Intramolecular reactions occurring during the pyrolysis of a polymer obtained by an addition of dichlorocarbene to 1,4-cis-polybutadiene were investigated. It was found that intensive dehydrochlorination of the polymer occurs in two temperature ranges. Dehydrochlorination with the formation of tetraenes in the polymer chain, separated by methylene groups, is preceded by the cyclopropyl-allyl transformation of gem-dichlorocyclopropane groups in the temperature range of 240–269 °C. Cyclobutene structures are probably formed at the ends of tetraene sequences at the temperatures of 447–493 °C. The opening of this ring leads to the formation of sections of a branched system of conjugated double bonds in the polymer chain.