Intrinsic Viscosity of Pullulan in Ionic Liquid Solutions Studied by Rheometry

Intrinsic viscosity [eta] of nine pullulan samples with different molecular weights and narrow molecular weight distributions are obtained in 1-butyl-3-methylimidazolium chloride (BmimC1) 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, samples, [eta] in BmimC1 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 BmimC1 and EmimAc at higher M, are somewhat stronger than in aqueous solutions. Mark-Houwink-Sakurada equations for pullulan in BmimC1 and EmimAc are determined in 20 kg/mol < M-w < 100 kg/mol. It is conclude that measurement of [eta] by rheometer is a promising method for characterization of polymers in ionic liquids.