COMPARISON OF THE PHYSICAL-PROPERTIES OF CARBOXYLATED AND SULFONATED MODEL POLYURETHANE IONOMERS

A series of carboxylated and sulfonated model polyurethane ionomers based on tolylene diisocyanate and three polyols is investigated to determine the influence of pendant anion type on physical properties. Tensile testing results demonstrate that sulfonated ionomers give higher tensile strengths than carboxylated ionomers, as expected based on arguments of the higher acid strength of the sulfonate groups. DSC and DMTA results confirm the model ionomers based on 1000 molecular weight soft segments are more phase separated in the sulfonated than in the carboxylated ionomers. However, the surprisingly high Young's moduli for the carboxylated ionomers illustrates the dependence of ionomer properties on the morphology of the sample. DMTA results indicate a higher cross-linking efficiency in the carboxylated ionomers, corresponding to their larger ionic aggregate sizes, which counterbalances the lower acid strength of the carboxylate groups to give higher than expected moduli. The moduli of all ionomers investigated are significantly higher than predicted on the basis of ionic aggregates acting as cross-links and fillers. The modulus enhancement is attributed to entanglements formed in the process of ionic aggregation.