An American chemist known as Joseph Cecil Patrick discovered Polysulfide
rubber in 1926 by, while he was attempting to obtain ethylene glycol for use
as an antifreeze. This rubber was commercialized under the trade name
Thiokol, which eventually became generic. This was one of the earliest
commercial synthetic polymers and was made by the reaction of sodium
polysulfide with an organic dichloride.
Properties of Polysulfide Rubber (PSR)
- This rubber is known for its excellent resistance to solvents.
- It has low temperature flexibility.
- It has flex-crack resistance.
- It also has oxygen and ozone resistance.
- It is resistant to light.
- It is impermeable to gases.
- Poor tensile strength and abrasion resistance.
Advantages of Polysulfide Rubber
These rubber is very soft,
stretchy and long lasting. It is good for making molds with severe undercuts
and/or very fine detail. There are some molds still in production which are
more than 40 years old. Unlike other mold rubbers, PSR is not characterized
by sulfur or water based modeling clays. Model preparation is very less.
Once cured, these molds are good for casting wax and gypsum plasters.
However, since heat resistance, compression set and mechanical strength are
not very great, polysulfide rubber is recommended for specific applications
which cannot be satisfied by any other elastomer. Temperature range required
is -54 degrees to +107 degrees celcius. Polysulfide seals are recommended
for service involving contact with solutions of ketones, ethers and
Disadvantages of Polysulfide Rubber
- The most common problem of these rubber is that this rubber with lead
curatives has an offensive odor.
- Newly built polysulfide molds stain plaster.
- Polysulfides have poor abrasion resistance and hence are not good for
- It is not suitable for production casting of resins.
- Polysulfides must be mixed accurately by weight with other elastomers
or they will not work.
- This rubber is of moderate cost. It is higher than latex and
urethanes but lower than silicones.
Other Types of Synthetic Rubber