Infrared Spectroscopic Study of the Binary Blends of Sodium and Zinc Salt Ionomers Produced from Poly(ethylene-<i>co</i>-methacrylic acid)

Abstract

Infrared (IR) and far-infrared studies were performed for the binary blends of sodium and zinc salt ionomers of poly(ethylene-co-methacrylic acid) (EMAA), 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 cations. When temperature was raised, the bandwidth began to increase at around 310 K, just below a transition temperature (Ti = ca. 325 K) observed by DSC and far below the melting of polyethylene crystalline region (Tm = ca. 360 K); this increase was almost linear with temperature and continued to 403 K above Tm, reflecting the increased distribution of the states of the bridging mode with temperature. These results are explained by a structural transition of ionic aggregates at Ti in EMAA ionomers, which was proposed in our previous publications.