  Polymer dynamics at large fields in Rubinstein-Duke repton model is
investigated theoretically. Simple diagrammatic approach and analogy with
asymmetric simple exclusion models are used to analyze the reptation dynamics
of polymers. It is found that for polyelectrolytes the drift velocity decreases
exponentially as a function of the external field with an exponent depending on
polymer size and parity, while for polyampholytes the drift velocity is
independent of polymer chain size. However, for polymers, consisting of charged
and neutral blocks, the drift velocity approaches the constant limit which is
determined by the size of the neutral block. The theoretical arguments are
supported by extensive numerical calculations by means of density-matrix
renormalization group techniques.
