Polyphosphazenes-based flame retardants: A review

The general flammability of polymer materials is a crucial problem to be solved in industrial applications. Polyphosphazenes, a kind organic-inorganic polymer and whose main chain is alternating by single and double bonds of phosphorus, nitrogen are endowed with excellent natural flame retardant synergies and thermal stability. Therefore, utilizing the designability of molecular structure and excellent flame retardant performance of polyphosphazene, a series of polyphosphazene flame retardants based on linear and cyclocrosslinked structures have been synthesized to improve the comprehensive properties especially the flame retardant properties, thermal stability and mechanical properties of materials, which is reviewed here. In particular, the molecular structure design and morphological changes of polyphosphazenes, flame retardant mechanism and the performance of flame retardant materials have been systematically discussed. As an important member of environmentally friendly halogen-free flame retardants, the challenges and opportunities encountered by polyphosphazene flame retardant materials have also been proposed in this review. In view of the excellent physical and chemical properties of polyphosphazenes, it's believed that an increasingly important role would be played by polyphosphazenes not only in flame retardant application but also in other application fields such as biomedicine and environmental adsorption.