Structure of charge‐transfer reaction complexes in anionic polymerization of isoprene: Quantum chemical calculations

Abstract

ABSTRACT:A new mechanism of isoprene anionic polymerization is proposed. Its central moment is thermal electronic excitation of a living polyisoprene-isoprene complex into the quasi-degenerate electronically excited state (S ⅐ T) 1 , which is of the charge (electron) transfer character. It is asserted that the probability of chemical bond formation is determined by the free valence index on carbon atoms and by the geometry of reacting complex in the excited state (S ⅐ T) 1 . Semi-empirical AM1 and ab initio 6-31G* quantum chemical calculations revealed low energies of triplet excited levels (Ͻ10 kcal/mole). Comparison of isoprene polymerization on free anions and on solvated ion pairs shows that both types of active centers produce vinyl 1,2 (4,3)-units. Free anions generate predominantly 1,2-units, whereas solvated ion pairs tend to form units with the 4,3-structure. Analysis of energies of excited isoprenyl lithium ϩ isoprene complexes shows that the formation of 1,4 (4,1)-cis-polyisoprene in an inert media is most preferable.