Polymers shape memory

Shape memory is the ability of a material to remember its original shape, either after mechanical deformation, which is a one-way effect, or by cooling and heating, which is a two-way effect. This phenomenon is based on a structural phase transformation. 

Potential uses of shape memory polymers in medicine are to prepare sutures that have a rigid enough composition to provide for 

The first materials known to exhibit shape memory were shape memory metal alloys. Shape memory pol)nners are being developed to replace the use of Shape memory alloys, in part because the polymers are light, high in shape recovery ability, easy to manipulate, and economical in comparison to shape memory alloys 

When the shape memory polymer is heated above the glass transition temperature of the hard segment, the material can be shaped. This original shape can be memorized by cooling the shape memory polymer below the glass transition temperature of the hard segment. 

When the material is heated above the melting point of the soft segment, but below glass transition temperature of the hard segment, the stresses and strains are relieved and the material returns to its original shape. The recovery of the original shape, which is induced by an increase in temperature, is called the thermal shape memory effect. Properties that describe the shape memory capabU- 

The recovery of oriented polymers has long been recognised as having significant applications, and more recently in medical applications [127-130]. The term shape memory polymers has been coined for such materials. 

The stress relaxation behaviour has been addressed in terms of complex constitutive equations and simpler models based on Maxwell and Kelvin-Voigt elements [131-134]. 

Recently Bonner et al. [135] have shown that the recovery behaviour of a lactide based copolymer can be predicted by a Kelvin-Voigt model (see Chapter 5, Section 5.2.5) where the recovery stress in the spring and the dashpot viscosity can be determined using the transient stress dip test of Fotheringham and Cherry [70]. The recovery stress ory is 

The viscosity stress ay is determined by the recovery temperature and the strain rate e. The viscosity is then given by 

The validity of this simple model was confirmed by Heuchel et al. [136]. 

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Shape-memory polymers (SMPs) are a class of smart materials with the ability to change shape on demand in response to an environmental stimuli [322-325]. So far, the most commonly investigated SMPs are temperature-induced SMPs, whose shape-recovery behavior is triggered by thermal stimuli. Such SMPs have one shape at certain temperature and are converted to another shape at a different temperature (Fig. 22). Temperature-responsive SMPs usually require the combination... 

Chemical mineral size reduction, 16 613 Chemical netpoints, in shape-memory polymers, 22 356, 358 Chemical nomenclature, 17 384. See also Nomenclature... 

Cyclic stresses/strains, 13 481-483 Cyclic stress-strain curves, 13 491 Cyclic structures, nonaromatic, 15 5 Cyclic thermomechanical characterization, of shape-memory polymers, 22 358-362 Cyclic trimer ketone peroxides, 14 292 Cyclic trioxides, 18 448 Cyclic voltammetry, 9 580 Cyclitols, 4 710 Cyclization(s)... 

Degradable implants, shape-memory polymers in, 22 355 Degradable-pendant-chain hydrogels, 13 741... 

Olfaction, research in, 18 383-384 Olfactory membrane, 11 567 Olfactory perceptions, 11 510-511 Olfactory receptors, 18 383-384 Olfactory response, 11 566-567 01igo(2-propenyloxy)methyloxyirane, sulfonation of, 23 720 Oligocyclic lattice host inclusion compounds, 14 177-179 Oligocyclic lattice hosts, 14 177 01igo(y-caprolactone)dimethylacrylate, in shape- memory polymer networks, 22 364... 

Permanent shape, of shape-memory polymer, 22 355-356, 357 Permanent wet drum separators, 15 443 Permanent wet-strength resins, in paper manufacture, 18 115-116 Permanent Yellow FGL, pigment for plastics, 7 366t... 

Polycatenanes, 17 60 Poly(y-caprolactone)dimethylacry, in shape-memory polymers, 22 357 Poly(y-caprolactone)/OMLS nanocomposite, 20 311 Poly(y-caprolactone) switching segment, in shape-memory polymers, 22 362-363 Polychlorinated biphenyls (PCBs),... 

Polymers, 20 389-412. See also Ethylene-propylene polymers Filled polymers Higher olefin polymers Polymerization Polysaccharides Shape-memory polymers (SMPs) SiC>2 polymer Special polymers Sulfur-containing polymers Thermosetting reactive polymers Water-soluble polymers aging of, 20 167... 

Web sites for, 22 722 Smartness, of smart materials, 22 707 Smart polymers. See Shape-memory polymers (SMPs)... 

Stimuli-responsive materials, shape-memory polymers as, 22 355-356 Stirling cycle, 8 43 Stirred autoclave, 14 89, 92t Stirred autoclave reactor, 20 216 Stirred batch RO unit, 21 644 Stirred mills, 16 615 Stirred tank bioreactors, 1 737-740 oxygen transfer driving force, 1 734 Stirred tank electrochemical reactor (STER), 9 660-662... 

Strained silicon wafers, in scaling to deep submicron dimensions, 22 256 Strainers, in refrigeration systems, 27 539 Strain fixity rate (R ), in testing shape-memory polymers, 22 361... 

Strain hardening effect, 20 224 Straining efficiency, 77 340 Strain rate, 73 473 Strain recovery rate (Rr), in testing shape-memory polymers, 22 361 Strain sensors, 77 150, 151-152 Strain tensor, for noncentrosymmetry pont group crystals, 77 93-94 Strain versus time curve factors affecting, 73 473 material and microstructure effect on, 73 473-474... 

Thermal techniques, in nondestructive evaluation, 17 420-421. See also Heat entries Heating entries Thermal-transfer printing, 9 242, 338 Thermal transfer processes, 19 320 Thermal transition, in shape-memory polymers, 22 357-358, 359t, 360, 361-362... 

The PPDX-fr-PCL diblock copolymers were recently synthesized [111] and apart from the references already mentioned, only the contribution of Lendlein and Langer [112] deals with chemically similar materials, although structurally quite different since they employed multiblock copolymers of PPDX and PCL with very low molecular weights to prepare shape memory polymers for biomedical applications. 

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