Preparation method of in-situ polymerized high-temperature-resistant polyimide composite wave-absorbing foam
By performing surface functionalization treatment on nanofillers and forming chemical bonds between polyimide matrices through in-situ polymerization, the problems of nanofiller agglomeration and poor interfacial connectivity were solved, and the stability and performance of polymer foam materials under high temperature and strong radiation environments were improved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-02-26
- Publication Date
- 2026-04-21
AI Technical Summary
Existing polymer foam materials suffer from nanofiller agglomeration and poor interfacial connectivity under high temperature and strong radiation environments, resulting in unstable and unreliable performance.
By performing surface functionalization on the nanofillers, grafting active functional groups, and forming chemical bonds between the polyimide matrix through in-situ polymerization, the dispersibility and interfacial bonding strength of the nanofillers are improved.
Uniform dispersion and stable interfacial bonding of nanofillers in polyimide matrix were achieved, improving the electromagnetic properties and long-term reliability of the material.
Smart Images
Figure CN121895587A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of polymer foam composite materials technology, and more specifically, to a high-temperature resistant polyimide foam composite microwave absorbing material prepared by in-situ polymerization and its preparation method. Background Technology
[0002] With the rapid development of high-tech industries such as aerospace, microelectronics, and defense, the market has an urgent need for lightweight, high-performance electromagnetic wave absorbing materials that can maintain stable operation under harsh conditions such as high temperature and strong radiation. Against this backdrop, polymer foams with porous structures have become a highly promising technological approach due to their low density, high specific strength, and properties that improve impedance matching. However, currently commercialized traditional foam materials such as polyurethane (PU) or polymethacrylamide (PMI) have inherent and unavoidable drawbacks: PU foam has severely insufficient thermal stability and produces toxic gases during combustion; while PMI foam has improved temperature resistance, its inherent flammability necessitates the use of flame retardants, which often comes at the cost of compromised overall mechanical and heat resistance properties, limiting its application in high-end fields.
[0003] In contrast, aromatic polyimide (PI) foam exhibits significant advantages. Its wide operating temperature range of -250°C to 500°C, excellent mechanical properties, and inherent safety characteristics requiring no additional flame retardants make it an ideal matrix choice for preparing microwave absorbing materials in extreme environments. However, pure polyimide has a low intrinsic dielectric constant, requiring composite formation with electromagnetic loss media such as graphene and carbon nanotubes to achieve efficient microwave absorption. Current technologies for preparing such composite materials generally face two fundamental obstacles: First, the spontaneous aggregation tendency of nanofillers due to extremely strong intermolecular forces is the primary challenge in achieving homogeneous dispersion, directly leading to fluctuations and unreliability in the final product's performance. Second, and more critically, the poor interfacial compatibility between the microwave absorbing filler and the polyimide matrix results in insufficient interfacial adhesion strength. This weak interface, lacking effective chemical bonding, not only fails to effectively transfer stress, easily becoming a source of mechanical damage, but also hinders the construction of a continuous and stable conductive loss network, thus limiting the improvement of the material's electromagnetic properties and long-term reliability. Therefore, merely improving dispersion while neglecting the strengthening of interfacial bonding has become a limiting factor in current development, and there is an urgent need to develop a new preparation strategy that can synergistically solve the problems of dispersion and interface. Summary of the Invention
[0004] To address the problems of nanofiller agglomeration and interfacial bonding in existing technologies, this invention provides a method for preparing high-temperature resistant polyimide composite microwave absorbing foam by in-situ polymerization.
[0005] The present invention adopts the following technical solution:
[0006] A method for preparing in-situ polymerized high-temperature resistant polyimide composite microwave absorbing foam:
[0007] Step 1: Dissolve the polyimide dianhydride monomer in a polar solvent, add a catalyst, and carry out an esterification reaction under reflux heating to obtain a homogeneous and transparent esterified dianhydride monomer solution, which provides conditions for subsequent homogeneous polymerization reaction.
[0008] Furthermore, the polyimide dianhydride monomer used is 3,3',4,4'-benzophenone tetracarboxylic dianhydride or pyromellitic dianhydride; the catalyst is 2-methylimidazole; and the polar solvent is a mixture of methanol and tetrahydrofuran in a volume ratio of 1:1.5 to 1:3.
[0009] Furthermore, the reflux temperature was 70 °C for 2 h.
[0010] Step 2: The microwave absorber is surface functionalized with a silane coupling agent to graft active functional groups that can participate in subsequent polymerization reactions onto its surface, thus obtaining a modified microwave absorber.
[0011] Furthermore, the microwave absorbing agent used is one or more combinations of multi-walled carbon nanotubes, carboxylated multi-walled carbon nanotubes, and graphene oxide; the silane coupling agent used is KH-550, KH-560, or KH-570, all of which contain functional groups such as amino or epoxy groups that can react with polyimide monomers in their molecular structure.
[0012] Step 3: Add the polyimide diamine monomer to the esterified dianhydride monomer solution obtained in Step 1, and then immediately add the modified microwave absorber obtained in Step 2 to allow for a complete reaction. During this process, the active functional groups on the surface of the modified microwave absorber undergo a copolymerization reaction with the polyimide monomer, anchoring the microwave absorber to the polymer molecular chain through the formation of chemical bonds, thereby obtaining a chemically bonded polyester ammonium salt precursor solution.
[0013] Furthermore, the polyimide diamine monomer used is 4,4'-diaminodiphenyl ether or p-phenylenediamine, and the reaction time is 2 h.
[0014] Step 4: Add a surfactant to the precursor solution obtained in step 3 to regulate the subsequent foaming pore structure. After stirring thoroughly, remove part of the solvent by vacuum drying to obtain a homogeneous precursor composite resin with a predetermined solvent content.
[0015] Furthermore, the surfactant used is DC-193 silicone oil or sodium dodecyl sulfate; the vacuum degree of vacuum drying is -0.6~0.8 Bar, the drying temperature is 60~80 ℃, the drying time is 2~3 h, and the final solvent content of the resulting precursor composite resin is 11~15%.
[0016] Step 5: Grind and sieve the blocky precursor composite resin obtained in Step 4 to obtain a precursor composite powder with a specific particle size range and good flowability.
[0017] Furthermore, the precursor powder was sieved through a standard sieve of 60-160 mesh, and the resulting powder had a particle size of 100-300 μm.
[0018] Step 6: Place the precursor composite powder obtained in Step 5 into a mold for thermal foaming. During this process, the precursor powder melts, and the residual solvent and small alcohol molecules generated by the esterification reaction are heated and vaporized to form a cellular structure, thus obtaining a preliminary precursor composite foam.
[0019] Furthermore, the temperature for thermal foaming is 130~150 ℃, and the foaming time is 60~90 min.
[0020] Step 7: Perform multi-stage programmed temperature curing on the precursor composite foam obtained in Step 6. This process aims to complete the imidization reaction of the polymer, further crosslink it and remove all residual volatiles, and finally form a high-temperature resistant rigid polyimide composite microwave absorbing foam with a stable three-dimensional network structure.
[0021] Furthermore, the curing temperature program is as follows: hold at 180 ℃ for 1~2 h, hold at 240 ℃ for 0.5~1 h, and hold at 300 ℃ for 0.5~1 h; the heating rate is 5~10 ℃ / min.
[0022] In summary, this invention addresses the agglomeration problem of nanofillers and their interfacial connectivity with the polyimide matrix. By modifying the surface of the nanofillers and grafting functional groups onto them, a chemical bond is formed between the nanofillers and the polyimide matrix through in-situ polymerization. This effectively improves the dispersibility of the nanofillers and the interfacial bonding strength with the polyimide matrix. It is applicable to fields such as aerospace. Attached Figure Description
[0023] Figure 1 The Fourier transform infrared spectrum of the polyimide composite microwave absorbing foam obtained in Example 1;
[0024] Figure 2 The image shows the XRD pattern of the polyimide composite microwave absorbing foam obtained in Example 1.
[0025] Figure 3 Here is a SEM image of the polyimide composite microwave absorbing foam obtained in Example 1;
[0026] Figure 4 The image shows the DSC diagram of the polyimide composite microwave absorbing foam obtained in Example 1.
[0027] Figure 5 This is a flowchart of Example 1. Detailed Implementation
[0028] The present invention can also be implemented or applied through various differentiated technical solutions, as illustrated in the following examples and accompanying drawings. The technical details contained in this specification can be modified or adapted to different technical perspectives and application requirements without departing from the technical concept of the present invention.
[0029] Example 1
[0030] Step 1: In a three-necked flask equipped with a reflux condenser, add 32.22 g (0.1 mol) of 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), 0.1 g of 2-methylimidazole as a catalyst, and a mixed solvent consisting of 14 mL of methanol and 20 mL of tetrahydrofuran. Heat the mixture at 70 °C with stirring, and reflux for 2 hours to obtain a homogeneous and transparent esterified dianhydride monomer solution.
[0031] Step 2: Weigh 1 g of multi-walled carbon nanotubes (MWCNTs) and add them to 200 mL of anhydrous ethanol. Disperse the mixture ultrasonically for 30 min to form a uniform suspension. Dissolve 2 g of KH-550 silane coupling agent in 20 mL of an ethanol-water mixture (95:5 volume ratio) and stir for 30 min to ensure complete hydrolysis. Slowly add the hydrolyzed KH-550 solution dropwise to the ethanol suspension of MWCNTs. Heat at 70 °C and stir continuously for 6 h. After multiple centrifugation and washing cycles, the product is vacuum dried at 80 °C for 12 h to obtain KH-550 modified multi-walled carbon nanotube (MWCNT-KH550) powder.
[0032] Step 3: Add 20.02 g (0.1 mol) of 4,4'-diaminodiphenyl ether (ODA) to the esterified dianhydride monomer solution obtained in Step 1, and then immediately add 0.5 g of the KH-550 modified multi-walled carbon nanotube powder described in Step 2. Continue to react at 70 °C for 2 h to obtain a polyester ammonium salt precursor solution composited with MWCNT-KH550.
[0033] Step 4: Add 0.4 g of DC-193 silicone oil as a surfactant to the polyester ammonium salt precursor solution obtained in Step 3, and stir for 1 h to disperse it evenly. Place the product in a vacuum drying oven and dry it for 2 h under a vacuum of -0.6 Bar and a temperature of 80℃ to obtain a blocky precursor composite resin with a final solvent content of approximately 13%.
[0034] Step 5: Grind the precursor composite resin obtained in Step 4 using a mortar and pestle, and then sieve it through a 60-mesh standard sieve to obtain a precursor composite powder with a particle size of approximately 300 μm.
[0035] Step 6: Accurately weigh 10 g of precursor composite powder and evenly spread it in a stainless steel mold. Place the mold in a 130℃ forced-air oven and foam for 1 hour to obtain precursor composite foam filling the mold cavity.
[0036] Step 7: Place the precursor composite foam obtained in Step 6 (no demolding required) in a muffle furnace and perform thermosetting according to the following procedure: heat from room temperature to 180℃ at a rate of 5℃ / min and hold for 1.5 h; then heat to 240℃ at a rate of 5℃ / min and hold for 1 h; finally heat to 300℃ at a rate of 5℃ / min and hold for 1 h. After the procedure is completed, allow it to cool naturally to room temperature in the furnace before removing it to obtain the final product.
[0037] Example 2
[0038] Step 1: In a three-necked flask equipped with a reflux condenser, add 21.82 g (0.1 mol) of pyromellitic dianhydride (PMDA), 0.1 g of 2-methylimidazole as a catalyst, and a mixed solvent consisting of 14 mL of methanol and 30 mL of tetrahydrofuran. Heat the mixture at 70 °C with stirring, and reflux for 2 hours to obtain a homogeneous and transparent esterified dianhydride monomer solution.
[0039] Step 2: Weigh 1 g of graphene oxide (GO) and add it to 200 mL of anhydrous ethanol. Disperse the mixture ultrasonically for 30 min to form a uniform suspension. Dissolve 2 g of KH-550 silane coupling agent in 20 mL of a 95:5 ethanol-water mixture and stir for 30 min to ensure complete hydrolysis. Slowly add the hydrolyzed KH-550 solution dropwise to the ethanol suspension of graphene oxide. Heat at 70 °C and stir continuously for 6 h. After multiple centrifugations and washings, the product is vacuum dried at 80 °C for 12 h to obtain KH-550 modified graphene oxide (GO-KH550) powder.
[0040] Step 3: Add 20.02 g (0.1 mol) of 4,4'-diaminodiphenyl ether (ODA) to the esterified dianhydride monomer solution obtained in Step 1, and then immediately add 0.5 g of KH-550 modified graphene oxide powder described in Step 2. Continue to react at 70 °C for 2 h to obtain a polyester ammonium salt precursor solution composited with GO-KH550.
[0041] Step 4: Add 0.1 g of sodium dodecyl sulfate as a surfactant to the polyester ammonium salt precursor solution obtained in Step 3, and stir for 1 h to disperse it evenly. Place the product in a vacuum drying oven and dry it for 2 h under a vacuum of -0.6 Bar and a temperature of 60°C to obtain a blocky precursor composite resin with a final solvent content of approximately 15%.
[0042] Step 5: Grind the precursor composite resin obtained in Step 4 using a mortar and pestle, and then sieve it through a 60-mesh standard sieve to obtain a precursor composite powder with a particle size of approximately 300 μm.
[0043] Step 6: Accurately weigh 10 g of precursor composite powder and evenly spread it in a stainless steel mold. Place the mold in a 130℃ forced-air oven and foam for 1 hour to obtain precursor composite foam filling the mold cavity.
[0044] Step 7: Place the precursor composite foam obtained in Step 6 (no demolding required) in a muffle furnace and perform thermosetting according to the following procedure: heat from room temperature to 180℃ at a rate of 5℃ / min and hold for 2 hours; then heat to 240℃ at a rate of 5℃ / min and hold for 0.5 hours; finally heat to 300℃ at a rate of 5℃ / min and hold for 1 hour. After the procedure is completed, allow it to cool naturally to room temperature in the furnace before removing it to obtain the final product.
[0045] Example 3
[0046] Step 1: In a three-necked flask equipped with a reflux condenser, add 32.22 g (0.1 mol) of 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), 0.1 g of 2-methylimidazole as a catalyst, and a mixed solvent consisting of 14 mL of methanol and 20 mL of tetrahydrofuran. Heat the mixture at 70 °C with stirring, and reflux for 2 hours to obtain a homogeneous and transparent esterified dianhydride monomer solution.
[0047] Step 2: Weigh 1 g of graphene oxide (GO) and add it to 200 mL of anhydrous ethanol. Disperse the mixture ultrasonically for 30 min to form a uniform suspension. Dissolve 2 g of KH-560 silane coupling agent in 20 mL of a 95:5 ethanol-water mixture and stir for 30 min to ensure complete hydrolysis. Slowly add the hydrolyzed KH-560 solution dropwise to the ethanol suspension of graphene oxide. Heat at 70 °C and stir continuously for 6 h. After multiple centrifugation and washing cycles, vacuum dry the product at 80 °C for 12 h to obtain KH-560 modified graphene oxide (GO-KH560) powder.
[0048] Step 3: Add 10.81 g (0.1 mol) of p-phenylenediamine (PPD) to the esterified dianhydride monomer solution obtained in Step 1, and then immediately add 0.5 g of KH-560 modified graphene oxide powder described in Step 2. Continue to react at 70 °C for 2 h to obtain a polyester ammonium salt precursor solution composited with GO-KH560.
[0049] Step 4: Add 0.4 g of DC-193 silicone oil as a surfactant to the polyester ammonium salt precursor solution obtained in Step 3, and stir for 1 h to disperse it evenly. Place the product in a vacuum drying oven and dry it for 3 h under a vacuum of -0.6 Bar and a temperature of 80℃ to obtain a blocky precursor composite resin with a final solvent content of approximately 11%.
[0050] Step 5: Grind the precursor composite resin obtained in Step 4 with a mortar and pestle, and sieve it through a 160-mesh standard sieve to obtain a precursor composite powder with a particle size of about 100 μm.
[0051] Step 6: Accurately weigh 10 g of precursor composite powder and evenly spread it in a stainless steel mold. Place the mold in a 130℃ forced-air oven and foam for 1 hour to obtain precursor composite foam filling the mold cavity.
[0052] Step 7: Place the precursor composite foam obtained in Step 6 (no demolding required) in a muffle furnace and perform thermosetting according to the following procedure: heat from room temperature to 180℃ at a rate of 5℃ / min and hold for 1 hour; then heat to 240℃ at a rate of 5℃ / min and hold for 1 hour; finally heat to 300℃ at a rate of 5℃ / min and hold for 0.5 hours. After the procedure is completed, allow it to cool naturally to room temperature in the furnace before removing it to obtain the final in-situ polymerized polyimide composite microwave absorbing foam product.
Claims
1. A method for preparing an in-situ polymerized high-temperature resistant polyimide composite microwave absorbing foam, characterized in that, Includes the following steps: Step 1: Dissolve the polyimide dianhydride monomer in a polar solvent, add a catalyst, and esterify under reflux conditions to obtain an esterified dianhydride monomer solution. Step 2: The microwave absorber is surface functionalized with a silane coupling agent to graft active functional groups that can participate in subsequent polymerization reactions onto its surface, thus obtaining a modified microwave absorber. Step 3: Add the polyimide diamine monomer and the modified microwave absorber obtained in Step 2 to the esterified dianhydride monomer solution obtained in Step 1, and carry out an in-situ polymerization reaction. This allows the modified microwave absorber to copolymerize with the polyimide monomer through its surface active functional groups, and to be grafted onto the polymer molecular chain in the form of chemical bonds, thus obtaining a polyester ammonium salt precursor solution. Step 4: Add surfactant to the precursor solution obtained in step 3, stir evenly, and then vacuum dry to obtain precursor composite resin. Step 5: Grind and sieve the resin obtained in Step 4 to obtain precursor composite powder. Step 6: The precursor powder obtained in Step 5 is thermally foamed to obtain precursor foam. Step 7: Perform multi-stage programmed temperature rise thermosetting and imidization on the precursor composite foam obtained in step 6 to obtain the high-temperature resistant polyimide composite microwave absorbing foam based on in-situ polymerization.
2. The method for preparing an in-situ polymerized structural polyimide composite microwave absorbing foam as described in claim 1, characterized in that: The polyimide dianhydride monomer in step 1 is 3,3',4,4'-benzophenone tetracarboxylic dianhydride or pyromellitic dianhydride; the polar solvent is a mixture of methanol and tetrahydrofuran (methanol:tetrahydrofuran volume ratio = 1:1.5~1:3); and the catalyst is 2-methylimidazole.
3. The method for preparing an in-situ polymerized structural polyimide composite microwave absorbing foam as described in claim 1, characterized in that: The microwave absorbing agent in step 2 is one or more combinations of multi-walled carbon nanotubes, carboxylated multi-walled carbon nanotubes, or graphene oxide; the silane coupling agent is KH-550, KH-560, or KH-570.
4. The method for preparing an in-situ polymerized structural polyimide composite microwave absorbing foam as described in claim 1, characterized in that: The polyimide diamine monomer mentioned in step 3 is 4,4'-diaminodiphenyl ether or p-phenylenediamine.
5. The method for preparing an in-situ polymerized structural polyimide composite microwave absorbing foam as described in claim 1, characterized in that: The surfactant mentioned in step 4 is DC-193 silicone oil or ammonium dodecyl sulfate, with a content of 0.1~0.5 wt%; the vacuum drying conditions are: vacuum degree -0.6 ~ -0.8 Bar, temperature 60~80 ℃, duration 2~3 h, so that the final solvent content of the obtained precursor composite resin is 11~15%.
6. The method for preparing an in-situ polymerized structural polyimide composite microwave absorbing foam as described in claim 1, characterized in that: In step 5, the ground resin is sieved through a standard sieve of 60-160 mesh to obtain a precursor composite powder with a particle size of 100-300 μm.
7. The method for preparing an in-situ polymerized structural polyimide composite microwave absorbing foam as described in claim 1, characterized in that: The thermal foaming temperature in step 6 is 130~150 ℃, and the foaming time is 60~90 min.
8. The method for preparing an in-situ polymerized structural polyimide composite microwave absorbing foam as described in claim 1, characterized in that: The conditions for thermosetting and imidization in step 7 are as follows: heating at a rate of 5~10 ℃ / min, holding at 180 ℃ for 1~2 h, holding at 240 ℃ for 0.5~1 h, and holding at 300 ℃ for 0.5~1 h.