A UV-crosslinkable all-organic composite dielectric material and its preparation method

Abstract

The present invention provides a UV-crosslinked all-organic composite dielectric material and a preparation method thereof, belonging to the technical field of dielectric material preparation. In this method, a photosensitive group is introduced as a crosslinking unit into a polymer containing aromatic rings to obtain a polymer through a nucleophilic substitution reaction; a nanoscale carbonized polymer dot and a polymer solution are blended and an organic composite film is prepared; the organic composite film is irradiated under an ultraviolet lamp to obtain the UV-crosslinked all-organic composite dielectric material. The all-organic composite dielectric film of the present invention has excellent dielectric energy storage performance under high temperature and high electric field, and is a very promising electric energy storage material.

Description

Technical Field

[0001] The present invention belongs to the technical field of dielectric material preparation, and particularly relates to a UV-crosslinked all-organic composite dielectric material and a preparation method thereof. Background Art

[0002] In the field of electrical energy storage devices, electrostatic capacitors play a crucial role in pulsed power systems and electric thrusters due to their fast charge and discharge rates and ultra-high power density. Among various dielectric materials, dielectric polymers have become the preferred dielectrics for high energy density capacitors due to their high breakdown strength, low energy loss, high reliability, and easy processing. Nowadays, with the increasingly wide application of electrostatic capacitors, many extreme environments such as electrical transportation and aerospace systems have put forward higher requirements for their performance under high temperature and high electric field. However, dielectric polymers not only exhibit a sharp decline in dielectric properties due to the molecular chain segment movement above their glass transition temperature, but also the leakage current inside them increases exponentially under high temperature and high electric field, which leads to a sharp decline in their breakdown strength (E b ), discharge energy density (U e ), and charge and discharge efficiency (η), and their application at high temperature is greatly restricted. Therefore, the research on dielectric materials that meet the requirements of long-term application of electrostatic capacitors under extreme conditions still faces challenges.

[0003] In recent years, researchers have found that the crosslinking strategy is an effective method to restrict molecular chain movement. At the same time, it can also significantly improve the breakdown strength of polymers and effectively suppress leakage current. Therefore, researchers at home and abroad are committed to constructing a crosslinking system in polymers to obtain high-temperature-resistant dielectric materials. In addition, in view of the effective improvement of the dielectric energy storage performance of polymer materials under the coupling of high temperature and high electric field by the crosslinking strategy, researchers have also applied this method to composite materials, hoping to further improve the energy storage density of the materials. However, traditional thermal crosslinking usually requires a relatively high reaction temperature, and the operation process not only consumes a large amount of energy but also is difficult to control, and is not suitable for large-scale continuous production.

[0004] UV irradiation crosslinking, that is, irradiating polymer materials with ultraviolet light, uses ultraviolet light to penetrate into the interior of the polymer, enabling photosensitive groups to react to achieve crosslinking of macromolecules. Compared with chemical crosslinking and thermal crosslinking, this UV crosslinking technology can not only be operated under normal temperature and pressure conditions, without damage to polymer materials, but also does not bring any residual toxins and wastes, and has the advantages of high efficiency, energy saving, environmental protection, and simple control method. It is a technology suitable for industrialization and large-scale production.

[0005] Therefore, developing a dielectric polymer that can construct a crosslinked structure through simple operation and achieve excellent dielectric energy storage performance under high temperature and high electric field is the main technical problem faced currently. Summary of the Invention

[0006] The object of the present invention is to provide a UV-crosslinked all-organic composite dielectric material and a preparation method thereof. This material can achieve its efficient application under extreme environmental conditions of high temperature and high electric field.

[0007] The present invention first provides a preparation method of a UV-crosslinked all-organic composite dielectric material, including:

[0008] Step 1: Introduce a photosensitive group as a crosslinking unit into an aromatic-ring-containing polymer, and obtain a polymer through a nucleophilic substitution reaction;

[0009] Step 2: Blend the nanoscale carbonized polymer dots and the polymer solution obtained in Step 1 and prepare an organic composite film;

[0010] Step 3: Irradiate the organic composite film obtained in Step 2 under an ultraviolet lamp to obtain a UV-crosslinked all-organic composite dielectric material.

[0011] Preferably, the photosensitive group described in Step 1 is vinyl ether, allyl group, epoxy compound or propenyl ether.

[0012] Preferably, the aromatic-ring-containing polymer described in Step 1 is polyarylether sulfone, polyarylether ketone or polyethersulfone.

[0013] Preferably, the reaction process described in Step 1 specifically includes: dissolving a compound containing a photosensitive group, an aromatic-ring-containing polymer, and anhydrous potassium carbonate in a solvent and a water-carrying agent, and carrying out a polymerization reaction to obtain a polymer.

[0014] Preferably, the temperature of the nucleophilic substitution reaction described in Step 1 is 160-170 °C, and the reaction time is 6-12 h.

[0015] Preferably, the nanoscale carbonized polymer dots described in Step 2 are citric acid-ethylenediamine type polymer dots or phthalic acid-ethylenediamine type polymer dots.

[0016] Preferably, the mass fraction of the nanoscale carbonized polymer dots described in Step 2 is 0.1-0.7 wt%.

[0017] Preferably, the blending temperature described in Step 2 is room temperature, and the blending time is 4-6 h.

[0018] Preferably, the irradiation time described in Step 3 is 40-45 min for each side irradiation

[0019] The present invention also provides a UV-crosslinked all-organic composite dielectric material obtained by the above preparation method.

[0020] Advantages of the Present Invention

[0021] The present invention provides a UV-crosslinkable all-organic composite dielectric material and a preparation method thereof. In the present invention, a photosensitive group is introduced as a crosslinking unit into a polymer containing aromatic rings to prepare a high-performance polymer capable of UV crosslinking. Through a period of UV irradiation, the photosensitive groups react to achieve crosslinking of the polymer. This process does not involve the introduction of additional crosslinking agents and the generation of small-molecule by-products, enabling the obtained crosslinked polymer to have significantly improved thermal stability without introducing excessive impurities. In addition, in order to further improve the dielectric properties of the pure polymer material and its ability to capture charges under high electric fields, zero-dimensional carbonized polymer dots are introduced into the polymer matrix to prepare an all-organic composite material. The relatively high electron affinity of the polymer dots is used to capture the electrons injected by the electrodes under high electric fields, reducing the leakage current and dielectric loss inside the composite material. At the same time, due to the easy modification and adjustable bandgap of the polymer dots, their conjugation degree and the internal carbon hybridization type can be changed by UV light irradiation, effectively broadening their bandgap and further reducing the conduction loss of the composite material, and improving its high-temperature energy storage performance. In this way, polymer crosslinking and bandgap broadening of the polymer dots are simultaneously achieved through one-step UV irradiation, and the synergistic effect of the two is utilized to greatly improve the high-temperature dielectric energy storage performance of the polymer dielectric.

[0022] From the test results, it can be seen that in the temperature range of 20 °C - 200 °C, the dielectric constant and dielectric loss of the crosslinked all-organic composite dielectric remain stable, above 3.5 and below 0.007 respectively. In addition, at 200 °C, the breakdown field strength of the crosslinked all-organic composite dielectric exceeds 550 MV / m, and the charge-discharge efficiency reaches 80% at 400 MV / m, and the discharge energy density also reaches 4.0 J / cm³ at 600 MV / m. 3 Experiments prove that the all-organic composite dielectric film of the present invention has excellent dielectric energy storage performance under high temperature and high electric fields and is a very promising electrical energy storage material. Description of the Drawings

[0023] Figure 1 Infrared spectra of the UV-crosslinked poly(aryl ether sulfone) film of Comparative Example 1 before and after the crosslinking reaction.

[0024] Figure 2 UV-visible absorption spectra of the polymer dots in Example 1 before and after UV irradiation and the calculated bandgap diagrams.

[0025] Figure 3 Dielectric temperature spectra of the crosslinked poly(aryl ether sulfone) films and crosslinked all-organic composite dielectrics of Comparative Example 1 and Example 1.

[0026] Figure 4 High-temperature Weibull breakdown strength diagrams of the crosslinked poly(aryl ether sulfone) films and crosslinked all-organic composite dielectrics of Comparative Example 1 and Example 1.

[0027] Figure 5 For the high-temperature charge-discharge efficiency and discharge energy density diagrams of the crosslinked polyarylether sulfone film and the crosslinked all-organic composite dielectric of Comparative Example 1 and Example 1.

[0028] Figure 6 For the reaction structural schematic diagram of phthalic acid-based polymer dots PAPD in Example 2. Detailed implementation manners

[0029] The present invention first provides a preparation method of a UV-crosslinked all-organic composite dielectric material, including:

[0030] Step 1: Introduce a photosensitive group as a crosslinking unit into a polymer containing an aromatic ring, and obtain a polymer through a nucleophilic substitution reaction;

[0031] The specific preferred reaction process includes: dissolving a compound containing a photosensitive group, a polymer containing an aromatic ring, and anhydrous potassium carbonate in a solvent and a water-carrying agent, and performing a polymerization reaction to obtain a polymer. The temperature of the polymerization reaction is preferably 160 - 170 °C, the reaction time is preferably 6 - 12 h, more preferably 7 h. The photosensitive group is preferably vinyl ether, allyl group, epoxy compound or propenyl ether. The compound containing a photosensitive group is preferably 2,2'-diallylbisphenol A. The polymer containing an aromatic ring is preferably polyarylether sulfone, polyarylether ketone or polyethersulfone, more preferably 4,4'-difluorodiphenyl sulfone. The solvent is preferably N,N-dimethylacetamide DMAc, and the water-carrying agent is preferably toluene. The molar ratio of the compound containing a photosensitive group, the polymer containing an aromatic ring, and anhydrous potassium carbonate is 1:1.1:1;

[0032] Step 2: Blend the nanoscale carbonized polymer dots and the polymer solution in Step 1 and prepare an organic composite film;

[0033] The electron affinity of the nanoscale carbonized polymer dots is greater than 3 eV, preferably citric acid-ethylenediamine type polymer dots or phthalic acid-ethylenediamine type polymer dots. The preparation method of the citric acid-ethylenediamine type polymer dots or phthalic acid-ethylenediamine type polymer dots adopts the hydrothermal method of the existing technology, and preferably includes: using ethylenediamine and phthalic acid or citric acid as precursors, and synthesizing nanoscale carbonized polymer dots through the hydrothermal method. The temperature of the hydrothermal method is preferably 200 °C, and the time is preferably 5 h. The mass g of citric acid: the volume μL of ethylenediamine is 1.0507:335; the mass g of phthalic acid: the volume μL of ethylenediamine is 1.66:670. The size of the obtained nanoscale carbonized polymer dots is 5 - 7 nm.

[0034] The blending is to dissolve the nanoscale carbonized polymer dots and the polymer obtained in Step 1 in a solvent respectively. The solvent is preferably N,N-dimethylacetamide (DMAc). Then the solutions are mixed and stirred, and a polymer thin film is prepared by the casting method. The blending temperature is preferably room temperature, and the blending time is preferably 4 - 6 h. The mass fraction of the nanoscale carbonized polymer dots in the blend is 0.1 - 0.7 wt%.

[0035] Step 3: Irradiate the organic composite thin film obtained in Step 2 under an ultraviolet lamp to obtain a UV-crosslinked all-organic composite dielectric material. The irradiation conditions are preferably: at a distance of 10 cm from the ultraviolet lamp, irradiate both sides of the thin film for 40 - 45 min each.

[0036] The present invention also provides a UV-crosslinked all-organic composite dielectric material obtained by the above preparation method.

[0037] To further understand the present invention, the preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention patent.

[0038] The test methods for the performance of each sample in the examples are as follows:

[0039] The infrared spectrum was measured using a Thermo Fisher Scientific iS10 Fourier transform infrared spectrometer. The ultraviolet-visible absorption spectrum was measured using a Shimadzu spectrophotometer, model UV-1800. The dielectric loss was tested using an HP4294 dielectric instrument produced by Agilent Technologies, USA. The breakdown field strength, charge-discharge efficiency, and discharge energy density were measured using a Trek610C type PE loops tester produced by PolyK, USA.

[0040] Comparative Example 1 Preparation of a UV-crosslinked polyarylether sulfone thin film

[0041] A UV-crosslinkable polyarylether sulfone thin film was prepared by the solution casting method. 0.2 g of the polymer prepared in Step 1 of Example 1 was dissolved in 5 mL of DMAc and stirred for 5 h. After the polymer was completely dissolved, the polymer solution was obtained by filtration through a filter head. Subsequently, the solution was dropped onto a clean glass plate (8 cm × 8 cm) and placed in an oven at 80 °C for 12 h to remove the solvent. Then it was heated to 100 °C and 120 °C for 2 h respectively to remove the residual solvent. After cooling to room temperature, the film was peeled off from the glass in deionized water and vacuum dried at 120 °C for 12 h to obtain an uncrosslinked polyarylether sulfone thin film pPAES. The prepared pPAES thin film was placed under a 365 nm ultraviolet lamp and irradiated for 40 minutes on each side to obtain a crosslinked thin film pPAES-UV.

[0042] Figure 1FTIR spectra of the UV-crosslinked poly(aryl ether sulfone) film before and after crosslinking reaction for Comparative Example 1. It can be observed from the FTIR spectra that in pPAES-UV, the absorption peaks at 1668 cm -1 and 967 cm -1 are significantly weakened, indicating that the crosslinking reaction has occurred.

[0043] Preparation of UV-Crosslinked Poly(Aryl Ether Sulfone)-Based All-Organic Composite Films in Example 1

[0044] Step 1: Dissolve diallylbisphenol A (12.337 g, 0.040 mol), 4,4′-difluorodiphenyl sulfone (10.682 g, 0.044 mol) and anhydrous potassium carbonate K 2 CO 3 (6.082 g, 0.04 mol) in 82 mL of N,N-dimethylacetamide DMAc (solvent) and 26 mL of toluene (water-carrying agent), and carry out the water-carrying salification reaction under an argon atmosphere at the reflux temperature of the water-carrying agent. Subsequently, distill out the water-carrying agent and raise the temperature to 160 °C and reflux for 7 h for polymerization. Observe the change in the viscosity of the system during the reaction. After the solution shows viscosity, the reaction is completed. Pour the product into deionized water and filter to obtain a white strip solid. After the obtained polymer is crushed, it is boiled and washed with methanol and deionized water, and then vacuum dried at 80 °C for 24 h to obtain a white powder. The reaction process is as follows:

[0045]

[0046] Step 2: Select a polymer dot of the classic citric acid-ethylenediamine type as the filler. Weigh 1 mg of the polymer dot and dissolve it ultrasonically in 3 mL of DMAc. At the same time, weigh 0.2 g of the above polymer and stir it to dissolve in 3 mL of DMAc. Then mix the polymer dot and the polymer solution and stir for 5 h. After that, drop the mixed solution onto a clean glass plate (8 cm × 8 cm) and place it in an oven at 80 °C for 12 h to remove the solvent, and then raise the temperature to 100 °C and 120 °C and place it for 2 h respectively to remove the residual solvent. After cooling to room temperature, peel the film from the glass in deionized water and vacuum dry it at 120 °C for 12 h to obtain the uncrosslinked poly(aryl ether sulfone)-based all-organic composite film pPAES / PD.

[0047] Step 3: Place the prepared pPAES / PD film under a 365 nm UV lamp and irradiate each side for 40 minutes to obtain the crosslinked film pPAES / PD-UV.

[0048] Figure 2UV-visible absorption spectra and calculated bandgap diagrams of polymer dots before and after UV irradiation in Example 1. It can be observed from the figure that, compared with before UV irradiation, the absorption peak of the polymer dots shows an obvious blue shift and the peak width becomes wider. In addition, we used the formula αhν 1 / n = A(hν - E g ) to calculate the bandgap values of the polymer dots before and after UV irradiation. From the calculation results, it can be seen that after UV irradiation, the bandgap of the polymer dots increased from 3.6 eV to 3.9 eV, which indicates the modification effect of UV on the polymer dots.

[0049] Figure 3 Dielectric temperature spectra of crosslinked polyarylethersulfone films and crosslinked all-organic composite dielectrics of Comparative Example 1 and Example 1. Among them, Figure a is the temperature-dielectric constant curve, and Figure b is the temperature-dielectric loss curve. First, it can be observed from the figure that compared with the pure polymer film, the all-organic composite films pPAES / PD and pPAES / PD-UV with added polymer dots have higher dielectric constants, increasing from 3.4 of pPAES and 3.0 of pPAES-UV to 4.0 and 3.7 respectively, and the dielectric loss decreases to a certain extent. In addition, compared with the film without UV irradiation, the dielectric constants and dielectric losses of pPAES-UV and pPAES / PD-UV remain stable in a wide temperature range of 20 °C - 200 °C, which indicates that the crosslinked structure has a very significant effect on improving the thermal stability of the polymer.

[0050] Figure 4 Weibull breakdown strength diagrams of crosslinked polyarylethersulfone films and crosslinked all-organic composite dielectrics of Comparative Example 1 and Example 1 at 200 °C. It can be seen from the figure that under the synergistic effect of UV crosslinking of the polymer matrix and the broadening of the bandgap of the polymer dots, the breakdown strength of the crosslinked all-organic composite dielectric pPAES / PD-UV reaches 569 MV m -1 , far higher than other thin film materials.

[0051] Figure 5 Charge-discharge efficiency (Figure a) and discharge energy density diagrams (Figure b) of crosslinked polyarylethersulfone films and crosslinked all-organic composite dielectrics of Comparative Example 1 and Example 1 at 200 °C. It can be seen from the figure that the charge-discharge efficiency and discharge energy density of the pure polymer film pPAES decrease rapidly at high temperatures. The high-temperature performance of the crosslinked all-organic composite dielectric pPAES / PD-UV after UV irradiation is greatly improved. Its efficiency at 400 MV m -1 exceeds 80%, and the highest energy density value reaches 4.0 J cm -1 .

[0052] Preparation of UV-crosslinked all-organic composite film of phthalic acid-ethylenediamine polymer dots in Example 2

[0053] Phthalic acid (1.66 g) and ethylenediamine (670 μL) were selected as precursors, and phthalic acid-ethylenediamine polymer dots PAPD with a size of about 7 nm were prepared by hydrothermal synthesis in a high-pressure reactor at 200 °C for 5 h. The reaction structural schematic diagram is as shown in Figure 6 shown.

[0054] Weigh 1 mg of PAPD and dissolve it in 3 mL of DMAc by ultrasound. At the same time, weigh 0.2 g of the polymer prepared in Step 1 of Example 1 and stir it to dissolve in 3 mL of DMAc. Then mix the polymer dot and polymer solution and stir for 5 hours. After that, drop the mixed solution onto a clean glass plate (8 cm × 8 cm) and place it in an oven at 80 °C for 12 h to remove the solvent, and then raise the temperature to 100 °C and 120 °C for 2 hours respectively to remove the residual solvent. After cooling to room temperature, peel the film from the glass in deionized water and vacuum dry it at 120 °C for 12 hours to obtain the uncrosslinked polyarylethersulfone-based all-organic composite film pPAES / PAPD. The prepared

[0055] pPAES / PAPD film was placed under a 365 nm ultraviolet lamp and irradiated for 40 minutes on each side to obtain a crosslinked film

[0056] pPAES / PAPD-UV.

Claims

1. A preparation method of a UV-crosslinked all-organic composite dielectric material, which is characterized in that, It includes: Step 1: Introduce a photosensitive group as a crosslinking unit into an aromatic-ring-containing polymer, and obtain a polymer through a nucleophilic substitution reaction; Step 2: Blend the nanoscale carbonized polymer dots and the polymer solution obtained in Step 1 and prepare an organic composite film; Step 3: Irradiate the organic composite film obtained in Step 2 under an ultraviolet lamp to obtain a UV-crosslinked all-organic composite dielectric material; The nanoscale carbonized polymer dots described in Step 2 are citric acid-ethylenediamine type polymer dots or phthalic acid-ethylenediamine type polymer dots; The mass fraction of the nanoscale carbonized polymer dots described in Step 2 is 0.1-0.7 wt%.

2. According to the preparation method of a UV-crosslinked all-organic composite dielectric material described in Claim 1, which is characterized in that the photosensitive group described in Step 1 is vinyl ether, allyl group, epoxy group or propenyl ether.

3. According to the preparation method of a UV-crosslinked all-organic composite dielectric material described in Claim 1, which is characterized in that the aromatic-ring-containing polymer described in Step 1 is polyarylether sulfone, polyarylether ketone or polysulfone.

4. According to the preparation method of a UV-crosslinked all-organic composite dielectric material described in Claim 1, which is characterized in that the specific reaction process in Step 1 includes: Dissolve a compound containing a photosensitive group, 4,4'-difluorodiphenyl sulfone, and anhydrous potassium carbonate in a solvent and a water-carrying agent, and carry out a polymerization reaction to obtain a polymer.

5. According to the preparation method of a UV-crosslinked all-organic composite dielectric material described in Claim 4, which is characterized in that the temperature of the polymerization reaction described in Step 1 is 160-170 °C, and the reaction time is 6-12 h.

6. According to the preparation method of a UV-crosslinked all-organic composite dielectric material described in Claim 1, which is characterized in that the blending temperature described in Step 2 is room temperature, and the blending time is 4-6 h.

7. According to the preparation method of a UV-crosslinked all-organic composite dielectric material described in Claim 1, which is characterized in that the irradiation time described in Step 3 is 40-45 min for each side irradiation.

8. A UV-crosslinked all-organic composite dielectric material obtained by the preparation method described in Claim 1.

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