The base poly sulphide polymers are usually prepared by a suspension
process. Typically, the aqueous sodium polysulphide (about 20% solids) is
heated to 80℃ in a stirred reactor and an alkyl aryl sulphonate (surfactant) is
added together with aqueous sodium hydroxide and magnesium chloride.
(The latter reagents form magnesium hydroxide which serves as a nucleating
agent.) This system leads to a dispersion which does not coagulate during
polymerization but which settles readily when stirring is stopped, so that the
polymer particles can be washed easily. The bis(2-chloroethyl)formal is added
slowly over 2 hours with stirring; the reaction is exothermic and cooling is
applied to keep the temperature at 90℃. The mixture is then heated for 1-2
hours to complete reaction. In order to assist in greater utilization of the alkyl
halide, a stoichiometric deficiency (about 20%) is used in the process.
Sometimes a further 20% excess of sodium polysulphide is added toward the
end of the process to ensure complete reaction of the halide; this operation is
known as 'toughening' since it gives a polymer of increased molecular weight.
Finally, the resulting polymer dispersion is washed with hot water.
