Tailoring the Reprocessability of Thiol-Ene Networks through Ring Size Effects

Recycling thermosetting materials presents itself as a major challenge in achieving sustainable material use. Dynamic covalent cross-linking of polymers has emerged as a viable solution that can combine the structural integrity of thermosetting materials with the (re-)processability of thermoplastics. Thioether linkages between polymer chains are quite common, and their use dates back to the vulcanization of rubbers. While it is known that thioether bonds can be triggered to exchange through transalkylation reactions, this process is usually slow, as thioether moieties not only have to be activated by an alkylating agent, but the activated thioether also has to associate with a second thioether moiety in a classical S_N2-type process. Here, we present the rational design of dynamic polymer networks based on simple dithiol-based monomers and a fatty acid derived triene. Two neighboring thioethers can undergo a much faster bond exchange reaction, and we found that the exchange dynamics can be further tuned over almost three orders of magnitude by tailoring the distance between two thioether functionalities. This resulted in thioether-cross-linked materials that could be processed by extrusion, a continuous reprocessing technique that was previously not accessible for this class of cross-linked materials, while still exhibiting appealing creep-resistance below 70 °C.