Facile preparation of low shrinkage polybenzoxazine aerogels for high efficiency thermal insulation

High performance thermal insulation materials are urgently demanded for energy saving and thermal protection applications. Organic aerogels are considered as promising and highly efficient thermal insulation materials, but high shrinkage has been a major obstacle to limit their development and application. Herein, by a co-polymerization of formaldehyde (F) and benzoxazine prepolymers, polybenzoxazine with increased crosslink density and thus enhanced gel strength was formed, leading to low shrinkage polybenzoxazine (PBOF) aerogels with hierarchical micro/nanostructures. The hierarchical porous nanoskeleton of PBOF aerogels, composed of stacked thick-united spherical nanoparticles, was formed due to the different solubility of the reactants in N,N-dimethylformamide and F aqueous solution. Benefitting from the low shrinkage (13.22%, exceeding 60% reduction), the PBOF aerogels exhibit a low thermal conductivity of 0.0397 W m⁻¹ K⁻¹ at room temperature and outstanding thermal protection ability at high temperature. A 13 mm thick sample could resist a butane flame of 1300°C for 90 s, and the hand was not burn when touching the back. This strategy enables PBOF aerogels with a new perspective for their applications in civil and military fields.