Inorganic rubbers — polyphosphazenes

A further class of polymer does not contain carbon atoms in the main chain such polymers are called inorganic polymers. The most important of these polymers are the silicone rubbers containing silicium rather than carbon. These polymers are often built up through a sequence of — Si—O— units. Another group of inorganic pol mer. are the polyphosphazene.s which contain phosphorus in the main chain ((—P=N—]i. Whereas the —Si—O— chain i.< crv flexible the —P=N— chain is quite rigid. 

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