NA-23 NUCLEAR MAGNETIC-RESONANCE IN POLYANION SOLUTION - CORRELATION TIMES AND QUADRUPOLE COUPLING-CONSTANTS OF NA+ BOUND TO POLY(METHACRYLIC ACID)

The information obtained on the interaction between small ions and polyions from studies of an ion's quadrupole relaxation is examined in some detail. Important features usually found in the NMR studies of polyelectrolyte systems are inequality of the longitudinal (T1) and transverse (T2) relaxation times, relaxation given by the sum of two exponential decays, and a non-Lorentzian resonance signal. The utilization of these features to deduce the correlation time of the polymer-bound counterion is described as well as the estimation of the quadrupole coupling constant. An illustration of the principles developed is given by the system Na+-poly(methacrylic acid), for which detailed experimental data are presented. The analysis gives a description in terms of the correlation times, quadrupole coupling constants, and degree of counterion binding. The correlation time is found to increase strongly with decreasing degree of ionization and this is attributed to a conformational transition. An increase in the quadrupole coupling constant at low ionization degrees is suggested to be due to the involvement of both carboxylate and carboxylic acid groups in the ion binding, and this is supported by 23Na+ chemical shifts. The results are compared with those of the system Na+-poly(acrylic acid) and marked differences are found between the two polyanions. © 1978, American Chemical Society. All rights reserved.