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 fact or 1/S(q) as a function of the square of the wave vector q(2). Using a n epsilon expansion and scaling arguments, we show that in a good solv ent the situation is more complex and that the molecular weight determ ination is difficult to justify. The corrections to the asymptotic beh avior of the structure factor at large wave vector involve several ter ms that are difficult to separate experimentally. This is qualitativel y explained by the nonuniform swelling of a polymer chain in a good so lvent due to the existence of the chain ends.