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

Abstract

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 linear polydithioacetal (PDTA) via ring-closing depolymerization (RCD) and entropy-driven ring-opening polymerization (ED-ROP). Furthermore, 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. Pristine linear 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.