Liquid‐liquid phase separation in multicomponenent polymer systems: XV thermodynamic aspects of polymer compatibility

Cloud‐point curves in mixtures of short‐chain polymers often have irregular shapes, showing shoulders or two maxima. Limits of the thermodynamic stability as measured by Pulse Induced Critical Scattering also appear to be bimodal in such cases. A possible explanation of this phenomenon might be that the constituent molecules influence each other's chain flexibility, the more flexible chains becoming less flexible upon addition of stiffer ones, and vice versa. Such a feature is incorporated i.a. in Huggins' new theory in which orientational entropy correction terms relate the average randomness of orientation of a segment with respect to the preceding one in the chain to the surroundings of the segment.