Synthesis of Chlorinated Polyphosphazenes with Improved Interfacial Strength for Novel Flexible Heat Shielding Materials

The interfacial interaction between fibers and polyphosphazene is a crucial factor for efficient ablative resistance. Herein, a series of polyphosphazenes with aryloxy and substituted-aryloxy side groups were designed and synthesized, guided by molecular dynamics simulation. Effects of the type and position of the substitutions on properties of polyphosphazenes such as glass transition temperature (T_g) were investigated. The introduction of polar chlorine-substituted side groups increases the interfacial interaction of polyphosphazenes with fibers, as evidenced by the binding energy and the number of hydrogen bonds, and the composites exhibited enhanced mechanical and ablative properties. The linear ablation, mass ablation, and charring rate of the composite reach 0.0148, 0.041, and 0.088 mm/s, respectively, which is superior to the composites using conventional rubbers as the matrix. These results make the chlorinated polyphosphazene a competitive candidate for thermal protection under the high-temperature service environment of vehicles and rockets.