Piperazine as a Water-Solubilizing Agent for Cross-Linking and Mechanical Enhancements in Freeze-Dried PI Aerogels

This study explores the innovative application of piperazine as a water-soluble cross-linking and solubilizing agent in the synthesis of polyimide (PI) aerogels through freeze-drying. Piperazine was used to dissolve poly(amic acid) (PAA) into salt and cross-link it into a 3D network structure. A suite of analytical techniques characterized the interaction between piperazine and PAA, including Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and nuclear magnetic resonance (NMR). These methods elucidated the mechanisms of salt formation and chemical cross-linking. The performance and microstructure of PI aerogels with different structures were also evaluated by compression strength, cyclic compression, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). The results demonstrate that piperazine significantly enhances PI aerogels' compressive strength, resilience, and thermal insulation properties. This study provides a cost-effective and environmentally friendly approach to producing high-performance PI aerogels using freeze-drying and provides fresh insight into PI aerogel preparation.