The potential of diffusion-ordered 2D NMR spectroscopy (DOSY) for the
analysis of solutions of polymer mixtures and polymers with complex mo
lecular mass distributions is investigated. Diffusion coefficient labe
ling in NMR is generally achieved by stepwise ramping up of the amplit
udes of pairs of pulsed field gradients (PFGs). After Fourier transfor
mation in the acquisition dimension and an inverse Laplace transform (
ILT) with respect to the square of the gradient strength, 2D spectra a
re obtained that show the chemical shift along one dimension and the t
ranslational diffusion coefficient along the other. Since polymers may
have broad, nonsymmetric or complex (bi- and multimodal) molecular we
ight distributions (MWDs), the diffusion coefficient distribution shou
ld follow the main features of the MWD. However, the calculation of th
e diffusion coefficient distribution involves a numerically unstable d
ata inversion (ILT), which limits the resolution in the diffusion dime
nsion. The applications of DOSY NMR techniques to the study of polymer
blends and for the determination of MWDs of polymers with PFG NMR are
assessed. DOSY spectra recorded from industrial polypropylene and pol
ystyrene samples and mixtures are shown and interpreted to illustrate
the features of this technique.