Polymeric triple-shape materials

Abstract

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 ...

Mechanisms of the Shape Memory Effect in Polymeric Materials

“…The concept of polymeric composite, in which two or more layers of polymers with different transition temperatures, provides an alternative to achieve the multiple-SME [32]. By means of having two transition components with different transition temperatures, instead of having only one as in most of previous studies, in 2006, Professor Lendlein's group demonstrated a convenient approach to achieve the triple-SME [107]. In 2010, Dr. Xie demonstrated that a polymer with a broad transition temperature range can be programmed to have more than one intermediate shape [108].…”

Design of Triple-Shape Memory Polyurethane with Photo-cross-linking of Cinnamon Groups

“…For example, Lendlein reported that crosslinked poly(ε-caprolactone), which contained polyethylene glycol (PEG) as side chains (CLEG), could be inserted into the body as a removable stent used a compressed shape A, and when placed at a requisite position, the stent could be recovered to shape B, lastly it could contracted to shape C under the external stimulus for easy to remove. 24 Furthermore, future desired SMP devices will require multifunction, which includes multi-stimuli shape memory, triple shape memory, two-way SMP, and more. 25 SMPU based on poly(ε-caprolactone) (PCL) is a representative SMP.…”

Thermal Responsive Shape Memory Polymers for Biomedical Applications

“…Conventional SMPs are designed to memorize only one permanent shape that corresponds to the most relaxed state of the switching segments, exhibiting the so-called dual-shape memory effect. The first example of triple-shape memory effect was reported by Bellin et al where two types of polymeric chains with discrete transition temperatures were incorporated within a crosslinked network (Bellin, 2006). One of the polymer networks containing poly(ε-caprolactone) (PCL) segments and poly(cyclohexyl methacrylate) (PCHMA) segments, named MACL, exhibited a T m around 50 ºC and a T g around 140 °C.…”