Shape memory polymers materials

Kalita H, KarakN (2013) Hyperbranched polyurethane/Fc304 thermosetting nanocomposites as shape memory materials. Polym Bull 70(ll) 2953-2965... 

Kalita H, Karak N (2013) Bio-based hyperbranched polyurethane/Fe304 nanocomposites as shape memory materials. Polymer Adv Technol 24(9) 819-823... 

Buckley, C. P, Piisacariu, C., Caraculacu, A. (2007), Novel triol-crosslinked polyurethanes and their thermo-rheological characterization as shape-memory materials. Polymer, 48,1388-96. 

Shape-memory materials are those materials that return to a specific shape after being exposed to specific temperatures. In other words, these materials are able to remember their initial shape. This process of changing the shape of the material can be repeated several times. The shape-memory effect has been observed in different materials, such as metallic alloys, ceramics, glasses, polymers and gels. 

As compared to metallic compounds used as shape memory materials, shape memory polymers have low density, high shape recoverability, easy processability, and low cost. Since the discovery by Mitsubishi in 1988, polyurethane SMPs have attracted a great deal of attention due to their unique properties, such as a wide range of shape recovery temperatures (— 30°C to 70°C) and excellent biocompatibility, besides the usual advantages of plastics. A series of shape memory polyurethanes (SPMUs), prepared from polycaprolactone diols (PCL), 1,4-butanediol (BDO) (chain extender), and 4,4 -diphenylmethane diisocyanate (MDI) or toluene diisocyanate (TDI) have recently been introduced [200—202]. 

Under specific stimulus, shape memory materials could move from a temporary shape to their original shape. The stimulus could be light, pH, or electric or magnetic field, but the most common shmulus is heat. In this case, a shape memory polymer (SMP) possesses a switch transihon temperature. When the SMP is subject to deformation, its cross-linking structure could store internal stress if it is cooled below this switch temperature. When the polymer is heated above this temperature, it returns to its original shape. Shape memory polymer blends could be achieved using irradiahon. 

Fig. 14 Access to shape-memory materials from photocross-linked metallo-supramolecular polymers. (a) Formation of shape-memory materials using light as a stimulus (a) UV light is absorbed by the metal-ligand complexes and is converted to localized heat, which disrupts the metal complexation (i>) the material can then be deformed (c) removal of the light while the material is deformed allows the metal-ligand complexes to re-form and to lock-in the temporary shape id) additional exposure to UV light allows a return to the permanent shape, (b) Images demonstrating the shape-memory behavior. Reprinted with permission from [274]. Copyright 2011 American Chemical Society...

In the literature, the constitutive equation for both the amorphous polymer and crystalline polymer has been well established. Therefore, we can direcdy use these relations to model the amorphous phase and crystalline phase of the SMPFs. We then need to consider the cychc texture change of both subphases because the mechanical behaviors of the individual microconstituents may vary when they are packed in a multiphase material system and a certain deviation in their mechanical responses may exist between the individual and their assembled configurations. Since this is a shape memory material, we also need to model the shape recovery behavior. After that, we can use the above micromechanics relation to assemble the macroscopic constitutive relation. In order to determine the parameters used in the constitutive model, we need to consider the kinematic relations under large deformation. Finally, we will discuss the numerical scheme to solve the coupled equations. 

Neuser, S., Michaud, V., and White, S.R. (2012) Improving solvent-based self-healing materials through shape memory alloys. Polymer, 53, 370-378. 

Yoshida M, Longer R, Lendlein A, Lahann J (2006) From advanced biomedical coatings to multi-functionalized biomaterials. Polym Rev (Phila) 46 347-375 (Smart and shape memory materials)... 

Du, J., Armstrong, S.R., and Baer, E. (2013) Co-extruded multilayer shape memory materials comparing layered and blend architectures. Polymer, 54 (20), 5399-5407. 

FIGURE 5.2.3 Classification of soft shape-memory materials from the viewpoint of nanoaivhitectonics. (a-c) Structures and (d) molecular mechanism, (a) Chemically cross-linked polymer network, (b) supramolecular network with clay nanosheets [29], and (c) inorganic/polymer composite network system, and their shape-memory profiles [30]. (d) The nanoscale molecular mechanism for one-way and two-way SME of a cross-linked semicrystalline polymer system. 

A relatively new and exciting application for polymers is as shape memory materials. Therefore, one of the objectives which we will continue to follow in the immediate future will be to focus on novel crosslinked shape-memory polyurethanes. 

The latest embodiment of an SMP clot retrieval system demonstrates a hybrid shape-memory material system. The design of SMP biomedical devices should not be limited to purely polymer-based devices but rather can be combined with other smart or active materials. Novel multifunctional SMP-hybrid systems could lead to multiple unique and novel platform technologies for future development. 

To date, three general approaches for design of self-folding polymer films using inhomogeneous materials are reported (Fig. 1.1). First approach is based on shape-memory polymers, which are partially liquid crystalline with directional anisotropy of properties (Fig. 1.1a). At low temperature, the shape-memory materials are in their temporary shape. The films recover their permanent shape by heating. In second... 

Poly(methyl acrylate) (PMA) may be used as start material for production of shape-memory material [lOWl]. The addition of poly(ethylene glycol) diacrylate (PEGDA) assists crosslinking process. The insoluble content formed in EB-irradiated PMA increases sharply even at low doses (Table 37) because polymer matrix provides radicals at a yield of 0.77 and PEGDA plays the role of sensitizer. 

Water-activated shape-memory materials are a particularly attractive subset of shape-memory polymers, as they can be considered for applications where temperature activation is not desirable. Combining the mechanically adaptive properties of CNC-containing composites and the shape-shifting abilities of shape-memory materials, Mendez et... 

---