Multi-shape Memory Effect Research Articles

Chemically-crosslinked zwitterionic polyurethanes with excellent thermally-induced multi-shape memory effect and moisture-induced shape memory effect

In this contribution, shape memory polymers (SMPs) of chemically-crosslinked zwitterionic polyurethanes (CZPUs) were fabricated by crosslinking of the N,N-bis(2-hydroxyethyl) isonicotinamide (BINA)/hexamethylene diisocyanate (HDI) polyurethanes system by using pentaerythritol (PER), followed by zwitterionization with 1, 3-propanesultone (PS). As the zwitterionic units increased, it was found that the glass transition of hard phase in CZPUs remains constant while that of soft phase shifted at lower temperature, and a broad glass transition was obtained. The broad glass transition enables CZPUs to display triple, quadruple, and quintuple shape memory behaviours. Meanwhile, due to the chemically-crosslinked structure, the CZPUs exhibited an excellent shape fixation and recovery. Furthermore, the CZPU also exhibited good moisture-induced shape memory effect (SME) with a fast and high shape recovery observed below 70% RH and at 37 °C. The excellent thermally-induced multi-shape memory effect and moisture-induced shape memory effect enable CZPUs to be applied as smart materials for many applications among them the biomedical fields.

A multi-branch thermoviscoelastic model based on fractional derivatives for free recovery behaviors of shape memory polymers

A multi-branch thermoviscoelastic model based on fractional derivatives is proposed for the prediction of temperature-dependent free recovery behaviors of amorphous shape memory polymers (SMPs). The model is similar to the generalized fractional Maxwell model, which gives an approximation of the temperature-dependent storage modulus, loss modulus and loss factor by introducing the shift factor, usually derived from time-temperature superposition of isothermal data obtained at different temperatures. The simulation results show a satisfactory agreement with the experimental free recovery curves from shape memory tests. Moreover, this method is also proved valid for the triple-shape memory effect and multi-shape memory effect of shape memory polymers. In addition, it is an effective approach for the prediction of free recovery behaviors of the SMP-based syntactic foam consisting of hollow glass microspheres dispersed in a shape memory polymer matrix. The application of the fractional derivatives to the thermoviscoelastic constitutive model can effectively reduce the number of the required parameters while give an accurate prediction of viscoelastic behaviors and free recovery behaviors of SMPs.

Stereocomplexed and Homochiral Polyurethane Elastomers with Tunable Crystallizability and Multishape Memory Effects.

Design of the polymer networks with tunable mechanical properties and multishape memory effects (multi-SMEs) is highly desired in the engineering applications. Herein, we report on the stereocomplexed and homochiral polyurethane (PU) elastomers with tunable multi-SMEs by cross-linking the triblock prepolymers bearing the poly(l-lactic acid) (PLLA) and poly(d-lactic acid) (PDLA) enantiomeric segments. The homochiral PU is nearly amorphous, yet the stereocomplexed PU becomes highly crystalline due to the stereocomplexation of enantiomeric segments. Moreover, the two distinct thermal (glass, melting) transitions of PLLA (or PDLA) segments in PUs are integrated to realize the thermally induced triple- and quadruple-SMEs. Control over the enantiomeric segmental ratios allows the feasible manipulation of crystallizability, mechanical and thermal properties, and multi-SMEs of PUs.

A Facile and General Approach to Recoverable High-Strain Multishape Shape Memory Polymers.

Fabricating a single polymer network with no need to design complex structures to achieve an ideal combination of tunable high-strain multiple-shape memory effects and highly recoverable shape memory property is a great challenge for the real applications of advanced shape memory devices. Here, a facile and general approach to recoverable high-strain multishape shape memory polymers is presented via a random copolymerization of acrylate monomers and a chain-extended multiblock copolymer crosslinker. As-prepared shape memory networks show a large width at the half-peak height of the glass transition, far wider than current classical multishape shape memory polymers. A combination of tunable high-strain multishape memory effect and as high as 1000% recoverable strain in a single chemical-crosslinking network can be obtained. To the best of our knowledge, this is the first thermosetting material with a combination of highly recoverable strain and tunable high-strain multiple-shape memory effects.

Conductive multi-shape polymer composites towards stimuli sensing

Electrically conductive polymer composites were exploited to response stimuli based on multi-shape memory effect. Silver nanowires (AgNWs) network was embedded into a shape memory polymer blend possessing two discrete melting transition temperatures. The composites exhibited sequential triple shape recovery behaviors under the heat stimulation. Electro-mechanical measurements disclosed that the conduction varied along with the shape changes. Particularly, the influence of the compositions and stretching percentages on the electric/shape recovery was disclosed. The underlying morphology and microstructure evolutions were investigated. It is unprecedented to achieve the different temperatures sensing by one conductive polymer composite. The findings may greatly benefit the intelligent polymers in the multi-functional flexible electronics.

Fe3+-, pH-, Thermoresponsive Supramolecular Hydrogel with Multishape Memory Effect

Poor, nontunable mechanical properties as well as finite shape memory performance pose a barrier to shape memory hydrogels to realize practical applications. Here, a new shape memory hydrogel with tunable mechanical properties and multishape memory effect was presented. Three programmable reversible systems including PBA-diol ester bonds, AAc-Fe3+, and coil-helix transition of agar were applied to memorize temporary shapes and endow the hydrogel with outstanding multishape memory functionalities. Moreover, through changing the cross-linking densities, the mechanical properties of the as-prepared hydrogel can be adjusted.

Polyolefin Thermoplastics for Multiple Shape and Reversible Shape Memory.

This work reports the first pure hydrocarbon thermoplastic polyolefin material with reversible shape memory effect under stress-free or very small external loading condition. A thermoplastic ethylene/1-octene diblock copolymer with designed chain microstructure was synthesized. The polyolefin material performed not only the conventional one-way multishape memory effects, but also a two-way reversible shape memory effect (RSME). The elongation and contraction induced by oriented crystallization with heating was confirmed as the mechanism of RSME without chemical cross-linking. This work demonstrated that the thermoplastic reversible shape memory could be achieved through careful design of chain microstructure, based on sole hydrocarbon materials such as ethylene-1-octene copolymer.

Multi-shape memory effect of polyimides with extremely high strain

Polyimides exhibited high strain and multi-shape memory properties with the synergistic effects of physical and chemical crosslinks.

Multishape and Temperature Memory Effects by Strong Physical Confinement in Poly(propylene carbonate)/Graphene Oxide Nanocomposites.

The importance of filler-matrix interactions is generally recognized for mechanical property enhancement; their direct impact by physical confinement on diverse functional properties has remained poorly explored. We report here our effort in achieving versatile shape memory performances for a biodegradable poly(propylene carbonate) (PPC) matrix containing high contents of graphene oxide (GO). The excellent dispersion in the entire filler range (up to 20 wt %) allows precise morphological tuning, along with physical filler-matrix interactions, contributing overall to a strong nanoconfinement effect that positively affects the thermomechanical properties of nanocomposites. Only one glass-transition temperature (Tg) of PPC is detected when the GO content is below 10 wt %, corresponding to a slightly confined system, whereas two distinct Tg's are observed with a GO content over 10 wt %, corresponding to a highly confined system. As such, a tunable multishape memory effect can be achieved simply by tuning the filler contents. A dual-shape memory effect (DSME) is observed for a slightly confined system, whereas a triple-shape memory effect (TSME) can be achieved by deformation at two distinct Tg's for a highly confined system. More importantly, it is interesting to find that the switch temperature (Tsw) evolves linearly with the programing temperature (Tprog) for both slightly and highly confined systems, with Tsw ≈ Tprog for a highly confined system but Tsw < Tprog for a slightly confined system. Our work suggests a highly flexible approach to take advantage of the strong nanoconfinement effect by tuning the content of GO within a single polymer to access versatile SMEs, such as DSME and TSME, and the temperature memory effect.

Flexible Material Based on Poly(lactic acid) and Liquid Crystal with Multishape Memory Effects

Construction of novel multishape memory materials from biobased polymers is of particular interest in recent years. Herein, a series of linear poly(lactic acid) (PLA)-based copolymers containing a smectic liquid crystal in the main-chain are designed and synthesized, of which the molecular structures are confirmed by NMR and GPC analyses. By introducing the liquid crystal, poly[4,4′-bis(6-hydroxyhexyloxy) biphenyl phenylsuccinate] (PBDPS), the brittleness of PLA is overcome, and flexible materials are successfully prepared. Relying on the crystallization of PLA as well as the π–π interaction that originated from PBDPS, the copolymers exhibit excellent thermoinduced triple- and quadruple-shape memory behaviors with high shape fixation and recovery ratios. Taking advantage of these features, the multishape memory polymers can bring more chances for versatile applications.

Shape memory polymeric materials based on aliphatic polyesters

Shape memory polymers (SMPs) have the capacity of memorizing a temporary shape and recovering their initial shape in response to various external stimuli. As one of promising class of intelligent materials, it has attracted great attention because of its potential applications in many areas, such as biomaterials and biotechnology, automotive industry, and aerospace field. Aliphatic polymers play an important role in the molecular design of SMPs owing to its excellent biodegradability and biocompatibility, and suitable thermal transition temperature range. This review focuses on the recent progress of shape memory polymers based on the aliphatic polyesters such as poly(lactic acid) (PLA), poly ( p -dioxanone) (PPDO), poly(butylene succinate) (PBS), poly( ω -pentadecalactone) (PPDL) and poly( ɛ -caprolactone) (PCL) and so on. From the view of architecture design, different systems are classified by block copolymers, crosslinking networks and interpenetrating networks. The influence of architectural features on the shape memory behaviors is also discussed. The block copolymers have been identified a typical mature system in design of dual-shape material, and the crystalline aliphatic polyesters can be served as the netpiont or the molecular switch in a SMP, depending on its transition temperature range among the binary systems. The thermoplastic feature of block copolymers endows an easy processibility. The various architectures of crosslinking network meet the increasing demand of SMPs design. Constructing network with crystallizable polyester segment such as PCL may achieve SMPs in one-way and two-way mode, and the stress-free two-way mode can also be realized by an elaborate architecture with pre-programed treatment. Embedding two segments in one network may achieve a triple-shape memory effect, meanwhile, incorporating two segments in an interpenetrating polymer network may result in a triple-shape material with improved performance. Recently, the SMPs based on dynamic networks become the new trend, which may combine the self-healing with shape memory effect in one system, and both dynamic covalent bond and non-covalent bond have been concerned. In order to fulfill the increasing requirement of application, the SMPs with multi-shape memory effect, multi-responsibility and multi-functionality are highly expected.

Multi-shape active composites by 3D printing of digital shape memory polymers.

Recent research using 3D printing to create active structures has added an exciting new dimension to 3D printing technology. After being printed, these active, often composite, materials can change their shape over time; this has been termed as 4D printing. In this paper, we demonstrate the design and manufacture of active composites that can take multiple shapes, depending on the environmental temperature. This is achieved by 3D printing layered composite structures with multiple families of shape memory polymer (SMP) fibers – digital SMPs - with different glass transition temperatures (Tg) to control the transformation of the structure. After a simple single-step thermomechanical programming process, the fiber families can be sequentially activated to bend when the temperature is increased. By tuning the volume fraction of the fibers, bending deformation can be controlled. We develop a theoretical model to predict the deformation behavior for better understanding the phenomena and aiding the design. We also design and print several flat 2D structures that can be programmed to fold and open themselves when subjected to heat. With the advantages of an easy fabrication process and the controllable multi-shape memory effect, the printed SMP composites have a great potential in 4D printing applications.

Multi‐stimuli responsive shape memory polymers synthesized by using reaction‐induced phase separation

ABSTRACTThermo‐induced multishape memory polymers are a growing focus of smart materials because of its promising applications. Multishape memory effect is generally attained by using polymers with broad phase transition and multiphase polymers. The latter is of particular interest for copolymerization and polymer compositing. One requirement has to be fulfilled to achieve multishape memory effect, which is to have two reversible phase transitions. In this study, we report synthesis of polymer composite composed of strong segregated polymers by using reaction‐induced phase separation. We demonstrate the method by using polyurethane (PU) and poly(methacrylic acid) (PMAA). With adjusting the weight ratio, the polymer composites exhibit a phase spectrum from phase separation to miscible composite. The composite with PU/PMAA =3:1 demonstrated triple‐shape memory effect. Based on the results, we argued the effect of segregation on the shape memory effect for polymer composites. With the addition of PMAA, the polymer composite also exhibits pH/water‐induced shape memory effect. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43534.

Pyridine type zwitterionic polyurethane with both multi-shape memory effect and moisture-sensitive shape memory effect for smart biomedical application

The pyridine type zwitterionic SMPUs have thermal-induced dual-SMEs, triple-SMEs and quadruple-SMEs, and moisture-sensitive SMEs. Zwitterionic segments improve the biocompatibility of pyridine containing SMPUs.

Digital manufacture of shape changing components

In this paper, we demonstrate the feasibility of controlling the shape changing sequence of shape memory polymers created from digital manufacturing by exploiting multi-shape memory effects. We create shape memory polymer components with precise architectures by 3D printing. After subjecting them to model-based thermomechanical programming steps, the components assume specified configurations in a precisely controlled shape changing sequence. The use of the 3D printing technique enables the digital manufacturing route with the advantages of easy implementation, large design freedom, and high printing resolution of shape memory polymer components. The results in this paper provide a method for precisely controlling the shape recovery profile and enabling the manufacture of devices with complicated geometries and unprecedented multifunctional performance.

Development of zwitterionic copolymers with multi-shape memory effects and moisture-sensitive shape memory effects.

Shape memory polymers (SMP) and zwitterionic polymers both have great applications in biomedical fields. This works successfully combines functionalities of zwitterionic polymers and SMP, developing new kind of zwitterionic copolymers having a multi-shape memory effect (SME) and a moisture-sensitive SME. The results demonstrate that a series of zwitterionic multi-SMPs, coded as p(DMAPS-co-AA), were synthesized from DMAPS and acrylic acid (AA). A micro-phase separated structure is formed in the resulting p(DMAPS-co-AA). The strong hydrogen bonding between AA segments serves as a reversible switch, while the strong electrostatic forces among DMAPS segments serve as physical crosslinkers. Therefore, shape memory testing demonstrates that p(DMAPS-co-AA) shows not only dual-SME, but also triple-SME and quadruple-sSME. Moreover, in addition to the thermally-induced SME, p(DMAPS-co-AA) also shows moisture-sensitive SME. It is thus proposed that this zwitterionic multi-SMP could find great potential applications in smart biomedical fields.

Development of zwitterionic polyurethanes with multi-shape memory effects and self-healing properties

Novel zwitterionic polyurethanes containing sulfobetaines, featuring excellent multi-shape-memory properties and self-healing properties, are prepared from N-methyldiethanolamine, hexamethylene diisocyanate and 1,3-propanesultone.

Selectively actuated multi-shape memory effect of a polymer multicomposite

The multicomposite styrene-based shape memory polymer can be selectively actuated by applying selective stimuli due to the selective heating properties of Fe3O4(30 kHz alternating magnetic field) and CNT (13.56 MHz radiofrequency field) nanofillers. Therefore, the multicomposite possesses a well-controlled multiple temporary shape recovery capability.

New insights into multi-shape memory behaviours and liquid crystalline properties of supramolecular polyurethane complexes based on pyridine-containing polyurethane and 4-octyldecyloxybenzoic acid

This paper develops a supramolecular liquid crystalline complex exhibiting a multi-shape memory effect and liquid crystalline properties.

A finite deformation thermomechanical constitutive model for triple shape polymeric composites based on dual thermal transitions

Shape memory polymers (SMPs) have gained strong research interests recently due to their mechanical action that exploits their capability to fix temporary shapes and recover their permanent shape in response to an environmental stimulus such as heat, electricity, irradiation, moisture or magnetic field, among others. Along with interests in conventional “dual-shape” SMPs that can recover from one temporary shape to the permanent shape, multi-shape SMPs that can fix more than one temporary shapes and recover sequentially from one temporary shape to another and eventually to the permanent shape, have started to attract increasing attention. Two approaches have been used to achieve multi-shape shape memory effects (m-SMEs). The first approach uses polymers with a wide thermal transition temperature whilst the second method employs multiple thermal transition temperatures, most notably, uses two distinct thermal transition temperatures to obtain triple-shape memory effects (t-SMEs). Recently, one of the authors’ group reported a triple-shape polymeric composite (TSPC), which is composed of an amorphous SMP matrix (epoxy), providing the system the rubber-glass transition to fix one temporary shape, and an interpenetrating crystallizable fiber network (PCL) providing the system the melt-crystal transition to fix the other temporary shape. A one-dimensional (1D) material model developed by the authors revealed the underlying shape memory mechanism of shape memory behaviors due to dual thermal transitions. In this paper, a three-dimension (3D) finite deformation thermomechanical constitutive model is presented to enable the simulations of t-SME under more complicated deformation conditions. Simple experiments, such as uniaxial tensions, thermal expansions and stress relaxation tests were carried out to identify parameters used in the model. Using an implemented user material subroutine (UMAT), the constitutive model successfully reproduced different types of shape memory behaviors exhibited in experiments designed for shape memory behaviors. Stress distribution analyses were performed to analyze the stress distribution during those different shape memory behaviors. The model was also able to simulate complicated applications, such as a twisted sheet and a folded stick, to demonstrate t-SME.