Synthesis and Polymerization of cis, cis-1-Methylcyclooctadiene-1,5

l‐Methyl‐cis, cis‐cyclooctadiene‐1,5 was obtained by mixed butadiene‐isoprene dimerization in the presence of a catalyst prepared by treating nickel acetylacetonate with lithium boron hydride in the presence of triphenyl phosphite. In analogy with cis, cis‐cyclooctadiene‐1,5, methyleyclooctadiene can be polymerized, in the presence of the Al(iC4H9)3 + TiCl4 eatalytic system (molar ratio of Al to Ti = 0.5), to an essentially saturated product. Also in this case a transannular polymerization of the following type occurs: In the terpolymerization with ethylene and propylene, on the contrary, methyl cyclo‐octadiene reacts, in the presence of catalysts prepared from vanadium and alkyl aluminum compounds, by opening of the nonsubstituted double bond. The IR spectra of the monomer and of the polymers are here described.