Thermal Imidization Research Articles

Synthesis and characterization of nanocomposites based on polyimide bearing benzimidazole side groups filled with titania nanoparticles

ABSTRACT This study reports on the fabrication and property investigation of nanocomposites based on polyimide (PI) containing benzimidazole pendant groups reinforced with titania nanoparticles (TiO2 NPs) via the in-situ thermal imidization approach. This method involves the formation of poly(amic acid) (PAA), as the precursor of PI, by polycondensation of an equimolar amount of dianhydride, pyromellitic dianhydride (PMDA), with a benzimidazole-containing diamine monomer, 5-(2-benzimidazole)-1,3-bis(4-aminophenoxy)benzene (BIDA), in dimethylacetamide (DMAc) solvent, followed by embedding various weight percentages (3, 5, and 8 wt%) of amine-functionalized titania nanoparticles (NH2-TiO2 NPs) in PAA media, and subsequent thermal imidization to be converted to PI/TiO2 nanocomposite films. The structural, morphological, and thermal properties of the obtained neat PI and its nanocomposite films were studied by various methods, such as FT-IR spectroscopy, X-ray diffraction (XRD) analysis, thermal gravimetric analysis (TGA), and scanning electron microscopy (SEM). The data resulted from TGA analysis indicated that the incorporation of NH2-TiO2 NPs into the PI matrix show higher thermal stability when compared to the neat PI. The SEM images revealed that the dispersion of titania NPs was uniformly done in PI matrix, with a particle size of around 42 nm.

Promoting the electrical conductivity of polyimide/in-situ reduced graphene oxide nanocomposites by controlling sheet size

Polyimide (PI)-based nanocomposite films have found promising applications in electronics. However, despite their superior thermomechanical properties, PI/graphene oxide (GO) nanocomposites have a lower electrical conductivity compared to the case when pre-reduced graphene oxide (rGO) is used. To address this gap, we aimed to increase the electrical conductivity of PI/GO nanocomposite films without sacrificing other properties by forming in-situ reduced GO (irGO) particles and enhancing their aspect ratio. We produced GO nanosheets with various sizes via the modified Hummer method and used them to prepare PI/irGO nanocomposites via in-situ polymerization. The in-situ reduction of GO particles occurred along with the thermal imidization. Analysis of IR spectroscopy, XRD patterns, DMTA, and SEM images suggested the formation of chemical bonds between GO particles and PI matrix, which fortified the interface compared to PI/rGO nanocomposites. Thermal analyses revealed that enhancing the sheet size led to a decrease in the degradation rate below 200 °C and an increase in the ash residual. More importantly, the electrical resistance of PI/irGO was significantly decreased, even below that of the PI/rGO nanocomposite, by increasing the size of the nanosheets. These results are promising for the application of PI/irGO nanocomposites in electronics, and they may even replace PI/rGO nanocomposites when higher thermomechanical properties are desired.

Large interfacial polarization in metal–organic framework hollow ZIF-8/polyimide low-k nanocomposite films

Polymer films with tailored dielectric properties and large electrical displacement are required for applications in microelectronics due to the need for ultrahigh speed and low transmission delays. In this study, we developed a low-k polyimide (PI) nanocomposite incorporated with metal–organic framework hollow ZIF-8 (HZIF-8) nanocrystals to achieve a high energy storage capacity. The PI nanocomposite film was prepared by solution casting a mixture of HZIF-8/polyamide acid with thermal imidization. A dielectric constant of 2.26 was obtained at 100 Hz for the 5 wt% nanocomposite with a multi-stage pore architecture. Due to improved interfacial polarization, the 1 wt% nanocomposite had a high energy density of 12.2 J/cm3 and a charge–discharge efficiency of 70% at 600 MV/m. The PI nanocomposite film exhibited dielectric reliability with inherent flexible performance, and it is expected to be a primary candidate for polymer dielectric applications in microelectronics.

Having Your Cake and Eating It Too: Electrode Processing Approach Improves Safety and Electrochemical Performance of Lithium-Ion Batteries

A layered Li[NixCoyMn1-x-y]O2 (NCM)-based cathode is preferred for its high theoretical specific capacity. However, the two main issues that limit its practical application are severe safety issues and excessive capacity decay. A new electrode processing approach is proposed to synergistically enhance the electrochemical and safety performance. The polyimide's (PI) precursor is spin-coated on the LiNi0.5Co0.2Mn0.3O2 (NCM523) electrode sheet, and the homogeneous sulfonated PI layer is in situ produced by thermal imidization reaction. The PI-spin coated (PSC) layer provides improvements in capacity retention (86.47% vs 53.77% after 150 cycles at 1 C) and rate performance (99.21% enhancement at 5 C) as demonstrated by the NCM523-PSC||Li half-cell. The NCM523-PSC||graphite pouch full cell proves enhanced capacity retention (76.62% vs 58.58% after 500 cycles at 0.5 C) as well. The thermal safety of the NCM523-PSC cathode-based pouch cell is also significantly improved, with the critical temperature of thermal safety T1 (the beginning temperature of obvious self-heating temperature) and thermal runaway temperature T2 increased by 60.18 and 44.59 °C, respectively. Mechanistic studies show that the PSC layer has multiple effects as a passivation layer such as isolation of electrode-electrolyte contact, oxygen release suppression, solvation structure tuning, and the decomposition of carbonate solvents as well as LiPF6 inhibition. This work provides a new path for a cost-effective and scalable design of electrode decoration with synergistic safety-electrochemical kinetics enhancement.

Scalable, Versatile Synthesis of Ultrathin Polyetherimide Films and Coatings via Interfacial Polymerization

AbstractPolyetherimides (PEI) are high‐performance thermoplastic polymers featuring a high dielectric constant and excellent thermal stability. In particular, PEI thin films are of increasing interest for use in solid‐state capacitors and membranes, yet the cost and thickness are limited by conventional synthesis and thermal drawing techniques. Here, a method of synthesizing ultrathin PEI films and coatings is introduced based on interfacial polymerization (IP) of poly(amic acid), followed by thermal imidization. Control of transport, reaction, and precipitation kinetics enables tailoring of PEI film morphology from a nanometer‐scale smooth film to a porous micrometer‐scale layer of polymer microparticles. At short reaction times (≈1 min) freestanding films are formed with ≈1 µm thickness, which to our knowledge surpass commercial state‐of‐the‐art films (3–5 µm minimum thickness) made by thermal drawing. PEI films synthesized via the IP route have thermal and optical properties on par with conventional PEI. The use of the final PEI is demonstrated in structurally colored films, dielectric layers in capacitors, and show that the IP route can form nanometer‐scale coatings on carbon nanotubes. The rapid film formation rate and fine property control are attractive for scale‐up, and established methods for roll‐to‐roll processing can be applied in future work.

Long-term atomic oxygen resistant polyimide films containing carborane nanocage structure in the main chains

High-temperature durable polymer films with long-term atomic oxygen (AO) resistant capabilities are highly desired for the development of spacecraft with long-servicing lifetimes in low earth orbit (LEO). The relatively poor AO resistance of conventional polyimide (Kapton® H) film severely limited its applications in LEO spacecraft. In this work, carborane nanocage rich in boron element was introduced into polyimide molecular chain to prolong the atomic oxygen resistance life of polyimide film. A series of carborane-containing polyimide (CBPI) nanocomposite films with ultrahigh AO resistance have been prepared by casting precursor polyamic acid (PAA) solution on a glass plate, followed by thermal imidization at several elevated temperatures. The AO exposure experiments were tested in a ground-based AO effects simulation facility in our laboratory with the filament discharge and bound of magnetic field. Incorporation of carborane nanocage structure apparently improved the thermal stability and AO resistance of the PI nanocomposite films. The CBPI-50 film exhibited the lowest AO average erosion yield (Es) of 2.3 × 10−25 cm3·atom−1 under AO exposure with a fluence of 3.33 × 1020 atoms·cm−2, which is more than one order of magnitude lower than the reference Kapton® H film. The protective mechanism of CBPI nanocomposite films during AO exposure was proposed.

Facile preparation of Zr@carbon electrodes based on polyimide/UiO-66 composites for supercapacitors

Herein, we propose an effective strategy for preparing Zr@C composite electrodes. First, the UiO-66 crystals are synthesized and introduced into polyimide (PI) by in-situ polymerization and thermal imidization to fabricate composite films. After carbonization, the Zr@C composites are obtained, and the influences of UiO-66 content and carbonization temperature on the structures and electrochemical behaviors are investigated. After optimization, the specific capacitance of the PI/5%UiO-66–800 reaches a maximum of 345F/g at 0.5 A/g, superior to corresponding PI matrix and UiO-66 crystals. As the current density gradually increases to 10 A/g, the specific capacitance drops to 252F/g with a retention of 73 %. Additionally, the PI/5%UiO-66–800 composites are assembled into symmetric supercapacitors, which show a favorable specific capacitance of 271.2 F/g and an outstanding cycling stability about 99 % after 10,000 charge–discharge cycles. Furthermore, the supercapacitor device has delivered a high specific energy of 37.67 Wh kg−1 with a specific power of 500 W kg−1. Moreover, only one coin cell can successfully power a LED, suggesting its promising potential as an alternative electrode material for high-performance supercapacitor applications. Thus, this study demonstrates a simple way to boost capacitive performances of Zr@C composite electrodes for power sources.

Rational design of polymer nanofiber aerogels with aligned micrometer-sized porous structures and their high separation performance

In this article, a new type of pre-oxidized polyacrylonitrile/polyimide (OPAN/PI) nanofiber aerogels (NFAs) with aligned micrometer-sized hierarchical porous structures was fabricated via oriented ice-segregation-induced self-assembly and thermal imidization process. Polyimide was chosen as an adhesive and cross-linker because of its excellent chemical resistance, thermal stability and mechanical strength. The resulted OPAN/PI NFA have good resilience and high hydrophobicity (water contact angle 136.0°), ultralow density (8.65 mg m−3), which can be used as good oil absorbents and efficient separation of oil and water. The optimized OPAN/PI NFAs can collect various oily solvents with high absorption capacities up to 135 times of their own weight. Moreover, surfactant-stabilized water-in-oil emulsions and oil/water mixture can be fully separated under gravity driving and the filtration efficiency has only 1% loss after 20 separation processes. The elution flux can be up to 8.7 × 105 L m−2 h−1. This work opens up the avenue of exploring novel for application in the field of oil/water separation.

High-performance electrochromic supercapacitor based on an electroactive polyimide containing pentaaniline

Attributed to their obvious color transition, good electrochemical reversibility, and high theoretical capacitance, polyaniline-based electrochromic supercapacitors have recently garnered significant attention in wearable devices, intelligent power supplies, and smart windows. However, its limited processability as well as poor electrochemical endurability have severely hampered polyaniline's practical application in this regard. Herein, a new electroactive polyimide containing pentaaniline in the main chain has been facilely designed and synthesized using oxidative coupling polymerization followed by thermal imidization. Rational matched with vanadium pentoxide ion-storage counter electrode, a quasi-solid-state electrochromic supercapacitor device (QSES) is manufactured with desirable simultaneous optical change and energy storage performance of high optical contrast of 68%, fast switching speed of 1.29/1.58 s, good open circuit memory (1.28% decay after power off for 3600 s), wide voltage window of 2 V, large capacitance of 41.53 mF/cm2, and outstanding cycling durability (85% capacitance and 96% optical modulation retention after 10000 cycles at 0.2 mA/cm2). This study provides a feasible approach of molecular designing for achieving processable electroactive polymer and shows the promising potential of the resultant electrochromic supercapacitor in smart power supply devices with energy level indication functionality.

Effects of organoclay on colorless and transparent polyimide nanocomposites: thermomechanical properties, morphology, and optical transparency.

Although aromatic polyimide (PI) exhibits excellent mechanical performance and thermal stability, its dark color limits applicability in optical displays. Therefore, it is desirable to manufacture colorless, transparent PI (CPI) nanocomposite films that retain excellent physical properties. In this study, a solution intercalation method was used to disperse organoclay (Cloisite 25A; CS25A) in poly(amic acid), which was prepared using 4,4'-oxydiphthalic dianhydride and 3,4'-oxydianiline as monomers. This dispersion was then subjected to thermal imidization to synthesize CPI hybrid films. The influence of the CS25A content (0-1.00 wt%) on the thermomechanical properties, optical transmittance, and morphology of the prepared films was investigated. The hybrid film with a CS25A content of 0.50 wt% exhibited the best thermomechanical properties. However, upon further increasing the organoclay content to 1.00 wt%, the physical properties deteriorated. At 0.50 wt% CS25A, some agglomeration occurred but most of the clay was well dispersed as nano-sized particles, as revealed by transmission electron microscopy. In contrast, when the CS25A content exceeded a critical content, most of the clay was agglomerated and the physical properties were reduced. All the obtained CPI hybrid films were colorless and transparent, regardless of the organoclay content.

Colorless and transparent poly(amide imide) nanocomposites containing organically modified hectorite.

Polyamic acid (PAA) was synthesized using the diamine monomer N,N'-[2,2'-bis(trifluoromethyl)-4,4'-biphenylene]bis(4-aminobenzamide) and dianhydride monomer 4,4'-oxydiphthalic anhydride. Colorless and transparent poly(amide imide) (CPAI) hybrid films were prepared via multi-step thermal imidization of PAA in which various contents of nano-filler were dispersed. The CPAI hybrid films were prepared by dispersing organoclay STN, which was obtained by organically modifying hectorite, in CPAI by solution intercalation with various contents ranging from 1 to 7 wt%. The thermomechanical properties, morphologies, and optical transparencies of the obtained CPAI hybrid films were investigated based on the dispersed STN content, and the results were compared. Some of the clay in the CPAI hybrid film were agglomerated, which was observed using a transmission electron microscope; however, most clays were well-dispersed, with a nano-size of less than 10 nm. The best thermomechanical properties of the CPAI hybrid film were exhibited with an STN content of 3 wt%, but these properties decreased above the critical content. The coefficients of thermal expansion of all the hybrid films were below 20 ppm per °C regardless of the amount of STN, and the yellow index was 1-2 even when the STN content increased to 7 wt%.

Polyimide/crown ether composite film with low dielectric constant and low dielectric loss for high signal transmission.

Dielectric properties of polyimide (PI) are constrained by its inherent molecular structure and inter-chain packing capacities. The compromised dielectric properties of PI, however, could be rescued by introducing trifluoromethyl and forming a host-guest inclusion complex with the introduction of crown ethers (CEs). Herein, we report PI/crown ether composite films as a communication substrate that could be applied under high frequency circumstances. In this work, three kinds of bisphenol A-containing diamine (2,2'-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(2-methyl-4-aminophenoxy)phenyl]propane, and 2,2-bis[4-(2-trifluoro methyl-4-aminophenoxy)phenyl]propane) are synthesized and polymerized with 4,4'-(hexafluoroisopropylidene)diphthalic anhydride to prepare low-dielectric PI films by means of thermal imidization. Crown ethers are introduced into the PI with different mass fractions to obtain three series of PI films. Following the combination of trifluoromethyl into the molecular chain of PI, high frequency dielectric loss of modified PI films can be effectively reduced. The properties of these materials (especially the dielectric properties) are thoroughly explored by crown ether addition. The results show that the crown ether addition process can offer crown ethers with increased free volume of PI matrix, thus allowing them to generate a special necklace-like supramolecular structure, which makes the crown ether disperse more uniformly in the PI matrix, resulting in improved dielectric properties. Importantly, the dielectric constant and dielectric loss of the composite films at high frequencies are remarkably reduced to 2.33 and 0.00337, respectively. Therefore, these composite films are expected to find extensive use as a 5G communication substrate at high frequencies in the future.

Comparative Studies of the Dielectric Properties of Polyester Imide Composite Membranes Containing Hydrophilic and Hydrophobic Mesoporous Silica Particles.

In this paper, comparative studies of hydrophilic and hydrophobic mesoporous silica particles (MSPs) on the dielectric properties of their derivative polyester imide (PEI) composite membranes were investigated. A series of hydrophilic and hydrophobic MSPs were synthesized with the base-catalyzed sol-gel process of TEOS, MTMS, and APTES at a distinctive feeding ratio with a non-surfactant template of D-(-)-Fructose as the pore-forming agent. Subsequently, the MSPs were blended with the diamine of APAB, followed by introducing the dianhydride of TAHQ with mechanical stirring for 24 h. The obtained viscous solution was subsequently coated onto a copper foil, 36 μm in thickness, followed by performing thermal imidization at specifically programmed heating. The dielectric constant of the prepared membranes was found to show an obvious trend: PEI containing hydrophilic MSPs > PEI > PEI containing hydrophobic MSPs. Moreover, the higher the loading of hydrophilic MSPs, the higher the value of the dielectric constant and loss tangent. On the contrary, the higher the loading of hydrophobic MSPs, the lower the value of the dielectric constant with an almost unchanged loss tangent.

Superhydrophobic polyimide/cattail-derived active carbon composite aerogels for effective oil/water separation

The frequent oil spill accidents have created increasingly environmental and ecological problems. Therefore, the development of effective oil-cleaning materials is of great importance. In this study, we prepared superhydrophobic polyimide/cattail-derived active carbon composite (PI/CAC) aerogels for efficient oil/water separation through a facile approach based on freeze-drying and thermal imidization. The resultant aerogel shows ultralight weight (29.7 mg/cm3), superhydrophobicity (water contact angle = 151.3°), excellent compressibility, and ideal chemical stability, which are conducive to the oil sorption and extrusion at various harsh conditions including acidic, alkaline, and saline solutions, as well as oil-in-water emulsions. Typically, the optimized sample PI/CAC-3 aerogel could achieve saturation within 5–20 s, delivering a high oil sorption capacity of 25.1–71.0 g/g for various oils. When used for continuous oil/water separation, high flux of 4.47 × 104 L m-2 h−1 and separation efficiency of 98.3% were achieved for chloroform/water mixture by gravity-driven separation method. Furthermore, due to the high compressibility, the aerogel can be used for cycling separation through sorption-extrusion process with less than 3% decrease in separation efficiency after 10 cycles. These advantages make it a potential candidate for the treatment of wastewater polluted by various oils and/or organic solvents.

Porous highly fluorinated polyimide/polydopamine nanocomposite films with simultaneously enhanced toughness, UV-shielding and photostability for aerospace applications

Polydopamine (PDA), also known as artificial melanin, was adopted as ultraviolet absorbent to prepare a series of porous highly fluorinated polyimide/polydopamine (FPI/PDA) films by cyclodehydration via chemical and thermal imidization. The hydrogen bond and porous structure endowed the reinforced thermal, mechanical, UV-shielding and photostability. The initial decomposition and glass transition temperatures of FPI/PDA (1 wt %) film were as high as 461.5 °C and 341.5 °C, respectively beyond pure FPI by 54.1 °C and 26.0 °C. The stress-strain curves indicated that tensile strength and fracture elongation first increased and then decreased with the increase of PDA content, and reached the maximum at 0.5 wt % PDA content, which were 1.41 and 29.47 times of FPI, respectively. UV–vis transmittance spectra, curcumin photolysis and recyclability measurement confirmed the splendid UV-shielding properties with simultaneous excellent visible light transmittance and durability of porous FPI/PDA film. FTIR and AFM manifested its superior photostability with mild variation in carbonyl absorption peaks and surface roughness after 720 h UV irradiation. The above enhancement mechanisms included synergistic UV absorption of porous FPI and PDA, photothermal conversion in a stable FPI, and PDA's free radical trapping, promoting porous FPI/PDA film as an aerospace UV shielding material.

Development of sulphonated co-polyimide based sensor for metal ions detection in aqueous media

• Sulphonated co-polyimide (OBM-20) was synthesized by thermal imidization. • UV-Vis spectroscopy was carried out to evaluate the sensing behaviour of OBM-20. • Sensor showed appreciable increase in absorption intensity upon interaction with metal ions. • Sensor detected the nM concentration of metal ions under optimized conditions. This study reports a facile approach towards sensing properties of hydrophilic sulphonated co-polyimide (OBM-20) for the detection of metal ions in water through UV-Vis spectroscopy. Anionic sulphonated co-polyimide (OBM-20) was synthesized by a two-step thermal imidization reaction. Hydrophilic anionic sulphonate group possessing strong affinity towards heavy metal ions resulted in improved interaction of OBM-20 with metal ions in aqueous media. OBM-20 showed different absorptions in UV region upon interacting with Ni (II), Co (II), and Cr (III) ions in deionized water at room temperature and neutral pH. Interestingly, OBM-20 demonstrated that it can serve as an optical chemical sensor and metal ion receptor for nanomolar detection of toxic metal ions, particularly Ni (II), Co (II), and Cr (III) existing in aqueous media. Sulphonated co-polyimide resulted in efficient sensing of Ni (II) as compared to slightly larger metals such as Co (II) and Cr (III) in aqueous solution. Ultimately, the assessment of the sensing properties of OBM-20 revealed that it can function as a selective Ni (II) ions sensor.

High enthalpy efficiency lignin-polyimide porous hybrid aerogel composite phase change material with flame retardancy for superior solar-to-thermal energy conversion and storage

Liquid-solid organic phase change materials (PCMs) exist shortcomings of leakage, poor solar-to-thermal conversion efficiency, and flammability, which restrict the application scope of solar-thermal energy storage. To meet these problems, PCMs (ZrP-PI@PEG) with excellent thermal energy storage, solar-to-thermal conversion, and flame retardancy were fabricated in this study. The polyimide (PI)/sodium lignosulfonate-zirconium phosphate (SL-ZrP) hybrid-aerogels (ZrP-PI) were prepared by freeze-drying and thermal imidization. ZrP-PI aerogels composited with polyethylene glycol (PEG) via vacuum impregnation to fabricate the composite PCMs (CPCMs, ZrP-PI@PEG). The in-situ biochar generated from SL-ZrP increases both solar-to-thermal conversion and flame retardant of CPCMs. The final result demonstrates that ZrP-PI@PEG exhibits a superior adsorption ratio (95.5%) and outstanding latent heat (157.67 J/g), as well as about 13% flame retardant index decrease in heat release rate (HRR) and total heat release rate (THR). Furthermore, ZrP-PI@PEG shows great thermal stability and reliability after conducting a leakage experiment and thermal cycling test. These superior resultants indicate that ZrP-PI@PEG has a good potential for widespread and long-term use in solar thermal energy storage. • A novel biomass/polyimide aerogel composite phase change material was successfully prepared by a simple method. • The as-prepared composite exhibited excellent thermal energy storage, solar-to-thermal conversion and flame retardancy. • The relative enthalpy efficiency of the composite reaches up to ∼95.5%.

High-strength and high-temperature-resistant multilayer interconnected polyimide paper derived from anisotropic aerogel via a hot-extrusion strategy for aerospace applications

The continuous improvement of papermaking technology has attracted widespread attention. However, the prevention of high-temperature decomposition and a subsequent decline in mechanical strength is still a significant challenge with current papermaking technology. Herein, a newly developed multilayer interconnected polyimide aerogel-based paper was successfully prepared via an anisotropic aerogel hot-extrusion strategy. Precursor solutions of highly rigid benzimidazole units containing intermolecular hydrogen bonds and linear rod-like benzimide units were first prepared. Anisotropic precursor polyimide (PAAS) aerogels with a thickness of 3 mm were then manufactured by unidirectional freeze-drying. Then, aerogel-based papers with a thickness of 40 μm and microstructure multilayer interconnected properties were obtained by a hot extrusion strategy and a thermal imidization process. This polyimide structural paper exhibited excellent thermal and mechanical properties. Through the design of micro and macro structures, the tensile strength of the aerogel-based paper was much higher than that of commercial paper at both room temperature and 400 ℃. This aerogel-based paper also exhibited high-temperature cycle stability, high flexibility, and good stretchable bending properties. The successful preparation of this aerogel-based paper demonstrates the feasibility of the hot extrusion strategy. This work provides a new papermaking technology method and broadens the application field of paper.

Mechanically Robust and Flexible GO/PI Hybrid Aerogels as Highly Efficient Oil Absorbents.

Herein, mechanically robust and flexible graphene oxide/polyimide (GO/PI) hybrid aerogels (GIAs) were fabricated by a facile method, in which the mixed suspensions of the water-soluble polyimide precursor and graphene oxide (GO) sheets were freeze-dried, which was followed by a routine thermal imidation process. The porous GIAs obtained not only exhibit excellent elasticity and extremely low density values (from 33.3 to 38.9 mg.cm-3), but they also possess a superior compressive strength (121.7 KPa). The GIAs could support a weight of up to 31,250 times of its own weight, and such a weight-carrying capacity is much higher than that of other typical carbon-based aerogels. Having such a porous structure, and high strength and toughness properties make GIAs ideal candidates for oil spill cleanup materials. The oil/organic solvents' absorption capacity ranges from 14.6 to 85, which is higher than that of most other aerogels (sponges). With their broad temperature tolerance and acidic stability, the unique multifunctional GIAs are expected to further extend their application range into extreme environments.

Mechanically Strong and Thermally Stable Chemical Cross-Linked Polyimide Aerogels for Thermal Insulator.

High-performance thermal insulating materials are highly desirable in several fields, especially for thermal insulation of buildings to reduce energy consumption. Owing to the remarkable thermal stability, high porosity, low density, and outstanding mechanical features, polyimide (PI) aerogels have attracted great attention. In this work, chemical cross-linked PI (CCPI) aerogels were fabricated via freeze-drying and thermal imidization, which possess outstanding mechanical properties, good thermal stability, and excellent thermal insulation characteristics. The chemically cross-linked structure can effectively inhibit shrinkage, while retaining the structural integrity, resulting in the lower density and lower shrinkage of the materials. In this paper, completely imidized and highly cross-linked polyimide aerogels were synthesized by using p-phenylenediamine (PDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), and the cross-linker 2,3,6,7,14,15-hexaaminotriptycene (HMT). The CCPI aerogels with excellent properties, such as covalently cross-linked chemical structure, low density (0.069 g/cm3), low volume shrinkage (10%), high decomposition temperature (Td5% = 587 °C), and low thermal conductivity (25 mW m-1K-1) are in high demand in the field of thermal insulation. This work furnishes a new method for the development of polymer-based thermal insulation materials for various prospective applications.