Reprocessable and 3D-printable polyurethane thermosets with dynamic covalent urea networks

Abstract

Conventional photocurable polyurethanes possess permanently crosslinked networks that impede recyclability, thereby raising significant environmental concerns. In this work, a general molecular strategy is proposed to impart dynamic reversibility to photocurable systems by incorporating dynamic covalent bonds into both the prepolymer and crosslinker domains. Tert-Butylaminoethyl methacrylate (TBEMA) was utilized to construct a dynamic urea-based crosslinker (HTB) and to end-cap polyurethane prepolymers, ensuring chemical compatibility within the system. By combining these components with flexible (CTFA) or rigid (IBMA) active diluents, a series of UV-curable formulations suitable for digital light processing (DLP) were developed. The cured flexible and rigid resins exhibited tensile strengths of approximately 12 MPa and over 45 MPa, respectively, along with excellent printing fidelity. Rheological analysis revealed a persistent long relaxation process within the networks, which fundamentally governs their thermomechanical behavior and directly guided the selection of hot-pressing as the optimal reprocessing technique. Leveraging this dynamic character, the crosslinked networks were successfully reprocessed via hot-pressing. Furthermore, a practical recycling route for mixed polyurethane waste was established by blending the reprocessed resins with virgin thermoplastic polyurethane (TPU), affording homogeneous composites with well-preserved mechanical integrity. This study provides a versatile molecular design paradigm for recyclable thermosetting resins and contributes to advancing the sustainability of photocurable 3D printing materials.