 The percentage of repeating units of polyisoprene comprising each type of polymer bond is dependent on the reaction mechanism.Anionic chain polymerization, which is initiated by n-Butyllithium, produces cis-1,4-polyisoprene dominant polyisoprene.90–92% of repeating units are "cis"-1,4-, 2–3% "trans"-1,4- and 6–7% 3,4-units.