Case II UCST

Fignre 5.3 phase diagram (T versus (pi) shows one UCST. 

One method of calculating the different cases of phase diagrams listed here is by expressing the polymer blend interaction parameter, 5 as a fnnction of temperature 

FIGURE 5.2 Phase diagram (T versus cpi)-I LCST (lower critical solution temperature). 

Where b, bi, do, d, and d2 are adjustable parameters. It was assumed that the excess partial molar heat capacity of blend is independent of temperature. A quadratic dependence on composition was chosen from observations made in polymer-solvent systems. When the coefficients of d and do in Equation (5.14a) are both positive, the resulting phase diagram is of the combined LCST/UCST or hourglass type, as discussed for different cases in this section. The system acetone and polystyrene has been found to undergo a transition from a combined LCST/UCST to the hourglass behavior as the molecular weight of the polystyrene is increased. 

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A combined Case I LCST and Case II UCST can be illustrated for a polymer-polymer system with the interaction parameter varying as follows ... 

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