Two-Way Shape Memory Polymers: Evolution of Stress vs Evolution of Elongation

• Published in: Macromolecules Vol. 54; no. 12; pp. 5838 - 5847
• Main Authors: Murcia, Andrés Posada, Gomez, Juan Manuel Uribe, Sommer, Jens-Uwe, Ionov, Leonid
• Format: Journal Article
• Language: English
• Published: American Chemical Society 22.06.2021
• Subjects: crosslinking; crystallization; drugs; evolution; fabrics; nanomedicine
• ISSN: 0024-9297; 1520-5835; 1520-5835
• DOI: 10.1021/acs.macromol.1c00568

Stimuli-responsive polymers are a subject of numerous studies in recent decades due to its variety of possible applications ranging from nanomedicine, drug delivery systems, biosensing, to smart textile development and aerospace engineering. The current demand of reliable and easy-programmable polymeric-actuating components underlines the necessity to understand the mechanism that governs the actuation of materials. This work sheds new light on the understanding of the two-way shape memory effect (2W-SME) of cross-linked semicrystalline polymers. We investigated and compared melting/crystallization of cross-linked polycaprolactone under constant stress and constraint strain conditions. We observed three regions of behavior upon cooling: rubbery, semicrystalline, and an intermediate one associated with entropic softening of the network prior to crystallization. Based on obtained observations, we proposed possible mechanisms for the processes occurring in cross-linked polymers upon their crystallization/melting and quantitatively investigated the effects of applied stress, elongation, and cross-linking density to allow programmable design of reversible actuators.