A more efficient route for the synthesis of phosphonated dimethyl isophthalate, disodium salt is shown to provide a significantly higher yield (42%), in contrast to a previously reported yield (15%). This higher yield enabled the synthesis of phosphonated poly(ethylene terephthalate) (PPET) ionomers using conventional melt polycondensation with ethylene glycol and dimethyl terephthalate. The physical properties of these phosphonated PET ionomers (Na+-PPET) were characterized using differential scanning calorimetry (DSC), melt rheology, and tensile testing. DSC analysis showed that the crystalline melting temperatures, crystallization temperatures, degrees of crystallinity, and crystallization rates decreased with increasing ionic content. Melt rheology confirmed the existence of physical crosslinks in Na+-PPET ionomers, as indicated by a crossover of the storage and loss moduli, attributed to strong electrostatic associations between phosphonated units on the polymer chains. Tensile tests of the Na+-PPET samples showed enhanced Young's modulus and yield stress compared to pure PET.
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