The twice-renormalized rouse formalism of polymer dynamics: Segment diffusion, terminal relaxation, and nuclear spin-lattice relaxation

The twice-renormalized Rouse formalism, a refined version of Schweizer's re normalized Rouse treatment of chain dynamics in entangled polymers, is pres ented. The time scale of validity is extended to include the terminal chain relaxation and center-of-mass diffusion. In clear contrast to the laws con cluded from other polymer dynamics concepts (such as the reptation (tube) m odel or the polymer mode-mode coupling formalism), the predictions perfectl y coincide with all the results of recent spin-lattice relaxation dispersio n and diffusion experiments as well as with computer simulations. On the ot her hand, the twice-renormalized Rouse formalism fails to explain the rubbe r-elastic plateau of stress relaxation. It is inferred that this is a conse quence of the single-chain nature of the present approach not accounting fo r the fact that viscoelasticity is largely a manifestation of collective mu ltichain modes. In the rigorous sense, no such multichain treatment has yet been established to our knowledge. The necessity to consider interchain co operativity in any real comprehensive polymer dynamics theory is concluded from low-frequency spin-lattice relaxation data, which are shown to reflect fluctuations of long-distance intermolecular dipole-dipole interactions. ( C) 2000 MAIK "Nauka/Interperiodica".