Structure factor of a self-avoiding polymer chain at high momentum transfer

The molecular weight of a Gaussian polymer chain can be obtained from the intercept of the asymptote in a plot of the inverse structure factor 1/S(q) as a function of the square of the wave vector q². Using an ϵ expansion and scaling arguments, we show that in a good solvent the situation is more complex and that the molecular weight determination is difficult to justify. The corrections to the asymptotic behavior of the structure factor at large wave vector involve several terms that are difficult to separate experimentally. This is qualitatively explained by the nonuniform swelling of a polymer chain in a good solvent due to the existence of the chain ends.