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

ABSTRACT 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 ( n D > 1.65), excellent thermal stability ( T d ∼ 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.