Moon Junho, Sang Zhen, Rajagopalan Kartik Kumar, Gardea Frank, Sukhishvili Svetlana
Department of Materials Science and Engineering, Texas A&M University, College Station, TX, 77843, USA.
U.S. Army Combat Capabilities Development Command Army Research Laboratory South, Army Research Directorate, College Station, TX, 77843, USA.
Small. 2025 Jan;21(2):e2407858. doi: 10.1002/smll.202407858. Epub 2024 Nov 7.
The intrinsic reversibility of dynamic covalent bonding, such as the furan-maleimide Diels-Alder (DA) cycloaddition reactions, enables reprocessable, self-healing polymer materials that can be reconfigured via the mechanism of solid-state plasticity. In this work, the temperature-dependent exchange rates of stereochemically distinct endo and exo DA bonds are leveraged to achieve tunable, temperature- and stress-activated shape morphing in Diels-Alder polymer (DAP) networks. Through thermal annealing, ≈35% of endo DA isomers are converted in neat DAP networks to the thermodynamically favored exo form, achieving ≈97% exo after complete annealing at 60 °C. This conversion results in a ≈1.7 fold increase in elastic modulus, from 1.7 to 3.0 MPa, and significantly alters the stress relaxation and shape recovery behavior. Spatially resolved annealing, is further showcased enabling the precise control of spatial distributions of endo and exo DA bonds across planar geometries. The locally distinct concentrations of endo/exo isomers, achieved by temperature-induced conversion of endo DA isomers to the thermodynamically stable exo DA isomers, gave rise to the spatial distributions of stress relaxation rates and elastic strain recovery mismatch to enable controlled stereochemical shape morphing. This approach provides a simplified, thermally driven method for shape morphing, with potential applications in soft robotics and flexible electronics.
动态共价键的固有可逆性，如呋喃 - 马来酰亚胺狄尔斯 - 阿尔德（DA）环加成反应，使得可再加工、自修复的聚合物材料能够通过固态可塑性机制进行重新配置。在这项工作中，利用立体化学上不同的内型和外型DA键的温度依赖性交换速率，在狄尔斯 - 阿尔德聚合物（DAP）网络中实现了可调谐的、温度和应力激活的形状变形。通过热退火，在纯DAP网络中约35%的内型DA异构体转化为热力学上更有利的外型形式，在60°C完全退火后达到约97%的外型。这种转化导致弹性模量增加约1.7倍，从1.7 MPa增加到3.0 MPa，并显著改变了应力松弛和形状恢复行为。空间分辨退火进一步展示了能够精确控制平面几何结构中内型和外型DA键的空间分布。通过温度诱导内型DA异构体转化为热力学稳定的外型DA异构体实现的内型/外型异构体的局部不同浓度，导致了应力松弛速率和弹性应变恢复失配的空间分布，从而实现可控的立体化学形状变形。这种方法提供了一种简化的、热驱动的形状变形方法，在软机器人和柔性电子学中有潜在应用。
