Cross-linked polyimide rigid foam and preparation method thereof

Abstract

The invention relates to cross-linked polyimide rigid foam and a preparation method thereof. The method comprises the following steps: step 01, preparing a tri-functionality isocyanate group cross-linking agent from aliphatic isocyanate, tributyl phosphine and o-toluene sulfonamide; 02, according to the adding sequence of the first bifunctional aromatic dianhydride, the alcohol solvent, the ether solvent and the polar organic solvent, a first single-acid and single-ester mixed solution is obtained; according to the adding sequence of a second bifunctional aromatic dianhydride, an alcohol solvent, an ether solvent, a ring-opening catalyst and a polar organic solvent, obtaining a second single-acid and single-ester mixed solution; mixing the first single-acid and single-fat mixed solution and the second single-acid and single-fat mixed solution to obtain a foaming material A; step 03, mixing a three-functionality isocyanate group cross-linking agent, isocyanate, a foam stabilizer and deionized water to obtain a foaming material B; step 04, mixing the foaming material A and the foaming material B to obtain the cross-linked polyimide rigid foam.

Description

Technical Field

[0001] The invention relates to the technical field of polymer materials, and in particular to a cross-linked polyimide rigid foam and a preparation method thereof. Background Art

[0002] In the field of traditional foam plastics, the most widely used foam material is polyurethane foam, which has good elasticity, wear resistance and thermal insulation properties, and is a foam cushioning material with excellent performance. However, polyurethane foam is generally not suitable for long-term exposure to temperatures above 150°C, which will cause its physical and mechanical properties to deteriorate significantly. There are many solutions to improve the temperature resistance of foam. The more practical solution is to use isocyanate resins containing polycarboxylic acids or polyanhydrides to form imide bonds, which is called polyimide foam. Polyimide foam not only has better mechanical and heat resistance, but also can withstand extremely low temperatures. It has the advantage of not breaking at -267°C. In recent years, it has been used in high-tech fields such as liquefied natural gas ocean transportation, spacecraft cryogenic fuel storage tanks, rocket shells or missile interlayer materials. At present, there have been many studies on polyimide foam at home and abroad.

[0003] Chinese patents CN111748094A and CN107540839A disclose a method for preparing polyimide foam, wherein an anhydride-terminated polyimide precursor solution is first prepared, and then polyisocyanate is slowly added to react completely, and then cooled to room temperature to obtain a polyimide precursor solution, and then most of the polar solvents in the polyimide precursor solution are removed, and then cured in a vacuum oven under vacuum conditions to obtain imidized polyimide precursor foam. The polyimide foam prepared by this method has low density, uniform pores, and excellent high temperature resistance, but the foam has low hardness, poor mechanical properties, and a high slag drop rate, which is difficult to meet the use requirements.

[0004] US Patents US5298531, US4952611A and Chinese Patent CN110014714A add aromatic dianhydride to a tetrahydrofuran / methanol mixed solvent, heat it to dissolve it and perform an esterification reaction, add aromatic diamine and foam stabilizer after the solution becomes transparent and mix them evenly to obtain a foam precursor solution; dry the foam precursor solution, and then crush the solid product obtained after drying to obtain polyester ammonium salt (PEAS) powder, and then perform foaming and imidization reaction to prepare polyimide foam. The polyimide foam prepared by this method has uniform pores, stable quality, good high temperature resistance, and can be recycled repeatedly; however, the foam preparation process is complicated and costly, and no chemical crosslinking occurs during the production process, so the strength is low.

[0005] Chinese patent CN112126106A discloses a high-density rigid flame-retardant polyimide foam material and a preparation method thereof, wherein the method comprises the following steps: uniformly mixing anhydride, low molecular weight alcohol, surfactant I, catalyst, and foaming agent to obtain a foaming white material; mixing isocyanate, flame retardant, and surfactant II to obtain a foaming black material; and mixing the foaming white material and the black material in proportion and subjecting them to microwave aging treatment to obtain a polyimide foam material. The polyimide foam material prepared by the method has the advantages of good temperature resistance and low moisture absorption rate, but the crosslinking degree of the product is low and the foam rigidity is poor, which makes it difficult to meet the high-strength use requirements in the fields of ships, aerospace, etc.

[0006] Therefore, it is urgent to find a more suitable way to solve the problems existing in the above-mentioned practical applications and to prepare a weight-reducing structural foam material that is resistant to high temperatures, has strong rigidity, and has excellent mechanical properties and can meet the requirements of large-scale industrial preparation and can be used as a substitute for steel materials in aviation, aerospace, and shipbuilding. Summary of the invention

[0007] The present invention provides a cross-linked polyimide rigid foam and a preparation method thereof to solve the above-mentioned deficiencies of the prior art. The present invention uses aliphatic difunctional isocyanate polymerization reaction to prepare a trifunctional isocyanate-based cross-linking agent, and the cross-linking degree is increased by the cross-linking agent, thereby increasing the physical and mechanical properties and rigidity of the polyimide foam product. The cross-linked polyimide rigid foam prepared by the present invention has controllable density, high strength, strong rigidity, and stable foam quality, and can be used as a weight-reducing structural foam material in the fields of aviation, aerospace, and ships as a substitute for steel materials.

[0008] In order to achieve the purpose of the present invention, the following technologies are proposed: A cross-linked polyimide rigid foam, the chemical structure is Wherein R1 is selected from: A method for preparing a cross-linked polyimide rigid foam comprises the following steps: Step 01, preparing a trifunctional isocyanate crosslinking agent by using aliphatic isocyanate, tributylphosphine and o-toluenesulfonamide; Step 02, according to the order of adding the first difunctional aromatic dianhydride, alcohol solvent, ether solvent, and polar organic solvent, reacting at 55° C. for 10-16 hours to obtain a first monoacid monolipid mixed solution; According to the order of adding the second bifunctional aromatic dianhydride, alcohol solvent, ether solvent, ring-opening catalyst, and polar organic solvent, the reaction is carried out at 55° C. for 10-16 hours to obtain a second monoacid monolipid mixed solution; Mixing the first mono-acid mono-fat mixed liquid and the second mono-acid mono-fat mixed liquid to obtain a foaming material A; Step 03, mixing a trifunctional isocyanate crosslinking agent, isocyanate, a foam stabilizer, and deionized water to obtain a foaming material B; Step 04, mixing the foaming material A after the temperature is lowered to 10°C with the foaming material B, injecting air at a rate of 0.5-1NL / min, and subjecting the mixture to stepwise heating and aging at 140°C×6h and then 200°C×8h, and then removing the solvent by vacuum removal at 180°C×8h to obtain a cross-linked polyimide rigid foam.

[0009] Furthermore, the chemical structural formula of the monoacid monolipid is: Wherein R1 is selected from: The mono-acid mono-lipid mixed liquid is a mixture of one mono-acid mono-lipid or a plurality of mono-acid mono-lipids, and each mono-acid mono-lipid mixed liquid is prepared by a separate preparation method.

[0010] Furthermore, the aliphatic isocyanate is one of hexamethylene diisocyanate, pentamethylene diisocyanate and isophorone diisocyanate.

[0011] Furthermore, the mass ratio of tributylphosphine, o-toluenesulfonamide and aliphatic isocyanate is 0.1-0.2:0.2-0.5:100.

[0012] Further, 3. The difunctional aromatic dianhydride is one or more monomers of bis-anhydride groups such as 2,3,3',4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, pyromellitic dianhydride, 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride, 4,4'-(4,4'-isopropylidene diphenyloxy)bis(phthalic anhydride), 3,3',4,4'-triphenyl bisether tetracarboxylic dianhydride, and 3,3',4,4'-tetracarboxylic diphenyl ether dianhydride, and more preferably one or more of 2,3,3',4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, and pyromellitic dianhydride.

[0013] Furthermore, the alcohol solvent is one or more alcohols such as methanol, ethanol, propanol, furfuryl alcohol, etc., and the molar ratio of the alcohol solvent to the difunctional aromatic dianhydride is 1:1.

[0014] Furthermore, the ether solvent is tetrahydrofuran, and the amount of the ether solvent used should be 1-2 times the mass of the difunctional aromatic dianhydride.

[0015] Furthermore, the polar organic solvent is one or more of ethyl acetate, dichloromethane, acetonitrile, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide.

[0016] Furthermore, the foam stabilizer is one or more of AK-8805, AK-158, DC-193, DC-198, L550, L6900, AK-8803, L550, AK-168, octadecyl dimethyl amine oxide, MQ803 and other auxiliary agents, and the mass ratio of the foam stabilizer to the difunctional aromatic dianhydride is 0.5-2:100.

[0017] Furthermore, the isocyanate is one or more of PM-200, PM-400, PM-2010, PM-130, polymethylene polyphenyl polyisocyanate, and the molar ratio of isocyanate group to difunctional aromatic dianhydride in the isocyanate is 99:50.

[0018] Furthermore, the ring-opening catalyst is one or more of dimethylimidazole and isoquinoline, and the mass ratio of the ring-opening catalyst to the difunctional aromatic dianhydride is 0.5-2:100.

[0019] Furthermore, the mass ratio of the trifunctional isocyanate-based crosslinking agent to the difunctional aromatic dianhydride is 10-20:100.

[0020] The advantages of the above technical solution are: The present invention refers to the principle of polyimide synthesis, uses aliphatic difunctional isocyanate polymerization reaction to prepare a trifunctional isocyanate crosslinking agent, which can be mixed with material B to participate in the foaming process for chemical reaction, thereby increasing the physical and mechanical properties and rigidity of the polyimide foam product by increasing the degree of crosslinking. At the same time, the product has more excellent thermodynamic properties and will not soften and melt due to increased ambient temperature.

[0021] The present invention adopts an extrusion foaming process to prepare polyimide foam, first prepares material A and material B respectively, after the temperature of material A and material B is reduced to a specified temperature, they are stirred and mixed and extruded into a mold for foaming, the foaming process is highly mechanized, continuous and stable, the foam production efficiency is high, and the needs of large-scale low-cost industrial production can be met. Before the foaming system releases gas, the present invention reduces the temperature of material A and material B, and slows down the foaming speed of the foaming system by controlling the reaction temperature, thereby avoiding process defects such as collapse of foam products, cracking of foams, and uneven pores caused by excessively fast foaming speed.

[0022] In the selection of aromatic dianhydrides, the present invention selects different aromatic dianhydrides to design the polyimide molecular chain in structure, and increases the intramolecular rotation activation energy by reducing the use ratio of difunctional aromatic dianhydrides containing "bridge" bonds such as -O-, -C(=O)-, and -S-, thereby enhancing the rigidity of the molecular chain and the interaction force between the molecular chains, and preparing a thermosetting polyimide foam that meets the requirements.

[0023] The scalable present invention can be used in specific applications to use additional fillers such as flame retardants, glass fibers, carbon fibers, wollastonite, and absorbents when adding foam stabilizers to enhance the performance of foam materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings.

[0025] Figure 1 The density-pressure dependence of a cross-linked polyimide rigid foam is shown.

[0026] Figure 2 The infrared spectrum of the cross-linked polyimide rigid foam after imidization is shown.

[0027] Figure 3 The drawings of materials prepared by various embodiments and comparative examples are shown, wherein sample No. 1 in the drawings is the foam material prepared by embodiment 1, sample No. 2 is the foam material prepared by embodiment 2, sample No. 3 is the foam material prepared by embodiment 3, sample No. 4 is the foam material prepared by comparative example 1, and sample No. 5 is the foam material prepared by comparative example 2.

[0028] Figure 4 The results of the flat pull test of the materials prepared by each embodiment and each comparative example are shown in FIG. Figure 3 The samples shown in correspondence. DETAILED DESCRIPTION

[0029] The present invention constructs a cubic constrained foaming space on the hot pressing plane to prepare polyimide rigid foam. The size of the foaming space can be designed to achieve the preparation of polyimide rigid foams of different densities. Considering the dramatic increase in pressure during the foaming process, the constant pressure that the press can provide must be large enough. In order to avoid the press being unable to suppress the foaming foam, resulting in foaming failure, or even safety accidents such as machine explosion, the relationship between density and pressure during foam preparation is studied. Figure 1As shown in the figure, it can be seen that as the pressure increases, the foam density of the cross-linked polyimide rigid foam also increases accordingly. Therefore, in specific applications, a reasonable pressure setting can be made according to actual needs. In the production process, the safety of foam production can be increased to meet the needs of safe and sustainable production of enterprises.

[0030] In order to verify the preparation effect of the preparation method of the cross-linked polyimide rigid foam proposed in the present invention, the prepared cross-linked polyimide rigid foam was subjected to infrared spectrum test. The test results are as follows: Figure 2 As shown in the figure, combined with the infrared characteristic absorption peak analysis chart of the main chemical groups in the Handbook of Chemical and Chemical Engineering Experimenters, it can be seen that 1371.01cm -1 It should be the stretching vibration peak of CN, 1778.93cm -1 and 1719.00cm -1 They are the asymmetric stretching vibration absorption peak and the symmetric stretching vibration absorption peak of C=O, 1371.01cm -1 and 729.67cm -1 They are the characteristic absorption peaks of the stretching and bending vibrations of the CNC bonds on the imide ring.

[0031] Example 1 Step 01, under N2 conditions, add 3.36 kg of hexamethylene diisocyanate to the flask, stir and heat to 70°C, then drop a mixed solution of 3.36 g of tributylphosphine and 800 g of xylene. After the dropwise addition is completed, continue the reaction for 2 hours, add 6.72 g of o-toluenesulfonamide, continue the reaction for 0.5 hours, and recover the trifunctional isocyanate crosslinking agent by distillation.

[0032] Step 02, add 11.16 kg of 3,3',4,4'-dibenzophenone tetracarboxylic dianhydride, 1.61 kg of ethanol, 11.16 kg of tetrahydrofuran, 2.23 kg of N,N-dimethylformamide, and 0.11 kg of dimethylimidazole to the flask in sequence, and reflux and stir at 55°C for 10 hours to obtain the first mono-acid and mono-fat mixed solution.

[0033] Take another flask and add 7.56 kg of pyromellitic anhydride, 1.61 kg of ethanol, 7.56 kg of tetrahydrofuran, 1.51 kg of N,N-dimethylformamide and 0.07 kg of dimethylimidazole in sequence, and reflux and stir at 55°C for 10 hours to obtain the second mono-acid and mono-fat mixed solution.

[0034] The first monoacid monofat mixed liquid and the second monoacid monofat mixed liquid are mixed to obtain foaming material A.

[0035] Step 03, add 2.81 kg of trifunctional isocyanate crosslinking agent, 9.8 kg of PM-200, 9.8 kg of PM-400, 0.18 kg of DC-193, and 1.8 kg of deionized water in sequence, stir and mix to obtain foamed material B.

[0036] Step 04, add foaming material A and foaming material B into material tank A and material tank B respectively, after the temperature drops to 10°C, mix foaming material A and foaming material B and inject air at a rate of 1NL / min, extrude into a steel mold of 1300mm×700mm×300mm after 10s, seal the steel mold and maintain pressure for 3h to complete curing, heat and mature at 140°C×6h and 200°C×8h, remove the solvent at 180°C×8h under vacuum conditions to obtain a cross-linked polyimide rigid foam.

[0037] Example 2 Step 01, under N2 conditions, add 3.36 kg of hexamethylene diisocyanate to a flask, stir and heat to 70°C, then dropwise add a mixed solution of 3.36 g of tributylphosphine and 800 g of xylene.

[0038] After the dropwise addition was completed, the reaction was continued for 2 h, 6.72 g of o-toluenesulfonamide was added, and the reaction was continued for 0.5 h. The trifunctional isocyanate crosslinking agent was recovered by distillation.

[0039] Step 02, add 11.16 kg of 3,3',4,4'-dibenzophenone tetracarboxylic dianhydride, 1.61 kg of ethanol, 11.16 kg of tetrahydrofuran, 2.23 kg of N,N-dimethylformamide, and 0.11 kg of dimethylimidazole to the flask in sequence, and reflux and stir at 55°C for 10 hours to obtain the first mono-acid and mono-fat mixed solution.

[0040] Take another flask and add 10.29 kg of 3,3',4,4'-biphenyltetracarboxylic dianhydride, 1.61 kg of ethanol, 10.29 kg of tetrahydrofuran, 2.05 kg of N,N-dimethylformamide and 0.10 kg of dimethylimidazole in sequence, and reflux and stir at 55°C for 10 hours to obtain the second mono-acid and mono-lipid mixed solution.

[0041] The first monoacid monofat mixed liquid and the second monoacid monofat mixed liquid are mixed to obtain foaming material A.

[0042] Step 03, add 3.21 kg of trifunctional isocyanate crosslinking agent, 9.80 kg of PM-200, 9.80 kg of PM-400, 0.21 kg of DC-193, and 2.14 kg of deionized water in sequence, stir and mix to obtain foamed material B.

[0043] Step 04, add foaming material A and foaming material B into material tank A and material tank B respectively, after the temperature drops to 10°C, mix foaming material A and foaming material B and inject air at a rate of 1NL / min, extrude into a steel mold of 1300mm×700mm×300mm after 10s, seal the steel mold and maintain pressure for 3h to complete curing, heat and mature at 140°C×6h and 200°C×8h, remove the solvent at 180°C×8h under vacuum conditions to obtain a cross-linked polyimide rigid foam.

[0044] Example 3 Step 01, under N2 conditions, add 3.36 kg of hexamethylene diisocyanate to a flask, stir and heat to 70°C, then dropwise add a mixed solution of 3.36 g of tributylphosphine and 800 g of xylene.

[0045] After the dropwise addition was completed, the reaction was continued for 2 h, 6.72 g of o-toluenesulfonamide was added, and the reaction was continued for 0.5 h. The trifunctional isocyanate crosslinking agent was recovered by distillation.

[0046] Step 02, add 11.16 kg of 3,3',4,4'-dibenzophenone tetracarboxylic dianhydride, 1.61 kg of ethanol, 11.16 kg of tetrahydrofuran, 2.23 kg of N,N-dimethylformamide, and 0.11 kg of dimethylimidazole to the flask in sequence, and reflux and stir at 55°C for 10 hours to obtain the first mono-acid and mono-fat mixed solution.

[0047] Take another flask and add 7.56 kg of pyromellitic anhydride, 1.61 kg of ethanol, 7.56 kg of tetrahydrofuran, 1.51 kg of N,N-dimethylformamide and 0.07 kg of dimethylimidazole in sequence, and reflux and stir at 55°C for 10 hours to obtain the second mono-acid and mono-fat mixed solution.

[0048] The first monoacid monofat mixed liquid and the second monoacid monofat mixed liquid are mixed to obtain foaming material A.

[0049] Step 03, add 2.81 kg of trifunctional isocyanate crosslinking agent, 19.60 kg of PM-200, 0.18 kg of DC-193, and 1.80 kg of deionized water in sequence, stir and mix to obtain foaming material B.

[0050] Step 04, add foaming material A and foaming material B into material tank A and material tank B respectively, after the temperature drops to 10°C, mix foaming material A and foaming material B and inject air at a rate of 1NL / min, extrude into a steel mold of 1300mm×700mm×300mm after 10s, seal the steel mold and maintain pressure for 3h to complete curing, heat and mature at 140°C×6h and 200°C×8h, remove the solvent at 180°C×8h under vacuum conditions to obtain a cross-linked polyimide rigid foam.

[0051] Comparative Example 1 Step 01, add 11.16 kg of 3,3',4,4'-dibenzophenone tetracarboxylic dianhydride, 1.61 kg of ethanol, 11.16 kg of tetrahydrofuran, 2.23 kg of N,N-dimethylformamide, and 0.11 kg of dimethylimidazole to the flask in sequence, and reflux and stir at 55°C for 10 hours to obtain the first mono-acid and mono-fat mixed solution.

[0052] Take another flask and add 7.56 kg of pyromellitic anhydride, 1.61 kg of ethanol, 7.56 kg of tetrahydrofuran, 1.51 kg of N,N-dimethylformamide and 0.07 kg of dimethylimidazole in sequence, and reflux and stir at 55°C for 10 hours to obtain the second mono-acid and mono-fat mixed solution.

[0053] The foaming material A is obtained by mixing the first mono-acid mono-fat mixed liquid and the second mono-acid mono-fat mixed liquid.

[0054] Step 02, add 9.80 kg of PM-200, 9.80 kg of PM-400, 0.18 kg of DC-193, and 1.8 kg of deionized water in sequence, and stir and mix to obtain foamed material B.

[0055] Step 03, add foaming material A and foaming material B into material tank A and material tank B respectively, after the temperature drops to 10°C, mix foaming material A and foaming material B and inject air at a speed of 1NL / min, extrude into a steel mold of 1300mm*×700mm×300mm after 10s, seal the steel mold and maintain pressure for 3h to complete curing, heat and mature at 140°C×6h and 200°C×8h, remove the solvent at 180°C×8h under vacuum conditions to obtain polyimide rigid foam.

[0056] Comparative Example 2 Step 01, add 11.16 kg of 3,3',4,4'-dibenzophenone tetracarboxylic dianhydride, 1.61 kg of ethanol, 11.16 kg of tetrahydrofuran, 2.23 kg of N,N-dimethylformamide, and 0.11 kg of dimethylimidazole to the flask in sequence, and reflux and stir at 55°C for 10 hours to obtain the first mono-acid and mono-fat mixed solution.

[0057] Take another flask and add 10.85 kg of 3,3',4,4'-tetracarboxylic acid diphenyl ether dianhydride, 1.61 kg of ethanol, 10.85 kg of tetrahydrofuran, 2.17 kg of N,N-dimethylformamide and 0.10 kg of dimethylimidazole in sequence, and reflux and stir at 55°C for 10 hours to obtain the second mono-acid and mono-fat mixed solution.

[0058] The foaming material A is obtained by mixing two monoacid and monolipid mixed liquids.

[0059] Step 02, add 9.80 kg of PM-200, 9.80 kg of PM-400, 0.22 kg of DC-193, and 2.20 kg of deionized water in sequence, and stir and mix to obtain foamed material B.

[0060] Step 03, add foaming material A and foaming material B into material tank A and material tank B respectively, after the temperature drops to 10°C, mix foaming material A and foaming material B and inject air at a rate of 1NL / min, extrude into a steel mold of 1300mm×700mm×300mm after 10s, seal the steel mold and maintain pressure for 3h to complete curing, heat and mature at 140°C×6h and 200°C×8h, remove the solvent at 180°C×8h under vacuum conditions to obtain polyimide foam.

[0061] Among them, in the above embodiments, compared with Example 1 and Comparative Example 1, Comparative Example 1 does not use a self-made trifunctional isocyanate crosslinking agent. Comparative Example 2, on the basis of Comparative Example 1, uses a large amount of aromatic dianhydrides containing "bridge" bonds such as -O-, -C(=O)-, and -S-.

[0062] Table 1 of various properties of the cross-linked polyimide rigid foam or polyimide foam prepared in various embodiments and comparative examples Test items Test Method Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 <![CDATA[Density (kg / m 3 )]]> GB / T6343 149.7 149.5 150.1 150.0 149.6 Tensile strength (MPa) GB / T6344 1.63 1.65 1.50 1.42 1.37 Compressive stress at 10% relative deformation (MPa) GB / T8813 1.37 1.38 1.29 0.97 0.81 Thermal conductivity (W / m·K) GB / T10295 0.03913 0.03988 0.03952 0.04004 0.03989 Flame resistance GB / T2408 After the material is ignited, it will extinguish itself within 1 second after leaving the fire source and there will be no molten droplets, V-0 After the material is ignited, it will extinguish itself within 1 second after leaving the fire source and there will be no molten droplets, V-0 After the material is ignited, it will extinguish itself within 1 second after leaving the fire source and there will be no molten droplets, V-0 After the material is ignited, it will extinguish itself within 1 second after leaving the fire source and there will be no molten droplets, V-0 After the material is ignited, it will extinguish itself within 1 second after leaving the fire source and there will be no molten droplets, V-0 Combining the above table and Figure 3 and Figure 4 It was concluded that, firstly, after using a trifunctional isocyanate-based cross-linking agent to increase the cross-linking degree of polyimide foam, the mechanical properties and rigidity of the product were significantly improved, especially the compressive stress at 10% relative deformation increased by about 41.2%.

[0063] Secondly, reducing the proportion of aromatic dianhydrides containing "bridge" bonds further increases the rigidity of the foam.

[0064] Finally, for ships, reduced weight equates to reduced fuel consumption or increased carrying capacity.

[0065] The polyimide foam prepared by the present invention can be used as a weight-reducing structural foam to replace some steel materials of traditional ships. Compared with the steel material solution, it can reduce the weight of the ship and reduce the energy demand while meeting the use requirements.

[0066] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A cross-linked polyimide rigid foam, characterized in that: The chemical structure is: Wherein R1 is selected from: 。 2. A method for preparing a cross-linked polyimide rigid foam, characterized in that: Includes steps: Step 01, preparing a trifunctional isocyanate crosslinking agent by using aliphatic isocyanate, tributylphosphine and o-toluenesulfonamide; Step 02, according to the order of adding the first difunctional aromatic dianhydride, alcohol solvent, ether solvent, and polar organic solvent, reacting at 55° C. for 10-16 hours to obtain a first monoacid monolipid mixed solution; According to the order of adding the second bifunctional aromatic dianhydride, alcohol solvent, ether solvent, ring-opening catalyst, and polar organic solvent, the reaction is carried out at 55° C. for 10-16 hours to obtain a second monoacid monolipid mixed solution; Mixing the first mono-acid mono-fat mixed liquid and the second mono-acid mono-fat mixed liquid to obtain a foaming material A; Step 03, mixing the trifunctional isocyanate cross-linking agent obtained in step 01 with isocyanate, foam stabilizer and deionized water to obtain foaming material B; Step 04, mixing the foaming material A and the foaming material B in step 02, and injecting air at a rate of 0.5-1NL / min, through stepwise heating and aging conditions of 140°C×6h and then 200°C×8h, and then removing the solvent by vacuum removal at 180°C×8h to obtain a cross-linked polyimide rigid foam.

3. The method for preparing the cross-linked polyimide rigid foam according to claim 2, characterized in that: The chemical structure of monoacid monolipid is: Wherein R1 is selected from: The mono-acid mono-lipid mixed liquid is a mixture of one mono-acid mono-lipid or multiple mono-acid mono-lipids, and each mono-acid mono-lipid mixed liquid is prepared by a separate preparation method.

4. The method for preparing the cross-linked polyimide rigid foam according to claim 2, characterized in that: The aliphatic isocyanate is one of hexamethylene diisocyanate, pentamethylene diisocyanate and isophorone diisocyanate.

5. The method for preparing the cross-linked polyimide rigid foam according to claim 2, characterized in that: The mass ratio of tributylphosphine, o-toluenesulfonamide and aliphatic isocyanate is 0.1-0.2:0.2-0.5:

100.

6. The method for preparing the cross-linked polyimide rigid foam according to claim 2, characterized in that: The difunctional aromatic dianhydride is one or more monomers of bis-anhydride groups such as 2,3,3',4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, pyromellitic dianhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, 4,4'-(4,4'-isopropylidenediphenoxy)bis(phthalic anhydride), 3,3',4,4'-triphenylbisethertetracarboxylic dianhydride, and 3,3',4,4'-tetracarboxylic diphenyl ether dianhydride, and more preferably one or more monomers of 2,3,3',4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, and pyromellitic dianhydride.

7. The method for preparing the cross-linked polyimide rigid foam according to claim 2, characterized in that: The alcohol solvent is one or more alcohols such as methanol, ethanol, propanol, furfuryl alcohol, etc., and the molar ratio of the alcohol solvent to the difunctional aromatic dianhydride is 1:

1.

8. The method for preparing the cross-linked polyimide rigid foam according to claim 2, characterized in that: The ether solvent is tetrahydrofuran, and the amount of the ether solvent used should be 1-2 times the mass of the difunctional aromatic dianhydride; The isocyanate is one or more of PM-200, PM-400, PM-2010, PM-130, polymethylene polyphenyl polyisocyanate, and the mass ratio of isocyanate group to difunctional aromatic dianhydride in the isocyanate is 99:

50.

9. The method for preparing the cross-linked polyimide rigid foam according to claim 2, characterized in that: The polar organic solvent is one or more of ethyl acetate, dichloromethane, acetonitrile, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide; The ring-opening catalyst is one or more of dimethylimidazole and isoquinoline, and the mass ratio of the ring-opening catalyst to the difunctional aromatic dianhydride is 0.5-2:

100.

10. The method for preparing the cross-linked polyimide rigid foam according to claim 2, characterized in that: The foam stabilizer is one or more of AK-8805, AK-158, DC-193, DC-198, L550, L6900, AK-8803, L550, AK-168, octadecyl dimethyl amine oxide, MQ803 and other auxiliary agents, and the mass ratio of the foam stabilizer to the difunctional aromatic dianhydride is 0.5-2:100; The mass ratio of the trifunctional isocyanate-based crosslinking agent to the difunctional aromatic dianhydride is 10-20:100.

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