Mechanically Strong, Thermally Stable Poly(imide-imine) Covalent Adaptable Networks with Full Recyclability

As a representative class of covalent adaptable networks (CANs), polyimines are characterized by flexible molecular structure design, straightforward preparation, and a wide range of raw material sources. However, their physical properties and hydrolytic stability remain relatively inadequate to meet high-demand applications. To address the limitations in mechanical and thermal properties of current polyimine-based CANs, this study introduces a diamine monomer containing a bisimide linkage (EBIDA) into the polyimine network. By adjusting the ratio of EBIDA to a triamine cross-linker, the content of imide units in the network was modulated, leading to the preparation of a series of poly(imide-imine) (PIIE) thin films. The resulting films exhibit outstanding properties: a tensile modulus exceeding 2.0 GPa, a maximum tensile strength as high as 97.4 MPa, a glass transition temperature (Tg) up to 207.9 °C, along with remarkable hydrolytic resistance and creep resistance. Leveraging the dynamic nature of imine bonds, PIIEs can be efficiently repaired at low temperature (80 °C, 2 h) in the presence of trace amounts of primary amines without compromising mechanical properties. When exposed to an excess of primary amines, the prepared PIIEs can be degraded into soluble low-molecular-weight oligomers. By replenishing stoichiometric amounts of EBIDA and dialdehyde, PIIE films can be reconstructed while largely retaining their original properties, demonstrating good recyclability. This work offers a new strategy for developing high-performance, repairable, and fully recyclable CANs, contributing positively to advancing the sustainability of high-performance thermosetting materials.