Molecular motion of polyethylene oxide in dilute solutions studied by electron spin resonance and nuclear magnetic relaxation

Abstract

The isotropic rotational model appears a satisfactory approximation for describing both e.s.r. and ¹H and ¹³C n.m.r. relaxation measurements of PEO in dilute solution, indicating the highly flexible nature of this polymer. Correlation times determined by e.s.r. are proportional to the solvent viscosity as predicted by the Stokes–Einstein law. In contrast, the dependence of correlation times obtained by n.m.r. techniques as a function of solvent viscosity must be described in terms of the Magee diffusion model. These different modes of behaviour are expected to arise from a somewhat larger free volume available for the terminal segment than for central segments of the macromolecule.