POLYSULPHIDEPOLYMERS

POLYSULPHIDEPOLYMERS Chemische Eigenschaften,Einsatz,Produktion Methoden

• synthetische

  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.