Efficient One-step Synthesis of Mechanically Strong, Flame Retardant Polyurea Aerogels

We demonstrate a facile one-step synthesis of strong lightweight polyurea (PUA) aerogels from di and triisocyanates reacting with amines formed in situ from the reaction of the same isocyanates with controlled amounts of water and triethylamine as catalyst. Densities were varied from 0.015 g cm ^-3 to 0.55 g cm ^-3 by controlling the amount of the isocyanate. The amount of water and triethylamine were also varied systematically relative to the isocyanate and found to have no effect on the morphology of the aerogels, only on the gelation time. All samples are chemically identical and ~35% crystalline. Microscopically, low-density PUA aerogels are fibrous, while high-density samples are particulate. Once ignited with a flame, lower density samples burn completely, while higher density samples get self-extinguished. At room temperature, the ultimate strength of the higher density PUA aerogels (0.55 g cm ^-3 ) was determined to be 640 MPa, comparable to that of polymer crosslinked aerogels investigated by our group previously. We envision applications in mechanically strong thermal insulation.