Synthesis of an episulfide intermediate

In order to prepare monomers for high refractive index resin, an episulfide intermediate, methoxycarbonyldithiothiirane, was synthesized, which could react with thiols to make episulfide monomers in a mild condition. Monomer 2,2'-[methylene bis-dithiol-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 n(D)/V-D = 1.79/28.