Stress-Free Two-Way Shape-Memory Mechanism of a Semicrystalline Network with a Broad Melting Transition

作者：Jin Wang, He Zhang, Junjie Lei, Mengxuan Wu, Weifeng Liu, Jinping Qu · 发表于：Macromolecules · 年份：2022 · DOI：10.1021/acs.macromol.2c01971 · 被引用次数：30 · 研究领域：Polymer composites and self-healing、Advanced Materials and Mechanics、Shape Memory Alloy Transformations

Stress-free two-way shape-memory (2W-SM) polymers are highly desired for soft actuators and flexible sensors. Semicrystalline networks with a broad melting transition can be imparted with stress-free 2W-SM effects by facile thermal-mechanical programming. However, the reversible elongation achieved is generally in the range of 5–20%. Further improvement of the reversible elongation requires deep insights into the stress-free 2W-SM mechanism. Herein, we reported a broad melting transition semicrystalline network that can be programmed with a reversible elongation above 10%, investigated structural origins of the reversible elongation by experiments, and theoretically analyzed thermodynamic and molecular mechanisms associated with the reversible elongation. The results show that a semicrystalline skeleton composed of oriented crystals and compressed amorphous chains is formed in the programmed network, which provides internal tensile stress required for the stress-free 2W-SM effect. In addition, it is found that the reversible elongation is primarily a direct result of variation in amorphous orientation of the network; crystalline orientation of the network varies only slightly during actuation. Furthermore, the theoretical analysis reveals that although the direct contribution of the crystalline orientation to the reversible elongation is small, the crystalline orientation induces an entropy increase in the amorphous section, which enhances the reversible elongation significan...