Tunable Temperature Memory Effect of Photo-Cross-Linked Star PCL–PEG Networks

In this study, we synthesized one type of biocompatible and biodegradable cross-linked star poly(epsilon-caprolactone) poly(ethylene glycol) (c-4sPCL-PEG) with an excellent temperature memory effect (TME) by photo-cross-linking of cinnamon group terminated four arms poly(epsilon-caprolactone) (4sPCL-CA) and cinnamon group terminated poly(ethylene glycol) (PEG CA) through the irradiation of 365 nm ultraviolet (UV) light. The results of differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) demonstrated that the c-4sPCL PEG networks possessed a broad transition temperature region from 20 to 55 degrees C, which including a wide high elasticity transition region and a melting transition region. A remembered temperature in this temperature range, which is close to body temperature, could be gained by adjusting the deformed temperature (T-d). Moreover, the TME could be tuned by simply changing the molecular weight or the content of PCL segment. The mechanism of the TME was investigated in detail for the first time with X-ray diffractometry (XRD) and two-dimensional infrared correlation spectroscopy (2D-FTIR) at different temperatures, and the results indicated that the TME was resulted from a change in partial crystallization of the star cross-linked polymer networks, which led to the wide transition temperature. The study provides a facile strategy toward the design and engineering of a promising smart material for applications in the field of smart biomedical devices.