Intrinsic viscosity of pullulan in ionic liquid solutions studied by rheometry

Intrinsic viscosity [η] of nine pullulan samples with different molecular weights and narrow molecular weight distributions are obtained in 1-butyl-3-methylimidazolium chloride (BmimCl) and 1-ethyl-3-methylimidazolium acetate (EmimAc) from the Newtonian viscosities measured by oscillatory and steady shear flow in conventional rheometer for dilute solutions. For low molecular weight M_w samples, [η] in BmimCl and EmimAc almost coincide with that in aqueous solutions compared at the same M_w. The data at M_w < 30 kg/mol can be represented by M_w ^0.5 dependence. The excluded volume effects observed in BmimCl and EmimAc at higher M^w are somewhat stronger than in aqueous solutions. Mark-Houwink-Sakurada equations for pullulan in BmimCl and EmimAc are determined in 20 kg/mol < M_w < 100 kg/mol. It is conclude that measurement of [η] by rheometer is a promising method for characterization of polymers in ionic liquids.