DSC behaviour of polyurethane elastomers based on single diisocyanates

1 DSC behaviour of polyurethane elastomers based on single diisocyanates 

DSC maintains the sample and reference at the same temperature through varying the heat flow. When the differential heat flow supplied is plotted as a function of temperature, it is possible, after normalizing the sample mass, to obtain enthalpic information, such as the heat of fusion. 

The DSC experiments to investigate the PUs phase separation are based on the fact that the To of the homogeneous mixtures in general obey the following copolymer equation  

Since the phase mixing is partial, three separate phase transitions usually occur. In practice the amount of mixed material is small compared to the mass of pure phases, so that the third Tg is not observable. Usually some increases of the soft segment Tg and decrease of the hard segment Tg is observed [4]. 

Modifications in the PUs microphase separation characteristics through changes in the glass transitions of the components can be observed in the phase transformation from the DSC endothermic and exothermic maxima of the polymer depending on the nature of the hard domains (diisocyanate and chain extender couple), HS content or ordering of the elements constituting the HS [60,127]. 

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