Tee effect of sulfonation and counterion type on the thermal transitions of sulfonated poly(ethylene terephthalate)

The effect of ionic interactions on the thermal properties of sulfonated poly(ethylene terephthalate) (SPET) has been investigated, Thermal transitions were determined by DSC analysis of isothermally crystallized samples. Although no apparent ionic cluster transition was observed by DSC analysis, evidence of ionic aggregation has been verified by solid-state Na-23 NMR. Preliminary results indicate the matrix glass transition is greatly elevated relative to PET containing a comparable content of non-ionic isophthalic acid units. However the T-g of SPET has little or no dependence on counterion type. The counterion type has been found to significantly affect the crystallization behavior of SPET. This behavior is consistent with the results of recent studies involving model semicrystalline ionomers.