Hydrophobic polyimide aerogel

Abstract

Generally described are aerogels including a hydrophobic polyimide moiety including a hydrophobic polyimide aerogel, and a method for manufacturing the same and applications thereof.

Description

[0001] Related Applications

[0002] This application claims priority to U.S. Provisional Application No. 62 / 914,281, filed on October 11, 2019, entitled "Hydrophobic Polyimide Aerogels", which is hereby incorporated by reference in its entirety for all purposes. Technical Field

[0003] Generally described are aerogels comprising hydrophobic polyimide moieties, as well as methods of making and applications thereof, said aerogels comprising hydrophobic polyimide aerogels. Summary of the Invention

[0004] Generally described are aerogels comprising hydrophobic polyimide moieties, as well as methods of making and applications thereof, said aerogels comprising hydrophobic polyimide aerogels. In some cases, the subject matter of the present invention relates to related products, alternative solutions to particular problems, and / or various different uses of one or more systems and / or articles.

[0005] Certain embodiments relate to polyimide aerogels having water repellent properties. In some embodiments, the aerogel comprises the reaction product of bisaniline-m.

[0006] Certain embodiments relate to porous crosslinked polyimide networks. In some embodiments, the porous crosslinked polyimide network comprises acid anhydride-terminated poly(amic acid) oligomers, where the oligomers (i) comprise repeating units of dianhydride and diamine and terminal acid anhydride groups, (ii) have an average degree of polymerization of 10 to 50, (iii) have been crosslinked with a crosslinking agent comprising three or more functional groups in a stoichiometry approximately balanced with the terminal acid anhydride groups, and (iv) have been chemically imidized and / or thermally imidized to produce a porous crosslinked polyimide network.

[0007] In one aspect, an aerogel is provided. In some embodiments, the aerogel comprises the following [M1] moiety:

[0008]

[0009] Certain aspects relate to methods. In certain embodiments, the method comprises combining an amount of biphenyl-3,3',4,4'-tetracarboxylic dianhydride (BPDA), a first diamine, and a solvent such that a first intermediate medium comprising an acid anhydride-terminated poly(amic acid) trimer is formed; subsequently, combining the first intermediate medium and a second diamine such that a second intermediate medium comprising a pentamer is formed; subsequently, combining the second intermediate medium and an additional amount of BPDA such that a third intermediate medium comprising a heptamer is formed; subsequently, combining the third intermediate medium and a third diamine such that a fourth intermediate medium comprising an oligomer chain is formed; and subsequently, combining the fourth intermediate medium with a crosslinking reagent to form a gel, wherein the first diamine is different from the second diamine and the third diamine, and the second diamine is different from the third diamine.

[0010] In some embodiments, a method for making an aerogel comprises providing a solvent, adding a first diamine to the solvent, adding a first amount of dianhydride to the solvent after adding the first diamine, adding a second diamine to the solvent after adding the first amount of dianhydride, adding a second amount of dianhydride to the solvent after adding the second diamine, adding a third diamine to the solvent after adding the second amount of dianhydride, adding a crosslinking agent to the solvent, adding a catalyst to the solvent, and adding a water scavenger to the solvent to form a gel comprising poly(amic acid) and / or polyimide, optionally replacing at least a portion of the liquid in the resulting gel with a second liquid, and then removing at least a portion of the liquid from the gel to form an aerogel.

[0011] When considered in conjunction with the accompanying drawings, other advantages and novel features of the present invention will become apparent from the following detailed description of the various non-limiting embodiments of the invention. In the event of conflicts and / or inconsistent disclosures in this specification and the documents incorporated by reference, this specification shall prevail. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying drawings, which are schematic and are not intended to be drawn to scale. In the drawings, each identical or nearly identical component shown is generally represented by a single reference numeral. For the sake of clarity, not every component is labeled in every drawing where illustration is not necessary to enable a person of ordinary skill in the art to understand the invention, nor is every component of every embodiment of the invention shown. In the drawings:

[0013] Figure 1A A hydrophobic polyimide moiety according to certain embodiments is depicted.

[0014] Figure 1B Depicts according to certain embodiments Figure 1A An enlarged view of the hydrophobic polyimide moiety shown in Figure 1AThe left side of the part in Figure 1B is shown in the enlarged view at the top of Figure 1A The right side of the part in Figure 1B is shown in the enlarged view at the bottom of

[0015] Figure 2 Depicts the molecular structures of several monomers according to certain embodiments.

[0016] Figure 3 Is an image of a polyimide aerogel according to certain embodiments.

[0017] Figure 4 Is an image of a water droplet on the surface of a polyimide aerogel that can exhibit hydrophobicity according to certain embodiments.

[0018] Figure 5 Is a scanning electron microscope (SEM) micrograph of a polyimide aerogel according to certain embodiments.

[0019] Figures 6A to 6B Is a graph of (A) nitrogen adsorption isotherm and (B) pore size distribution data of a polyimide aerogel according to certain embodiments.

[0020] Figure 7 Is a graph of the stress versus strain curve of a polyimide aerogel in compression according to certain embodiments. Detailed Description

[0021] Aerogels are various types of low-density solid materials that contain a porous three-dimensional solid network. Aerogels typically exhibit a variety of desirable material properties, including high specific surface area, low bulk density, high specific strength and stiffness, low thermal conductivity, and / or low dielectric constant, among others.

[0022] Certain aerogel compositions can incorporate several such properties into the same material package and can thus be beneficial for applications including thermal insulation, sound insulation, lightweight structures, electronics, shock damping, electrodes, catalysts and / or catalyst supports, and / or sensors. Some aerogel materials also have mechanical properties that make them suitable as structural materials and can, for example, be used as lightweight alternatives to plastics.

[0023] Aerogels containing polyimide can potentially incorporate many valuable material properties into a single material package, such as high quality-normalized strength and stiffness properties, low density, low and constant dielectric constant and loss tangent over a wide frequency range, low sound velocity, high sound transmission loss, low flammability or non-flammability, machinability, and low thermal conductivity. Potential applications of aerogels containing polyimide include aircraft interior components such as wall panels, floor panels, cockpit doors, and galley furniture; engine covers for automobiles; shock wave reflection and / or energy absorption materials in ballistic protection products; insulation components for shoes, boots, and insoles; vibration and sound insulation for rocket fairings; low-k substrates for electronics and antennas; and other applications. Most commercial polyimide materials, such as films and bulk plastics, traditionally contain hydrophilic polymers, i.e., they absorb and retain moisture and / or liquid water. Thus, most aerogels containing polyimide are likewise hydrophilic. However, many potential engineering applications of polyimide aerogels require materials that can resist contact with liquid and / or gaseous water without degrading, gaining a significant amount of weight, or losing performance. Thus, aerogels containing polyimide that exhibit waterproof properties are highly desirable for many applications.

[0024] Certain embodiments relate to inventive aerogels. In some embodiments, the aerogel comprises a polymeric aerogel. A polymeric aerogel is an aerogel made at least in part from a polymeric material. In some embodiments, at least 25 wt%, at least 50 wt%, at least 75 wt%, at least 90 wt%, at least 95 wt%, at least 98 wt%, at least 99 wt%, at least 99.9 wt% or all of the polymeric aerogel is made from a polymeric material. In some embodiments, at least 25 wt%, at least 50 wt%, at least 75 wt%, at least 90 wt%, at least 95 wt%, at least 98 wt%, at least 99 wt%, at least 99.9 wt% or all of the polymeric aerogel is made from an organic polymer (i.e., a polymer having carbon atoms in its backbone).

[0025] In some embodiments, the polymeric material has a polymeric structure. In some embodiments, the [M1] moiety (instances of which are provided below and a specific instance of which is shown in Figures 1A to 1Bis part of a polymeric structure having repeating units of the [M1] moiety. In some embodiments, the polymeric structure comprises at least 2, at least 3, at least 4, at least 5, at least 10, at least 15, at least 20, at least 30, at least 40, and / or at least 50 repeating units of the [M1] moiety. In some preferred embodiments, the aerogel comprises 2 to 20 repeating units of the [M1] moiety. In some cases, the [M1] moiety can account for at least 50 wt%, at least 60 wt%, at least 70 wt%, at least 80 wt%, at least 90 wt%, at least 95 wt%, and / or at least 99 wt% of the polymer in the aerogel.

[0026] In some embodiments, at least 50 wt%, at least 60 wt%, at least 70 wt%, at least 80 wt%, at least 90 wt%, at least 95 wt%, and / or at least 99 wt% of the aerogel is composed of a material comprising the [M1] moiety. In some preferred embodiments, at least 90 wt% of the aerogel is composed of the [M1] moiety.

[0027] In some embodiments, the aerogel comprises a polyimide aerogel. A polyimide aerogel is an aerogel made at least in part from a polyimide material. In some embodiments, at least 25 wt%, at least 50 wt%, at least 75 wt%, at least 90 wt%, at least 95 wt%, at least 98 wt%, at least 99 wt%, at least 99.9 wt% or all of the polymeric aerogel is made of polyimide. In some embodiments, the polyimide aerogel can exhibit one or more material properties that are of particular value for engineering applications.

[0028] Hydrophobic polyimides have been produced previously, but contain expensive fluorinated monomers and can degrade other material properties of the polymer. Similarly, polyimide aerogels containing such fluorinated monomers have been developed, which while providing improved water repellent properties in some cases compared to non-fluorinated polyimide aerogels, may exhibit reduced strength and / or stiffness properties and / or higher thermal conductivity values, which are not ideal for applications where high quality normalized strength / stiffness and / or low thermal conductivity properties of the aerogel are desired. According to certain embodiments, a hydrophobic polyimide moiety free of any fluorine is provided. In some embodiments, the aerogel contains less than 1 wt%, less than 0.5 wt%, less than 0.1 wt%, less than 0.01 wt%, and / or less than 0.001 wt% fluorine. In some embodiments, the aerogel is substantially free of fluorine.

[0029] According to certain embodiments, a hydrophobic polyimide moiety that does not contain any fluorine is provided. In some embodiments, compared to a polyimide-containing aerogel that does not contain this moiety, an aerogel containing this moiety exhibits improved resistance to liquid water absorption and / or vapor water absorption. In some preferred embodiments, a polyimide aerogel in which greater than about 80% of the polyimide contains this moiety exhibits particularly excellent water absorption resistance and high hydrophobicity.

[0030] According to certain embodiments, methods for making the moiety and methods for making a polyimide aerogel containing the moiety are described.

[0031] As described elsewhere, the [M1] moiety corresponds to the following structure:

[0032]

[0033] In some preferred embodiments, the moiety comprises a specific repeating octamer of the reaction product of four monomers, the octamer having the following sequence, such that the imide groups are understood to replace the amines and acid anhydrides in the monomers accordingly: biphenyl-3,3',4,4'-tetracarboxylic dianhydride (BPDA), then 2,2'-dimethylbenzidine (DMBZ), then BPDA, then 4,4'-[1,3-phenylene bis(1-methylethylene)]bis-aniline (bis-aniline-m), then BPDA, then 4,4'-diaminodiphenyl ether (ODA), then BPDA, then bis-aniline-m. In some preferred embodiments, a polyimide aerogel containing this moiety exhibits excellent strength, stiffness, flexibility, machinability, low thermal conductivity, low flammability, and high water-proofing characteristics. In some preferred embodiments, the polyimide aerogel comprises polyimide chains containing repeating segments of this moiety, where the moiety repeats 1, 2, 3, 4, 5, or more than 5 times. In some preferred embodiments, the polyimide chains containing this moiety are interconnected by a crosslinking agent. In some preferred embodiments, the specific alternating pattern of the constituent monomers from which this moiety is derived gives rise to the hydrophobic and / or water-proofing characteristics of the polyimide aerogel. Without wishing to be bound by any particular theory, this moiety may confer enhanced water-proofing characteristics to the polyimide aerogel due to its high density of aryl, isopropylidene, and methyl groups (all of which are hydrophobic groups), thereby offsetting the inherent hydrophilicity of the imide groups. Without wishing to be bound by any particular theory, including one ODA (which contains a flexible oxygen bridge) unit can impart flexibility to the moiety providing the polyimide aerogel, and the moiety has reduced brittleness compared to a moiety that does not contain a flexible oxygen bridge.

[0034] In some embodiments, the aerogel contains the [M1] moiety.

[0035] In some embodiments, an aerogel comprising the [M1] moiety can exhibit hydrophobicity. The term hydrophobicity refers to the lack and / or partial lack of attraction between a material and a large amount of water. In some embodiments, the hydrophobicity of a bulk material refers to this behavior when it is applied to a surface. In certain embodiments, the apparent hydrophobicity of a textured surface can be higher than the chemical hydrophobicity of the bulk material.

[0036] The hydrophobicity of the resulting aerogel can be expressed as liquid water uptake. The term liquid water uptake refers to the ability of a material or composition to absorb, adsorb, or otherwise retain water upon contact with water in the liquid state. Liquid water uptake can be expressed in one of several ways, e.g., as a fraction or percentage of the open pore volume or envelope volume of the aerogel, or as a fraction or percentage relative to the mass of the un-wetted aerogel. The reported liquid water uptake is understood to be the result of measurements conducted under specific conditions. An aerogel material having excellent or improved liquid water uptake relative to different aerogel materials is understood to have a lower liquid water uptake.

[0037] In some embodiments, when measured according to standard ASTM C1511, the liquid water uptake can be less than 100 wt%, less than 80 wt%, less than 70 wt%, less than 60 wt%, less than 50 wt%, less than 40 wt%, less than 30 wt%, less than 20 wt%, less than 10 wt%, less than 5 wt%, less than 4 wt%, less than 3 wt%, less than 2 wt%, less than 1 wt%, or less than 0.1 wt% relative to the weight of the aerogel before contact with liquid water.

[0038] In some embodiments, when measured according to standard ASTM C1763, the liquid water uptake can be less than 100 wt%, less than 80 wt%, less than 70 wt%, less than 60 wt%, less than 50 wt%, less than 40 wt%, less than 30 wt%, less than 20 wt%, less than 10 wt%, less than 5 wt%, less than 4 wt%, less than 3 wt%, less than 2 wt%, less than 1 wt%, or less than 0.1 wt% relative to the weight of the aerogel before contact with liquid water.

[0039] In some embodiments, when measured according to standard EN 1609, the liquid water uptake can be less than 100 wt%, less than 80 wt%, less than 70 wt%, less than 60 wt%, less than 50 wt%, less than 40 wt%, less than 30 wt%, less than 20 wt%, less than 10 wt%, less than 5 wt%, less than 4 wt%, less than 3 wt%, less than 2 wt%, less than 1 wt%, or less than 0.1 wt% relative to the weight of the aerogel before contact with liquid water.

[0040] In some embodiments, when the aerogel is immersed underwater at 25 °C for 24 hours, the aerogel absorbs less than 20% of the mass of water relative to the dry mass of the aerogel before immersion in water within its outer boundary.

[0041] The hydrophobicity of the aerogel can be expressed in terms of water vapor absorption. The term water vapor absorption refers to the ability of a material or composition to absorb, adsorb, or otherwise retain water upon contact with water in the vapor state. Water vapor absorption can be expressed as a fraction or percentage of water retained relative to the mass of the aerogel before exposure to water vapor. The reported water vapor absorption is understood to be the result of measurements conducted under specific conditions. An aerogel material having excellent or improved water vapor absorption relative to different aerogel materials is understood to have lower water vapor adsorption or retention. In some embodiments, when measured according to standard ASTM C1104, the water absorption can be less than 100 wt%, less than 80 wt%, less than 70 wt%, less than 60 wt%, less than 50 wt%, less than 40 wt%, less than 30 wt%, less than 20 wt%, less than 10 wt%, less than 5 wt%, less than 4 wt%, less than 3 wt%, less than 2 wt%, less than 1 wt%, or less than 0.1 wt% relative to the weight of the aerogel before exposure to water vapor. In some embodiments, the aerogel absorbs less than 20% of the mass of water relative to the dry mass of the aerogel before exposure to the water vapor within its outer boundary.

[0042] The hydrophobicity of the aerogel material can be expressed in terms of the water contact angle. The term water contact angle refers to the equilibrium contact angle of a water droplet in contact with the surface of the aerogel material. An aerogel having excellent or improved hydrophobicity relative to different aerogel materials can have a larger water contact angle. In some embodiments, when measured according to standard ASTM D7490, the water contact angle can be greater than 90°, greater than 100°, greater than 110°, greater than 120°, greater than 130°, greater than 140°, greater than 150°, greater than 160°, greater than 170°, or from 170° to 180°. In some preferred embodiments, when measured according to standard ASTM D7490, the aerogel exhibits a water contact angle greater than 90° in an ambient air environment at 1 atmosphere and 25 °C.

[0043] In some embodiments, the aerogel can exhibit an internal specific surface area. As used herein, internal surface area and specific surface area have the same meaning and describe the same phenomenon. As described herein, these values can also be referred to as the BET surface area. In some embodiments, the internal specific surface area of the aerogel can be determined using nitrogen adsorption porosimetry and obtaining the surface area value using the Brunauer-Emmett-Teller (BET) model. For example, nitrogen adsorption porosimetry can be performed using a Micromeritics Tristar II 3020 surface area and porosity analyzer. Prior to porosimetry analysis, the sample can be subjected to a vacuum of about 100 Torr for 24 hours to remove adsorbed water or other solvents from the pores of the sample. The porosimeter can provide adsorption and desorption isotherms, which include the amount of analyte gas adsorbed or desorbed as a function of the partial pressure. The specific surface area can be calculated using the BET method based on the adsorption isotherm within the range typically used for measuring surface area. In some embodiments, the BET surface area of the aerogel is greater than 50 m 2 / g, greater than 100 m 2 / g, greater than 200 m 2 / g, greater than 300 m 2 / g, greater than 400 m 2 / g, greater than 500 m 2 / g, greater than 600 m 2 / g, greater than 700 m 2 / g, greater than 800 m 2 / g, greater than 1000 m 2 / g, greater than 2000 m 2 / g, greater than 3000 m 2 / g, or less than 4000 m 2 / g. In certain preferred embodiments, the BET surface area of the aerogel is 50 m 2 / g to 800 m 2 / g. BET surface area values of aerogels outside these ranges can be possible. In some preferred embodiments, the aerogel exhibits a BET surface area greater than 200 m 2 / g. In some preferred embodiments, the aerogel exhibits a BET surface area greater than 350 m 2 / g.

[0044] In some embodiments, the bulk density of the aerogel can be determined by dimensional analysis. For example, the bulk density can be measured by first carefully machining the specimen into a regular shape (e.g., a block or a rod). The length, width, and thickness (or length and diameter) can be measured using calipers (accuracy ±0.001"). Then, in the case of a block, the specimen volume can be calculated by multiplying the length × width × height, or in the case of a disk, by multiplying the height × radius squared × π, using these measurements. The mass can be measured using a digital analytical balance with an accuracy of 0.001 g. Then the bulk density can be calculated as density = mass / volume. In some embodiments, the bulk density of the aerogel can be from 0.05 g / cc to 0.1 g / cc, 0.05 g / cc to 0.2 g / cc, 0.05 g / cc to 0.3 g / cc, 0.05 g / cc to 0.4 g / cc, 0.05 g / cc to 0.5 g / cc, 0.05 g / cc to 0.6 g / cc, 0.05 g / cc to 0.7 g / cc, or greater than 0.7 g / cc. In certain embodiments, the density can be from 0.15 g / cc to 0.7 g / cc. In certain preferred embodiments, the density can be from 0.07 g / cc to 0.2 g / cc. In some preferred embodiments, the aerogel exhibits a bulk density of 0.06 g / cc to 0.2 g / cc.

[0045] In some embodiments, the aerogel comprises silica. In some embodiments, the aerogel comprises trimethylsilyl-functionalized silica. In some embodiments, the aerogel comprises trimethylsilyl-functionalized silica aerogel containing sodium ions. In some embodiments, the aerogel comprises discrete silica aerogel particles. In some embodiments, the aerogel comprises discrete trimethylsilyl-functionalized silica aerogel particles. In some embodiments, the aerogel comprises silica in an amount of up to 5 wt%, up to 10 wt%, up to 20 wt%, or up to 25 wt%. In some embodiments, the aerogel comprises silica aerogel and polyimide aerogel.

[0046] In some embodiments, the aerogel has a compressive modulus (also known as Young's modulus, which is approximately equal to the bulk modulus in some embodiments) and a yield strength, which can be determined using standard uniaxial compression testing. The compressive modulus and yield strength can be measured as described using the method outlined in the standard ASTM D1621-10 “Standard Test Method for Compressive Properties of Rigid Cellular Plastics”, except that the specimen is compressed at a crosshead displacement rate of 1.3 mm / second (as specified in standard ASTM D695) instead of 2.5 mm / second. In some embodiments, the aerogel can exhibit any suitable compressive modulus. In certain embodiments, the compressive modulus of the aerogel is greater than 100 kPa, greater than 500 kPa, greater than 1 MPa, greater than 10 MPa, greater than 50 MPa, greater than 100 MPa; or less than 100 MPa, less than 50 MPa, less than 10 MPa, less than 1 MPa, less than 500 kPa, less than 100 kPa, or less than 50 kPa. Combinations of the above ranges or values outside of these ranges are possible for the compressive modulus of the aerogel. In some preferred embodiments, the aerogel exhibits a compressive modulus greater than 1 MPa.

[0047] In some embodiments, the aerogel can exhibit any of a variety of suitable compressive yield strengths. In certain embodiments, the compressive yield strength of the aerogel is greater than 40 kPa, greater than 100 kPa, greater than 500 kPa, greater than 1 MPa, greater than 5 MPa, greater than 10 MPa, greater than 50 MPa, greater than 100 MPa, greater than 500 MPa; or less than 500 MPa, less than 100 MPa, less than 50 MPa, less than 10 MPa, less than 5 MPa, less than 1 MPa, less than 500 kPa, less than 100 kPa, or less than 50 kPa. Combinations of the above ranges or values outside of these ranges are possible for the compressive yield strength of the aerogel. In some preferred embodiments, the aerogel exhibits a compressive yield strength greater than 300 kPa.

[0048] In some embodiments, the aerogel has a flexural modulus and a flexural yield strength that can be determined using standard mechanical testing methods. The flexural modulus and yield strength can be measured as described according to the method outlined in the standard ASTM D790-10, “Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials,” except that the specimen span is equal to a fixed value of 45 mm rather than varying as a proportion of the specimen thickness. The specimen length is at least 10 mm greater than the span. The specimen depth is in the range of 5 mm to 7 mm. The specimen width is in the range of 15 mm to 20 mm. In certain embodiments, the flexural modulus of the aerogel, as measured by the method described, can be 10 MPa to 20 MPa, 20 MPa to 50 MPa, 50 MPa to 100 MPa, 100 MPa to 200 MPa, 200 MPa to 300 MPa, or greater than 300 MPa. In some preferred embodiments, the aerogel exhibits a flexural modulus greater than 1 MPa.

[0049] In some embodiments, the flexural yield strength of the aerogel is greater than 0.2 MPa, greater than 0.5 MPa, greater than 1 MPa, greater than 1.5 MPa, greater than 2 MPa, greater than 2.5 MPa, greater than 3 MPa, greater than 3.5 MPa, or greater than 4 MPa. In some preferred embodiments, the aerogel exhibits a flexural yield strength greater than 500 kPa.

[0050] In some embodiments, the aerogel has a dielectric constant and a loss tangent that can be determined using standard test methods. The dielectric constant and the loss tangent can be measured using the methods outlined in the standard ASTM D2520-13, "Complex Permittivity (Dielectric Constant) of Solid Electrical Insulating Materials at Microwave Frequencies and Temperatures up to 1650 °C". In certain embodiments, the aerogel exhibits an average dielectric constant less than 100, less than 10, less than 5, less than 2, less than 1.75, less than 1.5, or less than 1.25 in the range from 0 GHz to 50 GHz. In certain preferred embodiments, the aerogel exhibits an average dielectric constant less than 1.4 in the range from 0 GHz to 50 GHz. In certain embodiments, the aerogel exhibits an average loss tangent less than 1, less than 0.1, less than 0.01, less than 0.001, or less than 0.0001 in the range from 0 GHz to 50 GHz. In certain preferred embodiments, the aerogel exhibits an average loss tangent less than 0.01 in the range from 0 GHz to 50 GHz.

[0051] In some embodiments, at least one dimension of the aerogel is from 10 micrometers to 1 mm.

[0052] In some embodiments, at least one dimension of the aerogel is equal to or greater than 10 cm, greater than 30 cm, greater than 50 cm, and / or greater than 100 cm. In some preferred embodiments, at least one dimension of the aerogel is greater than or equal to 30 cm.

[0053] In some embodiments, the aerogel can exhibit relatively high acoustic attenuation. The acoustic attenuation of the aerogel can be expressed in terms of the transmission loss. The term transmission loss is defined in the standard ASTM C634. In certain embodiments, when measured according to the standard ASTM E2611, the aerogel exhibits a transmission loss greater than 1 dB / cm, greater than 5 dB / cm, greater than 10 dB / cm, greater than 11 dB / cm, greater than 12 dB / cm, greater than 13 dB / cm, greater than 14 dB / cm, greater than 15 dB / cm, greater than 16 dB / cm, greater than 17 dB / cm, greater than 18 dB / cm, greater than 19 dB / cm, greater than 20 dB / cm, greater than 30 dB / cm, greater than 40 dB / cm, and / or greater than 50 dB / cm. In certain embodiments, when measured according to the standard ASTM E90, the aerogel exhibits a transmission loss greater than 1 dB / cm, greater than 5 dB / cm, greater than 10 dB / cm, greater than 11 dB / cm, greater than 12 dB / cm, greater than 13 dB / cm, greater than 14 dB / cm, greater than 15 dB / cm, greater than 16 dB / cm, greater than 17 dB / cm, greater than 18 dB / cm, greater than 19 dB / cm, greater than 20 dB / cm, greater than 30 dB / cm, greater than 40 dB / cm, and / or greater than 50 dB / cm. In some preferred embodiments, the aerogel exhibits an average transmission loss greater than 5 dB / cm in the frequency range of 300 Hz to 2000 Hz.

[0054] The aerogel can exhibit any suitable pore structure. The pore width distribution, pore area distribution, and average pore size can be calculated from the nitrogen desorption isotherm using the Barrett-Joyner-Halenda (BJH) method in the range typically re-used for measuring pore width and pore area distributions. In some embodiments, the aerogel contains pores less than 100 microns, less than 10 microns, less than 1 micron, less than 500 nm, less than 250 nm, less than 100 nm, less than 50 nm, less than 25 nm, less than 20 nm, less than 15 nm, and / or less than 10 nm. In some embodiments, the aerogel contains pores greater than 10 nm, greater than 15 nm, greater than 20 nm, greater than 25 nm, greater than 50 nm, greater than 100 nm, greater than 250 nm, greater than 500 nm, greater than 1 micron, greater than 10 microns, and / or greater than 100 microns. In some preferred embodiments, the aerogel contains pores 1 micron or greater. The average pore width, e.g., average pore size (assuming cylindrical pores), can be calculated using pore width = 4*(total specific volume) / (specific surface area), where the total specific volume and specific surface area can also be calculated using the BJH analysis of the desorption isotherm. In some embodiments, the average pore width is less than 10 nm, less than 20 nm, less than 30 nm, less than 40 nm, less than 50 nm, less than 60 nm, less than 70 nm, less than 80 nm, less than 90 nm, less than 100 nm, less than 500 nm, less than 1 μm, less than 10 μm, less than 100 μm, or less than 1 mm. In certain preferred embodiments, the average pore width is less than 50 nm. In some preferred embodiments, the average pore width of the aerogel is less than 20 nm.

[0055] In some embodiments, the pore width distribution of the aerogel can be unimodal (i.e., exhibit a single maximum). In some embodiments, the pore width distribution maximum occurs at less than 10 nm, less than 20 nm, less than 30 nm, less than 40 nm, less than 50 nm, less than 60 nm, less than 70 nm, less than 80 nm, less than 90 nm, less than 100 nm, less than 500 nm, less than 1 μm, less than 10 μm, less than 100 μm, or less than 1 mm. In some embodiments, the aerogel contains a unimodal pore size distribution.

[0056] In some embodiments, the pore width distribution of the aerogel can be bimodal, or at least bimodal. In some embodiments, the aerogel material can have two different pore populations, one having an average pore size less than a certain critical pore width and one having an average pore size greater than a certain critical pore width. In some embodiments, the critical pore width is less than 10 nm, less than 20 nm, less than 30 nm, less than 40 nm, less than 50 nm, less than 60 nm, less than 70 nm, less than 80 nm, less than 90 nm, less than 100 nm, less than 500 nm, less than 1 μm, less than 10 μm, less than 100 μm, or less than 1 mm. In some embodiments, the aerogel comprises a bimodal pore size distribution.

[0057] The thermal conductivity of the aerogel can be measured using a calibrated hot plate (CHP) apparatus. The CHP method is based on the principles underlying the standard ASTM E1225, “Standard Test Method for Thermal Conductivity of Solids by Means of the Guarded-Comparative-Longitudinal Heat Flow Technique”. An apparatus in which the aerogel and / or other sample material (whose mass, thickness, length, and width have been measured as described in the process for measuring bulk density) and a standard reference material (such as an NIST SRM 1453 EPS board) with precisely known thermal conductivity, density, and thickness are continuously placed between a hot surface and a cold surface. The hot side of the system includes an aluminum block (4"×4"×1") in which three cartridge heaters are embedded. The cartridge heaters are controlled by a temperature controller operating in an on / off mode. The set point feedback temperature of the controller is measured by a type K thermocouple (referred to as TC_H) at the center of the top surface of the aluminum block (at the interface between the block and the sample material). A second identical thermocouple (referred to as TC_1) is placed directly next to this thermocouple. The sample material is placed on top of the aluminum block such that the thermocouple is near its center. A third identical thermocouple (TC_2) is placed directly above the other thermocouples at the interface between the sample material and the reference material. The reference material is then placed on top of the sample material covering the thermocouples. A fourth identical thermocouple (TC_3) is placed on top of the reference material, in line with the other three thermocouples. A 6" diameter stainless steel cup filled with ice water is placed on top of this material stack, providing an isothermal cold surface. Power is supplied to the heater and regulated by the temperature controller such that the hot side of the system is maintained at a constant temperature of approximately 37.5 °C. After ensuring that all components are correctly in place, the system is turned on and allowed to reach an equilibrium state. At this point, the temperatures at TC_1, TC_2, and TC_3 are recorded. This recording is repeated every 15 minutes for at least one hour. From each set of temperature measurements (a set being the three temperatures measured simultaneously), the unknown thermal conductivity can be calculated as follows. By assuming one-dimensional conduction (i.e., neglecting edge losses and conduction perpendicular to the line where TC_1, TC_2, and TC_3 are located), it can be said that the heat flux through each material is defined by the temperature difference across the material divided by the thermal resistance per unit area of the material (where the thermal resistance per unit area is defined by R” = t / k, where t is the thickness in meters and k is the thermal conductivity in W / m-K). The thickness t is measured while subjecting the sample material to a pressure equal to the pressure the sample material experiences during the CHP thermal conductivity test.For example, the thickness of a sample material can be measured by sandwiching the sample material between a fixed rigid surface and a movable rigid plate parallel to the rigid surface, and applying a known pressure to the sample material by applying a known force to the rigid plate. The thickness t_1 of such a stack of materials can be measured using any suitable device, such as a dial indicator or a depth gauge. The sample material is then removed from this stack of materials and the thickness t_2 of the rigid plate is measured under the same force as previously specified. Thus, the thickness of the sample material under the specified pressure can be calculated by subtracting t_2 from t_1. The preferred range for the thickness of the sample material used in this thermal conductivity measurement is from 2 mm to 10 mm. Using a sample material thickness outside this range may introduce a certain degree of uncertainty and / or error in the thermal conductivity calculation, such that the measured value is no longer accurate and / or reliable. The thermal conductivity of the sample material (the only unknown in the equation) can be solved by setting the heat flux through the sample material equal to the heat flux through a reference material. This calculation is performed for each temperature group, and the average value is reported as the sample thermal conductivity. The thermocouples used can be individually calibrated against a platinum RTD and unique corrections can be assigned for zero offset and slope, such that the measurement uncertainty is ±0.25 °C instead of ±2.2 °C. In certain embodiments, as measured by the methods described herein, the thermal conductivity of the aerogel at 25 °C can be less than 100 mW / m-K, less than 75 mW / m-K, less than 50 mW / m-K, less than 35 mW / m-K, less than 25 mW / m-K, less than 23 mW / m-K, less than 20 mW / m-K, or 26 mW / m-K. In some preferred embodiments, the aerogel exhibits a thermal conductivity at 25 °C of less than 30 mW / m-K.

[0058] In certain embodiments, the aerogel is non-flammable.

[0059] In some embodiments, the aerogel meets the criteria for fire performance classes A1, A2, and / or B of the European classification standard EN 13501-1.

[0060] In certain embodiments, the aerogel meets the criteria for afterflame time, drips self-extinguishing time, and / or burning length stated in Part 25.853a of the Federal Aviation Regulations of the United States.

[0061] In some embodiments, the aerogel meets the criteria for total heat release, peak heat release rate, and / or 4.0 minute smoke density within the first two minutes stated in Part 25.853d of the Federal Aviation Regulations of the United States.

[0062] According to some embodiments, aerogels can be prepared in a variety of shape factors. In some embodiments, monolithic components can be produced. One of ordinary skill in the art will understand that monolithic means an entire, continuous, macroscopic component or object, as opposed to, for example, a powder or particulate form of a material, a sub-volume of a component or object, or an embedded / integrated component of a material (e.g., one of the networks in an aerogel containing an interpenetrating network). In some embodiments, the component can have complex features. In some embodiments, flexible tapes can be produced. In some embodiments, films having a thickness in the range of 1 micron to 1 mm can be produced. In some embodiments, the shape of the aerogel can be changed by CNC milling, sawing, drilling, stamping, sanding, grinding, bending, compressing, rolling, and / or thermoforming.

[0063] In some embodiments, aerogels are used in vehicles. In some embodiments, the vehicle is an automobile, an airplane, a rocket, and / or a ship. In some embodiments, the aerogel is used as an aircraft wall panel. In some embodiments, the aerogel is used as an engine hood.

[0064] In some embodiments, aerogels are suitable for use as sound insulation materials; components in bulletproof articles, panels, armors, protective vests, and / or bulletproof armors; and / or vibration damping insulation materials. In some preferred embodiments, aerogels are used in bulletproof armors, protective articles, panels, composite materials, and / or protective vests.

[0065] In some embodiments, aerogels are used in shoes, boots, or shoe insoles.

[0066] In some embodiments, aerogels can be carbonizable. In some embodiments, carbonized derivatives of aerogels can be produced.

[0067] According to certain embodiments, aerogel materials can be made from precursor gel materials. For example, some embodiments include preparing a precursor gel and removing the liquid from the gel to form an aerogel. Various methods of forming aerogels are described below and elsewhere herein. Similarly, various methods of forming aerogel precursors (e.g., gels) are described below.

[0068] As provided herein, a gel is a colloidal system in which a porous solid network spans a volume occupied by a liquid medium. Thus, a gel has two components: a spongy solid skeleton that gives the gel its solid-like cohesion; and a liquid that penetrates the pores of the skeleton.

[0069] Certain aspects relate to methods of forming aerogels, gels, or precursors thereof.

[0070] In certain embodiments, the method includes combining an amount of biphenyl-3,3',4,4'-tetracarboxylic dianhydride (BPDA), a first diamine, and a solvent. The combining can be carried out in any of a variety of ways. Some embodiments include first combining the BPDA and the solvent and subsequently adding the first diamine. Other embodiments include first combining the first diamine and the solvent and subsequently adding the BPDA. Still other embodiments include combining the BPDA, the first diamine, and the solvent simultaneously.

[0071] In some embodiments, the combining of the amount of BPDA, the first diamine, and the solvent is carried out such that a first intermediate medium comprising acid anhydride-terminated poly(amic acid) trimers is formed.

[0072] In certain embodiments, the method includes combining the first intermediate medium and a second diamine. In some embodiments, the combining of the first intermediate medium and the second diamine is carried out such that a second intermediate medium comprising pentamers is formed.

[0073] In some embodiments, the method includes combining the second intermediate medium and an additional amount of BPDA. In certain embodiments, the combining of the second intermediate and the additional amount of BPDA is carried out such that a third intermediate comprising heptamers is formed.

[0074] In some embodiments, the method includes combining the third intermediate medium and a third diamine such that a fourth intermediate medium is formed. In certain embodiments, the combining of the third intermediate and the third diamine is carried out such that a fourth intermediate medium comprising an oligomer chain is formed.

[0075] In certain embodiments, the method includes combining the fourth intermediate medium and a crosslinking reagent. In some embodiments, the combining of the fourth intermediate medium and the crosslinking reagent is carried out such that a gel is formed. In some embodiments, the crosslinking agent comprises three or more amine groups. In some embodiments, the crosslinking agent comprises functional groups that react with end groups on the oligomer to produce crosslinking agent-terminated oligomers. In some embodiments, the crosslinking agent comprises functional groups that react with another crosslinking agent molecule and / or another crosslinking agent-terminated oligomer to link the crosslinking agent-terminated oligomers together. In some embodiments, the crosslinking agent is introduced in a balanced stoichiometry of functional groups that are reactive towards end groups on the polyimide oligomer to complementary end groups on the polyimide oligomer. In some embodiments, two or more oligomers are linked to the same crosslinking agent. In some embodiments, the resulting network is chemically imidized to produce a porous crosslinked polyimide network. In some embodiments, the oligomers are imidized before crosslinking. In some embodiments, the oligomers are imidized while being crosslinked.

[0076] In some embodiments, the crosslinking agent includes triamine; aliphatic triamine; aromatic amine containing three or more amino groups; aromatic triamine; 1,3,5-tris(aminophenoxy)benzene (TAB); tris(4-aminophenyl)methane (TAPM); tris(4-aminophenyl)benzene (TAPB); tris(4-aminophenyl)amine (TAPA); 2,4,6-tris(4-aminophenyl)pyridine (TAPP); 4,4’,4”-methylidynetrianiline; N,N,N’,N’-tetrakis(4-aminophenyl)-1,4-benzenediamine; polyoxypropylene triamine; N’,N’-bis(4-aminophenyl)benzene-1,4-diamine; triisocyanate; aliphatic triisocyanate; aromatic isocyanate containing three or more isocyanate groups; aromatic triisocyanate; triisocyanate based on hexamethylene diisocyanate; trimer of hexamethylene diisocyanate; hexamethylene diisocyanate; polyisocyanate; polyisocyanate containing isocyanurate; N3200; Desmodur N3300; Desmodur N100; Desmodur N3400; Desmodur N3390; DesmodurN3390 BA / SN; Desmodur N3300 BA; Desmodur N3600; Desmodur N3790 BA; DesmodurN3800; Desmodur N3900; Desmodur XP 2675; Desmodur blulogiq 3190; Desmodur XP2860; Desmodur N3400; Desmodur XP 2840; Desmodur N3580 BA; Desmodur N3500; Desmodur RE; tris(isocyanatophenyl)methane; Desmodur RC; MR; Mondur MRS; methylene diphenyl diisocyanate; diphenylmethane 2,2'-diisocyanate, diphenylmethane 2,4'-diisocyanate and / or diphenylmethane 4,4'-diisocyanate (MDI); naphthylene 1,5-diisocyanate (NDI); toluene diisocyanate; toluene 2,4-diisocyanate and / or toluene 2,6-diisocyanate (TDI); 3,3'-dimethylbiphenyl diisocyanate; 1,2-diphenylethane diisocyanate and / or p-phenylene diisocyanate (PPDI); trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, heptamethylene diisocyanate and / or octamethylene diisocyanate; 2-methylpentamethylene 1,5-diisocyanate; 2-ethylbutylene 1,4-diisocyanate; pentamethylene 1,5-diisocyanate; butylene 1,4-diisocyanate; 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (isophorone diisocyanate, IPDI); 1,4-bis(isocyanatomethyl)cyclohexane and / or 1,3-bis(isocyanatomethyl)cyclohexane (HXDI); cyclohexane 1,4-diisocyanate; 1-methylcyclohexane 2,4-diisocyanate and / or 1-methylcyclohexane 2,6-diisocyanate; dicyclohexylmethane 4,4'-diisocyanate, dicyclohexylmethane 2,4'-diisocyanate and / or dicyclohexylmethane 2,2'-diisocyanate; octakis(aminophenoxy)silsesquioxane (OAPS); 4,4-diaminodiphenyl ether (ODA); (3-aminopropyl)triethoxysilane (APTES); modified graphene oxide (m-GO); 1,3,5-benzenetricarbonyl trichloride (BTC); poly(maleic anhydride) (PMA); imidazole or substituted imidazole; triazole or substituted triazole; purine or substituted purine; pyrazole or substituted pyrazole; and / or melamine.

[0077] In some embodiments, the crosslinker comprises an isocyanurate group, a silicon-oxygen bridge, a trisubstituted benzene ring, a silsesquioxane group, a phenoxy group, a tris(phenyl)methyl group, an imidazole group and / or an alkyl group.

[0078] In some embodiments, the first diamine is different from the second diamine and the third diamine. In certain embodiments, the second diamine is different from the third diamine.

[0079] In some embodiments, the first diamine, the second diamine, and the third diamine are selected from 3,4'-diaminodiphenyl ether (3,4-ODA); 4,4'-diaminodiphenyl ether (4,4-ODA or ODA); p-phenylenediamine (pPDA); m-phenylenediamine (mPDA); p-phenylenediamine (mPDA); 2,2'-dimethylbenzidine (DMBZ); 4,4'-bis(4-aminophenoxy)biphenyl; 2,2'-bis[4-(4-aminophenoxy)phenyl]propane; bisaniline p-xylidine (BAX); 4,4'-methylenedianiline (MDA); 4,4'-[1,3-phenylenebis(1-methylethylidene)]bisaniline (bis-aniline-m); 4,4'-[1,4-phenylenebis(1-methylethylidene)]bisaniline (bis-aniline-p); 3,3'-dimethyl-4,4'-diaminobiphenyl (o-tolidine); 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP); 3,3'-dihydroxy-4,4'-diaminobiphenyl (HAB); 3,3'-diaminodiphenyl sulfone (3,3'-DDS); 4,4'-diaminodiphenyl sulfone (4,4'-DDS); 4,4'-diaminodiphenyl sulfide (ASD); 2,2-bis[4-(4-aminophenoxy)phenyl]sulfone (BAPS); 2,2-bis[4-(3-aminophenoxy)benzene] (m-BAPS); 1,4-bis(4-aminophenoxy)benzene (TPE-Q); 1,3-bis(4-aminophenoxy)benzene (TPE-R); 1,3'-bis(3-aminophenoxy)benzene (APB-133); 4,4'-bis(4-aminophenoxy)biphenyl (BAPB); 4,4'-diaminobenzanilide (DABA); 9,9'-bis(4-aminophenyl)fluorene (FDA); o-tolidine sulfone (TSN); methylenebis(anthranilic acid) (MBAA); 1,3'-bis(4-aminophenoxy)-2,2-dimethylpropane (DANPG); 2,3,5,6-tetramethyl-1,4-phenylenediamine (TMPD); 3,3',5,5'-tetramethylbenzidine (3355TMB); 1,5-bis(4-aminophenoxy)pentane (DA5MG); 2,5-diaminobenzotrifluoride (25DBTF); 3,5-diaminobenzotrifluoride (35DBTF); 1,3-diamino-2,4,5,6-tetrafluorobenzene (DTFB); 2,2'-bis(trifluoromethyl)benzidine (22TFMB); 3,3'-bis(trifluoromethyl)benzidine (33TFMB); 2,2-bis[4-(4-aminophenoxyphenyl)]hexafluoropropane (HFBAPP); 2,2-bis(4-aminophenyl)hexafluoropropane (bis-A-AF); 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (bis-AP-AF); 2,2-bis(3-amino-4-methylphenyl)hexafluoropropane (bis-AT-AF); o-phenylenediamine; diaminobenzanilide;3,5-diaminobenzoic acid; 3,3'-diaminodiphenyl sulfone; 4,4'-diaminodiphenyl sulfone; 1,3-bis(4-aminophenoxy)benzene; 1,3-bis(3-aminophenoxy)benzene; 1,4-bis(4-aminophenoxy)benzene; 1,4-bis(3-aminophenoxy)benzene; 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane; 2,2-bis(3-aminophenyl)hexafluoropropane; 4,4'-isopropylidenedianiline; 1-(4-aminophenoxy)-3-(3-aminophenoxy)benzene; 1-(4-aminophenoxy)-4-(3-aminophenoxy)benzene; bis[4-(4-aminophenoxy)phenyl]sulfone; bis[4-(3-aminophenoxy)phenyl]sulfone; bis(4-[4-aminophenoxy]phenyl)ether; 2,2'-bis(4-aminophenyl)hexafluoropropene; 2,2'-bis(4-phenoxyaniline)isopropylidene; 1,2-diaminobenzene; 4,4'-diaminodiphenylmethane; 2,2-bis(4-aminophenyl)propane; 4,4'-diaminodiphenylpropane; 4,4'-diaminodiphenyl sulfide; 4,4-diaminodiphenyl sulfone; 3,4'-diaminodiphenyl ether; 4,4'-diaminodiphenyl ether; 2,6-diaminopyridine; bis(3-aminophenyl)diethylsilane; 4,4'-diaminodiphenyldiethylsilane; benzidine-3'-dichlorobenzidine; 3,3'-dimethoxybenzidine; 4,4'-diaminobenzophenone; N,N-bis(4-aminophenyl)butylamine; N,N-bis(4-aminophenyl)methylamine; 1,5-diaminonaphthalene; 3,3'-dimethyl-4,4'-diaminobiphenyl; 4-aminophenyl-3-aminobenzoate; N,N-bis(4-aminophenyl)aniline; bis(p-β-aminotert-butylphenyl)ether; p-bis-2-(2-methyl-4-aminopentyl)benzene; p-bis(1,1-dimethyl-5-aminopentyl)benzene; 1,3-bis(4-aminophenoxy)benzene; m-xylenediamine; p-xylenediamine; 4,4'-diaminodiphenyl ether phosphine oxide; 4,4'-diaminodiphenyl N-methylamine; 4,4'-diaminodiphenyl N-aniline; amino-terminated polydimethylsiloxane; amino-terminated polypropylene oxide; amino-terminated polybutylene oxide; 4,4'-methylenebis(2-methylcyclohexylamine); 1,2-diaminoethane; 1,3-diaminopropane; 1,4-diaminobutane; 1,5-diaminopentane; 1,6-diaminohexane; 1,7-diaminoheptane; 1,8-diaminooctane; 1,9-diaminononane; 1,10-diaminodecane; 4,4'-methylenebis(aniline); 2,2'-dimethylbenzidine; bisaniline-p-xylidine; 4,4'-bis(4-aminophenoxy)biphenyl; 3,3'-bis(4-aminophenoxy)biphenyl; 4,4'-(1,4-phenylenediisopropylidene)bis(aniline); and / or 4,4'-(1,3-phenylenediisopropylidene)bis(aniline).;

[0080] In some preferred embodiments, the first diamine, the second diamine, and the third diamine are selected from 2,2'-dimethylbenzidine (DMBZ), 4,4'-oxydianiline (4,4-ODA), and 4,4'-[1,3-phenylene bis(1-methylethylidene)]bisbenzenamine (bis-aniline-m). In some further preferred embodiments, the first diamine, the second diamine, or the third diamine is bis-aniline-m.

[0081] In certain embodiments, the first diamine is DMBZ, the second diamine is 4,4-ODA, and the third diamine is bis-aniline-m. In certain embodiments, the first diamine is bis-aniline-m, the second diamine is DMBZ, and the third diamine is 4,4-ODA. In certain embodiments, the first diamine is bis-aniline-m, the second diamine is 4,4-ODA, and the third diamine is DMBZ. In certain embodiments, the first diamine is 4,4-ODA, the second diamine is DMBZ, and the third diamine is bis-aniline-m. In certain embodiments, the first diamine is 4,4-ODA, the second diamine is bis-aniline-m, and the third diamine is DMBZ. In some preferred embodiments, the first diamine is DMBZ, the second diamine is bis-aniline-m, and the third diamine is 4,4-ODA.

[0082] In some embodiments, combining the amount of BPDA, the first diamine, and the solvent includes combining the first diamine and the amount of BPDA in a relative amount having a ratio of the amount of BPDA to the first diamine of 0.9:1 to 1.1:1, 1.4:1 to 1.6:1, 1.6:1 to 1.8:1, 1.9:1 to 2.1:1, and / or 2.9:1 to 3.1:1. In some preferred embodiments, combining the amount of BPDA, the first diamine, and the solvent includes combining the first diamine and the amount of BPDA in a relative amount having a ratio of the amount of BPDA to the first diamine of 1.9:1 to 2.1:1. In some embodiments, combining the first intermediate medium and the second diamine includes combining the acid anhydride-terminated poly(amic acid) trimer and the second diamine in a relative amount having a molar ratio of the second diamine to the acid anhydride-terminated poly(amic acid) trimer of 0.9:1 to 1.1:1, 1.4:1 to 1.6:1, 1.6:1 to 1.8:1, 1.9:1 to 2.1:1, and / or 2.9:1 to 3.1:1. In some preferred embodiments, combining the first intermediate medium and the second diamine includes combining the acid anhydride-terminated poly(amic acid) trimer and the second diamine in a relative amount having a molar ratio of the second diamine to the acid anhydride-terminated poly(amic acid) trimer of 1.9:1 to 2.1:1. In some embodiments, combining the second intermediate medium with an additional amount of BPDA includes combining the pentamer and the additional amount of BPDA in a relative amount having a molar ratio of the additional amount of BPDA to the pentamer of 0.9:1 to 1.1:1, 1.4:1 to 1.6:1, 1.6:1 to 1.8:1, 1.9:1 to 2.1:1, and / or 2.9:1 to 3.1:1. In some preferred embodiments, combining the second intermediate medium and the additional amount of BPDA includes combining the pentamer and the additional amount of BPDA in a relative amount having a molar ratio of the additional amount of BPDA to the pentamer of 1.9:1 to 2.1:1. In some embodiments, combining the third intermediate medium and the third diamine includes combining the heptamer and the third diamine in a relative amount having a molar ratio of the third diamine to the heptamer of 0.4:1 to 0.6:1, 0.8:1 to 1.1:1, 0.8:1 to 1.1:1, 1.8:1 to 2.2:1. In some preferred embodiments, combining the third intermediate medium and the third diamine includes combining the heptamer and the third diamine in a relative amount having a molar ratio of the third diamine to the heptamer of 0.8:1 to 1.1:1. In some embodiments, combining the fourth intermediate medium and the crosslinking reagent includes combining the oligomer chain and the crosslinking reagent in a relative amount having a molar ratio of the crosslinking agent to the oligomer chain of 0.5:1 to 0.75:1, 0.8:1 to 1.1:1, and / or 1.4:1 to 1.6:1.In some embodiments, the ratios are 0.9:1 to 1.1:1, 1.4:1 to 1.6:1, 1.6:1 to 1.8:1, 1.9:1 to 2.1:1, and / or 2.9:1 to 3.1:1. In some preferred embodiments, combining the fourth intermediate medium and the crosslinking reagent comprises combining the oligomer chains and the crosslinking reagent in a relative amount of 1.9:1 to 2.1:1 based on the molar ratio of crosslinking agent to oligomer chains. In some preferred embodiments, combining the fourth intermediate medium and the crosslinking reagent comprises combining the oligomer chains and the crosslinking reagent in a relative amount of 0.5:1 to 0.75:1 based on the molar ratio of crosslinking agent to oligomer chains.

[0083] In some embodiments, combining the fourth intermediate medium and the crosslinking agent further comprises combining a catalyst with the fourth intermediate medium and the crosslinking agent. In some embodiments, the catalyst comprises pyridine; picoline; quinoline; isoquinoline; 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU); DBU phenolate; carboxylate of DBU; triethylenediamine; carboxylate of triethylenediamine; lutidine; n-methylmorpholine; triethylamine; tripropylamine; tributylamine; N,N-dimethylbenzylamine; N,N'-dimethylpiperazine; N,N-dimethylcyclohexylamine; N,N',N''-tris(dialkylaminopropyl)-s-hexahydrotriazine, such as N,N',N''-tris(dimethylaminopropyl)-s-hexahydrotriazine; tris(dimethylaminomethyl)phenol; bis(2-dimethylaminoethyl)ether; N,N,N,N,N-pentamethyldiethylenetriamine; methylimidazole; dimethylimidazole; dimethylbenzylamine; 1,6-diazabicyclo[5.4.0]undec-7-ene (IUPAC: 1,4-diazabicyclo[2.2.2]octane); triethylenediamine; dimethylaminoethanolamine; dimethylaminopropylamine; N,N-dimethylaminoethoxyethanol; N,N,N-trimethylaminoethylethanolamine; triethanolamine; diethanolamine; triisopropanolamine; diisopropanolamine; and / or any suitable trialkylamine. In some preferred embodiments, the catalyst comprises triethylamine and / or tripropylamine.

[0084] In some embodiments, combining the fourth intermediate medium and the crosslinking reagent further comprises combining a water scavenger with the fourth intermediate medium and the crosslinking agent. In some embodiments, combining the fourth intermediate medium and the crosslinking reagent comprises combining the oligomer chains and the water scavenger in a relative amount of 2:1 to 4:1, 4:1 to 6:1, 6:1 to 8:1, and / or 8:1 to 10:1 based on the molar ratio of water scavenger to BPDA. In some preferred embodiments, the ratio is 7:1 to 9:1. In some embodiments, the water scavenger comprises acetic anhydride, propionic anhydride, n-butyric anhydride, benzoic anhydride, trifluoroacetic anhydride, phosphorus trichloride, and / or dicyclohexylcarbodiimide. In some preferred embodiments, the water scavenger comprises acetic anhydride.

[0085] In some embodiments, a solvent is used. In some embodiments, the solvent includes dimethyl sulfoxide; diethyl sulfoxide; N,N-dimethylformamide; N,N-diethylformamide; N,N-dimethylacetamide; N,N-diethylacetamide; N-methyl-2-pyrrolidone; 1-methyl-2-pyrrolidone; N-cyclohexyl-2-imidazolidinone; diethylene glycol dimethyl ether; o-dichlorobenzene; phenols; cresols; xylenols; catechol; butyrolactone; acetone; methyl ethyl ketone; ethyl ethyl ketone; methyl propyl ketone; acetonitrile; ethyl acetate; and / or hexamethylphosphoramide. In some preferred embodiments, the solvent includes N-methyl-2-pyrrolidone.

[0086] In some embodiments, the total amount of monomers is determined relative to the amount of solvent used. In certain embodiments, the total mass of all monomers is greater than 5% of the total mass of the solvent.

[0087] In some embodiments, a gel is formed. In some embodiments, the liquid is removed from the gel to produce an aerogel.

[0088] In some embodiments, the polyimide aerogel can be made from a suitable polyimide gel using any suitable drying technique (such as supercritical CO2 drying, supercritical extraction, evaporation drying, boiling, vacuum freeze drying, and / or atmospheric pressure freeze drying).

[0089] In some embodiments, the gel is a solvent that is exchanged for an organic solvent, i.e., the pore fluid (also known as the pore liquid) within the gel is substantially replaced with the organic solvent by diffusion immersion in a bath of the target organic solvent, after which the gel is then dried by any suitable method to produce the aerogel. In some embodiments, the gel is a solvent that is exchanged for acetone and then subsequently dried by any suitable method to produce the aerogel. In some embodiments, the liquid in the gel is first at least partially replaced with carbon dioxide, after which the carbon dioxide is then removed from the gel. In some embodiments, the drying method includes subcritical CO2 evaporation drying, supercritical drying from CO2, supercritical drying from an organic solvent, ambient pressure evaporation of the solvent from the gel, freeze drying of the gel, and / or ambient pressure freeze drying of the gel.

[0090] Aerogels can be made by removing liquid from a gel in a way that substantially preserves both the porosity and integrity of the complex nanostructured solid network of the gel. For most gel materials, if the liquid in the gel evaporates, capillary stresses will be generated as the gas-liquid interface retreats into or out of the gel, causing the solid network of the gel to shrink and / or pull in on itself and collapse. The resulting material is a dry, fairly dense, low-porosity (usually <10% by volume) material commonly referred to as an xerogel material, or a solid formed by drying the gel with unhindered shrinkage. However, alternatively, the liquid in the gel can be heated and pressurized beyond its critical point, which is the specific temperature and pressure at which the liquid will transform into a semi-liquid / semi-gas or supercritical fluid that exhibits little (if any) surface tension. Below the critical point, the liquid is in equilibrium with the gas phase. However, as the system is heated and pressurized towards its critical point, the molecules in the liquid gain an increasing amount of kinetic energy and thus move past each other more and more quickly until eventually their kinetic energy exceeds the intermolecular cohesive forces that give the liquid its cohesion. At the same time, the pressure in the vapor also increases, causing the molecules to be on average closer together until the density of the vapor becomes almost and / or substantially as dense as the liquid phase. When the system reaches the critical point, the liquid and gas phases become essentially indistinguishable and merge into a single phase that exhibits a density and thermal conductivity comparable to that of a liquid and is also capable of expanding and compressing in a manner similar to a gas. Although technically a gas, the term supercritical fluid can refer to a fluid that is near but exceeds its critical point because such a fluid exhibits liquid-like properties that an ideal gas typically does not due to its density and kinetic energy, such as the ability to dissolve other substances. Since there is usually no phase boundary beyond the critical point, the supercritical fluid does not exhibit surface tension and thus does not exert capillary forces and can be removed from the gel without causing the solid framework of the gel to collapse due to the isothermal depressurization of the fluid. After the fluid is removed, the resulting dry, low-density, high-porosity material is an aerogel.

[0091] The critical points of most substances typically lie at relatively high temperatures and pressures, and thus supercritical drying typically involves heating the gel to elevated temperatures and pressures and is thus carried out in a pressure vessel. For example, if the gel contains ethanol as its pore fluid, the ethanol can be extracted supercritically from the gel by placing the gel in a pressure vessel containing additional ethanol, slowly heating the vessel above the critical temperature of ethanol (241 °C), and allowing the spontaneous vapor pressure of ethanol to pressurize the system above the critical pressure of ethanol (60.6 atmospheres). Under these conditions, the vessel can then be quasi-isothermally depressurized such that the ethanol diffuses out of the pores of the gel without recondensing into a liquid. Similarly, if the gel contains a different solvent in its pores, the vessel can be heated and pressurized above the critical point of that solvent. However, extracting organic solvents from gels requires specialized equipment because organic solvents can be dangerously flammable and explosive at their critical points. Instead of directly extracting the organic solvent supercritically from the gel, it is alternatively possible to first exchange the liquid in the gel pores with a safer, non-flammable liquid (i.e., carbon dioxide, which is generally miscible with most organic solvents and has a relatively low critical point of 31.1 °C and 72.9 atmospheres). In some embodiments, instead of first displacing the liquid in the gel pores with liquid CO2 and then carrying out supercritical extraction of the CO2, it is alternatively possible to extract the liquid in the gel by flowing supercritical CO2 through the gel. Such a so-called supercritical CO2 drying method is commonly used to manufacture aerogel materials. According to some embodiments described herein, supercritical CO2 drying can be used to manufacture aerogels.

[0092] In some embodiments, the aerogel can be made by removing the liquid from the gel by drying via evaporation of a solvent. In some embodiments, the pore fluid exhibits a surface tension low enough to prevent damage to the gel upon evaporation, e.g., less than 20 dynes / cm, less than 15 dynes / cm, less than 12 dynes / cm, or less than 10 dynes / cm. In certain embodiments, the surface tension of the solvent is equal to or less than 20 dynes / cm, equal to or less than 15 dynes / cm, equal to or less than 12 dynes / cm, or equal to or less than 10 dynes / cm. Combinations of these ranges are also possible (e.g., at least 5 and less than or equal to 25). Other ranges are also possible. In some preferred embodiments, the pore fluid selected for evaporation drying is ethoxy-nonafluorobutane (e.g., Novec 7200). In some embodiments, the solvent evaporates at room temperature. In some preferred embodiments, the solvent evaporates in an atmosphere of dry air (i.e., substantially water-free), nitrogen, and / or another substantially water-free inert gas. In some other preferred embodiments, the pore fluid selected for evaporation drying is carbon dioxide at a temperature below the critical temperature and pressure of carbon dioxide of about 31.1 °C and 72.8 atmospheres (1071 psi). In one such embodiment, the gel is dried by evaporation from liquid carbon dioxide at a temperature of about 28 °C and a pressure of about 68.0 atmospheres (1000 psi).

[0093] In some embodiments, the aerogel can be made from the gel by sublimation of the frozen pore fluid rather than evaporation of the liquid-phase pore fluid. The pore fluid can be suitably frozen and sublimed with little to no capillary forces, thereby producing the aerogel. That is, instead of removing the solvent by evaporation from the liquid state, the solvent is sublimed from the solid state (which has been frozen), thus minimizing the capillary forces that might otherwise be generated by evaporation. In some embodiments, the sublimation of the frozen pore fluid is carried out under vacuum or partial vacuum conditions such as lyophilization. In some embodiments, the sublimation of the frozen pore fluid is carried out at atmospheric pressure. In some embodiments, the method includes providing a gel material having a solvent located within the pores of the gel material, freezing the solvent within the pores of the gel material, and subliming the solvent under ambient conditions to remove the solvent from the pores of the gel material to produce an aerogel material. In some embodiments, the sublimation of the solvent is carried out in dry (i.e., substantially water-free) air, nitrogen, and / or another substantially water-free inert gas. In yet another preferred embodiment, the pore fluid selected for the method is tert-butanol.

[0094] Aerogels can be made from a variety of materials and can exhibit a variety of geometries. Generally, an aerogel is a dry, highly porous solid material that can exhibit various extreme and valuable material properties such as low density, low thermal conductivity, high density-normalized strength and stiffness, and / or high specific internal surface area. In some embodiments, the diameter of the pores within the aerogel material is less than about 100 nm, and in some preferred embodiments, the diameter of the pores within the aerogel material falls between about 2 nm and 50 nm, i.e., the aerogel is mesoporous. In some embodiments, the aerogel can include pores having a diameter greater than about 100 nm, and in some embodiments, the aerogel can even include pores having a diameter of several micrometers. In some embodiments, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, at least 99%, or more of the pore volume is composed of pores having a diameter less than 100 nm. In some embodiments, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, at least 99%, or more of the pore volume is composed of pores having a diameter less than 50 nm. In some preferred embodiments, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, at least 99%, or more of the pore volume is composed of pores having a diameter less than 25 nm. In some embodiments, the aerogel can include pores having a unimodal distribution, a bimodal distribution, or a multimodal distribution. Suitable aerogel material compositions can include, for example, silica, metal and / or metalloid oxides, metal chalcogenides, metals and / or metalloids, metal and / or metalloid carbides, metal and / or metalloid nitrides, organic polymers, biopolymers, amorphous carbon, graphitic carbon, diamond, and discrete nanoscale objects such as carbon nanotubes, boron nitride nanotubes, viruses, semiconductor quantum dots, graphene, 2D boron nitride, or combinations thereof.

[0095] In some embodiments, the aerogel comprises: polyureas, polyurethanes, polyisocyanates, polyisocyanurates, polyimides, polyamides, poly(imide-amide), polyacrylonitrile, polycyclopentadiene, polybenz azines, polybenzazazines, polyacrylamides, polynorbornenes, poly(ethylene terephthalate), poly(ether ether ketone), poly(ether ketone ketone), phenolic polymers, resorcinol-formaldehyde polymers, melamine-formaldehyde polymers, resorcinol-melamine-formaldehyde polymers, furfural-formaldehyde polymers, novolacs, phenol-formaldehyde varnishes, acetic acid-based polymers, polymer-crosslinked oxides, silica-polysaccharide polymers, silica-pectin polymers, polysaccharides, glycoproteins, proteoglycans, collagen, proteins, polypeptides, nucleic acids, amorphous carbon, graphitic carbon, graphene, diamond, carbon nanotubes, boron nitride, boron nitride nanotubes, two-dimensional boron nitride, alginates, chitin, chitosan, pectin, gelatin, gellan gum, gums, agarose, agar, cellulose, viruses, biopolymers, organically modified silicates (ormosils), organic-inorganic hybrid materials, rubbers, polybutadienes, poly(methylpentene), polyesters, polyether ether ketone, polyether ketone ketone, polyisoprenes, polybutenes, polytetrafluoroethylene, polyethylene, polypropylene, polyolefins, metal nanoparticles, metalloid nanoparticles, metal chalcogenides, metalloid chalcogenides, metals, metalloids, metal carbides, metalloid carbides, metal nitrides, metalloid nitrides, metal silicides, metalloid silicides, metal phosphides, metalloid phosphides, phosphorus-containing organic polymers, and / or carbonizable polymers.

[0096] In some embodiments, polymer aerogels comprising organic polymers can offer certain advantages over more commercially widespread inorganic aerogels, such as silica aerogels. For example, silica aerogels generally exhibit low fracture toughness and are thus brittle and fragile. Accordingly, most silica aerogel materials are generally considered unsuitable for use as structural elements. In some embodiments, polymer aerogels comprising organic polymers can exhibit improved strength, stiffness, and toughness properties compared to silica aerogels and can thus be used in lightweight structural elements as an alternative to traditional plastics or fiber-reinforced composites (which are denser by comparison).

[0097] In some embodiments, polyimide gels suitable for producing polyimide aerogels are prepared by the reaction of one or more amines with one or more acid anhydrides. In some embodiments, the amine can be a monoamine, diamine, or polyamine. In some embodiments, the acid anhydride can be a monoanhydride, dianhydride, or polyanhydride. In some embodiments, the amine and acid anhydride react to form poly(amic acid), and then the poly(amic acid) is imidized to form a polyimide. In certain embodiments, the poly(amic acid) is chemically imidized. In some embodiments, the polyamic acid is thermally imidized.

[0098] In some embodiments, biphenyl-3,3’,4,4’-tetracarboxylic dianhydride (BPDA), 2,2’-dimethylbenzidine (DMBZ), and 4,4’-oxydianiline (4,4-ODA or ODA) are combined to form an acid anhydride-terminated poly(amic acid) oligomer, where the oligomer comprises repeating units of the reaction product of BPDA, ODA, and DMBZ (e.g., units comprising the reaction product of BPDA-ODA-BPDA-DMBZ), and comprises terminal acid anhydrides and / or amine groups, and the oligomer has an average degree of polymerization of from 10 to 50. In some embodiments, the oligomer is crosslinked by a crosslinking agent (also referred to as a crosslinker). In some embodiments, the crosslinking agent comprises three or more amine groups. In some embodiments, the crosslinking agent comprises functional groups that react with the end groups on the oligomer to produce a crosslinking agent-terminated oligomer. In some embodiments, the crosslinking agent comprises functional groups that react with another crosslinking agent molecule to link the crosslinking agent-terminated oligomers together. In some embodiments, the crosslinking agent is introduced in a balanced stoichiometry of the functional groups on the crosslinking agent that are reactive towards complementary end groups on the polyimide oligomer. In some embodiments, two or more oligomers are linked to the same crosslinking agent. In some embodiments, the resulting network is chemically imidized to produce a porous crosslinked polyimide network. In some embodiments, the oligomer is imidized prior to crosslinking. In some embodiments, the oligomer is imidized while being crosslinked.

[0099] In some preferred embodiments, the polymeric aerogel comprises a three-dimensional network of an organic polymer, the three-dimensional network of the organic polymer comprising monomers and / or crosslink bonds having a functionality of three or greater, e.g., it comprises the reaction product of a crosslinking agent with three or more oligomers and / or the reaction product of a monomer with three or more other monomers. In some preferred embodiments, the polymeric network comprising trifunctional or higher functionality monomers and / or crosslinking agents provides an aerogel having suitable strength, stiffness, and toughness properties for use as a structural material. In some embodiments, the strength, stiffness, and toughness properties of the aerogel are suitable for producing aerogel components having large (e.g., greater than about 30 cm) dimensions. As will be understood by those of ordinary skill in the art, the length of a particular dimension of an aerogel corresponds to the distance between the outer boundaries of the aerogel along that dimension. As will also be understood by those of ordinary skill in the art, when measuring the three dimensions of an aerogel, each dimension will be perpendicular to the other two dimensions (such that the second dimension will be perpendicular to the first dimension, and the third dimension will be perpendicular to both the first dimension and the second dimension).

[0100] In some embodiments, the polyimide gel from which the polyimide aerogel can be made is derived from the reaction of one or more amines with one or more acid anhydrides. In some embodiments, the amine and the acid anhydride react to form poly(amic acid), and then the poly(amic acid) is imidized to form a polyimide. In certain embodiments, the poly(amic acid) is chemically imidized. In some embodiments, the poly(amic acid) is thermally imidized.

[0101] In some preferred embodiments, biphenyl-3,3’,4,4’-tetracarboxylic dianhydride (BPDA), 2,2’-dimethylbenzidine (DMBZ), and 4,4’-oxydianiline (4,4-ODA or ODA) are combined to form an acid anhydride-terminated poly(amic acid) oligomer, where the oligomer contains repeating units in the order of BPDA, ODA, BPDA, and DMBZ and terminal acid anhydride groups, and the average degree of polymerization (number or repeating units) of the oligomer is from 10 to 50. In some such embodiments, the oligomer is crosslinked by a crosslinking agent containing three or more amine groups at an equimolar stoichiometry of the amine groups and the terminal acid anhydride groups, and is chemically imidized by adding acetic anhydride (AA) to produce a porous, highly crosslinked polyimide network.

[0102] In some embodiments, the polyimide gel is derived from the reaction of one or more acid anhydrides with one or more isocyanates. In some embodiments, the acid anhydride includes dianhydride. In some embodiments, the isocyanate includes diisocyanate, triisocyanate, tris(isocyanatophenyl)methane, tolylene diisocyanate trimer, and / or methylene diphenyl diisocyanate trimer. In some embodiments, the acid anhydride and the isocyanate are contacted in a suitable solvent.

[0103] In some embodiments, the isocyanate includes triisocyanate; aliphatic triisocyanate; aromatic isocyanate containing three or more isocyanate groups; aromatic triisocyanate; triisocyanate based on hexamethylene diisocyanate; trimer of hexamethylene diisocyanate; hexamethylene diisocyanate; triisocyanate containing isocyanurate; diisocyanate containing isocyanurate; N3200; Desmodur N3300; Desmodur N100; Desmodur N3400; Desmodur N3390; Desmodur N3390 BA / SN; Desmodur N3300 BA; Desmodur N3600; Desmodur N3790 BA; Desmodur N3800; Desmodur N3900; Desmodur XP 2675; Desmodur blulogiq 3190; Desmodur XP 2860; Desmodur N3400; Desmodur XP 2840; Desmodur N3580 BA; Desmodur N3500; Desmodur RE; Tris(isocyanatophenyl)methane; Desmodur RC; MR; Mondur MRS; Methylene diphenyl diisocyanate; Diphenylmethane 2,2'-diisocyanate, diphenylmethane 2,4'-diisocyanate, and / or diphenylmethane 4,4'-diisocyanate (MDI); Naphthylene 1,5-diisocyanate (NDI); Toluene diisocyanate; Toluene 2,4-diisocyanate and / or toluene 2,6-diisocyanate (TDI); 3,3'-Dimethylbiphenyl diisocyanate; 1,2-Diphenylethane diisocyanate and / or p-phenylene diisocyanate (PPDI); Trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, heptamethylene diisocyanate, and / or octamethylene diisocyanate; 2-Methylpentamethylene 1,5-diisocyanate; 2-Ethylbutylene 1,4-diisocyanate; Pentamethylene 1,5-diisocyanate; Butylene 1,4-diisocyanate; 1-Isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (isophorone diisocyanate, IPDI); 1,4-Bis(isocyanatomethyl)cyclohexane and / or 1,3-bis(isocyanatomethyl)cyclohexane (HXDI); Cyclohexane 1,4-diisocyanate; 1-Methylcyclohexane 2,4-diisocyanate; 1-Methylcyclohexane 2,6-diisocyanate; Dicyclohexylmethane 4,4'-diisocyanate; Dicyclohexylmethane 2,4'-diisocyanate; and / or dicyclohexylmethane 2,2'-diisocyanate.

[0104] In some embodiments, the acid anhydride includes aromatic dianhydrides; aromatic trianhydrides; aromatic tetracarboxylic dianhydrides; aromatic acid anhydrides having 6 to about 24 carbon atoms and 1 to about 4 aromatic rings, which aromatic rings may be fused, linked by a biphenyl bond, or connected by one or more linking groups selected from C1 to C6 alkylene groups, oxygen, sulfur, ketone, sulfoxide, sulfone, etc.; biphenyl-3,3’,4,4’-tetracarboxylic dianhydride (BPDA); 3,3’,4,4’-biphenyltetracarboxylic dianhydride; 2,3,3’,4’-biphenyltetracarboxylic dianhydride (a-BPDA); 2,2’,3,3’-biphenyltetracarboxylic dianhydride; 3,3’,4,4’-benzophenonetetracarboxylic dianhydride; benzophenone-3,3’,4,4’-tetracarboxylic dianhydride (BTDA); pyromellitic dianhydride; 4,4’-hexafluoroisopropylidene bis(phthalic anhydride) (6FDA); 4,4’-(4,4’-isopropylidenediphenoxy)-bis(phthalic anhydride); 4,4’-oxydiphthalic anhydride (ODPA); 4,4’-oxydiphthalic dianhydride; 3,3’,4,4’-diphenylsulfonetetracarboxylic dianhydride (DSDA); hydroquinone dianhydride; hydroquinone bis(phthalic anhydride) (HQDEA); 4,4’-bisphenol A dianhydride (BPADA); ethylene glycol bis(trimesic anhydride) (TMEG); 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride; bis(3,4-dicarboxyphenyl) sulfoxide dianhydride; poly(siloxane-containing dianhydride); 2,3,2’,3’-benzophenonetetracarboxylic dianhydride; 3,3’,4,4’-benzophenonetetracarboxylic dianhydride; naphthalene-2,3,6,7-tetracarboxylic dianhydride; naphthalene-1,4,5,8-tetracarboxylic dianhydride; 3,3’,4,4’-biphenylsulfonetetracarboxylic dianhydride; 3,4,9,10-perylenetetracarboxylic dianhydride; bis(3,4-dicarboxyphenyl) sulfide dianhydride; bis(3,4-dicarboxyphenyl) methane dianhydride; 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride; 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropylene; 2,6-dichloronaphthalene 1,4,5,8-tetracarboxylic dianhydride; 2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride; 2,3,6,7-tetrachloronaphthalene-1,4,5,8-tetracarboxylic dianhydride; phenanthrene-8,9,10-tetracarboxylic dianhydride; pyrazine-2,3,5,6-tetracarboxylic dianhydride; benzene-1,2,3,4-tetracarboxylic dianhydride; and / or thiophene-2,3,4,5-tetracarboxylic dianhydride. In some preferred embodiments, the dianhydride includes biphenyl-3,3’,4,4’-tetracarboxylic dianhydride (BPDA).

[0105] In some embodiments, the polyimide gel is derived from the reaction of an amine and an anhydride. In some embodiments, the reaction of the amine and the anhydride forms poly(amic acid) oligomers. In some embodiments, the poly(amic acid) oligomers are chemically imidized to produce polyimide oligomers. In some embodiments, the chemical imidization is achieved by contacting the poly(amic acid) oligomers with a dehydrating agent. In some embodiments, the dehydrating agent includes acetic anhydride, propionic anhydride, n-butyric anhydride, benzoic anhydride, trifluoroacetic anhydride, phosphorus trichloride, and / or dicyclohexylcarbodiimide. In some embodiments, the chemical imidization is catalyzed by contacting a solution comprising the poly(amic acid) oligomers and the dehydrating agent with an imidization catalyst.

[0106] In some embodiments, the polyimide gel is derived from the reaction of an amine and an anhydride. In some embodiments, the reaction of the amine and the anhydride forms poly(amic acid) oligomers. In some embodiments, the poly(amic acid) oligomers are thermally imidized to produce polyimide oligomers. In some embodiments, the poly(amic acid) oligomers are heated to a temperature greater than about 80°C, greater than about 90°C, greater than about 100°C, greater than about 150°C, greater than about 180°C, greater than about 190°C, or any suitable temperature.

[0107] In some embodiments, the diamine and / or dianhydride can be selected based on commercial availability and / or price. In some embodiments, the diamine and / or dianhydride can be selected based on desired material properties. In some embodiments, specific diamines and / or dianhydrides can impart specific properties to the polymer. For example, in some embodiments, diamines and / or dianhydrides having a flexible linking group between phenyl groups can be used to fabricate polyimide aerogels having increased flexibility. In some embodiments, diamines and / or dianhydrides containing side methyl groups can be used to fabricate polyimide aerogels having increased hydrophobicity. In other embodiments, diamines and / or dianhydrides containing fluorinated moieties such as trifluoromethyl groups can be used to fabricate polyimide aerogels having increased hydrophobicity.

[0108] In some embodiments, two or more diamines and / or two or more dianhydrides are used. In an illustrative embodiment, two diamines are used. The mole percentage of the first diamine relative to the sum of the two diamines can vary from about 0% to about 100%. In some embodiments, the mole percentage of the first diamine relative to the sum of the two diamines includes less than about 99.9%, less than about 90%, less than about 80%, less than about 70%, less than about 60%, less than about 50%, less than about 40%, less than about 30%, less than about 20%, less than about 10%, less than about 0.1%, or less. In other embodiments, where more than two diamines are used, the mole percentage of each diamine relative to all the diamines can vary from about 0.1% to about 99.9%. In yet another illustrative example, two dianhydrides are used. The mole percentage of the first dianhydride relative to the sum of the two dianhydrides can vary from about 0.1% to about 99.9%. In some embodiments, the mole percentage of the first dianhydride relative to the sum of the two dianhydrides includes less than about 99.9%, less than about 90%, less than about 80%, less than about 70%, less than about 60%, less than about 50%, less than about 40%, less than about 30%, less than about 20%, less than about 10%, less than about 0.1%, or less. In other embodiments, where more than two dianhydrides are used, the mole percentage of each diamine relative to all the dianhydrides can vary from about 0.1% to about 99.9%.

[0109] In some embodiments, multiple diamines are used. In some embodiments, the first diamine is added to a solvent, after which the dianhydride is then added. In some embodiments, each amino site on the diamine reacts with an anhydride site on a different dianhydride such that an anhydride-terminated oligomer is formed. In some embodiments, the second diamine is then added to the solution. These diamines react with the terminal anhydrides on the oligomers in the solution to form longer amino-terminated oligomers. Oligomers of different lengths are produced by such a process, and an alternating motif of the first diamine, then the dianhydride, then the second diamine is produced. Without wishing to be bound by any particular theory, it is believed that this method promotes spatial uniformity of properties throughout the gel network, where simply mixing all the monomers together simultaneously and allowing the dianhydrides and diamines to react randomly with each other simultaneously may result in phase separation and / or spatial heterogeneity of domains rich in a particular diamine.

[0110] In some embodiments, the weight percentage of polymer in the solution, i.e., the mass percentage, is controlled during the synthesis of the polyimide gel. The term weight percentage of polymer in the solution refers to the weight of the monomers in the solution minus the weight of the by-products generated by the condensation reaction between the monomers, relative to the weight of the solution. The weight percentage of polymer in the solution can be less than about 1%, less than about 2%, less than about 3%, less than about 4%, less than about 5%, less than about 6%, less than about 7%, less than about 8%, less than about 9%, less than about 10%, less than about 12%, less than about 14%, less than about 16%, less than about 18%, less than about 20%, and / or 20% to 30%. In some preferred embodiments, the weight percentage of polymer is 5% to 15%.

[0111] In some embodiments, the reaction of diamine and dianhydride produces oligomers containing repeating units of at least diamine and dianhydride. In some embodiments, the oligomers contain about 1 repeating unit, less than about 2 repeating units, less than about 5 repeating units, less than about 10 repeating units, less than about 20 repeating units, less than about 30 repeating units, less than about 40 repeating units, less than about 50 repeating units, less than about 60 repeating units, less than about 80 repeating units, less than about 100 repeating units, or less than about 200 repeating units. In some embodiments, the average degree of polymerization of the oligomers is less than about 10, less than about 20, less than about 30, less than about 40, less than about 60, less than about 80, or less than about 100. In some embodiments, the oligomers contain terminal anhydride groups, i.e., the two ends of the oligomers contain terminal anhydride groups. In some embodiments, the oligomers contain terminal amino groups, i.e., the two ends of the oligomers contain terminal amino groups.

[0112] In certain embodiments, the aerogel can pass a vertical burn test of the process described in Section 25.853 Aircraft Interior Combustion Requirements of the United States Federal Aviation Regulations (FAR). The vertical burn test described in Section (4) “Vertical Burn” of Appendix F to FAR 25.853 is conducted as written, with some exceptions. A typical process including the exceptions is described subsequently. The sample for testing is approximately 2.5" in width × 3.5" in height × 0.25" in thickness. The sample is prepared by adjusting the ambient temperature and relative humidity to be approximately 50% relative humidity and 70°F (21.1°C). The flame source is a Bunsen burner using propane fuel, adjusted to a flame height of approximately 1.5". Instead of measuring the temperature of the flame, the shorter 2.5" edge of the sample is suspended approximately 0.75" from the top of the Bunsen burner such that the 3.5" edge is vertical, i.e., perpendicular to gravity. The flame is applied to the sample for a time of approximately 1 minute and then removed. After the flame is removed, the tested sample automatically extinguishes in less than approximately 1 second. In fact, the aerogel sample never seems to burn extensively or sustain a flame at any time, but rather is charred in the presence of the flame.

[0113] In some embodiments, a screening test can be conducted in which the aerogel material is annealed at 200°C. This temperature indicates the upper end of the operating temperature range for many high-temperature applications (such as underhood applications). This temperature is also the point at which virgin polymeric aerogels such as polyimide aerogels often start to exhibit significant dimensional changes due to temperature. In some embodiments, the aerogel at 25°C in air at 1 atmosphere is transferred to an oven uniformly heated to 20°C with air at 1 atmosphere. After annealing at 200°C in the oven for 60 minutes, the sample can be removed, and then the dimensional change is measured and optionally photographed.

[0114] In some embodiments, the aerogel exhibits low flammability when in contact with a flame. In some embodiments, the aerogel is nonflammable when a vertical burn test is conducted above a Bunsen burner burning propane.

[0115] According to embodiments, the aerogel exhibits ease of production and cost-effective production. For example, samples of aerogel with dimensions of 3.5" × 15" × 0.5" including complex features have been produced both by CNC milling and by direct molding using a polydimethylsiloxane (PDMS) mold. Both material samples exhibit very high feature resolution and verify that this material is easy to machine and mold into shape, and notably, molding can be a cost-effective way to mass-produce complex parts from this material.

[0116] As used herein, "maximum operating temperature" is given its ordinary meaning in the art and refers to a temperature above which the article undergoes significant chemical and / or mechanical degradation. Examples of chemical degradation include denaturation, decomposition, phase change, and ignition. Examples of mechanical degradation include mechanical warping, cracking, etc.

[0117] In some embodiments, the maximum operating temperature refers to a temperature above which the article cracks.

[0118] In some embodiments, the maximum operating temperature refers to a temperature above which the article cannot maintain its structural integrity.

[0119] In some embodiments, the maximum operating temperature refers to a temperature above which the article ignites in air (i.e., starts to burn).

[0120] In some embodiments, the maximum operating temperature refers to a temperature above which the article undergoes a phase change (e.g., melting, evaporation, and / or sublimation).

[0121] In some embodiments, the maximum operating temperature refers to a temperature above which the article continues to lose mass even after reaching thermal equilibrium.

[0122] In some embodiments, the maximum operating temperature of the aerogel is greater than about 100 °C, greater than about 200 °C, greater than about 250 °C, greater than about 300 °C, greater than about 325 °C, or greater than about 350 °C.

[0123] In some embodiments, the aerogel has desired material properties for engineering applications. In some embodiments, an aerogel can be produced that has a working temperature greater than about 100 °C, greater than about 200 °C, greater than about 250 °C, greater than about 300 °C, greater than about 325 °C, and / or greater than about 350 °C. In some embodiments, the aerogel will not ignite in air at any temperature below 100 °C, at any temperature below 200 °C, at any temperature below 250 °C, at any temperature below 300 °C, at any temperature below 325 °C, or at any temperature below 350 °C. In some embodiments, for at least one dimension of the aerogel, the size changes by no more than 20%, no more than 10%, no more than 5%, or no more than 2% at any temperature below 100 °C, at any temperature below 200 °C, at any temperature below 250 °C, at any temperature below 300 °C, at any temperature below 325 °C, or at any temperature below 350 °C. In some embodiments, after exposure to a temperature of about 200 °C, the size of the aerogel falls within about 50%, about 30%, about 20%, or about 10% of the size of the aerogel before exposure to the temperature. In some embodiments, after exposure to a temperature of about 250 °C, the size of the aerogel falls within about 80%, about 50%, about 30%, or about 10% of the size of the aerogel before exposure to the temperature. In some embodiments, after exposure to a temperature of about 300 °C, the size of the aerogel falls within about 80%, about 50%, about 30%, or about 10% of the size of the aerogel before exposure to the temperature. In some embodiments, after exposure to a temperature of about 350 °C, the size of the aerogel falls within about 80%, about 50%, about 30%, or about 10% of the size of the aerogel before exposure to the temperature. In some embodiments, when first exposed to the maximum working temperature, the aerogel undergoes an irreversible one-time linear shrinkage of less than about 20%, less than about 15%, less than about 10%, or less than about 5%. In some embodiments, when exposed to a flame, the aerogel undergoes an irreversible one-time linear shrinkage of less than about 20%, less than about 15%, less than about 10%, or less than about 5%. In some embodiments, the surface area of the aerogel is greater than about 10 m 2 / g, greater than about 20 m 2 / g, greater than about 40 m 2 / g, greater than about 60 m 2 / g, greater than about 80 m 2 / g, greater than about 100 m 2 / g, greater than about 150 m 2 / g, greater than about 200 m 2 / g, greater than about 250 m 2 / g, greater than about 300 m 2 / g, greater than about 350 m 2 / g, greater than about 400 m 2 / g, greater than about 600 m 2 / g, or greater than about 800 m 2 / g. In some embodiments, after exposure to its maximum operating temperature, the surface area of the aerogel is greater than about 10 m 2 / g, greater than about 20 m 2 / g, greater than about 40 m 2 / g, greater than about 60 m 2 / g, greater than about 80 m 2 / g, greater than about 100 m 2 / g, greater than about 150 m 2 / g, greater than about 200 m 2 / g, greater than about 250 m 2 / g, greater than about 300 m 2 / g, greater than about 350 m 2 / g, greater than about 400 m 2 / g, or greater than about 600 m 2 / g, greater than about 800 m 2 / g. In some embodiments, when exposed to the maximum operating temperature, the flatness of a monolithic aerogel changes by less than about 1%, less than about 2%, less than about 3%, less than about 4%, less than about 5%, less than about 6%, less than about 7%, less than about 8%, less than about 9%, or less than about 10% relative to its flatness. In some embodiments, when exposed to the maximum operating temperature, the flatness of a monolithic aerogel changes by less than about 1%, less than about 2%, less than about 3%, less than about 4%, less than about 5%, less than about 6%, less than about 7%, less than about 8%, less than about 9%, or less than about 10% relative to its initial flatness. In some embodiments, when exposed to the maximum operating temperature, the thickness of a monolithic aerogel changes by less than about 1%, less than about 2%, less than about 3%, less than about 4%, less than about 5%, less than about 6%, less than about 7%, less than about 8%, less than about 9%, or less than about 10% relative to its initial thickness. In some embodiments, the aerogel exhibits low thermal conductivity at room temperature and / or at temperatures above room temperature. In some embodiments, the thermal conductivity of the polymeric aerogel at room temperature is less than about 150 mW / m-K, less than about 100 mW / m-K, less than about 90 mW / m-K, less than about 80 mW / m-K, less than about 70 mW / m-K, less than about 60 mW / m-K, less than about 50 mW / -K, less than about 40 mW / m-K, less than about 30 mW / m-K, or less than about 20 mW / m-K.

[0124] In some embodiments, the aerogel can withstand a flexural strain of greater than 1%, greater than 5%, greater than 10%, greater than 20%, greater than 30%, greater than 40%, greater than 50%, greater than 60%, greater than 70%, or greater than 80% without breaking.

[0125] In some embodiments, methods for making an aerogel include: providing a solvent (e.g., any solvent described elsewhere herein), adding a first diamine (e.g., any diamine described elsewhere herein) to the solvent, adding a first amount of dianhydride (e.g., any dianhydride described elsewhere herein) to the solvent after adding the first diamine, adding a second diamine (e.g., any diamine described elsewhere herein) to the solvent after adding the first amount of dianhydride, adding a second amount of dianhydride (e.g., any dianhydride described elsewhere herein) to the solvent after adding the second diamine, adding a third diamine to the solvent after adding the second amount of dianhydride, adding a crosslinker (e.g., any crosslinker and / or crosslinking agent described herein) to the solvent, adding a catalyst (e.g., any catalyst described herein) to the solvent, and adding a water scavenger (e.g., any water scavenger described herein) to the solvent to form a gel comprising poly(amic acid) and / or polyimide, optionally replacing at least a portion of the liquid in the resulting gel with a second liquid (e.g., at least a portion of the solvent and / or pore fluid described herein), and then removing at least a portion of the liquid from the gel (e.g., using any suitable drying method described herein) to form an aerogel.

[0126] Figure 1A Depicts a hydrophobic polyimide moiety according to certain embodiments.

[0127] Figure 1B Depicts according to certain embodiments Figure 1A An enlarged view of the hydrophobic polyimide moiety shown in Figure 1A The left side of the portion in Figure 1B Is shown in an enlarged view at the top of Figure 1A And the right side of the portion in [[ID=2C]] Figure 1B Is shown in an enlarged view at the bottom of ]

[0128] Figure 2 Depicts the molecular structures of several monomers according to certain embodiments. According to certain embodiments, a moiety is produced by reacting one or more of these monomers. In some embodiments, the reaction occurs in a solvent. In some embodiments, the reaction occurs in the presence of a catalyst. In some embodiments, the reaction occurs in the presence of a water scavenger. According to certain embodiments, the moiety produced is the [M1] moiety as shown in Figure 1A Shown.

[0129] Figure 3 An image of a polyimide aerogel according to certain embodiments. The aerogel is the polyimide aerogel described in Example 1.

[0130] Figure 4 An image of water droplets on the surface of a polyimide aerogel that can exhibit hydrophobicity according to certain embodiments. The aerogel is the polyimide aerogel described in Example 1.

[0131] Figure 5 An SEM micrograph of a polyimide aerogel according to certain embodiments.

[0132] Figures 6A to 6B A graph of (A) nitrogen adsorption isotherm and (B) pore size distribution data of a polyimide aerogel according to certain embodiments. The aerogel is the polyimide aerogel described in Example 4.

[0133] Figure 7 A graph of the stress versus strain curve of a polyimide aerogel under compression according to certain embodiments. The aerogel is the polyimide aerogel described in Example 4.

[0134] U.S. Provisional Patent Application No. 62 / 914,281, filed on October 11, 2019 and entitled "Hydrophobic Polyimide Aerogels", is hereby incorporated by reference in its entirety for all purposes.

[0135] Example

[0136] The following examples are intended to illustrate certain embodiments of the invention and not to exemplify the full scope of the invention.

[0137] Example 1. Synthesis of polyimide aerogels produced by the reaction of amines, acid anhydrides, and triisocyanate crosslinkers via supercritical CO2 drying Synthesis of polyimide aerogels produced by the reaction of amines, acid anhydrides, and triamine crosslinkers via supercritical CO2 drying

[0138] Synthesis of polyimide gel by reaction of amine and acid anhydride. 0.92 g of 2,2'-dimethylbenzidine (DMBZ) was dissolved in 75.87 g of N-methyl-2-pyrrolidone (NMP). After stirring for 10 minutes, 2.56 g of biphenyl-3,3',4,4'-tetracarboxylic dianhydride (BPDA) was added to the mixture and stirred for 10 minutes. After stirring for 10 minutes, 2.99 g of 4,4'-[1,3-phenylenebis(1-methylethylene)]bis-aniline (bis-aniline-m) was added to the mixture and stirred for 10 minutes. After stirring for 10 minutes, 2.56 g of BPDA was added to the mixture and stirred for 10 minutes. After stirring for 10 minutes, 0.78 g of 4,4'-diaminodiphenyl ether (ODA) was added to the mixture and stirred for 10 minutes. After 10 minutes, a mixture of 0.15 g of Desmodur N3300A and 8.43 g of NMP was added to the first mixture and stirred for 10 minutes. After stirring for 10 minutes, 14.22 g of acetic anhydride and 3.52 g of triethylamine were added rapidly and continuously. The resulting sol was stirred for 2 to 5 minutes until well mixed and then poured into a mold. Then the mold was closed and placed in an airtight container and left at room temperature for 24 hours. After 24 hours, the gel was removed from its mold and transferred to a solvent exchange bath, i.e., a sealed container partially filled with about 500 mL of acetone. It was kept immersed in the acetone in the container for 72 hours, during which time the acetone was poured out and replaced with fresh acetone of equal volume twice.

[0139] After the solvent exchange was completed, the gel was transferred to a pressure vessel and immersed in excess acetone. Then the pressure vessel was sealed and liquid CO2 was introduced into the pressure vessel. The CO2-acetone mixture was discharged periodically while fresh liquid CO2 was supplied until all the acetone was removed. Then, while still filled with liquid CO2, the pressure vessel was separated from the CO2 supply. The pressure vessel was heated until the internal temperature reached 54 °C, during which time the pressure increased. The pressure was regulated by actuation of a solenoid valve and not allowed to exceed 1400 psi. At this time, the CO2 inside the container was in a supercritical state and held under these conditions for three hours. At this time, the pressure vessel was slowly vented isothermally so that the supercritical fluid became gaseous without forming a two-phase liquid-gas system until the pressure vessel returned to atmospheric pressure. Before removing the aerogel composite, the pressure vessel was finally cooled to room temperature.

[0140] The resulting aerogel is shown in Figure 3 It is a yellow monolithic material with a bulk density of 0.115 g / cc. The material has a compression modulus of 8.02 MPa, a compression yield strength of 0.4 MPa, and a thermal conductivity of 23.5 mW / m-K. Its specific surface area is 380 m 2 / g. When performing the liquid water absorption test described herein, the material exhibited a liquid water absorption of 14 wt%.

[0141] Example 2. Synthesis of polyimide aerogels produced by the reaction of amines, acid anhydrides, and triamine crosslinkers via supercritical CO2 drying Synthesis of polyimide aerogels produced by the reaction of amines, acid anhydrides, and triamine crosslinkers via supercritical CO2 drying

[0142] A polyimide gel was synthesized by the reaction of an amine and an acid anhydride. 0.92 g of 2,2'-dimethylbenzidine (DMBZ) was dissolved in 75.87 g of N-methyl-2-pyrrolidone (NMP). After stirring for 10 minutes, 2.56 g of biphenyl-3,3',4,4'-tetracarboxylic dianhydride (BPDA) was added to the mixture and stirred for 10 minutes. After stirring for 10 minutes, 2.99 g of 4,4'-[1,3-phenylene bis(1-methylethylene)] bisaniline (bis-aniline-m) was added to the mixture and stirred for 10 minutes. After stirring for 10 minutes, 2.56 g of BPDA was added to the mixture and stirred for 10 minutes. After stirring for 10 minutes, 0.78 g of 4,4'-diaminodiphenyl ether (ODA) was added to the mixture and stirred for 10 minutes. After 10 minutes, a mixture of 0.08 g of melamine and 8.43 g of NMP was added to the first mixture and stirred for 10 minutes. After stirring for 10 minutes, 14.22 g of acetic anhydride and 3.52 g of triethylamine were added rapidly and continuously. The resulting sol was stirred for 2 to 5 minutes until well mixed, and then poured into a mold. Then the mold was closed and placed in an airtight container and left at room temperature for 24 hours. After 24 hours, the gel was removed from its mold and transferred to a solvent exchange bath, i.e., a sealed container partially filled with about 500 mL of acetone.

[0143] The remaining solvent exchange and drying processes were carried out as described in Example 1.

[0144] The resulting aerogel was a yellow monolithic material with a bulk density of 0.111 g / cc and a thermal conductivity of 24 mW / m-K.

[0145] Example 3. Synthesis of polyimide aerogels produced by the reaction of amines, acid anhydrides, and triamine crosslinkers via supercritical CO2 drying Synthesis of polyimide aerogels produced by the reaction of amines, acid anhydrides, and triamine crosslinkers via supercritical CO2 drying

[0146] Polyimide gels were synthesized by the reaction of amines and acid anhydrides. A crosslinking solution was prepared in advance by adding 0.04 g of melamine and 0.28 g of BPDA to 25 g of NMP and stirring for 24 hours. After stirring for 24 hours, 0.19 g of DMBZ was added to the crosslinking mixture and stirred for 20 minutes. Then the crosslinking solution was stored in a sealed container. 0.92 g of 2,2'-dimethylbenzidine (DMBZ) was dissolved in 59.29 g of N-methyl-2-pyrrolidone (NMP). After stirring for 10 minutes, 2.56 g of biphenyl-3,3',4,4'-tetracarboxylic dianhydride (BPDA) was added to the mixture and stirred for 10 minutes. After stirring for 10 minutes, 2.99 g of 4,4'-[1,3-phenylene bis(1-methyl-ethylidene)] bisaniline (bis-aniline-m) was added to the mixture and stirred for 10 minutes. After stirring for 10 minutes, 2.56 g of BPDA was added to the mixture and stirred for 10 minutes. After stirring for 10 minutes, 0.78 g of 4,4'-diaminodiphenyl ether (ODA) was added to the mixture and stirred for 10 minutes. After 10 minutes, the pre-prepared crosslinking solution was added to the first mixture and stirred for 10 minutes. After stirring for 10 minutes, 14.22 g of acetic anhydride and 3.52 g of triethylamine were added rapidly and continuously. The resulting sol was stirred for 2 to 5 minutes until well mixed and then poured into a mold. Then the mold was closed and placed in an airtight container and left at room temperature for 24 hours. After 24 hours, the gel was removed from its mold and transferred to a solvent exchange bath, i.e., a sealed container partially filled with about 500 mL of acetone.

[0147] The remaining solvent exchange and drying processes were carried out as described in Example 1.

[0148] The resulting aerogel is a yellow monolithic material with a bulk density of 0.113 g / cc and a thermal conductivity of 24.8 mW / m-K. Its specific surface area is 346 m 2 / g.

[0149] Example 4. Synthesis of polyimide aerogels produced by the reaction of amines, acid anhydrides, and triisocyanate crosslinkers via supercritical CO2 drying Synthesis of polyimide aerogels produced by the reaction of amines, acid anhydrides, and triisocyanate crosslinkers via supercritical CO2 drying

[0150] Synthesize a polyimide gel through the reaction of an amine and an acid anhydride. Dissolve 1.14 g of 2,2'-dimethylbenzidine (DMBZ) in 71.96 g of N-methyl-2-pyrrolidone (NMP). After stirring for 10 minutes, add 3.16 g of biphenyl-3,3',4,4'-tetracarboxylic dianhydride (BPDA) to the mixture and stir for 10 minutes. After stirring for 10 minutes, add 3.70 g of 4,4'-[1,3-phenylenebis(1-methylethylidene)] bisaniline (bis-aniline-m) to the mixture and stir for 10 minutes. After stirring for 10 minutes, add another 3.16 g of BPDA to the mixture and stir for 10 minutes. After stirring for 10 minutes, add 0.97 g of 4,4'-diaminodiphenyl ether (ODA) to the mixture and stir for 10 minutes. After 10 minutes, add a mixture of 0.18 g of Desmodur N3300A and 8.00 g of NMP to the first mixture and stir for 10 minutes. After stirring for 10 minutes, quickly and continuously add 17.55 g of acetic anhydride and 4.35 g of triethylamine. Stir the resulting sol for 2 to 5 minutes until well mixed, then pour it into a mold. Then close the mold and place it in an airtight container and leave it at room temperature for 24 hours. After 24 hours, remove the gel from its mold and transfer it to a solvent exchange bath, i.e., a sealed container partially filled with about 500 mL of acetone.

[0151] Perform the remaining solvent exchange and drying processes as described in Example 1.

[0152] The resulting aerogel is a yellow monolithic material with a bulk density of 0.123 g / cc and a thermal conductivity of 27.6 mW / m-K. It has a specific surface area of 367 m 2 / g and an average pore diameter of 12.6 nm, as shown in Figure 6. It has a compressive modulus of 29.8 MPa and a compressive yield strength of 1.1 MPa. The plot of stress versus strain data is shown in Figure 7 in.

[0153] Example 5. Synthesis of polyimide aerogels produced by the reaction of amines, acid anhydrides, and triamine crosslinkers via supercritical CO2 drying Synthesis of polyimide aerogels produced by the reaction of amines, acid anhydrides, and triamine crosslinkers via supercritical CO2 drying

[0154] Synthesize polyimide gel through the reaction of amine and anhydride. Dissolve 1.14 g of 2,2'-dimethylbenzidine (DMBZ) in 71.96 g of N-methyl-2-pyrrolidone (NMP). After stirring for 10 minutes, add 3.16 g of biphenyl-3,3',4,4'-tetracarboxylic dianhydride (BPDA) to the mixture and stir for 10 minutes. After stirring for 10 minutes, add 3.70 g of 4,4'-[1,3-phenylenebis(1-methylethylidene)]bis-aniline (bis-aniline-m) to the mixture and stir for 10 minutes. After stirring for 10 minutes, add another 3.16 g of BPDA to the mixture and stir for 10 minutes. After stirring for 10 minutes, add 0.97 g of 4,4'-diaminodiphenyl ether (ODA) to the mixture and stir for 10 minutes. After 10 minutes, add a mixture of 0.05 g of melamine and 8.00 g of NMP to the first mixture and stir for 10 minutes. After stirring for 10 minutes, quickly and continuously add 17.55 g of acetic anhydride and 4.35 g of triethylamine. Stir the resulting sol for 2 to 5 minutes until well mixed, then pour it into a mold. Then close the mold and place it in an airtight container and leave it at room temperature for 24 hours. After 24 hours, remove the gel from its mold and transfer it to a solvent exchange bath, i.e., a sealed container partially filled with about 500 mL of acetone.

[0155] Perform the remaining solvent exchange and drying processes as described in Example 1.

[0156] The resulting aerogel is a yellow monolithic material with a bulk density of 0.131 g / cc and a thermal conductivity of 27.2 mW / m-K.

[0157] Example 6. Synthesis of polyimide aerogels produced by the reaction of amines, acid anhydrides, and triamine crosslinkers via supercritical CO2 drying Synthesis of polyimide aerogels produced by the reaction of amines, acid anhydrides, and triamine crosslinkers via supercritical CO2 drying

[0158] Polyimide gels are synthesized through the reaction of amines and acid anhydrides. A crosslinking mixture is prepared in advance by adding 0.05 g of melamine and 0.33 g of BPDA to 8 g of NMP and stirring for 24 hours. After stirring for 24 hours, 0.24 g of DMBZ is added to the crosslinking mixture and stirred for 20 minutes. 1.14 g of 2,2'-dimethylbenzidine (DMBZ) is dissolved in 71.96 g of N-methyl-2-pyrrolidone (NMP). After stirring for 10 minutes, 3.16 g of biphenyl-3,3',4,4'-tetracarboxylic dianhydride (BPDA) is added to the mixture and stirred for 10 minutes. After stirring for 10 minutes, 3.70 g of 4,4'-[1,3-phenylenebis(1-methylethylidene)]bis-aniline (bis-aniline-m) is added to the mixture and stirred for 10 minutes. After stirring for 10 minutes, an additional 3.16 g of BPDA is added to the mixture and stirred for 10 minutes. After stirring for 10 minutes, 0.97 g of 4,4'-diaminodiphenyl ether (ODA) is added to the mixture and stirred for 10 minutes. After 10 minutes, the pre-prepared crosslinking solution is added to the first mixture and stirred for 10 minutes. After stirring for 10 minutes, 17.55 g of acetic anhydride and 4.35 g of triethylamine are added rapidly and continuously. The resulting sol is stirred for 2 to 5 minutes until well mixed and then poured into a mold. Then the mold is closed and placed in an airtight container and left at room temperature for 24 hours. After 24 hours, the gel is removed from its mold and transferred to a solvent exchange bath, i.e., a sealed container partially filled with approximately 500 mL of acetone.

[0159] The remaining solvent exchange and drying processes are carried out as described in Example 1.

[0160] The resulting aerogel is a yellow monolithic material with a bulk density of 0.137 g / cc and a thermal conductivity of 27.4 mW / m-K. Its specific surface area is 331 m 2 / g.

[0161] Example 7. Synthesis of polyimide aerogels produced by the reaction of amines, acid anhydrides, and triisocyanate crosslinkers from organic solvents using dry air via atmospheric freeze drying Synthesis of polyimide aerogels produced by the reaction of amines, acid anhydrides, and triisocyanate crosslinkers via subcritical CO2 drying

[0162] The polyimide gel is synthesized using the process described in Example 1 up to the solvent exchange step. After aging, the gel is transferred to a bath of tert-butanol (i.e., tert-butyl alcohol) instead of being transferred to acetone. The volume of the alcohol bath is 5 times the volume of the gel. The alcohol in the bath is changed 5 times, once every 24 hours. The bath is maintained at 40 °C throughout the solvent exchange. After the solvent exchange, the gel is placed in a sealed package and transferred to a cold room maintained at 10 °C for 12 hours to freeze the solvent.

[0163] The gel is then removed from the package and transferred to a temperature-controlled drying chamber. In the drying chamber, the gel is placed on a support that thermally isolates it from the walls of the chamber and allows unobstructed gas flow on all sides of the gel. Gas is supplied at one end of the chamber and exhausted at the opposite end such that the gas continuously flows over and around the gel. The temperature of the inlet gas is measured inside the drying chamber by a thermocouple placed directly downstream of the inlet.

[0164] In this case, the gas is dry compressed air. The air is supplied at 100 psi by a compressor. The regulated gas flow is controlled using a needle valve and the resulting flow rate of 25 SCFH is measured using a gas flow rotameter. After passing through the rotameter, the gas flows through a liquid-cooled finned heat exchanger. The heat exchanger is cooled using a recirculating cooler pumping a cooling mixture of water and ethylene glycol and operates at a temperature and flow rate sufficient to maintain the drying chamber temperature of 0 °C as measured by the thermocouple at the inlet to the drying chamber. The effluent gas (a mixture of air and tert-butanol vapor) from the drying chamber passes through a cold trap designed to capture the tert-butanol vapor. The remaining air is then vented to the atmosphere through a standard exhaust system.

[0165] During the drying process, the gel is optionally removed from the drying chamber periodically and its mass is measured before quickly returning it to the drying chamber (before the remaining tert-butanol in the gel may start to melt). The mass of the drying gel is thus tracked over time and when the mass stops changing from one measurement to the next, the resulting aerogel is considered to be completely dry.

[0166] The resulting aerogel is a yellow monolithic material with a bulk density of 0.199 g / cc and a thermal conductivity of 24.0 mW / m-K. Its specific surface area is 279 m 2 / g.

[0167] Example 8. Synthesis of polyimide aerogels produced by the reaction of amines, acid anhydrides, and triisocyanate crosslinkers via subcritical CO2 drying Synthesis of polyimide aerogels produced by the reaction of amines, acid anhydrides, and triisocyanate crosslinkers via subcritical CO2 drying

[0168] A polyimide gel is prepared as described in Example 1 up to the step after the pressure vessel containing liquid CO2 is separated from the CO2 tank. At this point, alternatively, the vessel is heated to 28 °C. The pressure is adjusted in the same manner as described in Example 2 but limited to 1000 psi so as not to exceed the critical point of CO2. After holding the pressure for three hours under these conditions, the pressure vessel is isothermally depressurized such that the surface tension of the liquid phase is minimized, thereby reducing the drying stress applied to the solid skeleton of the porous gel. Once the vessel reaches atmospheric pressure, it is allowed to return to room temperature before removing the final polyimide / mat composite.

[0169] The resulting aerogel is a yellow monolithic material with a bulk density of 0.115 g / cc. The material has a compression modulus of 8.02 MPa, a compression yield strength of 0.4 MPa, and a thermal conductivity of 23.5 mW / m-K. Its specific surface area is 380 m 2 / g.

[0170] Example 9. Synthesis of polyimide aerogels produced by the reaction of amines, acid anhydrides, and triamine crosslinkers via supercritical CO2 drying Synthesis of polyimide aerogels produced by the reaction of amines, acid anhydrides, and triamine crosslinkers via supercritical CO2 drying

[0171] A polyimide gel was synthesized by the reaction of an amine and an acid anhydride. 0.960 g of 4,4'-diaminodiphenyl ether (ODA) was dissolved in 83.78 g of N-methyl-2-pyrrolidone (NMP). After stirring for 10 minutes, 2.17 g of biphenyl-3,3',4,4'-tetracarboxylic dianhydride (BPDA) was added to the mixture and stirred for 10 minutes. After stirring for 10 minutes, 1.02 g of 2,2'-dimethylbenzidine (DMBZ) was added to the mixture and stirred for 10 minutes. After stirring for 10 minutes, 2.17 g of BPDA was added to the mixture and stirred for 10 minutes. After stirring for 10 minutes, 1.65 g of 4,4'-[1,3-phenylene bis(1-2-methyl-ethylene)] bisaniline (bis-aniline-m) was added to the mixture and stirred for 10 minutes. After 10 minutes, a mixture of 0.10 g of 1,3,5-triaminophenoxybenzene (TAB) and 9.31 g of NMP was added to the first mixture and stirred for 10 minutes. After stirring for 10 minutes, 12.04 g of acetic anhydride and 2.98 g of triethylamine were added rapidly and continuously. The resulting sol was stirred for 2 to 5 minutes until well mixed, and then poured into a mold. The mold was then closed and placed in an airtight container and left at room temperature for 24 hours. After 24 hours, the gel was removed from its mold and transferred to a solvent exchange bath, i.e., a sealed container partially filled with approximately 500 mL of acetone. It was kept immersed in the acetone in the container for 72 hours, during which time the acetone was poured out and replaced with fresh acetone of equal volume twice.

[0172] The remaining solvent exchange and drying processes were carried out as described in Example 1.

[0173] The resulting aerogel is a yellow monolithic material and has a bulk density of 0.082 g / cc. Based on the manufacture and testing of similar materials, the aerogel is expected to have a thermal conductivity of approximately 24.6 mW / m-K and a specific surface area of approximately 560 m 2 / g. The material is very brittle mechanically and cracks significantly during processing and handling.

[0174] Example 10. Synthesis of polyimide aerogels produced by the reaction of amines, acid anhydrides, and triamine crosslinkers via supercritical CO2 drying Synthesis of polyimide aerogels produced by the reaction of amines, acid anhydrides, and triamine crosslinkers via supercritical CO2 drying

[0175] Polyimide gels were synthesized by the reaction of amines and acid anhydrides. 0.93 g of 2,2'-dimethylbenzidine (DMBZ) was dissolved in 75.82 g of N-methyl-2-pyrrolidone (NMP). After stirring for 10 minutes, 2.57 g of biphenyl-3,3',4,4'-tetracarboxylic dianhydride (BPDA) was added to the mixture and stirred for 10 minutes. After stirring for 10 minutes, 3.01 g of 4,4'-[1,3-phenylene bis(1-methyl-ethylidene)] bisaniline (bis-aniline-m) was added to the mixture and stirred for 10 minutes. After stirring for 10 minutes, an additional 2.57 g of BPDA was added to the mixture and stirred for 10 minutes. After stirring for 10 minutes, 0.79 g of 4,4'-diaminodiphenyl ether (ODA) was added to the mixture and stirred for 10 minutes. After 10 minutes, a mixture of 0.12 g of 1,3,5-triaminophenoxybenzene (TAB) and 8.42 g of NMP was added to the first mixture and stirred for 10 minutes. After stirring for 10 minutes, 14.26 g of acetic anhydride and 3.53 g of triethylamine were added rapidly and continuously. The resulting sol was stirred for 2 to 5 minutes until well mixed and then poured into a mold. The mold was then closed and placed in an airtight container and left at room temperature for 24 hours. After 24 hours, the gel was removed from its mold and transferred to a solvent exchange bath, i.e., a sealed container partially filled with approximately 500 mL of acetone.

[0176] The remaining solvent exchange and drying processes were carried out as described in Example 1.

[0177] The resulting aerogel was a yellow monolithic material with a bulk density of 0.123 g / cc and a thermal conductivity of 27.6 mW / m-K. The structure of the aerogel is shown in Figure 5 the SEM micrograph in. Liquid water droplets applied to the outer surface of the aerogel formed beads on the surface, as shown in Figure 4 indicating that the material is hydrophobic. The contact angle of the water droplets was 102°.

[0178] Although several embodiments of the present invention have been described and illustrated herein, those of ordinary skill in the art will readily envision numerous other ways and / or structures for performing the functions and / or obtaining the results and / or one or more of the advantages described herein, and each such variation and / or modification is considered to be within the scope of the present invention. More generally, those of skill in the art will readily understand that all parameters, dimensions, materials, and configurations described herein are intended to be exemplary, and the actual parameters, dimensions, materials, and / or configurations will depend upon one or more specific applications of the teachings of the present invention. Those of skill in the art will recognize or be able to ascertain using no more than routine experimentation many equivalents to the specific embodiments of the invention described herein. Accordingly, it is to be understood that the foregoing embodiments are presented by way of example only, and that within the scope of the appended claims and their equivalents, the invention may be practiced otherwise than as specifically described and claimed. The present invention is directed to each individual feature, system, article, material, and / or method described herein. Furthermore, any combination of two or more such features, systems, articles, materials, and / or methods, if such features, systems, articles, materials, and / or methods are not mutually inconsistent, is included within the scope of the present invention.

[0179] Unless explicitly stated to the contrary, a noun in the specification and claims herein that is not qualified with a quantity term should be understood to mean "at least one."

[0180] As used in the specification and claims herein, the phrase "and / or" should be understood to mean "one or both" of the elements so conjoined, i.e., in some instances the elements coexist and in other instances the elements exist separately. Unless explicitly stated to the contrary, there may optionally be other elements in addition to those explicitly recited by the "and / or" conjunction, whether related or unrelated to those elements explicitly recited. Thus, as a non-limiting example, when used in conjunction with open-ended language such as "comprising," a reference to "A and / or B" in one embodiment may refer to A without B (optionally including elements other than B); in another embodiment it may refer to B without A (optionally including elements other than A); in yet another embodiment it may refer to both A and B (optionally including other elements); and so forth.

[0181] As used herein in the specification and claims, "or" shall be understood to have the same meaning as "and / or" as defined above. For example, when separating items in a list, "or" or "and / or" shall be understood to be inclusive, i.e., including at least one of a plurality of elements or of a list of elements, but also including more than one of them, and optionally including additional unrecited items. Only terms to the contrary are expressly stated, such as "only one" or "exactly one", or "consisting of" when used in a claim, which refer to including exactly one element of a plurality of elements or of a list of elements. In general, the term "or" as used herein shall only be understood to represent an exclusive alternative (i.e., "one or the other, but not both") when preceded by an exclusive term such as "either", "one of", "only one of", or "exactly one of". When used in a claim, "consisting essentially of" shall have its ordinary meaning as used in the field of patent law.

[0182] As used herein in the specification and claims, the phrase "at least one" when referring to a list of one or more elements shall be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically recited in the list of elements, nor excluding any combinations of elements in the list of elements. This definition also allows that there may optionally be additional elements other than those specifically recited in the list of elements referred to in the phrase "at least one", whether related or unrelated to those specifically recited. Thus, as a non-limiting example, "at least one of A and B" (or equivalently, "at least one of A or B", or equivalently, "at least one of A and / or B") may in one embodiment refer to at least one A, optionally including more than one A, but no B (and optionally including elements other than B); in another embodiment, it may refer to at least one B, optionally including more than one B, but no A (and optionally including elements other than A); in yet another embodiment, it may refer to at least one A, optionally including more than one A, and at least one B, optionally including more than one B (and optionally including other elements); and so on.

[0183] In the claims as well as in the above specification, all transitional phrases such as "comprising", "including", "carrying", "having", "containing", "involving", "holding", etc. shall be understood to be open-ended, i.e., meaning including but not limited to. As stated in Section 2111.03 of the Manual of Patent Examining Procedure of the United States Patent and Trademark Office, only the transitional phrases "consisting of" and "consisting essentially of" shall be closed or semi-closed transitional phrases, respectively.

Claims

1. An aerogel comprising the following [M1] portion:

2. The aerogel according to claim 1, wherein the [M1] portion is part of a polymer structure comprising repeating units of the [M1] portion.

3. The aerogel according to claim 2, wherein the polymer structure comprises at least 5 repeating units of the [M1] portion.

4. The aerogel according to claim 2, wherein the aerogel comprises 2 to 20 repeating units of the [M1] portion.

5. The aerogel according to any one of claims 1 to 3, wherein at least 90% by weight of the aerogel is composed of the [M1] portion.

6. The aerogel according to any one of claims 1 to 3, wherein the aerogel comprises a polyimide aerogel.

7. The aerogel according to any one of claims 1 to 3, wherein When the aerogel is immersed in water at 25 °C for 24 hours, the aerogel absorbs less than 20% of the mass of water of the dry mass of the aerogel before immersion in water within its outer boundary.

8. The aerogel according to any one of claims 1 to 3, wherein the aerogel absorbs less than 20% of the mass of water of the dry mass of the aerogel before exposure to water vapor within its outer boundary.

9. The aerogel according to any one of claims 1 to 3, wherein the aerogel exhibits a contact angle with water greater than 90° in an ambient air environment at 1 atmosphere and 25 °C.

10. The aerogel according to any one of claims 1 to 3, wherein the aerogel exhibits a BET surface area greater than 200 m 2 / g.

11. The aerogel according to any one of claims 1 to 3, wherein the aerogel exhibits a bulk density of 0.06 g / cm 3 to 0.2 g / cm 3 .

12. The aerogel according to any one of claims 1 to 3, wherein the aerogel comprises a silica aerogel and a polyimide aerogel.

13. The aerogel according to any one of claims 1 to 3, wherein the aerogel exhibits a compressive modulus greater than 1 MPa.

14. The aerogel according to any one of claims 1 to 3, wherein the aerogel exhibits a compressive yield strength greater than 300 kPa.

15. The aerogel according to any one of claims 1 to 3, wherein the aerogel exhibits a flexural modulus greater than 1 MPa.

16. The aerogel according to any one of claims 1 to 3, wherein the aerogel exhibits a flexural yield strength greater than 500 kPa.

17. The aerogel according to any one of claims 1 to 3, wherein the aerogel exhibits an average dielectric constant less than 1.4 in the range of 0 GHz to 50 GHz.

18. The aerogel according to any one of claims 1 to 3, wherein the aerogel exhibits an average loss tangent less than 0.010 in the range of 0 GHz to 50 GHz.

19. The aerogel according to any one of claims 1 to 3, wherein at least one dimension of the aerogel is from 10 microns to 1 mm.

20. The aerogel according to any one of claims 1 to 3, wherein at least one dimension of the aerogel is equal to or greater than 30 cm.

21. The aerogel according to any one of claims 1 to 3, wherein the aerogel exhibits an average sound transmission loss greater than 5 dB / cm in the frequency range of 300 Hz to 2000 Hz.

22. The aerogel according to any one of claims 1 to 3, wherein the average pore size of the aerogel is less than 20 nm.

23. The aerogel according to any one of claims 1 to 3, wherein the aerogel comprises pores of 1 micron or greater.

24. The aerogel according to any one of claims 1 to 3, wherein the aerogel comprises a bimodal pore size distribution.

25. The aerogel according to any one of claims 1 to 3, wherein the aerogel exhibits a thermal conductivity of less than 30 mW / m-K at 25 °C.

26. The aerogel according to any one of claims 1 to 3, wherein the aerogel is fluorine-free.

27. The aerogel according to any one of claims 1 to 3, wherein the aerogel meets the criteria of Class A1, Class A2 and / or Class B fire performance of the European classification standard EN13501-1.

28. The aerogel according to any one of claims 1 to 3, wherein the aerogel meets the criteria of afterflame time, drip flame self-extinguishing time and / or burning length stated in Part 25.853a of the United States Federal Aviation Regulations.

29. The aerogel according to any one of claims 1 to 3, wherein the aerogel meets the criteria of total heat release, peak heat release rate and / or 4.0-minute smoke density within the first two minutes stated in Part 25.853d of the United States Federal Aviation Regulations.

30. The aerogel according to any one of claims 1 to 3, wherein the aerogel is non-flammable.

31. The aerogel according to any one of claims 1 to 3, wherein the maximum operating temperature of the aerogel is greater than 100 °C.

32. The aerogel according to any one of claims 1 to 3, wherein the maximum operating temperature of the aerogel is greater than 200 °C.

33. The aerogel according to any one of claims 1 to 3, wherein the maximum operating temperature of the aerogel is greater than 250 °C.

34. The aerogel according to any one of claims 1 to 3, wherein the maximum operating temperature of the aerogel is greater than 300 °C.

35. The aerogel according to any one of claims 1 to 3, wherein the maximum operating temperature of the aerogel is greater than 325 °C.

36. The aerogel according to any one of claims 1 to 3, wherein the maximum operating temperature of the aerogel is greater than 350 °C.

37. An aircraft wall panel comprising the aerogel according to any one of claims 1 to 36.

38. An engine hood comprising the aerogel according to any one of claims 1 to 36.

39. A bulletproof armor, protective article, panel, composite material or protective vest comprising the aerogel according to any one of claims 1 to 36.

40. A shoe, boot or insole comprising the aerogel according to any one of claims 1 to 36.

41. A flexible strip comprising the aerogel according to any one of claims 1 to 36.

42. A film comprising the aerogel according to any one of claims 1 to 36.

43. A monolithic material comprising the aerogel according to any one of claims 1 to 36.

44. A carbonized derivative of the aerogel according to any one of claims 1 to 36.

45. A method for manufacturing an aerogel, comprising: combining a quantity of biphenyl-3,3',4,4'-tetracarboxylic dianhydride (BPDA), a first diamine, and a solvent such that a first intermediate medium containing acid anhydride-terminated polyamic acid trimers is formed; subsequently, combining the first intermediate medium and a second diamine such that a second intermediate medium containing pentamers is formed; subsequently, combining the second intermediate medium and an additional quantity of BPDA such that a third intermediate medium containing heptamers is formed; subsequently, combining the third intermediate medium and a third diamine such that a fourth intermediate medium containing oligomer chains is formed; and subsequently, combining the fourth intermediate medium and a crosslinking reagent to form a gel, wherein: the first diamine is different from the second diamine and the third diamine, and the second diamine is different from the third diamine, wherein each of the first diamine, the second diamine, and the third diamine is selected from 2,2'-dimethylbenzidine (DMBZ), 4,4'-oxydianiline (4,4-ODA), and 4,4'-[1,3-phenylenebis(1-methylethylidene)]bisbenzenamine (bis-aniline-m).

46. The method according to claim 45, wherein combining the quantity of BPDA, the first diamine, and the solvent comprises first combining the BPDA and the solvent and subsequently adding the first diamine.

47. The method according to claim 45, wherein combining the quantity of BPDA, the first diamine, and the solvent comprises first combining the first diamine and the solvent and subsequently adding the BPDA.

48. The method according to claim 45, wherein combining the quantity of BPDA, the first diamine, and the solvent comprises combining the quantity of BPDA, the first diamine, and the solvent simultaneously.

49. The method according to any one of claims 45 to 48, wherein: the first diamine is DMBZ, the second diamine is 4,4-ODA, and the third diamine is bis-aniline-m.

50. The method according to any one of claims 45 to 48, wherein: the first diamine is DMBZ, the second diamine is bis-aniline-m, and the third diamine is 4,4-ODA.

51. The method according to any one of claims 45 to 48, wherein: the first diamine is bis-aniline-m the second diamine is DMBZ, and the third diamine is 4,4-ODA.

52. The method according to any one of claims 45 to 48, wherein: the first diamine is bis-aniline-m [[ID=2 ​ ​ ​ ​ ​ 54. The method according to any one of claims 45 to 48, wherein: the first diamine is 4,4-ODA, the second diamine is bisaniline-m, and the third diamine is DMBZ.

55. The method according to any one of claims 45 to 48, wherein combining the amount of BPDA, the first diamine, and the solvent comprises combining the first diamine and the BPDA in relative amounts based on a ratio of the amount of BPDA to the first diamine of 1.9:1 to 2.1:

1.

56. The method according to any one of claims 45 to 48, wherein combining the first intermediate medium and the second diamine comprises combining the acid anhydride-terminated polyamic acid trimer and the second diamine in relative amounts based on a molar ratio of the second diamine to the acid anhydride-terminated polyamic acid trimer of 1.9:1 to 2.1:

1.

57. The method according to any one of claims 45 to 48, wherein combining the second intermediate medium and the additional amount of BPDA comprises combining the pentamer and the additional amount of BPDA in relative amounts based on a molar ratio of the additional amount of BPDA to the pentamer of 1.9:1 to 2.1:

1.

58. The method according to any one of claims 45 to 48, wherein combining the third intermediate medium and the third diamine comprises combining the heptamer and the third diamine in relative amounts based on a molar ratio of the third diamine to the heptamer of 0.8:1 to 1.1:

1.

59. The method according to any one of claims 45 to 48, wherein combining the fourth intermediate medium and the crosslinking agent comprises combining the oligomer chain and the crosslinking agent in relative amounts based on a molar ratio of the crosslinking agent to the oligomer chain of 0.5:1 to 0.75:1 or 1.9:1 to 2.1:

1.

60. The method according to any one of claims 45 to 48, wherein combining the fourth intermediate medium and the crosslinking agent further comprises combining a catalyst with the fourth intermediate medium and the crosslinking agent.

61. The method according to claim 60, wherein the catalyst comprises triethylamine.

62. The method according to claim 60, wherein the catalyst comprises tripropylamine.

63. The method according to any one of claims 45 to 48, wherein combining the fourth intermediate medium and the crosslinking agent comprises combining the oligomer chain and a water scavenger in relative amounts based on a molar ratio of the water scavenger to BPDA of 2:1 to 10:

1.

64. The method according to any one of claims 45 to 48, wherein combining the fourth intermediate medium and the crosslinking agent further comprises combining a water scavenger with the fourth intermediate medium and the crosslinking agent.

65. The method according to claim 64, wherein the water scavenger comprises acetic anhydride.

66. The method according to any one of claims 45 to 48, wherein the solvent comprises N-methyl-2-pyrrolidone, dimethyl sulfoxide, a ketone, acetonitrile, ethyl acetate, dimethylformamide, and / or dimethylacetamide.

67. The method according to any one of claims 45 to 48, the method further comprising removing liquid from the gel to produce an aerogel.

68. A method for manufacturing an aerogel, comprising: providing a solvent, adding a first diamine to the solvent, adding a first amount of dianhydride to the solvent after adding the first diamine, adding a second diamine to the solvent after adding the first amount of dianhydride, adding a second amount of dianhydride to the solvent after adding the second diamine, adding a third diamine to the solvent after adding the second amount of dianhydride, adding a crosslinking agent to the solvent, adding a catalyst to the solvent, and adding a water scavenger to the solvent to form a gel comprising polyamic acid and / or polyimide, optionally replacing at least a portion of the liquid in the resulting gel with a second liquid, and then removing at least a portion of the liquid from the gel to form an aerogel, wherein the dianhydride is biphenyltetracarboxylic dianhydride, wherein the first diamine, the second diamine, and the third diamine are selected from 2,2'-dimethylbenzidine (DMBZ), 4,4'-oxydianiline (4,4-ODA), and 4,4'-[1,3-phenylenebis(1-methylethylidene)]bisbenzenamine (bis-aniline-m), wherein the first diamine is different from the second diamine and the third diamine, and the second diamine is different from the third diamine.

69. The method according to claim 68, wherein the first diamine, the second diamine, or the third diamine is bis-aniline-m.

70. The method according to any one of claims 68 to 69, wherein the liquid is removed from the gel by supercritical extraction.

71. The method according to any one of claims 68 to 69, wherein the liquid in the gel is first at least partially replaced by carbon dioxide, after which the carbon dioxide is removed from the gel.

72. The method according to any one of claims 68 to 69, wherein the liquid in the gel is removed by subcritical extraction.

73. The method according to any one of claims 68 to 69, wherein the liquid in the gel is removed by evaporation and / or boiling.

74. The method according to any one of claims 68 to 69, wherein the liquid in the gel is removed by freeze-drying under vacuum.

75. The method according to any one of claims 68 to 69, wherein the liquid in the gel is removed by freeze-drying at atmospheric pressure.

76. The method according to any one of claims 68 to 69, wherein the solvent comprises N-methyl-2-pyrrolidone, dimethyl sulfoxide, ketone, acetonitrile, ethyl acetate, dimethylformamide, and / or dimethylacetamide.

77. The method according to any one of claims 68 to 69, wherein the catalyst comprises a trialkylamine and / or pyridine.

78. The method according to any one of claims 68 to 69, wherein the crosslinking agent comprises an isocyanurate group, a silicon-oxygen bridge, a trifunctional benzene ring, a silsesquioxane group, a phenoxy group, a trityl group, an imidazole group, and / or an alkyl group.

79. The method according to any one of claims 68 to 69, wherein the total mass of all monomers added to the solvent is greater than 5% of the total mass of the solvent.

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