Pulsed field gradient NMR

We show that self-diffusion coefficients derived indirectly from sedimentation or mutual diffusion do not agree with those obtained directly with PFGNMR. We believe that indirect determinations are not valid for random coils at finite concentrations. However the different physical factors governing self-diffusion and sedimentation can be exploited to obtain information on the static and dynamic critical exponents for polymers in semi-dilute solution. We show that such an analysis leads to an anomalously high static index for 110 000 M polystyrene in toluene.Presented at the 22nd Microsymposium, Characterization of Structure and Dynamics of Macromolecular Systems by NMR Methods, Prague, July 20–23, 1981Presently on leave at Physics Department, University of British Columbia, Vancouver, Canada