Elemental sulfur and cyclic sulfides. Homo- and copolymerizations. Kinetics, thermodynamics and DFT analysis

Abstract

The kinetics, thermodynamics and mechanistic studies of sulfur homo- and copolymerization with cyclic and vinyl monomers are described as the major subjects of our review article. Besides, the syntheses, homo- and copolymerization of cyclic mono- and polysulfides are added. The analytical text is complemented with review of the related theoretical topics (mostly DFT), and include theoretical studies of the experimental data of the corresponding sections. Recently, mostly because of the elaboration of the novel process of sulfur copolymerization, so called “inverse vulcanization”, there is renewed interest in polymers of sulfur, with expectation of finding industrial applications, mostly as the Li-sulfur batteries, in optics, removal of toxic metals and biomaterials. We are also discussing papers on the equilibrium between polysulfur and sulfur, in homo- and copolymerization of sulfur with cyclic sulfides and with vinyl monomers. Copolymerization of sulfur is described for cyclic sulfides and vinyl monomers. Analysis of interaction with vinyl monomers involves both low temperatures - then sulfur is merely acting as the chain transfer agent, and for temperatures around the floor temperature, when more or less stable copolymers are formed with high sulfur content. It is also shown that with cyclic monomers the high molar mass copolymers of sulfur were prepared (up to 80 % of sulfur). Analysis of papers describing the molecular structures of copolymers of sulfur are complementing the analysis of the kinetics, thermodynamics and DFT of the studied processes, including the living/controlled polymerization of sulfur with cyclic sulfides. In the final section we analyse the published DFT and other theoretical analyses of the subjects discussed in the major text. These methods have been successfully applied to make predictions of the bond dissociation energies, enthalpies of formation, reaction energies and energy barriers, etc., contributing to a deeper understanding of the chemical processes, as it is shown in this review.