Supramolecular Shape Memory Research Articles

Ultra-Highly Stiff and Tough Shape Memory Polyurea with Unprecedented Energy Density by Precise Slight Cross-Linking.

Shape memory polymers (SMPs) have attracted significant attention and hold vast potential for diverse applications. Nevertheless, conventional SMPs suffer from notable shortcomings in terms of mechanical properties, environmental stability, and energy density, significantly constraining their practical utility. Here, inspired by the structure of muscle fibers, an innovative approach that involves the precise incorporation of subtle, permanent cross-linking within a hierarchical hydrogen bonding supramolecular network is reported. This novel strategy has culminated in the development of covalent and supramolecular shape memory polyurea, which exhibits exceptional mechanical properties, including high stiffness (1347MPa), strength (82.4MPa), and toughness (312.7MJm-3), ensuring its suitability for a wide range of applications. Furthermore, it boasts remarkable recyclability and repairability, along with excellent resistance to moisture, heat, and solvents. Moreover, the polymer demonstrates outstanding shape memory effects characterized by a high energy density (24.5MJm-3), facilitated by the formation of strain-induced oriented nanostructures that can store substantial amounts of entropic energy. Simultaneously, it maintains a remarkable 96% shape fixity and 99% shape recovery. This delicate interplay of covalent and supramolecular bonds opens up a promising pathway to the creation of high-performance SMPs, expanding their applicability across various domains.

Continuous liquid interface production of alginate/polyacrylamide hydrogels with supramolecular shape memory properties

A recently developed three-dimensional (3D) gel-printing technology, namely continuous liquid interface production (CLIP), was utilized to fabricate supramolecular shape memory hydrogels with high resolutions and complex 3D geometries. The UV-curable ink for CLIP was composed of hydrogel precursors (alginate and acrylamide) and a photo-initiator (ammonium persulfate). As expected, the double network formed from ionically crosslinked alginate and covalently crosslinked polyacrylamide endowed the printed hydrogels with excellent mechanical properties. Meanwhile, due to the reversible metal-ligand coordination interaction, the hydrogel could be temporarily immobilized into an optional shape after introducing calcium ions and return to its original shapes upon ion removal, exhibiting ion-triggered shape memory effect. Moreover, the presence of ions greatly improved the conductivity of the resultant hydrogels. Such 3D printed versatile hydrogels with complex geometries demonstrated the potential for selected applications, particularly in load-bearing materials and flexible electronic devices.

Novel photo-thermal staged-responsive supramolecular shape memory polyurethane complex

Photo-responsive polymers attracted a great deal of interest in recent years. This paper reports a facile preparation of supramolecular shape memory polyurethane complexes from the pyridine-containing polyurethanes and azobenzene-containing mesogens. The results showed that the azobenzene-containing mesogens are grafted on the polyurethane networks via hydrogen bonds between pyridine rings and carboxyl of mesogens. The addition of azobenzene-containing mesogens greatly affected the intermolecular interactions, increasing the glass transition temperature, thermal stability, and storage modulus while promoting the micro-phase separation. The complexes exhibited multi-shape memory properties and excellent photo-thermal staged-responsive shape memory properties showing photo-responsive deformation, temporary shape fixation under visible light irradiation at room temperature and thermal-responsive shape recovery. Particularly, the photo-deformation was achieved even at 2 wt % mesogens added to the polymer network. However, the photo-response greatly increased when the content of mesogen reached 6 wt%. Finally, the proposed mechanism of photo-deformation revealed that this property is due to the photo-isomerization of azobenzene groups of the mesogens, whereas the shape recovery was ascribed to the thermal-responses of polymer networks. It is thus anticipated that these supramolecular polyurethane complexes could be widely applied in smart devices, photo-thermal sensors, and other fields.

A supramolecular hydrogel with monitorable macro/microscopic shape memory performance.

A supramolecular shape memory hydrogel (SMH) with monitorable shape memory performance both in macro and microscopic scales was prepared through a combination of pH-responsive fluorescent carbon nanoparticles, polyvinyl alcohol and cross-linked polyacrylamide. The investigation of our SMH will provide a good understanding of the shape memory mechanism and guide in the structure design of the novel SMH.

Supramolecular shape memory hydrogels: a new bridge between stimuli-responsive polymers and supramolecular chemistry.

Supramolecular shape memory hydrogels (SSMHs) refer to shape memory polymers, in which temporary shapes are stabilized by reversible crosslinks such as supramolecular interactions and dynamic covalent bonds. Following a brief introduction of the conventional shape memory polymers (SMPs), this tutorial review is focused to summarize the recent advancement in various reversible crosslinks employed to construct SSMHs (supramolecular interactions and dynamic covalent bonds) and different shape memory behaviors (dual and triple shape memory effects). In addition, current challenges and future perspectives in this field are also discussed to suggest a new developing direction.

Stretchable supramolecular hydrogels with triple shape memory effect.

Shape memory polymers based on reversible supramolecular interactions have invoked growing research interest, but still suffer from limitations such as poor mechanical strength and finite shape memory performance. Here, we present a novel mechanical stretchable supramolecular hydrogel with a triple shape memory effect at the macro/micro scale. The introduction of a double network concept into supramolecular shape memory hydrogels endows them with excellent mechanical properties. The design of two non-interfering supramolecular interaction systems of both dynamic phenylboronic (PBA)-diol ester bonds and the chelation of alginate with Ca2+ endues the hydrogel with outstanding triple shape memory functionalities.

Development of supramolecular liquid-crystalline polyurethane complexes exhibiting triple-shape functionality using a one-step programming process

Supramolecular shape memory liquid crystalline polyurethanes showing smectic C properties and exhibiting triple-shape functionality using a one-step programming process are prepared.

Effect of MDI–BDO hard segment on pyridine-containing shape memory polyurethanes

Shape memory polymers are attractive for both science and industrial application. In this article, a series of pyridine-containing supramolecular shape memory polyurethanes (Py-SMPUs) with various diphenylmethane diisocyanate–butanediol (MDI–BDO) contents are synthesized from the 1,6-hexamethylene diisocyanate (HDI), N,N-bis(2-hydroxylethyl) isonicotinamide (BINA), BDO, and MDI. Then, they are investigated systematically using FT-IR, DSC, DMA, WAXD, and shape memory testing. The results show that the addition of MDI–BDO segment improves the strength of hydrogen bonding of Py-SMPUs. It promotes the formation of hard domains, but not influences the phase-separation structure, the intensity, and distribution of physical netpoints. In addition, the MDI–BDO segment improves the rubber modulus and drops the energy loss of Py-SMPUs. However, it does not influence the shape memory behaviors which are mainly influenced by the BINA content. If the BINA content is beyond 30 wt%, good shape memory effect can be achieved in the BINA–HDI–BDO–MDI system; and high shape recovery force can be obtained by increasing the MDI–BDO segment.

Study on the structure and morphology of supramolecular shape memory polyurethanecontaining pyridine moieties

Fabricating smart materials has been an attractive research topic in recent years. In thisstudy, a series of pyridine-containing shape memory polyurethanes (Py-SMPUs) withdifferent pyridine contents were synthesized. Based on the theoretical analysis, thestructure and morphology of Py-SMPUs were studied systematically with FT-IR, DSC,WAXD, DMA, AFM, etc. Results show that a hydrogen-bonded supramolecular structureis formed in the Py-SMPUs. Hydrogen bonds present in the urethane group and pyridinering are the most favorable hydrogen bonds which play an important role in themovement of the polymer chain. Microphase separation consisting of a soft phase andhard phase occurs in the Py-SMPUs. The soft phase is influenced greatly by theN, N-bis(2-hydroxyl ethyl) isonicotinamide (BINA) unit and the hard phase is mainly a result ofthe hexamethylene diisocyanate and 1,4-butanediol (HDI–BDO) units. As the BINAcontent decreases, the soft phase tends to change gradually from a continuousamorphous phase to a droplet-like dispersion phase, whereas the hard phase developsfrom a droplet-like dispersion amorphous phase to a continuous crystalline phase.

A novel supramolecular shape memory material based on partial α-CD–PEG inclusion complex

A novel supramolecular shape memory material was prepared based on partial α-CD–PEG inclusion complex, which contains α-CD–PEG inclusion crystallites as a fixing phase and naked PEG crystallites as a reversible phase. The recovery ratio of these materials could reach 97%. The characteristics of the material were investigated and a mechanism for the shape memory behavior was proposed.