Tailoring the ionic association and microstructure of ionomers with various metal salts

In this work, we investigated the effects of metal stearate salts on the structure, morphology, and properties of poly(ethylene-acrylic acid) neutralized by zinc salts (PI). The samples were characterized in detail with spectroscopic [Fourier transform infrared (FTIR) spectroscopy], microscopic (hot-stage optical microscopy), thermal [thermogravimetric analysis, modulated differential scanning calorimetry, and dynamic mechanical analysis], mechanical, and scattering (small-angle neutron scattering and small-angle X-ray scattering) techniques. The melt rheological properties of the samples were also investigated. The structure of the ionic domains was determined by the type of cations and the salt proportion (FTIR). The predominant interaction was found to exist between the metal stearate and the ionic group. Na+cation exhibited a unique behavior, whereas Zn2+showed a coordinated structure and, hence, properties. The ionic groups in the Na and Zn stearate systems existed as multiplets and clusters, but multiplets were the main structure in the Al salt system. The salts acted as plasticizers above their melting points (mp's) but as fillers below their mp's. The melt flow properties of PI were significantly affected by the metal cation and salt proportion and were improved greatly by the introduction of the salts. © 2012 Wiley Periodicals, Inc.