A hyperbranched polyimide flexible foam and a method of making the same

Abstract

A hyperbranched polyimide flexible foam and its preparation method are disclosed. The method includes the following steps: Step 01, sequentially mixing a first type of difunctional aromatic dianhydride, an alcohol solvent, an ether solvent, and a polar organic solvent, and reacting under reflux and stirring to obtain a first type of monoacid-monoester mixture; Step 02, sequentially mixing a second type of difunctional aromatic dianhydride, an alcohol solvent, an ether solvent, a ring-opening catalyst, and a polar organic solvent, and reacting under reflux and stirring to obtain a second type of monoacid-monoester mixture; Step 03, mixing the first type of monoacid-monoester mixture obtained in Step 01 and the second type of monoacid-monoester mixture obtained in Step 02, and adding a polyfunctional isocyanate, stirring until the gas evaporates; Step 04, adding a foam stabilizer and deionized water to the mixture obtained in Step 03, and stirring; Step 05, injecting air into the mixture obtained in Step 04 to obtain a hyperbranched polyimide flexible foam.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a hyperbranched polyimide flexible foam and its preparation method. Background Technology

[0002] Polyimide foam (PI) is a foam material formed by the polymerization and foaming reaction of polyimide resin raw materials with foaming agents, fillers, and other additives. The polyimide foam molecular chain contains imide rings, and these imide rings are heterocyclic rings containing nitrogen and oxygen atoms. This unique rigid imide cyclic molecular structure endows it with excellent heat resistance, oxidation resistance, insulation, radiation resistance, and low-temperature resistance. High-performance polyimide foam can even withstand extremely low temperatures, exhibiting the advantage of not breaking at -267°C. It is widely used in aerospace, aviation, and engineering materials, and has also driven the rapid development of the polyimide foam industry.

[0003] Chinese patent CN118005987A discloses a method for preparing polymethacrylimide foam (PMI). The method involves mixing and polymerizing methacrylic acid, 1-aminooctadecane, allyl methacrylate, tridecyl methacrylate, an initiator, a blowing agent, and a solvent to prepare a copolymer board. This board is then subjected to stepwise heating and drying to obtain polymethacrylimide foam (PMI). This method is a commonly used polyimide preparation process in the industry. The imide structure is formed by the rearrangement and cyclization of cyano and carboxyl groups. Furthermore, the -CN groups in the MAN segment can also rearrange to form a ladder structure. Therefore, although this foam has high strength and good high-temperature resistance, making it suitable as a substitute for steel materials in various industries, its high rigidity makes it brittle and prone to breakage, and its high foam density greatly limits its application in shipbuilding, aerospace, and other fields.

[0004] Patents WO2004072032A2, US6956066B2, US7541388, US2006063848, and Chinese patent CN114854009A disclose a method for preparing a diacid diester precursor solution by reacting dianhydride, alcohol, catalyst, crosslinking agent, excipients, and solvent, and then adding isocyanate to the precursor solution to prepare polyimide foam. The polyimide foam prepared by this method has good overall performance, but it suffers from severe foam shedding, low tensile strength, and rapid spontaneous gas generation after the addition of isocyanate during processing, making it difficult to stir evenly, control the foaming process, and resulting in a low yield of foam products.

[0005] US patents US4804504, US4814357, US4855332, US4952611, and US5064867, and Chinese patent CN114044903A disclose a method for preparing rigid polyimide foam. This method uses acid anhydride, norborneol, a polar solvent, a catalyst, and aromatic diamines as raw materials to react and generate polyester ammonium salt (PEAS), which is then heated and foamed to obtain polyimide foam. While this polyimide foam exhibits high temperature resistance, good toughness, low compression deformation at high temperatures, and recyclability, the process is complex, and the polyimide segments within the foam have a one-dimensional linear structure without three-dimensional network cross-linking. This results in lower strength and poor high-temperature resistance in the finished product, making it difficult to use for extended periods in complex high-temperature and high-strength environments.

[0006] Currently, the preparation of polyimide foam using a self-foaming method still suffers from problems such as excessively vigorous foaming, severe cell collapse, and low yield. Therefore, there is an urgent need to develop a flexible polyimide foam with low density, uniform cell size, adequate strength, and low shedding rate, which can be used as a weight-reducing, heat-insulating, and flame-retardant material in aerospace, aviation, and shipbuilding fields. Summary of the Invention

[0007] This invention provides a hyperbranched polyimide flexible foam and its preparation method to overcome the shortcomings of the prior art. The polyimide foam intermediate prepared by this invention is a monoacid monoester rather than a diacid diester structure, which can improve the quality problems of high slag shedding rate and low strength of foam products.

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

[0009] A hyperbranched polyimide flexible foam, with the following chemical structural formula:

[0010] ;

[0011] in,

[0012] R1 is selected from:

[0013] .

[0014] A method for preparing hyperbranched polyimide flexible foam, comprising the following steps:

[0015] Step 01: The first type of bifunctional aromatic dianhydride, alcohol solvent, ether solvent and polar organic solvent are mixed in sequence, and the reaction is carried out by reflux and stirring to obtain the first type of monoacid monoester mixture. The reaction temperature is about 55℃ and the reaction time is 10-16h.

[0016] Step 02: The second type of bifunctional aromatic dianhydride, alcohol solvent, ether solvent, ring-opening catalyst, and polar organic solvent are mixed sequentially, and the reaction is carried out by reflux and stirring to obtain the second type of monoacid monoester mixture. The reaction temperature is about 55℃ and the reaction time is 10-16h.

[0017] Step 03: Mix the first monoacid monoester mixture obtained in Step 01 and the second monoacid monoester mixture obtained in Step 02, and add polyfunctional isocyanate, stirring until the gas evaporates;

[0018] Step 04: Add foam stabilizer and deionized water to the mixture obtained in step 03, and mechanically stir at 1000-1500 r / min for 1-2 h, and then stir by microwave stirring at 20 kHz for 1-2 h.

[0019] Step 05: Inject air into the mixture obtained in Step 04 at a rate of 0.5-1 NL / min, then inject the mixture into the mold and successively heat it at 60°C for 4 hours, 150°C for 4 hours, and 220°C for 4 hours in a stepped heating or microwave curing manner to obtain hyperbranched polyimide flexible foam.

[0020] Furthermore, the chemical structural formula of the monoacid monoester is as follows:

[0021] ;

[0022] R1 is selected from:

[0023] ;

[0024] The monoacid-monolithic acid mixture can be a mixture of one or more monoacid-monolithic acids, and each monoacid-monolithic acid mixture is prepared separately.

[0025] Furthermore, the first type of difunctional aromatic dianhydride and the second type of difunctional aromatic dianhydride are one or more monomers containing diacid 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'-isopropylidenediphenoxy)bis(phthalic anhydride), 3,3',4,4'-triphenyl diether tetracarboxylic dianhydride, and 3,3',4,4'-tetracarboxylic diphenyl ether dianhydride.

[0026] Furthermore, the alcohol solvent is one or more alcohols such as methanol, ethanol, propanol, and furfuryl alcohol, and the mass ratio of the alcohol solvent to the first type of difunctional aromatic dianhydride or the second type of difunctional aromatic dianhydride is 1:1. When the alcohol solvent is in excess, esterification is performed to form a diacid ester.

[0027] Furthermore, the ether solvent is tetrahydrofuran, and the mass of the ether solvent is 4-6 times that of the first or second type of difunctional aromatic dianhydride. When the ether solvent is used in excess, it can reduce the surface tension of the system, thereby facilitating the release of gas.

[0028] Furthermore, the polar organic solvent is one or more of ethyl acetate, dichloromethane, acetonitrile, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide.

[0029] Furthermore, the foam stabilizer is one or more of the following additives: AK-8805, AK-158, DC-193, DC-198, L550, L6900, AK-8803, L550, AK-168, octadecyl dimethylamine oxide, MQ803, etc., and the mass ratio of the foam stabilizer to the first type of difunctional aromatic dianhydride or the second type of difunctional aromatic dianhydride is 0.5-2:100.

[0030] Furthermore, the polyfunctional isocyanate is one or more of PM-200, PM-400, PM-2010, PM-130, and polymethylene polyphenyl polyisocyanate, and the mass ratio of the isocyanate group to the first difunctional aromatic dianhydride or the second difunctional aromatic dianhydride in the polyfunctional isocyanate is 99:50.

[0031] Furthermore, the ring-opening catalyst is one or more of dimethylimidazolium and isoquinoline, and the mass ratio of the ring-opening catalyst to the first difunctional aromatic dianhydride or the second difunctional aromatic dianhydride is 0.5-2:100.

[0032] The advantages of the above technical solution are:

[0033] This invention uses aromatic dianhydrides with different difunctionalities dissolved in alcohol solvents, ether solvents, and catalysts, and refluxes them at high temperatures to generate a mixture of monoacid and monoester. Then, polyfunctional isocyanates are added. After the system spontaneously generates gas CO2 and it completely evaporates, foam stabilizers, foaming agents, etc. are added, stirred evenly, and foamed by stepwise heating to obtain hyperbranched polyimide flexible foam material.

[0034] The polyimide foam prepared by this invention has anhydride-terminated groups, which improves the physical and mechanical properties of the foam products. Furthermore, preliminary experiments show that directly esterifying difunctional aromatic dianhydrides into dicarboxylic acid esters results in foam products with high slagging rate and low strength. Esterifying them into monocarboxylic acid esters solves this quality problem. Since different difunctional aromatic dianhydrides have varying active electron affinities (Ea), and it is difficult to ensure consistent reaction rates among the different difunctional aromatic dianhydrides, material A is prepared by first esterifying each into a monocarboxylic acid ester separately and then mixing them according to usage requirements. Under the original process, the addition of isocyanate caused the mixture to react rapidly and violently, generating bubbles that easily led to large-scale foam collapse. Bubble size was difficult to control, and insufficient stirring time resulted in uneven mixing, leading to a series of product quality problems.

[0035] This invention does not use the system's own generated gas CO2 for foaming. Instead, it reduces the surface tension of the system to completely break the bubbles generated by the system's own generated gas CO2. After the gas evaporates, foam stabilizer and water are added, and the mixture is stirred evenly under the combined action of long-term mechanical stirring and ultrasonic stirring. The hyperbranched polyimide flexible foam is prepared by continuously foaming and imidizing through a step-by-step heating method.

[0036] The hyperbranched polyimide flexible foam prepared by this invention has controllable foam density and cell size, stable foam product quality, and uniform cell size, which can meet the needs of continuous large-scale industrial production.

[0037] This invention injects a small amount of air into the foaming system, which can form a large number of micro-bubble nuclei inside the polyimide under high-speed stirring. This makes the foam produced by the polyimide foam more uniform and delicate in terms of pore size, and less prone to flaking, thereby enhancing product performance and meeting the needs of continuous large-scale industrial production.

[0038] The hyperbranched polyimide flexible foam prepared by this invention can be further enhanced with fillers such as flame retardants, glass fibers, carbon fibers, wollastonite, and absorbents when adding foam stabilizers, depending on the intended use. Attached Figure Description

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will now be described in further detail with reference to the accompanying drawings.

[0040] Figure 1 The infrared spectrum of the hyperbranched polyimide flexible foam material after imidization is shown.

[0041] Figure 2 A physical image of the hyperbranched polyimide flexible foam prepared in Example 1 is shown.

[0042] Figure 3A physical image of the hyperbranched polyimide flexible foam prepared in Comparative Example 2 is shown.

[0043] Figure 4 A cross-sectional view of the hyperbranched polyimide flexible foam prepared in Comparative Example 2 is shown. Detailed Implementation

[0044] To verify the foam synthesis effect, foam was prepared using the stated preparation method and subjected to infrared spectroscopy testing. For example... Figure 1 The image shows the infrared spectrum of hyperbranched polyimide flexible foam material after imidization. Combined with the infrared characteristic absorption peak analysis chart of major chemical groups in the "Chemical and Chemical Engineering Experimenter's Handbook," the peak value at 1371.14 cm⁻¹ is [missing information]. -1 It should be the stretching vibration peak of CN, 1778.00 cm⁻¹ -1 and 1719.41cm -1 These are the absorption peaks of the asymmetric stretching vibration and the symmetric stretching vibration of C=O, respectively, at 1371.14 cm⁻¹. -1 and 722.06cm -1 These are the characteristic absorption peaks of the stretching and bending vibrations of the CNC bond on the imide ring, respectively.

[0045] Example 1

[0046] Step 01: 322.2g of 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 46.0g of ethanol, 1288.8g of tetrahydrofuran, 322.2g of N,N-dimethylformamide, and 3.2g of dimethylimidazole were added sequentially to the flask. The mixture was refluxed and stirred at 55°C for 10 hours until the mixture became clear and transparent, thus obtaining the first monoacid-monoester mixture.

[0047] Step 02: Add 310.2g of 3,3',4,4'-tetracarboxylic acid diphenyl ether dianhydride, 46.0g of ethanol, 1240.8g of tetrahydrofuran, 310.2g of N,N-dimethylformamide, and 3.2g of dimethylimidazole to the flask in sequence. Reflux and stir at 55°C for 10 hours until the mixture is clear and transparent to obtain the second monoacid monoester mixture.

[0048] Step 03: Mix the first monoacid monoester mixture and the second monoacid monoester mixture, add 554.4g of polyphenyl polymethylene polyisocyanate, and continue stirring until the gas is completely volatilized. Then add 6.3g of AK-8805 and 63g of deionized water, and continue stirring at 1000r / min for 2h using mechanical stirring. Then stir under microwave at 20kHz for 2h.

[0049] Step 04: Inject a small amount of air into the mixture at a rate of 0.8 NL / min, transfer the mixture to the mold, and allow it to foam freely at 60℃×4h, 150℃×4h, and 220℃×4h in sequence to obtain hyperbranched polyimide flexible foam.

[0050] Comparative Example 1

[0051] Step 01: 322.2g of 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 92.0g of ethanol, 1288.8g of tetrahydrofuran, 322.2g of N,N-dimethylformamide, and 6.3g of dimethylimidazole were added sequentially to the flask. The mixture was refluxed and stirred at 55°C for 10 hours until the mixture became clear and transparent, thus obtaining the first monoacid-monoester mixture.

[0052] Step 02: 310.2g of 3,3',4,4'-tetracarboxylic acid diphenyl ether dianhydride, 92.0g of ethanol, 1240.8g of tetrahydrofuran, 310.2g of N,N-dimethylformamide, and 6.3g of dimethylimidazole were added sequentially to the flask. The mixture was refluxed and stirred at 55°C for 10 hours until the mixture became clear and transparent, thus obtaining the second monoacid monoester mixture.

[0053] Step 03: Mix the first monoacid monoester mixture and the second monoacid monoester mixture, add 554.4g of polyphenyl polymethylene polyisocyanate, and continue stirring until the gas is completely volatilized. Then add 6.3g of AK-8805 and 63g of deionized water, and continue stirring at 1000r / min for 2h using mechanical stirring. Then stir under microwave at 20kHz for 2h.

[0054] Step 04: Inject a small amount of air into the mixture at a rate of 0.8 NL / min, transfer the mixture to the mold, and allow it to foam freely at 60℃×4h, 150℃×4h, and 220℃×4h in sequence to obtain polyimide flexible foam.

[0055] Comparative Example 2

[0056] Step 01: 322.2g of 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 92.0g of ethanol, 644.4g of tetrahydrofuran, 322.2g of N,N-dimethylformamide, and 6.3g of dimethylimidazole were added sequentially to the flask. The mixture was refluxed and stirred at 55°C for 10 hours until the mixture became clear and transparent, thus obtaining the first monoacid-monoester mixture.

[0057] Step 02: 310.2g of 3,3',4,4'-tetracarboxylic acid diphenyl ether dianhydride, 92.0g of ethanol, 644.4g of tetrahydrofuran, 310.2g of N,N-dimethylformamide, and 6.3g of dimethylimidazole were added sequentially to the flask. The mixture was refluxed and stirred at 55°C for 10 hours until the mixture became clear and transparent, thus obtaining the second monoacid-monoester mixture.

[0058] Step 03: Mix the first monoacid monoester mixture and the second monoacid monoester mixture, then add 6.3g of AK-8805 and 554.4g of polyphenyl polymethylene polyisocyanate sequentially, and continue stirring to foam. After foaming, heat and cure at 150℃×4h and 220℃×4h to obtain polyimide flexible foam.

[0059] In Comparative Example 1, the amount of alcohol solvent used was doubled compared to Example 1, which enabled all the difunctional aromatic dianhydrides to react into diacid esters. Comparative Example 2, based on Comparative Example 1, reduced the amount of ether solvent used, and subsequently generated CO gas. 2 Foaming molding.

[0060] Table of properties of hyperbranched polyimide flexible foams prepared in each embodiment and comparative example

[0061] ;

[0062] In summary, and in combination with Figures 2 to 4 As shown in the table above, after changing the synthetic dicarboxylic acid ester to monocarboxylic acid ester, the mechanical strength of the foam was significantly improved, and the problem of foam shedding was basically solved. At the same time, after improving the foaming process, the foam cells were more uniform, the density was controllable, and no obvious collapse phenomenon was found.

[0063] For ships, weight reduction equates to fuel savings or increased carrying capacity. The polyimide foam prepared in this invention can serve as a substitute for traditional shipbuilding mineral wool materials. Compared to the original solution, it can reduce ship weight and energy demand while meeting usage requirements.

[0064] The above description is merely 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 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 equivalents, the present invention also intends to include these modifications and variations.

Claims

1. A method for preparing hyperbranched polyimide flexible foam, comprising the following steps: Step 01: 322.2g of 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 46.0g of ethanol, 1288.8g of tetrahydrofuran, 322.2g of N,N-dimethylformamide, and 3.2g of dimethylimidazole were added sequentially to the flask. The mixture was refluxed and stirred at 55°C for 10 hours until the mixture became clear and transparent, thus obtaining the first monoacid monoester mixture. Step 02: Add 310.2g of 3,3',4,4'-tetracarboxylic acid diphenyl ether dianhydride, 46.0g of ethanol, 1240.8g of tetrahydrofuran, 310.2g of N,N-dimethylformamide, and 3.2g of dimethylimidazole to the flask in sequence. Reflux and stir at 55°C for 10 hours until the mixture is clear and transparent to obtain the second monoacid monoester mixture. Step 03: Mix the first monoacid monoester mixture and the second monoacid monoester mixture, add 554.4g of polyphenyl polymethylene polyisocyanate, and continue stirring until the gas is completely volatilized. Then add 6.3g of AK-8805 and 63g of deionized water, and continue stirring at 1000r / min for 2h using mechanical stirring. Then stir under microwave at 20kHz for 2h. Step 04: Inject air into the mixture at a rate of 0.8 NL / min, transfer the mixture to the mold, and allow it to foam freely at 60℃×4h, 150℃×4h, and 220℃×4h in sequence to obtain hyperbranched polyimide flexible foam.

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