Material scientists predict a prominent role in the future for self‐repairing and intelligent materials. Throughout the last few years, this concept has found growing interest as a result of the rise of a new class of polymers. These so‐called shape‐memory polymers by far surpass well‐known metallic shape‐memory alloys in their shape‐memory properties. As a consequence of the relatively easy manufacture and programming of shape‐memory polymers, these materials represent a cheap and efficient alternative to well‐established shape‐memory alloys. In shape‐memory polymers, the consequences of an intended or accidental deformation caused by an external force can be ironed out by heating the material above a defined transition temperature. This effect can be achieved because of the given flexibility of the polymer chains. When the importance of polymeric materials in our daily life is taken into consideration, we find a very broad, additional spectrum of possible applications for intelligent polymers that covers an area from minimally invasive surgery, through high‐performance textiles, up to self‐repairing plastic components in every kind of transportation vehicles.

Significant advances have recently been made in the development of functional polymers that are able to undergo light‐induced shape changes. The main challenge in the development of such polymer systems is the conversion of photoinduced effects at the molecular level to macroscopic movement of working pieces. This article highlights some selected polymer architectures and their tailored functionalization processes. Examples include the contraction and bending of azobenzene‐containing liquid‐crystal elastomers and volume changes in gels. We focus especially on light‐induced shape‐memory polymers. These materials can be deformed and temporarily fixed in a new shape. They only recover their original, permanent shape when irradiated with light of appropriate wavelengths. Using light as a trigger for the shape‐memory effect will extend the applications of shape‐memory polymers, especially in the field of medical devices where triggers other than heat are highly desirable.

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.

Degradable polymers having a thermally induced shape memory can be fixed in a new, temporary shape after they have been processed into a permanent shape. They have great potential for biomedical applications, especially in the area of minimally invasive surgery. [1] One example is the insertion of a bulky medical device in a compressed temporary shape through a small surgical incision. When the implant is heated above a switching temperature (T trans ), it returns to its application-relevant permanent shape. After a given time the device degrades, and a second surgery for its removal is not necessary. [2,3] Shape-memory polymers generally consist of two components: cross-links determining the permanent shape and switching segments fixing the temporary shape at temperatures below T trans . Cross-linkage can be achieved either by physical interaction (e.g., in thermoplastic polymers) or by chemical bonds (e.g., in thermosets or photosets). In covalently cross-linked shape-memory polymer networks a maximum weight content of switching segments is possible. In constrast, thermoplastic materials must contain a sufficient amount of hard-segment-determining blocks so that a sufficient number of physical cross-links exist at temperatures above T trans . [4] The blocks that determine the switching segment may display T trans as either a melting temperature or a glass transition temperature. In biodegradable shape-memory polymers previously described as thermoplastic multiblockcopolymers [3] or photoset AB polymer networks [2,5] T trans is the melting point of crystallizable oligo(e-caprolactone) segments. Hydrogels with hydrophobic and crystallizable side chains as molecular switches also can show a thermoresponsive one-way shape-memory effect. [6] Based on noncrystallizable switching segments, completely amorphous shape-memory polymer networks having a glass transition temperature as T trans can be designed. These networks are transparent, and they should show a more