SEPTEMBER, 1943
The Preparation of Thiokol A Lecture Demonstration ELTON M . BAKER Fresno State College, Fresrur, Ollifornia
rubber is an example of one of the SYNTHETIC polymers of importance in the present industrial chemical development. The preparation of one of the types of synthetic rubber as a class demonstration or laboratory experiment not only lends interest but also illustrates in a measure some of the chemistry of polymers. Thiokol and similar sulfur polymers may be prepared by the polymerization of an alkali or alkaline earth metal polysul6de and a halogen substituted olefinic hydrocarbon. Ellis' states that the amount of sulfur in the polysulfide determines the elastic quality of the rubber. If the sulfur content of the polysul6de is that represented by the formula Na&, or greater, the polymer will be elastic; lower amounts of sulfur give a hard, brittle resin. Sodium polysulfide may be made from sulfur and sodium hydroxide or sodium snl6de. The reaction with ethylene dichloride may be expressed as follows, H H S NarS4
+ GH4C1, + 2Naf + 2C1- + *
In a beaker containing 100 ml. of water dissolve 4 g. 'ELLIS, ,,The Chemistry of Synthetic Resins,w Reinhold Publishing Company, New York. 1935, p. 1172.
of sodium hydroxide and heat to boiling. Add 7 to 10 g. of sulfur flowers, stimng until all of the sulfur has dissolved. This liquid containing the polysulfide will turn from light yellow to a dark brown color as the sulfur content of the polysulfide increases. If the sulfur does not dissolve completely after several minutes, allow the solution to cool and decant the dark brown liquid from the undissolved sulfur. To this liquid add 20 ml. of ethylene dichloride. The mixture should be warmed to a point below the boiling point of the ethylene dichloride, i. e., 83OC. For best results, the polysulfide solution should have a specific gravity nearly the same as that of the ethylene dichloride. Stir the mixture thoroughly so that the latter will be suspended in the polysulfide mixture. The synthetic rubber will slowly form a t the junction between the two immiscible liquids and will collect as a spongy lump a t the bottom of the beaker if stimng is continuous during the process. The synthetic rubber should be removed from the solution and washed thoroughly. Its color will vary from white to yellow, and it will have a degree of elasticity depending on the sulfur content of the polysulfide. This polymer will resist organic solvent action, a characteristic which distinguishes it from natural rubber, practice it is mixed with zinc oxide, and some natural rubber to make i t harder and to give it better wearing qualities.
