Synthetic Rubber A Classroom Demonstration ALBERT C. HOLLER United States Metal Products Company, Erie, Pennsylrnnio
OLYMERIZATION is always quite vague to the Pbegmnmg . . chemistry student. It was found that a
reacted sulfur, catching tlie filtrate in a 600-ml. beaker. Wash out the beaker and funnel with water and dilute class demonstration in the production of a synthetic the polysulfide solution to about 400 ml. The final rubber helped considerably to elucidate the mechanism solution should be dark red in color. Polymerization and Preparation of Thiokol Latex: of polymerization. The Thiokol type of synthetic rubber was chosen because of its ease of preparation Heat the polysulfide solution to 75'C. and add 20 ml. and also because it could be prepared from materials of hot 5 per cent soap solution to act as an emulsifying that could he easily obtained. In the following demon- agent. Add slowly; with vigorous stirring, 20 ml. of stration the processes are carried out in the same man- ethylene dichloride. Keep the reaction mixture bener as in the industrial production, namely, first, the low 72'C. during the polymerization by occasionally polymerization and formation of the latex, and second, cooling in a pan of cold water. After all of the ethylene the coagulation of the latex to give the rubber. In dichloride has been added keep stirring the reaction this respect the following demonstration differs from the mixture vigorously until the color changes from dark red to white (about 5 to 7 minutes). Then add 10 ml. one described by Baker.' Thiokol is made from sodium polysulfide and ethylene of conc. ammonium hydroxide to stabilize the emulsion dichloride. The reaction involves the loss of sodium and allow to stand overnight or until the next laboratory chloride and linking the ethylene and polysulfide groups period. Coagulation of Latex and Production of Synthetic into long c h a i n ~ . ~ J Rubber: After setting overnight the latex will have CICH?CH.CI + NaS,Na + CICHSCHICI+ NaS,Na settled to the bottom of the heaker. Decant as much C1CH1CH&(CHnCH2S,)YCH2CH~CI 4- (2" 2) NaCl of the upper layer (unreacted materials) as possible and Preparation of Polysul@e Solution: Dissolve 10 g. resuspend the latex by adding about 400 ml. of water of sodium sulfide and 5 g. of sodium hydroxide in 100 which contains 10 ml. of ammonia. With stirring, add ml. of water. Heat the solution to boiling and add 15 g. an excess of 20 per cent acetic acid to coagulate the of flowers of sulfur, with stirring. Allow the solu- latex. A ball of synthetic rubber about two inches in tion to boil for about 5 minutes and filter off the un- diameter will form in the bottom of the beaker. Remove the ball and wash it thoroughly. The color will 1 BARER.J. CHEM. EDUC.,20, 427 (1943). 3 Fuso~,CONNOR, PRICE,AND SNYDER, "A Brief Course in vary from yellow to white and the elasticity of the Organic Chemistry," John Wiley and Sons, Inc., New York, product will depend upon the degree of polymerization 1941, p. 125. and of the sulfur content. Wmm AND PATRICK, I d . Eng. Chem., 28, 1145 (1936).
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