Anionic polymerization of isoprene: Effect of ionic character of the growing ion pair on polymer structure

The styrene content of styrene‐isoprene copolymers initiated by alkali metals in different solvents is correlated with the total 1,4‐adduct content of isoprene homopolymers initiated in the same manner. A very good linear relationship is obtained over the whole range which is dependent on the ionic character of the propagating species highly ionic systems (i.e., Na in ethers) give high styrene and low 1,4‐adduct contents, while less ionic systems, i.e., butyllithium in aromatic ethers and in hydrocarbons, give progressively lower styrene and higher 1,4‐adduct contents.