Effect of Vulcanization on Rubber Structure. A Problem in Probabilities

Abstract

The older chemical studies of vulcanization usually were attempts to explain the profound physical changes produced in rubber in terms of the normal properties of small molecules.

Sulfur Linkage in Vulcanized Rubbers

“…The addition of methyl iodide to organic sulfides with the formation of sulfonium salts has been known for eighty years and studied at frequent intervals during that time without exhausting the subject. The reaction proceeds thus: C3H7S-CsH, + CHSI -(C3H7)2CH3SI (6) No data on the rate of reaction at room temperature could'be found except the statement by Brown and Hauser (7) that the reaction with n-butyl sulfide was quantitative in 48 hours when the sulfide had been diffused into a crude rubber sample. This claim has been confirmed and will be described later.…”

“…The use of methanol or ethanol as solvent is reported to give the best yields of sulfonium salts (6). When the reaction was carried out with n-propyl sulfide in equal volumes of methyl iodide and ethanol, the yield was quantitative in about 17 hours.…”

“…This decomposition could be stopped completely if the reaction was carried out in the absence of oxygen. The sulfonium salt indicated in Equation 6was isolated, purified, and analyzed following the procedures of Bost and Everett (6). The analysis (Table I) showed it to be methyl di-ra-propyl sulfonium iodide.…”

“…Sulfide can be determined in the presence of disulfide in 24 hours by the weight gain of the reaction vessel after the excess methyl iodide has been evaporated. 6. Mercuric iodide catalyzes the sulfide and disulfide reactions; the former is quantitative in 1 hour, and the latter in 3 days at room temperature.…”