Characterization of metal-ion containing polyesters

Summary

The glass transition behavior of poly(diethylene glycol-co-succinic acid) (DEGSA) and its complexes obtained in the reaction with MgO have been investigated. The number average molar mass ($\bar M_N$) of the DEG-SA samples prior to complexation was determined by titration of the terminal COOH groups. The glass transition temperature (T_g) was measured as a function of molar mass and Mg²⁺ ion content. The dependence of T_g on$\bar M_N$ obeyed the Fox-Flory relationship. Addition of increasing amounts of MgO to DEG-SA led to a gradual increase in T_g, and a decrease in the heat capacity change (Δc_p). This behavior is associated with complex formation between COO^-and Mg²⁺. The decrease in Δc_p is a result of ion-ion and to a lesser extent ion-dipole interactions which lower chain mobility. The common limiting T_g value for the three DEG-SA samples at an Mg²⁺/COO^- ratio of ca. 0.5 approaches T_g,∞, which is the corresponding T_g of a polymer of infinite molar mass.