Organocatalytic selective coupling of episulfides with carbon disulfide for the synthesis of poly(trithiocarbonate)s and cyclic trithiocarbonates

Abstract

This work reports how to efficiently utilize carbon disulfide (CS₂) as a sulfur-containing C1 resource for the purpose of synthesizing both linear poly(trithiocarbonate)s and cyclic trithiocarbonates. When initiated by PPNCl or phosphazene benzoxide, the copolymerization of CS₂ with episulfides affords perfectly alternating poly(trithiocarbonate)s in the absence of any catalyst. In contrast, when initiated by tetrabutylammonium halide, the same coupling reaction of CS₂ with episulfides results in the formation of cyclic trithiocarbonates. The role played by initiating onium salts in the linear/cyclic selectivity as well as reaction conditions such as the temperature, the type of solvent, and the feeding ratio of CS₂ to episulfides was investigated. Lastly, when placed in the presence of a radical source or treated with UV irradiation, poly(trithiocarbonate)s undergo complete unzipping to produce cyclic trithiocarbonates. This remarkable feature has been harnessed to prepare degradable polymers using oligotrithiocarbonates as self-immolating linkers between dithiol alkyl precursors.