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 (Tf = 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 (δ[Hbar][Xbar], and δ [Sbar][Xbar]) on [Xbar], as described by the equilibrium …-CH2CH(CH3)SX − + S8 = …-CH2CH(CH3)SX+8 −, has shown that at [Xbar] ⇋; 9 the experimental δ[Hbar][Xbar] and δ [Sbar][Xbar] approach values determined earlier for the free radical homopolymerization of elemental sulfur …-Sn • + S8 ≤ …-S• n+8& The corresponding values are 3.1 kcal/mol and 4.76 cal/mol · degree.