Stress-Free Two-Way Shape Memory Effects of Semicrystalline Polymer Networks Enhanced by Self-Nucleated Crystallization

Abstract

Stress-free two-way shape memory polymers (2W-SMPs) capable of reversible shifting between two distinct shapes are versatile platforms for the development of future smart devices. However, it is challenging to prepare stress-free 2W-SMPs with good actuation performance and shape programmability from single-component semicrystalline polymers. Herein, we demonstrate a straightforward and universal strategy for preparing 2W-SMPs through self-nucleated crystallization (SNC) of semicrystalline polymers. SNC enables the formation of two types of crystals in the 2W-SMPs, annealed and primary crystals, which function as the skeleton phase and actuation phase, respectively. We achieved a high reversible actuation strain of 17.6% and a good reprogrammability of the SNC-treated polymer networks. Complex shape transformations were obtained, and smart devices were fabricated from the SNC-treated networks by using a locally designed folding and kirigami structure. The SNC strategy provides a generalized approach to improve the 2W-shape memory behavior of semicrystalline polymers.

In Situ Construction of Thermotropic Shape Memory Polymer in Wood for Enhancing Its Dimensional Stability

“…The shape is unchangeable after cooling, and the stress of the material is "frozen". When the deformed polymer is heated above the transition temperature again, the internal stress in the material is released, driving the malformed polymer back to its original shape [22][23][24].…”

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

“…According to the literature, two phasesskeleton and actuation phasesare required to realize the reversible 2W-SME. − ,, The skeleton phase provides structural anisotropy (or internal stress) and ensures that the actuation phase can repeatedly expand and collapse in the orientated direction, leading to the reversibly macroscopic actuation. ,, Numerous methods have been used to realize the reversible 2W-SME, including fabricating multiphase systems with at least two distinct melting transitions, , using a single phase with a broad melting transition, − postcuring the strained network of dual-cure networks, using polymer laminates, , and inducing self-nucleated crystallization (SNC) of single-component semicrystalline polymer networks . However, most reversible 2W-SMPs are thermosets, which cannot be efficiently reprocessed and recycled for high-value reuse, leading to poor sustainability and economic losses. − In addition, although achieving a permanent shape of thermoset or thermoplastic SMPs by mold processing is straightforward, attaining a sophisticated shape is difficult because of limitations of the molding and demolding processes. , …”

Triple one‐way and two‐way shape memory poly(ethylene‐co‐vinyl acetate)/poly(ε‐caprolactone) immiscible blends

“…The 1W‐SMPs need external reprogramming of the temporary shape for reuse, whereas the 2W‐SMPs are able to automatically repeat shape transformation under the stimulus, which is more desirable for practical applications 18,19 . In recent decades, many polymers have been used to realize the two‐way shape memory effect (2W‐SME), containing poly(ε‐caprolactone) (PCL), 20–22 poly(ethylene‐co‐vinyl acetate) (EVA), 23,24 and poly(cyclooctene) (PCO) 25 . The essence of 2W‐SME is the elongation induced by oriented crystallization upon cooling and the contraction induced by melting upon reheating.…”