4D Printed Thermoplastic Polyamide Elastomers with Reversible Two-Way Shape Memory Effect

4D printing has become a research hotspot in recent years. Only a few elastomer materials can be printed by selective laser sintering (SLS) and achieve a reversible two-way shape memory effect (2W-SME) at the same time, which greatly limits the applications of 4D printing. Therefore, it's still a challenge to develop a new elastomer possessing reversible 2W-SME. In this work, a series of thermoplastic polyamide elastomers (TPAEs) are synthesized successfully through the polycondensation reaction of PA1212 prepolymer and polyetheramine, which exhibited excellent thermal stability, flexibility, and resilience. The crystalline PA1212 hard domains acted as a skeleton to maintain the permanent shapes, and the polyether soft segments acted as actuation phase to realize crystallization-induced elongation (CIE) and melting-induced contraction (MIC) under internal stress. The reversible 2W-SME of T0.6-2 films is first realized, and the reversible response strain can reach 15.2% and a good shape recovery ratio is also achieved. After freeze-crushing and sieving, SLS-printable TPAE powder is obtained, and the SLS-processed samples also exhibited excellent reversible 2W-SME to realize 4D printing. This new TPAE material not only broadens 4D printable materials, but also has a potential in the fields of soft robots, temperature sensors, and even aerospace equipment.