NUCLEAR MAGNETIC RESONANCE INVESTIGATION OF CONFORMATIONS OF ISOTATIC POLYELECTROLYTES IN AQUEOUS SOLUTION

Nuclear magnetic resonance spectra of isotactic poly(acrylic acid) and its sodium salt, as well as those of its model compound, show no significant change in the vicinal coupling constants between α and β protons with neutralization. From this experimental result, it is concluded that the polyion and its model compound have practically fixed local conformations independent of their degrees of neutralization and, consequently, that expansion of the polyion with increasing degree of neutralization (of the polyion) may reasonably be interpreted by the long-range interaction, i.e., by the interactions between charged groups at long intervals, assuming that the change in the short-range interaction, i.e., the change in the size of the segment with degree of neutralization, is negligible. Moreover, detailed analysis shows that the isotactic polyacrylate ion has the local conformation of a 31 helical structure. It has also been shown that the relative chemical shifts of the characteristic peaks of stereoregular polymers are markedly changed by exchanging the substituents and, consequently, that the typical nmr patterns of isotactic polymers disappear by hydrolysis or by neutralization.