Fourier transform infrared spectroscopic study of flat surfaces of amphoteric-charged poly(acrylonitrile) membranes: Attenuated total reflection mode

Amphoteric-charged poly(acrylonitrile) (PAN) membranes possessing both carb oxyl and tertiary amine groups were prepared by radical graft polymerizatio n. By varying the molar ratio of acidic to basic monomers, we could obtain four kinds of amphoteric-charged membranes. These membranes were systematic ally analyzed by Fourier transform infrared spectroscopy/attenuated total r eflection (FT-IR/ATR) regarding the effects of feed monomer composition and pH change. Also, the spectra acquired were qualitatively compared with our previous electrokinetic data. From these results, it was found that the sp ectral difference among the amphoteric-charged PAN membranes can be charact erized by salt formation between the carboxyl group and the adjacent tertia ry amine group on the graft chains and/or sodium ions; the larger the terti ary amine group fraction, the more carboxyl groups take the ionized form.