NUCLEAR-SPIN-LATTICE RELAXATION AND THEORIES OF POLYMER DYNAMICS

The frequency dependence ('dispersion') of the proton spin-lattice rel axation times, T-1 and T-1 rho, in the laboratory and rotating frames of reference, respectively, in melts of 'entangled' polymers was inves tigated in the range 10(2)-10(8) Hz. The results can be characterized by a series of three apparently universal power laws corresponding to certain limits of polymer dynamics. The fluctuations of rotational iso merism within the Kuhn segments were independently identified in all i nvestigated cases by the minima of the temperature dependences of T-1. A theory linking the memory function formalism of polymer dynamics wi th the spin-lattice relaxation dispersion has been developed. On this basis, Schweizer's renormalized Rouse approach of polymer dynamics can suitably be employed for the derivation of expressions reproducing tw o of the experimentally deduced power laws very closely. One of these frequency dependences reflects a new short-time limit of the renormali zed Rouse approach not yet considered up to now. In addition, the time dependence of the mean-square segment displacements was derived for t he same limits yielding a series of new power laws. The third (low-fre quency) spin-lattice relaxation dispersion region has no theoretical c ounterpart in the frame of the renormalized Rouse theory.