Rate Memory of Structural Relaxation in Glasses and Its Detection by Multidimensional NMR

A new aspect of the nature of the relaxation rate distribution of α relaxation in glasses is analyzed for the example of a polymer: How long does a polymer segment remember its relaxation rate? For a two-state system we describe the rate memory in terms of a single dimensionless parameter. Applying the theory to multidimensional NMR exchange experiments, the rate memory of a polymer slightly above its glass transition temperature is determined. The rate memory is near its theoretical minimum, indicating strong coupling of the individual relaxation modes.