Elementary molecular processes that govern the chemical stimulation of a polyurethane-based shape memory polymer

Abstract

After programming, polyurethanes like ESTANE ETE 75DT3 (SMP-E) show chemically triggered one-way shape memory effect (1WE). When small molecules enter the polymer, weakening the hydrogen bonds between the SMP-E macromolecules and reducing TSWITCH below the environmental temperature. Herein, we investigate how three alcohols—methanol, ethanol and 1-propanol—perform in chemically actuating the 1WE in SMP-E. Weight gain studies show that a smaller size molecule more rapidly saturates SMP-E. The results from mechanical spectroscopy show that TSWITCH decreases with increasing alcohol molecular concentrations, independent of their chemical nature. In line with these findings, all three alcohols show the same amount of shape recovery, which is the fastest when using the smallest methanol molecule for chemical actuation. Infrared spectroscopy helps to identify the mechanism responsible for the decrease in TSWITCH during chemical exposure. Small alcohol molecules interrupt hydrogen bonds between macromolecular chains attaching to C=O groups and creating free NH groups.