Abstract
Pulsed deuteron NMR offers new possibilities for the determination of the distribution of correlation times for local motions in glassy polymers. The NMR line shape is a superposition of spectra corresponding to the different values of the correlation times. The weighting factors of these single spectra depend on the distribution function, which therefore can be characterized by a line shape analysis. Moreover, by combination with spin-lattice relaxation experiments the motional behaviour can be probed on a much longer time scale then by a line shape analysis alone. In this way homogeneous and heterogeneous distributions can clearly be distinguished. The method is explained in detail and is demonstrated by a simple example involving the methyl group rotation in glassy polycarbonate. in both polycarbonate itself and in mixtures with low molecular mass additives the results can be described by a log-Gausian distribution of correlation times. This distribution is heterogeneous in nature, probably resulting from a distribution of the activation energies at spatially different sites between 15 and 21 kJ/mole.
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