Novel two-way multiple shape memory effects of olefin block copolymer (OBC)/polycaprolactone (PCL) blends

Abstract

The shape memory properties of olefin block copolymer (OBC)/polycaprolactone (PCL) crosslinked blends at different blend compositions were investigated. This is the first OBC-based two-way shape memory blends processes without external load under thermal and vapor stimuli. The deformation temperature of 80 °C was selected far away between the respective melting temperatures of PCL (56.5 °C) and OBC (110.3 °C) for the thermo-triggered two-way multiple shape memory behavior. The internal stress developed between the unmelted OBC crystalline region and crystallized PCL during cooling under pre-strain conditions played an important role in further melting-induced contraction and cooling-induced elongation without external load, even though the deformation temperature caused the complete melting of the crystalline region of PCL and the crystallinity of unmelted OBC was very small. As for the solvent vapor-triggered cases, the THF and n-hexane solvents were used. The bent sample shrank in response to the vapor stimulation, followed by expanding in the air. The blends remarkably showed rare solvent vapor-triggered reversible shape memory behavior without any external stress and pre-soaking treatment. This interesting finding was not reported earlier until now, to the best of our knowledge. This current finding unveils numerous possibilities to prepare multi-triggered blending systems with reversible shape memory behavior.