Molar mass and viscometric characterisation of hydroxypropylmethyl cellulose

Abstract

The weight average molar masses and molar mass distributions of three different preparations (identical in chemical composition, but different in the average degree of polymerization) of hydroxypropylmethyl cellulose have been characterized by SEC/MALLS (size exclusion chromatography coupled to multiangle laser light scattering). The intrinsic viscosity and the viscosity in the semidilute region have also been measured. When the viscosity data is presented in the form of logarithmic plots of the zero shear specific viscosity against the coil overlap parameter ( c[ η]), a higher viscosity than would be expected from the usual ‘master curve’ relationships is found. This was particularly the case for the highest molar mass preparation ( M w = 2.2 × 10 6g/mol). It is suggested that the high viscosity is a consequence of enhanced intermolecular interactions as a result of solvent quality effects. Although the data is limited, the values of the Mark-Houwink-Kuhn-Sakurada exponent (0.4–0.5) suggested by the [η], M w data set would be consistent with water being a poor solvent for this polysaccharide. A related factor may be interactions induced when the chains are aligned during drying which are not completely disrupted on hydration.