Shape recovery

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... 

Any other data which the customer feels would be of help such as heat transfer data present conditions under which the product is produced and type of equipment used present crystal size and effects of agitation, additives and/or temper ature on crystal size, shape, recovery, or purity. 

Better dispersion of MWNTs in the polymer matrix caused by the formation of the chemical bonds leads to uniform stress distribution and enhanced shape memory (23). Jana et al. prepared nanocomposites of PU and MWNTs via in-situ polymerization and conventional method (105). PU nanocomposites obtained via an in-situ method with PCL-g-MWNTs showed better shape recovery, compared to conventional nanocomposites. 

Mather [5] prepared elastomeric materials having excellent shape recovery properties by polymerizing cyclooctene using the dihydroimidazolylidene-modified Grubbs catalyst, (I), and then crosslinking the intermediate with dicumyl peroxide. 

Elasticity—measures shape recovery after release of applied load... 

Shape recovery in a particular SMP may be triggered by a few different stimuli. For... 

Other measurable features in SMPs relate to the ability of the polymer to fix the imposed strain when subjected to deformation after cooling and offloading, otherwise known as shape fixity (Tobushi et al., 1998). Another relates to the ability of the polymer to recover from the collated strain during deformation after reheating to its former rubbery state. This is often referred to as shape recovery (Hu, 2007 Tobushi et al., 1998). Further elaborations on these important parameters are beyond the scope of this chapter and readers are referred to the targeted literature (Liu et al., 2007 Kang and Nho, 2001 Adler et al., 1991 Tobushi et al., 1998). 

Tobushi, H., Hashimoto, T., Ito, N., Hayashi, S., Yamada, E., 01/1998. Shape fixity and shape recovery in a film of shape memory polymer of polyurethane series. Journal of Intelligent Material Systems and Structures 9 (2), 127—136. http //dx.doi.org/10.1177/... 

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]. 

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