norbornene-terminated imide crosslinking foaming agents, their preparation methods and applications

Abstract

This invention relates to norbornene-terminated imide crosslinking blowing agents (NE-CBA), their preparation methods, and their application in thermosetting polyimide foaming. Using the aforementioned blowing agent, unsaturated end-terminated norbornene-terminated polyimide oligomers (NE-PIO), maleic anhydride-terminated polyimide oligomers (ME-PIO), and ethynyl-terminated polyimide oligomers (AE-PIO) can undergo high-ratio foaming and multiple crosslinking, reducing the density of the prepared rigid polyimide foam to 50 kg / m³. 3 It has a compressive strength of over 0.8 MPa at 10% strain, a glass transition temperature of over 360℃, a thermal weight loss temperature of over 480℃ at 5% strain, a thermal conductivity as low as 0.030 W / (m·K), and an oxygen index of over 40%. It has excellent comprehensive performance and has broad application prospects in high-tech fields such as aviation, aerospace, and shipbuilding.

Description

Technical Field

[0001] This invention belongs to the field of thermosetting polymer chemical foaming technology, specifically relating to norbornene-terminated imide crosslinking foaming agents, their preparation methods, and their applications in thermosetting polyimide foaming. Background Technology

[0002] Polyimide foams (PIFs) combine the high and low temperature resistance (-250 to 450°C) and high flame retardancy (oxygen index ~40%) of the polyimide matrix with the lightweight (5 to 200 kg / m³) of foam materials. 3 With numerous advantages such as damping and shock absorption, and heat insulation, it has become the lightweight material with the highest heat resistance and flame retardancy among polymer foam materials. It can meet the more stringent requirements of high-tech fields such as aviation, aerospace, navigation, and transportation for heat resistance and flame retardancy of foam materials.

[0003] Polyimide foams are classified into two types: flexible polyimide foams (PISFs) and rigid polyimide foams (PIRFs). Currently, PISFs are mainly prepared using a one-step isocyanate foaming method or a two-step polyamide ester precursor powder foaming method. Because the strength of the foaming solution in the one-step method or the precursor melt in the two-step method is very low, it is difficult to resist the internal pressure of the gas during the foaming process. This prevents the foaming solution or precursor melt from effectively sealing the expanded cells and forming an interconnected open-cell structure through capillary drainage, resulting in polyimide foams prepared by this method being flexible foams. Although the density of PISFs can be as low as 5 kg / m³... 3 Heat resistance (T) g Most of them are in the range of 200-300℃, but have low strength. They are mainly used as heat insulation, sound insulation and noise reduction, shock absorption and energy absorption materials in aviation, aerospace and shipbuilding fields.

[0004] Existing rigid polyimide foams (PIRFs) primarily utilize nadimide-end-capped polyimide oligomer (NE-PIO) powder as raw material, with a molecular weight between 1500 and 5000. At high temperatures, the NE-PIO end groups release cyclopentadiene (CPD) as a blowing agent via a reverse Diels-Alder reaction, while simultaneously undergoing unsaturated end-group self-crosslinking to prepare rigid polyimide foam. The heat resistance (T...) of PIRFs prepared using this method... g While possessing excellent flame retardant properties (approximately 250–350℃) and flame retardant properties (oxygen index ~40%), PIRFs suffer from limitations such as a limited number of NE-PIO end groups, a simple crosslinking network, low crosslinking density, and low foam closed-cell rate, making it difficult to reduce the density to 150 kg / m³. 3Furthermore, its mechanical properties are 30-50% lower than those of industrialized polymethacrylimide (PMI) foam of the same density. However, PMI foam has difficulty in exceeding 190°C in heat resistance and is not flame retardant, which limits its application in high-temperature and high-flame-retardant fields.

[0005] PIRFs (Polymerized Induced Refrigerants) are intended for use as core materials in a new generation of high-heat-resistant, high-flame-retardant, and high-strength sandwich composite materials, exhibiting significant advantages in heat resistance and flame retardancy. However, they suffer from disadvantages in terms of foaming ratio and strength. While the performance of PIRFs can be altered by controlling the molecular weight of NE-PIO, there are two issues. On the one hand, when the molecular weight of NE-PIO is low, although the gas evolution is high and the number of crosslinkable end groups is large, the melt strength is low, making it easy to form an open-cell structure through capillary effects, thus making it difficult to obtain high-strength PIRFs. On the other hand, when the molecular weight of NE-PIO is high, although it is beneficial to improve melt strength and obtain a closed-cell structure, the gas evolution is low, the prepared foam density is high, but the crosslinking density and foam strength are also low. Therefore, new technical solutions must be found to resolve this contradiction.

[0006] US Patent 6235803 discloses a method for preparing rigid closed-cell polyimide foam (PIRF) using a precursor microsphere method. First, residual solvent in the precursor powder is used for pre-foaming to form prepolymer microsphere intermediates. Then, these microsphere intermediates are filled into a mold, pressurized, foamed again, and melt-bonded together to prepare PIRFs. Although this method yields foams with high closed-cell ratio and good uniformity, the adhesion between microspheres is difficult to control. Furthermore, the linear molecular structure of polyimide results in poor mechanical properties of the foam, with a density ranging from 48 to 480 kg / m³. 3 At that time, the compressive strength was only 0.68 to 9.65 MPa, which is only 50 to 70% of that of PMI foam of the same density.

[0007] Chinese patent CN 107540841A discloses a method for preparing rigid closed-cell PIRFs. It uses vinyl or acetylene-terminated polyester ammonium salt (PEAS) powder as a precursor for thermosetting PIRFs. The precursor powder is then placed in a high-temperature, high-pressure autoclave for supercritical CO2 foaming to prepare rigid cross-linked PIRFs with a high foaming ratio and a density range of 40–150 kg / m³. 3 The closed-cell ratio can reach 80-95%. However, this method is highly dependent on equipment, the size of the prepared foam is greatly limited, and the compressive strength is more than 50% lower than that of PMI foam of the same density.

[0008] Chinese patent CN 102964834A discloses a method for preparing thermosetting PIRFs using norbornene anhydride (NA) as a capping agent, α-isomeric biphenyl anhydride (α-BPDA) as the main dianhydride, and aromatic diamine. The PIRF foam prepared by this method has a closed-cell rate of over 80% and a density greater than 100 kg / m³. 3 The foam has a compressive strength exceeding 1 MPa and a heat resistance greater than 320℃. However, due to the limited number of cross-linking sites and insufficient foaming gas, the mechanical strength of the prepared PIRFs is 3 to 4 times lower than that of PMI foam of the same density, and it is difficult to obtain PIRFs with even lower density. Summary of the Invention

[0009] The purpose of this invention is to address the problems of low crosslinking density, low closed-cell rate, low mechanical properties, and low gas generation in traditional norbornene-terminated thermosetting polyimide rigid foams, which cannot achieve high-ratio foaming. This invention provides norbornene-terminated imide crosslinking foaming agents, their preparation methods, and applications.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a norbornene-terminated imide crosslinked blowing agent (NE-CBA), characterized in that: the blowing agent molecule contains 2 to 4 functional norbornene imide end groups, with a molecular weight of 400 to 850, and its molecular structure is as follows:

[0011] Where Ar represents different aromatic diamine structures, Ar1 represents different aromatic triamine structures, and Ar2 represents different aromatic tetraamine structures:

[0012]

[0013] The chemical structure and molecular weight of the norbornene-terminated imide crosslinking foaming agent (NE-CBA) can be changed by altering the structure of the aromatic polyamine.

[0014] Furthermore, the aromatic diamine structure (Ar) in NE-CBA is any one of 4,4'-diaminodiphenyl ether (ODA), 4,4'-diaminodiphenylmethane (MDA), 4,4'-diaminodiphenyl sulfone (DDS), and m-phenylenediamine (m-PDA); the aromatic triamine structure (Ar1) is 1,3,5-triaminobenzene (1,3,5-TAB), melamine (TAP), or 1,3,5-tris(4-aminophenoxy) The aromatic tetraamine structure (Ar2) is any one of 3,3',4,4'-tetraaminodiphenyl ether (TADE), 3,3',4,4'-tetraaminobenzophenone (TABP), 1,2,4,5-phenyltetramine (TAB), and 4-[(3,4-diaminophenyl)methyl]benzene-1,2-diamine (TADM), with the following structural formula:

[0015]

[0016] The preparation method of the norbornene-terminated imide crosslinking foaming agent (NE-CBA) includes the following specific steps:

[0017] Step 1, Preparation of norbornene ethyl ester (NE): The end-capping monomer 5-norbornene-2,3-dicarboxylic anhydride (NA) and a small amount of ring-opening catalyst 2-methylimidazole (2-MI) are added to a polar solvent and a small molecule fatty alcohol mixed solvent, and reacted at a certain temperature and time to obtain an esterification solution of norbornene ethyl ester (NE).

[0018] Step 2, Preparation of amide esterification solution: Aromatic polyamine is slowly added to the esterification solution of norbornene ethyl ester (NE). The amount of aromatic polyamine added is based on the molar ratio of aromatic polyamine to 5-norbornene-2,3-dicarboxylic anhydride (NA) of 1:(2-4). The reaction is continued at 60-90℃ for 60-120 min under inert gas protection. After the reaction is completed, a surfactant is added to the solution to obtain the amide esterification solution.

[0019] Step 3, Preparation of norbornene-terminated imide crosslinking foaming agent (NE-CBA): After solvent removal and imidization treatment of the amide esterification liquid at a certain temperature and time, the norbornene-terminated imide crosslinking foaming agent (NE-CBA) is obtained. After further pulverization, the norbornene-terminated imide crosslinking foaming agent (NE-CBA) powder with a particle size of 20-200 μm is obtained.

[0020] The synthesis reaction formula for NE-CBA, taking diamine as an example, is as follows:

[0021]

[0022] Further, in step 1, the polar solvent is any one of tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, or N-methylpyrrolidone; the small molecule fatty alcohol is any one of methanol, ethanol, or ethylene glycol; the molar ratio of the polar solvent to the small molecule fatty alcohol is (500-1000):1000; and the concentration of 5-norbornene-2,3-dicarboxylic anhydride (NA) in the esterification solution is 1.2-4 g / L.

[0023] In step 2, the aromatic polyamine is any one of aromatic diamine, aromatic triamine, or aromatic tetraamine; the aromatic diamine is added at a molar ratio of 1:2 of aromatic diamine to 5-norbornene-2,3-dicarboxylic anhydride (NA); the aromatic triamine is added at a molar ratio of 1:3 of aromatic triamine to 5-norbornene-2,3-dicarboxylic anhydride (NA); the aromatic tetraamine is added at a molar ratio of 1:4 of aromatic tetraamine to 5-norbornene-2,3-dicarboxylic anhydride (NA); the surfactant is any one of FSO-100, AK8805, or DC193.

[0024] In step 3, the solvent removal and imidization are carried out at a temperature of 120–200°C for 1–4 hours.

[0025] The specific method for preparing rigid polyimide foam (PIRFs) using the aforementioned norbornene-terminated imide crosslinking blowing agent (NE-CBA) is as follows:

[0026] Step 1: Aromatic dianhydride, end-capping agent and ring-opening catalyst are added to a mixed solvent of polar solvent and small molecule fatty alcohol in a certain proportion, and esterification is carried out at a temperature of 60-90℃ for 2-5 hours to obtain an esterified solution of aromatic dianhydride.

[0027] Step 2: Add aromatic diamine and surfactant to the esterification solution of aromatic dianhydride, and react for 2-4 hours to obtain polyester ammonium salt (PEAS) solution.

[0028] Step 3: The polyester ammonium salt (PEAS) solution is dried to obtain precursor powder, and then the precursor powder is imidized at high temperature to obtain polyimide oligomer (PIO) powder.

[0029] Step 4: Add norbornene-terminated imide crosslinking foaming agent (NE-CBA) and polyimide oligomer (PIO) powder to ethanol solvent in proportion and mix. Then remove the solvent by rotary evaporation to obtain foaming powder. Place the foaming powder in a sealed graphite mold and foam in a high-temperature oven at 300-380℃ for 2-5 hours to prepare polyimide rigid foam (PIRFs).

[0030] Further, in step 1, the aromatic dianhydride is one or a mixture of two or more of 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), pyromellitic tetracarboxylic dianhydride (PMDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA), and 2,3,3',4'-biphenyltetracarboxylic dianhydride (α-BPDA); the end-capping agent is one or more of 5-norbornene-2,3-dianhydride (NA), maleic anhydride (MA), and 4-phenylethynylphthalic anhydride (PEPA). A mixture of two or more substances; the ring-opening catalyst is 2-methylimidazole (2-MI); the polar solvent and the small molecule fatty alcohol mixed solvent are at least two selected from methanol, ethanol, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide or N-methylpyrrolidone; the mass ratio of aromatic dianhydride, end-capping agent, ring-opening catalyst, polar solvent and small molecule fatty alcohol is 32.2:(10-20):(0.05-0.1):(25-200):(50-150).

[0031] In step 2, the mass ratio of the esterification solution, the aromatic diamine, and the surfactant is 100:(15-30):(1.5-5); the aromatic diamine is any one of 4,4'-diaminodiphenyl ether (ODA), 4,4'-diaminodiphenylmethane (MDA), 4,4'-diaminodiphenyl sulfone (DDS), and m-phenylenediamine (m-PDA).

[0032] In step 3, the polyimide oligomer (PIO) specifically refers to: norbornene-terminated polyimide oligomer (NE-PIO), maleic anhydride-terminated polyimide oligomer (ME-PIO), and ethynyl-terminated polyimide oligomer (AE-PIO).

[0033] In step 4, the molar ratio of the norbornene-terminated imide crosslinking foaming agent (NE-CBA) to the imide oligomer (PIO) powder is 1 to 1.2:1.

[0034] The mechanism of this invention is as follows: The norbornene-terminated imide crosslinking foaming agent (NE-CBA) has a small molecular weight and contains 2-4 norbornene end groups, which can release a large amount of cyclopentadiene as a gas source during the foaming process of thermosetting polyimide oligomers (PIO), thereby increasing the foam expansion ratio. It can also undergo co-crosslinking or self-crosslinking reactions with ethylene end groups, acetylene end groups, and norbornene end groups in different types of polyimide oligomers (PIO), increasing the crosslinking density of rigid polyimide foams (PIRFs). The decomposition, gas release, and self-crosslinking reactions of the norbornene-terminated imide crosslinking foaming agent (NE-CBA) are shown below:

[0035]

[0036] The beneficial effects of this invention are:

[0037] 1. The norbornene-terminated imide crosslinking blowing agent (NE-CBA) prepared in this invention is used to form a blended foaming system with norbornene-terminated polyimide oligomers (NE-PIO), maleic anhydride-terminated polyimide oligomers (ME-PIO), and ethynyl-terminated polyimide oligomers (AE-PIO). The norbornene imide end groups of these low molecular weight NE-CBAs can release a large amount of cyclopentadiene (CPD) at high temperatures as a blowing agent, enabling the foam to undergo high expansion ratio foaming. At the same time, it can also self-crosslink and co-crosslink, which is beneficial to increase melt strength and prepare polyimide rigid foam with high closed-cell ratio, high expansion ratio, and high mechanical strength. Its high gas production capacity makes up for the problem that the traditional (NE-PIO) has insufficient gas production capacity, which makes it difficult to prepare high expansion ratio PIRFs.

[0038] 2. This invention can also effectively solve the problem of lack of gas source for acetylene-terminated polyimide oligomers (AE-PIO) and maleic anhydride-terminated polyimide oligomers (ME-PIO), effectively broadening the range of chemical structures that can be selected for rigid polyimide foams. Furthermore, by adjusting the foaming agent content, the long-standing problem of difficulty in reducing the density of PIRFs can be solved, thereby achieving a synergistic effect of "high strength" and "low density" in rigid polyimide foam, significantly improving the performance and application prospects of rigid polyimide foam materials.

[0039] 3. The density of the prepared rigid polyimide foam can be reduced to 50 kg / m³. 3 It has a compressive strength of over 0.8 MPa at 10% strain, a glass transition temperature of over 360℃, a thermal weight loss temperature of over 480℃ at 5% strain, a thermal conductivity as low as 0.030 W / (m·K), and an oxygen index of over 40%. It has excellent comprehensive performance and has broad application prospects in high-tech fields such as aviation, aerospace, and shipbuilding. Attached Figure Description

[0040] Figure 1 This is a flowchart of the invention;

[0041] Figure 2 The FTIR curve of a diamine-type norbornene-terminated imide crosslinking foaming agent (NE-CBA) is shown.

[0042] Figure 3 This is a physical image and scanning electron microscope image of a diamine-type norbornene-terminated imide crosslinking foaming agent (NE-CBA);

[0043] Figure 4 Thermogravimetric analysis curve of a diamine-type norbornene-terminated imide crosslinking foaming agent (NE-CBA);

[0044] Figure 5 The DSC curve of a diamine-type norbornene-terminated imide crosslinking foaming agent (NE-CBA) is shown.

[0045] Figure 6 These are physical images, DSC, TGA, and DTG curves of the PIRFs prepared in Example 2.

[0046] Figure 7 These are physical images, DSC, TGA, and DTG curves of the PIRFs prepared in Example 3. Detailed Implementation

[0047] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0048] Example 1:

[0049] A norbornene-terminated imide crosslinking foaming agent (NE-CBA) is provided, wherein the foaming agent molecule contains two functional norbornene imide end groups with a molecular weight of 400-500, and its molecular structure is as follows: wherein Ar represents 4,4'-diaminodiphenyl ether (ODA).

[0050]

[0051] The foaming agent is a diamine type NE-CBA-ODA.

[0052] A method for preparing thermosetting polyimide rigid foam using norbornene imide as an end-group crosslinking blowing agent mainly includes the following steps:

[0053] (1) Preparation of diamine type NE-CBA-ODA: Add 100 mL of tetrahydrofuran to a three-necked flask, then add 16.42 g of norborneol olefinic anhydride (NA), add 100 mL of anhydrous ethanol, and then add 0.03 g of 2-methylimidazole. Heat to 60 °C and stir at a constant temperature for 2 h under nitrogen protection. After the solution becomes clear, add 10 g of 4,4'-diaminodiphenyl ether (ODA) and continue the reaction for 2 h until the reaction is complete. Finally, add 2 mL of FSO-100 and stir for 30 min until the mixture is homogeneous. Cool to room temperature and pour into a rotary evaporator to obtain solution A, which is denoted as NE-CBA-ODA.

[0054] The FTIR curve of this diamine-type norbornene-terminated imide crosslinking foaming agent (NE-CBA) is shown in [Figure Number]. Figure 2 This proves the accuracy of its molecular structure.

[0055] Physical images and scanning electron microscope images of this diamine-type norbornene-terminated imide crosslinking foaming agent (NE-CBA) powder are shown below. Figure 3 As can be seen, the powder has an irregular polyhedral shape and a particle size between 20 and 50 μm.

[0056] The thermogravimetric analysis curve of this diamine-type norbornene-terminated imide crosslinking foaming agent (NE-CBA) is shown in the figure. Figure 4 The TGA and DTG results indicate that the weight loss occurring around 170°C is due to the release of residual CBA solvent, the weight loss occurring around 270°C is due to further imidization, dehydration, and de-alcoholization of CBA, and the weight loss around 350°C indicates that CBA releases cyclopentadiene and crosslinks, and the amount of gas released is about 7-15% of its mass, indicating that CBA can be used as a crosslinking foaming agent, and its foaming and crosslinking temperature is around 350°C.

[0057] The DSC curve of this diamine-type norbornene-terminated imide crosslinking foaming agent (NE-CBA) is shown in the figure. Figure 5 As can be seen, CBA exhibits an endothermic peak around 270℃, indicating that the CBA molecular chain still contains linear imide groups, resulting in melting and further complete imidization. After complete cyclization of the imide groups, the rigidity of the molecular chain increases. The endothermic peak around 300℃ represents the remelting of fully imidized NE-CBA; the exothermic peak around 340℃ represents the cross-linking reaction of the NE groups on the molecular chain.

[0058] (2) Preparation of norbornene-terminated polyimide oligomer (NE-PIO): 150 mL of tetrahydrofuran was added to a three-necked flask, followed by 32.22 g of 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride (BTDA) and 10.9 g of 5-norbornene-2,3-dianhydride (NA). 150 mL of anhydrous ethanol was added, followed by 0.05 g of 2-methylimidazole. The mixture was stirred at 60 °C for 2 h under nitrogen protection. After the solution became clear, 26.6 g of 4,4'-diaminodiphenyl ether (ODA) was added, and the reaction was continued for 2 h until the reaction was complete. Finally, 5 mL of FSO-100 was added, and the mixture was stirred for 1 h until homogeneous. The mixture was cooled to room temperature to obtain solution B, denoted as NE-PIO.

[0059] (3) Preparation of rigid polyimide foam: Pour liquid B into a rotary evaporator containing liquid A, and mix liquid A and liquid B at a molar ratio of 1:1 using a rotary evaporator. Mixing and solvent removal of liquid A and liquid B are carried out at a rotary evaporation temperature of 60℃ and a pressure of 0.1MPa. After rotary evaporation, the powder after solvent removal is placed in a forced-air drying oven at 120℃ for 2 hours to obtain a mixed powder of NE-CBA-ODA / NE-PIO. The mixed powder is placed in a graphite mold and placed in a high-temperature drying oven at 320℃ for 1 hour to foam, and then cured at 320℃ for 2 hours to obtain rigid polyimide foam (PIRFs).

[0060] The density of PIRFs was tested to be 90 kg / m³. 3 It has a 10% compressive strength of 2.5 MPa, a glass transition temperature of 380℃, a 5% thermogravimetric temperature of 500℃, a thermal conductivity of 0.032 W / (m·K), and an oxygen index greater than 40%.

[0061] Example 2:

[0062] A norbornene-terminated imide crosslinking foaming agent (NE-CBA) is provided, wherein the foaming agent molecule contains two functional norbornene imide end groups with a molecular weight of 400-500, and its molecular structure is as follows: wherein Ar represents 4,4'-diaminodiphenyl ether (ODA).

[0063]

[0064] The foaming agent is a diamine type NE-CBA-ODA.

[0065] A method for preparing thermosetting polyimide rigid foam using norbornene imide as an end-group crosslinking blowing agent mainly includes the following steps:

[0066] (1) Preparation of diamine-type NE-CBA-ODA: Same as Example 1;

[0067] (2) Preparation of maleic anhydride-terminated polyimide oligomer (ME-PIO): 150 mL of tetrahydrofuran was added to a three-necked flask, followed by 32.22 g of 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride (BTDA) and 6.54 g of maleic anhydride (MA). 150 mL of anhydrous ethanol was added, followed by 0.1 g of 2-methylimidazole. The temperature was raised to 70 °C and stirred at a constant temperature for 2 h under nitrogen protection. After the solution became clear, 26.6 g of ODA was added, and the reaction continued for 2 h until the reaction was complete. Finally, 5 mL of FSO-100 was added, and the mixture was stirred for 1 h until homogeneous. The solution was cooled to room temperature to obtain solution B, denoted as ME-PIO.

[0068] (3) Preparation of rigid polyimide foam: Liquid B was poured into a rotary evaporator containing liquid A. Liquid A and liquid B were mixed at a molar ratio of 1:1 using a rotary evaporator. The mixing and solvent removal of liquid A and liquid B were carried out at a rotary evaporation temperature of 60℃ and a pressure of 0.1MPa. After rotary evaporation, the solvent-removed powder was placed in a high-temperature oven at 120℃ for 2 hours to obtain a mixed powder of NE-CBA-ODA / ME-PIO. The mixed powder of NE-CBA / ME-PIO was placed in a graphite mold and foamed in a high-temperature oven at 320℃ for 1 hour, and then cured at 340℃ for 2 hours to finally obtain rigid polyimide foam (PIRFs).

[0069] Physical images, DSC, TGA, and DTG curves of PIRFs are shown below. Figure 6 .

[0070] The density of the maleic anhydride-terminated PIRFs prepared in this example was tested to be 100 kg / m³. 3 It has a 10% strain compressive strength of 3.5 MPa, a glass transition temperature of 360℃, a 5% thermal weight loss temperature of 480℃, a thermal conductivity of 0.032 W / (m·K), an oxygen index of over 40%, and mechanical properties that are close to those of commercially available PMI foam of the same density. Its flame retardant and heat-resistant properties are far superior to those of current PMI foam.

[0071] Example 3:

[0072] A norbornene-terminated imide crosslinking foaming agent (NE-CBA) is provided, wherein the foaming agent molecule contains two functional norbornene imide end groups with a molecular weight of 400-500, and its molecular structure is as follows: wherein Ar represents 4,4'-diaminodiphenyl ether (ODA).

[0073]

[0074] The foaming agent is a diamine type NE-CBA-ODA.

[0075] A method for preparing thermosetting polyimide rigid foam using norbornene imide as an end-group crosslinking blowing agent mainly includes the following steps:

[0076] (1) Preparation of diamine-type NE-CBA-ODA: Same as Example 1;

[0077] (2) Preparation of acetylene-terminated polyimide oligomer (AE-PIO): 200 mL of tetrahydrofuran was added to a three-necked flask, followed by 32.22 g of 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride (BTDA) and 16.55 g of phenylethynyl phthalic anhydride (PEPA). 100 mL of anhydrous ethanol was added, followed by 0.1 g of 2-methylimidazole. The mixture was heated to 80 °C and stirred at a constant temperature for 2 h under nitrogen protection. After the solution became clear, 16.2 g of m-phenylenediamine (m-PDA) was added, and the reaction continued for 2 h until the reaction was complete. Finally, 5 mL of FSO-100 was added, and the mixture was stirred for 1 h until homogeneous. The mixture was cooled to room temperature to obtain solution B, denoted as AE-PIO.

[0078] (3) Preparation of rigid polyimide foam: Liquid B was poured into a rotary evaporator containing liquid A. Liquid A and liquid B were mixed at a molar ratio of 1:1 using a rotary evaporator. The mixing and solvent removal of liquid A and liquid B were carried out at a rotary evaporation temperature of 60℃ and a pressure of 0.1MPa. After rotary evaporation, the solvent-removed powder was placed in a high-temperature oven at 120℃ for 2 hours to obtain a mixed powder of NE-CBA-ODA / AE-PIO. The mixed powder of NE-CBA-ODA / AE-PIO was placed in a graphite mold and foamed in a high-temperature oven at 320℃ for 1 hour, and then cured at 370℃ for 2 hours to finally obtain rigid polyimide foam (PIRFs).

[0079] Physical images, DSC, TGA, and DTG curves of PIRFs are shown below. Figure 7 .

[0080] The density of the phenylacetylene-terminated PIRFs prepared in this example was tested to be 120 kg / m³. 3 It has a 10% compressive strength of 4.2 MPa, a glass transition temperature of 420℃, a 5% thermogravimetric temperature of 520℃, a thermal conductivity of 0.030 W / (m·K), and an oxygen index exceeding 40%.

[0081] Example 4:

[0082] A norbornene-terminated imide crosslinking foaming agent (NE-CBA) is provided, wherein the foaming agent molecule contains three functional norbornene imide end groups with a molecular weight of 550-850, and its molecular structure is as follows: wherein Ar1 represents melamine (TAP).

[0083]

[0084] The foaming agent is a triamine-type NE-CBA-TAP.

[0085] A method for preparing thermosetting polyimide rigid foam using norbornene imide as an end-group crosslinking blowing agent mainly includes the following steps:

[0086] (1) Preparation of NE-CBA-TAP of the triamine type: 100 mL of tetrahydrofuran was added to a three-necked flask, followed by 24.63 g of norborneol adipic anhydride (NA), 100 mL of anhydrous ethanol, and 0.03 g of 2-methylimidazole. The temperature was raised to 80 °C and stirred at a constant temperature for 4 h under nitrogen protection. After the solution became clear, 6.25 g of melamine (TAP) was added and the reaction was continued for 4 h until the reaction was complete. Finally, 2 mL of FSO-100 was added and stirred for 30 min until the mixture was homogeneous. The solution was cooled to room temperature and poured into a rotary evaporator to obtain solution A, which was denoted as NE-CBA-TAP.

[0087] (2) Preparation of maleic anhydride-terminated polyimide oligomer (ME-PIO): 150 mL of tetrahydrofuran was added to a three-necked flask, followed by 32.22 g of 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride (BTDA) and 6.54 g of maleic anhydride (MA). 150 mL of anhydrous ethanol was added, followed by 0.1 g of 2-methylimidazole. The mixture was heated to 70 °C and stirred at a constant temperature for 2 h under nitrogen protection. After the solution became clear, 26.6 g of ODA was added, and the reaction continued for 2 h until the reaction was complete. Finally, 5 mL of FSO-100 was added, and the mixture was stirred for 1 h until homogeneous. The mixture was cooled to room temperature to obtain solution B, denoted as ME-PIO.

[0088] (3) Preparation of rigid polyimide foam: Liquid B was poured into a rotary evaporator containing liquid A. Liquid A and liquid B were mixed at an anhydride molar ratio of 1:1 using a rotary evaporator. The mixing and solvent removal of liquid A and liquid B were carried out at a rotary evaporation temperature of 70℃ and a pressure of 0.1MPa. After rotary evaporation, the solvent-removed powder was placed in a high-temperature oven at 120℃ for 2 hours to obtain a mixed powder of NE-CBA-TAP / ME-PIO. The mixed powder of NE-CBA / ME-PIO was placed in a graphite mold and foamed in a high-temperature oven at 350℃ for 1 hour, followed by curing at 350℃ for 2 hours to finally obtain rigid polyimide foam (PIRFs).

[0089] The density of the maleic anhydride-terminated PIRFs prepared in this example was tested to be 80 kg / m³. 3 This indicates that adding NE-CBA, prepared using triamine as a monomer, to the foaming system can further reduce the density of polyimide foam. The foam exhibits a 10% compressive strength of 2.1 MPa, a glass transition temperature of 420℃, a 5% thermogravimetric temperature of 520℃, a thermal conductivity of 0.030 W / (m·K), and an oxygen index exceeding 40%.

[0090] Example 5:

[0091] A norbornene-terminated imide crosslinking foaming agent (NE-CBA) is provided, wherein the foaming agent molecule contains four functional norbornene imide end groups and has a molecular weight of 700-850. Its molecular structure is as follows: wherein Ar2 represents 4-[(3,4-diaminophenyl)methyl]phenyl-1,2-diamine (TADM).

[0092]

[0093] The foaming agent is a tetraamine type NE-CBA-TADM.

[0094] A method for preparing thermosetting polyimide rigid foam using norbornene imide as an end-group crosslinking blowing agent mainly includes the following steps:

[0095] (1) Preparation of tetraamine-type NE-CBA-TADM: Add 100 mL of tetrahydrofuran to a three-necked flask, then add 32.84 g of norbornene adiene anhydride (NA), 100 mL of anhydrous ethanol, and 0.03 g of 2-methylimidazole. Heat to 85 °C and stir at a constant temperature for 4 h under nitrogen protection. After the solution becomes clear, add 10.71 g of 4-[(3,4-diaminophenyl)methyl]benzene-1,2-diamine (TADM), and then add 2.5 g of dibutyl phosphate. Continue the reaction for 4 h until the reaction is complete. Finally, add 2 mL of FSO-100 and stir for 30 min until the mixture is homogeneous. Cool to room temperature and pour into a rotary evaporator to obtain solution A, which is denoted as NE-CBA-TADM.

[0096] (2) Preparation of acetylene-terminated polyimide oligomer (AE-PIO): 200 mL of tetrahydrofuran was added to a three-necked flask, followed by 32.22 g of 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride (BTDA) and 16.55 g of phenylethynyl phthalic anhydride (PEPA). 100 mL of anhydrous ethanol was added, followed by 0.1 g of 2-methylimidazole. The mixture was heated to 80 °C and stirred at a constant temperature for 2 h under nitrogen protection. After the solution became clear, 16.2 g of m-phenylenediamine (m-PDA) was added, and the reaction continued for 2 h until the reaction was complete. Finally, 5 mL of FSO-100 was added, and the mixture was stirred for 1 h until homogeneous. The mixture was cooled to room temperature to obtain solution B, denoted as AE-PIO.

[0097] (3) Preparation of rigid polyimide foam: Liquid B was poured into a rotary evaporator containing liquid A. Liquid A and liquid B were mixed at an anhydride molar ratio of 1:1 using a rotary evaporator. The mixing and solvent removal of liquid A and liquid B were carried out at a rotary evaporation temperature of 60℃ and a pressure of 0.1MPa. After rotary evaporation, the solvent-removed powder was placed in a high-temperature oven at 120℃ for 2 hours to obtain a mixed powder of NE-CBA-TADM / AE-PIO. The mixed powder of NE-CBA / AE-PIO was placed in a graphite mold and foamed at 380℃ for 1 hour in a high-temperature oven, followed by curing at 380℃ for 2 hours to finally obtain rigid polyimide foam (PIRFs).

[0098] The density of the phenylacetylene-terminated PIRFs prepared in this example was tested to be 50 kg / m³. 3 The foam exhibits a 10% compressive strength of 0.8 MPa, a glass transition temperature of 425℃, a 5% thermogravimetric temperature of 534℃, a thermal conductivity of 0.030 W / (m·K), and an oxygen index exceeding 40%. Its specific mechanical strength and heat resistance surpass all currently reported rigid polyimide foams, indicating that this method synthesizes a tetraamine-based NE-CBA crosslinking foaming agent. When added to the ME-PIO system for co-foaming, it achieves the synergistic preparation of low-density, high-strength, and high-heat-resistant rigid polyimide foam, demonstrating promising application prospects.

[0099] To more clearly illustrate the differences between the examples, the main component structures, molar ratios, and key properties of the rigid polyimide foams (PIRFs) prepared in the five examples are listed below:

[0100]

Claims

1. A method for preparing rigid polyimide foam using norbornene-terminated imide crosslinking foaming agents, characterized in that, The specific steps are as follows: Step 1: 3,3',4,4'-benzophenone tetracarboxylic dianhydride, a capping agent, and a ring-opening catalyst, 2-methylimidazole, are added in a certain proportion to a mixed solvent of tetrahydrofuran and ethanol. Esterification is carried out at a temperature of 60–90°C for 2–5 h to obtain an esterified solution of 3,3',4,4'-benzophenone tetracarboxylic dianhydride. The capping agent is 5-norbornene-2,3-dianhydride, maleic anhydride, or 4-phenylethynyl phthalic anhydride. Step 2: Add 4,4'-diaminodiphenyl ether or m-phenylenediamine and surfactant FSO-100 to the esterification solution of 3,3',4,4'-benzophenone tetracarboxylic dianhydride, and react for 2-4 h to obtain a polyester ammonium salt solution. Step 3: Dry the polyester ammonium salt solution to obtain precursor powder, and then imidize the precursor powder at high temperature to obtain polyimide oligomer powder. Step 4: Add norbornene-terminated imide crosslinking foaming agent and polyimide oligomer powder to ethanol solvent in proportion and mix. Then remove the solvent by rotary evaporation to obtain foaming powder. Place the foaming powder in a sealed graphite mold and foam in a high temperature oven at 300-380℃ for 2-5 hours to prepare rigid polyimide foam. The molecular structure of the norbornene-terminated imide crosslinking foaming agent is as follows: ， in: ， ， 。 2. The method for preparing rigid polyimide foam using norbornene-terminated imide crosslinking foaming agents according to claim 1, characterized in that: In step 1, the mass ratio of 3,3',4,4'-benzophenone tetracarboxylic dianhydride, end-capping agent, ring-opening catalyst, tetrahydrofuran, and ethanol is 32.2:(10~20):(0.05~0.1):(25~200):(50~150).

3. The method for preparing rigid polyimide foam using norbornene-terminated imide crosslinking foaming agents according to claim 1, characterized in that: In step 2, the mass ratio of 3,3',4,4'-benzophenone tetracarboxylic dianhydride esterification solution, 4,4'-diaminodiphenyl ether or m-phenylenediamine, and surfactant is 100:(15-30):(1.5-5).

4. The method for preparing rigid polyimide foam using norbornene-terminated imide crosslinking foaming agents according to claim 1, characterized in that: In step 3, the polyimide oligomers are specifically: norbornene-terminated polyimide oligomers, maleic anhydride-terminated polyimide oligomers, and ethynyl-terminated polyimide oligomers.

5. The method for preparing rigid polyimide foam using norbornene-terminated imide crosslinking foaming agents according to claim 1, characterized in that: In step 4, the molar ratio of the norbornene-terminated imide crosslinking foaming agent to the polyimide oligomer powder is (1~1.2):

1.

6. The method for preparing rigid polyimide foam using norbornene-terminated imide crosslinking foaming agents according to claim 1, characterized in that, The specific steps for preparing the norbornene-terminated imide crosslinking foaming agent are as follows: Step (1), Preparation of norbornene ethyl ester: The end-capping reaction monomer 5-norbornene-2,3-dicarboxylic anhydride and a small amount of ring-opening catalyst 2-methylimidazole are added to a polar solvent tetrahydrofuran and ethanol mixture, and reacted at a certain temperature and time to obtain an esterified solution of norbornene ethyl ester. Step (2), preparation of amide esterification solution: Aromatic polyamine is slowly added to the esterification solution of norbornene ethyl ester. The molar ratio of aromatic polyamine to 5-norbornene-2,3-dicarboxylic anhydride is 1:(2~4). The reaction is continued at 60~90℃ for 60~120 min under inert gas protection. After the reaction is completed, a surfactant is added to the solution to obtain the amide esterification solution. Step (3) Preparation of norbornene-terminated imide crosslinking foaming agent: After solvent removal and imidization treatment of amide esterification liquid at a certain temperature and time, norbornene-terminated imide crosslinking foaming agent is obtained. After further pulverization, norbornene-terminated imide crosslinking foaming agent powder with a particle size of 20~200 μm is obtained.

7. A method for preparing rigid polyimide foam using norbornene-terminated imide crosslinking foaming agents according to claim 6, characterized in that: In step (1), the molar ratio of the polar solvent tetrahydrofuran to ethanol is (500~1000):1000, and the concentration of 5-norbornene-2,3-dicarboxylic anhydride in the esterification solution is 1.2~4 g / L.

8. A method for preparing rigid polyimide foam using norbornene-terminated imide crosslinking foaming agents according to claim 6, characterized in that: In step (2), the aromatic polyamine is any one of aromatic diamine, aromatic triamine, or aromatic tetraamine; the aromatic diamine is added in a molar ratio of 1:2 between aromatic diamine and 5-norbornene-2,3-dicarboxylic anhydride; the aromatic triamine is added in a molar ratio of 1:3 between aromatic triamine and 5-norbornene-2,3-dicarboxylic anhydride; the aromatic tetraamine is added in a molar ratio of 1:4 between aromatic tetraamine and 5-norbornene-2,3-dicarboxylic anhydride; and the surfactant is any one of FSO-100, AK8805, or DC193.

9. A method for preparing rigid polyimide foam using norbornene-terminated imide crosslinking foaming agents according to claim 6, characterized in that: In step (3), the solvent removal and imidization are carried out at a temperature of 120–200 °C for 1–4 h.

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