Shape-memory polymers

Article By:

Behl, Marc GKSS Research Centre Geesthacht, Institute of Polymer Research, Teltow, Germany.

Lendlein, Andreas GKSS Research Centre Geesthacht, Institute of Polymer Research, Teltow, Germany.

Last reviewed:2008

DOI:https://doi.org/10.1036/1097-8542.YB080140

Shape-memory polymers are an emerging class of actively moving polymers. They are able to respond to a specific stimulus by changing their shape. Shape-memory polymers are different from shape-changing materials. Both polymer concepts are based on elastic polymer networks equipped with molecular switches or stimuli-sensitive domains. The triggering of these switches results in the stimulated movement of the polymers. Shape-changing polymers are able to change their shape as long as they are exposed to a certain stimulus. Once the stimulus is terminated, they recover their original shape. This process of stimulated deformation and recovery can be repeated several times, while the geometry of shape changes is invariant from any alteration and is usually somehow related to the original shape. This is in contrast to shape-memory polymers whose temporary shape can be varied in each cycle. Most known shape-memory polymers are dual-shape materials. They are able to change from a shape A into shape B. While shape B is a permanent shape obtained during the polymer processing, shape A is a temporary shape. The temporary shape is created in a process called programming, in which the sample is mechanically deformed and subsequently fixed. The deformation leading to the temporary shape defines the change of shape. When exposed to an external stimulus, shape-memory polymers recover their permanent shape. This process of programming and recovery can be repeated several times with different temporary shapes in subsequent cycles.

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