Abstract
It is well known that a part of cis-1,4 double bonds in diene rubbers is converted to trans-1,4 double bonds during the vulcanization, which is called cis-trans isomerization. In this article, effects of compounding ingredients on the cis-trans isomerization were studied by using electron spin resonance (ESR) and solid-state 13C-NMR results. The combination of ESR and NMR results revealed that the cis-trans isomerization was induced by a side reaction of the vulcanization by sulfur radicals. It was also found that the cis-trans isomerization was suppressed by zinc oxide. It is suggested that the reactivity of free sulfur radicals is enhanced by zinc oxide, resulting in the formation of C-S linkages on polymer chains.
