Phosphorus-nitrogen synergistic polyethylene glycol basic sign flame-retardant phase change material and preparation method thereof

Abstract

The application discloses a phosphorus-nitrogen synergistic polyethylene glycol intrinsic flame-retardant phase change material and a preparation method thereof, relates to the technical field of phase change energy storage materials, and the material is prepared by taking polyethylene glycol long-chain aldehyde as a phase change skeleton, condensing with aromatic primary amine to obtain a Schiff base intermediate, and adding a phosphorus-containing compound to introduce a phosphorus-nitrogen flame-retardant group, so that the material has both phase change energy storage and intrinsic flame-retardant properties. Through molecular structure design, the application retains good phase change characteristics, and at the same time, excellent intrinsic flame-retardant properties are endowed to the material, so that the problem of flammability of traditional organic phase change materials is effectively improved.

Description

Technical Field

[0001] This invention relates to the field of phase change energy storage materials technology, specifically to a phosphorus-nitrogen synergistic polyethylene glycol-based flame-retardant phase change material and its preparation method. Background Technology

[0002] The excessive consumption of traditional energy sources has led to severe environmental pollution and an energy crisis. Developing renewable energy and efficient energy storage technologies is an important task for achieving low-carbon and sustainable economic development. Thermal energy is one of the most common forms of energy in nature. The rational collection, storage, and utilization of thermal energy will significantly improve energy efficiency and effectively alleviate the energy crisis and environmental problems. Thermal energy storage technology (TES) has proven to be a low-cost and highly promising energy-saving technology, among which phase change thermal energy storage technology has attracted much attention due to its advantages such as high thermal density and compact structure.

[0003] Phase change materials (PCMs) are a class of materials that utilize physical phase changes at a specific temperature to store and release energy, and are the key and core of phase change energy storage technology. PCMs can be classified according to their phase change form into solid-liquid phase change, liquid-gas phase change, solid-gas phase change, and solid-solid phase change. Among these, the liquid-gas and solid-gas phase changes involve huge volume changes, requiring pressure-resistant containers, leading to complex systems and high costs, thus limiting the effectiveness of solid-gas and liquid-gas systems. Solid-liquid and solid-solid phase changes are of practical significance. Of these two practical systems, solid-liquid systems have been studied most extensively and are the most commercially common.

[0004] Based on their material properties, phase change materials (PCMs) are mainly divided into organic PCMs and inorganic PCMs. Inorganic PCMs exhibit significant supercooling and phase separation, severely limiting their applications. Organic PCMs, on the other hand, are widely studied due to their wide and adjustable phase change temperatures, low supercooling, and lack of phase separation. However, organic PCMs are essentially hydrocarbons, exhibiting significant flammability and posing serious fire safety hazards, a drawback that restricts their further development.

[0005] Currently, to improve the flame retardant properties of organic phase change materials (PCMs), researchers have developed a series of flame retardant methods, mainly including adding flame retardants, encapsulation, and chemical modification. Flame retardants can effectively slow down, inhibit, or even block the combustion of substances. They are usually added to PCMs through physical blending to improve their flame retardant properties. This method is widely used due to its simplicity and low cost. Commonly used flame retardants include halogenated flame retardants, hydroxide flame retardants, intumescent flame retardants, silicon-based flame retardants, and inorganic nano-flame retardants. However, during the continuous melting-solidification cycle of PCMs, flame retardants migrate and separate from the PCM matrix, leading to a rapid decline in the overall flame retardant properties of the material, which is detrimental to its long-term application. Encapsulation involves encapsulating the PCM within a non-combustible shell, physically isolating it from the external environment to improve its flame retardant properties. However, the shell is at risk of cracking during long-term use, and once the shell cracks, its flame retardant properties will decrease significantly or even be lost. Chemical modification involves incorporating flame-retardant substances into the molecules of phase change materials through chemical bonds, making flame retardancy an intrinsic property. Even after processing or long-term cycling, the material retains excellent flame-retardant properties. Summary of the Invention

[0006] Therefore, the purpose of this invention is to provide a phosphorus-nitrogen synergistic polyethylene glycol-based flame-retardant phase change material and its preparation method.

[0007] The objective of this invention is achieved through the following technical solution: <First Aspect> A method for preparing a polyethylene glycol-based flame-retardant phase change material includes the following steps: The condensation reaction of aldehyde and amino groups is carried out to graft an aromatic primary amine onto the end of the dialdehyde PEG molecular chain to generate an intermediate containing a Schiff base structure. By utilizing the C=N double bond of the intermediate to undergo a nucleophilic addition reaction with the PH bond of DOPO, DOPO is grafted to the molecular chain end of the intermediate to obtain the polyethylene glycol-based flame-retardant phase change material.

[0008] As one embodiment, the molecular formula of the dialdehyde PEG is OHC-CH2-O-(CH2CH2O). n-2 -CH2-CHO, where n represents an integer from 46 to 180.

[0009] As one implementation scheme, the preparation method of the dialdehyde PEG is as follows: Polyethylene glycol was dissolved in anhydrous DMSO, TFA catalyst was added, and the mixture was stirred until homogeneous to obtain the first reaction solution. At 0~10℃, an anhydrous DMSO solution containing dissolved DCC is added dropwise to the first reaction solution, and the reaction is continued to be stirred until it is complete, to obtain the second reaction solution; The second reaction solution was diluted and filtered. The filtrate was concentrated and then precipitated by adding an alcohol solvent. The precipitate was collected, washed, and the dialdehyde PEG was obtained.

[0010] As one embodiment, the polyethylene glycol is one or more of PEG2000, PEG4000, PEG6000, and PEG8000.

[0011] As one embodiment, the aromatic primary amine is one or more of aniline, p-toluidine, o-toluidine, and phenylenediamine.

[0012] As one implementation, the intermediate is prepared by dissolving the dialdehyde PEG in anhydrous ethanol, adding aniline, and performing a first heat treatment at 45-55°C for 6-8 hours. During the second heat treatment, the mixture is stirred synchronously at a speed of 140-160 r / min.

[0013] As one implementation, the intermediate is dissolved in anhydrous ethanol, DOPO is added, and a second heat treatment is performed at 75~85°C for 12~14 hours, while the mixture is stirred synchronously at a speed of 140~160 r / min.

[0014] <Second aspect> An intrinsically flame-retardant phase change material has the following structural formula: The molecular backbone is a long polyoxyethylene chain.

[0015] As one embodiment, the molecular backbone is -CH2-O-(CH2CH2O). n-2 -CH2-, n=46~180.

[0016] As one implementation, the phase transition temperature of the material is 33~51℃, and the latent heat of phase transition is 71~145J / g.

[0017] As one implementation, the 5% thermal weight loss temperature of the material is 315~345℃, and the char residue rate is 5~10%.

[0018] As one implementation, the material forms a honeycomb-shaped expanded carbon layer after pyrolysis.

[0019] <Third aspect> Application of a polyethylene glycol-based flame-retardant phase change material.

[0020] As one implementation, the material is suitable for use in buildings, automobiles, solar energy, or batteries.

[0021] Compared with the prior art, the present invention has the following beneficial effects: (1) Effectively solves the problem of the prominent flammability and limited application of polyethylene glycol phase change materials. This invention imparts excellent flame-retardant properties to materials by introducing phosphorus-containing flame-retardant groups (DOPO) and nitrogen-containing flame-retardant groups (such as aniline). The principle is as follows: ① The pyrolysis of phosphorus-containing groups releases gaseous compounds, such as free radicals ·PO, ·HPO, and ·PO2, while simultaneously producing acidic substances such as polyphosphates and phosphoric acid; ② Phosphorus free radicals can capture highly reactive free radicals that maintain the combustion chain reaction, such as ·OH and H·, thus interrupting the combustion chain; ③ Polyphosphates and phosphoric acid promote substrate dehydration and char formation, forming a dense char layer that isolates heat and oxygen transfer; ④ The pyrolysis of nitrogen-containing groups releases nitrogen-containing non-combustible gases, carrying away heat and diluting combustible gases in the gas phase. Under the combined action of gas-phase and condensed-phase flame-retardant mechanisms, the modified material exhibits a significantly increased high-temperature char formation rate and a significantly reduced maximum thermal decomposition rate, resulting in excellent flame-retardant properties.

[0022] (2) Solving the long-term stability problem Traditional methods physically blend flame retardants with phase change materials (PCMs). However, during the continuous melting and solidification process of the PCM, the flame retardant and PCM separate, which is detrimental to long-term use. This invention, however, uses a chemical grafting method to attach flame-retardant groups to the ends of PEG, making flame retardancy an intrinsic property. The principle lies in the high chemical reactivity of the hydroxyl groups at the ends of PEG. Through chemical reactions between these functional groups, flame-retardant groups are grafted to the ends of PEG, achieving precise molecular modification of the PEG.

[0023] Compared to traditional mixing methods, chemical grafting gives PEG intrinsic flame retardant properties, fundamentally avoiding the problem of flame retardant and phase change material separating during the continuous melting and solidification process. This gives it both high-efficiency flame retardant performance and excellent long-term stability, while also ensuring the long-term stability of phase change performance.

[0024] (3) Significantly improves flame retardant efficiency This invention simultaneously introduces phosphorus-containing and nitrogen-containing groups to form a phosphorus-nitrogen synergistic flame-retardant system. The polyphosphates and phosphoric acid produced by the pyrolysis of the phosphorus-containing groups promote char formation of the substrate, while the non-flammable gases released by the pyrolysis of the nitrogen-containing groups promote char expansion. The resulting PEG-based flame-retardant phase change material possesses both phosphorus-containing and nitrogen-containing flame-retardant groups, and the expanded char layer formed after combustion exhibits excellent flame-retardant properties. Compared to modification with a single flame-retardant group, the flame-retardant efficiency is significantly improved.

[0025] (4) Retain the phase change characteristics of polyethylene glycol to achieve synergistic optimization of flame retardancy and energy storage. This invention employs a molecular design with symmetrical grafting at both ends, which maximizes the preservation of the structural integrity and crystallinity of the PEG backbone while introducing flame-retardant groups. During preparation, only the hydroxyl groups at both ends of the PEG molecule are chemically modified, while the long-chain polyoxyethylene backbone in the middle remains intact. Testing has shown that this material still exhibits reversible crystallization-melting phase transition behavior, resolving the technical contradiction in existing technologies where flame-retardant modification often leads to a significant decrease in phase transition performance.

[0026] (5) Suitable phase transition temperature The phase transition temperature of the polyethylene glycol flame-retardant phase change material provided by this invention is between 33 and 51°C, which meets the working requirements of buildings, automobiles, solar energy, and batteries. Attached Figure Description

[0027] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 The reaction route for the preparation method of polyethylene glycol-based flame-retardant phase change material provided by the present invention; Figure 2 The FTIR detection spectra of the relevant samples in Example 1 of this invention; Figure 3 The relevant samples of Example 1 in this invention 1 H NMR detection spectrum; Figure 4 The relevant samples of Example 1 in this invention 31 p NMR detection spectrum; Figure 5 The results are DSC analysis of the relevant samples in Example 1 of this invention. Figure 6 The thermogravimetric analysis (TGA) curves of the relevant samples in Example 1 of this invention are shown in (a) and (b) respectively. Figure 7 These are morphological images of the samples after thermogravimetric analysis in Example 1 of this invention. (a), (b), and (c) are morphological images of the samples after analysis of PEG2000, DPEG, and DAPEG, respectively, with a scale bar of 1 mm; (d), (e), and (f) are morphological images of the samples after analysis of PEG2000, DPEG, and DAPEG, respectively, with a scale bar of 100 μm. Figure 8 The thermogravimetric analysis results of DAPEG prepared in Example 1 of this invention are shown in (a) and (b) as P element surface distribution diagrams, and (c) as N element surface distribution diagram. Figure 9The Raman spectra of the relevant samples in Example 1 of this invention are shown. (a) corresponds to PEG2000, (b) corresponds to DPEG, and (c) corresponds to DAPEG. Figure 10 These are the microcalorimetric spectra of the relevant samples from Example 1 and Comparative Example 1 in this invention. Detailed Implementation

[0028] The present invention will be described in detail below with reference to embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several adjustments and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0029] To facilitate understanding, the abbreviations or nouns mentioned below will be explained first: DOPO: 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide; PEG: Polyethylene glycol; DMSO: Dimethyl sulfoxide; TFA: Trifluoroacetic acid; DCC: N'N-dicyclohexylcarbodiimide; DCM: Dichloromethane; DCU: N,N'-dicyclohexylurea; It should be noted that all the reagents involved in this invention are of analytical grade.

[0030] This invention provides a method for preparing a phosphorus-nitrogen synergistic polyethylene glycol (PEG) intrinsic flame-retardant phase change material. Using PEG as a matrix, a three-step chemical reaction is employed to covalently graft phosphorus-containing flame-retardant groups (DOPO) and nitrogen-containing flame-retardant aromatic primary amines onto the ends of the PEG molecular chains, making flame retardancy an intrinsic property of the material. The specific steps are as follows: S1, Polyethylene glycol oxidative modification The terminal hydroxyl groups of PEG are oxidized to aldehyde groups by the Pfitzner-Moffatt oxidation reaction to obtain aldehyde-terminated polyethylene glycol (OHC-PEG-CHO).

[0031] In some preferred embodiments, PEG is one or more of PEG2000, PEG4000, PEG6000, and PEG8000. If the molecular weight is too small, the hindering effect of the flame-retardant groups will lead to the loss of its phase transition ability; if the molecular weight is too large, the content of flame-retardant components will be low, and the flame-retardant effect will be insignificant.

[0032] In some embodiments, PEG2000 is selected as the PEG, and step S1 includes the following steps: S11. Dissolve 1~1.2 mmol of PEG2000 in 10~15 mL of anhydrous DMSO, add 50~60 μL of TFA, stir well, transfer the mixed solution into a three-necked flask with a magnetic stirrer, and stir at 140~160 r / min until well mixed. S12. Dissolve 9-11 mmol of DCC in anhydrous DMSO and slowly add it dropwise into a three-necked flask at 0-10°C, while continuing to stir and maintain the reaction for 12-14 hours. S13. Pour the reaction solution into 50-60 mL of anhydrous DCM, filter to remove DCU byproducts, concentrate the filtrate and pour it into 50-60 mL of cold ethanol at 0-2℃, filter to collect the precipitate, wash with cold ethanol to obtain aldehyde-polyethylene glycol-aldehyde (OHC-PEG-CHO), chemical formula: OHC-CH2-O-(CH2CH2O). n-2 -CH2-CHO, the structural formula is as follows: n = 46~180.

[0033] In the oxidation reaction, the terminal hydroxyl group of PEG is oxidized to an aldehyde group. A mixed solution of DCC and dimethyl sulfoxide (DMSO) is the oxidant for the reaction, and TFA is used as a protic acid auxiliary.

[0034] S2, Introduction of nitrogen-containing groups This step involves the introduction of nitrogen-containing flame-retardant groups. Through the condensation reaction of aldehyde and amino groups, aromatic primary amines are grafted to the ends of the PEG molecular chain to generate intermediate APEG containing a Schiff base structure.

[0035] As an example, aniline is selected as the aromatic primary amine. In actual implementation, one or more of p-toluidine, o-toluidine, and phenylenediamine can also be selected as the aromatic primary amine.

[0036] Step S2 includes the following steps: Dissolve OHC-PEG-CHO in 20-25 ml of anhydrous ethanol, add 2.5-3 mmol of aniline, and transfer the mixed solution into a three-necked flask equipped with a magnetic stirrer and reflux condenser. Place the three-necked flask in an oil bath and heat it to 45-55°C. Stir at 140-160 rpm for 6-8 hours.

[0037] The reaction solution was poured into 50-60 mL of cold ethanol at 0-2°C. The precipitate was collected by filtration and washed with cold ethanol to obtain a light yellow solid product, named APEG, with the following structural formula: .

[0038] S3, introduction of phosphorus-containing groups This step involves the introduction of phosphorus-containing flame-retardant groups. DOPO is grafted to the end of the PEG molecular chain via a nucleophilic addition reaction between the active pH bond on DOPO and the C=N double bond in the Schiff base structure, yielding the final product DAPEG. The steps are as follows: S31. Dissolve APEG in 20-25 mL of anhydrous ethanol, add 2.5-3 mmol of DOPO, and transfer the mixed solution into a three-necked flask equipped with magnetic stirring and reflux condenser. S32. Place the three-necked flask in an oil bath and heat it to 75~85℃. Stir continuously at 140~160r / min for 12~14h. S33. Pour the reaction solution into 50-60 mL of cold ethanol, filter to collect the precipitate, wash with cold ethanol to obtain a light yellow solid product, named DAPEG, with the following structural formula: .

[0039] The preparation method described above will be specifically introduced below through several examples and comparative examples.

[0040] Example 1 This embodiment provides a method for preparing a polyethylene glycol-based flame-retardant phase change material using PEG2000 and aniline as examples. The reaction route is as follows: Figure 1 As shown in (a), the steps are as follows: Dissolve 2g of PEG2000 (approximately 1mmol) in 10ml of anhydrous DMSO, add 50μL of TFA, stir until homogeneous, transfer the mixture to a 50ml three-necked flask equipped with a magnetic stirrer, and stir continuously at 150r / min for 12h.

[0041] Dissolve 2.1 g of DCC (approximately 10 mmol) in 10 ml of anhydrous DMSO and slowly add it dropwise to a three-necked flask at below 10°C, continuing to stir and maintain the reaction for 12 hours. Pour the reaction solution into 50 ml of anhydrous DCM, filter to remove the DCC byproduct, concentrate the filtrate and pour it into 50 ml of cold ethanol at 0°C, filter to collect the precipitate, wash three times with cold ethanol to obtain OHC-PEG-CHO.

[0042] The OHC-PEG-CHO obtained in the previous step was dissolved in 20 ml of ethanol, and 0.233 g of aniline (2.5 mmol) was added. The mixture was then transferred to a 50 ml three-necked flask equipped with a magnetic stirrer and reflux condenser. The flask was then placed in an oil bath and heated to 50 °C. After stirring continuously at 150 rpm for 6 h, the reaction mixture was poured into 50 ml of cold ethanol. The precipitate was collected by filtration and washed three times with cold ethanol to obtain a light yellow solid product, which was named APEG.

[0043] The APEG obtained in the previous step was dissolved in 20 ml of ethanol, and 0.54 g of DOPO (2.5 mmol) was added. The mixture was then transferred to a 50 ml three-necked flask equipped with a magnetic stirrer and reflux condenser. The flask was then placed in an oil bath and heated to 80 °C. After stirring continuously at 150 rpm for 12 h, the reaction mixture was poured into 50 ml of cold ethanol. The precipitate was collected by filtration, washed three times with cold ethanol, and dried under vacuum at 80 °C overnight to obtain a light yellow solid product, which was named DAPEG.

[0044] Comparative Example 1 This comparative example provides a method for preparing a flame-retardant phase change material with only a single phosphorus-containing flame-retardant group as the basic characteristic of polyethylene glycol using PEG2000 and DOPO. The reaction route is as follows: Figure 1 As shown in (b), the steps are as follows: First, 2 g of polyethylene glycol 2000 (PEG2000, 1 mmol) was dissolved in 10 ml of anhydrous dimethyl sulfoxide (DMSO), and 50 μL of trifluoroacetic acid (TFA) was added. The mixture was stirred until homogeneous, and then transferred to a 50 ml three-necked flask equipped with a magnetic stirrer. The mixture was stirred continuously at 150 rpm for 12 h. Subsequently, 2.1 g of N'N-dicyclohexylcarbodiimide (DCC) was dissolved in 10 ml of anhydrous DMSO, and the solution was stirred for 10 h. o The solution was slowly added dropwise to a three-necked flask at a temperature below 1°C, and the mixture was stirred continuously to maintain the reaction for 12 hours. The reaction solution was then poured into 50 ml of anhydrous dichloromethane (DCM), filtered, and the filtrate was concentrated and poured into 50 ml of cold ethanol. The precipitate was collected by filtration and washed three times with cold ethanol to obtain aldehyde-modified polyethylene glycol (OHC-PEG-CHO).

[0045] The OHC-PEG-CHO obtained in the previous step was dissolved in 20 mL of dichloromethane, and 0.54 g of DOPO (2.5 mmol) was added. The mixture was then transferred to a 50 mL three-necked flask equipped with a magnetic stirrer and reflux condenser. The flask was then placed in a water bath and heated to 35 °C, with stirring continuously for 48 h. The reaction solution was concentrated and poured into 50 mL of cold ethanol. The precipitate was collected by filtration, washed three times with cold ethanol, and dried under vacuum at 80 °C overnight to obtain a pale yellow solid product, named DPEG.

[0046] In this comparative example, the product DPEG was obtained through a nucleophilic addition reaction between an aldehyde group and DOPO, and its structural formula is as follows:

[0047] Detection and Analysis I. Infrared Spectroscopy Detection The DAPEG prepared in Example 1, the DPEG prepared in Comparative Example 1, PEG2000, and DOPO were compared and analyzed by FTIR detection. Figure 2As shown, DOPO is at 755cm -1 The absorption peak at that point corresponds to the PO-Ph vibration (dashed box in the figure). This peak is not present in PEG, but appears in DPEG and DAPEG, indicating that DOPO has been successfully introduced.

[0048] two, 1 H NMR detection The DAPEG prepared in Example 1, the DPEG prepared in Comparative Example 1, PEG2000, DOPO, and APEG were compared and analyzed by proton nuclear magnetic resonance spectroscopy. Figure 3 As shown, the signal peak of DOPO in the δ 7.31–8.05 ppm range is attributed to hydrogen on the benzene ring, while the signal peak in the δ 8.79 ppm range is attributed to hydrogen on the PH bond. The signal peaks in the δ 7.31–8.05 ppm range are still present in DPEG and DAPEG, but the signal peak in the δ 8.79 ppm range has disappeared, indicating that DOPO was successfully introduced through a reaction with the corresponding group via an active PH bond. Furthermore, a new aromatic hydrogen signal (δ = 6.91–7.53 ppm) was observed in DAPEG and its intermediate APEG, attributed to a proton on the benzene ring of the aniline group, indicating the successful introduction of the aniline structure.

[0049] three, 31 P NMR detection The DAPEG prepared in Example 1, the DPEG prepared in Comparative Example 1, and DOPO were compared and analyzed using phosphorus-31 nuclear magnetic resonance spectroscopy. Figure 4 As shown, the DOPO signal peak appears at δ 14.26 ppm. DPEG and DAPEG also show signal peaks, but with significant changes in chemical shift, indicating that DOPO is grafted onto the terminal carbon atom of PEG via a reaction. Furthermore, DPEG exhibits a doublet at δ = 33.36 ppm and δ = 33.81 ppm, while DAPEG shows a doublet at δ 33.35 ppm and δ 35.13 ppm. This is due to the influence of the chiral carbon atom bonded to the P atom, indicating that DOPO was successfully grafted onto the terminal carbon atom of PEG.

[0050] IV. DSC Testing The DAPEG prepared in Example 1, the DPEG prepared in Comparative Example 1, and PEG2000 were compared and analyzed by DSC detection. Figure 5As shown, compared to PEG2000, the melting points of DPEG and DAPEG decreased from 54.4℃ (PEG2000) to 39.24℃ (DPEG) and 39.59℃ (DAPEG), respectively, and their melting enthalpies decreased from 188.2 J / g (PEG2000) to 90.71 J / g (DPEG) and 73.21 J / g (DAPEG), respectively. This is because the incorporation of flame-retardant groups hinders the free movement and regular arrangement of PEG chain segments, causing a significant decrease in the melting points of both DPEG and DAPEG, weakening the phase transition behavior. Furthermore, DAPEG, due to the presence of additional aniline, exhibits a stronger hindering effect, resulting in a more significant decrease in phase transition enthalpy. However, the product DAPEG still exhibits a significant endothermic melting response, indicating that DAPEG retains solid-liquid phase transition characteristics.

[0051] V. Thermogravimetric Analysis Thermogravimetric analysis (TGA) was performed on the DAPEG prepared in Example 1, the DPEG prepared in Comparative Example 1, and PEG2000. The TG and DTG curves under a nitrogen atmosphere are shown below. Figure 6 As shown, PEG2000, DPEG, and DAPEG all exhibit a single thermogravimetric stage, attributed to the pyrolysis of long chain segments. The initial decomposition temperature of PEG (T...) 5% The maximum decomposition temperature (T) is 368.59℃. max The thermal decomposition temperature is 398.35℃. Simultaneously, its thermal decomposition rate is relatively fast, with a maximum thermal decomposition rate R0. max At 5.73% / ℃, the char rate dropped to only 0.51% at 700℃, indicating almost complete decomposition, further confirming the inherent difficulty of PEG2000 in forming char. Compared to PEG2000, the initial decomposition temperatures of DPEG and DAPEG decreased to 313.51℃ (DPEG) and 327.8℃ (DAPEG), respectively, because the DOPO group decomposes prematurely to release flame-retardant components, thus achieving a flame-retardant effect. The maximum decomposition temperature of DPEG increased to 402.28℃, as the introduction of the benzene ring structure improves its thermal stability. The maximum decomposition temperature of DAPEG increased even more significantly, reaching 407.62℃, due to the additional introduction of aniline. Furthermore, the char rate of DPEG and DAPEG showed a significant improvement because the phosphoric acid or polyphosphoric acid formed by the pyrolysis of the flame-retardant groups effectively enhances the char-forming ability of PEG, promoting char layer formation and thus insulating against heat and oxygen, achieving a flame-retardant effect. This is reflected in the maximum thermal decomposition rate R of DPEG and DAPEG in the DTG curve. max A significant decrease can confirm this.

[0052] VI. Residual Carbon Testing The DAPEG prepared in Example 1, and the DPEG and PEG2000 prepared in Comparative Example 1 were subjected to SEM morphology detection and EDS composition analysis, respectively. Residual carbon images are shown below.Figure 7 and Figure 8 As shown. Figure 7 (a) It shows that after pyrolysis of PEG2000, only a small amount of carbon residue remained at the bottom of the crucible, with virtually no residue. Figure 7 (b) is DPEG. Figure 7 (c) shows DAPEG, with a distinct carbon layer at the bottom of the crucible. SEM observation of the carbon layer morphology revealed that... Figure 7 (d) The PEG residue is irregularly loose and flocculent, while Figure 7 In (e) and (f), the DPEG and DAPEG char layers exhibit a loose honeycomb structure, which effectively provides heat insulation, oxygen barrier, and inhibits the release of flammable gaseous products, thus endowing them with excellent flame retardant properties. Furthermore, the DAPEG char layer shows better surface continuity than the DPEG char layer, demonstrating that the synergistic effect of phosphorus and nitrogen results in better flame retardant performance. In addition, Figure 8 The analysis revealed the distribution of phosphorus and nitrogen elements in the materials, showing a uniform and abundant distribution of phosphorus in both DPEG and DAPEG char layers, further demonstrating the role of phosphorus-containing groups in promoting char formation. Meanwhile, the phosphorus distribution in the DAPEG char layer was relatively sparser, because the non-flammable gases released during the thermal decomposition of nitrogen-containing groups in DAPEG further promote char layer expansion. The uniform nitrogen distribution observed in DAPEG also demonstrates the synergistic effect of phosphorus and nitrogen elements during the expansion char layer formation process.

[0053] VII. Raman Detection The DAPEG prepared in Example 1, the DPEG prepared in Comparative Example 1, and PEG2000 were subjected to Raman spectroscopy, and the spectra are shown below. Figure 9 As shown, for PEG2000, DPEG, and DAPEG, at 1358 cm⁻¹ -1 and 1602 cm -1 Two distinct peaks appear at each location, corresponding to the disordered (D) and ordered (G) structures of the residual char, respectively. The ratio of their integrated areas (I) D / I G () can effectively represent the degree of graphitization of residual carbon, where I D / I G A lower ratio indicates a higher degree of graphitization in the char residue, meaning higher resistance to thermal oxidation and strength, and better flame retardant properties. Compared to the I ratio of PEG2000 char residue... D / I G The value is 3.70, and the I of the DPEG and DAPEG carbon layers is... D / I G All showed a significant reduction, indicating that its residual char has a high degree of graphitization, which can bring better flame retardant effect. The I of the DAPEG char layer... D / I GThe value was 3.01, lower than DPEG's 3.14, which reflects the better flame retardant effect brought about by the synergistic effect of phosphorus and nitrogen, consistent with the above conclusion.

[0054] 8. Micro Calorimetry (MCC) Microcalorimetry (MCC) is an effective method for evaluating the flame retardant properties of polymers, often used to analyze the heat release behavior of materials during combustion. Microcalorimetry was performed on the DAPEG prepared in Example 1, and the DPEG and PEG2000 prepared in Comparative Example 1, respectively. The spectra are shown below. Figure 10 As shown, compared with PEG, the peak heat release rate (pHRR) of DPEG and DAPEG is significantly reduced, indicating that the introduction of flame-retardant groups brings good flame-retardant effects. Among them, the decrease in peak heat release rate of DAPEG is more significant than that of DPEG, from 730.8 w / g to 593.2 w / g (DPEG is 609.3 w / g), a decrease of 18.8%. This is the result of the synergistic effect of phosphorus and nitrogen flame-retardant groups, which is consistent with the results of char layer analysis.

[0055] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing an intrinsically flame-retardant phase change material, characterized in that, Includes the following steps: Aromatic primary amines are grafted to the ends of the dialdehyde PEG molecular chains via the condensation reaction of aldehyde and amino groups to generate intermediates containing Schiff base structures. DOPO is grafted onto the carbon atom sites of the C=N double bond of the intermediate via a nucleophilic addition reaction between the C=N double bond and the PH bond to obtain the polyethylene glycol-based flame-retardant phase change material.

2. The method according to claim 1, characterized in that, The molecular formula of the dialdehyde PEG is OHC-CH2-O-(CH2CH2O). n-2 -CH2-CHO, where n represents an integer from 46 to 180.

3. The method according to claim 1, characterized in that, The polyethylene glycol is one or more of PEG2000, PEG4000, PEG6000, and PEG8000.

4. The method according to claim 2 or 3, characterized in that, The preparation method of the dialdehyde PEG is as follows: Polyethylene glycol was dissolved in anhydrous DMSO, TFA catalyst was added, and the mixture was stirred until homogeneous to obtain the first reaction solution. At 0~10℃, an anhydrous DMSO solution containing dissolved DCC is added dropwise to the first reaction solution, and the reaction is continued to be stirred until it is complete, to obtain the second reaction solution; The second reaction solution was diluted and filtered. The filtrate was concentrated and then precipitated by adding an alcohol solvent. The precipitate was collected, washed, and the dialdehyde PEG was obtained.

5. The method according to claim 1, characterized in that, The intermediate is prepared by dissolving the dialdehyde PEG in anhydrous ethanol, adding aniline, and performing a first heat treatment at 45-55°C for 6-8 hours. During the second heat treatment, the mixture is stirred synchronously at a speed of 140-160 r / min.

6. The method according to claim 1, characterized in that, The intermediate was dissolved in anhydrous ethanol, DOPO was added, and a second heat treatment was performed at 75-85°C for 12-14 hours, while the mixture was stirred synchronously at a speed of 140-160 r / min.

7. The method according to claim 1, characterized in that, The aromatic primary amine is one or more of aniline, p-toluidine, o-toluidine, and phenylenediamine.

8. The intrinsically flame-retardant phase change material prepared by the method according to any one of claims 1 to 7, characterized in that, The structural formula is: The molecular backbone is a long polyoxyethylene chain.

9. The material according to claim 8, characterized in that, The phase transition temperature of the material is 33~51℃.

10. The application of the material according to claim 8 or 9 in construction, automobiles, solar energy or batteries.

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