INFRARED AND ULTRAVIOLET SPECTROSCOPIC STUDIES ON INTRAMOLECULAR HYDROGEN-BONDING OF POLY(ITACONIC ACID)

UV and IR absorption spectra of poly(itaconic acid) (PIA) were measured on salt-containing aqueous solutions of various degree of neutralizations (a), to confirm the existence of intramolecular hydrogen bonds between ionized and un-ionized carboxyl groups. Two kinds of isosbestic points were observed in UV spectra at lambda = 218 nm and lambda = 213 nm in the region of a less-than-or-equal-to 0.5 and a greater-than-or-equal-to 0.5, respectively. A stretching vibration frequency of C = O of un-ionized carboxyl groups and an asymmetric stretching vibration frequency of COO- shifted to lower wavenumbers by 20 cm-1 and by 8 cm-1, respectively, with increasing a above 0.5. Peak separations for the IR spectra were successfully carried out over a whole a, by assuming four species, free COOH, free COO-, hydrogen-bonded COOH, and hydrogen-bonded COO-. It was concluded that PIA forms an ionic intramolecular hydrogen bond between alpha- and beta-carboxyl groups in a single monomeric unit during neutralization. The strength and extent of hydrogen bonds were compared with those of the polyelectrolytes having maleic acid units reported previously. The anti- and gauche-staggered conformers in the monomeric unit of PIA at a = 0.5 could be determined to be 16 +/- 2% and 84 = 2%, respectively.