The butyllithium-initiated polymerization of 1,3-butadiene

The structure of polybutadiene prepared by butyllithium initation in n‐heptane has been studied by four infrared procedures. A typical polymer prepared by n‐butyllithium at 30° gave values of 48–58% trans‐1,4‐ and 33–45% cis‐1,4‐, and 7–10% 1,2‐addition, depending on the particular analytical technique used. Iso‐ or n‐butyllithium gave polybutadienes with the same structure. Polymer stereochemistry is independent of monomer and initiator concentration and extent of polymerization conversion. Polybutadiene prepared in experiments from 4 to 80° showed the same structure. Polymerization in the presence of small amounts of ethers yields 1,2‐addition as the major structural unit. These results contrast with the reported behavior of isoprene in similar polymerizations where increasing alkyllithium concentration and reaction temperature increase the amount of 3,4‐addition and decrease the amount of cis‐1,4‐structure. Possible reaction routes for these transformations are discussed.