Tuning the acoustic and thermal insulation properties of polyimide aerogels via molecular rigidity and solid content...

Polyimide aerogel (PIA) has garnered significant attention for high-performance thermal insulation and noise control applications due to their exceptional thermal stability and tunable porous structures. In this study, three PIAs with distinct molecular architectures were synthesized using ODA as the diamine monomer, polymerized with three different dianhydrides of varying rigidity: flexible ODPA, rigid BPDA, and more rigid PMDA. The resulting precursors were processed into aerogels via freeze-drying followed by thermal imidization. The systematic influence of solid content and molecular rigidity on the microstructural evolution and macroscopic properties of the aerogels was investigated. The results demonstrate that the rigidity of the dianhydride monomer significantly governs molecular chain packing and crosslinked network formation, thereby dictating the pore architecture. Concurrently, variations in solid content allow for further optimization of pore wall thickness and skeletal density, enabling precise control over the porous structure. In this work, we establish a quantitative synergistic regulation strategy of molecular rigidity and solid content, and reveal the underlying mechanism that dianhydride rigidity dominates the skeleton network architecture, while solid content further optimizes the pore parameters. Through this design, the thermal insulation, acoustic absorption/insulation and mechanical performances of the PIA can be tailored in a wide range, realizing the directional customization of sound absorption-dominated or sound insulation-dominated multifunctional materials. Meanwhile, the optimized PIA achieves a low thermal conductivity of 32.03 mW (m^-1 K^-1), a maximum average sound absorption coefficient of 0.79, and a maximum average sound transmission loss of 34.18 dB, which shows competitive comprehensive performance compared with reported aerogel materials. This study provides a quantitative design guideline for developing high-performance polyimide aerogels integrating thermal insulation, noise reduction and controllable mechanical properties for extreme environment applications.