Excellent mechanical strength and satisfactory thermal stability of polybenzoxazine aerogels through monomer structure optimization

Abstract

As a new member of the high-performance organic polymer aerogel, polybenzoxazine (PBz) aerogel has the advantages of high strength, good heat resistance and flame retardancy, which is an ideal thermal insulation and ablation-resistant material. However, the influence of the structure of PBz's monomers on their properties has not been thoroughly explored, resulting in a gap between their properties and theoretical values, which largely limits their applications. Herein, in order to optimize the properties of PBz aerogels, the benzoxazine aerogels with various structures were prepared by adjusting the ratio of the oxazine rings using a simple atmospheric pressure drying method. The results showed that the chemical structure played a crucial role in the properties of aerogels, which not only determined the extent of the sol-gel reaction, but also regulated the rigidity and hydrogen bonding interactions within the polymer. Through optimization and hydrogen bonding regulation, the compressive strength of aerogels can be reached up to 76.25 MPa which was superior to current reported works. In addition, the stabilized chemical structure enabled the aerogels to have good thermal stability (peak thermal decomposition temperature of more than 500 °C) as well as low thermal conductivities of the range of 0.0560–0.0627 W/m·K. The combination of good mechanical properties, high thermal stability and low thermal conductivities offers a potential materials system for robust thermal superinsulation under extreme conditions.