Cyclotriphosphazene based materials: Structure, functionalization and applications

In recent decades, cyclotriphosphazene (CTP) and its derivatives have garnered significant attention due to their exceptional physical and chemical properties, such as remarkable thermal/radiation stability, chain flexibility, flame retardancy, biocompatibility, and biodegradability. Substantial progress has been made in CTP chemistry, as well as the exploration of new topological structures, functionalities, and applications of CTP-based materials. Thus, it holds great significance to summarize these key advancements to drive the development and application of CTP derivatives. In this comprehensive review, we present a historical perspective on the structures and properties of CTP and its derivatives. We provide an overview of the main chemical reactions and reaction mechanisms involved in CTP chemistry. Furthermore, we assess the current status of various CTP derivatives, including multi-substituted compounds, copolymers, linear polymers, dendrimers/hyperbranched polyphosphazenes, and crosslinked polyphosphazene, elucidating their synthesis methodologies. Moreover, we emphasize the recent notable achievements in a range of applications encompassing fluorescence, nonlinear optics, biomedical materials, catalyst supports, adsorption and separation, flame retardancy, and battery materials. Finally, we address the future opportunities and challenges associated with CTP derivatives.