TABLE OF CONTENTS Polyphosphazenes, [N=PR 2] n, are the largest family of inorganic polymers. Over 800 different types of polyphosphazenes are known [ [16], [21] [22] [23]]. The common feature of all of these polymers is the backbone which is made up of alternate nitrogen and phosphorus atoms. While the nitrogen is trivalent and dicoordinate, phosphorus is pentavalent and tetracoordinate. Thus, nitrogen does not contain any substituents. Phosphorus, on the other hand, is attached to two substituents. Thus, the basic structural feature of the repeat unit of polyphosphazenes is exactly similar to what is found in cyclophosphazenes.
Although, the repeat unit in all the polyphosphazenes comprises the [N=PR 2] repeating unit, the properties of the polymers can be radically changed by varying the R groups on phosphorus. In this section, we will examine the preparative procedures, the structural features and the applications of polyphosphazenes.
The American Chemist Stokes discovered, towards the end of the nineteenth century, that heating the six-membered ring, N 3P 3Cl 6, to high temperatures leads to the formation of a polymeric material with an empirical formula [NPCl 2] n. This material was called inorganic rubber because of its properties. Thus, this was rubbery but had very poor solubility in common organic solvents. Instead of dissolving in solvents, the polymer would swell in them. The most serious concern about the inorganic rubber was its sensitivity towards hydrolysis upon exposure to moisture. The polymer was...
