And soft segments

One partieular form of thermoplastic polyurethane elastomers is the elastic fibre known as spandex fibre. Like the usual thermoplastic rubbers these materials consist of hard and soft segments but to qualify for the term spandex by the US Federal Trade Commission the polymer used should contain at least 85% of segmented polyurethane. The first commercial material of this type was introduced by Du Pont in 1958 (Lycra). Several other similar materials have since been introduced including Dorlastan (Bayer), Spanzelle (Courtaulds) and Vyrene (US Rubber). 

Linear chain polymers with repeating sequences of hard and soft segments Possibility of formation of liquid crystal polymers and thermoplastic elastomers... 

Puskas J.E., Antony P., ElFray M., and Altstadt V. The effect of hard and soft segment composition and molecular architecture on the morphology and mechanical properties of polystyrene-polyisobutylene thermoplastic elastomeric block copolymers, Eur. Polym. J., 39, 2041, 2003. 

Antony, P., Puskas, J.E., Ott, H., Altstadt, V., Kovar, M., and Norton, P.R. Effect of Hard and Soft Segment Composition on the Morphology and Mechanical Properties of Polystyrene-Polyisobutylene Thermoplastic Elastomeric Block Copolymers. Proceedings of the Polymer Processing Society Meeting, May 21-24, Montreal, Canada, 2001. 

Thermoplastic polyurethane elastomers are normally based on polyester prepolymers. The properties of these polymers can be systematically varied by tailoring the nature and ratio of the hard and soft segments. The stiffness of a polyurethane elastomer increases as the proportion of hard blocks increases. As the stiffness increases, the extensibility of the material decreases. 

In an NMR analysis of the effects of /-irradiation induced degradation on a specific polyurethane (PU) elastomer system, Maxwell and co-workers [87] used a combination of both H and 13C NMR techniques, and correlated these with mechanical properties derived from dynamic mechanical analysis (DMA). 1H NMR was used to determine spin-echo decay curves for three samples, which consisted of a control and two samples exposed to different levels of /-irradiation in air. These results were deconvoluted into three T2 components that represented T2 values which could be attributed to an interfacial domain between hard and soft segments of the PU, the PU soft segment, and the sol... 

Typical morphology showing hard and soft segments showing one chain only for simplicity... 

These materials have two-phase structures based on hard segments of polystyrene and soft segments of butadiene for SBS, or isoprene for SIS, etc. 

Note The types of domain in a segmented copolymer usually comprise hard- and soft-segment phase domains. 

Table I. Lignin source and soft segment type for polyurethanes discussed in this study...

We have alluded to the fact that MDI produces stiffer polymers than TDI, based on the hard-and-soft segment model of polymer design. In the experiment cited below, the concentration of MDI in a formulation was increased and the resultant polymer analyzed. 

Various x-ray diffraction techniques have been used to study the size and distribution of hard and soft segments near the surface of the polyurethane. 

The properties of PU depend on the proportions of hard and soft segments in the polymer structure. Paul and co-workers synthesised segmented block copolymers of NR and 1,3 butanediol - toluene diisocyanate oligomers [137], NR and bisphenolA-toluene diisocyanate oligomers [138] and characterised them by IR spectroscopy. The... 

Polyurethane TPE are block copolymers consisting of alternating hard and soft segments, separated into two phases [54] due to thermodynamic incompatibility. 

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