Structurally dynamic polydisulfide networks that inherently exhibit both shape-memory and healable properties have been synthesized. These materials are semicrystalline, covalently cross-linked network polymers and as such exhibit thermal shape-memory properties. Upon heating above its melting temperature (T m) films of the material can be deformed by a force. Subsequent cooling and removal of the force result in the material being “fixed” in this strained temporary shape through a combination of crystallinity and covalent cross-links until it is exposed to temperatures above the T m at which point it recovers to its remembered processed shape. The incorporation of disulfide bonds, which become dynamic/reversible upon exposure to light or elevated temperatures, into these networks results in them being structurally dynamic upon exposure to the appropriate stimulus. Thus, by activating this disulfide exchange, the network reorganizes, and the material can flow and exhibit healable properties. Furthermore, exposure to light also allows the film’s permanent “remembered” shape to be reprogrammed. Shape-memory experiments on these films show high degrees of both fixing and recovery (>95%), and photohealing experiments showed that the films were able to recover from a scratch whose depth is approximately half the thickness of the film. Using a combination of the thermal shape-memory behavior followed by photohealing allows wide scratches to also be efficiently healed.

A shape-memory adhesive has been prepared that exhibits two levels of reversible adhesion. The adhesive is a semicrystalline cross-linked polymer that contains dynamic disulfide bonds. Melting of the crystalline regions via heat causes a drop in the modulus of the material facilitating wetting of the substrate as well as enhancing the surface contact area with the substrate, which result in the formation of an adhesive bond. Exposure to higher heat or UV light results in dynamic exchange of the disulfide bonds, which yields a further drop in the modulus/viscosity that improves surface wetting/contact and strengthens the adhesive bond. This improvement in adhesion is shown to apply over different substrates, contact forces, and deformation modes. Furthermore, the adhesive acts as a thermal shape-memory material and can be used to create joints that can reposition themselves upon application of heat.

A liquid crystalline elastomer incorporating a mesogenic derivative of the 2,6-bisbenzimidazolylpyridine (Bip) ligand has been prepared, and its shape memory and actuating properties have been studied. The reversible liquid crystal to isotropic transition is utilized as the switching mechanism for these stimuli-responsive materials. As such, this material exhibits soft shape memory; that is, flexibility is retained in both the permanent and temporary shapes. In addition to the thermal shape memory/actuating properties exhibited by most liquid crystalline elastomers, the incorporation of the metal ion-binding Bip mesogen into the backbone of the network imparts both (i) photoresponsive properties, via a photothermal conversion process, and (ii) metal-ion-triggered shape recovery/actuation to the material. For the latter process, it is proposed that the metal-binding event induces liquid crystalline to isotropic transition in this material at room temperature, resulting in actuation/recovery of the permanent shape.

Application of shear stress at the surface of a block copolymer thin film has been shown to substantially orient the microdomains in the direction of the applied shear. The present work systematically examines the influence of key material, film, and process parameters on this alignment behavior using a series of cylinder-forming polystyrene−poly(n-hexyl methacrylate) copolymers. A parallel plate rheometer applies a radially dependent stress gradient to the film's surface through a viscous nonsolvent overlayer. The degree of alignment is assessed using atomic force microscopy and examined as a function of the applied stress. To quantitatively compare the alignment process across different block copolymer films, a melting− recrystallization model is fit to the data, which allows for the determination of two key alignment parameters: the critical stress needed for alignment and an orientation rate constant. For films containing a monolayer of cylindrical domains, as polystyrene weight fraction or overall molecular weight increases, the critical stress increases moderately, while the rate of alignment drastically decreases. As the number of layers of cylinders in the film increases, the critical stress decreases modestly, while the rate remains unchanged. Substrate wetting condition has no measurable influence on alignment response over the range of conditions investigated. Collectively, these results provide useful quantitative rules that enable predictions of the level of alignment which will occur under particular shearing conditions.

Thermoresponsive shape-memory polymer aerogels have been produced from thiol–ene networks of 1,6-hexanedithiol, pentaerythritol tetrakis­(3-mercaptopropionate), and triallyl-1,3,5-triazine-2,4,6-trione. The thiol–ene networks form organogels with either acetonitrile or acetone as the solvent, which can be subsequently removed using supercritical CO2 extraction. The resulting aerogels have nearly quantitative shape fixing and shape recovery with a glass transition temperature ranging from 42 to 64 °C, which serves as the thermal transition trigger for the shape-memory effect. The aerogels have a porosity of 72% to 81% but surface areas of only 5–10 m2/g.