Solution properties and chain flexibility of pullulan in aqueous solution

Molecular characteristics for pullulan, a polysaccharide produced by a fungus Aureobasidium pullulans , were measured by light scattering, viscometry, and gel‐permeation chromatography. From the experimental data the Mark‐Houwink‐Sakurada viscosity equation in water at 25°C was determined for samples having the molecular weight M ranging from 48 × 10 3 to 2.18 × 10 6 g mol −1 as [η] = (1.91 ± 0.02) × 10 −2 M w 0.67±0.01 (in cm 3 g −1 ); and as molecular weight decreased, the slope of the viscosity equation decreased, although the molecular weight values below 30 × 10 3 g mol −1 evaluated by gel‐permeation chromatography were somewhat unreliable. The unperturbed dimensions 〈 R 2 〉 0 1/2 of pullulan were estimated by determining the expansion factor α s , from the theoretical combination of theories for the interpenetration function Ψ and those for α s . The 〈 R 2 〉 0 / M value estimated from this procedure in 6.7 × 10 −17 cm 2 mol g −1 . We concluded that the polysaccharide chain that is linked by the α‐1,6‐glucosidic linkage behaves like a flexible chain in aqueous solution.