Waste‐Free Closed‐Loop‐Recyclable and Thermally Superinsulating Polyimide Aerogels Utilizing Diels‐Alder Chemistry

Organic aerogels are an advanced class of lightweight materials with ultralow thermal conductivity and high porosity, widely used in applications such as thermal insulation, energy storage, and aerospace engineering. Among them, polyimide aerogels stand out for their excellent thermal stability, mechanical strength, and chemical resistance. However, their permanently cross-linked networks make them non-recyclable, posing a significant sustainability challenge. Here, a novel closed-loop recycling approach for polyimide aerogels based on dynamic Diels-Alder chemistry is presented, utilizing an aerogel-sol-aerogel (ASA) process. Matrimid, a commercial polyimide, is post-functionalized with furfurylamine to form a furan-modified poly(amide-imide) (PAI-FU), which reacts with bismaleimide via a Diels-Alder reaction to create a thermally reversible cross-linked aerogel network. The resulting poly(amide-imide) aerogels (PAIAs) exhibit low bulk density (≈ 0.15 g cm^-3), high porosity (> 87%), ultralow thermal conductivity (16.0 mWm^-1K^-1), excellent thermal stability (T_d5% ≈ 400 °C), and remarkable mechanical strength (≈ 3.4 MPa). More importantly, PAIAs can be depolymerized at elevated temperatures into soluble oligomers that can be reconstructed into fresh aerogels without catalysts or purification steps. The recycled PAIAs retain their nanostructural morphology and key aerogel-specific properties, demonstrating efficient closed-loop recycling. This approach paves the way for advanced and sustainable thermally superinsulating materials.