Ultrafast Poly(disulfide) Synthesis in the Presence of Organocatalysts

Abstract

An organocatalyst-mediated, extremely rapid, robust, and practical poly(disulfide) synthesis method is introduced to polymer chemistry. A variety of organocatalysts were initially screened using commercially available 1,6-hexanedithiol and diisopropyl azodicarboxylate (DIAD) to reveal the best catalyst for the process. Remarkably, although a very low amount of catalyst loading (5%), all the catalysts examined afforded poly(disulfide) in 1 min with low to high molecular weights. Among them, triphenylphosphine was selected as the suitable catalyst after the kinetic measurements and used to determine the optimum conditions for polymerization. Various poly(disulfide)s with molecular weights up to 85.6 kDa could be successfully prepared using optimum conditions. Poly(disulfide) synthesis was also attempted with a "catalyst-free" approach, it was found that a polymer can be prepared under this condition, and its molecular weight increases with increasing temperature. The obtained polymers were characterized using common spectroscopic measurements, and the results revealed that the hydrazine unit derived from DIAD was incorporated into polymer chains as an end-capping agent. Also, a depolymerization study was achieved on a model poly(disulfide) using dithiothreitol as a reducing agent. It is believed the straightforward poly(disulfide) synthesis method comprising mild conditions introduced in this study will be of great interest in synthetic polymer chemistry.

Direct Introduction of Cysteine Derivatives into the Chain End of Helical Poly(quinoline-2,3-diylmethylene)s: Densely Packed Monolayers on Au Substrates

“…Sulfhydryl groups are valuable tools in organic chemistry, 9 materials science, 10 and biochemistry 11,12 owing to their abilities to rapidly and selectively react with specific functional groups under mild conditions. In addition to their well-known thiol−ene 13−15 and disulfide-formation 16,17 chemistries, sulf-hydryl groups have also been used to form self-assembled monolayers (SAMs) on Au surfaces through Au−S bonds. 18−20 Polymers bearing sulfhydryl groups at their chain end have been successfully synthesized, 10 thereby providing a convenient platform for further functionalization, 21−24 the introduction of diverse functional groups, 25−28 and the formation of block copolymers.…”

Controlled and Regioselective Ring-Opening Polymerization for Poly(disulfide)s by Anion-Binding Catalysis

“…The conventional methods for poly­(disulfide) synthesis include oxidative polycondensation of dithiols, , thermally induced polymerization in bulk, , and disulfide exchange. , Some approaches circumvent the direct construction of S–S bonds by polymerization of monomer with preinstalled disulfide bonds , or copolymerization with sulfur . Recently, the anionic ring-opening polymerization (ROP) of 1,2-dithiolanes has emerged as a promising method to synthesize poly­(disulfide)­s in a more controlled manner. , Liu and Moore found that using a thiolate initiator (RS – ) with high nucleofugality in the anionic ROP led to poly­(disulfide)­s with a cyclic topology .…”

“…The conventional methods for poly(disulfide) synthesis include oxidative polycondensation of dithiols, 42,43 thermally induced polymerization in bulk, 44,45 and disulfide exchange. 46,47 Some approaches circumvent the direct construction of S−S bonds by polymerization of monomer with preinstalled disulfide bonds 48,49 or copolymerization with sulfur.…”

Synthesis of Degradable Polyolefins Bearing Disulfide Units via Metathesis Copolymerization

“…Hence, the development of concise and highly effective pathways to access poly(disulfide)s have received great attention over the past decades. Various methods including oxidative coupling of thiols [ 16 , 17 , 18 , 19 ] and polymerization of disulfide-containing monomers [ 8 , 20 , 21 , 22 , 23 , 24 , 25 ] have been developed for the synthesis of poly(disulfide)s. Besides the synthesis of poly(disulfide)s with repeating disulfides, little success has been made in incorporating a low content of disulfides into the main chain of commodity polymers [ 19 , 26 ].…”