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
Thiokol developed many varieties of polysulphides with improved qualities.