The expanding field of polyphosphazene high polymers

The importance of phosphorus in polymer chemistry is illustrated by the growth of the broad field of polyphosphazene science. Several hundred high polymers are now known with a phosphorus-nitrogen backbone and combinations or more than 250 different organic side groups. The properties of these polymers depend on both the character of the inorganic backbone and the structure of the organic side groups. This summary reviews the synthesis pathways to these materials, the often-unique structure-property relationships, and challenges for the future expansion of this field. The wide variety of accessible poly(organophosphazenes) is a consequence of the unusual macromolecular substitution approach to their synthesis.