General considerations on the phase separation and morphological features

1 General considerations on the phase separation and morphological features 

In addition to chemical interactions, the physical arrangement of the molecules plays an important role. 

Remember the widely accepted paradigm that the whole is more than the sum of 

Morphology is defined as the science of structural forms. PUs properties originate in their nanoscale phase separation by the competition between the hard and soft phases. PUs morphology can be studied at different levels of structure according to their domain sizes [4], At an intermediate level a two phase structure is observed, where the dimensions of domains are of the order of 5-100 nm. 

It is well-known that the PUs tend to exhibit phase separation where the SS units confer elastomeric behaviour while the microphase rich in HS provides physical cross-linking—see [4, 74, 78, 80, 125-127], for example the review by Diet-rich and Hespe [126]. In addition to the microphase separation of segments, the macrophase separation of molecules with different composition has to be considered in discussing the PUs morphology and their properties. As this phenomenon is supposed to be common for PUs, it is also important to study the control and characterization of the heterogeneity of segmented macromolecules and also the relationship between properties and the molecular heterogeneity. 

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