Isotope Exchange between Sulfur Atoms in Vulcanization Accelerators in the Presence of Diphenylguanidine and Phenyl-2-Naphthylamine

Abstract

In previous work it was shown that in the process of vulcanization a continual series of isotope exchange reactions takes place between the sulfur atoms in the various sulfur-containing ingredients of the vulcanizate. It was established that the sulfur atoms which enter into this isotope exchange include not only those which go into the structure of the molecule of accelerator, e.g., mercaptobenzothiazole, benzothiazolyl disulfide, and tetramethylthiuram disulfide, carbamates, and sulfenamides, but also the sulfur atoms which form the polysulfide bonds, R—S_m—R, and, in addition, those present in the form of secondary products formed in the vulcanization process (hydrogen sulfide and zinc sulfide). Evidently the exchange reactions between sulfur atoms in the substances present in an accelerator-type vulcanization, in which sulfur in a reactive form is liberated, and active radicals are formed from the accelerator and take part in structure formation in the rubber, are of prime importance. The formation of a vulcanization network in which the rubber, sulfur, and carbon black are chemically combined, is another result of industrial vulcanization.