Homogeneous anionic polymerization. III. Molecular weight of polyisoprene initiated by butyllithium

A study has been carried out on the molecular weights and their distribution for polyisoprene prepared with butyl lithium as initiator in n ‐hexane and tetrahydrofuran solvents. A stoichiometry of one chain per initiator molecule was found to apply. As in the case of styrene, the initiation reaction in the hydrocarbon solvent was relatively slow compared to propagation, thus leading to a broadening of the molecular weight distribution. However, narrow distributions were obtained by using a preinitiation technique, whereby all chains had an opportunity of growing simultaneously. In the THF solvent, the molecular weight distribution waa somewhat broader ( M̄v / M̄n , ∽ 1.3) presumably due to a slow competitive chain termination reaction between the growing anionic chains and the solvent, a t room temperature.