Design strategies for shape memory polymers

Shape memory polymers (SMPs) are polymeric materials capable of recovering from a ‘fixed’ temporary shape to a ‘memorized’ permanent shape upon exposure to an external stimulus. Two structural elements are required for a polymer to exhibit useful shape memory: a network structure that defines the permanent shape (the ‘memory’), and a switching segment that induces a significant change in the mobility of the network chains. Four common strategies based on various chemical/physical principles and with different advantages/disadvantages have been established for the design and preparation of SMPs. A new design strategy, based on the concept of functional composite materials, allows for a greater control over material properties and functions and has shown great promise in designing SMPs for a wide variety of applications.

► Shape memory polymers (SMPs) are capable of undergoing controlled shape changes upon exposure to an external stimulus.
► The two required structural elements of SMPs are (1) a network structure, and (2) a switching segment.
► Depending on the natures of network structure and switching mechanism, SMPs can be categorized into four main classes.
► Four common design strategies have been established to prepare SMPs.
► A new composite design strategy can be implemented to design SMPs with well-controlled properties and functions.