Autonomous Off‐Equilibrium Morphing Pathways of a Supramolecular Shape‐Memory Polymer

Abstract

SMP) can only switch monotonically between its temporary and permanent shapes. Advanced hydrogels [11][12][13] incorporating distinct hydrogel components in a composite manner allow access to much more sophisticated shape-shifting behaviors such as reversible buckling. However, the behavior typically requires complex external triggering, for example, two/ more different stimuli. Similarly, multi-SMP capable of complex shifting amongst more than two shapes demands access to multi-step temperature control in both the programming and recovery processes. [14,15] From the standpoint of device applications, shape programming step is typically conducted outside the device deployment/utilization process. Complex programming thus does not compromise the device potential. On the contrary, the necessary conditions to trigger the device deployment may place severe limitation on the practical values. In other words, a mechanism that allows triggering complex shape-shifting with an easily accessible stimulation method is highly desirable. The recently emerged temporal programming comes into sight. [16][17][18] It utilizes time as a naturally available stimulus to control the shape-shifting behavior instead of other conventional physical stimuli such as temperature and pH. Although elegant, the concept suffers from two notable drawbacks. First, its shapeshifting starts immediately after the programming without a controlling mechanism for its onset. Second, accessing complex autonomous shape-shifting behaviors with temporal programming requires imposing correspondingly sophisticated programming forces. Both these limitations arise from the fact that current temporal shape-shifting systems utilize time as the sole programming parameter to control the shape-shifting behavior. [16] With the realization of the universal time-temperature superposition for polymers, we hypothesize that controlling the programming temperature can greatly extend the scope of autonomous shape-shifting. This is non-trivial since temperature control can be achieved digitally in a non-contact spatioselective way via for instance a photothermal mechanism. [19][20][21] We also conjecture that a glass transition below room temperature may allow switching on-off the autonomous shapeshifting. With these thoughts in mind, we design a T g -based network with strong time-temperature dependent ureidopyrimidinone hydrogen bonds (UPy) moieties. [15,[22][23][24][25] Herein, UPy motif is chosen because of its strong quadruple hydrogenThe diverse morphing behaviors of living creatures arise from their unlimited pathways. In contrast, the equilibrium-driven morphing pathways of common synthetic shape-shifting materials are very limited. For a shape-memory polymer (SMP), its recovery from the temporary shape(s) to the permanent shape typically requires external stimulation and follows a single fixed route. Herein, a covalently crosslinked SMP is designed with ample ureidopyrimidinone (UPy) supramolecular moieties in the network. The UPy units endow the SMP with strong time...

On-demand autonomous shape memory polymer

“…Amongst all stimuli-responsive shape-shifting polymers, shape memory polymer (SMP) [8][9][10][11][12][13] is uniquely attractive since it can be programmed to transform from an arbitrary temporary shape to its permanent shape. Typically, the shape transformation starts as soon as a stimulus is exerted 14 .…”

“…However, water diffusion and degradation are exceedingly slow and geometry dependent, making it di cult to control at the device level. Temporal programming 11,12 offers a drastically different alternative. It utilizes supramolecular interactions as the molecular switches for the shape transformation.…”

“…The externally triggered on-demand SMP [17][18][19] and the temporally programmable autonomous SMP 11,12 both have their own advantages and limitations. An ideal SMP should possess their respective desired attributes in one material, that is, autonomous shape transformation in an on-demand fashion.…”

A review of shape memory polymers based on the intrinsic structures of their responsive switches

“…3b). [46][47][48][49] Analogously, a shape memory polybenzoxazine lm consisting of arylamine mannich-type linkage was synthesized, whose chemical structure is different from that of the conventional polybenzoxazines. 50 Mannich polybenzoxazines possessed more weak hydrogen bonds of -OH/p that only existed at relatively lower temperatures and served as the responsive switch.…”

Smart Diffraction Gratings Based on the Shape Memory Effect

“…For example, Xie et al have demonstrated many wonderful works on SMPs, especially in the direction of photopolymerizable SMPs. [2][3][4] The rational use of methods such as optimizing 3D printing schemes and ingenious design of polymer components have realized the rapid and efficient preparation of multifunctional reversible shape memory devices. Without changing the equipment, the printing speed of 3D printing can be increased by order of magnitude to 400 mm h -1 by introducing the hydrogel interface.…”