High Cycle-life Shape Memory Polymer at High Temperature

High cycle-life is important for shape memory materials exposed to numerous cycles, and here we report shape memory polyimide that maintained both high shape fixity (R(f)) and shape recovery (R(r)) during the more than 1000 bending cycles tested. Its critical stress is 2.78 MPa at 250 °C, and the shape recovery process can produce stored energy of 0.218 J g(−1) at the efficiency of 31.3%. Its high R(f) is determined by the large difference in storage modulus at rubbery and glassy states, while the high R(r) mainly originates from its permanent phase composed of strong π-π interactions and massive chain entanglements. Both difference in storage modulus and overall permanent phase were preserved during the bending deformation cycles, and thus high R(f) and R(r) were observed in every cycle and the high cycle-life will expand application areas of SMPs enormously.