Infrared spectroscopic study of the binary blends of sodium and zinc salt ionomers produced from poly(ethylene-co-methacrylic acid)

Infrared (IR) and far-infrared studies were performed for the binary blends of sodium and zinc salt ionomers of poly(ethylene-co-methacrylic acid) (EM AA), which are known to show a dramatic improvement of small strain moduli (e.g., stiffness) compared with the two component salts. The IR spectra of the blends showed a new asymmetric carboxylate stretching band at 1569 cm(- 1), which is assigned to carboxylate groups bridging sodium and zinc cation s. When temperature was raised, the bandwidth began to increase at around 3 10 K, just below a transition temperature (T-i = ca. 325 K) observed by DSC and far below the melting of polyethylene crystalline region (T-m = ca. 36 0 K); this increase was almost linear with temperature and continued to 403 K above T-m, reflecting the increased distribution of the states of the br idging mode with temperature. These results are explained by a structural t ransition of ionic aggregates at T-i in EMAA ionomers, which was proposed i n our previous publications.