Hard segments elastomers, structure

Hard Segments. The hard segments are the linear reaction products of the diisocyanate component and the third monomer type in the TPU elastomer recipe, the small glycol-chain-extender component. In Figure 5 we see a typical TPU hard-segment structure which is formed from MDI and 1,4-BDO (1,4-butanediol). 

As can be seen, hard-segment domains are a necessary structural feature of TPU elastomers since they tie the polymer primary chains together. Without these domains TPU would lack elastic character and would be gumlike in nature. 

The Structure of the Hard Segments in MDI/ diol/PTMA Polyurethane Elastomers... 

In the absence of a blowing agent and with conditions favoring the formation of linear chains, thermoplastic polyurethane elastomers can be formed. Materials with different properties can be obtained by altering the ratio of hard to soft blocks, and it is also observed that, in many cases, the hard segments can crystallize. This can give rise to phase-separated structures, shown schematieally in Figure 2.6, which behave as thermoplastic elastomers (see also Section 15.6). 

FIGURE 13.2 Structures of commercially important thermoplastic elastomers HS = hard segment, SS =soft segment, (a) SBS (b) MDI-BD-PTMO polyurethane (c) PTMT and PTMO ct lyester (d) nylon 66 and PTMO copolyamide and (e) random o lymer ionomer E-MAA neutralized with sodium. 

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