polysulfide, any member of a class of chemical compounds containing one or more groups of atoms of the element sulfur linked together by covalent bonds. In inorganic compounds belonging to this class, these groups are present as ions having the general formula S_n^2-, in which n is a number from 3 to 10 or more; these compounds usually are prepared by dissolving sulfur in solutions containing the sulfide ion, S^2-. Sodium polysulfides are used in the tanning industry to remove hair from hides; lime–sulfur and sulfurated potash, prepared by heating sulfur with lime and potash, respectively, are mixtures containing polysulfides, used as insecticides and pesticides.

Sodium polysulfide, in which n has a value around 4, has been used as a starting material in the preparation of rubbery or resinous synthetic organic substances called Thiokols. The molecules of these products consist of long chains in which polysulfide groups alternate with small organic groups capable of forming two covalent bonds. They can be converted by heating with zinc oxide to tough, resilient materials used to make hoses and linings for storage tanks and in other applications requiring resistance to chemical and physical attack; they also have been used as solid fuels for rockets. Thiokols also can be prepared as aqueous dispersions useful for forming protective coatings on surfaces such as wood, metal, or concrete or for preparing caulking compositions.