SULFUR VULCANIZATION OF SIMPLE-MODEL OLEFINS .5. DOUBLE-BOND ISOMERIZATION DURING ACCELERATED SULFUR VULCANIZATION AS STUDIED BY MODEL OLEFINS

The sulfur vulcanization of unsaturated rubber has been studied with t he use of various olefins as simple, low-molecular models. By treatmen t of these olefins with a mixture of zinc oxide, sulfur, and tetrameth ylthiuram disulfide (TMTD) at 140 degrees C, a mixture of dialkenyl su lfides is obtained mimicking crosslinked rubber. Isomerization of the double bond may take place during this reaction, depending on the olef in used. The position of the double bond is on the one hand determined by crosslink formation mechanisms, and on the other hand by isomeriza tion, which takes place at higher temperatures. The position of the eq uilibrium between isomeric alkenyl sulfides is determined by the incre ased stability of the sulfide which in itself results from an increase d degree of alkyl substitution at the unsaturation. Due to the isomeri zation reaction, at higher temperatures no mechanism for crosslink for mation can be discerned. At room temperature, however, a radical mecha nism appears to be predominant during the vulcanization process.