A High‐Refractive‐Index and Partially Chemically Recyclable Polymer From a Sulfur‐Rich Spiro ‐and‐Fused Tricyclic Monomer

The development of chemically recyclable polymers with high refractive indices is desirable for sustainable optics. Herein, a sulfur-rich spiro-tetrathioorthocarbonate motif was integrated into a fused bicyclic framework, yielding a spiro-and-fused tricyclic monomer, trans-tetrathiaspiro[4.5]decane-fused cyclooctene (M1). Its ring-opening metathesis polymerization (ROMP) produced polymer P1, which exhibits a high refractive index (nD > 1.65), excellent thermal stability (Td ∼ 300°C), and good transparency. Depolymerization studies show that P1 can revert to monomer under dilute conditions, achieving up to ~ 76% conversion with elevated catalyst loadings. Unlike spiroketal-based analogues that depolymerize near-quantitatively under mild conditions, the sulfur-rich tetrathioorthocarbonate group introduces distinct challenges for depolymerization efficiency. This work establishes a new monomer platform for recyclable optical polymers and highlights the interplay between functional group design and catalyst compatibility in reversible ROMP.