Sulfur‐induced cis‐trans isomerization of polybutadiene

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Abstract
Both high cis‐1,4‐polybutadiene and high trans‐1,4‐polybutadiene were found to isomerize when heated in the presence of elemental sulfur. The kinetics of the sulfur induced isomerization of high cis‐1,4‐polybutadiene were studied over a wide range of temperature and sulfur concentration and found to obey a first‐order kinetic expression having an effective rate constant directly proportional to the initial sulfur concentration. The apparent activation energy was found to be 30.1 ± 0.4 kcal./mole. Isomerization was also found to be induced by dicumyl peroxide. A comparison of the mechanisms involved in the sulfur and peroxide induced isomerization indicate a basic difference in the nature of the initial interaction of the double bond with the sensitizing species. The initial interaction of the sulfur and the double bond is pictured as a π‐complex that decomposes to a freely rotating radical, whereas the peroxide induced isomerization is presumed to involve direct radical addition to the double bond.

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