Molecular interpretation of glass temperature depression by plasticizers

Abstract The view that the glass transition is basically thermodynamic in nature is used to derive an expression for glass temperature depression by plasticizers. The second‐order transition temperature is given as that temperature at which the configurational entropy first becomes zero as we cool the polymer–diluent system. The concentration of plasticizer, size of the plasticizing molecule, and its flexibility are found to be the main determinants of glass temperature depression. Available experimental data confirm the predictions of the theory, and it is thereby concluded that the thermodynamic view is sufficient to explain glass temperature depression. It is pointed out that data exist which contradict the free volume theory, as applied to glass temperature depression.