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The thermal degradation of polybutadiene (PB) samples having different initial contents of cis-l,4-, truns-l,4-and 1,2-units were investigated at temperatures lower than 250 "C, where cyclization, cross-linking and cis-trans isomerization occur without depolymerization. Changes of the cis-trans content and decrease of double bonds in the polymers were measured at different temperatures. The rates.of double bond loss were found to follow the order: truns-1,4 > 1,2 > cis-l,4, whereas the opposite occurred for the isomerization process. The reactions responsible for the structural changes of PB at temperatures lower than 250 "C are reviewed and discussed.

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