Shape memory polyurethanes cross-linked by surface modified silica particles

Thermoresponsive polyurethane (PU)-silica nanocomposites were synthesized by incorporating silica particles as multifunctional cross-linkers into the PU via sol-gel reactions. At 2 wt% silica, the composites showed over 99% shape fixity and shape recovery up to the 4th thermomechanical cycle along with outstanding mechanical properties in their rubbery as well as glass state. The incorporated nano-sized silica particles gave dual effects of multifunctional chemical cross-links and reinforcing fillers. The properties were favorably compared with those of uncross-linked PU and conventionally cross-linked PU.