One-Pot Preparation of Double-Network Epoxy Vitrimers with High Performance, Recyclability, and Two-Stage Stress Relaxation.

Although considerable progress has been made in developing different types of vitrimers, ongoing challenges remain in tuning their mechanical and rheological properties, self-healing, and adhesion. Here, we demonstrate a one-pot method to produce a novel double-network epoxy vitrimer using an aliphatic amine cross-linker with a siloxane covalent bond and an aromatic amine cross-linker with a disulfide covalent bond. When a controlled two-stage curing process is employed, the markedly different reactivities of aliphatic amine and aromatic amine with epoxy allow for sequential cross-linked network formation, leading to the development of a double network that incorporates two types of dynamic covalent bonds. As a result, the produced vitrimers exhibit controllable mechanical, thermal, and rheological properties, as well as recyclability. This is evidenced by a tensile strength as high as 72 MPa, while maintaining ∼10% elongation at break, a wide glass-transition temperature range from 91 to 171 °C, and an adjustable two-stage stress relaxation. These characteristics suggest opportunities to develop high-performance cross-linked polymers with specific responses to time and temperatures.