The authors show that the errors in the work of Y. Shiwa et al. originate from the inconsistent use of formulas for different regimes. For specificity, the authors consider the concentration dependence of the relaxation time (τp) of the pth normal mode of polymer chains in dilute solutions. The initial concentration dependence of τp for linear flexible chains in three dimensions was derived. Since the internal modes of the chain are of concern, the characteristic length scale is shorter than the size of the polymer chain.