Triple-Network Biopolyester Elastomer Composites for Tailorable Shape-Shifting Performances in Response to Multiple Stimulus

For shape-memory polymers (SMPs), there are two main types of polymer networks: amorphous and crystallizable. However, amorphous cross-linked polymers cannot have too low cross-linking density in order to ensure that the shape-memory transition temperature (Ttrans) is above room temperature, thus sacrificing their stretchability. Crystallizable cross-linked polymers with fewer cross-links have a large stretchability, but their mechanical strength is usually very low above the Ttrans. Also, the intrinsic properties of polymers limit their response to external stimuli to heat only. In this work, a crystallizable polymer network with fewer cross-links is designed to fabricate multistimuli-responsive SMPs with large stretchability, high strength, and tunable Ttrans. (1) The introduction of a long-chain PCL combined ensured the material’s high stretchability and the contribution of the crystalline network to the material’s strength. (2) The chain entanglement of a cross-linked network with a long-chain PCL enhanced the mechanical strength of the material above its Ttrans. (3) The carbon nanofiber network was further introduced into the system as both a reinforcing component and an energy conversion mediator. The design of network structures not only significantly enhanced the mechanical properties of the material but also endowed the material with laser-/sunlight-/electricity-induced shape-shifting capacity. Furthermore, precise control of the response threshold and shape-shifting speed of the material was realized by regulating the content of CNF and the intensity of external stimuli. This work provides a universal solution for large stretchability, good mechanical strength, and multistimuli response, expanding the scenarios of engineering application and practicality of SMPs.