Reprocessable and Highly Creep-Resistant Covalent Adaptable Networks Incorporating Azine Dynamic Cross-Links via Free-Radical Polymerization

Abstract

Covalent adaptable networks (CANs) are a promising avenue for replacing conventional, unrecyclable thermosets with reprocessable, more sustainable networks incorporating dynamic cross-links. Azine dynamic chemistry has recently been explored and, thus far, has only been incorporated into step-growth CANs. We developed an azine-based cross-linker with methacrylate end groups, enabling radical-based CAN synthesis. Free-radical copolymerization of this cross-linker with n-hexyl methacrylate yielded robust CANs with full property recovery upon reprocessing by compression molding at 120 °C. The associative azine dynamic chemistry resulted in constant cross-link density across the rubbery plateau, extraordinary creep suppression at temperatures of 190–210 °C, and severely limited stress relaxation at temperatures as high as 200–210 °C; nevertheless, this did not hinder the CAN’s reprocessability by compression molding at 120 °C and 8 MPa pressure. Finally, preliminary injection molding and extrusion experiments at temperatures of 200–210 °C indicated the potential feasibility of these methods for azine-based CAN production.