4D printing of reprocessable thiocyanate covalent adaptable networks with reconfigurable shape memory ability

Shape memory polymers used in 4D printing only had one permanent shape after molding, which limited their applications in requiring multiple reconstructions and multifunctional shapes. Furthermore, the inherent stability of the triazine ring structure within cyanate ester (CE) crosslinked networks after molding posed significant challenges for both recycling, repairing, and degradation of resin. To address these obstacles, dynamic thiocyanate ester (TCE) bonds and photocurable group were incorporated into CE, obtaining the recyclable and 3D printable CE covalent adaptable networks (CANs), denoted as PTCE1.5. This material exhibits a Young's modulus of 810 MPa and a tensile strength of 50.8 MPa. Notably, damaged printed PTCE1.5 objects can be readily repaired through reprinting and interface rejoining by thermal treatment. Leveraging the solid-state plasticity, PTCE1.5 also demonstrated attractive shape memory ability and permanent shape reconfigurability, enabling its reconfigurable 4D printing. The printed PTCE1.5 hinges and a main body were assembled into a deployable and retractable satellite model, validating its potential application as a controllable component in the aerospace field. Moreover, printed PTCE1.5 can be fully degraded into thiol-modified intermediate products. Overall, this material not only enriches the application range of CE resin, but also provides a reliable approach to addressing environmental issue.