Intermolecular interaction and conformation in poly(ether ether ketone)/poly(ether imide) blends — An infrared spectroscopic investigation

The intermolecular interaction and the conformation in miscible blends of poly(ether ether ketone) (PEEK) and poly(ether imide) (PEI) have been investigated by Fourier-transform infrared (FTIR) spectroscopy. The intensity of the C=O out-of-phase stretching (1725 cm^–1) of PEI shows a minimum at 70 wt% PEI, whereas that of the C=O in-phase stretching (1778 cm^–1) is not perturbed by blending. These intensity variations have been attributed to the effect of blending on the coplanarity of the two imide rings bridged by the phenylene group. Change in coplanarity of these two imide rings alters the intensity of the C=O out-of-phase stretching, but it can not affect the intensity of the C=O in-phase stretching. When the two imide rings are perpendicular to each other, the intensity of the C=O out-of-phase stretching is shown to reach the minimum, corresponding to the observation at 70 wt% PEI. The difference spectra (blend - PEEK - PEI) reveal that the bands associated with the diphenyl ether groups in PEEK are modified by blending with PEI. It is proposed that the favorable interaction takes place between the oxygen lone-pair electrons of the ether group in PEEK and the electron-deficient imide rings in PEI.