Reprocessable Flame Retardant Silicone Polyurethane Based on Dynamic Phenylborate Ester Covalent and N–P–Si Synergistic Effect

The silicone thermoplastic elastomer is highly attractive in various areas for good mechanical strength and aging resistance. However, its intrinsically high flammability limits its practical applications. Meanwhile, as a typical polymer material, its irreversible cross-linking structure makes it difficult to recycle and reprocess; a great deal of discarded silicone materials can pose a waste of resources and environmental problems. Herein, it is of great significance to prepare an intrinsic flame retardant (FR) and reprocessable silicone polyurethane (STPU). In this study, we introduce phosphorus-containing compounds (MDP) and a dynamic phenylborate ester (HDPM) bond into traditional silicone's molecular chain structure by in situ polymerization method, which endows the material with excellent flame retardance and reprocessing properties, respectively. The resulting STPU shows a limited oxygen index (LOI) value of 26.1% and reaches at VTM-0 rating. Furthermore, by regulating the decomposition and reconstruction of the phenylborate ester structure, STPU remain the initial tensile strength and keep 87.58% of tensile strain after twice reprocessing. This high-performance sustainable STPU materials hold great promise for fire safety behavior and reutilization in practical application.