Phosphazenes

Phosphazenes are compounds containing the [P═N] motif. Three broad classes of compounds fall in this category: (a) acyclic phosphazenes, also known as iminophosphoranes, (b) cyclophosphazenes and (c) polyphosphazenes. There has been a growing tendency in the literature to bunch all polymeric compounds containing the phosphazene motif in the category of polyphosphazenes. While we would be dealing all polymeric compounds in the subsection on polyphosphazenes, the distinction between the various types needs to be appreciated. Polyphosphazenes are those that contain a [P═N] backbone with substituents on phosphorus. Other forms of polymers could be regarded as hybrid polymers which often contain an organic backbone with phosphazene pendant groups or cross-linked polymers containing interconnected cyclophosphazene units. This chapter summarizes the literature on phosphazenes that was published in the calendar year 2020.