Daming Wang

Nowadays, lightweight dual-functional polymer composites with great heat conductance and high electromagnetic interference (EMI) shielding performance are urgently needed in modern developing technology. Furthermore, efficient multipaths within network designed with multifunctional fillers in composites prefer to be a better way to balance the heat flow or electromagnetic signal transmission generated in dense integrated electronic devices. In this study, a strategy of graphite-graphene combined network-loaded polyimide (PI) composites was enabled by a scalable and tractable polymer-infiltrated technique. In this network, the microscale reduced graphene oxide (rGO) serves as an adhesive interfacial bridge and thermal network architect, effectively maintaining the macroscale worm-like structure of expanded graphite (EG). The framework was built using a template-free method from hydrogel to aerogel at low temperatures by immersing polyamic acid salt in the ensemble, followed by freeze-drying and final hot-pressing to obtain polyimide composites (rGO@EG/PI). In composites, the microregion network built by macro-micro structured hybrid fillers provides the polymer with multiscale connection channels, leading to an enhancement of the final properties of the samples. The prepared composite exhibits a great thermal conductivity (λ// = 9.4 W·m–1 K–1) with a 47 wt % hybrid filler loading, achieving 1781% higher than the polymer, accompanied by an exceptional level of EMI SE (61 dB). Moreover, the PI composites are found to possess excellent thermal properties, thermal management, and electrical conductivity. With great comprehensive performance, the rGO@EG/PI composites are of good promise for thermal management applications and EMI shielding performance in the field of high integrated technology.

Carbon fiber reinforced polyetheretherketone (CF/PEEK) composites suffer from severe fiber‐matrix modulus mismatch and weak interfacial adhesion, limiting their mechanical performance. Herein, eco‐friendly waterborne sizing agents consisting of self‐crosslinkable polyamide‐imide (CPI) and carboxylated carbon nanotubes (CCNTs) are developed to construct a triple‐coupled organic‐nano‐transcrystalline interphase. Thermally robust CPI adapts to high processing temperature of PEEK, while uniformly dispersed CCNTs enrich surface active groups, increase fiber roughness and supply heterogeneous nucleation sites for thick transcrystalline (TC) layers. CCNT content governs interfacial morphology, TC thickness and composite mechanical properties. The optimized CF‐CPI‐25CCNT achieves tensile strength of 233.4 MPa, flexural strength of 348.0 MPa, impact strength of 41.0 MPa and IFSS of 84.4 MPa, rising by 70.4%, 55.1%, 54.1%, and 110.4% versus bare CF. CF‐CPI‐50CCNT delivers maximum tensile and flexural moduli, whereas CF‐CPI‐75CCNT obtains superior tensile strength at 200°C. AFM characterizations confirm the hybrid sizing builds a continuous gradient‐modulus interphase to mitigate interfacial stress concentration. Moreover, CF‐CPI‐25CCNT exhibits balanced tow integrity and flexibility suitable for industrial processing. Synergistic reinforcement originates from improved wettability, mechanical interlocking, TC induction and rigid‐flexible gradient architecture. This green sizing provides a scalable multi‐scale interfacial design route for high‐temperature‐resistant CF/PEEK composites.

Lightweight structures are often used for applications requiring higher strength-to-weight ratios and lower densities, such as in aircraft, vehicles, and various engine components. Three-dimensional (3D) printing technology has been widely used for lightweight polymer structures because of the superior flexibility, personalized design, and ease of operation offered by it. However, synthesis of lightweight polymeric structures that possess both high specific strength and glass transfer temperature (T_g) remains an elusive goal, because 3D printed polymers with these properties are still very few in the market. For example, 3,3′,4,4‘-biphenyl tetracarboxylic dianhydride (BPDA) and p-phenylenediamine (PDA)-type (UPILEX-S type) polyimides show exceptional thermal stability (T_g up to ≈400 °C) and mechanical properties (tensile strength exceeding 500 MPa) and are the first choice if extremely high temperatures of 400 °C or even higher (depending on the duration) are required, which hampers their processing using existing 3D printing techniques. However, their processing using existing 3D printing techniques is hampered due to their thermal resistance. Herein, a 3D printing approach was demonstrated for generating complex lightweight BPDA-PDA polyimide geometries with unprecedented specific strength and thermal resistance. The simple aqueous polymerization reaction of BPDA with water-soluble PDA and triethylamine (TEA) afforded the poly(amic acid) ammonium salt (PAAS) hydrogels. These PAAS solutions showed clear shear thinning and thermo-reversibility, along with high G′ gel-state moduli, which ensured self-supporting features and shape fidelity in the gel state. Postprinting thermal treatment transformed the PAAS precursor to BPDA–PDA polyimide (UPILEX-S type). The resulting layer-by-layer deposition onto lightweight polyimide honeycombs in the form of triangular, square, and hexagonal structures showed tailorable mechanical strength, exceptional compressive strength-to-weight ratio (highest up to 0.127 MPa (kg m^–3)⁻¹), and remarkable thermoresistance (T_g approximately 380 °C). These high-performance 3D printed polyimide honeycombs and unique synthetic techniques with general structures are potentially useful in fields ranging from automotive to aerospace technologies.

Spirobichroman-based polymers with high gas permeability and selectivity are promising for their applications as membranes in gas separation. In this study, three spirobichroman-based polyimides (PIs; 6FDA-FH, 6FDA-DH, and 6FDA-MH) were synthesised by the polyreaction between diamines containing different substituents (benzene ring, pyridine ring, and methyl group) and 4,4′-(hexafluoroisopropylidene)-diphthalic anhydride (6FDA). The physical properties, gas transport behaviour, d-spacing, dihedral angle of molecules, and fractional free volume of the PIs were investigated through experiments and molecular simulations. The PIs exhibited excellent thermal stability and good solubility in common organic solvents. The gas permeability of the PIs was investigated; the results highlighted the critical role of the substituents in the enhancement of the gas separation performance of polymer membranes. Detailed analysis of the PIs showed that 6FDA-FH exhibits the highest gas permeability. This can be ascribed to the loose packing of the polymer chain owing to the increased dihedral angle between the two planes. However, the methyl substituent in 6FDA-MH disrupts the polymer chain packing rather than changing the dihedral angle between the two planes, thus enhancing the gas permeability of 6FDA-MH. Furthermore, 6FDA-DH exhibited the highest CO₂/CH₄ selectivity, which is attributed to the CO₂ affinity of the polymer containing the pyridine unit.