Temperature Dependence of Solubility Parameters of Polymers
Two equations are proposed to describe the decrease of solubility parameter (δ) with increasing temperature (T) for the polymers which exhibit the glass-rubber transition. They are derived by considering the temperature effects on the free volume and the enthalpy change of the glass-rubber transition. These derivations hinge on an enthalpy assumed to be inversely proportional to the fourth power in molar volume of liquid polymer. The predicted results over a significant range of
temperatures are conveniently fitted to the linear equations of the form δ = δg + mi ( T - Tg ) where δg is the δ at the glass transition temperature (Tg), and the coefficient mi = ms , ml referring to the glassy and liquid polymers respectively. It has been found that ml surpasses ms consistently. The peculiarity of low-density polyethylene is explained. More important, the results of the present study compare favorably with the experimental δ data obtained at 60 °C for two glassy polymers and two rubbery polymers. The implication of the present finding is discussed.