Heterogeneous Structure and Morphology of IPNs

As is seen from the last equation, the value of xab consists of three parts, each being determined by the conditions of phase separation and by the deviation of the system from equihbrium. The experimentally found interaction parameter is determined by the system history. It has the physical meaning of characteristics of the system nonequihbrium degree. It also allows us to compare systems imder identical conditions, but with different paths leading to these conditions. 

In conclusion, one has to say that the general state of the investigation of the thermodynamics of IPN mixing and phase separation is far from the one we have for blends of linear polymers [52]. In particular, one very important factor is not accoimted for by studying the miscibihty of two networks, namely, the changes of volume by mixing. The last parameter is important not only for thermodynamics, but also for the structure and viscoelastic behavior of IPNs and is considered below. 

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