Arbitrarily Reconfigurable and Thermadapt Reversible Two-Way Shape Memory Poly(thiourethane) Accomplished by Multiple Dynamic Covalent Bonds

Abstract

The fabrication of a single polymer network that exhibits a good reversible two-way shape memory effect (2W-SME), can be formed into arbitrarily complex three-dimensional (3D) shapes, and is recyclable remains a challenge. Herein, we design and fabricate poly­(thiourethane) (PTU) networks with an excellent thermadapt reversible 2W-SME, arbitrary reconfigurability, and good recyclability via the synergistic effects of multiple dynamic covalent bonds (i.e., ester, urethane, and thiourethane bonds). The PTU samples with good mechanical performance simultaneously demonstrate a maximum tensile stress of 29.7 ± 1.1 MPa and a high strain of 474.8 ± 7.5%. In addition, the fraction of reversible strain of the PTU with 20 wt % hard segment reaches 22.4% during the reversible 2W-SME, where the fraction of reversible strain is enhanced by self-nucleated crystallization of the PTU. A sample with arbitrarily complex permanent 3D shapes can be realized via the solid-state plasticity, and that sample also exhibits excellent reversible 2W-SME. A smart light-responsive actuator with a double control switch is fabricated using a reversible two-way shape memory PTU/MXene film. In addition, the PTU networks are de-cross-linked by alcohol solvolysis, enabling the recovery of monomers and the realization of recyclability. Therefore, the present study involving the design and fabrication of a PTU network for potential applications in intelligent actuators and multifunctional shape-shifting devices provides a new strategy for the development of thermadapt reversible two-way shape memory polymers.

Thermo- and near infrared light-induced reversible multi-shape memory materials for actuators and sensors

“…The successful formation of TA/Fe 3+ coordination can be confirmed by the color change from yellow to black of EHTxF. It is well known that the mechanical properties of the composites usually decrease with the increase of the photothermal fillers due to aggregation, 3,28 while it could be avoided by the direct introduction of the photothermal factor into the polymer networks. As demonstrated in Fig.…”

“…Next, the NIR light responsiveness was realized by simply immersing cross-linked EVOH films in FeCl 3 solution to introduce Fe 3+ into the polymer networks based on the coordination interaction between TA and Fe 3+ . The successful formation of TA/Fe 3+ coordination can be confirmed by the color change from yellow to black of EHT x F. It is well known that the mechanical properties of the composites usually decrease with the increase of the photothermal fillers due to aggregation, 3,28 while it could be avoided by the direct introduction of the photothermal factor into the polymer networks. As demonstrated in Fig.…”

“…To obtain this function, hydrogels, liquid crystalline polymers and shape memory polymers (SMPs) are frequently used. [1][2][3] Therein, SMPs are a prominent smart material that can recover from a temporary shape to a predesigned original shape upon exposure to specific stimuli. 4 Besides, SMPs can show a variety of special functions, like a multiresponsive shape memory effect, multi-shape memory effect and reversible shape memory effect, allowing the realization of various reversible shape transformations to meet multifarious and complex application requirements.…”

Stress‐free two‐way shape memory property and microstructure evolution of single‐phase polymer networks

“…According to the functionality of the shape memory, SMPs can be divided into one‐way and two‐way shape memory polymers (1W‐SMPs and 2W‐SMPs, respectively) 19,20 . Unlike 1W‐SMPs, 2W‐SMPs can realize a reversible cycle between an initial shape and a temporary shape via a stimulus response without reprogramming, which is the two‐way shape memory effect (2W‐SME) 20–24 . Based on whether a persistent external stress is needed in the two‐way shape memory cycles, the 2W‐SMPs can be divided into quasi two‐way and stress‐free two‐way shape memory polymers (quasi 2W‐SMPs and stress‐free 2W‐SMPs, respectively) 19,25,26 .…”

“…19,20 Unlike 1W-SMPs, 2W-SMPs can realize a reversible cycle between an initial shape and a temporary shape via a stimulus response without reprogramming, which is the two-way shape memory effect (2W-SME). [20][21][22][23][24] Based on whether a persistent external stress is needed in the two-way shape memory cycles, the 2W-SMPs can be divided into quasi two-way and stressfree two-way shape memory polymers (quasi 2W-SMPs and stressfree 2W-SMPs, respectively). 19,25,26 Quasi 2W-SMPs always require a constant external stress in the shape memory cycle, while for stressfree 2W-SMPs, the external stress remains zero during the shape memory cycle, and the driving force of the shape memory comes from a pre-constructed internal stress.…”