STRUCTURAL-VISCOUS CHARACTERISTICS OF THERMOREVERSIBLE SOL-GEL TRANSITION OF METHYLCELLULOSE IN SYSTEMS WITH DIFFERENT CRITICAL DISSOLVING TEMPERATURES

The properties of diluted and moderately concentrated solutions of met hylcellulose (MC) in water and dimethylacetamide (DMAA) are studied at various temperatures and the differences in the behaviour of isolated macromolecules in water and DMAA are shown as follows: in water MC be haves libe semi-rigid chain polymer, while in DMMA it evidences the pr operties of a flexible-chain polymer. In aqueous solutions of MC, the increase of temperature leads to decreasing of [eta] of the polymer. I n solutions of MC in DMAA over the 20-40 degrees temperature range, in crease of [eta] is observed, while at temperatures higher than 40 degr ees, decrease of [eta] occurs. Such differences in the behaviour of MC macromolecules are explained by the differences in the thermodynamics of the solvents' interactions with the polymer and, respectively with each other. The thermokinetic laws of the rheological properties of a queous and DMAA solutions of MC are shown as different. The viscosity of 1.5% solutions of MC in water is by an order of magnitude higher th an that of MC solutions in DMAA. The influence of both temperature and shear stress on the viscosity-of the studied systems is different, wh ich may be explained by differences in the mechanism of MC dissolution in water and DMAA and in the rate of the relaxation processes as well .