Classification of polar additives with respect to their influence on the microstructure in anionic polymerization of isoprene with butyllithium by transition energy measurements

A transition energy scale was established on the basis of dimethyl indoanil ine as organic dye for 23 mono- and bidentate polar additives. From polymer ization experiments of isoprene with s-butyllithium in mixtures of n-hexane and the selected bases, the microstructure of polyisoprenes was determined by H-1-NMR spectroscopy. The vinyl contents of these polymers could be sat isfactorily correlated with the transition energy measurements. However, it turned out that especially bidentate bases do not fit into this scheme. Ob viously, besides their influence on the polarity of the reaction solution, they exhibit special interactions with the growing centers. The developed c orrelations allow the prediction of 1,2- and 3,4-linkages in polyisoprenes from anionic polymerization of isoprene with butyllithium in polar solvents in the presence of low concentrations, also of bases hitherto not investig ated. The temperature dependence of the microstructure can likewise be esti mated. As in the case of butadiene, at least for weak bases, it was found t hat the vinyl contents depend primarily on the polarity of the reaction mix ture determined by the base concentration and not on the molar ratio of bas e to initiator. (C) 1999 John Wiley & Sons, Inc.