Design of Multistimuli-Responsive Shape-Memory Polymer Materials by Reactive Extrusion

Shape-memory polymers (SMPs) are a class of stimuli-responsive materials that have attracted tremendous attention in various applications, especially in the medical field. While most SMPs are thermally actuated, relating to a change of thermal transition (e.g., melting temperature), SMPs that can be actuated upon exposure to light are emerging. Recently, there has been new interest into multiple stimuli-responsive SMPs in order to cover the range of applications for these smart materials. In this work, poly­(ester-urethane)­s (PURs) made of heating-responsive poly­(ε-caprolactone) (PCL) segments of various degrees of crystallinity and photoresponsive N,N-bis­(2-hydroxyethyl) cinnamide (BHECA) monomer were successfully prepared using reactive extrusion technology to design dual-stimuli-responsive SMPs (DSRSMP). In order to tune the SMP properties (temperature or light), the crystallinity of the PCL segment was finely adjusted by the copolymerization of ε-caprolactone with para-dioxanone in bulk at 160 °C using tin­(II) octoate. The resulting polyester segments were then coupled with BHECA using n-octyl diisocyanate at 130 °C. The SMP properties of resulting PURs were correlated with DSC and DMTA measurements. Further addition of di- and tetracinnamate PCL segments into these SMPs was also studied in order to enhance the photoactuated SMP properties.