C-13 NMR T-1 and NOE were measured for atactic polypropylene over the temperature range 325-425 K at C-13 Larmor frequencies of 25, 75, and 125 MHz. Because of the wide range of Larmor frequencies employed, the data discriminate among commonly used models for segmental dynamics; the modified KWW distribution function provides a much better fit than the DLM and the modified log chi(2) models. The temperature dependence of the segmental dynamics is very similar to that of the viscosity. An extrapolation of the calculated correlation times is consistent with previous NMR measurements near T-g. Interestingly, the full width half-maximum (fwhm) of the distribution of relaxation times remains unchanged at 1.3 decades, while previous NMR measurements nearer T-g reported a fwhm of 3.0 decades. Recent MD simulations are in qualitative agreement with the results reported here.