Non-equilibrium relaxation law for entangled polymers

We study the far-from-equilibrium relaxation of an initially stretched, ent angled polymer by using an exactly solvable lattice gas model for reptation . Over a significant time range, including an initial universal power law r egime, the predicted tube length relaxation is in very good agreement with experimental data for the relaxation of DNA. Experimental evidence and theo retical arguments suggest an observed systematic long-time deviation to be due to entanglement fluctuations. This view is confirmed by the analysis of an extension of the lattice gas model which appears to be a reliable found ation for further study of reptation dynamics.