Many literatures have reported the relationship between glass transition temperature and composition in polymer solutions. These equations are mostly based on classical thermodynamic theory

free volume theory

and the results derived from these equations are fit well in some polymer solution systems. In the curve of T

g

vs. composition

anomalous " cusp" and double Tgs have been observed in some polymer-solvent systems

and these anomaly could be explained through free volume theory and self-concentration theory qualitatively

but the experimental results were quite different from the results derived from the equations

and these theories failed in some polymer solutions. So in order to account for and expect the occurrence of anomalous phenomena

general theories are needed to develop the relationship between T

g

and composition and explain the "cusp" .