Effect of Cation Size and Valency on the Ionic Aggregates in Poly(styrene-ran-methacrylic acid) Ionomers

Previous STEM studies of fully-neutralized poly(styrene-ran-methacrylic acid) (SMAA) ionomers have shown spherical or vesicular aggregates when neutralized with Zn or Cs, respectively. The current study probes the effects of cation size and valency on the morphology of the ionic aggregates by examining SMAA neutralized with cations from Groups 1 (Na, K, Rb and Cs) and 2 (Mg, Ca, Sr and Ba) of the periodic table. In addition to the shape of the ionic aggregates, their size and number density are measured to further understand the influence of the cations on the ionomer morphology. Results to date suggest that the cation size is more significant than the cation valency. For example, fully neutralized SMAA ionomers exhibit spherical aggregates with Na+ (ionic radius 0.095 nm) and vesicular aggregates with Cs+ (ionic radius 0.169 nm). Complimentary studies are underway in our group using poly(ethylene-ran-methacrylic acid) neutralized with same range of cations, as well as computer simulations and rheological measurements.