POLYMERIZATION AND COPOLYMERIZATION OF ELEMENTAL SULFUR

Abstract

Anionic copolymerization of elemental sulfur (S₈) with cyclic monosulfides (thiiranes) is shortly reviewed. More recent work on homopolymerization of cyclic trisulfides (1,2,3-trithiolanes) and their copolymerization with S₈ is discussed in more detail. Anionic homopolymerization of cyclic trisulfides is a living, highly reversible process. Repeating units of the resulting polymers have exclusively alkylene trisulfides structure. No elemental sulfur is eliminated in polymerization. The thermodynamic parameters of equilibrium have been determined for both homopolymerization of norbornene trisulfide (NS₃) and endo-dicyclopentadiene trisulfide (DS₃): ΔH^o _ss = -5.8±0.7 and -6.6±0.6 kJ/mol, ΔS^o _ss =-31.4±2.3 and -29.3±2.1 J/mol · K (first values for NS₃). Spectroscopic data (Laser Raman and NMR spectra) clearly indicate that in the copolymerization of elemental sulfur with cyclic trisulfides copolymers are formed. The ultimate number of sulfur atoms in the polysulfide units approaches nine (like in the copolymerization of thiiranes with S₈). Copolymers are high molecular elastomers, in contrast to the rigid, glassy homopolymers of NS₃ and DS₃.