Final answer:
Phase separation and the formation of immiscible blends in polymers are influenced by differences in intermolecular interactions and the entropy of mixing. Polymers have lower entropy of mixing compared to small molecules due to the restricted mobility of their long chains.
Step-by-step explanation:
When two polymers phase separate and form immiscible blends, it is mainly due to differences in their intermolecular interactions and the entropy of mixing. Polymers are composed of long chains of repeated units called monomers, and these chains tend to entangle with each other. When two different polymers are mixed together, the entanglements between the chains of each polymer can hinder their ability to mix uniformly, leading to phase separation and the formation of immiscible blends.
The entropy of mixing in polymers is generally lower than in small molecules. Entropy is a measure of the disorder or randomness in a system. When small molecules mix, they have more degrees of freedom and can move more randomly, resulting in a higher entropy of mixing. In polymers, the long chains restrict the mobility of the molecules, reducing the number of possible configurations and decreasing the entropy of mixing.