Thermoplastic shape-memory polymers

Testing of Magnetically-Induced Shape-Memory Effect of Composites from Magnetic Nanoparticles and Thermoplastic Shape-Memory Polymers... 

The following examples show thermally induced shape-memory. The first three examples are exclusively physically cross-linked. These examples are two polyurethanes representing thermoplastic shape-memory polymers with Ttrans = Tm or Tg, and a high molecular weight, amorphous polynorbornene. Examples of covalently cross-linked shape-memory networks are so-called heat-shrinkable materials and a shape-memory network with a crystallizable switching segment (Ttrans = Tm) that has been developed for biomedical application. 

Fig. 9 A fiber of a thermoplastic shape-memory polymer was programmed by stretching about 200%. After forming a loose knot, both ends of the suture were fixed. The photo series shows, from top to bottom, how the knot tightened in 20 s when heated to 40 °C. (Reprinted with permission from Lendlein A, hanger R (2002) Science 269 1673, copyright 2002 AAAS)...

Nji, J. and Li, G. (2012) Damage healing ability of a shape memory polymer based particulate composite with small thermoplastic contents. Smart Materials and Structures, 21, paper 025011 (10 pages). 

Thermoplastic Q Shape memory polymer (PSMP) Tgi Glass transition temperature of PSMP particle (CP) matrix... 

Conventional shape memory polymers are segmented polyfur-ethane) s and have hard segments that include aromatic moieties (70,71). But a series of other thermoplastic block copolymers with thermally induced shape memory effects have been summarized (69). 

Shape Memory Polymer, Thermoplastic polyurethane elastomer, Mitsubishi Heavy ndus-tries America... 

Among shape memory materials, shape memory alloys and bimetals are well known. Compared to these metallic compounds, SMP have a lower density, high shape recoverability, easy processability, and lower cost. Similar to conventional thermoplastics, SMP can be easily molded by the common methods, such as injection, extrusion, compression, and casting. In addition, their shape recovery temperature can be set at any value in the range room temperature 50 C, which allows a wide variety of applications. Also, SMP can be colored if desired because they are transparent. However, since the retractive force of the polymer is based on the small entropy elasticity, the SMP applications differ from those of metallic alloys. The basic differences between shape memory polymers and alloys are listed in Table 1. 

Shape-memory polymers (SMP) are stimuli-responsive. They have the capability of recovering their shape npon the application of an external stimulus. This external stimulus can be heat or an electrical voltage if the material shows electrical conductivity. Thermoplastic polyurethanes with SMP behavior were discovered at Mitsnbishi Co. in 1988. However, it was since 1996 that their investigation turned out to be more systematic." In this type of TPU, hard segments act as cross-links and are responsible for the permanent shape. Above the melting temperature of the hard segment domains, the polymer can... 

There are four main classifications for shape memory polymers with different sources of their transition temperature 1) covalently crosslinked glassy polymers where the glass transition (Tg) is the temporary network transition temperature (To) 2) covalently-crosslinked, semicrystalline elastomers where Tm is T 3) physically-crosslinked, semicrystalline thermoplastics where Tc = Tg and 4) physically-crosslinked, semicrystalline block copolymers where T = T of the soft segment. Each of these types of SMPs requires considerable polymer syntheses if one wishes to vary T(, and/or the modulus of the SMP. 

Shrinkablefilm and tubing Cross linked semicrystalline thermoplastics display rubberlike properties at temperatures above their melting points. On deformation followed by fast cooling the polymer maintains its deformed shape. The polymer returns to its original shape when reheated. This memory effect is applied in the production of heat shrinkable films and tubing. Radiation doses of the order of 40 — 1(X) kGy are used in the production of heat shrinkable products. 

---