Low shrinkage polyimide aerogels with excellent thermal insulation: Boosted by "paddle-shaped" benzhydrylidenefluorene-based diamines

Polyimide (PI) aerogels are widely employed as thermal insulating materials in the aerospace and transportation industry in extreme environments. However, there is a lack of research that focused on the development of novel monomers for the preparation of high-performance PI aerogels. In this study, we proposed a "rigid-soft" strategy to design structurally unconventional diamine compounds. These compounds effectively enhance the rigidity of the PI chain, leading to improved thermostability, while still maintaining flexibility and moderate mechanical properties. Accordingly, two brand-new monomers (BDFD and BDFA) incorporating a twisted "paddle-shaped" benzhydrylidenefluorene (BDF)-based diamine were successfully developed. These monomers consisted of a flexible diphenylmethylene moiety coupled to a rigid fluorene building block. Leveraging these distinctive characteristics, two series of PI aerogels were prepared and exhibited exceptional performance, including a low shrinkage rate, high surface area, and uniform pore size. Notably, the PI-D1 aerogel, composed entirely of BDFD, demonstrated the highest surface area of 674.8 m(2) s(-1). With a molar ratio of 1/3 for BDFA/ODA, PI-A4 demonstrated the ability to achieve high-performance thermal insulation (54.3 mW m(-1) K-1 at 200 degrees C) with excellent thermostability (T-d 5% > 580 degrees C, T-g > 299 degrees C) and satisfactory dimensional stability (shrinkage at 7.7 %), thanks to its smaller pore size (similar to 24 nm) and well-balanced rigid and flexible structure property. This research provides an effective method for creating high-performance PI aerogels with an exceptionally low shrinkage rate, which makes them appropriate for thermal management materials that require superior thermal insulation properties.