Co-extruded multilayer shape memory materials: Comparing layered and blend architectures

Shape memory polymers (SMPs) are a class of materials that exhibit the ability to form multiple temporary shapes, with shape change most often occurring upon exposure to heat. Applications of SMPs can be found in many areas such as sensors, packaging, smart fabrics, and most commonly medicine. Often, thermoplastic SMPs are based on block copolymer or blend morphologies that create two distinct phases, which are on the nano- or micro-scale respectively, to facilitate shape fixing and shape recovery. Forced assembly multilayer co-extrusion of commercially available polyurethane (PU) and polycaprolactone (PCL) polymers was used to create a continuous periodic alternating layer architecture that exhibits shape memory behavior. Similar shape memory properties were observed between PU/PCL layers and blends at 50/50 volume composition; however, offset compositions showed significantly different behavior. The layered structure was maintained across all compositions, as compared with blends that exhibit a composition dependent morphology. The difference in morphology was directly attributed to the difference in shape memory behavior observed between layered and blend films with domain sizes on the micro-scale.