Lipoic Acid Without the Side Chain: Sublimable Homopolymers and Degradable Copolymers Based on 1,2-Dithiolane

Abstract

Depolymerization, the complete degradation of a polymer into its monomers, is of great interest for the development of circular materials. But current depolymerizations require high temperatures, suffer from low monomer recovery, and/or require a separate repolymerization step. Herein, unsubstituted 1,2-dithiolane, which is unstable in pure form, was successfully prepared, stored, and polymerized in solution. Poly(1,2-dithiolane), i.e., poly(trimethylene disulfide), was prepared through radical and cationic ring-opening polymerization procedures in solution, but also, leveraging the monomer instability, upon evaporation of a monomer solution. Poly(1,2-dithiolane) depolymerized efficiently to monomer when heated to 90 °C. Uniquely, the monomer was gaseous at this temperature and spontaneously repolymerized into a solid polymer upon cooling. The resulting polymer could be sublimed repeatedly. The widespread applicability was demonstrated through depositing insoluble hydrophobic waterproof coatings, the thermal removal of such coatings, and the purification of a contaminated polymer through sublimation. Additionally, 1,2-dithiolane was found to undergo radical ring-opening copolymerization with styrene, acrylates, vinyl acetate, and methyl methacrylate, introducing cleavable S−S and C−S bonds into the backbone. Key requirements for the development of other sublimable polymers are discussed and anticipated to lead to the development of tailored depolymerizable circular materials.