PET-ionomers and PETi/MMT nanocomposites: A comparison of the effect of ionic groups on their crystallinities and physical properties

Poly(ethylene terephthalate) (PET) and PET/modified montmorillonite (A10-MMT) nanocomposites containing up to 3 mol% of dimethyl 5-sulfoisophthalte sodium salt (DMSi) were prepared by in situ polymerization (PETi and PETNi, respectively). In results from transmission electron microscopy (TEM, â 10 nm), clusters were observed with sizes of 30 nm at an ionic content of 3 mol%. Clusters were not observed in the PETNi samples due to the favorable interaction between the positively charged edges of the clay platelets and the negatively charged ionic groups. On the other hand, the degree of exfoliation was considerably improved by the small ionic content. Remarkable increases in the storage moduli of PETi and PETNi were also observed with increasing DMSi content in the glassy region. However, the storage modulus of PETi decreased rapidly in the rubbery region above the transition temperature as temperature increased. The dynamic viscosity of PETNi decreased with DMSi content, indicating that ion-pair sites located at the clay edges acted as selective plasticizers in the PET ionic region. Moreover, the introduction of a small ionic content into the PET matrix led to a decrease in crystallinity and slower crystallization rates than in the pure PET.