Influence of co‐neutralization by sodium and zinc on the ethylene ionomer structure and properties

Abstract

This study investigates the properties and structure of poly(ethylene‐co‐methacrylic acid) (EMAA) ionomers co‐neutralized by zinc and sodium, and compares them with ionomers neutralized by a single metal: zinc (EMAA‐Zn) and sodium (EMAA‐Na). The bending stiffness and the degree of crystallization for the co‐neutralized ionomer (Na:Zn = ~1:1 on a molar basis) gives 16.5% and 9.8% increase compared to the simple average of their single cation counterparts. Such unusual properties are seen in mechanical, thermal, and rheological properties and water uptake rate in this study. Infrared spectra of the co‐neutralized ionomer shows changes at the carboxylate antisymmetric stretching band, which correspond to the formation of carboxylates bridging zinc and sodium ions. X‐ray scattering identified that the number density of ionic multiplets for the co‐neutralized ionomers are equivalent to EMAA‐Na and ~ 1.7 times higher than EMAA‐Zn. The fraction of side groups forming ionic multiplets, β, in co‐neutralized ionomers were 0.7–0.8, close to EMAA‐Na (1.0) and higher than EMAA‐Zn (0.3), indicating that sodium promote zinc to form ionic multiplets. The synergistic properties induced by co‐neutralization are ascribed not only to a formation of new ionic multiplets where both cations are included but also to the change in the number density of ionic multiplets.

Thermogravimetric, Morphological and Infrared Analysis of Blends Involving Thermoplastic Starch and Poly(ethylene-co-methacrylic acid) and Its Ionomer Form

“…In our case, a better fit is achieved with a band at 1565 cm −1 . The band existing at 1585 cm −1 is assigned to a 4-coordination (COO − ) configuration around the cation [66]. This band is dominant in Zn 2+ neutralized ionomers because of its strong and well-designed complexion with (COO − ) groups.…”

“…Water, temperature, pressure and neutralization percentage have been shown to change the fingerprint spectrum in this region [67,[71][72][73]. Simultaneous neutralization by more than one cation also modifies the spectrum [66,74,75]. It was concluded that this is due to local disturbance of the configurations of the coordination complexes.…”

“…In this range, the only band which may interfere with the analysis is the one at 1650 cm −1 assigned to (O-H) bending vibration of the alcohol group of polysaccharides, glycerol and to the bonded water. The second range is between 1500 cm −1 and 1600 cm −1 and includes asymmetrical vibration modes of the carboxyl group (COO − ) in EMAA-54Na only [66]. Bands are not resolved, and a maximum appears around 1548 cm The first range concerns bands between 1600 cm −1 and 1800 cm −1 , assigned to (C=O) stretching vibration of the acid form of the carboxyl group existing in EMAA and EMAA-54Na.…”