Preparation of Lightweight Polyphosphazene Microcellular Foams and Their Thermal Insulation, Flame Retardancy, and Compressive Properties

To overcome the limitations on the application scope expansion caused by the flammability of polymer microcellular foams, herein, polyphosphazene microcellular foams are prepared through a simple process involving blending with thermally expandable microspheres (EM) and thermal foaming. By precisely controlling the foaming temperature and EM content, independent control of cell diameter and cell density is achieved for polyphosphazene microcellular foams. The thermal insulation properties of polyphosphazene microcellular foams are enhanced with increases in both cell diameter and cell density. Meanwhile, the flame‐retardant properties improve with rising cell diameter but deteriorate with increasing cell density. After foaming at 140°C, the polyphosphazene microcellular foam containing 10 wt% EM achieves a thermal conductivity of 0.067 W·m −1 ·K −1 , a limiting oxygen index (LOI) of 24.7% at a foam density of only 0.29 g·cm −3 , along with well resilience, specifically a 5.13% stress reduction and an 78.05% strain recovery after 50 cycles of compression to 50% strain, which realizes the integration of lightweighting, resilience, thermal insulation, and flame‐retardant properties.