Dynamic Circular Sulfur‐Rich Polymer Glasses From Elemental Sulfur

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Elemental sulfur (S 8 ) is a commodity‐priced petroleum byproduct suitable for upcycling as a neat molten medium for sustainable polymer synthesis. Inverse vulcanization is an attractive approach for converting S 8 into sulfur‐rich plastics, yet scalable manufacturing remains challenging. The chemistry of molten sulfur is poorly understood, limiting progress using this unconventional medium. Herein, molten sulfur homogeneity is identified as a critical parameter for accessing sulfur‐rich (70–80 wt.%) polymer glasses, termed inverse vulcanized glass (IVG). Application of ultra‐high‐purity sulfur melts uncovers a hidden boundary condition governing sulfur plastic manufacturing, enabling fabrication of large IVG precision optics with high refractive index and landmark broadband transparency across the visible–infrared spectrum. The inclusion of S–S bonds afford covalent adaptable networks with rheology dominated by dynamic bond reorganization. IVG functions as an affordable, broadband Vis–IR optical glass whose damaged components can be melt‐reprocessed, providing a circular advantage over traditional inorganic optical materials.