A Very Simple Strategy for Preparing External Stress‐Free Two‐Way Shape Memory Polymers by Making Use of Hydrogen Bonds

• Published in: Macromolecular rapid communications. 2018-06, Vol.39 (12), p.e1700714-n/a
• Main Authors: Fan, Long Fei, Rong, Min Zhi, Zhang, Ming Qiu, Chen, Xu Dong
• Format: Article
• Language: English
• Subjects: Crosslinking; Crystal structure; Crystallinity; Design criteria; Fabrication; Heat treatment; Hydrogen; Hydrogen bonding; Hydrogen bonds; internal stress provider; Materials selection; Organic chemistry; Polymers; Polyurethane; Polyurethane resins; Recrystallization; Residual stress; reversible shape memory polymers; Shape effects; Shape memory; Temperature dependence
• ISSN: 1022-1336; 1521-3927
• DOI: 10.1002/marc.201700714

Development of two‐way shape memory polymers that operate free of external force remains a great challenge. Here, the design criteria for this type of material are proposed, deriving a novel fabrication strategy accordingly, which employs conventional crosslinked polyurethane (PU) containing crystalline poly(ε‐caprolactone) (PCL) as the proof‐of‐concept material. Having been simply trained by stretching and thermal treatment without additional ingredients and chemicals, the PU is coupled with a two‐way shape memory effect. The core advancement of this study lies in the successful conversion of the inherent hydrogen bond network, which is often the easiest to overlook, into an internal stress provider. The temperature‐dependent reversible melting/recrystallization of the crystalline phases elaborately works with the tensed hydrogen bond network, leading to implementation of the two‐way shape memory effect. An average reversible strain of as high as ≈20% along the stretch direction is obtained through cooperation adjustment of chemical crosslinking density, crystallinity, and concentration of hydrogen bonds. Meanwhile, the highest internal tension offered by the hydrogen bond network is determined to be 0.10 MPa. Owing to the great convenience characterized by material selection, preparation, programming, and application, the current work may open up an avenue for production and usage of the smart material. A two‐way shape memory polymer is prepared by converting the inherent hydrogen bonds of crosslinked crystalline polyurethane into an internal stress provider. The temperature‐dependent reversible melting and recrystallization of the crystalline phases cooperate with the tensed hydrogen bond network, leading to implementation of the smart functionality. The fabrication process is very simple without the aid of additional ingredients and chemicals.