Dynamic viscoelasticity measurement was carried out for dilute and concentrated solutions of a water-soluble polysaccharide (SPS) extracted from soybean. The SPS solutions were able to be prepared up to the SPS concentration (c) of 30 wt% by using an ionic liquid 1-butyl-3-methylimidazolium acetate (BmimAc) as a solvent, while this “water-soluble” polysaccharide was actually soluble in water up to 3 wt%. The obtained dynamic viscoelasticity showed no rubbery plateau region, indicating that there was no entanglement coupling between SPS chains in the solutions. On the other hand, the c-dependence of the relative viscosity for the SPS solutions exhibited the critical concentration (cc) of ca. 9 wt% which in general corresponds to the onset of entanglement coupling between polymer chains in the solutions. The anomalous absence of the entanglement coupling in the SPS solutions above cc was attributed to the branching structure of SPS.
