Polyimide Aerogels Cross-Linked Using Amino-phenyl Polyhedral Oligomeric Silsesquioxanes

Cross-linking agents play a pivotal role in defining the chemical properties of the polyimide (PI) backbone. Even subtle modifications to the backbone chemistry can lead to profound changes in the structure and performance of PI materials. Therefore, selecting cross-linking agents with appropriate structures and properties is critical for tailoring PI materials to meet specific performance requirements. Amino-phenyl polyhedral oligomeric silsesquioxane (POSS) has shown great potential as an effective cross-linking agent for enhancing the performance of PI aerogels. However, systematic investigations into the effects of amino-phenyl POSS cross-linking agents with varying structures and amino group densities on the performance of PI aerogels remain limited. In this study, we synthesized PI aerogels using five different amino-phenyl POSS cross-linking agents. Due to their rigid molecular structures and hybrid organic-inorganic characteristics, the amino-phenyl POSS cross-linked PI aerogels exhibited superior mechanical and dielectric properties compared to PI-TAB aerogels, including a higher compressive modulus (25.17 MPa), lower dielectric constant (1.144 at 10 MHz), and lower dielectric loss (0.0085 at 10 MHz), thereby achieving excellent overall performance. Furthermore, we examined the relationship between the structures and amino group densities of POSS and the resulting properties of PI aerogels. We observed that the size of the POSS cage/ring had minimal influence on the aerogel properties when each phenyl group was connected to a single amino group, as the high cross-linking density mitigated the effect of the POSS cage or ring size. By contrast, larger POSS cages/rings improved the aerogel performance when the amino density was held constant, while lower amino density enhanced performance when the size of the POSS cages/rings was fixed. This study provides valuable insights into the structural-functional design of PI aerogels.