Dithioacetal Polymers Capable of Chemical Recycling to Macrocyclic Monomers and Formation of Vitrimers

Polymers capable of chemical recycling to monomers are highly desirable to produce sustainable materials with a circular economy. We here report a highly efficient ring-chain recycling of polydithioacetal (PDTA) via ring-closing depolymerization (RCD) and entropy-driven ring-opening polymerization (ED-ROP). Pristine PDTAs can be conveniently synthesized via a one-step reaction using 3,4,5-trimethoxybenzaldehyde and α,ω-alkyl dithiols with an acid catalyst. The resulting PDTAs undergo acid-catalyzed RCD with refluxing toluene to yield a mixture of macrocycles of various sizes with conversions of 75-95%. ED-ROP of these macrocyclic monomer mixtures in solution at room temperature affords virgin PDTAs, reaching high conversions of 80-95% within 2 h. Owing to the stability of dithioacetals, PDTAs are far more stable than the acetal counterparts, resisting hydrolysis under both acidic and basic conditions. With a floor temperature below 0 °C, depolymerization is not a concern in the bulk state even in the presence of residual catalysts as polymerization is favored at higher temperatures for ED-ROP. Once crosslinked, the network behaves as a vitrimer enabled by temperature-activated interchain exchange of dithioacetals in the bulk state. The vitrimer depolymerizes into macrocyclic monomers in solvent which can repolymerize to regenerate the vitrimer.