ANOMALOUS SEGMENT DIFFUSION IN POLYMERS AND NMR RELAXATION SPECTROSCOPY

The dynamics of polymer chains in melts, solutions and networks was studied by the aid of NMR relaxation spectroscopy. Proton data of the spin-lattice relaxation curves are reported. Frequency, temperature, frames, T1 and T1rho, respectively, and of transverse relaxation curves are reported. Frequency, temperature, concentration, molecular weight, and cross-link density dependences have been investigated. T1 was measured in a frequency range of 10(3) to 3 X 10(8) Hz predominantly using the field-cycling technique. The study refers to polyisoprene, polyisobutylene, poly(tetrahydrofuran), polystyrene, poly(ethylene oxide), polyethylene, and poly(dimethylsiloxane). The range of molecular weights was 10(3)-10(6). The power laws for the time dependence of the mean-square displacement, [r2] is-proportional-to t1/2 and [r2] is-proportional-to t1/4, predicted by the Doi/Edwards tube model for coil-internal segment diffusion are shown to have their counterparts in the frequency dependence of the spin-lattice relaxation time which is characterized by power laws T1 is-proportional-to omega0.5 and T1 is-proportional-to omega0.25 in corresponding dynamic ranges. The experimental data can be interpreted on the basis of three components of segment fluctuations. The crucial process is the reorientation of segments as a consequence of translational displacements. The orientation correlation function for this mechanism can be derived directly from limits of the time dependence of the mean-square segment displacements provided that the displacements are guided by the chain contour. The experiments show, on the other hand, that the chain dynamics in length scales less than the Doi/Edwards tube diameter is not compatible with the Rouse model, whereas that of melts below the critical molecular weight and solutions is.