Excellent Shape Memory Performance Research Articles

Superlight flame-retardant poly(aryl ether ketone)/polyurea nanocomposite foam with excellent solvent-resistance and shape memory performance

The preparation of engineering plastic foams with required performances by supercritical CO2 (sc-CO2) foaming method faces to some challenge, such as high foaming temperature and narrow foaming temperature window. In this work, we used polymeric methylene diphenyldiisocyanate (PMDI) as a reactive plasticizer for modifying poly(aryl ether ketone) (PAEK) to significantly reduce foaming temperature and widen foaming temperature window. The PAEK/PMDI blends presented excellent sc-CO2 foaming performance, such as dramatically low foaming temperature and higher expansion ratio. After the sc-CO2 foaming, the PMDI was gradually converted to polyurea (PUA) by introducing water and induce microphase separation process in the cell wall of PAEK/PMDI foams. As a result, PAEK/PUA nanocomposite foams with intrinsic fire-retardancy and heat resistance were formed, in which the nanosized PUA phase was dispersed in the PAEK matrix. The formation of nanostructure in the cell wall through chemical reaction of PMDI with water endowed outstanding performances of PAEK/PUA nanocomposite foams. Compared to the PAEK foam, the PAEK/PUA nanocomposite foam showed superlight and exceptional solvent resistance performance, and also presenting shape memory property at high temperature.

A Triple Shape Memory Material of Trans‐Polyisoprene/Polycaprolactone with Customizable Response Temperature Controlled by Crosslinking Density

AbstractBody‐temperature responsive shape memory polymers (SMPs) attract a lot of attention with the application in biomedicine. Multiple SMPs regulate the response temperature through the proportion of their stationary and reversible phases by changing the molecular weight of the polymer or the components of the composite. Herein, a crosslinking reaction of trans‐polyisoprene (TPI) and polycaprolactone (PCL) initiated by benzoyl peroxide gave a SMP of TPI/PCL, whose shape memory property is realized by stage‐division crystallization zone. Under the fixed ratio of TPI:PCL, the crystallization performance of TPI/PCL is controlled by the crosslinking density. The response temperatures of the components in TPI/PCL are selected for the stage‐division crystallization zone, making excellent shape memory performance at corresponding response temperatures. For the further achievement in controllable response temperature within a certain range, the relationship model between crosslinking density and response temperature is established, obtaining the customizable response temperature ranging 37–55 °C. The presented facile regulation method for response temperature will provide a new idea for the SMPs development.

4D-printing of high-temperature shape-memory polymers based on polyimide, N,N-dimethylacrylamide and photoactive cross-linkers

Thermally responsive shape memory polyimides (PIs) have attracted significant attention in the high-tech fields like aerospace industry. At the same time creating of materials and approaches to the formation of three-dimensional (3D) shape memory structures containing PIs remains an urgent task. In this work we have developed new photopolymeric compositions (PPCs) based on high-performance readily soluble PI, reactive solvent (N,N-dimethylacrylamide) and photoactive cross-linker (bisphenol A ethoxylate diacrylate (BAEDA) or tris[2-(acryloyloxy)ethyl] isocyanurate (TAI)). The resulting PPCs were used to form 3D-structures using LCD 3D-printing. It has been found that the nature of the cross-linker and post-processing temperature have a significant impact on the thermal and mechanical properties of the materials. The tensile strength has the maximum value after the thermal post-curing at 250°С for 1 h (83.3 ± 7.4 MPa and 60.8 ± 4.8 MPa for PPCs with TAI and BAEDA, respectively). Moreover, 4D-printed PI-containing materials exhibit an excellent shape memory performance at recovery temperatures >150 °C, with shape fixity ratio >99% and shape recovery ratio up to 95.6%.

3D printed epoxy/acrylate hybrid polymers with excellent mechanical and shape memory properties via UV and thermal cationic dual-curing mechanism

Fabricating shape memory polymers with complex configurations and high mechanical performance for application as structural materials remains a significant challenge. Here, an epoxy/acrylate hybrid material with remarkable mechanical properties and excellent shape memory performance is fabricated using vat photopolymerization printing technology through photo-thermal dual curing mechanism. The UV-curing component comprises of a polyurethane acrylate and a rigid active diluent to ensure robustness and toughness. Meanwhile, the thermal curing epoxy constituent utilizes a benzylanilinium salt as the cationic initiator for its storage and handling stability throughout the UV curing stage. The interpenetrating polymer network and the unique two-phase molecular microstructure impart the hybrid material with good shape memory and high mechanical properties. Many complex objects are fabricated using vat photopolymerization printing technology and employed in self-deploying antennas, intelligent mechanical grippers, and switches. Combining with excellent printability, mechanical and shape memory properties, the hybrid materials have great potential applications in various fields.

Development, performance research and shape memory multifunctional exploration of epoxy/PEG shape memory nanofibers

To improve the spinnability of thermoplastic epoxy resin and develop epoxy resin-based shape memory nanofiber materials, polyethylene glycol (PEG) was utilized to regulate the properties of thermoplastic epoxy. The process involved the preparation of thermoplastic epoxy/PEG nanofibers using melt-dispersion and electrospinning techniques. The addition of PEG has enabled the electrospinning of the thermoplastic epoxy, with EPP-5 having the smallest average diameter (227 nm) and EPP-10 showing the most uniform morphology. FTIR analysis confirmed sufficient polymerization of epoxy resin. The water contact angle analysis revealed that an appropriate amount of PEG reduced the hydrophilicity of the nanofiber membranes, with the EPP-10 showing a 14.9 ° increase in water contact angle compared to the EPP-5. The mechanical analysis demonstrated that an appropriate amount of PEG improved the nanofibers’ yield stress, breaking strain, and maximum tensile stress. The EPP-10 exhibited a 3.27 MPa increase in yield stress, a 19.54 % increase in breaking strain, and a 1.17 MPa increase in maximum tensile stress compared to the EPP-5. Thermal analysis showed that epoxy/PEG nanofibers decomposed mainly between 400 ℃ and 500 ℃. Thermomechanical analysis revealed a reduction in the Tg of epoxy/PEG films with the addition of PEG, among which the Tg of EPP-25 was 55.1 ℃ lower than that of EPP-0. The epoxy/PEG nanofiber membrane exhibits excellent shape memory performance, among which the EPP-10 exhibits the best shape recovery effect. In addition, the EPP-10 yarn stretched to 160 % of original length recovered within 25 s, and EPP-10 yarn tied in a temporary shape recovered to original shape within 15 s. In conclusion, by modulating the properties of thermoplastic epoxy through PEG, the spinnability of thermoplastic epoxy was achieved, and shape memory epoxy/PEG nanofibers with potential applications in the field of smart textiles were developed.

Large-scale fabrication of superhydrophobic shape memory composite films for efficient anti-icing and de-icing

Ice and snow accretion on outdoor facilities may degrade their functions and reduce their service life. Superwetting materials have been widely studied and present high potential in anti-icing and de-icing applications. However, it remains challenging that the materials cannot prevent and remove the ice accretion spontaneously in harsh conditions. Penguins can freely jump in and out of extremely cold water (−40 °C) without forming macroscopic ice because of the superhydrophobic performance of their flexible feathers. Here, Penguins-inspired superhydrophobic shape memory composite films with unique properties, including lightweight and shape morphing, are fabricated via a two-step method consisting of spraying and peeling processes. It presents good superhydrophobic performance with a large WCA of 152.4 ± 5° and a small WSA of 6 ± 1° in addition to excellent shape memory performance (recovery ratio > 99%) and good mechanical strength. The simple fabrication methods make it possible to produce large-size films at low cost, which is versatile for different applications. Most importantly, the film displays the capabilities of inhibiting freezing, ice, and snow accumulation with improved ice removal efficiency due to the synergetic effects of the superhydrophobic and efficient photothermal activity. Furthermore, its robustness and durability make it a good candidate for industrial applications.

Unexpected super anti-compressive styrene-acrylonitrile copolymer/polyurea nanocomposite foam with excellent solvent resistance, re-processability and shape memory performance

High-performance, recycling and environmental protection are the goal of the development of polymer materials in the future. The introduction of crosslinking and composite are two main ways to improve the comprehensive properties of materials, however, which leads to the non-recyclability of materials or brings difficulties to the recovery process. Here, we report a polymer nanocomposite foam with superior compression properties to most existing commercial foams, just originating from common commercial styrene-acrylonitrile copolymer (SAN) and polyurea (PUA), and develop a green and energy-efficient method to fabricate high-performance rigid foam by reactive plasticizing and reaction induced phase-separation combining with supercritical CO2 (sc-CO2) foaming. Reaction induced phase-separation results in the in-situ formation of nanoscale structure in the cell walls of the resultant foams, in which the crosslinked PUA is the dispersed phase with the size of 10–40 nm in the matrix of SAN. Optimizing crosslinking network structure of PUA dramatically improve the comprehensive performance of SAN/PUA nanocomposite foams. The resultant SAN/PUA nanocomposite foam shows some performance characteristic of thermosetting polymers, such as excellent heat resistance and solvent resistance than the SAN matrix, meanwhile the performance characteristic of thermoplastic polymers, such as re-processability. More interestingly, the SAN/PUA nanocomposite foam presents excellent shape memory performance. With the above exceptional performances, this polymer nanocomposite foam will be a perfect substitute for the existing commercial rigid foams.

Mechanically robust waterborne polyurethane with excellent room temperature self-healing and shape memory performance

Achieving severe damage restoration and the ideal combination of good mechanical properties and healing efficiency are two significant challenges for self-healing materials. In this study, a series of shape-memory, self-healing aqueous polyurethane (SMPU) were synthesized based on the molecular self-assembly design of 5-(2-hydroxyethyl)-6-methyl-2-aminuracil (HMA), 4-aminopyridine (4-APD) and polycaprolactone diol (PCL) moieties. The effects of HMA and 4-APD on mechanical properties, self-healing properties, and shape memory properties of SMPU were investigated. The dynamic crosslinking network generated by quadruple hydrogen bonds and multiple coordination bonds not only consumed strain energy but also promoted rapid re-formation after fracture, resulting in superior self-healing ability (healing efficiency 96.3%), excellent mechanical properties (tensile strength 39.1 MPa and elongation at break 908%) and recyclable capabilities of SMPU. Meanwhile, the SMPU showed a noteworthy shape memory effect; its shape fixation rate and recovery rate could reach 99% and 98%, respectively. The temperature and time dependence of the self-healing process were studied by molecular dynamics (MD), and the self-healing mechanism was clarified further. When SMPU was used for leather finishing, the finished and self-healing samples exhibited excellent wear resistance (wear rating: 4 ∼ 5). These advantageous properties endow SMPU with great potential applied value in leather and other regions.

Interpenetrating shape memory polyimide‐polyaniline composites with electrical conductivity

AbstractShape memory polyimides (SMPI) with adjustable shape recovery temperatures have been paid much attention in both fundamental research and practical applications. However, the intrinsically electrical insulation of SMPIs limits their applications. In this article, the electrically conductive shape memory polyimide‐polyaniline (SMPI‐PANI) composite with interpenetrating networks was synthesized by in situ polycondensation. Compared with pure SMPI, the electrical resistivity of SMPI‐PANI composites reduced by about 12 orders of magnitude when the PANI content was 15 wt%. The addition of PANI had less influence on the glass transition temperature and storage modulus in glassy state. But the storage modulus of SMPI‐PANI composites in rubbery state was over 40 times higher than that of pure SMPI, indicating that SMPI‐PANI composites have higher stiffness during shape recovery. The SMPI‐PANI composites demonstrate excellent shape memory performance with shape fixation ratio higher than 97% and shape recovery ratio higher than 93%. The SMPI‐PANI composites also have good thermal stability with the effective decomposition temperatures higher than 150°C. The SMPI‐PANI composite in our work is a potential material for deployable aerospace structure.

Preparing flame-retardant poly(phenylene oxide)/polyurea nanocomposite foam with excellent heat-resistance and shape memory performance

Superlight polymer foams with excellent heat resistance and flame retardancy are highly expected in many application fields. However, the challenge for preparing polymer foams with the required performances by green method needs to be overcome. Here, using “Plasticizing-Foaming-Reinforcing” (PFR) strategy, we combined poly(phenylene oxide) (PPO) and polyurea (PUA) to fabricate intrinsic fire-retardant PPO/PUA nanocomposite foam with excellent heat resistance and solvent resistance and shape memory. The supercritical CO2 (sc-CO2) foam processing was realized at a much lower temperature, stemming from the fact that the monomer of PUA, polymeric methylene diphenyldiisocyanate (PMDI), acted as a reactive plasticizer for PPO during the foaming process, and the expansion ratio of the resultant PPO/PUA foams was greatly increased. The in-situ formation of nanostructure in the cell wall during the crosslinking of PMDI takes place, in which the PUA is the dispersed phase with 10–40 nm in the matrix of PPO. Compared to the PPO foam and PPO/polystyrene blend foam, the PPO/PUA nanocomposite foam has excellent heat resistance and solvent resistance. Furthermore, the PPO/PUA nanocomposite foam also has excellent shape memory performance at high temperature.

High strength, recyclable and shape memory polyhydroxyurethanes with intrinsic fluorescent properties

AbstractPolyhydroxyurethanes (PHUs), which are synthesized through the aminolysis of cyclic carbonates, avoid the use of toxic isocyanates compared with traditional polyurethanes (PUs) and have aroused great interest. The large number of hydroxyl groups in the network endows PHUs with unique features, such as recyclable properties and fluorescent properties. To establish the high performance and multifunctionality of PHUs, we designed a molecular structure to fabricate PHUs with mechanical robustness, shape memory properties, fluorescent properties, and recyclable properties. The yielded PHU crosslinked by the quaternary thiol and weak but dense hydrogen bonds (H‐bonds) shows unprecedented high mechanical properties with a tensile Young's modulus of 3.13 GPa, comparable to that of polyimide, a tensile strength of 59.2 MPa at room temperature and an excellent toughness of 27.9 MJ/m3 at 50°C, and good damping properties (tanδ ≥ 0.3, temperature range of 35.2°C). Interestingly, fluorescence caused by the aggregation of carbamate within PHUs allows it to be applied for damage self‐reporting to visualize tiny cracks or magnify fractures. Furthermore, both the thermosetting PHUs and recycled thermosetting PHUs presented excellent shape memory performance. This study provides certain inspiration for the design and development of highly rigid multifunctional polymers.

Developing Reprocessable shape memory thermosetting resins with high thermal resistance and strength through building a crosslinked network based on bismaleimide and epoxy resins

AbstractIt is difficult to endow reprocessable shape memory thermosetting resins with outstanding heat resistance and high mechanical strength. Herein, a new kind of reprocessable shape memory thermosetting resins (DBE) are developed through building a crosslinked network based onN,N′‐4,4′‐diphenylmethane bismaleimide (BDM), bisphenol A epoxy resin and 4,4′‐dithiodiphenylamine. The influence of the composition of DBE resins on their structure and comprehensive properties was studied. Results show that DBE resins have multiple phase structures. With the increase of BDM content of DBE resin, the glass transition temperature (Tg), initial thermal decomposition temperature and flexural modulus increase, the impact strength and reprocessing efficiency decrease, while the flexural and tensile strengths increase initially and then decrease. 0.8DBE cannot be reprocessed, while 2DBE, 1.5DBE and 1DBE are reprocessable, and also have good shape reconfiguration and shape memory performances. Among them, 1DBE has the best integrated performance, which has attractively highTg(210°C), high tensile strength (76 ± 3.2 MPa), good reprocessability and excellent shape memory performance, its shape fixation rate and shape recovery rate reach 100% and 99.6%, respectively, overcoming the bottleneck problems of low heat resistance and insufficient mechanical strength of existing reprocessable shape memory thermosetting resins.

A photosensitive composition based on an aromatic polyamide for LCD 4D printing of shape memory mechanically robust materials

High-temperature shape memory polymers (SMPs) draw growing interest from researchers due to their potential as materials for application in the field of high-temperature smart devices. However, in the majority of cases the processing of high-temperature SMPs is limited by fabrication of two-dimensional films. Here, we have prepared a photosensitive composition based on high-performance heat resistant poly-N,N′-(m-phenylene)isophthalamide (MPA) and photosensitive components (N,N-dimethylacrylamide and bisphenol A ethoxylate diacrylate (BAEDA)). It has been shown by IR spectroscopy, that LCD 3D printing followed by post-curing at 150 °C results in the formation of semi-interpenetrating polymer networks, while thermal processing at a temperature ≥200 °C leads to the formation of fully crosslinked structures due to the interaction of NH groups from MPA and acrylic groups from BAEDA via the Michael addition. The post-curing temperature has a significant effect on the thermal and mechanical properties of materials. Thermal post-curing of 3D printed samples at 250 °C for 1 h results in the fabrication of materials with the highest tensile strength (92.4 ± 6.1 MPa), glass transition temperature (148 °C) and thermal decomposition temperature (above 350 °C). Remarkably, MPA-based materials exhibit an excellent shape memory performance at temperatures >150 °C, with fixity ratio (Rf) of 99.7 % and recovery ratio (Rr) of 99.9 %. Moreover, we showed that the glass transition temperature decreased by no more than 1 % after γ-radiation of 200 Gy. In addition, the material maintains a high storage modulus and good shape memory performance after being irradiated, and thus has a great potential in the field of aerospace structural materials.

Shape memory property of polybutylene adipate-co-terephthalate

PurposeThe purpose of this study is to investigate the thermomechanical condition on the shape memory property of Polybutylene adipate-co-terephthalate (PBAT). PBAT is a widely researched and rapidly developed biodegradable copolyester. In a tensile test, we found that the fractured PBAT samples had a heat-driven shape memory effect which piqued our interest, and it will lay a foundation for the application of PBAT in new fields (such as heat shrinkable film).Design/methodology/approachThe shape memory effect of PBAT and the effect of the thermomechanical condition on its shape memory property were confirmed and systematically investigated by a thermal mechanical analyzer and tensile machine.FindingsThe results showed that the PBAT film had broad shape memory transform temperature and exhibited excellent thermomechanical stability and shape memory properties. The shape memory fixity ratio (Rf) of the PBAT films was increased with the prestrain temperature and prestrain, where the highest Rf exceeded 90%. The shape memory recovery ratio (Rr) of the PBAT films was increased with the shape memory recovery temperature and decreased with the prestrain value, and the highest Rr was almost 100%. Moreover, the PBAT films had high shape memory recovery stress which increased with the prestrain value and decreased with the prestrain temperature, and the highest shape memory recovery stress can reach 7.73 MPa.Research limitations/implicationsThe results showed that PBAT had a broad shape memory transform temperature, exhibited excellent thermomechanical stability and shape memory performance, especially for the sample programmed at high temperature and had a larger prestrian, which will provide a reference for the design, processing and application of PBAT-based heat shrinkable film and smart materials.Originality/valueThis study confirmed and systematically investigated the shape memory effect of PBAT and the effect of the thermomechanical condition on the shape memory property of PBAT.

4D printing light-/thermo-responsive shape memory composites based on thermoplastic polyurethane/polylactic acid/polyaniline blends

In this work, a series of polylactic acid/thermoplastic polyurethane/polyaniline (PLA/TPU/PANI) blends with different weight ratios were prepared by Fused deposition molding First, six groups of PLA/TPU (U9A1/U8A2/U7A3/U6A4/U5A5/U4A6) and three groups of PLA/TPU/PANI (821/823/825) with different ratios were fabricated by melt blending. Then, the effects of different filament forming and printing process parameters on print resolution and quality were investigated. Next, printed samples were characterized by Fourier transform infrared (FTIR), Thermogravimetric analysis (TGA), Scanning electron microscopy (SEM) and mechanical experiments. The results of FTIR and TGA showed no chemical reaction between different components, and uniform distribution of the material was observed in the SEM. The tensile and compressive curves of the samples showed an inverted U-shape. Finally, the shape-memory property was evaluated by differential scanning calorimetry. For PLA/TPU blends, U8A2 had the best shape memory capability ([Formula: see text] = 80.8% and [Formula: see text] = 100%). Based on the excellent shape memory performance of PLA/TPU, the addition of PANI can introduce a light-actuated mechanism to form a binary-driven shape memory material. The composite materials prepared in this work can be applied to tissue engineering scaffolds, medical devices, soft robots and so on.

3D biodegradable shape changing composite scaffold with programmable porous structures for bone engineering

This study developed a biodegradable composite porous polyurethane scaffold based on polycaprolactone and polyethylene glycol by sequential in-situ foaming salt leaching and freeze-drying process with responsive shape changing performance. Biomineral hydroxyapatite (HA) was introduced into the polyurethane matrix as inorganic fillers. Infrared spectroscopy results proved a successful synthesis, scanning electron microscopy showed that the scaffold’s porosity decreased with the addition of HA while the average pore size increased. X-ray diffraction and differential scanning calorimetry showed that the addition of HA lowered the melting point of the scaffold, resulting in a transition temperature close to the human body temperature. From the bending experiments, it could be demonstrated that PUHA20 has excellent shape memory performance with shape fixity ratio >98.9% and shape recovery ratio >96.2%. Interestingly, the shape-changing capacity could be influenced by the porous structures with variation of HA content. The shape recovery speed was further accelerated when the material was immersed in phosphate buffered saline at 37 °C. Additionally, in vitro mineralization experiments showed that the scaffold incorporating HA had good osteoconductivity, and implantation assessment proved that scaffolds had good in vivo biocompatibility. This scaffold is a promising candidate for implantation of bone defects.

Thermo-responsive programmable shape memory polymer based on amidation cured natural rubber grafted with poly(methyl methacrylate)

This work proposes a facile and new approach that uses graft copolymerization and amidation reaction to prepare shape memory polymer (SMP) based on natural rubber (NR). The poly(methyl methacrylate) modified NR (MGNR) is cross-linked with diamine through an amidation reaction. In this kind of approach, a novel type of cross-linked MGNR with a three-dimensional network of amide linkage was prepared. The solvent resistance, mechanical properties, and phase morphology of MGNRs were significantly improved after being cross-linked by a diamine cross-linker. Additionally, the cross-linked MGNR40 also exhibited excellent shape fixation and shape recovery. This is a direct result of the vitrification of the grafted PMMA domains at low temperatures, preventing elastic recovery. Meanwhile, a cross-linked network from amide linkage facilitates recovery force upon heating. Hence, the shape memory performance of MGNRs can be tuned with both grafted PMMA content and the degree of diamine cross-link. The strategy in this research work offered an effective and convenient method to obtain cross-linked MGNR with unique molecular architecture. Consequently, this cross-linked MGNR delivered excellent mechanical strength and shape memory performance.

Double-skeleton based shape-stabilized phase change materials with excellent solar-thermal energy conversion and shape memory performance

Polyethylene glycol (PEG) is widely used for thermal energy storage, but its practical application is limited by its strong rigidity, poor shape stability. In this work, a kind of melamine foam/graphene aerogel (MF/GA) double-skeleton was prepared, then PEG was stably encapsulated into MF/GA by vacuum melt impregnation method to obtain MF/GA@PEG shape-stabilized phase change materials (SSPCMs). Structural characterization and performance tests were performed on MF/GA@PEG SSPCMs, including morphological observation, latent heat, thermal conductivity, shape stability, and photothermal conversion capability. The experimental results show that the MF/GA@PEG SSPCMs show high energy storage density (168.3 J/g), good shape stability, shape memory performance and excellent solar-thermal energy conversion capability with a high efficiency of 84.8%, the thermal conductivity of MF/GA@PEG SSPCMs is 161% higher than that of pure PEG. The MF/GA@PEG SSPCMs with comprehensive properties have promising application in solar-thermal energy storage and thermal management in microelectronic devices.

Body-temperature programmable ultra-soft shape memory elastomers for comfort fitting

Shape memory materials can be utilized to realize fast shape customization for personalized comfort fitting experiences. In this paper, a series of body-temperature programmable shape memory elastomers are developed for comfort fitting. Unlike the reported ones, in which the shape switch is realized due to body-temperature phase transition (around 37 °C), these newly developed ones are fabricated with silicone rubber (as elastic component) and a kind of polycaprolactone (PCL, as transition component) that has melting point of about 56 °C and much lower crystallization temperature. The thermal properties, shape memory performances, mechanical behaviors under uni-axial tension at room temperature and at human body temperature (37 °C) are investigated. The specialty of these shape memory elastomers is that the programming is not carried out at around melting point of the transition component. Instead, it could be done upon cooling to 37 °C. The temporary shape is fixed only after completion of PCL crystallization. As the melting point of PCL is much higher (56 °C), the mechanical properties of these shape memory elastomers are ensured rather stable near 37 °C, which eliminates the concern of shaping/fitting failure when ambient temperature fluctuates. Besides, ultra-softness and high stretchability at room temperature are revealed as well. Excellent shape memory performance of these elastomers at 37 °C is also confirmed. The shape fixity ratio is over 90% when PCL content reaches wt% of 35%. In such a way, these elastomers are able to well duplicate the local shapes of human body in actual fitting. Upon reheating to 80 °C, they also can completely recover to their original shapes. The fitting time window at 37 °C is revealed around 5 min, which is rather appropriate in practice. The yielding behaviors during tension and long-term shaping/fitting performance of these elastomers are also discussed. A simple wearable orthotic device for hallux valgus is developed for proof-of-concept. It is concluded that these newly developed shape memory elastomers are well suited candidates for comfort fitting.

Thermadapt shape memory polymers based on thermally induced dynamic covalent quinone methide–thiol click reaction

A novel thermadapt shape memory polymer networks were prepared based on the conjugate addition reaction of quinone methide (QM) end-group-functionalized polycaprolactone and a thiol cross-linker, which can undergo the dynamic exchange reaction under thermal stimulation conditions. The resultant cross-linked polymers possessed excellent elasticity-based shape memory performance, cycle stability and solid-state plastically characteristics under high temperature conditions. This thermal-induced QM-thiol dynamic covalent click chemistry provided an effective method for realizing the solid-state plasticity of the polymers.