Water co-catalyst for polyimide process

Abstract

This disclosure relates to a method for forming polyimide gels. The method generally involves forming polyamide and dehydrating the polyamide in the presence of water using a dehydrating agent. The resulting polyimide gel can be converted into polyimide or carbon dry gels or aerogels. This method is advantageous for providing rapid or even instantaneous gelation, which can particularly facilitate the formation of beads containing the polyimide gel. Polyimide or carbon gel materials prepared according to the disclosed method are suitable for environments involving electrochemical reactions, such as as electrode materials in lithium-ion batteries.

Description

Technical Field

[0001] This case asserts priority to U.S. Provisional Patent Application No. 63 / 124,454, filed on December 11, 2020, which is incorporated herein by reference in its entirety.

[0002] This disclosure relates to a system for manufacturing porous polyimide materials and processes using water as a cocatalyst in the dehydration of polyamides. Prior Technology

[0003] Aerogels are solid materials comprising highly porous networks with micropore and mesopore sizes. Depending on the precursor materials used and the process employed, when the density of the aerogel is approximately 0.05 g / cm³, the total pore size of the aerogel accounts for more than 90% of its volume. The aerogel is prepared by removing the solvent from the gel (the solid network containing its solvent), such that the gel can be minimally or non-shrink by capillary forces on the gel surface. Methods for solvent removal include, but are not limited to, supercritical drying (or drying using a supercritical fluid, where the low surface tension of the supercritical fluid exchanges with the transient solvent within the gel), solvent exchange with a supercritical fluid, solvent exchange with a fluid subsequently converted to a supercritical state, subcritical or near-critical drying, and sublimation of the frozen solvent during a freeze-drying process. See, for example, PCT patent application publication number WO2016127084A1. It should be noted that when dried under ambient conditions, gel shrinkage can occur as the solvent evaporates, potentially forming a dry gel. Therefore, the preparation of aerogels by sol-gel processes or other polymerization processes generally involves the following series of steps: dissolution of the solute in a solvent, formation of a sol / solution / mixture, formation of a gel (which may include additional cross-linking), and removal of the solvent by supercritical drying or any other method of removing the solvent from the gel without causing pore collapse.

[0004] Aerogels can be formed from inorganic materials, organic materials, or mixtures thereof. When formed from organic materials (such as phenol, resorcinol-formaldehyde (RF), phloroglucinol-furfaldehyde (PF), polyacrylonitrile (PAN), polyimide (PI), polyurethane (PU), polyurea (PUA), polyamine (PA), polybutadiene, polydicyclopentadiene, and their precursors or polymeric derivatives), organic aerogels, such as those formed by carbonization (e.g., by thermal decomposition), can have different or overlapping properties (e.g., pore volume, pore size distribution, morphology, etc.) depending on the precursor materials and methods used.

[0005] Recently, efforts have been focused on improving the performance of carbon aerogels as electrode materials for applications such as the development and characterization of lithium-ion battery (LIB) energy storage devices. Therefore, there is a need for corresponding organic aerogels, such as polyimide aerogels. The polyimide aerogel system is prepared by reacting a diamine and a tetracarboxylic anhydride in an organic solvent, followed by dehydration of the resulting polymeric amido acid (“polyamic acid”) in the presence of a monoamine to form a polyimide gel. For economic, safety, environmental, and practical reasons, it is desirable to use a minimal amount of monoamine for this gelation and for gelation to occur as quickly as possible. Summary of the Invention

[0006] This technical system relates to a method for forming polyimide gels while minimizing the use of potentially harmful substances or hazardous agents. This method further facilitates rapid gelation, making it easy to configure in continuous processes, such as in the preparation of polyimide beads. The method generally involves providing polyamide and subsequently dehydrating the polyamide, wherein the dehydration is carried out in the presence of water. Unexpectedly, according to this disclosure, dehydration has been found to occur in the presence of water without significant decomposition of the dehydrating agent, and in fact, it occurs even faster when water is present as a co-catalyst.

[0007] Therefore, a method for forming a polyimide gel in a single-state sample is provided, the method comprising: a) Provides tetracarboxylic dianhydrides and polyfunctional amines; b) Add the tetracarboxylic dianhydride and the polyfunctional amine to an organic solvent to form a solution; c) React the tetracarboxylic acid dianhydride with the polyfunctional amine in solution to form a polyacrylic acid sol solution; d) Add a dehydrating agent, a monoamine, and water to the solution of the polyamide sol to form the polyimide gel.

[0008] In some embodiments, the tetracarboxylic dianhydride is selected from the group consisting of pyromellitic dianhydride (PMDA), biphenyltetracarboxylic dianhydride (BPDA), oxydiphthalic dianhydride (ODPA), benzophenone tetracarboxylic dianhydride (BTDA), ethylenediaminetetraacetic dianhydride (EDDA), 1,4,5,8-naphthalenetetracarboxylic dianhydride, and combinations thereof.

[0009] In some embodiments, the polyfunctional amine is 1,3,5-tris(4-aminophenoxy)benzene (TAPOB), tris(4-aminophenyl)methane, melamine, or a combination thereof.

[0010] In some embodiments, the polyfunctional amine is an alkyl diamine or an aryl diamine. In some embodiments, the alkyl diamine is ethylenediamine, 1,3-diaminepropane, 1,4-diaminebutane, 1,5-diaminepentane, 1,6-diaminehexane, or a combination thereof. In some embodiments, the aryl diamine is 1,4-phenylenediamine, 4,4'-diaminediphenyl ether, 4,4'-methylenebis(diphenylamine), or a combination thereof.

[0011] In some embodiments, the molar ratio of the tetracarboxylic dianhydride to the polyfunctional amine is about 0.9 to about 3, or about 0.9 to about 1.1.

[0012] In some embodiments, the molar ratio of the monoamine to the polyamide is about 0.1 to about 8. In some embodiments, the amount of monoamine required to form the polyimide gel with a gelation time of less than about 15 minutes is reduced by nearly about 50 times compared to the amount of monoamine required for forming the polyimide gel in anhydrous conditions.

[0013] In some embodiments, the monoamine is a third alkylamine, a third cycloalkylamine, a heteroaromatic amine, guanidine, or a fourth ammonium hydroxide. In some embodiments, the monoamine is selected from the group consisting of trimethylamine, triethylamine, tri-n-propylamine, tri-n-butylamine, N-methylpyrrolidine, N-methylpiperidine, diisopropylethylamine, pyridine, quinoline, guanidine, and tetraalkylammonium hydroxide. In some embodiments, the monoamine is pyridine.

[0014] In some embodiments, the molar ratio of the dehydrating agent to the tetracarboxylic dianhydride is about 2 to about 10, about 3 to about 6, or about 4 to about 5.

[0015] In some embodiments, the dehydrating agent is a carboxylic anhydride. In some embodiments, the carboxylic anhydride is an acetic anhydride.

[0016] In some embodiments, the organic solvent is N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, tetrahydrofuran, or ethyl acetate.

[0017] In some embodiments, the molar ratio of water to tetracarboxylic dianhydride is greater than about 5. In some embodiments, the molar ratio of water to tetracarboxylic dianhydride is about 5 to about 500.

[0018] In some embodiments, the concentration of the polyamide sol in the solution ranges from about 0.01 to about 0.3 g / cm³.

[0019] In some embodiments, the polyfunctional amine and the tetracarboxylic dianhydride are reacted over a period of about 0.5 hours to about 17 hours.

[0020] In some embodiments, the polyfunctional amine and the tetracarboxylic dianhydride are reacted at a temperature of about 10 to about 100°C, about 15 to about 60°C, about 15 to about 50°C, or about 15 to about 25°C.

[0021] In some embodiments, the time from the addition of the monoamine and water to the gelation of the polyimide is less than about 1 minute, or less than about 30 seconds, or less than about 15 seconds.

[0022] In some embodiments, the method further includes: a. The polyamide sol is cast into a mold to form a single polyamide wet gel block; b. Demold the polyimide wet gel piece individually; c. Wash or solvent-exchange the polyimide wet gel individually; and d. Dry the polyimide wet gel in individual pieces to form monolithic polyimide aerogels or dry gels.

[0023] In some embodiments, the monolith has a thickness of about 5 to about 25 millimeters. In some embodiments, the monolith is a film with a thickness of about 50 micrometers to about 1 millimeter.

[0024] In some embodiments, the washing or solvent exchange system uses water, C1 to C3 alcohols, acetone, acetonitrile, tetrahydrofuran, ethyl acetate, supercritical fluid carbon dioxide (CO2), or combinations thereof.

[0025] In some embodiments, drying includes freeze-drying the polyimide wet gel or contacting the polyimide wet gel with supercritical fluid CO2.

[0026] In some embodiments, the method further includes carbonizing the monolithic polyimide aerogel or dry gel to form a carbon aerogel or dry gel. In some embodiments, the carbon aerogel has substantially the same properties as a carbon aerogel prepared by carbonizing a corresponding polyimide wet gel, which has been prepared by an aqueous imidization method.

[0027] In some embodiments, the method further includes casting polyimide beads into an emulsion. In some embodiments, casting polyimide beads into an emulsion includes: a. Prior to gelation, the polyamide sol solution is added to mineral oil, silicone oil, or C5-C12 hydrocarbons (e.g., hexane or mineral concentrate) to form a mixture; and b. Stir the mixture under high shear conditions to form polyimide beads with a diameter of about 5 micrometers to about 200 micrometers.

[0028] In some embodiments, the method further includes adding one or more surfactants to the mixture.

[0029] In some embodiments, the method further includes drying the polyimide beads under elevated temperature conditions or with supercritical fluid CO2.

[0030] In some embodiments, the method further includes casting polyimide beads into an aerosol, the method comprising spraying the polyimide sol solution into air or into mineral oil, silicone oil, C5-C12 hydrocarbons or mineral concentrates prior to gelation, to form polyimide beads with a diameter of about 5 micrometers to about 250 micrometers.

[0031] In some embodiments, the method is performed as a continuous process, which further includes conveying the polyimide beads by one or more of the following: filtering; aging; solvent exchanging; drying; carbonizing.

[0032] In some embodiments, the method further includes adding silicone to the polyacrylic acid before dehydration or before gelation.

[0033] In another embodiment, a polyimide wet gel prepared by the method disclosed herein is provided.

[0034] In some embodiments, the polyimide wet gel contains terminal amine groups as determined by 15N-NMR.

[0035] In some embodiments, the wet gel is doped with silicon.

[0036] In another embodiment, a nanoporous aerogel material comprising a pore structure including a fiber morphology and an array of pores is provided.

[0037] In some embodiments, the nanoporous aerogel material is a polyimide aerogel, or wherein the nanoporous aerogel material is a carbon aerogel derived from polyimide aerogel. Simple Explanation of the Diagram

[0038] The accompanying drawings are provided to provide an understanding of embodiments of the present technology. These drawings are not necessarily drawn to scale. They are merely illustrative and should not be construed as limiting the scope of the technology. The disclosure described herein is illustrated in the drawings by way of example, not limitation.

[0039] [Figure 1] is a flowchart depicting a non-limiting embodiment of the disclosed method.

[0040] [Figure 2] is a flowchart depicting another non-limiting embodiment of the disclosed method.

[0041] [Figure 3A] is a graph showing the relationship between gelation time and the molar ratio of water to tetracarboxylic dianhydride in a non-limiting embodiment of the present disclosure.

[0042] [Figure 3B] is a graph showing the relationship between gelation time and the molar ratio of pyridine to tetracarboxylic dianhydride in a non-limiting embodiment of the present disclosure.

[0043] [Figure 4] is a table showing the physical and structural properties of carbonized carbon aerogels derived from synthetic polyimide aerogels, according to non-limiting embodiments of the present disclosure.

[0044] [Figure 5] is a table showing the physical and structural properties of carbonized carbon aerogels derived from synthetic polyimide aerogels, according to non-limiting embodiments of the present disclosure.

[0045] [Figure 6] is a graph showing the relationship between the surface area and pore volume of the non-limiting embodiments disclosed herein and the molar ratio of water to tetracarboxylic acid dianhydride.

[0046] [Figure 7A] is a scanning electron micrograph of the reference carbon aerogel.

[0047] [Figure 7B] is a scanning electron micrograph of a carbon aerogel according to a non-limiting embodiment of the present disclosure.

[0048] [Figure 8A] is a scanning electron micrograph of a carbon aerogel sample with PY / PMDA=0.25, H2O / PMDA=0, and carbon.

[0049] [Figure 8B] is a scanning electron micrograph of a carbon aerogel sample with PY / PMDA=0.25, H2O / PMDA=35.

[0050] [Figure 9A] is a scanning electron micrograph of a carbon aerogel sample with PY / PMDA=2.0, H2O / PMDA=0.

[0051] [Figure 9B] is a scanning electron micrograph of a carbon aerogel sample with PY / PMDA=2.0, H2O / PMDA=35.

[0052] [Figures 10A to 10C] are a series of scanning electron micrographs at magnifications of 50,000, 100,000 and 200,000 times, respectively, of the carbon aerogel produced by carbonization of polyimide aerogel prepared with a Py / PMDA ratio of 0.45 and an H2O / PMDA ratio of 0.

[0053] [Figures 10D to 10F] are a series of scanning electron micrographs at magnifications of 50,000, 100,000 and 200,000 times, respectively, of carbon aerogels produced by carbonization of polyimide aerogels prepared with a Py / PMDA ratio of 0.45 and an H2O / PMDA ratio of 10.

[0054] [Figures 10G to 10I] are a series of scanning electron micrographs of carbon aerogels produced by carbonization of polyimide aerogels prepared with a Py / PMDA ratio of 0.45 and an H2O / PMDA ratio of 35, magnified at 50,000, 100,000 and 200,000 times respectively.

[0055] [Figure 11] is a graph showing the relationship between gelation time and the molar ratio of water to tetracarboxylic dianhydride in the non-limiting embodiments disclosed herein.

[0056] [Figure 12] is a graph showing the relationship between gelation time and the molar ratio of water to tetracarboxylic dianhydride in the non-limiting embodiments disclosed herein.

[0057] [Figure 13] is a graph showing the relationship between gelation time and the molar ratio of water to tetracarboxylic dianhydride in the non-limiting embodiments disclosed herein.

[0058] [Figure 14] is a graph showing the relationship between gelation time and the molar ratio of water to tetracarboxylic dianhydride in the non-limiting embodiments disclosed herein.

[0059] [Figure 15] provides a table of sol-gel compositions for each gel synthesized according to non-limiting embodiments of the present disclosure.

[0060] [Figure 16] is a table providing the physical and structural properties of polyimide aerogels synthesized according to non-limiting embodiments of the present disclosure. Implementation

[0061] Before describing several embodiments of this technology, it should be understood that this technology is not limited to the details of the construction or process steps set forth in the following description. This technology can have other embodiments and can be practiced or implemented in various ways.

[0062] The method generally involves providing polyamide and subsequently dehydrating the polyamide, wherein the dehydration is carried out in the presence of water as a co-catalyst. Unexpectedly, according to this disclosure, it has been found that not only does dehydration occur in the presence of water and without the disruption of the expected dehydrating agent (e.g., anhydride such as acetic anhydride), but the gelation of the polyimide also occurs very rapidly. The resulting polyimide wet gel can be converted into an aerogel. When the polyimide wet gel is converted into a carbon aerogel, the carbon aerogel has a nanostructure with similar properties to the carbonized polyimide aerogel, wherein the corresponding polyimide wet gel is prepared by a conventional dehydration process (e.g., without adding water and using a large excess of a monoamine, such as pyridine). This method avoids large amounts of harmful and toxic reagents (e.g., pyridine) and their disposal, thus being superior to conventional dehydration processes. Furthermore, rapid gelation makes this method suitable for continuous processes used in the production of polyimide gel materials, such as polyimide beads. [definition]

[0063] The following definitions are provided for the terms used in this disclosure. This application will use the terms defined below unless the context of the text requires a different meaning.

[0064] The articles “a” and “an” are used herein to refer to one or more (i.e., at least one) grammatical objects of the article. The term “about” as used herein is used to describe and account for small variations. For example, the term “about” may refer to less than or equal to ±10%, less than or equal to ±5%, such as less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.2%, less than or equal to ±0.1%, or less than or equal to ±0.05%. Whether explicitly stated or not, all numerical values ​​herein are modified by the term “about.” Values ​​modified by the term “about” naturally include specific values. For example, “about 5.0” must include 5.0.

[0065] In the context of this disclosure, the term "framework" or "framework structure" refers to a network of interconnected oligomers, polymers, or colloidal particles that form a solid structure in a gel or aerogel. The polymers or particles constituting the framework structure generally have a diameter of about 100 angstroms. However, the framework structure of this disclosure may also include networks of interconnected oligomers, polymers, or colloidal particles of all diameter sizes forming a solid structure in a gel or aerogel.

[0066] As used herein, the term "aerogel" refers to a solid object, regardless of its shape or size, including a framework of interconnected solid structures having a corresponding interconnected network of pores integrally formed within the framework, and containing a gas, such as air, as a dispersed interstitial medium. Thus, regardless of the drying method used, an aerogel is an open, non-fluid colloidal or polymeric network formed by the expansion of gas throughout its volume and by the removal of all expanding agents from the corresponding wet gel. The term "aerogel" as used herein includes any open-celled porous material, which can be classified as aerogels, dry gels, cryogels, ambigels, microporous materials, etc., regardless of the material (e.g., polyimide, polyamide, or carbon), unless otherwise specified.

[0067] Generally, aerogels possess one or more of the following physical and structural properties: (a) an average pore diameter ranging from about 2 nanometers to about 100 nanometers; (b) a porosity of about 60% or higher; and (c) a specific surface area of ​​about 0 to about 100 m² / g or higher, generally about 0 to about 20, about 0 to about 100, or about 100 to about 1000 m² / g. These properties are generally determined using nitrogen porosimetry testing and / or helium pycnometry. It is understood that inclusions of additives, such as reinforcing materials or electrochemically active substances, such as silicon, can reduce the porosity and specific surface area of ​​the obtained aerogel composite. Densification can also reduce the porosity of the obtained aerogel.

[0068] In some embodiments, the gel material may be specifically referred to as a xerogel. As used herein, the term "xerogel" refers to an aerogel comprising an open, non-fluid colloid or polymer network, which is formed by removing all swelling agents from the respective gel without taking any precautions to avoid significant volume reduction or delayed compression. Xerogels generally comprise a dense structure. Xerogels undergo significant volume reduction during ambient pressure drying processes and have an overall surface area of ​​0 to 100 m² / g, for example, about 0 to about 20 m² / g as measured by nitrogen sorption analysis.

[0069] As used herein, the "conventional" method for dehydrating polyacrylic acid refers to a method in which polyacrylic acid is prepared by condensation of a diamine and a tetracarboxylic dianhydride in an organic solvent solution, and the polyacrylic acid is dehydrated using a large excess of pyridine in the presence of acetic anhydride. See, for example, U.S. Patent Nos. 7,071,287 and 7,074,880 to Rhine et al. and U.S. Patent Application Publication No. 2020 / 0269207 to Zafiropoulos et al.

[0070] As used herein, the terms "gelation" or "gel transition" refer to the formation of a wet gel from a polymer system, such as polyimide or polyamide as described herein. At the point defined as the "gel point" in the polymerization or dehydration reaction described herein, the sol loses its fluidity. Without being bound by any particular theory, the gel point can be considered as the point where the gelling solution exhibits flow resistance. In this paper, gelation begins in an initial sol state, where the solution primarily contains amine salts of polyamide, in a fluid colloidal dispersion state until sufficient polyimide is formed to reach the gel point. Gelation can then continue, producing a polyimide wet gel dispersion with increased viscosity. The amount of time taken for the polymer in solution (i.e., polyamide and / or polyimide) to transform into a gel form that can no longer flow is called the "phenomenological gelation time." Formally, the gelation time is measured using rheology. At the gel point, the elastic properties of the solid gel begin to dominate the viscosity of the fluid sol. The formal gelation time is approximately the time when the real and imaginary parts of the complex modulus of the gel sol intersect. These two moduli are monitored as a function of time using a rheometer. Time is calculated from the moment the last component of the sol is added to the solution. See, for example, HHWinter "Can the Gel Point of a Cross-linking Polymer Be Detected by the G'-G" Crossover?" Polym.Eng.Sci., 1987, 27, 1698-1702; S.-Y.Kim, D.-G.Choi and S.-M.Yang "Rheological analysis of the gelation behavior of tetraethylorthosilane / vinyltriethoxysilane hybrid solutions" Korean J.Chem.Eng., 2002, 19, 190-196; and M.Muthukumar "Screening effect on viscoelasticity near the gel point" Macro Moer ecules, 1989, 22, 4656-4658, for discussions on gelation.

[0071] As used herein, the term "wet-gel" refers to a gel in which the mobile interstitial phase within an interconnected network is primarily composed of a liquid phase, such as a common solvent, a liquefied gas (e.g., liquid carbon dioxide), or a combination thereof. Aerogels generally require the initial production of a wet gel, followed by processing and extraction to replace the mobile interstitial liquid phase in the gel with air or another gas. Examples of wet gels include, but are not limited to, alcohol gels, hydrogels, ketone gels, carbon gels, and any other wet gels known to those skilled in the art.

[0072] As used herein, the term "alkyl" refers to a straight-chain or branched saturated hydrocarbon group having a total of 1 to 20 carbon atoms (i.e., C1 to C20). Representative alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, n-butyl, n-pentyl, and n-hexyl; while branched alkyl groups include, but are not limited to, isopropyl, secondary-butyl, isobutyl, tertiary-butyl, isopentyl, and neopentyl. Alkyl groups may be unsubstituted or substituted.

[0073] As used herein, the term "alkenyl" refers to a hydrocarbon group having a total of 1 to 20 carbon atoms (i.e., C1 to C20) and having at least one unsaturated site (i.e., a carbon-carbon double bond). Examples include, but are not limited to: (ethylene)ethylene or vinyl, propenyl, 1-butenyl, 2-butenyl, isobutenyl, 1-pentenyl, 2-pentenyl, 3-methyl-1-butenyl, 2-methyl-2-butenyl, 2,3-dimethyl-2-butenyl, etc. Alkenyl groups may be unsubstituted or substituted.

[0074] As used herein, the term "alkynyl" refers to a hydrocarbon group having a total of 1 to 20 carbon atoms (i.e., C1 to C20) and having at least one carbon-carbon triple bond. Examples of alkynyl groups include, but are not limited to, ethynyl and propynyl. Alynyl groups can be unsubstituted or substituted.

[0075] As used herein, the term "aryl" refers to an aromatic carbocyclic group having a total of 6 to 20 carbon atoms (i.e., C6 to C20). Examples of aryl groups include, but are not limited to, phenyl, naphthyl, and anthracene. Aryl groups can be unsubstituted or substituted.

[0076] As used herein, the term "cycloalkyl" refers to a saturated carbocyclic group, which can be monocyclic or bicyclic. Cycloalkyl groups include monocyclic rings having 3 to 7 carbon atoms (i.e., C3 to C7) or bicyclic rings having 7 to 12 carbon atoms (i.e., C7 to C12). Examples of monocyclic cycloalkyl groups include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl. Cycloalkyl groups can be unsubstituted or substituted.

[0077] As used herein, and applicable to any of the aforementioned groups (alkyl, alkenyl, alkynyl, aryl, cycloalkyl, etc.), the term "substituted" means that one or more of the hydrogen atoms of the group are independently replaced by a substituent. Typical substituents include, but are not limited to, -X, -R, -OH, -OR, -SH, -SR, NH2, -NHR, -N(R)2, -N+(R)3, -CX3, -CN, -OCN, -SCN, -NCO, -NCS, -NO, -NO2, -N3, -NC(=O)H, -NC(=O)R, -C(=O)H, -C(=O)R, -C(=O)NH2, -C(=O)N(R)2, -SO3-, -SO3H, -S(=O)2R, -OS(=O)2OR, -S(=O)2NH2, -S =O)2N(R)2, -S(=O)R, -OP(=O)(OH)2, -OP(=O)(OR)2, -P(=O)(OR)2, -PO3, -PO3H2, -C(=O)X, -C(=S)R, -CO2H, -CO2R, -CO2-, -C(=S)OR, -C(=O)SR, -C(=S)SR, -C(=O)NH2, -C(=O)N(R)2, -C(=S)NH2, -C(=S)N(R)2, -C(=NH)NH2 and -C(=NR)N(R)2; wherein, X for each case is independently selected from F, Cl, Br and I; R for each case is independently selected from C1-C20 alkyl and C6-C20 aryl. Wherever the group is described as "optionally substituted", The group used in various contexts can be replaced by one or more of the aforementioned substituents.

[0078] It should be understood that certain nomenclature rules may encompass various linkage scenarios depending on the context. For example, if a substituent requires two connecting points to attach to the rest of the molecule, it should be understood that the substituent is a bicoordinate group. Examples of substituents identified as alkyl but requiring two connecting points include those such as -CH2-, -CH2CH2-, -CH2CH(CH3)CH2-, etc. Other nomenclature rules clearly indicate that groups such as "alkylene," "alkenylene," and "arylene" are bicoordinate groups. Unless otherwise stated, it should be understood that as long as a substituent is bicoordinated, it can be linked in any directional composition.

[0079] Unless otherwise stated, the term "substantially" as used herein means to a great extent, for example, depending on the specific circumstances (e.g., substantially pure, substantially identical, etc.), greater than about 95%, greater than about 99%, greater than about 99.9%, greater than 99.99%, or even 100% of the relevant reference features, quantities, etc. [Methods for forming aerogels and dry gels]

[0080] This disclosure generally provides methods for preparing polyimide gels (including aerogels and degels, and corresponding carbonized materials). As a non-limiting general method, the production of aerogels or degels generally includes the following steps: i) formation of a solution containing a gel precursor; ii) formation of a wet gel derived from the gel precursor solution; iii) aging and solvent exchange of the wet gel; and iv) extraction of the solvent from the wet gel under critical or ambient conditions to obtain dry aerogel or degel materials, respectively. These steps will be discussed in more detail below, particularly in the case of forming organic aerogels (such as polyimide aerogels) and corresponding carbonized aerogels. [Polyimide wet gel]

[0081] In one aspect disclosed herein, a method is provided for forming a polyimide gel by dehydrating polyamide in the presence of water as a co-catalyst. (Reference) [Figure 1], the method generally includes mixing at least one polyfunctional amine and at least one polyfunctional anhydride in a solvent to form a solution, and adding a dehydrating agent, a monoamine, and water to the solution. The order of addition of the reagents may vary. In some embodiments, the order of addition follows... The order shown in the exemplary flowchart of [Figure 1]. Therefore, referring to the figure... [1] In some embodiments, one or more polyfunctional amines and one or more polyfunctional anhydrides are dissolved in an organic solvent.

[0082] As used herein, the term "multifunctional amine" refers to a molecule having at least two primary amine groups that can be used in the reactions described below. In some embodiments, triamines, tetraamines, pentamines, hexaamines, etc., may be used instead of diamines or other substances besides diamines to optimize the properties of the gel material. In some embodiments, the multifunctional amine includes triamines, or the multifunctional amine is a triamine. Non-limiting examples of suitable triamines include propane-1,2,3-triamine, benzene-1,3,5-triamine, cyclohexane-1,3,5-triamine, 1,3,5-tris(4-aminophenoxy)benzene (TAPOB), tris(4-aminophenyl)methane, and 1,3,5-triazine-2,4,6-triamine (melamine). In some embodiments, the multifunctional amine is 1,3,5-tris(4-aminophenoxy)benzene (TAPOB), tris(4-aminophenyl)methane, melamine, or a combination thereof. In some embodiments, the polyfunctional amine is melamine. In a preferred embodiment, the polyfunctional amine is a diamine. Suitable diamines are further described below.

[0083] For clarity and simplicity, examples of the method are further described below with respect to the polyfunctional amine being a diamine. However, it should be understood that this is a non-limiting example, and the method can be carried out using other polyfunctional amines as described above. Those skilled in the art will recognize that suitable polyfunctional amines for use in the methods disclosed herein are alternatives to or complements to the diamines further described herein.

[0084] The term "multifunctional anhydride" refers to a molecule having at least two dicarboxylic acid anhydride groups that can be used in the reactions described below. In some embodiments, the multifunctional anhydride is a tetracarboxylic acid dianhydride. In some embodiments, trihydride, tetrahydride, penthydride, hexahydride, etc., may be used instead of tetracarboxylic acid dianhydride, or any other than tetracarboxylic acid dianhydride, to optimize the properties of the gel material.

[0085] For clarity and simplicity, the following description further illustrates an example of the method wherein the polyfunctional anhydride is a tetracarboxylic dianhydride. However, it should be understood that this is a non-limiting example, and the method can be carried out using other polyfunctional anhydrides as described above. Those skilled in the art will recognize that suitable polyfunctional anhydrides for use in the currently disclosed method are alternatives to or complements to the dianhydrides further described herein.

[0086] Therefore, in some embodiments, the method includes: providing a tetracarboxylic dianhydride and a polyfunctional amine; adding the tetracarboxylic dianhydride and the polyfunctional amine to an organic solvent to form a solution; reacting the tetracarboxylic dianhydride and the polyfunctional amine in the solution to form a polyamide sol solution; and adding a dehydrating agent, a monoamine, and water to the polyamide sol solution to form the polyimide gel.

[0087] In general, the diamine is allowed to react with the tetracarboxylic dianhydride to initially form polyamide, which is then dehydrated with a dehydrating agent in the presence of water and a monoamine to form polyimide as a wet gel.

[0088] The organic solvent may vary, but is generally polar and aprotic. Suitable solvents include, but are not limited to, N,N-dimethylacetamide, N,N-dimethylformamide, and N-methylpyrrolidone. In some embodiments, the solvent is N,N-dimethylacetamide.

[0089] A non-limiting general reaction sequence is provided in [Flowchart 1]. In some embodiments, the reaction is generally based on... [Flowchart 1] occurs, and the reagents, intermediates, and products have a basis The structure of the chemical formula in [Flowchart 1].

[0090] refer to [Flowchart 1] and [Figure 1], Diamine is dissolved in an organic solvent. In some embodiments, a combination of more than one diamine may be used. A combination of diamines may be used to optimize the properties of the gel material. In some embodiments, a single diamine is used.

[0091] The structure of diamines can vary. In some embodiments, diamines have a structure according to... The structure of [Chemical Formula I], wherein Z is each aliphatic (i.e., alkyl, alkenyl, ynyl, or cycloalkyl) or aryl as described above. In some embodiments, Z is an alkyl group, such as a C2 to C12 alkyl group (i.e., having 2 to 12 carbon atoms). In some embodiments, the diamine is a C2 to C6 alkyldiamine, such as, but not limited to, ethylenediamine, 1,3-diaminepropane, 1,4-diaminebutane, 1,5-diaminepentane, or 1,6-diaminehexane. In some embodiments, one or more carbon atoms of the C2 to C6 alkane of the diamine are substituted with one or more alkyl groups such as methyl.

[0092] In some embodiments, Z is an aryl group. In some embodiments, the aryl diamine is 1,4-phenylenediamine (PDA), 4,4'-diamine diphenyl ether, 4,4'-methylenebis(diphenylamine), or a combination thereof. In some embodiments, the diamine is PDA. In some embodiments, the diamine is 4,4'-diamine diphenyl ether. In some embodiments, the diamine is 4,4'-methylenebis(diphenylamine).

[0093] refer to [Flowchart 1] and [Figure 1], Tetracarboxylic dianhydride is added. In some embodiments, more than one type of tetracarboxylic dianhydride is added. To optimize the performance of the gel material, a combination of tetracarboxylic dianhydrides can be used. In some embodiments, a single tetracarboxylic dianhydride is added.

[0094] The structure of tetracarboxylic dianhydride can vary. In some embodiments, tetracarboxylic dianhydride has a structure according to... The structure of [Chemical Formula II], wherein each L is an alkyl, cycloalkyl, aryl, or combination thereof as described above. In some embodiments, L comprises an aryl group. In some embodiments, L comprises a phenyl, biphenyl, or diphenyl ether group. In some embodiments, The tetracarboxylic acid dianhydride of [Chemical Formula II] has a structure selected from one or more structures provided in Table 1.

[0095] In some embodiments, the tetracarboxylic dianhydride is selected from the group consisting of pyromellitic dianhydride (PMDA), biphenyltetracarboxylic dianhydride (BPDA), oxydiphthalic dianhydride (ODPA), benzophenone tetracarboxylic dianhydride (BTDA), ethylenediaminetetraacetic dianhydride (EDDA), 1,4,5,8-naphthalenetetracarboxylic dianhydride, and combinations thereof. In some embodiments, the tetracarboxylic dianhydride is PMDA.

[0096] refer to [Flowchart 1], polyfunctional amines and polyfunctional anhydrides (e.g., diamines and dianhydrides) are allowed to react with each other to form The gel precursor of [Chemical Formula III], referred to herein as polyamide.

[0097] The molecular weights of polyamides and their corresponding polyimides can vary based on reaction conditions (e.g., concentration, temperature, reaction duration, properties of the diamine and dianhydride, etc.). This molecular weight is based on the number of repeating units in the polyamide, such as... In [Flowchart 1] [Chemical Formula III] and The integer value of "n" in the structure of [Formula IV] is indicated. The repeating unit, as defined herein, is part of a polyamide or polyacetate, and its repetition is achieved by continuously linking the repeating units together along the polymer chain to produce a complete polymer chain (excluding the terminal amine group). The specific molecular weight range of the polyimide produced by the disclosed method can vary. Generally, the reaction conditions can be modified to provide polyimides with desired physical properties without specifically considering the molecular weight. In some embodiments, alternatives to the molecular weight are provided in the viscosity of the amine salt solution of the polyamide, which is determined by variables such as temperature, concentration, molar ratio of reactants, and reaction time.

[0098] The molar ratio of dianhydride to diamine can vary depending on the desired reaction time, reagent structure, and desired material properties. In some embodiments, the molar ratio is from about 0.9 to about 3, for example, from about 0.9 or about 1, to about 2 or about 3. In some embodiments, the ratio is about 1 (i.e., stoichiometric), for example, from about 0.9 to about 1.1. In a particular embodiment, the ratio is from about 0.99 to about 1.01.

[0099] A polyfunctional amine (e.g., a diamine) and a polyfunctional anhydride (e.g., a tetracarboxylic dianhydride) are reacted for a period of time to complete the reaction between the amine and anhydride groups, providing polyamide. The reaction is generally allowed to continue until all available reactants (e.g., the diamine and dianhydride) have reacted with each other. The time required to complete the reaction may vary depending on the reagent structure, concentration, and temperature. In some embodiments, the reaction time is from about 1 minute to about 1 week, for example, from about 15 minutes to about 5 days, from about 30 minutes to about 3 days, or from about 1 hour to about 1 day. In some embodiments, the reaction time is from about 0.5 hours to about 17 hours. In some embodiments, the reaction time is from about 1 hour to about 12 hours.

[0100] The reaction temperature can vary. A suitable temperature range generally lies between about 10°C and about 100°C. In some embodiments, the reaction temperature is about 10°C to about 100°C, or about 15°C to about 60°C, or about 15°C to about 50°C, or about 15°C to about 25°C. In some embodiments, as the temperature increases, the resulting polyimide gel may have a wider pore size distribution and weaker structural properties. It is not desirable to be bound by theory; it is generally believed that in some embodiments, properties such as pore size distribution and structural stiffness may vary with temperature due to the molecular weight of the polyimide, the degree of chemical crosslinking (if possible), and other factors that may exhibit temperature dependence.

[0101] In some embodiments, polyamide has the following properties: As shown in [Flowchart 1] The structure of [Chemical Formula III]. The concentration of polyacrylic acid in solution may vary. For example, in some embodiments, the concentration of polyacrylic acid (i.e., the density of polyacrylic acid in solution) is from about 0.01 to about 0.3 g / cm³. In some embodiments, the solvent volume is selected to provide a specific target density (Td) of polyacrylic acid in solution. Generally, based on the weight of polyacrylic acid, the concentration of polyacrylic acid present in solution ranges from about 0.01 to about 0.3 g / cm³.

[0102] In an alternative embodiment, pre-prepared polyamides for this dehydration method may be provided. For example, they may be commercially available or prepared in a separate step by reacting polyfunctional amines and polyfunctional anhydrides in an organic solvent according to general synthetic methods.

[0103] refer to [Figure 1] After the reaction that forms the polyamide gel precursor is completed (or after the pre-formed polyamide is dissolved in a solvent), a dehydrating agent, along with a monoamine and water, is added to initiate and drive amide imidization, thereby forming a polyamide gel.

[0104] The structure of the dehydrating agent may vary, but generally it is an agent that is at least partially soluble in the reaction solution, reacts with the carboxyl groups of the ammonium salt, and effectively drives the amide group formation of the polyamide carboxyl and amide groups, while having minimal reactivity with aqueous solutions. One example of a suitable class of dehydrating agents is a carboxylic anhydride, such as acetic anhydride, propionic anhydride, etc. In some embodiments, the dehydrating agent is acetic anhydride. Surprisingly, according to this disclosure, the addition of acetic anhydride to an aqueous solution of an ammonium salt results in rapid gelation of the polyamide without the significant hydrolysis of acetic anhydride with water that is intuitively expected. Any hydrolysis that does occur is insufficient to compete with the function of acetic anhydride in the formation of polyamide.

[0105] In some embodiments, the amount of dehydrating agent may vary based on the amount of polyfunctional anhydride (e.g., tetracarboxylic dianhydride). For example, in some embodiments, the dehydrating agent and dianhydride are present in various molar ratios. The molar ratio of the dehydrating agent to the dianhydride may vary depending on the desired reaction time, reagent structure, and desired material properties. In some embodiments, the molar ratio is from about 2 to about 10, for example, from about 2, about 3, about 4, or about 5, to about 6, about 7, about 8, about 9, or about 10. In some embodiments, the ratio is from about 3 to about 6, or from about 4 to about 5. In some embodiments, the ratio is 4.3.

[0106] refer to [Figure 1], adding a monoamine or a combination of monoamines to a solution. In the context of this disclosure, the term "monoamine" refers to a molecule having a single amino group that can be used to accept a proton. Suitable monoamines include tertiary alkylamines, tertiary cycloalkylamines, heteroaromatic amines, guanidines, and tertiary ammonium hydroxides.

[0107] In some embodiments, the monoamine is a tertiary alkyl or cycloalkylamine. As used herein in the context of amines, "tertiary" means that the nitrogen atom of the amine has three organic (i.e., carbon) substituents attached to it. In some embodiments, the tertiary amine is triethylamine, trimethylamine, tri-n-butylamine, N-methylpyrrolidine, N-methylpiperidine, or diisopropylethylamine.

[0108] In some embodiments, the monoamine is a heteroaromatic amine. As used herein, the term "heteroaromatic amine" refers to an aromatic ring system in which one or more ring atoms are nitrogen. Heteroaromatic amines generally comprise 2 to 20 carbon atoms and 1 to 3 heteroatoms selected from N, O, P, and S, wherein at least one heteroatom is nitrogen. Heteroaromatic amines can be monocyclic with 3 to 7 ring members (selected from 2 to 6 carbon atoms and 1 to 3 heteroatoms) or rings with 7 to 10 ring members (4 to 9 carbon atoms and 1 to 3 heteroatoms), for example, bicyclic [4,5], [5,5], [5,6], or [6,6] systems. Heteroaromatic amines can be unsubstituted or substituted. Particularly suitable are heteroaromatic amines having a monocyclic structure comprising 5 carbon atoms and 1 nitrogen atom, such as pyridine. In some embodiments, the monoamine is pyridine. In some embodiments, the monoamine is pyridine with one or more alkyl substituents at suitable positions on the aromatic ring. For example, suitable pyridines include those substituted with one or more methyl groups, tributyl groups, or combinations thereof. Non-limiting examples include 2-, 3-, and 4-methylpyridine, 2,6-dimethylpyridine, 2,6-di-tributylpyridine, etc. In some embodiments, the monoamine is pyridine.

[0109] In some embodiments, the monoamine is a guanidine, such as guanidine ((NH2)2C=NH) or an alkyl guanidine (e.g., chemical formula (NR1R2)C=NR3(NR4R5), wherein any one or more of R1-R5 are alkyl).

[0110] In some embodiments, the monoamine is a quaternary ammonium hydroxide. As used herein, the term "quaternary ammonium hydroxide" refers to an organic molecule containing a nitrogen atom with four substituents, thus having a positive (cationic) charge, in equilibrium with hydroxide (OH-) ions, and dissociating in solution into free quaternary ammonium cations and hydroxide anions. In some embodiments, the quaternary ammonium hydroxide is tetraalkylammonium hydroxide. In some embodiments, tetraalkylammonium hydroxide contains about 4 to about 16 carbon atoms, for example, 4, 5, 6, 7, 8, 9, or 10 carbon atoms, up to 11, 12, 13, 14, 15, or 16 carbon atoms. Non-limiting examples of suitable tetraalkylammonium hydroxide include, but are not limited to, tetramethylammonium hydroxide, tetraethylammonium hydroxide, and tetra-n-butylammonium hydroxide.

[0111] The amount of monoamine added can vary. In some embodiments, in the absence of water, to achieve a gelation time of less than about 3 minutes, the amount of monoamine required to form a polyimide gel is reduced by up to about 27 times compared to a method for forming a polyimide gel with a density in the range of 0.05 g / cm³. In some embodiments, in the absence of water, to achieve a gelation time of less than about 15 seconds, the amount of monoamine required to form a polyimide gel is reduced by up to about 50 times compared to a method for forming a polyimide gel with a density in the range of 0.01 g / cm³. The amount of monoamine added can be based on a molar ratio, for example, relative to the molar ratio of polyamide. The molar ratio of monoamine to polyamide can vary depending on the desired reaction time, reagent structure, and desired material properties. In some embodiments, the molar ratio is from about 0.1 to about 8. In some embodiments, the moiré ratio is about 0.1, about 0.2, about 0.3, about 0.43, about 0.5, about 0.6, about 0.7, about 0.8, about 0.9, or about 1, to about 2, about 3, about 4, about 5, about 6, about 7, or about 8.

[0112] refer to [Figure 1] and [Flowchart 1], Water is added. As mentioned above, it was unexpectedly found that adding water accelerates rather than delays the dehydration of polyamide. Without being bound by any particular theory, it is generally believed that the presence of a catalytic amount of water solubilizes the ionic pairs of amine and carboxylic acid groups in polyamide, thereby promoting the reaction with the dehydrating agent. Notably, water alone does not lead to the formation of polyimide in the absence of a monoamine. Unexpectedly, the presence of water as a co-catalyst greatly accelerates the formation of polyimide gel, reducing the gelation time from hours to minutes, seconds, or even instantaneous, depending on the various factors described in the following examples.

[0113] The amount of water added may vary. In some embodiments, water is added in a molar ratio to tetracarboxylic dianhydride. In some embodiments, the molar ratio of water to tetracarboxylic dianhydride is greater than about 5. In some embodiments, the molar ratio of water to tetracarboxylic dianhydride is about 5 to about 500, for example about 5, about 10, about 25, about 50 or about 100, to about 200, about 300, about 400 or about 500.

[0114] The temperature at which the dehydration reaction can proceed may vary, but is generally less than about 50°C, for example, from about 10 to about 50°C, or from about 15 to about 25°C. gelation

[0115] The time from the addition of monoamine and water to the gelation of polyimide can vary. Generally, gelation occurs within less than about 1 minute, or less than about 30 seconds, or less than about 15 seconds from the addition of monoamine and water. In some embodiments, the polyimide gel has the following properties: According to [Flowchart 1] The structure of [Formula IV].

[0116] Those skilled in the art will recognize that the polyimide wet gels prepared according to either method A or method B described above will have unreacted terminal amine groups at one or both ends of a single polymer chain. In the polyimide wet gel, the percentage concentration of such amine groups will vary inversely with the average number of repeating units (i.e., molecular weight) present in the polyimide wet gel. In some embodiments, the terminal amine groups may react with a dehydrating agent to form, for example, terminal acetylamines. The relative concentration of such terminal amines or acetylamines can be determined according to methods known in the art (including, but not limited to, nuclear magnetic resonance spectroscopy).

[0117] In some embodiments, prior to any solvent exchange or drying, the water content in the wet gel is substantially the total amount of water initially used as the reaction solvent, regardless of any water generated or destroyed during any evaporation or various reactions occurring in the polyimide synthesis process as described above. Therefore, in some embodiments, for formulations having a target density (Td) of about 0.07 to about 0.10 g / cm³, the water content in the wet gel varies by volume from about 75% to about 83%.

[0118] In some embodiments, the method further includes casting the polyamide sol into a mold to form a polyimide wet gel monolith prior to gelation. Generally, the wet gel material is allowed to remain in the mold for a period of time (“casting”). This period can vary based on a variety of factors, such as the desirability of aging the material.

[0119] The process of converting a gel-forming component into a wet gel material can be replicated by including an aging step (also known as curing) prior to liquid-phase extraction. Aging the wet gel material after it has reached its gel point can further strengthen the gel framework. For example, in some embodiments, the framework can be strengthened during aging. The duration of gel aging can be adjusted to control various properties within the corresponding aerogel material. This aging process can be used to prevent potential volume loss and shrinkage during liquid-phase extraction of the wet gel material. Aging may include: holding the gel (before extraction) in a static state for an extended period; maintaining the gel at high temperatures; or any combination thereof. Preferred aging temperatures are generally between about 10°C and about 200°C. The aging of the wet gel material generally continues until the liquid-phase extraction of the wet gel material.

[0120] In some embodiments, the method includes casting a gelled acetic acid sol into a mold to form a polyimide wet gel monolith. In some embodiments, the monolith has a thickness of about 5 to about 25 millimeters. In some embodiments, the monolith is in the form of a film, for example, a film having a thickness of about 50 micrometers to about 1 millimeter. Solvent exchange

[0121] After molding and any aging, the resulting wet gel material can be demolded and washed, or the solvent can be exchanged in a suitable auxiliary solvent to replace the primary reaction solvent (i.e., N,N-dimethylacetamide, N,N-dimethylformamide, etc.) present in the wet gel. This auxiliary solvent can be a straight-chain alcohol having one or more aliphatic carbon atoms, a diol having two or more carbon atoms, or a branched-chain alcohol, cyclic alcohol, alicyclic alcohol, aromatic alcohol, polyol, ether, ketone, cyclic ether, or derivative thereof. In some embodiments, the auxiliary solvent is water, C1 to C3 alcohols (e.g., methanol, ethanol, propanol, isopropanol), acetone, tetrahydrofuran, ethyl acetate, acetonitrile, supercritical fluid carbon dioxide (CO2), or combinations thereof. In some embodiments, the auxiliary solvent is ethanol. [Bead formation]

[0122] Polyimide gels may need to be provided in bead form for various applications. While the methods described above generally provide polyimide gels in molded form (e.g., monolithic gels), the methods are applicable to bead formation. As used herein, the term "bead" is intended to include discrete small units or blocks having a generally spherical shape. In some embodiments, gel beads are substantially spherical. The composition of the beads is generally homogeneous, which results in each bead in a plurality of beads containing substantially the same amount of the same polyimide within the normal range of variation expected when preparing such beads. The size of the beads may vary depending on the desired properties and the preparation method.

[0123] Therefore, in some embodiments, the method further includes casting polyimide beads into an emulsion. Non-limiting embodiments of the method are described below. As shown in [Figure 2]. (Refer to the figure) [2] Polyamide is formed and dehydrated as described above, and beads can be prepared by mixing a sol, a water-immiscible carrier, and optionally one or more surfactants before rapid gelation occurs, and the two-phase mixture is mixed under high shear conditions to provide micron-sized beads. In some embodiments, the water-immiscible carrier and surfactant are added to the sol. In some embodiments, the sol is added to the water-immiscible carrier and surfactant.

[0124] The water-immiscible carrier can vary. Suitable carriers include, but are not limited to, oils, such as silicone oil or mineral oil, aliphatic hydrocarbons, aromatic hydrocarbons, and chlorinated hydrocarbons. In some embodiments, the water-immiscible carrier is a C5-C12 aliphatic or aromatic hydrocarbon. In some embodiments, the water-immiscible carrier is hexane. In a particular embodiment, the water-immiscible carrier is a mineral concentrate.

[0125] Surfactants can vary in their presence. As used herein, the term "surfactant" refers to a substance that contributes to emulsion formation and stabilization by promoting the dispersion of hydrophobic and hydrophilic (e.g., oil and water) components.

[0126] Suitable surfactants are generally nonionic and include, but are not limited to, polyethylene glycol esters, propylene glycol esters, polysorbate esters, polyglycerol esters, and dehydrated sorbitan esters of fatty acids. Suitable surfactants have an HLB value of about 0 to about 20. In some embodiments, the HLB value is about 3.5 to about 6. Those skilled in the art will understand that HLB is a hydrophilic-lipophilic balanced emulsifier and a measure of its degree of hydrophilicity or lipophilicity. HLB values ​​can be determined by calculating the values ​​of different regions of a molecule, as in Griffin in Griffin, William C. (1949), "Classification of Surface-Active Agents by 'HLB'" (PDF), Journal of the Society of Cosmetic Chemists, 1(5):311-26; and Griffin, William C. (1954), "Calculation of HLB Values ​​of Non-Ionic Surfactants" (PDF), Journal of the Society of Cosmetic Chemists, 5(4):249-56; and Davies in Davies JT (1957), "A quantitative kinetic theory of emulsion type, I. Physical chemistry of the emulsifying agent" (PDF), Gas / Liquid and Liquid / Liquid Interface, Proceedings of the International Congress of Surface Activity, pp.426-38. HLB values ​​can be determined according to industry standard textbooks, namely "The HLB SYSTEM, a time-saving guide to emulsifier selection" ICI Americas Inc., Published 1976 and Revised, March 1980.

[0127] Examples of suitable surfactants generally include, but are not limited to: polyoxyethylene-sorbitan-fatty acid esters; for example, mono- and tri-lauryl, palmityl, stearyl, and oleyl esters; for example, products of the type known as polysorbate esters and commercially available under the brand name Tween®; polyoxyethylene fatty acid esters, such as polyoxyethylene stearate esters of known types and commercially available under the brand name Myrj®; polyoxyethylene ethers, such as those available under the brand name Brij®; polyoxyethylene castor oil derivatives, such as products of known types and commercially available Cremophors®; and sorbitan fatty acid esters, such as those of known types and commercially available under the brand name Span® (e.g., Span...). 80); polyoxyethylene-polyoxypropylene copolymers, such as known and commercially available products of the Pluronic® or Poloxamer® type; triglycerides; and monoglycerides and acetylated monoglycerides, such as glyceryl mono-disco-carboxylate (Imwitor® 928), glyceryl monocaprylate (Imwitor® 308), and mono- and di-acetylated monoglycerides. In some embodiments, the one or more surfactants comprise commercially available polymeric surfactants of the known type under the trade name Hypermer® (Croda Industrial Chemicals; Edison, NJ, USA).

[0128] In some embodiments, one or more surfactants include Tween 20, Tween 80, Span 20, Span 40, Span 60, Span 80, or combinations thereof. In some embodiments, the surfactant is Span 20, Tween 80, or a mixture thereof. In some embodiments, one or more surfactants are Hypermer® B246SF. In some embodiments, one or more surfactants are Hypermer® A70.

[0129] The concentration of the surfactant may vary. In some embodiments, the surfactant or mixture of surfactants is present in a water-immiscible carrier in an amount of about 1 to about 5% by weight, for example, about 1, about 2, about 3, about 4 or about 5%.

[0130] Due to interfacial tension, spherical droplets of the hydrosol form in a water-immiscible carrier. The droplets gel and are enhanced in the water-immiscible carrier (e.g., hexane). Agitation of the mixture is generally used to form an emulsion and / or prevent droplet aggregation. For example, a mixture of an aqueous sol and a water-immiscible carrier can be agitated (e.g., stirred) to form an emulsion, which can be stable or transient. Exemplary embodiments of agitation to provide gel beads from the sol mixture and the water-immiscible carrier include magnetic stirring (up to about 600 rpm), mechanical mixing (up to about 1500 rpm), and homogenization (i.e., high-shear mixing up to about 9000 rpm). In some embodiments, mixing is performed under high-shear conditions, for example, using a high-shear mixer or homogenizer. Fluid undergoes shear when fluid travels at a different speed relative to adjacent regions. High-shear mixers (homogenizers) use rotating impellers or high-speed rotors or a series of such impellers or embedded rotors to "work" the fluid, thereby generating flow and shear. The tip velocity (i.e., the velocity the fluid encounters at the outer diameter of the rotor) will be higher than the velocity encountered at the center of the rotor, and this velocity difference will generate shear. Overall, the higher shear results in smaller beads. In some embodiments, a solvent, such as water or ethanol, may be added after gelation to produce smaller beads and reduce the aggregation of large clusters of beads.

[0131] The size of the wet gel beads may vary. In some embodiments, the wet gel beads have a size range of about 5 to about 500 micrometers in diameter, for example about 5, about 10, about 20, about 30, about 40 or about 50, to about 60, about 70, about 80, about 90, about 100, about 200, about 300, about 400 or about 500 micrometers.

[0132] In some embodiments, polyimide gel beads are cast into an aerosol. Therefore, in some embodiments, the method further includes spraying a polyimide sol solution into the air or into a water-immiscible carrier prior to gelation to form polyimide gel beads with a diameter of about 5 micrometers to about 250 micrometers. The spraying method may include forming droplets with gas assistance or by means of electrospraying. In some embodiments, the solution is sprayed into the air. In some embodiments, the solution is sprayed into a water-immiscible carrier. The water-immiscible carrier may vary. In some embodiments, the water-immiscible carrier is an oil, such as mineral oil or silicone oil. In some embodiments, the water-immiscible carrier is a hydrocarbon, such as an aliphatic or aromatic hydrocarbon, which may be halogenated. In some embodiments, the water-immiscible carrier is a C5-C12 hydrocarbon, such as hexane. In a particular embodiment, the water-immiscible carrier is a mineral concentrate.

[0133] In some embodiments, the method is performed as a continuous process, the opposite of a batch process. In some embodiments, the continuous process includes immediately spraying and agglomerating an imine sol (e.g., in the form of spherical beads) using a spray device. The gel beads are then continuously conveyed to an inert medium (e.g., air or a water-immiscible carrier) for subsequent process steps, such as filtration, aging / rinsing, drying, and carbonization. Solvent exchange

[0134] After forming beads by any of the foregoing methods, the obtained wet gel beads can be washed or the solvent can be exchanged in a suitable auxiliary solvent to replace the main reaction solvent present in the wet gel. Such auxiliary solvents can be straight-chain alcohols having one or more aliphatic carbon atoms, diols having two or more carbon atoms, or branched-chain alcohols, cyclic alcohols, alicyclic alcohols, aromatic alcohols, polyols, ethers, ketones, cyclic ethers, or derivatives thereof. In some embodiments, the auxiliary solvent is water, C1 to C3 alcohols (e.g., methanol, ethanol, propanol, isopropanol), acetone, tetrahydrofuran, ethyl acetate, acetonitrile, supercritical fluid carbon dioxide (CO2), or combinations thereof. In some embodiments, the auxiliary solvent is ethanol. [Formation of polyimide dry gels and aerogels]

[0135] Once the wet gel material (monolithic or bead-like) is formed and prepared, the liquid phase of the wet gel material can then be extracted from the wet gel material using extraction methods, including processing and extraction techniques, to form an aerogel material. Among other factors, liquid-phase extraction plays a significant role in designing the properties of the aerogel (such as porosity and density) and related properties (such as thermal conductivity). Generally, when extracting the liquid phase from the wet gel, the aerogel is obtained in a manner that causes low or no shrinkage to the porous network and framework of the wet gel. Various techniques can be used to dry the wet gel to provide an aerogel or dry gel material. In exemplary embodiments, the wet gel material can be dried under ambient pressure, under vacuum (e.g., by freeze-drying), under subcritical conditions, or under supercritical conditions to remove the solvent present in the wet gel to form the corresponding dry gel (e.g., an aerogel or dry gel).

[0136] In some embodiments, it may be necessary to fine-tune the surface area of ​​the dry gel. If surface area fine-tuning is required, the aerogel can be completely or partially converted into a dry gel with various porosities. The high surface area of ​​the aerogel can be reduced by forcing some pores to collapse. This can be done, for example, by immersing the aerogel in a solvent such as ethanol or acetone for a period of time or by exposing it to solvent vapor. The solvent is then removed by drying under ambient pressure. This method can be used to synthesize poreless shell / porous core beads, provided that the solvent is prevented from completely filling the beads, so that pore collapse occurs only on the surface of the beads.

[0137] Aerogels are generally formed by removing the liquid phase from the pores of a wet gel material at temperatures and pressures close to or above the critical point of the liquid mobile phase. Once the critical point is reached (near critical) or exceeded (supercritical; i.e., the system pressure and temperature are equal to or above the critical pressure and critical temperature, respectively), a new supercritical phase, distinct from the liquid or gas phase, emerges in the fluid. The solvent can then be removed without introducing liquid-vapor interfaces, capillary forces, or any mass transfer limitations generally associated with the liquid-gas boundary. Furthermore, the supercritical phase is generally more miscible with organic solvents, thus exhibiting better extraction capabilities. Co-solvent and solvent exchange are also frequently used to optimize supercritical fluid drying processes.

[0138] If evaporation or extraction occurs below the supercritical point, the capillary forces generated by liquid evaporation can lead to shrinkage and pore collapse within the gel material. Maintaining the liquid phase at or above the critical pressure and temperature during solvent extraction processes can reduce the negative impact of these capillary forces. In some embodiments disclosed herein, using conditions just below the critical point of the solvent system allows for the production of aerogels or aerogel-like materials or compositions with low shrinkage rates.

[0139] Various techniques can be used to dry wet gels to provide dry gel or aerogel materials. In exemplary embodiments, the wet gel material can be dried under ambient pressure, subcritical conditions, or supercritical conditions.

[0140] Room temperature and / or high temperature processes can be used to dry gel materials under ambient pressure. In some embodiments, a slow ambient pressure drying process can be used, wherein the wet gel is exposed to air in an open container for a period of time sufficient to remove the solvent, for example, from several hours to several weeks, depending on the solvent, the amount of wet gel, the exposed surface area, the size of the wet gel, etc.

[0141] In another embodiment, the wet gel material is dried by heating. For example, the wet gel material may be heated in a convection oven for a period of time to evaporate most of the solvent (e.g., ethanol). After partial drying, the gel may be left at ambient temperature for a period of time to dry completely, for example, from several hours to several days. Overall, the aerogel is obtained by this process.

[0142] In some embodiments, the wet gel material is dried by freeze-drying. "Freeze-drying" or "lyophilization" refers to a low-temperature process for removing solvents, including freezing the material (e.g., the wet gel material), reducing the pressure, and then removing the frozen solvent by sublimation. Since water represents the ideal solvent to be removed by freeze-drying, and water is the solvent in the methods disclosed herein, freeze-drying is particularly suitable for forming aerogels from the disclosed polyimide wet gel material.

[0143] Both supercritical and subcritical drying can be used to dry wet gel materials. In some embodiments, the wet gel material is dried under subcritical or supercritical conditions. In an exemplary embodiment of supercritical drying, the gel material can be placed in an autoclave to extract the solvent with supercritical CO2. After removing the solvent, such as ethanol, the vessel can be maintained above the critical point of CO2 for a period of time, for example, about 30 minutes. After supercritical drying, the vessel is depressurized to atmospheric pressure. Overall, the aerogel is obtained by this process.

[0144] In an example of subcritical drying, the gel material is dried using liquid CO2 at room temperature under a pressure of approximately 800 psi to approximately 1200 psi. This process is faster than supercritical drying; for example, a solvent (e.g., ethanol) can be extracted in approximately 15 minutes. Overall, the aerogel is obtained via this process.

[0145] Several additional aerogel extraction techniques are known in the art, including a range of different methods using supercritical fluids in the drying of aerogels, as well as environmental drying techniques. For example, Kistler (J. Phys. Chem. (1932) 36:52-64) describes a simple supercritical extraction process in which the gel solvent is maintained above its critical pressure and temperature, thereby reducing evaporative capillary forces and maintaining the structural integrity of the gel network. U.S. Patent No. 4,610,863 describes an extraction process in which the gel solvent is exchanged with liquid carbon dioxide, followed by extraction under supercritical conditions. U.S. Patent No. 6,670,402 teaches the production of aerogels by injecting supercritical (not liquid) carbon dioxide into an extractor that has been preheated and pre-pressurized to substantially supercritical conditions or higher, thereby extracting the liquid phase from the gel via rapid solvent exchange. U.S. Patent No. 5,962,539 describes a method for obtaining aerogels from polymeric materials in sol-gel form in an organic solvent by exchanging the organic solvent for a fluid with a critical temperature below the polymer decomposition temperature, and supercritically extracting the fluid from the sol-gel. U.S. Patent No. 6,315,971 discloses a method for preparing a gel composition, comprising: drying a wet gel containing a gel solid and a desiccant to remove the desiccant under drying conditions sufficient to reduce gel shrinkage during the drying process. U.S. Patent No. 5,420,168 describes a method for manufacturing resorcinol / formaldehyde aerogels using a simple air-drying process. U.S. Patent No. 5,565,142 describes a drying technique in which the gel surface is modified to be stronger and more hydrophobic, thereby enabling the gel framework and pores to resist collapse during ambient drying or subcritical extraction. Further embodiments of extracting a liquid phase from aerogel materials can be found in U.S. Patents 5,275,796 and 5,395,805.

[0146] In some embodiments, supercritical conditions using carbon dioxide are used to extract the liquid phase from a wet gel, including, for example: first, fully exchanging the primary solvent present in the gel's pore network with liquid carbon dioxide; then heating the wet gel (generally in an autoclave) above the critical temperature of carbon dioxide (approximately 31.06°C) and increasing the system pressure to a level greater than the critical pressure of carbon dioxide (approximately 1070 psig). Slight fluctuations in pressure around the gel material can facilitate the removal of supercritical carbon dioxide fluid from the gel. The carbon dioxide can be recycled via the extraction system to facilitate continuous removal of the primary solvent from the wet gel. Finally, the temperature and pressure are slowly restored to ambient conditions to produce a dried aerogel material. Pretreatment to a supercritical state may also be used before injecting carbon dioxide into the extraction chamber. In other embodiments, any suitable mechanism can be used for extraction, such as varying the pressure, time, and solvent described above. [Formation of carbon aerogels and dry gels]

[0147] In some embodiments, the dried polyimide dry gel or aerogel (monolith or beads) as disclosed herein is carbonized, meaning the polyimide dry gel or aerogel is heated to a temperature and time sufficient to convert substantially all organic materials into carbon. The required time and temperature may vary. In some embodiments, the dried polyimide aerogel is subjected to processing temperatures of 400°C or higher, 600°C or higher, 800°C or higher, 1000°C or higher, 1200°C or higher, 1400°C or higher, 1600°C or higher, 1800°C or higher, 2000°C or higher, 2200°C or higher, 2400°C or higher, 2600°C or higher, 2800°C or higher, or values ​​within a range of any two, for the carbonization of the polyimide aerogel. Generally, pyrolysis is carried out under an inert atmosphere to prevent combustion of the organic or carbonaceous material. Suitable atmospheres include, but are not limited to, nitrogen, argon, or combinations thereof. In some embodiments, pyrolysis is carried out under nitrogen atmosphere. [Formation of silicon-doped gels]

[0148] In some embodiments, any wet gel as disclosed herein may be doped with silicon, such as silicon particles, to provide silicon-doped polyimide or carbon gels (wet gels, dry gels, or aerogels, monoliths, or beads). In the context of this disclosure, the term "silicon particle" refers to a silicon or silicon-based material having a range of particle sizes suitable for use with the polyimide or carbon gels disclosed herein. The silicon particles disclosed herein may be nanoparticles, such as two-dimensional or three-dimensional particles having a range from about 1 nanometer to about 150 nanometers. The silicon particles disclosed herein are fine particles, such as micron-sized particles having a maximum size (e.g., the diameter of a substantially spherical particle) in the range from about 150 nanometers to about 10 micrometers or larger. For example, the silicon particles disclosed herein may have a maximum size, for example, the diameter of a substantially spherical particle within the range of about 10 nm, 50 nm, 100 nm, 150 nm, 200 nm, 500 nm, 1 μm, 1.5 μm, 2 μm, 3 μm, 5 μm, 10 μm, 20 μm, 40 μm, 50 μm, 100 μm, or any two of these values. In some embodiments, the particles are flat, fragment-shaped, such as flakes, having two dimensions, for example, a length and width within the range of about 10 nm, 50 nm, 100 nm, 150 nm, 200 nm, 500 nm, 1 μm, 1.5 μm, 2 μm, 3 μm, 5 μm, 10 μm, 20 μm, 40 μm, 50 μm, 100 μm, or any two of these values. In some embodiments, the silicon particles may be monodisperse or substantially monodisperse. In other embodiments, the silicon particles may have a particle size distribution. In the context of this disclosure, the size of the silicon particles is provided based on the median of the particle size distribution, i.e., D50. The silicon particles disclosed herein may be silicon wire, crystalline silicon, amorphous silicon, silicon alloys, silicon oxide (SiOx), coated silicon, such as carbon-coated silicon, and any combination of the silicon particle materials disclosed herein. In some embodiments, the silicon particles may be substantially planar flakes, i.e., having a flat, fragmented shape, also referred to as sheet-like. For example, the particles have two substantially flat primary surfaces connected by a secondary surface defining the thickness between the primary surfaces. In other embodiments, the particles of silicon or other electroactive materials may be substantially spherical, cubic, oblate, elliptical, disc-shaped, or toroidal.

[0149] Silicon particles can be produced using various techniques, including electrochemical reduction and mechanical grinding, or polishing. Polishing can be performed using either wet or dry processes. In a dry polishing process, powder is added to a container along with polishing media. Polishing media generally include balls or rods made of zirconium oxide (yttrium-stabilized), silicon carbide, silicon oxide, quartz, or stainless steel. The particle size distribution of the resulting abrasive material is controlled by the energy applied to the system and by matching the starting material particle size to the polishing media size. However, dry polishing is an inefficient and energy-intensive process. Wet polishing is similar to dry polishing, but with the addition of a polishing slurry. One advantage of wet polishing is that it consumes 15 to 50% less energy than dry polishing to produce the same results. Another advantage of wet polishing is that the polishing slurry protects the abrasive material from oxidation. Wet polishing has also been found to produce finer particles and result in less particle agglomeration.

[0150] A variety of liquid components can be used for wet milling. In exemplary embodiments, the milling slurry or components contained therein are selected to reduce or eliminate chemical functionalization on the surface of silicon particles during or after milling. In other embodiments, the milling slurry or components contained therein are selected to provide the desired surface chemical functionalization of the particles, such as silicon particles, during or after milling. The milling slurry or components contained therein can also be selected to control the chemical reactivity or crystal morphology of the particles, such as silicon particles. In exemplary embodiments, the milling slurry or components contained therein may be selected based on compatibility or reactivity with downstream materials, process steps, or the intended use of the particles, such as silicon particles. For example, the milling slurry or components contained therein may be compatible, useful, or identical to liquids or solvents used in processes for forming or manufacturing organic or inorganic aerogel materials. In yet another embodiment, the polishing slurry may be selected such that the polishing slurry or components contained in the polishing slurry form a coating on the surface of silicon particles or an intermediate substance (such as an aliphatic or aromatic hydrocarbon), or through crosslinking or the formation of a transfunctional compound that reacts with an organic or inorganic aerogel material.

[0151] The solvent or solvent mixture used for grinding can be selected to control the chemical functionalization of the particles during or after grinding. Taking silicon as an example, without being bound by theory, grinding silicon in an alcoholic solvent (e.g., isopropanol) can functionalize the surface of silicon and covalently bond alkyl surface groups (e.g., isopropyl groups) to the surface of the silicon particles. FTIR-ATR analysis has shown that, upon exposure to air, alkyl groups can be oxidized to the corresponding alkoxides. In exemplary embodiments, grinding can be carried out in a polar aprotic solvent, such as DMSO, DMF, NMP, DMAC, THF, 1,4-dioxane, diethylene glycol dimethyl ether, acetonitrile, water, or any combination thereof.

[0152] Silicon particles can be incorporated into polyimides or carbon gels as disclosed herein in various ways. Generally, silicon particles are added during a sol-gel process. In one non-limiting embodiment, the silicon particles are dispersed in a polyamide sol prior to acetylation. In some embodiments, the silicon particles are dispersed in a solvent, such as water or a polar aprotic solvent, prior to combination with a polyimide precursor. In some embodiments, the silicon particles are dispersed in a polyamide sol during the acetylation process. [Properties of polyimide and carbon aerogel]

[0153] In some embodiments, polyimide and carbon aerogels, as disclosed herein, can be in monolithic form. As used herein, the term "monolithic" refers to an aerogel material in which the majority (by weight) of the aerogel contained within is in the form of a macroscopic, single, continuous, self-supporting object. Monolithic aerogel materials include aerogel materials that are initially formed with a well-defined shape but may subsequently break, fracture, or fragment into non-repeating objects. For example, irregular blocks can be considered monolithic. Monolithic aerogels can be in the form of freestanding structures or in the form of fiber-reinforced materials or interpenetrating foams.

[0154] In other embodiments, the aerogels disclosed herein, such as polyimide or carbon aerogels, may be in particulate form, for example as beads or particles derived from, for example, broken monolithic materials. Particulate aerogels may have various particle sizes. In the case of spherical particles (e.g., beads), particle size is the diameter of the particle. In the case of irregular particles, the term particle size refers to the maximum dimension (e.g., length, width, or height). Particle size can vary depending on the physical form, preparation method, and any subsequent physical steps performed. In some embodiments, particulate aerogels may have a particle size of about 1 micrometer to about 10 millimeters. For example, aerogels in particulate form may have particle sizes of about 1 micrometer, about 2 micrometers, about 3 micrometers, about 4 micrometers, about 5 micrometers, about 6 micrometers, about 7 micrometers, about 8 micrometers, about 9 micrometers, about 10 micrometers, about 15 micrometers, about 20 micrometers, about 25 micrometers, about 30 micrometers, about 35 micrometers, about 40 micrometers, about 45 micrometers, about 50 micrometers, about 60 micrometers, about 70 micrometers, about 80 micrometers, about 90 micrometers, about 100 micrometers, about 200 micrometers, about 300 micrometers, about 400 micrometers, about 500 micrometers, about 600 micrometers, about 700 micrometers, about 800 micrometers, about 900 micrometers, about 1 millimeter, about 3 millimeters, about about 4 millimeters, about 5 millimeters, about 6 millimeters, about 7 millimeters, about 8 millimeters, about 9 millimeters, about 10 millimeters, or in any range between these values. In some embodiments, the aerogel may have a particle size in the range of about 5 micrometers to about 100 micrometers or about 5 to about 50 micrometers. In some embodiments, the aerogel may have a particle size in the range of about 1 to about 4 millimeters.

[0155] Polyimide and carbon aerogels, as disclosed herein, have densities. As used herein, the term "density" refers to a measurement of the mass per unit volume of an aerogel material or composition. The term "density" generally refers to the true or skeletal density of the aerogel material and the bulk density of the aerogel composition. Densities are generally reported in kg / m³ or g / cm³. The skeletal density of polyimide or carbon aerogels can be determined by methods known in the art, including but not limited to the helium gravimetric method. The bulk density of polyimide or carbon aerogels can be determined by methods known in the art, including but not limited to: standard test methods for the dimensions and density of preformed block and panel insulation materials (ASTM C303, ASTM International, West Conshohocken, Pa.); standard test methods for the thickness and density of blanket or felt insulation materials (ASTM C167, ASTM International, West Conshohocken, Pa.); or determination of the apparent density of prefabricated pipe insulation materials (ISO 18098, International Organization for Standardization, Switzerland). In the context of this disclosure, unless otherwise stated, density measurements are obtained by nitrogen adsorption measurements at 77°K according to ASTM C167. In some embodiments, the polyimide or carbon aerogel disclosed herein has a bulk density of about 0.01 to about 0.1 g / cm³.

[0156] Polyimide and carbon aerogels, as disclosed herein, exhibit pore size distributions. As used herein, the term "pore size distribution" refers to the statistical distribution or relative amount of each pore size within a sample volume of a porous material. A narrower pore size distribution refers to a larger proportion of pores within a narrower pore size range. In some embodiments, a narrower pore size distribution may be required, for example, to optimize the number of pores that can surround an electrochemically active material and to maximize the use of the available pore volume. Conversely, a wider pore size distribution refers to a relatively smaller proportion of pores within a narrower pore size range. Thus, the pore size distribution is generally measured as a function of pore volume and recorded as a unit size of the full width at half maximum (FWHM) of the dominant peak in a pore size distribution plot. The pore size distribution of porous materials can be determined by methods known in the art, such as, but not limited to, surface area, framework density, and porosity determinations, from which the pore size distribution can be calculated. Suitable methods for determining such characteristics include, but are not limited to, measurements of gas adsorption / desorption (e.g., nitrogen), helium specific gravity determinations, mercury porosity determinations, etc. Unless otherwise stated, the measurements of the pore size distribution reported herein were obtained by nitrogen adsorption analysis. In some embodiments, the polyimide or carbon aerogel disclosed herein has a relatively narrow pore size distribution.

[0157] The polyimide and carbon aerogels disclosed herein possess pore volumes. As used herein, the term "pore volume" refers to the total volume of pores within a porous material sample. Pore volume is specifically measured as the volume of void spaces within the porous material, generally recorded as cubic centimeters per gram (cm³ / g or cubic centimeters / g). The pore volume of a porous material can be determined by methods known in the art, such as, but not limited to, surface area and porosity analysis (e.g., nitrogen porosity determination, mercury porosity determination, helium specific gravity determination, etc.). In some embodiments, the polyimide or carbon aerogels disclosed herein have relatively large pore volumes of about 1 cubic centimeter / g or more, 1.5 cubic centimeter / g or more, 2 cubic centimeter / g or more, 2.5 cubic centimeter / g or more, 3 cubic centimeter / g or more, 3.5 cubic centimeter / g or more, 4 cubic centimeter / g or more, or within any two of these values. In other embodiments, the polyimide or carbon aerogel and degel disclosed herein have pore volumes of about 0.03 cubic centimeters / g or more, 0.1 cubic centimeters / g or more, 0.3 cubic centimeters / g or more, 0.6 cubic centimeters / g or more, 0.9 cubic centimeters / g or more, 1.2 cubic centimeters / g or more, 1.5 cubic centimeters / g or more, 1.8 cubic centimeters / g or more, 2.1 cubic centimeters / g or more, 2.4 cubic centimeters / g or more, 2.7 cubic centimeters / g or more, 3.0 cubic centimeters / g or more, 3.3 cubic centimeters / g or more, 3.6 cubic centimeters / g or more, or within any two of these values.

[0158] In some embodiments disclosed herein, the gel material (polyimide or carbon, aerogel or dry gel, monolith or bead) may include a fibrous morphology. In the context of this disclosure, the term "fibrous morphology" refers to the structural morphology of a nanoporous material (e.g., carbon aerogel), including struts, rods, fibers, or filaments.

[0159] Unless otherwise stated herein or clearly contradicted by the context, all methods described herein may be performed in any suitable order. Unless otherwise stated, the use of any and all embodiments or illustrative language (e.g., "such as") provided herein is intended only to better illustrate the materials and methods and does not constitute a limitation on the scope. No language in this specification should be construed as representing any unclaimed element necessary for the practice of the disclosed materials and methods.

[0160] It will be apparent to those skilled in the art that suitable modifications and adjustments can be made to the compositions, methods, and applications described herein without departing from the scope of any embodiments or variations thereof. The compositions and methods provided are illustrative and are not intended to limit the scope of the claimed embodiments. The various embodiments, variations, and options disclosed herein can be combined in all possible variations. The scope of the compositions, formulations, methods, and processes described herein includes all actual or potential combinations of the embodiments, variations, options, examples, and preferences described herein.

[0161] Although the technology described herein has been referenced to specific embodiments, it should be understood that these embodiments are merely illustrative of the principles and applications of the technology. It is obvious that various modifications and variations can be made to the methods and apparatus of this technology by those skilled in the art without departing from the spirit and scope of the technology. Therefore, this technology is intended to include modifications and variations within the scope of the appended claims and their equivalents.

[0162] References to "one embodiment," "some embodiments," "one or more embodiments," or "an embodiment" in this specification mean that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the present technology. Therefore, phrases such as "in one or more embodiments," "in some embodiments," "in one embodiment," or "in one embodiment" appearing throughout this specification do not necessarily refer to the same embodiment of the present technology. Furthermore, specific features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments. All scope referenced herein is included.

[0163] The following embodiments are provided to illustrate the various aspects of this technology more fully. Before describing several exemplary embodiments of this technology, it should be understood that this technology is not limited to the details of the construction or process steps set forth in the following description. This technology can have other embodiments and can be practiced or implemented in various ways. The following embodiments are presented to illustrate certain aspects of this technology, but should not be construed as limiting it. [Example]

[0164] The present invention can be further illustrated by the methods and materials described in the following non-limiting embodiments. [Example 1. Preparation of PMDA-PDA polyimide gel with fixed pyridine concentration and no added water (reference)]

[0165] Polyimide gel was prepared with a target density of 0.05 g / cm³. Solid pyromellitic dianhydride (PMDA, 3.38 g, 0.0155 moles) was dissolved in 77 g of dimethylacetamide (DMAc). After stirring for 30 minutes, 1,4-phenylenediamine (PDA, 1.67 g, 1:1 mole / mole ratio to PMDA) was added to the PMDA solution. The mixture was stirred at room temperature for 4 hours. Acetic anhydride (6.8 g, 4.3 moles / mole ratio to PMDA) was added to the obtained polyimide solution, and the mixture was stirred for another 20 minutes. At the end of this period, pyridine (1.23 g, 1.0 moles / mole ratio to PMDA) was added to the solution. After the addition of pyridine, the resulting sol was stirred for 2 minutes and then poured into a mold for gelation. It gels at room temperature within approximately 90 minutes. [Example 2. Preparation of PMDA-PDA polyimide gels with different pyridine concentrations without adding water (reference)]

[0166] The polyimide gel was prepared as in Example 1, but the molar ratio of pyridine to PMDA used was 2 and 4 (Examples 2.1 and 2.2, respectively). Gelation of the two sols occurred at 38 minutes and 26 minutes, respectively. [Example 3. Preparation of PMDA-PDA polyimide gel with added water and fixed pyridine concentration]

[0167] The polyimide gel was prepared at a target density of 0.05 g / cm³. PMDA (3.38 g, 0.0155 moles) was dissolved in 68 g of DMAc. After stirring for 30 minutes, PDA (1.67 g, 1:1 mole / mole ratio relative to PMDA) was added to the PMDA solution. The mixture was stirred at room temperature for 4 hours. Acetic anhydride (6.8 g, 4.3 moles / mole ratio relative to PMDA) was added to the obtained polyimide solution, and the mixture was stirred for 20 minutes. At the end of this period, pyridine (1.23 g, 1.0 moles / mole ratio relative to PMDA) was added to the solution. The resulting sol was stirred for 2 minutes, and 9.8 g of water (35 moles / mole ratio relative to PMDA) was added. Gelation occurred at room temperature within approximately 3.5 minutes (compared to 90 minutes in anhydrous conditions; see Example 1). [Example 4. Preparation of PMDA-PDA polyimide gels with different water and pyridine concentrations at a fixed target density (0.05 g / cm³).]

[0168] A study was conducted to evaluate the effect of five different pyridine / PMDA molar ratios (0.25, 0.45, 1, 2, and 4) of H2O / PMDA molar ratio on the gelation time of PMDA-PDA polyimide with a gel density of 0.05 g / cm³ in DMAc using acetic anhydride as a dehydrating agent. This H2O / PMDA molar ratio varied between 10 and 35 (0, 10, 15, 20, 25, 30, and 35) (see Table 2 below). Several representative procedures for the preparation of polyimide gels are provided below as Examples 4.1, 4.2, and 4.3. [Example 4.1: Using pyridine / PMDA = 0.45 and H] [2] [O / PMDA=20 Synthetic Polyimide Gel]

[0169] Solid PMDA (3.38 g, 0.0155 moles) was dissolved in 72 g of DMAc. After stirring for 30 minutes, PDA (1.67 g, 1:1 mole / mole ratio relative to PMDA) was added to the PMDA solution. The mixture was stirred at room temperature for 4 hours. Acetic anhydride (6.8 g, 4.3 moles / mole ratio relative to PMDA) was added to the obtained polyacrylic acid solution, and the mixture was stirred for 20 minutes. At the end of the reaction period, pyridine (0.55 g, 0.45 moles / mole ratio relative to PMDA) was added to the solution. The resulting sol was stirred for 2 minutes, and 5.58 g of water (20 moles / mole ratio relative to PMDA) was added to the sol. Gelation occurred at room temperature within approximately 11 minutes. [Example 4.2: Using pyridine / PMDA = 0.25 and H] [2] [O / PMDA=10 Synthetic Polyimide Gel]

[0170] Solid PMDA (3.38 g, 0.0155 mol) was dissolved in 75 g of DMAc. After stirring for 30 minutes, PDA (1.67 g, mol / mol ratio of PMDA 1:1) was added to the PMDA solution. The mixture was stirred at room temperature for 4 hours. Acetic anhydride (6.8 g, mol / mol ratio of PMDA 4.3) was added to the obtained polyacrylic acid solution, and the mixture was stirred for 20 minutes. At the end of the reaction period, pyridine (0.30 g, mol / mol ratio of PMDA 0.25) was added to the solution. The resulting sol was stirred for 2 minutes, and 2.79 g of water (mol / mol ratio of PMDA 10) was added to the sol. Gelation occurred at room temperature within approximately 97 minutes. [Example 4.3: Using pyridine / PMDA=2 and H] [2] [O / PMDA=15 Synthetic Polyimide Gel]

[0171] Solid PMDA (3.38 g, 0.0155 mol) was dissolved in 72 g of DMAc. After stirring for 30 minutes, PDA (1.67 g, mol / mol ratio of PMDA 1:1) was added to the PMDA solution. The mixture was stirred at room temperature for 4 hours. Acetic anhydride (6.8 g, mol / mol ratio of PMDA 4.3) was added to the obtained polyacrylic acid solution, and the mixture was stirred for 20 minutes. At the end of the reaction period, pyridine (2.45 g, mol / mol ratio of PMDA 2.0) was added to the solution. The resulting sol was stirred for 2 minutes, and 4.18 g of water (mol / mol ratio of PMDA 15) was added to the sol. Gelation occurred at room temperature within approximately 8.2 minutes. [Results: Examples 1 to 4]

[0172] Showing [Figure 3A] and The data in [Figure 3B] show that the gelation time decreases rapidly with increasing water content, and all curves converge at the highest H2O / PMDA molar ratio of 35, indicating that the effect of the pyridine / PMDA molar ratio becomes almost negligible.

[0173] To evaluate the properties corresponding to the carbon aerogel, polyimide aerogels were prepared from various wet gels in Example 4. The polyimide wet gels were washed with ethanol and dried by supercritical CO2 extraction to provide the corresponding polyimide aerogels. These polyimide aerogels were then carbonized under nitrogen to provide the corresponding carbon aerogels.

[0174] exist [Figure 4] (PY / PMDA=0.25) and [Figure 5] (PY / PMDA=0.45) provides the physical and structural properties of polyimide (PI) and the corresponding carbon aerogel. The surface area and pore volume of the carbon aerogel are evaluated as a function of the molar ratio of water to PMDA. [Figure 6] provides results for carbon aerogels produced from polyimide aerogels prepared with a fixed target density of pyridine / PMDA = 0.65 and 0.05 g / cm³, and different H₂O / PMDA molar ratios. The results in [Figure 6] show that the effect of the H2O / PMDA molar ratio on the surface area is small (from about 550 to about 600 m2 / g for H2O / PMDA molar ratios from 0 to 35), while the pore volume decreases with increasing H2O / PMDA molar ratio.

[0175] like [Figure 7A] and As shown in [Figure 7B], from the described method (Example 3) ( The carbon aerogel prepared by carbonization of polyimide aerogel (Figure 7B) has comparable properties to that of Example 1 by the reference method ( [Figure 7A] shows the fibrous structure of a reference carbon aerogel prepared by carbonization of polyimide aerogel. The concentration of pyridine (PY / PMDA) and the amount of water added before gelation do not appear to have any effect on the structure of the carbon aerogel. [Figure 8A] and [Figure 8B] shows SEM images of carbon aerogel samples prepared with PY / PMDA at H2O / PMDA ratios of 0 and 35 and PY / PMDA of 0.25, respectively. [Figure 9A] and [9B] SEM images of carbon aerogel samples prepared with a PY / PMDA ratio of 2.0 at H2O / PMDA ratios of 0 and 35 are shown respectively. SEM micrographs of carbon aerogel samples prepared with a PY / PMDA ratio of 0.45 and H2O / PMDA ratios of 0, 10, and 35 are provided respectively. [Figures 10A to 10C] [Figures 10D to 10F] and [Figures 10G to 10I]. Regardless of the concentrations of water and pyridine, all samples exhibited a fibrillar structure. [Example 5. Preparation of PMDA-PDA polyimide gels with different water and pyridine concentrations at a fixed target density (0.1 g / cm³).]

[0176] In another study, the effect of the H2O / PMDA molar ratio at two different pyridine / PMDA molar ratios (0.25 and 0.45) on the gelation time of PMDA-PDA polyimide at 0.1 g / cm³ was evaluated. This H2O / PMDA molar ratio varied between 0 and 25 (0, 5, 10, 15, 20, 25; Table 3). Several representative procedures for the preparation of polyimide gels are provided below as Examples 5.1 and 5.2. [Example 5.1: Using pyridine / PMDA = 0.25 and H] [2] [O / PMDA=10 Synthetic Polyimide Gel]

[0177] Solid PMDA (6.76 g, 0.031 mol) was dissolved in 66 g of DMAc. After stirring for 30 minutes, PDA (3.35 g, mol / mol ratio of PMDA 1:1) was added to the PMDA solution. The mixture was stirred at room temperature for 4 hours. Acetic anhydride (13.6 g, mol / mol ratio of PMDA 4.3) was added to the obtained polyacrylic acid solution, and the mixture was stirred for 20 minutes. At the end of the reaction period, pyridine (0.61 g, mol / mol ratio of PMDA 0.25) was added to the solution. The resulting sol was stirred for 30 seconds, and 5.58 g of water (mol / mol ratio of PMDA 10) was added to the sol. Gelation occurred at room temperature within approximately 3.15 minutes. [Example 5.2: Using pyridine / PMDA = 0.45 and H] [2] [O / PMDA=5 Synthetic Polyimide Gel]

[0178] Solid PMDA (6.76 g, 0.031 mol) was dissolved in 69 g of DMAc. After stirring for 30 minutes, PDA (3.35 g, mol / mol ratio of PMDA 1:1) was added to the PMDA solution. The mixture was stirred at room temperature for 4 hours. Acetic anhydride (13.6 g, mol / mol ratio of PMDA 4.3) was added to the obtained polyacrylic acid solution, and the mixture was stirred for 20 minutes. At the end of the reaction period, pyridine (1.10 g, mol / mol ratio of PMDA 0.45) was added to the solution. The resulting sol was stirred for 30 seconds, and 2.79 g of water (mol / mol ratio of PMDA 5) was added to the sol. Gelation occurred at room temperature within approximately 5 minutes. [result]

[0179] The data in Examples 5.1 and 5.2 are provided in [Figure 11] shows that the gelation time decreases rapidly with increasing water concentration. At H2O / PMDA molar ratios of 15 to 25, a plateau is reached in the gelation time at 2.5 minutes, where the effect of the pyridine / PMDA molar ratio becomes negligible. [Example 6. Preparation of BTDA-PDA polyimide gel without adding water and with a fixed pyridine concentration (reference)]

[0180] Polyimide gel was prepared with a target density of 0.14 g / cm³. Solid 3,3',4,4'-benzophenone-tetracarboxylic acid dianhydride (BTDA, 10 g, 0.031 moles) was dissolved in 104 g of dimethylacetamide. After stirring for 30 min, 1,4-phenylenediamine (PDA; 3.8 g, mole / mole ratio of 1:1 relative to BTDA) was added to the BTDA solution. The mixture was stirred at room temperature for 2 h. Acetic anhydride (14.9 g, mole / mole ratio of 4.3 relative to BTDA) was added to the obtained polyimide solution, and the mixture was stirred for 1 h. At the end of the reaction period, pyridine (1.28 g, mole / mole ratio of 0.52 relative to BTDA) was added to the solution. After the addition of pyridine, the resulting sol was stirred for 2 min and then poured into a mold for gelation. Gel formation occurs and is completed at room temperature within approximately 68 minutes. [Example 7. Preparation of BTDA-PDA polyimide gel by adding water at two different pyridine concentrations.]

[0181] A study similar to Example 4 was conducted using BTDA instead of PMDA. To evaluate the effect of the H2O / BTDA molar ratio on gelation time at two different pyridine / BTDA molar ratios (0.24, 0.52), BTDA-PDA polyimide was prepared in DMAc with acetic anhydride at a gel density of 0.14 g / cm³ as a dehydrating agent. This H2O / BTDA molar ratio varied between 0 and 54 (0, 8, 18, 36, and 54). Several representative procedures for the preparation of polyimide gels are provided below as Examples 7.1 and 7.2. [Example 7.1: Pyridine / BTDA = 0.24 and H] [2] Synthesis of polyimide gel with O / BTDA=36

[0182] 10 g of solid BTDA (0.031 moles) was dissolved in 120 g of DMAc. After stirring for 30 minutes, 3.8 g of PDA (1:1 mole / mole ratio to BTDA) was added to the BTDA solution. The mixture was stirred at room temperature for 2 hours. Acetic anhydride (14.9 g, 4.3 moles / mole ratio to BTDA) was added to the obtained polyacrylic acid solution, and the mixture was stirred for 1 hour. At the end of the reaction period, pyridine (0.59 g, 0.24 moles / mole ratio to BTDA) was added to the solution. The resulting sol was stirred for 2 minutes, and 40 g of water (36 moles / mole ratio to BTDA) was added to the sol. Gelation occurred at room temperature within approximately 12 minutes. [Example 7.2: Pyridine / BTDA = 0.52 and H] [2] Synthesis of polyimide gel with O / BTDA=54

[0183] 10 g of solid BTDA (0.031 moles) was dissolved in 120 g of dimethylacetamide. After stirring for 30 minutes, 3.8 g of PDA (1:1 mole ratio to BTDA) was added to the BTDA solution. The mixture was stirred at room temperature for 2 hours. Acetic anhydride (14.9 g, 4.3 moles / moles ratio to BTDA) was added to the obtained polyacrylic acid solution, and the mixture was stirred for 1 hour. At the end of the reaction period, pyridine (1.28 g, 0.52 moles / moles ratio to BTDA) was added to the solution. The resulting sol was stirred for 2 minutes, and 60 g of water (54 moles / moles ratio to BTDA) was added to the sol. Gelation occurred at room temperature within approximately 3 minutes. [result]

[0184] exist [Figures 12 and 13] show the effect of the H2O / BTDA ratio on gelation time at two different pyridine / BTDA molar ratios in Example 6. Reference [Figure 13] The data show that the gelation time is similar under different dianhydride and water co-catalyst conditions. Specifically, the gelation time decreases with increasing water molar ratio. Notably, despite the low pyridine concentration (0.52 vs 1.0), the gelation of BTDA-PDA polyimide is similar to that of PMDA-PDA polyimide (target density 0.05 g / cm³) across the entire water range. [Example 8. Preparation of BPDA-PDA polyimide gel using different water concentrations and a fixed pyridine concentration]

[0185] A study was conducted to evaluate the effect of different molar ratios of water on the gelation of polyimide prepared using different dianhydrides (biphenyltetracarboxylic dianhydride; BPDA). The study was performed using the procedure of Example 4, but with BPDA instead of PMDA, and using the molar ratios provided in Table 4. A representative procedure for preparing polyimide gels is provided below as Example 8.1. [Example 8.1. Pyridine / BPDA = 0.93 and H] [2] [Preparation of polyimide gel using O / BPDA=35BPDA-PDA.]

[0186] Solid BPDA (10 g, 0.034 moles) was dissolved in 187 g of dimethylacetamide. Dissolution of BPDA was only complete after the addition of the diamine. After stirring for 15 minutes, PDA (3.66 g, 1:1 mole / mole ratio to BPDA) was added to the BPDA solution. The mixture was stirred at room temperature for 2 hours. Acetic anhydride (14.5 g, 4.3 moles / mole ratio to BPDA) was added to the resulting polyacrylic acid solution, and the mixture was stirred for 1 hour. At the end of the reaction period, pyridine (2.51 g, 0.93 moles / mole ratio to BPDA) was added to the solution. The resulting sol was stirred for 2 minutes, and 21.5 g of water (35 moles / mole ratio to BPDA) was added to the sol. Gelation occurred at room temperature within approximately 12 minutes.

[0187] result( [Figure 14] demonstrates that the polyamide sol prepared by BPDA has a longer gelation time, although a higher water concentration is required to achieve rapid gelation compared to those with higher pyridine concentrations used with BTDA. [Example 9. Data Summary]

[0188] exist [Figure 15] provides the sol-gel compositions of the various gels synthesized in Examples 1 to 8. The density, shrinkage, and carbon yield of the polyimide aerogels described in Examples 1 to 7 before and after carbonization (1050°C for 2 hours under nitrogen) are provided as follows. [Figure 16]

Claims

1. A method for forming a polyimide gel, the method comprising: a) Provides tetracarboxylic dianhydride and polyfunctional amines; b) Add the tetracarboxylic acid dianhydride and the polyfunctional amine to an organic solvent to form a solution; c) reacting the tetracarboxylic dianhydride with the polyfunctional amine in solution to form a polyamide sol solution; and d) adding a dehydrating agent, a monoamine, and water to the polyamide sol solution to form a gelling mixture, and gelling the gelling mixture to form the polyimide gel, wherein the water is added at a molar ratio of about 5 to about 500 for the tetracarboxylic dianhydride.

2. The method as described in request item 1, wherein, The following are applicable: the tetracarboxylic dianhydride is selected from the group consisting of pyromellitic dianhydride (PMDA), biphenyltetracarboxylic dianhydride (BPDA), oxydiphthalic dianhydride (ODPA), benzophenone tetracarboxylic dianhydride (BTDA), ethylenediaminetetraacetic dianhydride (EDDA), 1,4,5,8-naphthalenetetracarboxylic dianhydride and combinations thereof; and the polyfunctional amine is 1,3,5-tris(4-aminophenoxy)benzene (TAPOB), tris(4-aminophenyl)methane, melamine or combinations thereof.

3. The method as described in request item 1, wherein, This polyfunctional amine is an alkyl diamine or an aryl diamine.

4. The method as described in request item 3, wherein, The alkyldiamine is ethylenediamine, 1,3-diaminepropane, 1,4-diaminebutane, 1,5-diaminepentane, 1,6-diaminehexane, or a combination thereof.

5. The method as described in request item 3, wherein, The aryl diamine is 1,4-phenylenediamine, 4,4'-diamine diphenyl ether, 4,4'-methylenebis-diphenylamine, or a combination thereof.

6. The method as described in request item 1, wherein, One or more of the following applies: the molar ratio of the tetracarboxylic dianhydride to the polyfunctional amine is about 0.9 to about 3; the molar ratio of the monoamine to the polyamide sol is about 0.1 to about 8; the molar ratio of the dehydrating agent to the tetracarboxylic dianhydride is about 2 to about 10; the concentration of the polyamide sol in the solution is in the range of about 0.01 to about 0.3 g / cm³; compared with the amount of monoamine required for forming polyimide gel under anhydrous conditions, the amount of monoamine required to form polyimide gel with a gelation time of less than about 15 minutes is reduced by nearly about 50 times.

7. The method as described in request item 1, wherein, The monoamine is a third alkylamine, a third cycloalkylamine, a heteroaromatic amine, a guanidine, or a fourth ammonium hydroxide.

8. The method as described in request item 1, wherein, The monoamine system is selected from the group consisting of trimethylamine, triethylamine, tri-n-propylamine, tri-n-butylamine, N-methylpyrrolidine, N-methylpiperidine, diisopropylethylamine, pyridine, quinoline, guanidine, and tetraalkylammonium hydroxide.

9. The method as described in claim 1, wherein, This is a monoamine pyridine.

10. The method as described in claim 1, wherein, The dehydrating agent is a carboxylic anhydride.

11. The method as described in claim 10, wherein, The carboxylic anhydride is acetic anhydride.

12. The method as described in claim 1, wherein, The organic solvent is N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, tetrahydrofuran, ethyl acetate, or a combination thereof.

13. The method as described in claim 1, wherein, One or more of the following applies: the polyfunctional amine and the tetracarboxylic dianhydride are reacted over a period of about 0.5 hours to about 17 hours; the polyfunctional amine and the tetracarboxylic dianhydride are reacted at a temperature of about 10 to about 100°C; and the time from the addition of the monoamine and water to the gelation of the polyimide is less than about 1 minute.

14. The method as described in claim 1, further comprising: Before the gelled mixture is fully gelled, it is cast into a mold to form a polyimide wet gel monolith; The polyimide wet gel is demolded; the polyimide wet gel is washed or solvent-exchanged; and the polyimide wet gel is dried to form a monolithic polyimide aerogel or dry gel.

15. The method as described in claim 14, wherein, The single piece has a thickness of approximately 5 to approximately 25 millimeters.

16. The method as described in claim 14, wherein, The single piece has a thickness of approximately 50 micrometers to approximately 1 millimeter.

17. The method of claim 1 further includes carbonizing the monolithic polyimide aerogel or dry gel to form a carbon aerogel or dry gel.

18. The method as described in claim 1, wherein, The method further comprises: e) adding the gelled mixture to mineral oil, silicone oil, C5-C12 hydrocarbons or mineral concentrate to form an emulsion before the gelled mixture is fully gelled; and f) stirring the emulsion under high shear conditions to form polyimide beads with a diameter of about 5 micrometers to about 200 micrometers.

19. The method of claim 18 further comprises adding one or more surfactants to the gelled mixture or the emulsion.

20. The method as described in claim 18, wherein, The method is carried out as a continuous process, which further includes conveying the polyimide beads by one or more of the following: filtration; aging; solvent exchange; drying; carbonization.

21. The method of claim 1 further includes adding silicone to the polyamide before or prior to dehydration.

22. A method for forming a polyimide gel, the method comprising: a) Provides tetracarboxylic dianhydride and polyfunctional amines; b) Add the tetracarboxylic acid dianhydride and the polyfunctional amine to an organic solvent to form a solution; c) Reacting the tetracarboxylic dianhydride with the polyfunctional amine in solution to form a polyamide sol solution; d) Adding a dehydrating agent, a monoamine, and water to the polyamide sol solution to form a gelling mixture, and gelling the gelling mixture to form the polyimide gel, wherein the water is added at a molar ratio of about 5 to about 70 for the tetracarboxylic dianhydride.

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