Analysis of the glass transition behavior of polymer-salt complexes: An extended configurational entropy model

A new molecular thermodynamic model is developed of the glass transition temperatures (T_g) of binary polymer-salt complexes by combining configurational entropy theory with Guggenheim's form of the Debye-Hückel theory. The interactions between the polymer chains and the salt as well as those between cations and anions are accounted for by this model. The predictions of this extended configurational entropy theory are compared with the T_g values of poly(2-ethyl-2-oxazoline) (POZ) complexed with AgBF₄, AgClO₄, AgCF₃SO₃, and AgNO₃ at various compositions, as obtained by differential scanning calorimetry (DSC). The model accurately predicts the experimental T_g values even at high concentrations of silver salt (i.e., up to a mole ratio of [Ag]/[C=O] = 1/1), where the deviation of the simple configurational entropy theory from experimental data is large. Moreover, the maximum in the glass transition temperature, i.e., the increase in T_g with salt concentration at low salt concentrations but its decrease at high salt concentrations, is explicable with this model.