Recycling of Poly(thiourethane) Thermosets Enabled by Thiourethane Bonds

Recycling of polyurethanes is an inviable process due to the harsh reprocessing conditions and high risk of side reactions. Constructing polymer networks incorporating covalent dynamic bonds becomes an attractive strategy in the design of recyclable materials. Here, we report findings on the dynamic nature of thiourethanes, and their application as a new class of recyclable analogs of urethane materials. A series of small molecule experiments was initially conducted to determine equilibrium constant and reverse reaction kinetic constant for the thiourethane reaction. Furthermore, incorporating those thiourethane moieties into a cross-linked network resulted in thermoset materials that can be facilely depolymerized to liquid oligomers. The resultant oligomers can be recrosslinked back to thiourethanes without any loss of performance nor properties (peak stress of 30 MPa with Young’s modulus of 1 GPa). Moreover, the increase in value that thiourethane network can undergo when upcycled to the thiol oligomer enables a potential pathway to build materials with properties that exceed its pristine material. Overall, this reprocessing strategy may advance many global sustainability goals, and is applicable to other low-cost commodity materials.