Polyphosphazenes thermal behavior

Figure 2 Properties in polyphosphazenes are determined hy (1) the backbone bonds that control the inherent flexibility of the polymer via their influence on bond torsional freedom, and also provide photo-and thermo-oxidative stahihty (2) the side groups control polymer solubility, reactivity, thermal stability, crystallinity, cross-linking, and (indirectly) polymer flexibility (3) free volume between the side groups affects polymer motion, solvent penetration, membrane behavior, and density (4) functional groups (usually introduced hy secondary reactions) affect soluhihty, biological behavior, proton conduction, cross-hnking, and many other properties...

Crystallinity. Polyphosphazenes with a single substituent that is either small or rigid are semicrystalline. Their melting behavior consists of two first-order transitions, T(l) and Tm, separated by a 150-200°C gap. Optical microscopy showed that the crystalline structure was not lost at T(l), but rather existed as a mesophase until Tm was reached (2). Most fluoroalkoxy and aryloxy derivatives exhibited very high thermal stability with decomposition temperatures of 300-400°C. 

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