ANOMALOUS SEGMENT DIFFUSION IN POLYMERS AND NMR RELAXATION SPECTROSCOPY

The dynamics of polymer chains in melts, solutions and networks was st udied by the aid of NMR relaxation spectroscopy. Proton data of the sp in-lattice relaxation curves are reported. Frequency, temperature, fra mes, T1 and T1rho, respectively, and of transverse relaxation curves a re reported. Frequency, temperature, concentration, molecular weight, and cross-link density dependences have been investigated. T1 was meas ured in a frequency range of 10(3) to 3 X 10(8) Hz predominantly using the field-cycling technique. The study refers to polyisoprene, polyis obutylene, poly(tetrahydrofuran), polystyrene, poly(ethylene oxide), p olyethylene, and poly(dimethylsiloxane). The range of molecular weight s 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-proporti onal-to t1/4, predicted by the Doi/Edwards tube model for coil-interna l segment diffusion are shown to have their counterparts in the freque ncy dependence of the spin-lattice relaxation time which is characteri zed by power laws T1 is-proportional-to omega0.5 and T1 is-proportiona l-to omega0.25 in corresponding dynamic ranges. The experimental data can be interpreted on the basis of three components of segment fluctua tions. The crucial process is the reorientation of segments as a conse quence of translational displacements. The orientation correlation fun ction for this mechanism can be derived directly from limits of the ti me dependence of the mean-square segment displacements provided that t he displacements are guided by the chain contour. The experiments show , on the other hand, that the chain dynamics in length scales less tha n the Doi/Edwards tube diameter is not compatible with the Rouse model , whereas that of melts below the critical molecular weight and soluti ons is.