Thermally insulating polybenzoxazine aerogels based on 4,4′-diamino-diphenylmethane benzoxazine

Polybenzoxazine (PBO) aerogels were prepared from 4,4′-diamino-diphenylmethane (MDA) benzoxazine monomer by HCl-catalyzed ring-opening polymerization at room temperature after CO₂ supercritical drying. This study systematically analyzes the microstructures, thermal insulation properties, compressive properties, and thermal stabilities of the PBO aerogels. The aerogel structure was a cross-linked three-dimensional network with a pore size of 10–140 nm. The conductivity of the aerogels was 0.035–0.057 W/m K under ambient conditions, reducing to 0.009 W/m K at 3 Pa. The compressive strength reached 14.42 MPa under 10% strains, much greater than in SiO₂ aerogels of similar density (0.40 g/cm³) reinforced by high-silica glass fiber, which is only 1.30 MPa. Hydrogen bonding interaction was found to be critical for constructing the three-dimensional network structure of the aerogels. This work provides a valuable reference for exploring new structures and expanding the thermal insulation applications of PBO aerogels.