initial decomposition temperature of the sample is approximately 300 °C, which meets the thermal stability requirements of most catalytic and adsorption applications. In the range of 300–500 °C, the material enters the main thermal decomposition stage, experiencing a dramatic weight loss of approximately 60 wt%, corresponding to the thermal degradation of the ILs side chains and the large-scale breakage of the organic covalent backbone. The maximum decomposition rate temperature is approximately 420 °C. When the temperature rises to 500–800 °C, the material enters a slow carbonization stage.

[0063] (6) CO2-TPD analysis The surface basic sites of the PIL-Cyc-1 catalyst were characterized by CO2 temperature-programmed desorption, and the results are as follows: Figure 7 As shown, the sample exhibits a distinct CO2 desorption peak at approximately 275.2 °C, attributed to a moderately strong basic site in the catalyst. This desorption temperature falls within the 200–400 °C range, indicating that these basic sites possess moderate base strength. Combined with structural analysis of the catalyst, the basic sites in PIL-Cyc-1 primarily originate from two sources: firstly, the unsubstituted secondary amine nitrogen atom in the single-arm Cyclen unit, whose lone pair electrons can interact with CO2 molecules as Lewis base sites; and secondly, the basic nitrogen atom of the imidazole ring in the hydroxyethyl imidazole onium salt unit. The desorption peak at 275.2 °C can be mainly attributed to the contribution of the secondary amine in the Cyclen unit, while the imidazole ring, being relatively weakly basic, may have its desorption peak partially overlapping with the secondary amine peak in the lower temperature region.

[0064] (7) N2 adsorption-desorption test The pore structure of PIL-Cyc-1 was characterized using nitrogen adsorption / desorption. Nitrogen adsorption / desorption isotherms were measured at 77 K, and the specific surface area was calculated using the BET method. The pore size distribution was analyzed using the BJH model. The results are as follows: Figure 8 As shown, the nitrogen adsorption / desorption isotherms of PIL-Cyc-1 exhibit typical Type IV isotherm characteristics, with a significant hysteresis loop indicating the presence of a mesoporous structure in the sample. The specific surface area of ​​PIL-Cyc-1, calculated using the BET method, is 89.43 m². 2 / g. The pore size distribution curve shows that the pore size of PIL-Cyc-1 is mainly distributed in the range of 2–3 nm, belonging to the mesoporous region. This mesoporous structure is beneficial to the diffusion of reaction substrates and the mass transfer of products during the catalytic reaction.

[0065] (8) CO2 adsorption curve and isochoric adsorption heat To evaluate the CO2 adsorption capacity of PIL-Cyc-1, CO2 adsorption isotherms of the sample were measured at 273 K and 298 K, respectively. The results are as follows: Figure 9 As shown in section (a), the CO2 adsorption capacity of PIL-Cyc-1 decreases with increasing temperature, exhibiting typical characteristics of physisorption. At 273 K and 0.1 MPa, the CO2 adsorption capacity of PIL-Cyc-1 is 0.68 mmol / g, decreasing to 0.44 mmol / g when the temperature rises to 298 K. This adsorption capacity can be attributed to the secondary amine groups of the Cyclen unit and the hydroxyl and imidazole rings of the hydroxyethylimidazolium salt unit in the material. These functional groups can generate a strong affinity for CO2 molecules through hydrogen bonding and acid-base interactions.

[0066] To further investigate the interaction strength between the polymer backbone and CO2 molecules, the isochoric heat of adsorption (Q) of the sample to CO2 was calculated using the Virial equation based on the adsorption isotherms at 273 K and 298 K. st ).like Figure 9 As shown in part (b): Q of PIL-Cyc-1 st The value is approximately 30.55 kJ / mol, which is within the typical range for physisorption (20–40 kJ / mol). This Q... st The adsorption heat value is higher than that of traditional pure carbon materials, confirming that the introduction of amine and hydroxyl functional groups effectively enhances the material's affinity for CO2.

[0067] By replacing the ratio of crosslinking agent DVB to Cyc-4VB from 1:1 to 2:1 and 3:1, products PIL-Cyc-2 and PIL-Cyc-3 were obtained.

[0068] Application Example 1

[0069] 50 mg of catalyst and a magnetic stir bar were loaded into a 25 mL Schlenk tube. The reaction system was evacuated and purged with carbon dioxide, a process repeated three times. Under a carbon dioxide atmosphere, 10 mmol of the epoxy substrate styrene (SO₄) was added. Subsequently, the reaction tube was connected to a carbon dioxide-filled balloon, and the epoxy substrate underwent a cycloaddition reaction with CO₂ under solvent-free, catalyst-free conditions, at 0.1 MPa CO₂ and 100 °C. After the reaction was carried out with stirring at a constant speed for 24 h, the composition of the reaction mixture was analyzed by 1H NMR spectroscopy, and the substrate conversion and product selectivity were calculated.

[0070] After the reaction was complete, the catalyst was separated by filtration and washed with dichloromethane. The catalyst was then dried overnight in a vacuum oven at 60°C and was ready for use in the next catalytic cycle.

[0071] Using styrene oxide (SO₄) as a model substrate, the catalytic performance of a series of prepared catalysts was investigated under solvent-free, metal-free, and catalyst-free conditions. The results are shown in Table 3. Blank experiments (No. 1) show that the reaction is almost impossible without the addition of a catalyst. The homogeneous catalyst Cyc-4VB has almost no catalytic activity (No. 2), indicating that although the Cyclen macrocyclic ligand alone can act as a Lewis base, it cannot effectively promote the ring-opening of the epoxy due to the lack of a nucleophile. In contrast, the homogeneous ILs monomer VIm-OH exhibits excellent catalytic activity (No. 3), with a conversion rate as high as 98.6% and a selectivity >99%. This result indicates that the Br₂ in hydroxyethyl imidazolium salts... - As a nucleophile, it plays a crucial role in catalytic cycling.

[0072] Introducing functional monomers into porous organic polymer networks significantly enhanced catalytic activity through the enrichment effect of the pore structure and the synergistic effect of active sites. Comparison of polymer catalysts with different compositions revealed that, with increasing proportions of the crosslinking agent DVB, the conversion rates of PIL-Cyc-1, PIL-Cyc-2, and PIL-Cyc-3 were 93.4%, 85.9%, and 80.7% (numbers 5–7), respectively, with PIL-Cyc-1 exhibiting the best catalytic performance. This trend is closely related to changes in specific surface area and pore structure; moderate crosslinking facilitates the exposure of active sites and substrate diffusion.

[0073] Table 3: Catalytic effects of different catalysts on the cycloaddition reaction of CO2 and SO a .

[0074] Application Example 2

[0075] In this embodiment, styrene oxide (SO₄) was used as a model substrate. The effects of reaction temperature and reaction time on the catalytic performance of PIL-Cyc-1 were systematically investigated under a CO₂ pressure of 0.1 MPa. The results are as follows: Figure 10 As shown.

[0076] First, the effect of reaction temperature on catalytic activity was investigated. Combined with... Figure 10 Part (a) of the reaction: Under the reaction conditions of PIL-Cyc-1: 50 mg, SO: 10 mmol, 0.1 MPa CO2, and 24 h, the conversion rate of SO gradually increased from 65.9% to 96.0% as the temperature increased from 70 °C to 110 °C. With increasing temperature, the reaction rate accelerated, and the conversion rate significantly improved. When the temperature reached 100 °C, the conversion rate exceeded 93%, and further increasing to 110 °C, the conversion rate increased by 3%. Considering both energy cost and catalytic effect, 100 °C was selected as the optimal reaction temperature.

[0077] The effect of reaction time on catalytic activity was then investigated. Figure 10 Part (b) of the reaction: Under the reaction conditions of PIL-Cyc-1: 50 mg, SO: 10 mmol, 0.1 MPa CO2, and 100 °C, the SO conversion rate gradually increased from 37.3% to 95.2% when the reaction time was extended from 6 h to 30 h. With the extension of reaction time, the conversion rate continued to increase, reaching 93.4% when the reaction time reached 24 h. Further extending the reaction time to 30 h only increased the conversion rate by about 2.6%. Considering both time cost and catalytic efficiency, 24 h was selected as the optimal reaction time.

[0078] Finally, the effect of catalyst dosage on catalytic activity was investigated. Figure 10 In part (c) of the reaction, under the conditions of SO: 10 mmol, 0.1 MPa CO2, 100 °C, and 24 h, the conversion rate of SO gradually increased from 50.1% to 96.0% when the catalyst dosage was increased from 20 mg to 50 mg. Further increasing the catalyst dosage resulted in a conversion rate of 97.1%, an increase of only about 1.1%. Considering both catalyst dosage and catalytic efficiency, 50 mg was selected as the optimal catalyst dosage.

[0079] Under optimal reaction conditions (50 mg PIL-Cyc-1, 100 °C, 24 h, 0.1 MPa CO2), the conversion rate of SO to CO2 cycloaddition catalyzed by PIL-Cyc-1 reached 93.4%, with a selectivity exceeding 99%. Compared to the homogeneous VIm-OH monomer (conversion rate 98.6%), the activity of the PIL-Cyc-1 catalyst was slightly decreased, possibly due to the embedding of some active sites or pore mass transfer limitation. However, the recyclability and stability advantages of the heterogeneous catalyst compensated for this slight difference, making it more suitable for practical applications.

[0080] To investigate the heterogeneous characteristics of the PIL-Cyc-1 catalyst in the reaction system, a thermal filtration experiment was conducted, and the results are as follows: Figure 11 As shown in section (a) of the figure: Under conditions of 100 °C and 0.1 MPa CO2, using styrene oxide (SO) as the substrate, the catalyst was separated from the reaction system by hot filtration after 12 h of reaction. The filtrate was then reacted under the same conditions for another 24 h. As can be seen from the figure, the conversion rate of the reaction solution hardly increased after filtration, indicating that no active species leach into the liquid phase during the reaction, confirming that the PIL-Cyc-1 catalyst is a heterogeneous catalyst.

[0081] The recycling performance of the PIL-Cyc-1 catalyst was investigated under optimal reaction conditions, and the results are as follows: Figure 11 As shown in section (b): After each reaction, the catalyst was recovered by filtration, thoroughly washed with dichloromethane, and vacuum dried at 60 °C before being used directly in the next reaction. In the first cycle, the conversion of SO was 93.4%. After five cycles, the conversion remained at 87.6%, a decrease of only 5.0 percentage points, and the selectivity remained above 99%. The slight decrease in catalyst activity can be attributed to two reasons: firstly, a small amount of Br during the cycle... −The loss of the reaction product leads to a reduction in nucleophiles; secondly, the small amount of reaction product remaining in the pores causes partial coverage of the active sites. Despite this, PIL-Cyc-1 maintained a conversion rate of over 87% after five cycles, fully demonstrating its excellent cycling stability.

[0082] To further investigate the structural changes of the catalyst before and after recycling, thermogravimetric analysis and infrared spectroscopy were performed on the fresh catalyst and the catalyst after five cycles. The results are as follows: Figure 11 As shown in sections (c) and (d), the TGA curves reveal that the thermal decomposition behaviors of the two samples are essentially the same, with both exhibiting an initial decomposition temperature of around 300 °C, indicating that recycling did not significantly damage the chemical structure of the polymer backbone. FT-IR analysis results show that the positions and relative intensities of most characteristic absorption peaks in the recycled catalyst did not change significantly compared to the fresh catalyst. Notably, the recycled catalyst exhibits a peak at 1795 cm⁻¹. -1 A new absorption peak appeared, which is attributed to the stretching vibration of the C=O bond in the residual cyclic carbonate product.

[0083] Based on the above characterization results, the chemical structure of the PIL-Cyc-1 catalyst remains stable during recycling. The decrease in activity is mainly due to the physical residues of products within the pores and trace amounts of Br. - The loss of the catalyst is not due to the destruction of the skeletal structure or the deactivation of active sites. This catalyst exhibits both good catalytic activity and recyclability, showing potential application prospects in CO2 cycloaddition reactions.

[0084] Application Example 3

[0085] This embodiment investigates the substrate versatility: Under optimized reaction conditions (100 °C, 0.1 MPa CO2, no solvent, no co-catalyst), the catalytic performance of the PIL-Cyc-1 catalyst for epoxides with different structures was investigated, and the results are shown in Table 4.

[0086] Table 4 shows that PIL-Cyc-1 exhibits good catalytic activity for various terminal epoxides. For epichlorohydrin and epibromopropane containing electron-withdrawing substituents, the yields reached 99.2% and 97.0% respectively after 18 h of reaction, with TON values ​​of 1218.7 and 1191.6, respectively. The electron-withdrawing effect of halogen atoms favors nucleophilic attack, promoting the ring-opening reaction. For aliphatic glycidyl ether substrates containing ether bonds, the yields of n-butyl glycidyl ether, isopropyl glycidyl ether, and tert-butyl glycidyl ether were all above 96%, with TON values ​​exceeding 1180, among which the yield of isopropyl glycidyl ether reached as high as 99.4%. As the steric hindrance of the substituents increased, the reaction time correspondingly prolonged, indicating that steric hindrance has a certain influence on the reaction rate.

[0087] For glycidyl oxypropylphenyl ether containing a benzene ring, the yield was 88.3% after 24 h due to the large steric hindrance of the phenyl group, with a TON value of 1084.8, slightly lower than that of aliphatic substrates. Glycidyl methacrylate, containing polymerizable olefin groups, achieved a yield of 96.6% after 24 h with a TON value of 1186.7, indicating good compatibility of the catalytic system with substrates containing sensitive functional groups. For the larger molecular size 3-glycidyl oxypropyltrimethoxysilane, the yield was 73.1% after 24 h with a TON value of 898.0, slightly lower than other substrates, possibly due to its larger steric hindrance.

[0088] The selectivity of all cyclic carbonate products was higher than 99%, indicating that the PIL-Cyc-1 catalyst has good substrate universality and selectivity.

[0089] Table 4: PIL-Cyc-1 catalyst catalyzes various epoxide substrates in cycloaddition reactions with CO2. .

[0090] To elucidate the mechanism of the cycloaddition reaction between PIL-Cyc-1-catalyzed epoxides and CO2, in-situ infrared spectroscopy was used to monitor the reaction process in real time. The results are as follows: Figure 12 As shown: Under conditions of 80 °C and ambient pressure CO2, with increasing reaction time, the concentration at 1795 cm⁻¹... -1 The absorption peak at 1164 cm⁻¹ gradually increases, which is attributed to the stretching vibration of the C=O bond in the cyclic carbonate product. Meanwhile, at 1164 cm⁻¹... -1 and 1064 cm -1 Two gradually increasing new peaks appeared, corresponding to the symmetric and asymmetric stretching vibrations of the COC bond in cyclic carbonates. Conversely, the characteristic absorption peak of the epoxy ring in the styrene oxide substrate (1255 cm⁻¹) was observed. -1 The intensity gradually decreases as the reaction proceeds, which intuitively reflects the consumption of the substrate and the formation of the product.

[0091] To further elucidate the mechanism of the PIL-Cyc-1-catalyzed cycloaddition reaction between epoxy substrates and CO2 at the atomic level, density functional theory was used to calculate the reaction pathway, and the results are as follows: Figure 13As shown. The entire catalytic cycle can be divided into three steps: ring-opening of the epoxide, insertion of CO2, and intramolecular ring-closure. Calculations show that the reaction first involves the interaction of oxygen atoms in the epoxide with hydrogen bond donors in the catalyst (including the NH bond of the secondary amine in the Cyclen unit and the OH bond of the hydroxyl group in the hydroxyethyl imidazolium salt unit) to form hydrogen bonds, thereby polarizing the CO bond. Simultaneously, Br... - As a nucleophile, it attacks from the less sterically hindered side of the epoxide, initiating a ring-opening reaction. The energy barrier for this ring-opening step is 98.0 kJ / mol, making it the rate-determining step of the entire reaction. The alkoxy anion intermediate formed after ring-opening rapidly combines with activated CO2, undergoing a CO2 insertion reaction. This step has a lower energy barrier of 49.0 kJ / mol. Finally, the carbonate intermediate closes the ring through an intramolecular nucleophilic substitution reaction, generating a cyclic carbonate product, while the catalyst is regenerated. This step has an energy barrier of 40.9 kJ / mol. The DFT calculation results and experimental observations from in-situ infrared spectroscopy corroborate each other, jointly confirming the three-step mechanism of the PIL-Cyc-1 catalyzed cycloaddition reaction between CO2 and epoxide: ring-opening-CO2 insertion-ring-closure. In this mechanism, the secondary amine of the Cyclen unit and the hydroxyl group of the hydroxyethyl imidazolium salt unit act as hydrogen bond donors, effectively activating the epoxide, while Br... - As nucleophiles, they facilitated the ring-opening step; the Cyclen unit secondary amine and the imidazolium salt unit hydroxyl group acted as hydrogen bond donors, synergistically activating the epoxide and Br. - As a bifunctional synergistic catalytic mechanism of "hydrogen bond donor-nucleophile" that promotes ring opening by nucleophiles, the synergistic effect of multiple active sites is the key to the excellent catalytic performance of the catalyst.

[0092] Based on experimental results from in-situ infrared spectroscopy and DFT theoretical calculations, we propose a reasonable mechanism for the PIL-Cyc-1 catalytic oxidation of styrene and the cycloaddition reaction with CO2, such as... Figure 14 As shown: First, the secondary amine NH of the Cyclen unit and the OH of the hydroxyethyl imidazolium salt unit in the catalyst act as hydrogen bond donors, forming hydrogen bonds with the oxygen atoms in styrene oxide, polarizing the CO bonds, thereby activating the epoxide. Simultaneously, the Br in the imidazolium salt... - As a nucleophile, it attacks from the less sterically hindered side of the epoxide, causing the epoxide ring to open and forming an alkoxy intermediate. This ring-opening step is the rate-determining step (RDS), consistent with DFT calculations. Subsequently, the activated CO2 molecule inserts into the ring-opening intermediate, generating a linear carbonate intermediate. This step exhibits a low energy barrier in the DFT calculations, indicating its rapid progression. Finally, the carbonate intermediate closes the ring via an intramolecular nucleophilic substitution reaction, generating a cyclic carbonate product, while Br... -Upon departure, the catalyst is regenerated. Throughout the catalytic cycle, the secondary amine of the Cyclen unit and the hydroxyl group of the hydroxyethyl imidazolium salt unit synergistically activate the epoxide via hydrogen bonding, Br - As a nucleophile promoting ring-opening, the combined effect of multiple active sites significantly improves catalytic efficiency. Furthermore, the porous structure of the catalyst facilitates the enrichment of substrate and CO2, further enhancing catalytic performance. These mechanisms corroborate experimental and theoretical calculations, confirming the highly efficient catalytic behavior of PIL-Cyc-1.

[0093] This application successfully prepared a series of ionic liquid / macrocyclic polyamine bifunctional porous organic polymer catalysts, PIL-Cyc-X, using monosubstituted tetraazacyclododecane (Cyc-4VB) and hydroxyethyl imidazolium salt ionic liquid (VIm-OH) as bifunctional building blocks, and divinylbenzene as a crosslinking agent via solvothermal free radical ternary copolymerization. Application examples show that under mild conditions without solvents, metals, or co-catalysts, PIL-Cyc-X catalyzes the oxidation of styrene to CO2 cycloaddition with a conversion rate of 93.4% and a selectivity exceeding 99%. Its catalytic activity is significantly superior to control catalysts without Cyclen units or hydroxyl groups, fully demonstrating the synergistic key role of Cyclen secondary amines and imidazolium hydroxyl groups as hydrogen bond donors. Furthermore, it exhibits good catalytic activity for various epoxides such as epichlorohydrin, epihexane, and allyl glycidyl ether.

[0094] More importantly, the thermal filtration experiment confirmed that no active species were leached during the reaction. After five cycles, the catalyst maintained a conversion rate of 87.6%, and its chemical structure remained stable, demonstrating excellent heterogeneous catalytic properties and regeneration performance. This provides a new strategy for green and efficient heterogeneous catalytic systems for CO2 cycloaddition.

[0095] The above-described embodiments are merely illustrative of several feasible implementations of the present invention, and their descriptions are relatively specific and detailed. However, they should not be construed as limiting the scope of the present invention, nor are the embodiments intended to limit the scope of protection in the claims of the present invention. For those skilled in the art, various modifications and improvements can be made without departing from the concept of the present invention. All equivalent implementations or changes that do not depart from the present invention should be included in the technology of the present invention.

Claims

1. A bifunctional porous organic polymer catalyst, characterized in that, The catalyst satisfies the general formula: ， Where a=1, b=1~3, c=1~3, d=1.

2. A method for preparing the bifunctional porous organic polymer catalyst according to claim 1, characterized in that: Cyclen monomer, 1-(2-hydroxyethyl)-4-vinylimidazolium bromide, crosslinking agent, and initiator are dissolved in an organic solvent and placed in a reactor for polymerization. The resulting product is a bifunctional porous organic polymer catalyst. The structural formula of the Cyclen monomer is: , The structural formula of 1-(2-hydroxyethyl)-4-vinylimidazolium bromide is: .

3. The preparation method according to claim 2, characterized in that: The crosslinking agent is divinylbenzene, and the initiator is azobisisobutyronitrile.

4. The preparation method according to claim 2, characterized in that: The polymerization reaction is carried out at a temperature of 110–130°C.

5. The preparation method according to claim 2, characterized in that: The organic solvent is N,N-dimethylformamide, methanol, or ethanol.

6. The preparation method according to claim 2, characterized in that, The method for synthesizing the Cyclen monomer is as follows: S1, di-tert-butyl dicarbonate was added dropwise to a mixed solution of 1,4,7,10-tetraazacyclododecane and triethylamine to give 1,4,7-tris(tert-butyloxycarbonyl)-1,4,7,10-tetraazacyclododecane; S2, 1,4,7-tris(tert-butoxycarbonyl)-1,4,7,10-tetraazacyclododecane reacts with 4-chloromethylstyrene under nitrogen protection to give 1-(4-vinylbenzyl)-4,7,10-tris(tert-butoxycarbonyl)-1,4,7,10-tetraazacyclododecane; S3,1-(4-vinylbenzyl)-4,7,10-tris(tert-butoxycarbonyl)-1,4,7,10-tetraazacyclododecane was dissolved in a solvent, cooled in an ice-water bath, and trifluoroacetic acid was slowly added dropwise. The mixture was then heated to room temperature and reacted. The solvent was removed under reduced pressure, toluene was added, and the resulting product was dissolved in water. The pH was adjusted to alkaline, and the mixture was extracted with chloroform. The organic phases were combined, dried, filtered, and the solvent was removed under reduced pressure to obtain the Cyclen monomer.

7. The preparation method according to claim 2, characterized in that, The synthesis method of 1-(2-hydroxyethyl)-4-vinylimidazolium bromide is as follows: 4-vinylimidazolium and 2-bromoethanol are evacuated and purged with nitrogen under ice-water bath cooling, and then heated to 30-60℃ under nitrogen protection to obtain 1-(2-hydroxyethyl)-4-vinylimidazolium bromide.

8. The application of the bifunctional porous organic polymer catalyst of claim 1 in cycloaddition reactions.

9. The application according to claim 8, characterized in that: A bifunctional porous organic polymer catalyst was added to the reaction system. The reaction system was evacuated and filled with carbon dioxide. Under the carbon dioxide atmosphere, an epoxy substrate was added. Under solvent-free and catalyst-free conditions, the epoxy substrate and CO2 underwent a cycloaddition reaction.

10. The application according to claim 8, characterized in that: The substrate for the cycloaddition reaction is any one of styrene oxide, epichlorohydrin, epibromopropane, n-butyl glycidyl ether, isopropyl glycidyl ether, tert-butyl glycidyl ether, glycidyl oxypropyl phenyl ether, glycidyl methacrylate, and 3-glycidyl etheroxypropyltrimethoxysilane.

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