Joint experimental and theoretical study of the poly(styryl sodium) and poly(α-methylstyryl sodium) polymerization/depolymerization

Abstract

Ab initio 6-31G* optimization of a fragment of poly(styryl sodium) and poly(α-methylstyryl sodium) composed of two monomer units in cis-configuration gives rise to low energies of the triplet state. The novel mechanism of living polymer depolymerization is proposed, involving thermal excitation into the low-lying triplet state of charge transfer character followed by bond breaking. In the elementary stage of depolymerization the electronic excitation of the reaction structure in the cis-configuration is accompanied by a minor (∽0.5 Å) displacement of the Na⁺ cation between the terminal and the penultimate monomer units. The direct reaction of adding the styrene molecule to the terminal unit of a living polymer was also considered. The reversible reaction of polymerization/depolymerization of poly(α-methylstyryl sodium) in THF was studied experimentally. A semi-empirical AM1 method was used to estimate the geometry and the charge distribution.