Comparison of methods for the determination of diffusion coefficients of polymers in dilute solutions: The influence of polydispersity

A comparison between various methods to determine diffusion coefficients of polymers in dilute solutions has been made. It is shown that Taylor disper sion analysis (TDA), dynamic light scattering (DLS), hydrodynamic chromatog raphy (HDC), and size exclusion chromatography (SEC) can all be used to acc urately determine diffusion coefficients when the polymer samples have low polydispersities. By the analysis of a series of practically representative styrene acrylonitrile copolymer (SAN) samples, it is shown that polydisper sity of the samples and the presence of low-molecular-mass material cause c onsiderable differences between the methods. It was found that TDA is mostl y disturbed by the presence of low-molecular-mass material, whereas DLS is more sensitive to the polydispersity of the polymer. With broad samples, DL S gives the Z-average diffusion coefficient. SEC can be used to obtain a di ffusion coefficient distribution as well as an average diffusion coefficien t of a polydisperse sample. Although, the same was expected for HDC, it was found that this method could only be successfully used for polymer samples having low polydispersities. Deviations between SEC, HDC, and TDA found fo r narrow samples were not related to the chemical composition of the sample s. (C) 1999 John Wiley & Sons, Inc.