There are two broad types of poly-sulphide polymer;
- High molecular weight rubbers and
- Low molecular weight liquids produced from these by a process of depolymerization
The hardening reaction may be exotermic, and in order to obtain a satisfactory pot like the addition of a retarding agent such as stearic acid is often necessary; such as adhesives has been recommended for bonding new concrete to old. The bond strength is not high but it can be substantially improved by adding say 5% of an epoxy resin (a hardener is not necessary if the epoxied molecule contains alcoholic hydroxyl group), or small amounts of a phenolic resin, again containing hydroxyl groups such as the methylol groups present in a resol.
Such thiokol adhesives have outstanding resistance to vibration, low temperature, and aromatic fuel, and therefore they have created interest in connection with integral fuel tanks in aircraft.