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Polysulphide Rubber Binder

Polysulphide was the first binder elastomer fuel. For rocket applications a low-molecular-weight polymer was made from dichlorodiethyl formal; sodium polysulfide was used as the liquid binder. When the mixture was heated with an appropriate curing agent such as zinc oxide, the links between adjacent polymer chains were joined together to form the rubber network. The resulting binder had a glass-transition temperature near -60°F., making it usable to about -40°F. This was a distinct advantage over the first composites.

An undesirable quality of the polysulphides was the presence of sulphur atoms in the system. They produced high-molecular-weight exhaust products (sulphur dioxide with a molecular weight of 64) thereby lowering specific impulse. Since a large amount of oxidiser had to be mixed with the binder to obtain the high energy desired, the binder lost much of its rubber-like quality.

There were many organic and inorganic materials that acted as oxidisers and could be used to cure liquid polysulphide polymers. Each had its advantages and disadvantages.
Thiokol developed many varieties of polysulphides with improved qualities.