A crosslinked polyimide rigid foam and its preparation method

Abstract

A crosslinked polyimide rigid foam and its preparation method. The method includes the steps: Step 01, preparing a trifunctional isocyanate group crosslinking agent through aliphatic isocyanate, tributylphosphine, and o-toluenesulfonamide; Step 02, obtaining a first monoacid monoester mixture according to the addition sequence of the first bifunctional aromatic dianhydride, alcohol solvent, ether solvent, and polar organic solvent; obtaining a second monoacid monoester mixture according to the addition sequence of the second bifunctional aromatic dianhydride, alcohol solvent, ether solvent, ring-opening catalyst, and polar organic solvent; mixing the first monoacid monoester mixture and the second monoacid monoester mixture to obtain foaming material A; Step 03, mixing the trifunctional isocyanate group crosslinking agent, isocyanate, foam stabilizer, and deionized water to obtain foaming material B; Step 04, mixing foaming material A and foaming material B to obtain the crosslinked polyimide rigid foam.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer materials, and particularly relates to a crosslinked 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 heat insulation performance, and is an excellent foam cushioning material. However, polyurethane foam is usually not suitable for long-term exposure to temperatures above 150 °C, which will cause significant deterioration of its physical and mechanical properties. At present, there are many solutions to improve the temperature resistance of foams. A 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 properties, but also can withstand extremely low temperatures, with the advantage of not breaking at -267 °C. In recent years, it has been applied to high-tech fields such as liquefied natural gas ocean transportation, cryogenic fuel storage tanks for aerospace vehicles, rocket shells or missile sandwich materials. At present, there are many studies on polyimide foam at home and abroad.

[0003] Chinese patents CN111748094A and CN107540839A disclose a preparation method of polyimide foam. First, an anhydride-terminated polyimide precursor solution is prepared, and then polyisocyanate is slowly added and reacted completely. After cooling to room temperature, the polyimide precursor solution is obtained. Then, most of the polar solvents in the polyimide precursor solution are removed, and then it is cured in a vacuum oven under vacuum conditions to obtain an imidized polyimide precursor foam. The polyimide foam prepared by this method has low density, uniform cell structure and excellent high-temperature resistance, but the foam has low hardness, poor mechanical properties and high slag loss rate, and it 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 and carry out an esterification reaction. After the solution becomes transparent, aromatic diamine and a foam stabilizer are added and mixed evenly to obtain a foam precursor solution; the foam precursor solution is dried, and then the solid product obtained after drying is crushed to obtain polyester ammonium salt (PEAS) powder, and then foaming and imidization reactions are carried out to prepare polyimide foam. The polyimide foam prepared by this method has uniform cell structure, stable quality, good high-temperature resistance and can be recycled; however, the foam preparation process is complex, the cost is high, and no chemical crosslinking occurs during the production process, resulting in low strength.

[0005] Chinese Patent CN112126106A discloses a high-density rigid flame-retardant polyimide foam material and a preparation method thereof. In this method, an anhydride, a low-molecular-weight alcohol, surfactant I, a catalyst, and a blowing agent are mixed evenly to obtain a white foaming material; an isocyanate, a flame retardant, and surfactant II are mixed and stirred to obtain a black foaming material; the white and black foaming materials are mixed in proportion and subjected to microwave curing treatment to obtain a polyimide foam material. The polyimide foam material prepared by this method has the advantages of good heat resistance and low moisture absorption rate, but its products have low crosslinking degree and poor foam rigidity, and it is difficult to meet the use requirements under high strength in fields such as ships, aerospace, etc.

[0006] Therefore, it is urgent to find a more suitable method to solve the problems existing in the above practical applications, and to prepare a weight-reducing structural foam material with high temperature resistance, strong rigidity, excellent mechanical properties, which can meet the requirements of large-scale industrial preparation and can be used as a substitute for steel materials in fields such as aviation, aerospace, and ships. Summary of the Invention

[0007] The present invention provides a crosslinked polyimide rigid foam and a preparation method thereof to solve the deficiencies of the above prior art. The present invention uses an aliphatic difunctional isocyanate polymerization reaction to prepare a trifunctional isocyanate-based crosslinking agent, and the crosslinking degree is increased through the crosslinking agent, thereby increasing the physical and mechanical properties and rigidity of the polyimide foam products. The crosslinked 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 to replace steel materials in fields such as aviation, aerospace, and ships.

[0008] In order to achieve the object of the present invention, the following technologies are proposed:

[0009] A crosslinked polyimide rigid foam, the chemical structural formula is

[0010] wherein R1 is selected from:

[0011]

[0012] A preparation method of a crosslinked polyimide rigid foam, comprising the steps:

[0013] Step 01, a trifunctional isocyanate-based crosslinking agent is prepared by using an aliphatic isocyanate, tributylphosphine, and o-toluenesulfonamide;

[0014] Step 02, according to the addition sequence of the first difunctional aromatic dianhydride, an alcohol solvent, an ether solvent, and a polar organic solvent, at a temperature of 55 °C, react for 10 - 16 h to obtain a first monoacid monoester mixed solution;

[0015] In the order of adding the second bifunctional aromatic dianhydride, alcohol solvent, ether solvent, ring-opening catalyst, and polar organic solvent, react at 55 °C for 10 - 16 h to obtain a second monoacid monoester mixture;

[0016] Mix the first monoacid monoester mixture and the second monoacid monoester mixture to obtain foaming material A;

[0017] Step 03, mix a trifunctional isocyanate-based crosslinking agent, isocyanate, foam stabilizer, and deionized water to obtain foaming material B;

[0018] Step 04, mix the foaming material A after reducing the temperature to 10 °C with the foaming material B, inject air at a rate of 0.5 - 1 NL / min, and cure under stepped heating conditions of first 140 °C × 6 h and then 200 °C × 8 h. Subsequently, remove the solvent by vacuum under the condition of 180 °C × 8 h to obtain crosslinked polyimide rigid foam.

[0019] Furthermore, the chemical structural formula of the monoacid monoester is:

[0020]

[0021] wherein R1 is selected from:

[0022]

[0023] The monoacid monoester mixture is composed of one kind of monoacid monoester or a mixture of multiple monoacid monoesters, and each monoacid monoester mixture is prepared by a separate preparation method.

[0024] Furthermore, the aliphatic isocyanate is one of hexamethylene diisocyanate, pentamethylene diisocyanate, and isophorone diisocyanate.

[0025] Furthermore, the mass ratio of tributylphosphine, o-toluenesulfonamide, and aliphatic isocyanate is 0.1 - 0.2 : 0.2 - 0.5 : 100.

[0026] Further, the bifunctional aromatic dianhydride is one or more of monomers with a dianhydride group 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'-isopropylidenediphenoxy)bis(phthalic anhydride), 3,3',4,4'-triphenyl diether tetracarboxylic dianhydride, 3,3',4,4'-tetracarboxylic diphenyl ether dianhydride, etc., 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, pyromellitic dianhydride.

[0027] Further, the alcohol solvent is one or more of alcohols such as methanol, ethanol, propanol, and furfuryl alcohol, and the molar ratio of the alcohol solvent to the bifunctional aromatic dianhydride is 1:1.

[0028] Further, the ether solvent is tetrahydrofuran, and the usage amount of the ether solvent should be 1-2 times the mass of the bifunctional aromatic dianhydride.

[0029] Further, the polar organic solvent is one or more of ethyl acetate, dichloromethane, acetonitrile, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide.

[0030] Further, the foam stabilizer is one or more of auxiliaries such as AK-8805, AK-158, DC-193, DC-198, L550, L6900, AK-8803, L550, AK-168, octadecyl dimethyl amine oxide, MQ803, etc., and the mass ratio of the foam stabilizer to the bifunctional aromatic dianhydride is 0.5-2:100.

[0031] Further, the isocyanate is one or more of PM-200, PM-400, PM-2010, PM-130, and polymethylene polyphenyl polyisocyanate, and the molar ratio of the isocyanate group in the isocyanate to the bifunctional aromatic dianhydride is 99:50.

[0032] Further, the ring-opening catalyst is one or more of dimethylimidazole and isoquinoline, and the mass ratio of the ring-opening catalyst to the bifunctional aromatic dianhydride is 0.5-2:100.

[0033] Further, the mass ratio of the trifunctional isocyanate group crosslinking agent to the bifunctional aromatic dianhydride is 10-20:100.

[0034] The advantages of the above technical solutions are as follows:

[0035] Referring to the synthesis principle of polyimide, a trifunctional isocyanate-based crosslinking agent was prepared by the polymerization reaction of aliphatic difunctional isocyanate. It can be mixed with component B and participate in the foaming process for chemical reaction, thereby increasing the crosslinking degree and further enhancing the physical and mechanical properties and rigidity of the polyimide foam products. Meanwhile, the products have more excellent thermodynamic properties and will not soften and melt due to the increase in environmental temperature.

[0036] The present invention prepares polyimide foam by an extrusion foaming process. First, component A and component B are prepared separately. After the temperatures of component A and component B are reduced to the specified temperature, they are stirred and mixed and then extruded into a mold for foaming. The foaming process is highly mechanized, continuous, and stable, with high foam production efficiency, which can meet the needs of large-scale low-cost industrial production. Before the gas is released in the foaming system, the present invention reduces the temperatures of component A and component B, and controls the foaming speed of the foaming system by controlling the reaction temperature, avoiding process defects such as the collapse of foam products, foam cracking, and uneven cell structure caused by too fast foaming speed.

[0037] In the selection of aromatic dianhydrides, the present invention selects different aromatic dianhydrides to design the polyimide molecular chain in terms of structure. By reducing the usage ratio of bifunctional aromatic dianhydrides containing "bridge" bonds such as -O-, -C(=O)-, -S-, etc., the intramolecular rotation activation energy is increased, thereby enhancing the rigidity of the molecular chain and the intermolecular interaction force, and preparing thermosetting polyimide foam that meets the requirements.

[0038] In the specific application of the expandable present invention, flame retardants, glass fibers, carbon fibers, wollastonite, absorbents and other fillers can be additionally used when adding foam stabilizers to enhance the properties of the foam material. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings.

[0040] Figure 1 Shows the "density-pressure" correlation of crosslinked polyimide rigid foam.

[0041] Figure 2 Shows the infrared spectrum of crosslinked polyimide rigid foam after imidization.

[0042] Figure 3 Shows the patterns of the materials prepared through each example and each comparative example. In the pattern, sample No. 1 is the foam material prepared in Example 1, sample No. 2 is the foam material prepared in Example 2, sample No. 3 is the foam material prepared in Example 3, sample No. 4 is the foam material prepared in Comparative Example 1, and sample No. 5 is the foam material prepared in Comparative Example 2.

[0043] Figure 4 The result patterns after the flat tensile test of the materials prepared through various embodiments and comparative examples are shown, and their placement order corresponds to the specimens shown in Figure 3 . Detailed implementation manners

[0044] In the present invention, a cubic constrained foaming space is constructed on a hot-pressed plane to prepare polyimide rigid foam. Different densities of polyimide rigid foam can be achieved through the design of the size of the foaming space. Considering the sharp increase in pressure during the foaming process, the constant pressure provided by the press must be large enough. To avoid the press being unable to press the foaming foam, resulting in foaming failure and even safety accidents such as machine explosion, the relationship between the density and pressure during foam preparation is studied. As Figure 1 shown, it can be seen from the figure that as the pressure increases, the foam density of the crosslinked polyimide rigid foam also increases accordingly. Therefore, in specific applications, the reasonable pressure can be set according to actual needs. Furthermore, during the production process, the safety of foam production can be increased, meeting the requirements for the safe and sustainable production of enterprises.

[0045] To verify the preparation effect of the preparation method of the crosslinked polyimide rigid foam proposed by the present invention, the prepared crosslinked polyimide rigid foam was subjected to infrared spectroscopy test, and the test results are as Figure 2 shown. Combining with the infrared characteristic absorption peak analysis diagram of the main chemical groups in the "Handbook of Chemical and Chemical Experimenters", it can be known that in the figure, 1371.01 cm -1 should be the stretching vibration peak of C-N, and 1778.93 cm -1 and 1719.00 cm -1 are respectively the asymmetric stretching vibration absorption peak and symmetric stretching vibration absorption peak of C=O, and 1371.01 cm -1 and 729.67 cm -1 are respectively the characteristic absorption peaks of the stretching and bending vibrations of the C-N-C bond on the imide ring.

[0046] Example 1

[0047] Step 01, under the condition of N2, add 3.36 kg of hexamethylene diisocyanate to the flask. After stirring and heating to 70 °C, dropwise add a mixed solution of 3.36 g of tributylphosphine and 800 g of xylene. After the dropping is completed, continue to react for 2 h, add 6.72 g of o-toluenesulfonamide, and continue to react for 0.5 h. The trifunctional isocyanate group crosslinking agent is obtained through distillation recovery.

[0048] Step 02: Add 11.16 kg of 3,3’,4,4’-benzophenone 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 into the flask in sequence, and reflux and stir for reaction at 55 °C for 10 h to obtain the first monoacid monoester mixture.

[0049] Take another flask and add 7.56 kg of pyromellitic dianhydride, 1.61 kg of ethanol, 7.56 kg of tetrahydrofuran, 1.51 kg of N,N-dimethylformamide, and 0.07 kg of dimethylimidazole into it in sequence, and reflux and stir for reaction at 55 °C for 10 h to obtain the second monoacid monoester mixture.

[0050] Mix the first monoacid monoester mixture and the second monoacid monoester mixture to obtain foaming material A.

[0051] Step 03: Add 2.81 kg of trifunctional isocyanate-based 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 into it in sequence, and stir and mix to obtain foaming material B.

[0052] Step 04: Add foaming material A and foaming material B into the A material tank and the B material tank respectively. After the temperature drops to 10 °C, mix foaming material A and foaming material B and inject air at a speed of 1 NL / min. After 10 s, extrude it into a steel mold of 1300 mm×700 mm×300 mm. Seal the steel mold and keep it under pressure for 3 h to complete curing. Cure it by heating at 140 °C for 6 h and 200 °C for 8 h, and remove the solvent at 180 °C for 8 h under vacuum conditions to obtain crosslinked polyimide rigid foam.

[0053] Example 2

[0054] Step 01: Under N2 condition, add 3.36 kg of hexamethylene diisocyanate into the flask, stir and heat up to 70 °C, and then dropwise add a mixed solution of 3.36 g of tributylphosphine and 800 g of xylene.

[0055] After the dropping is completed, continue the reaction for 2 h, add 6.72 g of o-toluenesulfonamide, and continue the reaction for 0.5 h, and obtain the trifunctional isocyanate-based crosslinking agent through distillation recovery.

[0056] Step 02: Add 11.16 kg of 3,3’,4,4’-benzophenone 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 into the flask in sequence, and reflux and stir for reaction at 55 °C for 10 h to obtain the first monoacid monoester mixture.

[0057] Another flask was successively added with 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, and refluxed and stirred at 55 °C for 10 h to obtain the second monoacid monoester mixture.

[0058] The first monoacid monoester mixture and the second monoacid monoester mixture were mixed to obtain the foaming material A.

[0059] In step 03, 3.21 kg of trifunctional isocyanate-based 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 were successively added, and after stirring and mixing, the foaming material B was obtained.

[0060] In step 04, the foaming material A and the foaming material B were respectively added to the tank A and the tank B. After the temperature was reduced to 10 °C, the foaming material A and the foaming material B were mixed and air was injected at a speed of 1 NL / min. After 10 s, it was extruded into a steel mold of 1300 mm×700 mm×300 mm. After sealing the steel mold, it was kept under pressure for 3 h to complete curing, and then heat-cured at 140 °C×6 h and 200 °C×8 h, and the solvent was removed at 180 °C×8 h under vacuum conditions to obtain the crosslinked polyimide rigid foam.

[0061] Example 3

[0062] In step 01, under N2 condition, 3.36 kg of hexamethylene diisocyanate was added to the flask, and after stirring and heating to 70 °C, a mixed solution of 3.36 g of tributylphosphine and 800 g of xylene was added dropwise.

[0063] After the dropwise addition was completed, the reaction continued for 2 h, 6.72 g of o-toluenesulfonamide was added, and the reaction continued for 0.5 h. The trifunctional isocyanate-based crosslinking agent was obtained by distillation and recovery.

[0064] In step 02, 11.16 kg of 3,3’,4,4’-benzophenone 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 were successively added to the flask, and refluxed and stirred at 55 °C for 10 h to obtain the first monoacid monoester mixture.

[0065] Another flask was successively added with 7.56 kg of pyromellitic dianhydride, 1.61 kg of ethanol, 7.56 kg of tetrahydrofuran, 1.51 kg of N,N-dimethylformamide, and 0.07 kg of dimethylimidazole, and refluxed and stirred at 55 °C for 10 h to obtain the second monoacid monoester mixture.

[0066] Mix the first monoacid monoester mixture and the second monoacid monoester mixture to obtain foaming material A.

[0067] Step 03: Sequentially add 2.81 kg of trifunctional isocyanate-based crosslinking agent, 19.60 kg of PM-200, 0.18 kg of DC-193, and 1.80 kg of deionized water. After stirring and mixing, foaming material B is obtained.

[0068] Step 04: Add foaming material A and foaming material B to the A material tank and the B material tank respectively. After the temperature drops to 10°C, mix foaming material A and foaming material B and inject air at a speed of 1 NL / min. After 10 s, extrude it into a steel mold of 1300 mm×700 mm×300 mm. After sealing the steel mold, keep the pressure for 3 h to complete curing. Heat and cure at 140°C×6 h and 200°C×8 h, and remove the solvent at 180°C×8 h under vacuum conditions to obtain crosslinked polyimide rigid foam.

[0069] Comparative Example 1

[0070] Step 01: Sequentially add 11.16 kg of 3,3’,4,4’-benzophenone 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 a flask. Stir and react under reflux at 55°C for 10 h to obtain the first monoacid monoester mixture.

[0071] Take another flask and sequentially add 7.56 kg of pyromellitic dianhydride, 1.61 kg of ethanol, 7.56 kg of tetrahydrofuran, 1.51 kg of N,N-dimethylformamide, and 0.07 kg of dimethylimidazole. Stir and react under reflux at 55°C for 10 h to obtain the second monoacid monoester mixture.

[0072] Mix the two first monoacid monoester mixtures and the second monoacid monoester mixture to obtain foaming material A.

[0073] Step 02: Sequentially 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. After stirring and mixing, foaming material B is obtained.

[0074] Step 03: Add foaming material A and foaming material B to the A material tank and the B material tank respectively. After the temperature drops to 10°C, mix foaming material A and foaming material B and inject air at a speed of 1 NL / min. After 10 s, extrude it into a steel mold of 1300mm*×700 mm×300 mm. After sealing the steel mold, keep the pressure for 3 h to complete curing. Heat and cure at 140°C×6 h and 200°C×8 h, and remove the solvent at 180°C×8 h under vacuum conditions to obtain polyimide rigid foam.

[0075] Comparative Example 2

[0076] Step 01: Add 11.16 kg of 3,3’,4,4’-benzophenone 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 into a flask in sequence. Stir and react under reflux at 55 °C for 10 h to obtain the first monoacid monoester mixture.

[0077] Take another flask and add 10.85 kg of 3,3’,4,4’-diphenylether tetracarboxylic dianhydride, 1.61 kg of ethanol, 10.85 kg of tetrahydrofuran, 2.17 kg of N,N-dimethylformamide, and 0.10 kg of dimethylimidazole into it in sequence. Stir and react under reflux at 55 °C for 10 h to obtain the second monoacid monoester mixture.

[0078] Mix the two monoacid monoester mixtures to obtain foaming material A.

[0079] 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 into a container in sequence. Stir and mix them to obtain foaming material B.

[0080] Step 03: Add foaming material A and foaming material B into the A material tank and the B material tank respectively. After the temperature drops to 10 °C, mix foaming material A and foaming material B and inject air at a speed of 1 NL / min. After 10 s, extrude the mixture into a steel mold with the size of 1300 mm × 700 mm × 300 mm. Seal the steel mold and keep it under pressure for 3 h to complete curing. Then, heat and cure it at 140 °C for 6 h and 200 °C for 8 h, and remove the solvent at 180 °C for 8 h under vacuum conditions to obtain polyimide foam.

[0081] Among the above examples, compared with Example 1, in Comparative Example 1, the self-made trifunctional isocyanate-based crosslinking agent was not used. On the basis of Comparative Example 1, in Comparative Example 2, a large amount of aromatic dianhydrides containing “bridge” bonds such as -O-, -C(=O)-, -S- were used.

[0082] Performance test table of crosslinked polyimide rigid foam or polyimide foam prepared in each example and comparative example

[0083] Test item Test method Example 1 Example 2 Example 3 Comparative example 1 Comparative example 2 <![CDATA[Density (kg / m 3 )]]> GB / T 6343 149.7 149.5 150.1 150.0 149.6 Tensile strength (MPa) GB / T 6344 1.63 1.65 1.50 1.42 1.37 Compression stress at 10% relative deformation (MPa) GB / T 8813 1.37 1.38 1.29 0.97 0.81 Thermal conductivity (W / m·K) GB / T 10295 0.03913 0.03988 0.03952 0.04004 0.03989 Flammability resistance GB / T 2408 The material extinguishes itself within 1 s after leaving the fire source and has no molten droplets, V-0 The material extinguishes itself within 1 s after leaving the fire source and has no molten droplets, V-0 The material extinguishes itself within 1 s after leaving the fire source and has no molten droplets, V-0 The material extinguishes itself within 1 s after leaving the fire source and has no molten droplets, V-0 The material extinguishes itself within 1 s after leaving the fire source and has no molten droplets, V-0

[0084] Combined with the above table and Figure 3 and Figure 4 It is concluded that, first of all, after using the trifunctional isocyanate-based crosslinking agent to increase the crosslinking degree of polyimide foam, the mechanical properties and rigidity of the product are significantly improved. Especially, the compressive stress at 10% relative deformation increases by about 41.2%.

[0085] Secondly, after reducing the usage ratio of the aromatic dianhydride containing "bridge" bonds, the foam rigidity is further increased.

[0086] Finally, for ships, a reduction in weight is equivalent to fuel consumption savings or an increase in carrying capacity.

[0087] The polyimide foam prepared by the present invention can be used as a weight-reducing structural foam to replace some of the traditional steel materials in ships. Compared with the steel material solution, it can reduce the ship weight and energy demand on the basis of meeting the usage requirements.

[0088] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Obviously, those skilled in the art can make various modifications and variations 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 equivalent technologies, 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 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, injecting air at a rate of 0.5-1NL / min, and performing 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; in, The aliphatic isocyanate is one of hexamethylene diisocyanate, pentamethylene diisocyanate and isophorone diisocyanate; The isocyanate is one or more of PM-200, PM-400, PM-2010, PM-130, and polymethylene polyphenyl polyisocyanate.

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 mass ratio of tributylphosphine, o-toluenesulfonamide and aliphatic isocyanate is 0.1-0.2:0.2-0.5:

100.

5. 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 of 2,3,3',4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride and pyromellitic dianhydride.

6. 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.

7. 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 mass ratio of isocyanate groups to difunctional aromatic dianhydride in isocyanate is 99:

50.

8. 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.

9. 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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