Compatibilization of Polyester/Polyamide Blends with a Phosphonated Poly(ethylene terephthalate) Ionomer: Comparison of Monovalent and Divalent Pendant Ions

The successful compatibilization of immiscible amorphous polyester (PETG) and semicrystalline polyamide (poly(m-xylylene adipamide) (MXD6)) blends using a phosphonated poly(ethylene terephthalate) ionomer in the Na+ form (Na+-PPET) as a minor-component compatibilizer was demonstrated. The Na+-PPET/PETG/MXD6 blends were prepared using a solution mixing method to enable thin film characterization. The phase morphology with respect to various phosphonated monomer concentrations was studied using phase contrast optical microscopy (PC-OM) and small-angle laser light scattering (SALLS). The phase-separated, interdomain spacing decreased with increasing mol % phosphonated monomers and was attributed to the specific interactions between the ionic phosphonate groups on the polyester ionomer and the amide linkages of polyamide. The ability of the divalent phosphonate pendant ions to compatibilize PETG/MXD6 blends was also compared to a conventional sulfonated PET (SPET) compatibilizer. This comparison showed that the Na+-PPET/PETG/MXD6 blends required 6 times fewer ionic monomers to achieve domain dimension <1 μm as compared to Na+-SPET-containing PETG/MXD6 blends. Moreover, on a mole percent of pendant ions basis, the divalent phosphonate pendant ions in PPET were found to be 3 times more effective at compatibilizing PETG/MXD6 blends compared to the monovalent sulfonate pendant ions in SPET.