The degree of acetylation of chitosans and its effect on the chain conformation in aqueous solution

The average degree of acetylation (DA) of chitosans from several sources as well as the distribution of the DA across the molecular weight distribution was measured by titration with poly(styrene sulphonate) as counter polyanion and toluidine blue as metachromatic indicator. The method was shown to be useful within a broad range of DAs. There was no compositional heterogeneity for more than 90% of the population in any sample. Parallel macromolecular characterisation by static light scattering and viscometry standing alone or connected with gel permeation chromatography (GPC) revealed no measurable effect of the DA on the chain conformation where the DA varied between a few percent and ∼60%. Relationships between intrinsic viscosity and radius of gyration with molecular mass were established. The data when considered with previous work suggest no evident differences between chitosans from different sources and no significant effect of the ionic strength between ∼0.1 and 0.3 M on the conformation.