Crystallinity soft segment

The electron diffraction results support the occurrence of soft-segment crystallinity and a more disordered hard-segment phase in the solvent-cast samples. Moreover, electron diffraction indicates isolated crystalline soft-segment regions persist even in samples of up to 43% hard segment. Electron diffraction is very sensitive to small local fluctuations in the overall structure because the diffraction patterns can be obtained from regions less than 1 /un in diameter and less than. l-/un thick, whereas DSC and WAXS, of course, measure bulk polymer which yields averages over the whole sample. 

For PU with crystalline soft segments, the crosslinking (introduced in the structure), decreases the crystallisation of the soft segment and upgrades the mechanical properties of the resulting crosslinked structure (Table 2.13). Buckley and co-workers [129] reported a novel thermosetting PU using 1,1,1-trimethylol propane as a crosslinker. Improvement in creep, and increase in recovery temperature and recovery window... 

Saralegi A et al (2013) Shape-memory bionanocomposites based on chitrn nanocrystals and thermoplastic polyurethane with a highly crystalline soft segment. Biomacromolecules 14(12) 4475 82... 

Zhu, Y, Hu, J., Choi, K. F., Yeung, K. W., Meng, Q., Chen, S. (2008a) Crystallization and melting behavior of the crystalline soft segment in a shape-memory polyurethane ionomer, J. Appl. Polym. Sci., 107, 599-609. 

Inspired by the spider silk, which is among the toughest natural materials, Pollock and Hammond [47] prepared an interesting silk-like thermoplastic polyurethane elastomer with main-chain liquid crystalline soft segments (Schemes 41-43). 

Pollock G S and Hammond P T (2002) Synthesis and characterization of siLk-hke polyurethanes with main-chain liquid crystalline soft segments, ACS Polym Prepr 43(l) 478-479. 

Below, we first consider the shape memory effect, as well as basic structure-property relationships of TPU having crystalline soft segments, e.g., poly(tetra-methylene adipate) glycol (PTAd, M = 2000), and hard segments composed of 4,4 -diphenylmethane diisocyanate (MDI) and ethylene glycol (EG) or ethylene diamine (EDA) [25],... 

In this paper, we present results on shape memory behavior of polyurethane (PU)/clay nanocomposites. These nanocomposites were prepared via bulk polymerization method and contained exfoliated clay particles as revealed by transmission electron microscopy and wide angle X-ray diffraction method. The PU matrix contained a crystalline soft segment, which was responsible for shape fixity. The presence of clay decreased the crystallinity of soft segments and consequently shape fixity, but the magnitude of shape recovery stress increased, e.g., by 20% with only 1 wt% clay. The mechanism of reinforcement was studied by monitoring stress relaxation and phase separation. 

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