Segmented polyurethanes structure

Spandex polymers n. Segmented polyurethane structure (Dupont Inc., KY, USA) with rubber-like elasticity. 

Segmented polyurethanes Structural analysis of up to 8 methylene nnits [52]... 

These structures are well defined by conducting the polymerization in the presence of appropriate mono- and difunctional reagents. They are of considerable interest for the preparation of segmented block copolymers.24,25 For instance, the fluorinated macrodiols 21 have already been used to prepare an interesting new series of partially fluorinated segmented polyurethanes,26 and we are investigating other novel polymers that can be prepared from these intermediates. 

As stated in Chapter 1, microdomain-structured surfaces are believed to play an important role in their interactions with cells, proteins, and other biological elements. In this Chapter, the author will discuss biomedical behavior of three types of microdomain-structured materials segmented polyurethanes, A-B-A block copolymers, and polyamine-graft copolymers. 

Atomic force microscopy has been used to evaluate the nature and size of the polyurethane structure at the surface of a sample. In this method, the surface of the sample is coated with a layer of gold and a probe scans over the surface. As the nature of the chemistry below the probe changes, the force field acting on the probe changes. The hard segment clusters can be visualized. 

Chemically, spandex is a thermoplastic elastomer. It is a polyurethane block copolymer consisting of long, soft, rubbery segments alternating with rigid, high-Tg segments (see structure below). 

Ophir, Z. Structure-Property Relationships in Solid Polymers I — Segmented Polyurethanes and II — Epoxy Thermosets. Ph. D. Thesis, Princeton University (1979)... 

The variation of Tg of the soft matrix in segmented polyurethanes as a function of composition or segmental chemical structure has been monitored and used as an indicator of the degree of microphase separation. Factors influencing the phase-separation process in these MDI-based polyurethanes have been summarized by Aitken and Jeffs (69) as follows (a) crystallization of either component, (b) the steric hin-... 

Xia et al. found that the incorporation of MWNTs and SWNTs did not improve the first degradation temperature, but did improve the second degradation temperature (21). This indicates that carbon nanotubes may preferably interact with the soft segment in polyurethane structure. There were no significant differences between... 

A recent example of XPS analysis of polyurethane surfaces has been provided by Yoon et al. [30]. In these studies polyurethanes were prepared with 4.4 -methylenebisfphenyl isocyanate) (MDI)and hexafluoro- l.5-pentancdiol (FP) extenders as the hard segment, and poly(tetramethylene glycol) (PTMO) as the soft segment. The authors introduced hydrophobic soft segments, either poly-(dimethylsiloxan) (PDMS) or polyisobutylene (PIB) into this polyurethane structure. The concept underlying this polymer design was the desire to modify sur-... 

As outlined before, the question of interest now is first, how the photochrome would react when incorporated in the backbone of amorphous and semicrystalline polymers such as segmented polyurethanes and if the isomerization behaviour of the photochrome would allow conclusions on the structure, morphology, and segmental mobility of this matrix. 

SEGMENTED POLYURETHANE ELASTOMERS SCHEME OF THE CHAIN STRUCTURE ... 

Figure 5. Scheme of primary chain structure of segmented polyurethane elastomers and chain segment organization. 

Figure 6. Scheme of the primary chain structure of photochromic segmented polyurethanes with aromatic azochromophores built in the polymer chain. 

There are several ways of changing the properties of segmented polyurethane copolymers. In this study, the chemical structure of the hard segments was changed to adjust the modulus of the adhesive. Further fine tuning is possible by varying the concentration of the different blocks. For example, the 87-series adhesives have a lower modulus than the 88-series adhesives because their hard segment concentration is lower. Studies of concentration effects (16) have shown that much wider variation of modulus is possible tTian was achieved here. 

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