Effect of Sulfonation Level on Solubility and Viscosity Behavior of Low to Medium Charged Sulfonated Polystyrenes

Theoretical treatments based on Fixman's theory and on the electrostatic wormlike theory are applied to sulfonated polystyrene (KSPS) with sulfonation levels ranging from 11 to 52 mol %. Good agreement between theory and experimental results was obtained for SPS with more than 19 mol % of ionic groups on the backbone. However, large deviations were observed for the data on KSPS with low sulfonation level, 11 mol %, which indicates the failure of the models originally developed for strongly charged polyelectrolytes to explain results for weakly charged polyelectrolytes (ionomers). Experimentally, SPS were prepared by the sulfonation of polystyrene with a milder method in homogeneous media so as to avoid chain degradation or cross-linking. Sulfur elemental analysis was used to calculate the sulfonation level while characterization using infrared and nuclear magnetic resonance spectroscopy confirmed that the SPS did not suffer cross-linking or degradation. Optimized conditions were established in solubility tests with THF/H 2 O mixtures to obtain viscosity data using dilute capillary viscometry measurements. Counterion condensation was observed at several polymer concentrations in measurements of reduced viscosity in salt-free solution and of intrinsic viscosity in the presence of NaCl up to 0.2 M. A sharp increase in viscosity with the sulfonation level occurred up to 25 mol %, after which it remained constant.