Synthesis of tri(aminophenyl)silsesquioxane cross-linker for polyimide aerogels with enhanced hydrophobic and low dielectric properties

Polyimide (PI) aerogels are extensively utilized in communication, electronics, and aerospace industries due to their commendable properties, such as being porous and lightweight. The introduction of a cross-linking agent is a critical step in the preparation of PI aerogels. Octa (aminophenyl)silsesquioxane (OAPS) is considerably used as a cross - linking agent. However, the presence of eight amino active sites leads to a high cross-linking density and poor hydrophobicity. To address this issue, this paper presents a method for synthesizing a tri(aminophenyl)silsesquioxane (OAPS-3) through initial hydrolysis condensation, followed by nitration, and then reduction reactions. Polyimide aerogel materials with superior hydrophobic properties (a water contact angle of 122°), dielectric properties (a dielectric constant as low as 2.49), mechanical properties (compressive strength up to 2.72 MPa, and specific modulus up to 88.00 J g^-1), and low shrinkage (a shrinkage ratio of 13.6 %) were prepared using the sol-gel and freeze-drying methods with OAPS-3 as the cross-linker. These exceptional properties are attributed to the organic-inorganic hybrid structure at the molecular level. Comparatively, the resulting trifunctional crosslinker achieved results similar to or better than those of the octa-functional crosslinker in the system. The findings demonstrate that OAPS-3 is a viable alternative to the octa (aminophenyl)silsesquioxane (OAPS) crosslinker. This research introduces a novel and simplified strategy for the application of PI aerogels in the field of communication, enabling the acquisition of excellent hydrophobic and dielectric properties without the need for additional hydrophobic treatment of the aerogel or the incorporation of high-cost fluorine-containing groups.