NONEXPONENTIAL RELAXATION FUNCTIONS ABOVE T(G) ANALYZED BY MULTIDIMENSIONAL NMR AND NOVEL SPIN-ECHO DECAY TECHNIQUES

New multidimensional NMR relaxation experiments are described. These e xperiments allow the measurement of slowly decaying relaxation functio ns for selected subensembles. They are applied for chain deuterated po lystyrene at temperatures slightly above the caloric glass transition. The usual nonexponential loss of correlation is observed for the over all sample. However, a subensemble of slow components can be selected. An analysis of the relaxation functions in terms of the Kohlrausch-Wi lliams-Watts function shows that the relaxation function of the select ed components corresponds to a narrower distribution of correlation ti mes than that of the entire sample. This gives clear evidence of a spa tially heterogeneous distribution of correlation times and not an intr insically nonexponential loss of correlation in a homogeneous system. For the hydrocarbon chain of polystyrene the observed nonexponential l oss of correlation due to motions on the 100 Hz range (a-process) is l inked to the nonexponential T1 relaxation observed close to T(g) which is dominated by rapid motions with spectral density in the range of 1 00 MHz (beta-process). Hence in spatial regions where the alpha-relaxa tion is slow, also slow T1 relaxation is observed.