Dicationic phosphorus-containing ionic liquid as well as preparation method and application thereof

Abstract

The invention discloses dicationic phosphorus-containing ionic liquid as well as a preparation method and application thereof, and belongs to the technical field of functional materials. The dicationic phosphorus-containing ionic liquid is prepared, imidazole is used as a cation core group, phosphite radicals are used as anions, the dicationic phosphorus-containing ionic liquid is used for modifying graphene and preparing a high-performance polyolefin composite material, the heat conductivity coefficient of the polyolefin material is increased, meanwhile, more excellent mechanical performance is achieved, and especially when the content of graphene is increased, the heat conductivity coefficient of the polyolefin material is increased. The impact strength of the polyolefin composite material is more reserved, and the bending modulus is more obviously improved.

Description

Technical Field

[0001] This application belongs to the field of functional materials technology, and in particular relates to a dual-cationic phosphorus-containing ionic liquid, its preparation method and application. Background Technology

[0002] Polyolefin materials are widely used in heating pipelines, including underfloor heating pipes, hot water delivery pipes, and solar thermal systems. However, their inherently low thermal conductivity is a key bottleneck restricting their application in high-performance thermal management. Especially in rapid response heating systems, the low thermal conductivity of traditional PERT pipes (approximately 0.35 W·m) is a significant limitation. -1 ·K -1 The thermal response time is as long as 30 to 40 minutes, which cannot meet the requirements of modern smart buildings for precise temperature control. In phase change energy storage devices, this low thermal conductivity will further reduce the energy storage / release efficiency by 20% to 30%.

[0003] Graphene, a two-dimensional material formed by sp² hybridization of a single layer of carbon atoms, has an extremely high thermal conductivity (approximately 5300 W·m). -1 ·K -1 Graphene, with its excellent mechanical strength, is an ideal filler for preparing high-performance polymer composites. Existing technologies disclose the use of modified graphene to improve the thermal conductivity of polyolefin materials. However, the strong van der Waals forces between graphene sheets make them prone to aggregation, hindering uniform dispersion in the polymer matrix and severely limiting their superior performance. Furthermore, graphene exhibits poor interfacial compatibility with most polymers (such as polyethylene), resulting in weak interfacial bonding, low stress transfer efficiency, and a decline in the polymer's mechanical properties. Therefore, surface functionalization modification of graphene is often necessary. Ionic liquids, especially those containing specific functional groups, can effectively modify the graphene surface through non-covalent mechanisms such as π-π interactions and cation-π interactions. Simultaneously, their organic cation moiety can improve compatibility with the polymer matrix, making them effective graphene modifiers. However, the modification effect of common ionic liquids on graphene is limited, and there is still room for improvement.

[0004] Existing technology discloses a dicationic ionic liquid with imidazole as the cationic core group for the modification of graphene, which is melt-blended with polypropylene, ABS, and acrylonitrile. butadiene The matrix can be styrene copolymer, epoxy resin, silicone rubber, etc., but the improvement in thermal conductivity is limited. At a graphene content of less than 10%, the thermal conductivity of PP is increased to 0.259 W·m. -1 ·K -1 The thermal conductivity of PERT was increased to 0.4 W·m. -1 ·K -1However, it is still difficult to meet the high-performance thermal management requirements of polyolefins.

[0005] Therefore, developing a dual-cationic phosphorus-containing ionic liquid for modifying graphene to prepare high-performance polyolefin composites, thereby improving the thermal conductivity of polyolefin materials while maintaining excellent mechanical properties, has significant research value and application implications. Summary of the Invention

[0006] To address the technical problems existing in the prior art, the primary objective of this invention is to provide a dual-cationic phosphorus-containing ionic liquid.

[0007] Another object of the present invention is to provide a method for preparing the above-mentioned dual-cationic phosphorus-containing ionic liquid.

[0008] Another object of the present invention is to provide the application of the above-mentioned dual-cationic phosphorus-containing ionic liquid as a graphene modifier.

[0009] Another object of the present invention is to provide ionic liquid functionalized graphene materials obtained by modifying graphene with the above-mentioned dual-cationic phosphorus-containing ionic liquid.

[0010] Another object of the present invention is to provide a polymer composite material comprising the above-mentioned ionic liquid functionalized graphene material.

[0011] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: This invention protects a dual-cation phosphorus-containing ionic liquid, named C4(n-bim)2(H2PO2)2, with the following structural formula: .

[0012] This invention prepares a dual-cationic phosphorus-containing ionic liquid with a symmetrical structure, using imidazole as the cation core group and phosphate as the anion.

[0013] This invention also protects a method for preparing the above-mentioned dual-cation type phosphorus-containing ionic liquid, comprising the following steps: S1. Imidazole reacts with benzyl bromide to produce N-benzylimidazole; S2.N-benzylimidazol reacts with 1,4-dibromobutane to give the dibromosal ionic liquid C4(n-bim)2Br2; S3. C4(n-bim)2Br2 and sodium hypophosphite are reacted, and the mixture is then distilled under reduced pressure, filtered, and dried to obtain the dicationic phosphorus-containing ionic liquid.

[0014] The synthetic route for the dual-cation type phosphorus-containing ionic liquid is as follows:

[0015] Preferably, the molar ratio of imidazole to benzyl bromide in step S1 is (1~1.2):1.

[0016] Preferably, the solvent for the reaction in step S1 is dimethyl sulfoxide.

[0017] Preferably, the reaction temperature in step S1 is 15~30℃.

[0018] Preferably, the reaction time in step S1 is 6 to 12 hours.

[0019] Preferably, the molar ratio of N-benzylimidazolium to 1,4-dibromobutane in step S2 is (2~2.2):1.

[0020] Preferably, the solvent for the reaction in step S2 is methanol or ethanol.

[0021] Preferably, the reaction temperature in step S2 is 80~90℃.

[0022] Preferably, the reaction time in step S2 is 24 to 28 hours.

[0023] Preferably, the molar ratio of the dibromosalt intermediate C4(n-bim)2Br2 to sodium hypophosphite in step S3 is 1:(1~1.2).

[0024] Preferably, the solvent for the reaction in step S3 is water.

[0025] Preferably, the reaction in step S3 is carried out at room temperature for 20 to 28 hours.

[0026] Preferably, the process further includes the following steps: after removing water from the reaction solution by vacuum distillation, acetonitrile is added for dispersion, insoluble byproducts are removed by filtration, and the filtrate is evaporated to remove acetonitrile to obtain the final product.

[0027] Preferably, the molar ratio of imidazole and benzyl bromide in step S1 is (1~1.2):1.

[0028] Preferably, the molar ratio of N-benzylimidazolium to 1,4-dibromobutane in step S2 is (2~2.2):1.

[0029] The application of the aforementioned dual-cationic phosphorus-containing ionic liquid as a graphene modifier is also within the scope of protection of this invention.

[0030] Preferably, the polyolefin material is selected from at least one of polyethylene, polypropylene, or heat-resistant reinforced polyethylene PERT.

[0031] This invention also protects an ionic liquid functionalized graphene material, which is prepared by mechanical ball milling of graphene and the above-mentioned dual-cationic phosphorus-containing ionic liquid.

[0032] Preferably, the mechanical ball milling method is wet ball milling, and the solvent used is ethanol.

[0033] Preferably, the mechanical ball milling method involves a rotation speed of 100-200 r / min and a time of 10-15 hours.

[0034] Preferably, the mass ratio of the dual-cationic phosphorus-containing ionic liquid to graphene is 0.5~20:1.

[0035] Preferably, the mass ratio of the dual-cationic phosphorus-containing ionic liquid to graphene is 0.5~2:1.

[0036] This invention protects a polymer composite material comprising a polyolefin material and the above-mentioned ionic liquid functionalized graphene dispersed therein; wherein the ionic liquid functionalized graphene has a mass fraction of 1% to 10% in the composite material.

[0037] Preferably, the ionic liquid functionalized graphene has a mass fraction of 5% to 7% in the composite material.

[0038] This application involves coating the surface of graphene with organic groups modified by a dicationic phosphorus-containing ionic liquid through surface adsorption. The synergistic effect of this dication and specific phosphorus-containing anion, compared to traditional monocationic or fluorine-containing ionic liquids, more effectively inhibits the re-agglomeration of graphene, resulting in a more uniform and stable dispersion within the polymer matrix. This optimized interfacial structure allows for more effective transfer of external loads from the polymer matrix to the high-strength graphene network, thereby achieving a significant improvement in tensile strength and flexural modulus with the same filler content, and mitigating the impact toughness degradation caused by filler introduction.

[0039] Uniform dispersion of graphene in a matrix is ​​a necessary condition for the formation of a continuous thermally conductive network. This invention achieves efficient and uniform dispersion of graphene through the aforementioned mechanism, enabling the formation of more and more complete thermally conductive pathways with the same amount added, thereby significantly improving heat transport efficiency.

[0040] The application of the aforementioned ionic liquid functionalized graphene materials in enhancing the heat resistance of polyethylene is also within the scope of protection of this invention.

[0041] Compared with the prior art, the present invention has the following beneficial effects: This invention prepares a dual-cationic phosphorus-containing ionic liquid with imidazole as the cation core group and phosphate as the anion, which is used to modify graphene to prepare high-performance polyolefin composite materials. While improving the thermal conductivity of polyolefin materials, it also has better mechanical properties. In particular, when the graphene content is increased, the impact strength of the polyolefin composite material is more preserved and the flexural modulus is more significantly improved. Attached Figure Description

[0042] Figure 1 Fourier transform infrared (FT-IR) spectrum of the dual-cationic phosphorus-containing ionic liquid C4(n-bim)2(H2PO2)2 prepared in this invention; Figure 2 The proton nuclear magnetic resonance spectrum of the dual-cationic phosphorus-containing ionic liquid C4(n-bim)2(H2PO2)2 prepared in this invention ( 1 H NMR spectrum; Figure 3 The carbon NMR spectrum of the dual-cationic phosphorus-containing ionic liquid C4(n-bim)2(H2PO2)2 prepared in this invention ( 13 C NMR spectrum; Figure 4 X-ray diffraction (XRD) spectra of thick sheet graphene (TSG) and ionic liquid functionalized graphene (TSG-IL) prepared in this invention; Figure 5 Raman spectra of TSG and TSG-IL prepared in this invention; Figure 6 Fourier transform infrared (FT-IR) spectra of TSG and TSG-IL prepared in this invention; Figure 7 X-ray photoelectron spectroscopy (XPS) total spectra of TSG and TSG-IL prepared in this invention, and C of TSG-IL. 1s P 2p High-resolution spectrum; Figure 8 SEM image of TSG (a) and SEM image of TSG-IL prepared by the present invention (b); TEM image of TSG (c) and TEM image of TSG-IL prepared by the present invention (d). Figure 9 : Surface distribution diagram of C, O, N, and P elements in TSG-IL prepared by this invention; Figure 10 Mechanical properties of pure PERT and PERT composites with different fillers: (a) tensile strength, (b) flexural modulus, (c) impact strength; Figure 11DSC curves of pure PERT and PERT composites filled with different fillers: (a) crystallization curve, (b) melting curve; Figure 12 Thermal conductivity diagrams of pure PERT and PERT composites with different fillers; Figure 13 Infrared thermal images of pure PERT, TSG / PERT, and the TSG-IL / PERT composite material of Example 4 during the cooling process; Figure 14 : Curves showing the surface temperature of pure PERT, TSG / PERT, and the TSG-IL / PERT composite material of Example 4 as a function of time. Detailed Implementation

[0043] The present invention is further illustrated below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions in the art or as recommended by the manufacturer; the raw materials and reagents used, unless otherwise specified, are all commercially available from the conventional market. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention are within the scope of protection claimed by the present invention.

[0044] I. Reagents used in the embodiments / comparative examples of this invention PERT: LG Chem (South Korea); PP: PPH-ED-003, Nanjing Jinling Plastics & Chemicals Co., Ltd.; IL2#: The anion is tetrafluoroborate (BF4). - Imidazolyl diionic liquid, C4(n-bim)2(BF4)2; IL3#: The anion is hexafluorophosphate (PF6). - Imidazole-based biionic liquid C4(n-bim)2(PF6)2; IL4#: 1 aminopropyl 3 Methylimidazolium bromide.

[0045] II. Experimental Methods 1. Synthesis and characterization of the dicationic phosphorus-containing ionic liquid C4(n-bim)2(H2PO2)2 S1. In a 250 mL three-necked flask equipped with a stirrer, a constant-pressure dropping funnel, and a nitrogen delivery tube, add 50 mL of dimethyl sulfoxide (DMSO), 4.0 g (0.1 mol) of sodium hydroxide, and 6.81 g (0.1 mol) of imidazole. Under nitrogen protection, mechanically stir at room temperature (20°C) for 1 hour. Subsequently, slowly add 17.1 g (0.1 mol) of benzyl bromide dropwise through the constant-pressure dropping funnel, controlling the dropping rate to maintain the reaction system temperature below 30°C. After the addition is complete, continue stirring the reaction at room temperature for 6 hours. After the reaction is complete, add 50 mL of dichloromethane to the reaction solution for extraction, separate the organic phase, and wash three times with deionized water to remove residual DMSO and inorganic salts. Finally, remove the dichloromethane solvent by rotary evaporation under reduced pressure to obtain the white solid intermediate product N-benzylimidazolium. S2. Add 50 mL of anhydrous ethanol to N-benzylimidazolium (15.8 g, 0.1 mol) and 6.52 g (30 mmol) of 1,4-dibromobutane obtained in step S1. Under a nitrogen atmosphere, the mixture is mechanically stirred and refluxed in an oil bath at 85 °C for 24 hours. After the reaction is complete, the ethanol solvent is removed by vacuum distillation. The crude product is dissolved in 20 mL of deionized water, and then the aqueous phase is washed three times each with ethyl acetate and petroleum ether to remove unreacted raw materials and low-polarity byproducts. The resulting aqueous phase is dried under reduced pressure to obtain a white solid product, 1,4-bis(N-benzylimidazolium)butane dibromide (C4(n-bim)2Br2). S3. Dissolve the dibromide intermediate obtained in step 2 (approximately 16 g, corresponding to 30 mmol of dication) and 3.42 g (30 mmol) of sodium hypophosphite in 50 mL of distilled water and stir magnetically at room temperature for 24 hours to carry out anion exchange reaction. After the reaction is completed, remove most of the water by vacuum distillation of the reaction solution. Add 30 mL of acetonitrile to the residue, disperse by ultrasonication, and filter to remove the insoluble byproduct sodium bromide. Collect the filtrate and remove the acetonitrile solvent again by rotary evaporation to finally obtain the pale yellow transparent viscous liquid product 1,4-bis(N-benzylimidazolium)butane hypophosphite (C4(n-bim)2(H2PO2)2).

[0046] Characterization of the product of this embodiment: FT-IR spectrum ( Figure 1 The graph shows 3150, 3112 (imidazolium and benzene ring CH), 2962, 2868 (-CH2-), 1605 (C=C), 1559 (C=N), 2398 (PH), 1207 (P=O), and 1050 cm⁻¹. -1 Characteristic absorption peaks such as (PO) 1 H NMR ( Figure 2 )and 13C NMR ( Figure 3 The chemical shifts in the spectrum match the structure of the target molecule. This indicates that the target ionic liquid was successfully synthesized.

[0047] 2. Preparation and characterization of ionic liquid functionalized graphene (TSG-IL) First, expanded graphite (EG) was heat-treated in a tube furnace at 500°C for 2 hours under nitrogen protection to obtain sheet graphene (TSG). 10 g of the dicationically cationic phosphorus-containing ionic liquid C4(n-bim)2(H2PO2)2 prepared by the above method and 10 g of TSG were weighed and dispersed together in 50 mL of anhydrous ethanol. The mixture was then sonicated for 30 minutes to achieve initial uniform dispersion. The suspension was then transferred to the ball mill jar of a planetary ball mill and wet-milled at 150 r / min for 12 hours. After milling, the product was filtered and repeatedly washed with anhydrous ethanol and deionized water until the filtrate was clear to remove physically adsorbed ionic liquid. Finally, the filter cake was dried in a vacuum drying oven at 60°C for 12 hours to obtain ionic liquid functionalized graphene (TSG-IL).

[0048] The product of this embodiment was characterized by XRD ( Figure 4 The (002) diffraction peak intensity of TSG-IL was significantly lower and broader than that of TSG, indicating a decrease in the orderliness of the layered structure and effective exfoliation of the lamellae. Raman spectroscopy ( Figure 5 The results showed that the I_D / I_G value of TSG-IL increased from 0.15 for TSG to 0.28, and the 2D peak shape became symmetrical, indicating that a small number of defects were generated and the number of layers was reduced during the peeling process. FT-IR ( Figure 6 ) and XPS ( Figure 7 Characteristic signals of N and P elements were detected in TSG-IL, confirming the successful loading of ionic liquid onto the graphene surface. SEM and TEM (…) Figure 8 The EDS (Elemental Distribution System) diagram shows that TSG-IL sheets are thinner, more transparent, and better dispersed. Figure 9 The graphene shows that N and P elements are uniformly distributed on the graphene surface.

[0049] Table 1 PERT Composite Material Formulation

[0050] As shown in Table 1, the contents of N (1.58%) and P (0.15%) in TSG-IL are significantly higher than those in TSG, with the oxygen content also increasing from 1.69% in TSG to 5.09%. This is largely due to the peroxidation of dangling bonds generated during the ball milling process of TSG. The ionic liquid C4(n-bim)2(H2PO2)2 has been successfully modified onto the graphene surface.

[0051] 3. Preparation and characterization of TSG-IL / PERT composite materials According to the formulation shown in Table 1, PERT resin and the TSG-IL prepared above were premixed at a certain mass ratio. Then, the mixture was melt-blended using a twin-screw extruder at a melt temperature of 200℃ and a screw speed of 200 r / min, and granulated to obtain composite masterbatch. The masterbatch was then injection molded into standard test strips at 210℃ using an injection molding machine.

[0052] III. Sample Preparation Table 2 Examples / Comparative Formulations

[0053] IV. Test Indicators (1) Mechanical properties: The tensile strength, flexural modulus and notched impact strength of the composite material were determined according to GB / T 1040.1-2006 (tensile rate 50 mm / min), GB / T 9341-2008 (bending rate 2 mm / min) and GB / T 1843-2008 standards. The average value of 5 samples was taken for each group of data. (2) Thermal conductivity: The thermal conductivity of the composite material was determined by the transient hot wire method according to ISO 22007-2:2008 standard.

[0054] V. Test Results Table 3. Test Results of Examples / Comparative Examples

[0055] Comparative Examples 7 and 8 provide two existing technologies for graphene-modified imidazole-based biionic ionic liquids, with the anionic portion being IL2# tetrafluoroborate (BF4). - ), IL3# hexafluorophosphate (PF6) - Imidazole-based dual-ionic liquids, Comparative Example 9 provides a prior art ionic liquid for modifying graphene. aminopropyl 3 According to comparative examples 7-9, the thermal conductivity improvement of ionic liquid-modified graphene using methylimidazolium bromide, at an addition of 5%, is limited, reaching a maximum of 0.4 W·m. -1 ·K -1 The original composite material exhibited poor mechanical properties, specifically a 21% increase in flexural modulus and a 23% decrease in impact strength. However, the modification described in this invention increases the thermal conductivity to 0.484~0.601 W·m. -1 ·K -1Furthermore, with an addition of 5%, the overall mechanical properties are significantly improved, specifically, the flexural modulus increases by 47.5% and the impact strength decreases by about 14%.

[0056] Examples 1-5 provide a series of graphene-PERT composite materials modified with the ionic liquid C4(n-bim)2(H2PO2)2 of the present invention. The thermal conductivity is compared with that of comparative examples 3-6, indicating that the ionic liquid modification improves the thermal conductivity, flexural modulus and impact strength, and has better mechanical properties while improving the thermal conductivity of polyolefin materials.

[0057] The 5% TSG-IL / PP provided in Example 6 improves both tensile strength and thermal conductivity compared to the performance of pure PP in Comparative Example 2, demonstrating that the ionic liquid of the present invention can also be used to modify the matrix PP and improve its performance.

[0058] Depend on Figure 10 It can be seen that when the TSG-IL addition amount is 7wt%, compared with pure PERT, the tensile strength increases from 18.53 MPa to 21.61 MPa (an increase of 16.6%), the flexural modulus increases from 257.11 MPa to 417.22 MPa (an increase of 62.24%), and the impact strength is also significantly higher than that of the TSG / PERT system with the same filling amount.

[0059] Depend on Figure 12 The thermal conductivity of the 7wt% TSG-IL / PERT composite material is 0.585 W / (m·K). -1 Compared to pure PERT (0.35 W / (m·K)) -1 This represents a 67.1% improvement, and is higher than the TSG / PERT system with the same filler content (0.561 W / (m·K)). -1 ).

[0060] Depend on Figure 13 (Infrared thermal imaging) and Figure 14 (Cooling curve) shows that the 7wt%TSG-IL / PERT composite material has the fastest heat dissipation rate, with the surface temperature dropping from 90℃ to 37.2℃ (a drop of 52.8℃).

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A dual-cationic phosphorus-containing ionic liquid, characterized in that, Named C4(n-bim)2(H2PO2)2, its structural formula is as follows: 。 2. The method for preparing the dual-cationic phosphorus-containing ionic liquid according to claim 1, characterized in that, Includes the following steps: S1. Imidazole reacts with benzyl bromide to produce N-benzylimidazole; S2.N-benzylimidazol reacts with 1,4-dibromobutane to give the dibromosal ionic liquid C4(n-bim)2Br2; S3. C4(n-bim)2Br2 and sodium hypophosphite are reacted, and the mixture is then distilled under reduced pressure, filtered, and dried to obtain the dicationic phosphorus-containing ionic liquid.

3. The preparation method according to claim 2, characterized in that, The molar ratio of imidazole and benzyl bromide in step S1 is (1~1.2):

1.

4. The preparation method according to claim 2, characterized in that, The molar ratio of N-benzylimidazolium to 1,4-dibromobutane in step S2 is (2~2.2):

1.

5. The application of the dual-cationic phosphorus-containing ionic liquid of claim 1 as a graphene modifier.

6. An ionic liquid functionalized graphene material, characterized in that, It is prepared by mechanical ball milling of graphene and the dual-cationic phosphorus-containing ionic liquid of claim 1.

7. The ionic liquid functionalized graphene material according to claim 5, characterized in that, The mass ratio of the dual-cationic phosphorus-containing ionic liquid to graphene is 0.5~20:

1.

8. A polymer composite material, characterized in that, The composite material includes a polyolefin material and ionic liquid functionalized graphene as described in claim 7 dispersed therein; the ionic liquid functionalized graphene has a mass fraction of 1% to 10% in the composite material.

9. The polymer composite material according to claim 8, characterized in that, The ionic liquid functionalized graphene has a mass fraction of 5% to 7% in the composite material.

10. The polymer composite material according to claim 8, characterized in that, The polyolefin material is selected from at least one of polyethylene, polypropylene, or heat-resistant reinforced polyethylene PERT.

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