In order to prepare monomers for high refractive index resin, an episulfide intermediate, meth-oxycarbonyldithiothiirane, was synthesized, which could react with thiols to make episulfide monomers in a mild condition. Monomer 2,2’-[methylene bis-dithio]-bis-thiirane was prepared with dimercaptomethane and the intermediate. Polymerization of this monomer gave a thermosetting optical resin with index and Abbe number as high as nD/νD＝1.79/28.

Key words: methoxycarbonyldithiothiirane, super-high refractive index, optical resin, 2,2’-[methylene bis-dithio]-bis-thiirane