Synthesis and Closed-Loop Recycling of Self-Immolative Poly(dithiothreitol)

Self-immolative polymers SIPs are promising members of the emerging class of recyclable polymers with the ability to end-to-end depolymerize to their monomers. Unfortunately, SIPs are often synthesized by cumbersome procedures at low temperatures in protected atmosphere. In this study, a SIP with a novel poly(disulfide) backbone is introduced, using DL-dithiothreitol (DTT) as the monomer. Remarkably, poly(DTT) can be produced by solid-state polymerization in a robust and easily scalable process by mechanically mixing DTT with 2,2'-dithiodipyridine as the end-capping agent. The new polymer possesses good thermal and chemical stabilities, but once its depolymerization is triggered, this proceeds smoothly within minutes to afford cyclic DTT because of a favorable intramolecular back-biting thiol-disulfide exchange reaction in the polymer backbone. As a proof of concept, the cyclic DTT waste was recovered, reduced to DTT monomer, and repolymerized in a closed-loop approach.