Anionic Copolymerization of Elemental Sulfur with Propylene Sulfide. Equilibrium Sulfur Concentration

In the anionic copolymerization of elemental sulfur (S₈) with propylene sulfide (P) below the floor temperature of elemental sulfur homopolymerization (T_f = 159°C), there is a certain concentration of elemental sulfur left when copolymerization is completed (S₈]_eq). The dependence of S₈]_eq on the feed ratio P]₀/S₈]₀ and temperature was determined by using laser Raman spectroscopy, and this enabled us to distinguish between the S-S bonds in elemental sulfur and in the linear polysulfide. S₈]_eq was found to decrease with increasing temperature and with an increasing P₀]/S₈]₀ ratio. The experimental dependence of the average enthalpy and entropy of polymerization (δHbar]_Xbar], and δ Sbar]_Xbar]) on Xbar], as described by the equilibrium …-CH₂CH(CH₃)S_X ^? + S₈ = …-CH₂CH(CH₃)S_X+8 ^?, has shown that at Xbar] ?; 9 the experimental δHbar]_Xbar] and δ Sbar]_Xbar] approach values determined earlier for the free radical homopolymerization of elemental sulfur …-S_n ^? + S₈ ≤ …-S^? _n+8&; The corresponding values are 3.1 kcal/mol and 4.76 cal/mol · degree.