Published:Journal of Chromatographic Science,
ISSN 0021-9665Volume
38, Number 5, May 2000, pp. 185-188
Near-Monodisperse
Sodium Polymethacrylates: Characterization by Linear Salt Gradient Anion-Exchange
ChromatographyAnke
Freydank, Theodora Krasia Gordon, J.T. Tiddy and Costas S. Patrickios
A family of
six near-monodisperse homopolymers of sodium methacrylate (Mn = 1100, 3200,
5500, 7200, 14100, and 21000) is characterized by linear salt gradient anion-exchange
chromatography. Although the retention times depend on the initial and final
salt concentrations of the gradient, they are almost independent of the molecular
weight of poly(sodium methacrylate). This suggests that anion-exchange chromatography
is incapable of resolving mixtures of a given polyelectrolyte to their components
of various molecular weights, and it is therefore impossible to identify the
polydispersity of such a sample using this method. The independence of the retention
times from molecular weight is also predicted by a theory based on stoichiometric
mass-action ion-exchange. Using this theory and our experimental retention times,
the equilibrium anion-exchange constant and the corresponding Gibbs free energy
of anion-exchange of the monomer repeat unit are calculated to be around 2.1
and –1.8 kJ/mol, respectively.
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