Cyclomatrix polyphosphazenes frameworks (Cyclo-POPs) and the related nanomaterials: Synthesis, assembly and functionalisation

Abstract

Poly (organophosphazene) (POP) is one of the most important inorganic polymers along with polysiloxane. The versatile phosphazene chemistry enables a wealth of functional inorganic-organic hybrid polymers with PN structures ranging from covalently crosslinked cyclomatrix phosphazene to linear POP copolymers. Cyclomatrix polyphosphazene framework materials (Cyclo-POPs) represent a novel type of molecular composites, and can be facilely formed via a rapid one-step polycondenzation and simultaneous self-assembly process under ambient conditions, and the stereoscopic morphologies are tuneable from zero-dimension (0D) to 3D depending on the compositions and reaction conditions. The novel cyclo-POPs have shown distinctive advantages over boron-containing covalent organic framework (COFs) materials in terms of the facile and rapid synthesis and integrated functionalities. Moreover, the highly crosslinked PN− backbone structures are readily to be transformed into porous carbon nanomaterials with intrinsically doped heteroatoms (P, N, S, O, B, depending on the framework skeletons), which are desirable for catalysis, sensors and energy storage applications. In this article, we critically overview the rational design, synthesis and functionalisation of the cyclo-POPs materials, and their emerging applications in optoelectronics, catalysis, adsorption and energy storage devices, along with the technical challenges and development perspectives.