Chemistry and Technology of Elastomeric Polysulfide Polymers

Abstract

Abstract The first synthetic rubber manufactured in the United States was of the polysulfide type. In 1927 Patrick and Mnookin had obtained the first of a series of patents on the products from the reaction of organic dihalides and inorganic polysulfides. Production was started in Kansas City in 1929 with the first of the polysulfide elastomers, the ethylene tetrasulfide polymer, under the trademark name Thiokol A. Thus, the Thiokol Chemical Corporation started its long association with the polysulfide polymers. Interest developed in many countries because of the potential cheapness and availability of the raw materials required. In the case of Thiokol A, these were sulfur, caustic soda, and ethylene dichloride from ethylene and chlorine. The most interesting property of these polymers was the unusual inertness to solvents and hydrocarbon fuels in contrast to the easy swelling of natural rubber. In this respect, Thiokol A was more inert than the polysulfide polymers to follow, but it had also some less desirable properties. It was difficult to process, had a bad odor that remained to some extent even when fully cured, and gave off irritating fumes during processing. It was subsequently found that the polymers from bis (2-chloroethyl) ether were free of this problem, processed better and gave improved physical properties. Thiokol B and Thiokol D were respectively the tetrasulfide and disulfide elastomers derived from bis-2-chloroethyl ether. These resulted from a study of the effect of polymer structure on polymer odor and properties that indicated a reduction in odor when the polysulfide units were separated by an increasing number of atoms. However, the process for making these polymers gave a high byproduct yield of the six atom heterocycle, thioxane, which has a pungent odor and no economic value. Five and six membered monosulfide rings are formed readily with the corresponding 1, 4- and 1, 5-dichloro aliphatic compounds.