Compatibilization of Polymer Blends by Complexation: 1. Spectroscopic Characterization of Interactions in Ionomer/Polyamide Blends
Electron paramagnetic resonance (EPR), Fourier transform infrared (FTIR), and solid-state 15N nuclear magnetic resonance (15N-NMR) spectroscopies were used to characterize the structure and relative strength of the interactions between metal sulfonate and amide groups in blends of lightly sulfonated polystyrene ionomers and an N-methylated polyamide, poly(N,N‘-dimethylethylene sebacamide), and low molecular weight model complexes. The metal sulfonate groups, which aggregate in the neat ionomer, were dispersed by the polyamide in the blend as a consequence of a complexation that involved the sulfonate cation and both the carbonyl oxygen and the amide nitrogen of the polyamide. The FTIR and 15N-NMR spectra were consistent with a 2pz electron redistribution model for the complex, in which electrons migrate from the nitrogen to the metal ion through the carbonyl group. The sulfonate anion did not appear to particpate in the complex, but it remained in the vicinity of the metal cation. The strength of the ion−amide complex increased with increasing electron-withdrawing power of the cation in the order of Zn2+ ≈ Cu2+ > Mn2+ ≥ Cd2+ > Li+.