A supercritical polyimide foam and a method of making the same

Abstract

The application discloses a supercritical polyimide foam and a preparation method thereof. The supercritical polyimide foam is prepared by chemical foaming and physical foaming of a polyimide precursor, polyamide acid, obtained by reaction of aromatic dianhydride and aromatic diamine in a polar solvent under a supercritical state, and the supercritical fluid can be integrated before imidization to form a rigid imine ring, so that fine and homogeneous cells are prepared by the supercritical fluid technology, the advantages of chemical foaming cells and supercritical foaming cells are combined, and the performance advantages of polyimide are fully exerted. The supercritical polyimide foam has the advantages of high-temperature resistance, heat insulation effect and buffer resilience characteristics, solves the problem of difficult penetration of polyimide supercritical fluid, and avoids the problems of complicated process and high energy consumption of thermal imidization of polyimide and re-penetration of supercritical fluid at high temperature.

Description

Technical Field

[0001] This invention relates to the field of polyimide foam technology, and particularly to a supercritical polyimide foam and its preparation method. Background Technology

[0002] Foamed plastics, as an important branch of polymer materials, possess excellent properties such as lightweight, heat insulation, sound absorption, and vibration damping due to their uniformly dispersed microbubble structure, making them widely used in numerous industrial fields. In recent years, the use of non-toxic and clean supercritical fluid foaming technology has become the mainstream development trend in this field. This technology has good applicability to most matrix resins or their modified materials, and can form a uniform and delicate micron-sized cell structure, thus showing broad application prospects in high-tech fields such as 5G communications, military equipment, sporting goods, and new energy.

[0003] Polyimide, as a high-performance polymer with an imide ring in its main chain, possesses outstanding advantages such as high temperature resistance, high mechanical properties, and excellent structural stability. However, its inherent rigid molecular chain structure leads to poor solubility and diffusion properties in supercritical fluids. Furthermore, the extremely high processing temperature, glass transition temperature, and melt viscosity of polyimide pose significant challenges to the formation and stable growth of cells during supercritical foaming, severely restricting its application and development in the field of supercritical foaming.

[0004] To address the aforementioned technical challenges, researchers have conducted a series of exploratory studies. Chinese patent CN115782222A discloses a method for preparing porous polyimide by cold-pressing and sintering polyimide resin powder, followed by swelling in N,N-dimethylformamide and supercritical foaming. However, due to the formation of rigid molecular chain segments during the cold and hot sintering process, the foaming effect of the supercritical fluid remains unsatisfactory even after swelling treatment. Chinese patent CN121362326A introduces an aliphatic diamine as a comonomer during polyimide synthesis, embedding flexible segments into the rigid backbone, effectively improving the dissolution and diffusion capabilities of the supercritical fluid. However, the introduction of the aliphatic diamine significantly reduces the material's heat resistance and mechanical strength. Chinese patent CN119039652A uses copolyester ammonium salt precursor powder for cold pressing followed by direct supercritical foaming. However, because the cold-pressed powder only has physical gaps, it is difficult to effectively retain the supercritical fluid, and the lack of sufficient melt strength to ensure fluid penetration and diffusion results in limited foaming effect and insufficient cell formation. Chinese patent CN121427160A proposes introducing ionic liquid into a polyamic acid solution, preparing an ionic liquid composite material through thermal imidization, and then performing supercritical foaming. While this method helps with the penetration and diffusion of the supercritical fluid, the addition of ionic liquid also causes a loss of heat resistance and mechanical properties, and the process route of hot pressing followed by foaming leads to a significant increase in energy consumption.

[0005] Therefore, there is an urgent need to develop a polyimide foam material that combines excellent high-temperature resistance, thermal insulation, and cushioning and rebound properties. Summary of the Invention

[0006] In view of the deficiencies in the prior art, this application provides a supercritical polyimide foam and its preparation method to solve the technical problem that polyimide foam in the prior art cannot simultaneously achieve high temperature resistance, heat insulation effect and cushioning and rebound properties.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: A supercritical polyimide foam is prepared by chemically and physically foaming polyamic acid in a supercritical state, wherein the polyamic acid is obtained by reacting aromatic dianhydride and aromatic diamine in a polar solvent.

[0008] In one embodiment, the polar solvent is N, N ， -Dimethylformamide, N,N ， One or more of dimethylacetamide, tetrahydrofuran, N-methyl-2-pyrrolidone, and dimethyl sulfoxide.

[0009] In one embodiment, the aromatic dianhydride is pyromellitic dianhydride (PMDA), 3,3, ,4,4 , -Biphenyltetracarboxylic dianhydride (BPDA), 3,3 , ,4,4 , -Diphenyl ether tetracarboxylic dianhydride (ODPA), 3,3 , ,4,4 , - One or more of benzophenone tetracarboxylic dianhydride (BTDA).

[0010] In one embodiment, the diamine is one or more of m-phenylenediamine, p-phenylenediamine, 4,4-diaminodiphenyl ether, 4,4-diaminodiphenylmethane, 4,4-diaminodiphenol, and 4,4-diaminodibenzophenone.

[0011] This application also provides a method for preparing the above-mentioned supercritical polyimide foam, including the following steps: S1. Preparation of polyamic acid: Under nitrogen protection, aromatic dianhydride and aromatic diamine are reacted in a polar solvent at 0-10℃ for 3-6 hours to obtain a polyamic acid solution. S2, Chemical imidization of polyamic acid: Dehydrating agent, catalyst, foam stabilizer and nucleating agent are added to polyamic acid solution to chemically imidize polyamic acid solution; S3. Viscosity control: Add a poor solvent for polyamic acid solution to the solution prepared in S2 to control the viscosity of the solution system; S4. Chemical Foaming and Supercritical Infiltration: The solution prepared in S3 is added to the mold, and the mold is placed in a supercritical reactor. Supercritical gas is then introduced into the supercritical reactor, which sequentially enters the low-temperature foaming and infiltration stage, the medium-temperature foaming and infiltration stage, and the high-temperature curing stage. The temperature of the low-temperature foaming and infiltration stage is 40-60℃, the pressure is 5-8 MPa, and the reaction time is 1-3 hours. The temperature of the medium-temperature foaming and infiltration stage is 120-150℃, the pressure is 7-10 MPa, and the reaction time is 1-3 hours. The temperature of the high-temperature curing stage is 180-210℃, the pressure is 10-12 MPa, and the reaction time is 2-4 hours. S5. Supercritical foaming: The supercritical reactor is depressurized to atmospheric pressure, and the phase inside the mold is depressurized and foamed to obtain polyimide foam blocks; S6. High-temperature post-treatment: The foaming body is placed in a high-temperature environment for a period of time for curing treatment to obtain supercritical polyimide foam.

[0012] In one embodiment, the catalyst is triethylamine, the undesirable solvent is ethanol, the foam stabilizer is a polysiloxane-polyether copolymer, the nucleating agent is nano-calcium carbonate, and the supercritical fluid is supercritical nitrogen and / or supercritical carbon dioxide.

[0013] In one implementation, in S5, the pressure relief rate is 20~100MPa / s.

[0014] In one embodiment, in S6, the temperature of the high-temperature environment is 230-250°C, and the polyimide foam block is placed in the high-temperature environment for 3-6 hours.

[0015] Compared with the prior art, this application has at least the following beneficial effects: The supercritical polyimide foam of this invention is prepared by simultaneously chemically and physically foaming polyamic acid, a polyimide precursor obtained by reacting aromatic dianhydride and aromatic diamine in a polar solvent, under supercritical conditions. This allows for the incorporation of supercritical fluid before the formation of rigid imide rings through imidization. Fine, homogeneous pores are produced using supercritical fluid technology, combining the advantages of both chemically and supercritically foamed pores to fully leverage the performance advantages of polyimide. The supercritical polyimide foam of this application includes... The foam produced by chemical foaming has a diameter of 500~1000μm and a diameter of 50~200μm produced by supercritical foaming. The foam includes open-cell and closed-cell structures. The overall density of the foamed material is 5~20kg / m3. The supercritical polyimide foam in this application combines high temperature resistance, thermal insulation effect and buffering and rebound characteristics. It solves the problem of the difficulty of supercritical fluid infiltration of polyimide and avoids the problems of complex process and high energy consumption of thermal imidization of polyimide and re-infiltration with high temperature supercritical fluid. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the invention is described below through specific embodiments. However, it should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0017] The terminology used in this disclosure is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. The singular forms “a,” “the,” and “the” as used in this disclosure and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any and all possible combinations of one or more of the associated listed items.

[0018] It should be understood that although the terms first, second, third, etc., may be used in this disclosure to describe various information, such information should not be limited to these terms and should not be construed as indicating or implying relative importance. These terms are used only to distinguish information of the same type from one another. For example, without departing from the scope of this disclosure, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to determination."

[0019] In the description of this invention, unless otherwise specified and limited, it should be noted that the terms "installation", "connection" and "linking" should be interpreted broadly. For example, they can refer to mechanical connection or internal connection between two components. They can be direct connection or indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0020] To better understand the technical solution of the present invention, the present invention will be described in detail below with reference to embodiments and comparative examples.

[0021] Example 1: A supercritical polyimide foam, prepared by the following steps: S1. Preparation of polyamic acid: Under nitrogen protection, at 5℃, 300 parts by weight of N, N ， -40 parts by weight of 4,4-diaminodiphenyl ether and 68 parts by weight of 3,3-dimethylacetamide were added to dimethylacetamide. , ,4,4 , - The reaction of benzophenone tetracarboxylic dianhydride for 3 hours yields a polyamic acid solution, which is a polyimide precursor. S2, Chemical imidization of polyamic acid: 60 parts by weight of acetic anhydride as a dehydrating agent, 18 parts by weight of triethylamine as a catalyst, 8 parts by weight of polysiloxane-polyether copolymer as a foam stabilizer, and 10 parts by weight of nano-calcium carbonate as a nucleating agent are added to 400 parts by weight of polyamic acid solution. The polyamic acid solution is dispersed and stirred at high speed to achieve uniformity, and the polyamic acid solution is chemically imidized. S3. Viscosity control: Add 20 parts by weight of ethanol as a poor solvent to the solution prepared in S2 to control the viscosity of the solution system. In this step, the polyamic acid molecular chains will shrink. S4. Chemical Foaming and Supercritical Infiltration: The solution prepared in S3 is added to the mold, and the mold is placed in a supercritical reactor. Supercritical carbon dioxide is then introduced into the supercritical reactor, which sequentially enters the low-temperature foaming and infiltration stage, the medium-temperature foaming and infiltration stage, and the high-temperature curing stage. The temperature of the low-temperature foaming and infiltration stage is 40℃, the pressure is 5 MPa, and the reaction time is 3 hours. The temperature of the medium-temperature foaming and infiltration stage is 120℃, the pressure is 7 MPa, and the reaction time is 3 hours. The temperature of the high-temperature curing stage is 200℃, the pressure is 12 MPa, and the reaction time is 2 hours. S5. Supercritical foaming: The supercritical reactor is rapidly depressurized to atmospheric pressure at a rate of 20~100MPa / s. The phase inside the mold is depressurized and foamed to obtain polyimide foam blocks. S6. High-temperature post-treatment: The polyimide foam block is placed in a high-temperature environment of 240℃ for 3 hours to obtain supercritical polyimide foam.

[0022] Example 2, a supercritical polyimide foam, prepared by the following steps: S1. Preparation of polyamic acid: Under nitrogen protection, at 10℃, 300 parts by weight of N, N ， Add 40 parts by weight of p-phenylenediamine and 115 parts by weight of 3,3-dimethylacetamide to dimethylacetamide. , ,4,4 , The reaction of 1-biphenyltetracarboxylic dianhydride for 3 h yields a polyamic acid solution, which is a polyimide precursor. S2, Chemical imidization of polyamic acid: 40 parts by weight of acetic anhydride as a dehydrating agent and 12 parts by weight of triethylamine as a catalyst, 6 parts by weight of polysiloxane-polyether copolymer as a foam stabilizer and 12 parts by weight of nano-calcium carbonate as a nucleating agent are added to 400 parts by weight of polyamic acid solution. The polyamic acid solution is dispersed and stirred at high speed to achieve uniformity, and the polyamic acid solution is chemically imidized. S3. Viscosity control: Add 30 parts by weight of ethanol as a poor solvent to the solution prepared in S2 to control the viscosity of the solution system. In this step, the polyamic acid molecular chains will shrink. S4. Chemical Foaming and Supercritical Infiltration: The solution prepared in S3 is added to the mold, and the mold is placed in a supercritical reactor. Supercritical carbon dioxide is then introduced into the supercritical reactor, which sequentially enters the low-temperature foaming and infiltration stage, the medium-temperature foaming and infiltration stage, and the high-temperature curing stage. The temperature of the low-temperature foaming and infiltration stage is 45℃, the pressure is 6 MPa, and the reaction time is 2 hours. The temperature of the medium-temperature foaming and infiltration stage is 140℃, the pressure is 9 MPa, and the reaction time is 2 hours. The temperature of the high-temperature curing stage is 180℃, the pressure is 10 MPa, and the reaction time is 3 hours. S5. Supercritical foaming: The supercritical reactor is rapidly depressurized to atmospheric pressure at a rate of 20~100MPa / s. The phase inside the mold is depressurized and foamed to obtain polyimide foam blocks. S6. High-temperature post-treatment: The polyimide foam block is placed in a high-temperature environment of 230°C for 4 hours to obtain supercritical polyimide foam.

[0023] Example 3, a supercritical polyimide foam, prepared by the following steps: S1. Preparation of polyamic acid: Under nitrogen protection, at 5℃, 300 parts by weight of N, N ， 40 parts by weight of 4,4-diaminodiphenyl ether and 46 parts by weight of pyromellitic dianhydride were added to dimethylformamide and reacted for 3 hours to obtain a polyimide precursor polyamic acid solution. S2, Chemical imidization of polyamic acid: 70 parts by weight of acetic anhydride as a dehydrating agent, 20 parts by weight of triethylamine as a catalyst, 8 parts by weight of polysiloxane-polyether copolymer as a foam stabilizer, and 10 parts by weight of nano-calcium carbonate as a nucleating agent are added to 400 parts by weight of polyamic acid solution. The polyamic acid solution is dispersed and stirred at high speed to achieve uniformity, and the polyamic acid solution is chemically imidized. S3. Viscosity control: Add 25 parts by weight of ethanol as a poor solvent to the solution prepared in S2 to control the viscosity of the solution system. In this step, the polyamic acid molecular chains will shrink. S4. Chemical Foaming and Supercritical Infiltration: The solution prepared in S3 is added to the mold, and the mold is placed in a supercritical reactor. Supercritical carbon dioxide is then introduced into the supercritical reactor, which sequentially enters the low-temperature foaming and infiltration stage, the medium-temperature foaming and infiltration stage, and the high-temperature curing stage. The temperature of the low-temperature foaming and infiltration stage is 60℃, the pressure is 5 MPa, and the reaction time is 3 hours. The temperature of the medium-temperature foaming and infiltration stage is 140℃, the pressure is 8 MPa, and the reaction time is 3 hours. The temperature of the high-temperature curing stage is 190℃, the pressure is 10 MPa, and the reaction time is 3 hours. S5. Supercritical foaming: The supercritical reactor is rapidly depressurized to atmospheric pressure at a rate of 20~100MPa / s. The phase inside the mold is depressurized and foamed to obtain polyimide foam blocks. S6. High-temperature post-treatment: Place the polyimide foam block in a high-temperature environment of 250°C for 3 hours to obtain supercritical polyimide foam.

[0024] The supercritical polyimide foams prepared in Examples 1-3 were compared with commercially available polyimide foams, and the results are shown in Table 1:

[0025] As can be seen from Table 1, the supercritical polyimide foam provided by this invention has high mechanical properties, especially in terms of toughness. When the density difference is not large, the micron-level uniform and fine cells brought about by supercritical foaming result in high compressive strain capacity, which can meet the compression and rebound performance requirements of high-end foams in different industrial sectors.

[0026] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them; although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. A supercritical polyimide foam, characterized in that, It is prepared by chemical foaming and physical foaming of polyamic acid in a supercritical state, wherein the polyamic acid is obtained by reacting aromatic dianhydride and aromatic diamine in a polar solvent.

2. The supercritical polyimide foam according to claim 1, characterized in that, The polar solvent is N, N ， -Dimethylformamide, N,N ， One or more of dimethylacetamide, tetrahydrofuran, N-methyl-2-pyrrolidone, and dimethyl sulfoxide.

3. The supercritical polyimide foam according to claim 1, characterized in that, The aromatic dianhydride is pyromellitic dianhydride (PMDA), 3,3 , ,4,4 , -Biphenyltetracarboxylic dianhydride (BPDA), 3,3 , ,4,4 , -Diphenyl ether tetracarboxylic dianhydride (ODPA), 3,3 , ,4,4 , - One or more of benzophenone tetracarboxylic dianhydride (BTDA).

4. The supercritical polyimide foam according to claim 1, characterized in that, The diamine is one or more of the following: m-phenylenediamine, p-phenylenediamine, 4,4-diaminodiphenyl ether, 4,4-diaminodiphenylmethane, 4,4-diaminodiphenol, and 4,4-diaminodibenzophenone.

5. The method for preparing supercritical polyimide foam according to any one of claims 1-4, characterized in that, Includes the following steps: S1. Preparation of polyamic acid: Under nitrogen protection, aromatic dianhydride and aromatic diamine are reacted in a polar solvent at 0-10℃ for 3-6 hours to obtain a polyamic acid solution. S2, Chemical imidization of polyamic acid: A dehydrating agent, catalyst, foam stabilizer, and nucleating agent are added to a polyamic acid solution to chemically imidize the polyamic acid solution; S3. Viscosity control: Add a poor solvent for polyamic acid solution to the solution prepared in S2 to control the viscosity of the solution system; S4. Chemical Foaming and Supercritical Infiltration: The solution prepared in S3 is added to the mold, and the mold is placed in a supercritical reactor. Supercritical gas is then introduced into the supercritical reactor, which sequentially enters the low-temperature foaming and infiltration stage, the medium-temperature foaming and infiltration stage, and the high-temperature curing stage. The temperature of the low-temperature foaming and infiltration stage is 40-60℃, the pressure is 5-8 MPa, and the reaction time is 1-3 hours. The temperature of the medium-temperature foaming and infiltration stage is 120-150℃, the pressure is 7-10 MPa, and the reaction time is 1-3 hours. The temperature of the high-temperature curing stage is 180-210℃, the pressure is 10-12 MPa, and the reaction time is 2-4 hours. S5. Supercritical foaming: The supercritical reactor is depressurized to atmospheric pressure, and the phase inside the mold is depressurized and foamed to obtain polyimide foam blocks; S6. High-temperature post-treatment: The foaming body is placed in a high-temperature environment for a period of time for curing treatment to obtain supercritical polyimide foam.

6. The preparation method according to claim 5, characterized in that, The dehydrating agent is acetic anhydride, the catalyst is triethylamine, the undesirable solvent is ethanol, the foam stabilizer is polysiloxane-polyether copolymer, the nucleating agent is nano-calcium carbonate, and the supercritical fluid is supercritical nitrogen and / or supercritical carbon dioxide.

7. The supercritical polyimide foam according to claim 5, characterized in that, In S5, the pressure relief rate is 20~100MPa / s.

8. The supercritical polyimide foam according to claim 5, characterized in that, In S6, the high-temperature environment is 230-250℃, and the resulting polyimide foam block is placed in the high-temperature environment for 3-6 hours.

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