The dynamics of a polymer in a network of entanglements is studied. The viscosity has been examined for chains up to 50 links and is found to scale with chain lengthLasL3.41plusmn;0.14in agreement with previous theoretical work, that attributes this anomalous exponent as a finite size effect because of the finite tube length. Numerical results for chains up to 100 links give that the diffusion coefficientD, scales asLminus;2.50plusmn;0.04. This result differs from theoretical predictions based on tube fluctuations which claim finite length effects are unimportant for diffusion and therefore imply a minus;2 power law dependence forD. The reason for this discrepancy is examined. Previous work used a onehyphen;dimensional rather than a threehyphen;dimensional diffusion coefficient as the starting point of analysis. By deriving the correct procedure for calculating the threehyphen;dimensionalD, one sees that it has corrections to its asymptotic behavior which are quite large, of orderLminus;1/2, rather thanLminus;1as was thought previously. This suggests that fluctuations in the tube length cannot provide an adequate explanation for the experimental data.
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