Synthesis of porous polyimide films with low dielectric constant and excellent mechanical properties by ambient pressure drying

Polyimide aerogels are high-performance polymer materials, but they have been restricted by costly drying and low mechanical strength in practical applications. Here, we report a family of porous polyimide (PI) aerogel films prepared through a partial pre-imidization process under ambient pressure drying and freeze-drying. The effect of pre-imidization degree (pre-ID) on the mechanical and dielectric properties of porous films was investigated in detail. The Fourier transform infrared spectra show that the partial pre-imidization process made the molecular chain with coexisted amide acid and imide rings. The porous structure of film was successfully controlled by adjusting the pre-ID, which was confirmed by pore size distributions. These aerogel films with nanoporous structures exhibit better mechanical properties (e.g., 10.61 MPa at 0.433 g cm−3 at room temperature) and lower dielectric constant (minimum of 1.414 at 106 Hz) over the entire bulk density range (0.398–0.5 g cm−3). Their morphology, pore characteristics, and properties were similar, whether by ambient pressure drying or freeze-drying. Moreover, this work will provide a new perspective on the fabrication of porous PI aerogel film via ambient pressure drying with efficient processability.Graphical abstract