Polysulfide
Polysulfides are a group of chemical compounds containing chains of sulfur atoms.
- 2.1 Production and use
Inorganic polysulfides
Inorganic polysulfides ( polysulfanes ) are salts of Polyschwefelwasserstoffe. They contain, as a doubly negatively charged anion polysulfide.
Production
Alkalimetallpolysulfide be obtained by reaction of alkali metal monosulfide with excess sulfur. The result is, for example, the melting of sodium sulfide with sulfur -yellow to red-brown sodium polysulfide:
The reaction of sodium hydrosulfide with sulfur leads to sodium polysulfides, which are characterized in this case by a high purity.
Industrially, polysulfides are obtained by reacting sodium hydroxide with sulfur and processed the same in aqueous solution, since the handling of pure, solid alkali metal polysulfide is difficult.
Use
Polysulfides are used in analytical chemistry for the detection of cyanide ions.
Organic polysulfides
Organic polysulphides are organic compounds containing sulfur as a functional group in the form of sulfur -sulfur bond.
PREPARATION AND USE
Organic polysulphides are of great industrial importance for the preparation of sealants, and in particular for use in the manufacture of insulating glass. Aliphatic organic polysulfides are obtained in a multistage process. Reaction of 2-chloroethanol with formaldehyde leads to a first stage to the bis (2- chloroethyl) formal:
The formal is reacted with sodium polysulfide with the addition of a trifunctional crosslinker to the aliphatic polysulfide the following simplified structure:
About the terminal mercapto groups, this viscous prepolymer slightly oxidative, such as with manganese dioxide, but also with lead dioxide and dichromate, are networked and results as a binder in appropriate adhesive and sealant formulations elastomeric products. This heterogeneous oxidation reaction is not stoichiometric and is therefore relatively insensitive to incorrect dosing of the curing agent, which is formulated as the base component, usually to paste-like consistency.
The properties of the cured Polysulfidcompounds are good weather resistance, high resistance to fuels and other chemicals, low gas permeability, in particular noble gases, and a certain relaxation under stress at bonding or stationary seals. This combination of properties is the reason for the wide use of Polysulfidkleb and sealants, such as in the manufacture of insulating glass units (main use ), sealants for the aerospace, gas station waterproofing, chemical-resistant coatings and sealants for the construction and civil engineering.