The Analytical Ultracentrifuge for the Characterization of Polydisperse Polyelectrolytes

Abstract

High molar mass polyelectrolytes, which are polydisperse concerning the molar mass, the charge density, and the chain architecture were characterized by hydrodynamic methods, in particular analytical ultracentrifugation. The samples of interest were a series of copolymers differing in the degree of branching at constant chemical composition/charge density and highly branched polyelectrolytes of various charge density/chemical composition. Combining synthetic boundary and sedimentation velocity experiments, and running at various speeds, allowed to identify the degree of homogeneity of the various distributions of the samples. It was illustrated that homogeneous batches of highly branched high molar mass polyelectrolytes can be synthesized with a negligible fraction of cross-linked molecules. Surprisingly, the sedimentation coefficient distribution of the main fraction was relatively narrow indicating a tight branching distribution. Overall, AUC delivers a variety of detail information, which cannot be obtained by other methods either due to lack of sensitivity or non-resolution of polydispersity.