POLYPHOSPHAZENE ELASTOMERS.

This is a review of preparation, reactions, properties, vulcanization, and applications of polyphosphazenes. The polymers could be substituted quantitatively with alkoxides or amines to give polymers of good thermal and hydrolytic stability. The polymers produced often have high crystalline melting points. The use of mixed alkoxy substituents gave elastomers with low glass-transition temperatures. Fluoroalkoxy substituents are particularly useful since elastomers with good resistance to swelling by petroleum fluids are obtained. Glass transition temperatures as low as minus 68 C have been observed so that the limitations of other oil-resistant elastomers at low temperatures are absent. Toughness and dynamic flex resistance are comparable with hydrocarbon polymers and much better than in siloxane polymers. Fluoroalkoxyphosphazene vulcanizates show adequate retention of properties at 150-200 C and withstand prolonged heating in aqueous alkali. They can be processed on conventional rubber machinery. Silica, carbon black, or clay fillers may be used. Vulcanization can be achieved with either peroxide or sulfur-accelerator systems.