The ratio of the unperturbed mean-square end-to-end distance to the molecular weight in the random-coil limit, ([R-2](of)/M)(infinity) in the free-rotation approximation was calculated for chains of linear polyurethanes PUR-D-k prepared from 4,4＇-methylenediphenyl diisocyanates and low-molecular-weight diols HO-(CH2)(k)-OH (k = 2, 3, 4 and 6). It was found that the experimental values of ([R-2](o)/M)(infinity) estimated in the previous paper are very close to the values of ([R-2](of)/M)(infinity) calculated under the assumption that the groups of bonds CH2-C6H5-NH and NH-CO-O-CH2 can be replaced by rigid virtual bonds.