Ambient-Dried, Ultra-high Strength, Low Thermal Conductivity, High Char Residual Rate F-type Polybenzoxazine Aerogel

[Image: see text] The effect of the curing temperature (T(c)) on the properties of PBO aerogel was investigated in this paper. The compressive strength of PBO aerogel prepared was much higher than that of PBO aerogel of the same density in other kinds of literature. With the robust F-type polybenzoxazine (PBO) aerogels with ultra-high Young’s modulus (733.7 MPa at 0.48 g/cm(3) and 1070 MPa at 0.57 g/cm(3)), excellent properties were obtained through a facile and scalable room-temperature HCl-catalyzed sol–gel method, followed by the ambient pressure drying technique. It is found that T(c) plays a vital role in the polymerization process and the evolution of the microstructure of the 3D porous PBO network, where the necks between the nanoparticles become thick and strong when T(c) is up to 150 °C, resulting in a pearl necklace-to-worm transformation in the micro-structure and significant growth in mechanical properties, but if T(c) is higher than 180 °C, the pore volume and specific surface area will decrease sharply. Moreover, all synthetic PBO aerogels here possessed inherent flame retardancy and a high residual char rate in the volume density (0.32–0.57 g/cm(3)). These properties make the F-type PBO aerogels a candidate material in aerospace applications or other fields.