Effect of Self-Nucleation and Stress-Induced Crystallization on the Tunable Two-Way Shape-Memory Effect of a Semicrystalline Network

Compared with the irreversible shape-shifting feature of the traditional one-way shape-memory effect (1W-SME), two-way shape-memory materials (2W-SMMs) can exhibit programmable and reversible shape switching between two or more distinct shapes and show great potential in many areas such as artificial muscles and robots. The stress-free 2W-SME can be simply realized in semicrystalline polymer networks with a broad melting temperature (Tm) range; however, the working mechanism of these two-way shape-memory polymers has not been clearly understood from the view of crystalline behavior such as stress-induced crystallization and self-nucleation. Herein, we develop a series of PCL-based networks (NW-PCLDA-BA) with a broad melting temperature range (ΔTm) via copolymerization of n-butyl acrylate (BA) and PCL-diacrylate (PCLDA) with gradient molecular weights. The stress-free 2W-SME with desirable reversible actuation was realized through the partial melting–recrystallization process of PCL crystalline domains by tuning the applied programming stress and actuating high temperature (Thigh) in a rational range of ΔTm. The influences of the self-nucleating effect and the changes in the microstructure of the crystalline domain on the stress-free 2W-SME were systematically investigated, and the mechanism of the actuation behavior was discussed. This work provides a facile strategy to achieve the tunable stress-free 2W-SME as well as the fast evaluation of the best 2W-SME performance in a semicrystalline network system.