Shape-memory polymers represent a promising class of materials that can move from one shape to another in response to a stimulus such as heat. Thus far, these systems are dual-shape materials. Here, we report a triple-shape polymer able to change from a first shape (A) to a second shape (B) and from there to a third shape (C). Shapes B and C are recalled by subsequent temperature increases. Whereas shapes A and B are fixed by physical cross-links, shape C is defined by covalent cross-links established during network formation. The triple-shape effect is a general concept that requires the application of a two-step programming process to suitable polymers and can be realized for various polymer networks whose molecular structure allows formation of at least two separated domains providing pronounced physical cross-links. These domains can act as the switches, which are used in the two-step programming process for temporarily fixing shapes A and B. It is demonstrated that different combinations of shapes A and B for a polymer network in a given shape C can be obtained by adjusting specific parameters of the programming process. Dualshape materials have already found various applications. However, as later discussed and illustrated by two examples, the ability to induce two shape changes that are not limited to be unidirectional rather than one could potentially offer unique opportunities, such as in medical devices or fasteners.active polymer ͉ polymer network ͉ shape-memory polymer ͉ stimuli-sensitive polymer ͉ two-step programming process A rubber band, which is a polymer network, can be elastically deformed and will snap back into its original shape as soon as the external stress is released. Polymer networks in their rubbery state consist of covalently cross-linked flexible polymer chains that are oriented from a coiled state during deformation. The recovery of the original shape is driven by regaining the entropy that was lost when chains were oriented (1). Primarily, the shape of a polymer network is defined by its chemical cross-links (netpoints). Depending on the type of chain segments, different macroscopic domains can be formed having individual transition temperatures (T trans ), like glass transition (T g ) and melting (T m ) temperatures (2). When a polymer network is cooled below a T trans of a specific domain, this domain is solidified and in this way forms physical cross-links. These physical cross-links can dominate the netpoints, so that a new shape can be fixed. In dual-shape materials (3-8), which have found various applications (9-12), this effect is used for temporary fixation of a second shape by deformation of the polymer network and subsequent cooling under stress. The original, memorized shape can be recovered by reheating above T trans .As a structural concept for triple-shape polymers, we selected polymer networks able to form at least two segregated domains. Although the original shape (C) is defined by netpoints resulting from the cross-linking reaction, shapes A and B are created by ...

Triple‐shape polymers can move from a first shape (A) to a second shape (B) and from there to a third shape (C), where both shape changes are induced by temperature increases. This triple‐shape capability is obtained for multiphase polymer networks after application of a complex thermomechanical programming process, which consists of two steps; these steps create shapes (B) and (A), while shape (C) is defined by the covalent crosslinks of the polymer network. Here, the creation of the triple‐shape capability for an AB polymer network system by a simple one‐step process similar to a conventional dual‐shape programming process is reported. The polymer networks are based on poly(ε‐caprolactone) (PCL) and poly(cyclohexyl methacrylate); favorable compositions for obtaining a triple shape effect have a PCL content between 35 and 60 wt%. This finding substantially facilitates handling of the triple‐shape technology and is an important step toward the realization of potential applications in which more than one shape change is required.

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