Insoluble sulfur is a form of common sulfur, which is made by thermal polymerization of common sulfur rhombohedral sulfur, and the microstructure state of sulfur changes with the change of temperature. It can also be made by the reaction of hydrogen sulfide and sulfur dioxide. The structure of insoluble sulfur is similar to that of polymer, which is a linear polymer of sulfur atoms, so it is called polymerized sulfur, with the structural formula of Sn, and the number of sulfur atoms n>200.

After the solid sulfur is heated and melted, the liquid sulfur viscosity changes dramatically when the temperature is lower than 160 ℃, mainly because the sulfur is heated and excited SR ring open, the long chain polymer is insoluble sulfur (IS), at 190 ℃, the n value of up to 10 at this time the viscosity is particularly large; when the temperature continues to rise, the polymer cleavage into a smaller n value of the polymer; when the temperature rises to the vaporization temperature of 44.6 ℃, the polymeric sulfur is broken again Back to the S8 structure.

The common sulfur molecule is an eight-membered ring (S8) composed of eight sulfur atoms, which has two forms: crystalline and amorphous. At room temperature and free state, sulfur exists in crystalline form, but when sulfur is heated above the melting point (116-119℃), it becomes liquid sulfur, i.e. amorphous sulfur. Therefore, when rubber is vulcanized, sulfur is in amorphous state.