Shape memory polymer


A resin that can recover its primary shape after being deformed when it is heated or receives any other stimuli.

To have the shape memory property, a resin has to have mixed domains of the bridged or partially crystallized fixed phase and the reversible phase. Memorizing and restoring a shape takes the following steps: The resin is kept above a specific temperature to soften both the fixed and reversible phases. Then, holding the resin in one shape (primary shape), temperature is lowered to freeze the fixed phase while the reversible phase is kept soft, thereby storing memory of the primary shape. Then the resin is deformed to another shape (secondary shape) by external force, and cooled further to freeze the reversible phase and keep the secondary shape. In this state, the secondary shape is retained even the external force is removed. The stored primary shape is restored if the resin is heated to the temperature at which only the reversible phase softens. Since restoration shape is enabled by softening by heat, the generated force is limited. Some resins recover shape not by heat but by changes in pH, electrical stimuli, or light stimuli. Shape memory resins are made of polyester, polyurethane, styrene butadiene, polynorbornane, transpolyisoprene, and so on.


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