Catalytic Effect\nof Potassium Xanthates and Related\nCompounds on Disulfide Bond Enrichment of Polyalkylene Sulfides Synthesized\nin the Course of Episulfide Polymerization

The original method for the preparation of high-molecular-weight\npolyalkylene sulfides was reported. Assuming anomalous peculiarities\nof the reaction (high polymerization rates, high degrees of polymerization,\nand huge discrepancy between the expected <i>M</i><sub>n</sub> values and the experimentally obtained values), the priority task\nwas set to study the mechanism underlying the observed new type of\npolymerization. Thus, it was demonstrated that xanthate and related\nmolecules could act as pure catalysts, facilitating both the chain-growth\npolymerization (ring-opening of episulfides) realized via an anionic\nroute and the direct attack of the sulfur atom of one episulfide molecule\non the methylene carbon atom of the second (neighbor) episulfide molecule,\naccompanied by the subsequent formation of a stable thiiranium-based\nzwitterionic adduct. The role of xanthate and related compounds as\ncatalysts and stabilizing particles was further supplemented by modeling\nthe attack of thiolate on the sulfur atom of a thiiranium-based adduct.\nThe xanthate molecule acting as a catalyst was found to be involved\nin all stages of the process discussed by sharing the potassium atom\nwith the sulfur atoms of active components of the system (the initial\nepisulfide molecule, thiolate, and the zwitterionic intermediate).\nThe subsequent analysis revealed the exceptional transparency of the\nmaterials obtained, which was found to exceed 99%. The pronounced\nself-healing ability was also found to be a distinctive feature of\nthe synthesized high-molecular-weight polyalkylene sulfides enriched\nwith disulfide bonds.