Question

Polyphosphazenes have alternate single and double bond, they are not considered aromatic why?

Answer 1

Answer:

Phosphazenes are a class of chemical compounds in which a phosphorus atom is covalently linked to a nitrogen atom by a double bond and to three other atoms or radicals by single bonds. While other substitutions produce relatively persistent compounds, in organic synthesis the term largely refers to species with three amino substituents bound to phosphorus. The compounds are unusually stable examples of the phosphorane class of molecules and have a remarkable proton affinity. As such, they are one of the eminent examples of neutral, organic superbases.[1] Two examples are hexachlorocyclotriphosphazene and bis(triphenylphosphine)iminium chloride. Phosphazenes are also known as iminophosphoranes and phosphine imides.

The corresponding polymers are polyphosphazenes. Phosphinimide ligands can be used in catalysis.

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Answer 2

Explanation:

Polyphosphazenes (Structure 23.10)

Polyphosphazenes consist of an inorganic phosphorous-nitrogen backbone, in contrast to the commonly employed hydrocarbon-based polymers [176a]. Consequently, the phosphazene backbone undergoes hydrolysis to phosphate and ammonium salts, with the concomitant release of the side group. Of the numerous polyphosphazenes that have been synthesized, those that have some potential use for medical products are substituted with amines of low pKa, and those with activated alcohol moieties [177–179]. Singh and colleagues have modified the side groups to tune polyphophazine properties such as glass transition temperature, degradation rate, surface wettability, tensile strength and elastic modulus, enabling these polymers to be considered for a wider range of biomedical applications [180]. The most extensively studied polyphosphazenes are hydrophobic, having fluoroalkoxy side groups. In part, these materials are of interest because of their expected minimal tissue interaction, which is similar to Teflon.

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STRUCTURE 23.10. Polyphosphazene.

Shown here is a polymer containing an amino acid ester attached to the phosphazene backbone.

Aryloxyphosphazenes and closely related derivatives have also been extensively studied. One such polymer can be crosslinked with dissolved cations such as calcium to form a hydrogel matrix because of its polyelectrolytic nature [181]. Using methods similar to alginate encapsulation, microspheres of aryloxyphosphazene have been used to encapsulate hybridoma cells without affecting their viability or their capacity to produce antibodies. Interaction with poly(L-lysine) produced a semi-permeable membrane. Similar materials have been synthesized that show promise in blood contacting and with novel drug delivery applications.