Shape fixing polyurethanes

SME of shape memory polyurethanes (SMPUs), the shape recoverability and shape fixing ability, ate dependent on the polyurethane network structure and phase transition of the SMPU, respectively. The roles played by the reversible phase and fixed phase are complex. Recovery stress is essential for most of the applications for SMPs since in practical applications the shape recovery can be impeded by external stimuli. 

SS) and the hard phase e (HS). The shape fixing and shape recovery are strongly related to (SS) and (HS). The distribution of viscoelastic deformation between soft and hard phases is dependent on the two-phase morphology such as phase separation, phase composition, domain sizes, domain concentration and coimectivity, etc. Thus the shape memory properties ate defined by the two-phase morphological stmcture of the segmented polyurethanes. 

Abstract This chapter introduces three sets of T -type shape memory polyurethanes. The thermal properties and morphological structure of polymers are shown to vary with chemical composition. The morphology of the T -SMPUs is thus correlated to shape memory properties. The influences of several important thermo-mechanical conditions including deformation temperature, deformation strain, and shape fixing temperature and time on shape memory properties are demonstrated. 

Shape memory properties of Tg-type high performance shape memory polyurethane shape fixing... 

Long-term shape fixing of iPPG400-b-xx segmented polyurethanes. 

Chapter 1 briefly introduces the mechanisms of the shape memoiy effect and shape memoiy polymers, summarizing key research in the subject. It also introduces one of the most important shape memory polymers, shape memory polyurethane, and its unique properties. Since a melting transition temperature (T ) or a glass transition temperature (T can act as the switch transition for shape memory polyurethane, it can be called either a T -type or a T -type shape memoiy polyurethane. Chapters 2 and 3 discuss T -type and T -type shape memoiy polymers. The effects of deformation temperature, deformation amplitude, shape fixing temperature and pre-deformation are discussed in terms of their influences on shape memoiy properties. 

Li et al. (2007) also described a type of supramolecular shape memory elastomer that contains reversibly associating side groups, namely ureidopyridinone (UPy). In addition to its excellent shape memory effects (SMEs) - about 90% strain fixity and 100% strain recovery - a unique feature of this new SMP is the dynamies of its shape-memory response. More recently, Zhu et al. (2009) synthesized a novel supramolecular polyurethane for utiUzation as a SMP, by grafting the UPy nnit to the elastic polyurethane. Supramolecular SMPs based on o-cyclodextrin (a-CD) network through the inclusion of either PEG or polycaprolactone (PCL) with a-CD. In this system, the a-CD-PEG inclusion crystalhtes and a-CD-PCL crystallites serve as a fixing phase, while the naked PEG crystallites and PCL crystallites act as a reversible phase (Luo et al., 2008 Zhang et al., 2008). Fan... 

However, when the temperature is raised to the higher dissociation temperature Th(T . < T < jjjg crystal of the soft phase is melted, but the hard domain is still fixed. The polyiuethane can then be deformed into a second shape by applying external force while the polyurethane is in the rabber state, and then coohng to Tj (Tj < Tjjjj) under the load, which will fix the deformed shapes. Moreover, when the temperature is again raised to above T the deformed strain will release immediately, resulting in macroscopic shape recovery. Both shape fixation and shape recovery can hence be achieved in segmented SMPU. 

In this section, mixed-phase polyurethanes prepared from 1,3-butane diol (1,3-BD), HDI, and MDI are reviewed [28]. When the TPU soft and hard segments are phase-mixed, a second element acting as a fixed phase should be introduced. This second element is typically crosslinks intoduced either by an allophanate reaction or by a multifunctional polyol. Shape memory properties, melt viscosities, dynamic mechanical and thermal properties, and stress relaxations in the glassy and rubbery states are discussed. 

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