Polymer Fox Equation
Tg, the glass transition temperature, is the temperature at which you get "onset of main chain segmental motion", i.e. when the polymer can really start to wriggle and move. Here the question is what is the Tg of a blend of two polymers with different Tg values. Just slide the sliders and find out.
The glass transition temperature, Tg1, of a polymer can be changed via an additive with Tg2. The effect is calculated from the weight fractions of the two components, w1 and w1, via the Fox Equation:
1/Tg = w1/Tg1 + w2/Tg2
Why is this equation included in Practical Solubility? Because it only works if the two components are rather compatible, i.e. their HSP Distance is rather low. As soon as the difference is significant, the two components tend to phase separate. To check this out, something like a DSC scan can tell you whether you have a single Tg or you see two peaks.