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Molecular Weight Studies on Hydroxypropyl Methylcellulose I. Osmometry

1997; Taylor & Francis; Volume: 4; Issue: 2 Linguagem: Inglês

10.1080/10236669708033944

1563-5341

Robert Lundqvist, Nikita Soubbotin,

Rheology and Fluid Dynamics Studies

Abstract Osmometry was employed to measure number-average molecular weight Mn of hydroxypropyl methylcellulose (HPMC) using membranes with different permeability for the solute (polymer or electrolyte) and solvent (water) in such a way that no pretreatment of the polymer solution was required to remove electrolyte impurities, thereby eliminating the risk of sample alteration. A novel osmometric method was developed, based on measurements of the kinetics of the pressure over the membrane, which allows the use of membranes permeable even to the polymer. It was shown that such membranes initially, at time t = 0, approaches the physics of a perfectly semipermeable membrane provided that the ratio of the solute/solvent permeability is sufficiently low (i.e., when the molecular weight cut-off, MWCO, of the membrane does not exceed Mn of the polymer). The obtained Mn for a range of viscosity grades of HPMC2910 (3 cP to 10,000 cP) compares favorably with previous estimates, based on analogy with methylcellulose.