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Polyimide (PI)-based carbon foams (CFs) with excellent compressive strength, thermal insulation, and electromagnetic interference (EMI) shielding properties were fabricated through microsphere foaming and carbonization processes. The cell size of CFs ranged from 207.8 to 563.9 μm and could be regulated by adjusting the size of polyester ammonium salts (PEASs), and the chemical structure depended on the carbonization temperature. The compressive strength of C1100-PIF-1 was 0.74 MPa with a density of 119.9 kg·m–3. The thermal conductivities of C800-PIF-1 at room temperature, 500, and 1000 °C were 0.126, 0.202, and 0.252 W·m–1K–1, respectively. Furthermore, CFs exhibited excellent EMI shielding properties, with C1100-PIF-2 and C1100-PIF-3 reaching 56.4 and 42.1 dB at 8.2–12.4 GHz. The electrical conductivity fell in the range of 5.5–38.5 S·m–1. The CFs fabricated in this work, which combined exceptional mechanical strength, thermal insulation, and EMI shielding properties, had potential applications in aerospace, high-temperature insulation, and chemical catalysis.

Mechanically robust lightweight polyimide foams (PIFs) with anisotropic pore structures were successfully prepared using microwave-assisted foaming and thermal imidization. The foaming behavior of polyester ammonium salt powders was assessed by rheological and TG-FTIR analyses. The release of volatile gases (e.g., H2O, tetrahydrofuran, and methanol) between 85 and 150 °C led to the directional growth of foam pores during microwave treatment, which was critical for endowing PIFs with excellent thermal insulation and mechanical properties. The use of 4,4′-diaminobenzanilide (DABA) as the copolymerization reagent enhanced the compressive strength@50% strain (92.25 kPa) in the vertical direction (i.e., pore growth direction) and high elasticity in the horizontal direction (compression response rate reached up to 98.95%). The PIFs demonstrated exceptional thermal stability under both inert and air atmospheres. Meanwhile, PIFs exhibited anisotropic thermal insulation behavior, exhibiting a thermal conductivity as low as 0.0264 W/(m·K) in the horizontal direction (i.e., perpendicular to the pore growth direction), which was ideal for thermal insulation purpose under high temperatures. Therefore, PIFs with excellent mechanical performance and exceptional heat resistance and thermal insulation properties were facilely prepared, which show promising applications in high-end engineering sectors.

Flexible polyimide foams (PIFs) with an anisotropic porous structure were prepared by a facile strategy, possessing exceptional mechanical robustness and thermal insulation performances. A comparison of the foaming and rheological behavior, microstructure, and mechanical and thermal and radiation-resistant properties of copolymerized and blended PIFs was conducted. Besides, the formation mechanism of the anisotropic structure and its influence on the mechanical and thermal insulation properties were explored in depth. By reasonably regulating the molecular structure, melt viscosity, melt volatile content, and foaming temperature, a favorable microscopic morphology and structure can be achieved. PIFs with regular porous near-spherical appearance and aligned ellipsoidal strip structures exhibited anisotropic mechanical performance. Meanwhile, PIFs showed anisotropic thermal insulation behavior, which possessed a minimum thermal conductivity (λ) of 0.0314 W/m·K along the pore growth direction (i.e., vertical direction) and a λ as low as 0.0279 W/m·K in the horizontal direction. The anisotropic thermal conduction behavior endowed PIFs with intelligent thermal protection and infrared stealth performance. In addition, the PIFs presented an exceptional thermal stability and compressive strength retention rate after experiencing a radiation dose of 10027.5 kGy. Therefore, a facile strategy for rapid fabrication of PIFs that can be positioned for structural design, thermal insulation, and radiation-resistant applications in high-end engineering sectors was proposed.

Rigid polyimide foams (PIFs) with excellent compressive and thermal properties were fabricated by thermal foaming of polyester ammonium salts (PEAS) precursors which were terminated by 5-norbornene-2,3-dicarboxylic anhydride (NA). The melt viscosities of PEAS precursors were found essential to obtaining PIFs with high closed cell ratios and improved interactions between foam cells, which were indispensable to improving mechanical properties. The room temperature compressive strength and compressive modulus of PIF (density: 146.3 kg m–3) with four repeating units reached 1.55 and 23.3 MPa, which were 7 and 9 times higher than that of PIF-∞ (230.9 kg m–3), respectively. Furthermore, the room temperature compressive strength of PIFs with foam densities of 358.3 kg m–3reached 9.79 MPa. The PIFs demonstrated outstanding thermal properties with initial thermal degradation and glass transition temperatures higher than 450 and 290 °C, respectively. The thermal conductivities of PIFs fell in a range of 0.071–0.073 W m–1K–1, which showed promising applications in the fields of aerospace, aeronautics, and marine use as high temperature-resistant structural materials.

This work focuses on the influence of chain structure on properties such as the structural, thermal, morphological, and mechanical properties of polyimide foams (PIFs) which were prepared by polyester ammonium salt powder foaming process. Results showed that the melt viscosity of PEAS is affected by the structure of dianhydrides, which can greatly determine the foaming process, cell structure, and final properties of PIFs. PIF which was derived from 3,3′,4,4′-benzophenonetetracarboxylic dianhydride and 4,4′-diaminodiphenylmethane exhibited the highest compressive strength (0.374 MPa-RT, 0.194 MPa-200 °C) and compressive modulus (9.24 MPa-RT, 7.37 MPa-200 °C). All PIFs exhibited excellent thermal stability as the initial thermal decomposition temperature reached as high as 544 °C. In addition, the thermal conductivity of the as-prepared PIFs fell in a range of 38–42 mW m–1K–1, which show potential applications in areas of aerospace, aeronautics, marine use, and transportation among others.

Conductive polymer composites (CPCs) play an important role in various industrial applications including anti-static materials, electromagnetic interference shielding, sensors, and so forth. However, the contradiction between high conductivity and mechanical properties, especially tensile strength, is hard to balance many CPCs. In this paper, a self-reinforced polypropylene (PP)/graphene composite with segregated structures was fabricated by a novel coating-reducing-pressing method. By controlling the hot-pressing parameters, a special structure consisting of both an interconnected conductive graphene network and an unmolten fiber phase in a PP matrix can be obtained. PP/graphene composites with such a structure showed not only excellent electric properties but also outstanding mechanical properties. A super-low electrical percolation threshold of 0.0043 vol % was reached for the composites because of an effective formation of the conductive graphene network. The conductivity of composites with only 1.85 wt % graphene reached to 4.09 S/m. The composites also showed good electromagnetic shielding effectiveness under an X band with the highest EMI of 29.3 dB at 10 GHz. The existence of the PP fiber phase contributed to the improved mechanical strength and toughness of the self-reinforcing conductive composites compared to the blending samples, which made it even stimuli-responsive for bending deformation. These results were believed helpful in the design and fabrication of a new kind of conductive self-reinforced polymer composites.

The development of lightweight materials with ultrabroadband microwave absorption (MA) performance and excellent mechanical properties is significant for structural stealth electromagnetic wave-absorbing materials. Herein, the polyimide-derived carbon foams (CPIFs) were fabricated through a microsphere foaming method and a carbonization process for obtaining outstanding MA performance and mechanical property. The effects of carbonization temperature and prefoaming temperature on the pore size and MA property were investigated. The absorption bandwidth of CPIFs can reach an ultrabroadband absorption of 14 GHz, covering the whole X and Ku bands and most of the C band. The low-density CPIFs exhibited impressive compressive strength (0.47–0.64 MPa) and thermal insulation property with the thermal conductivity in the range of 0.061–0.104 W/m·K. The CPIFs’ lightweightedness, excellent MA, thermal insulation, and mechanical properties make them suitable to be used as a structural material with great application prospects in the fields of civil and military defense.

Herein, lightweight rigid polyimide foams (PIFs) with excellent mechanical and thermal properties were fabricated by constructing dual crosslinking structures combined with the thermal foaming of polyester ammonium salt (PEAS) precursor powders. The dual crosslinking network relied on the self-crosslinking of pararosaniline base (PA) and active crosslinking derived from the breakage of C═C bonds in 5-norbornene-2, 3-dicarboxylic anhydride (NA) under heating. The results showed that melt viscosity and micro-foaming behavior of PEASs and the cell morphology of PIFs could be regulated by varying the molar ratio of PA/NA and the number of repeating units amid crosslinking points. The compressive strength of PIFP1BMN3-5 (density: 165.5 kg·m–3) with dual crosslinking structures at 10% strain reached 1.36 MPa at room temperature and 0.75 MPa at 200 °C. The PIFs exhibited outstanding thermal properties with the initial thermal degradation temperature falling in a temperature range of 458.2–503.0 °C and the glass-transition temperatures exceeding 310 °C. In addition, PIFs exhibited excellent thermal insulation properties since the thermal conductivity of PIFs was between 0.048 and 0.065 W·m–1K–1, and the temperature increase of the top surface of the cubic sample block (height: 15 mm) was approximately 20 °C when they were placed on a preheated hot stage at 200 °C for 30 min. Thus, mechanically strong rigid PIFs with dual crosslinking structures were successfully prepared, which show promising applications as lightweight, high-temperature-resistant structural materials in high-end engineering fields.