Elemental sulfur, a by-product of petroleum refining, is discarded at over 7 million tons annually. Although sulfur polymers exhibit unique properties, their synthesis typically requires radical-based process at high temperatures (~160 °C), producing toxic hydrogen sulfide (H₂S) and poorly defined structures. Here, we report a radical-free, room-temperature step-growth polymerization of sulfur and epoxides at liquid-liquid interfaces. This mild, scalable method yielded odorless, stable sulfur polymers without H₂S emission. Notably, our method enable for the first time the quantitative control and spectroscopic identification of consecutive S-S bonds, previously inaccessible due to synthetic limitations. This control revealed clear correlations between sulfur chain length and material properties; longer S-S sequences improved toughness and degradability. Our findings advance molecular-level understanding and provide a sustainable route for valorizing waste sulfur.