POLYMER DYNAMICS IN AQUEOUS POLY(ETHYLENE OXIDE) SOLUTIONS - AN NMR-STUDY

The spectral density functions of the H-2-methylene nuclei in poly(eth ylene oxide) (PEO) have been determined by magnetic relaxation measure ments in the 0-90 MHz range at six applied field strengths. The relaxa tion rates were determined in a concentration interval from 0.1 to 40 monomolal. No molecular weight dependence was observed in the 3000 les s-than-or-equal-to M(w) less-than-or-equal-to 50 000 range. In the dil ute ana semidilute regimes, the spectral density function is interpret ed in terms of anisotropic reorientation of a hydrodynamic unit. The c orresponding dimensions of the dynamic unit are similar to those of a Kuhn segment. At a concentration where the dynamic unit can no longer reorient freely, the nature of the reorientational dynamics of the pol ymer segments is severely altered. This point is indicative of the sta rt of the concentrated regime. Both the spectral density curve and the effective activation energies become strongly dependent on the polyme r concentration. The H-1- and H-2-NMR relaxation rates show qualitativ ely different molecular weight and concentration dependencies at a pol ymer concentration greater than the crossover concentration c*. From the determination of H-1-NMR relaxation rates in mixtures of perdeuter ated and hydrogenous polymers at c(p) > c*, it becomes clear that the different behavior of H-1 and H-2 is singularly due to an additional intermolecular dipolar coupling in the case of H-1. The latter interac tion is modulated on relatively long time scales (tau(c) > 10(-8) s).