Synthetic and Biological Polymers in Deionized Solution. 3. Expansion of Water-soluble Neutral Polymers and Polymers Having a Small Amount of Ionizable Groups

Abstract

Viscosities of water-soluble neutral polymers and the polymers having a small amount of carboxylic acid groups are measured in deionized solution and in the presence of a small amount of sodium chloride. These experiments are made in order to examine whether the electrical double layers are formed or not around the linear-type neutral polymers in the deionized solution. The neutral polymers examined are poly(vinylpyrrolidone)s (PVP) of molecular weights of 3.6 · 105, 4 · 104 and 1 · 104, poly(vinylalcohol) (PVA) of molecular weight of 8.8 · 104, poly(ethyleneglycol), hydroxypropyl cellulose, and poly(acrylamide) having no carboxylic acid groups. The reduced viscosities of PVP having the highest molecular weight (3.6 · 105) in the deionized solution are slightly higher than those in the presence of sodium chloride. This supports that the polymer chain is expanded slightly by the electrical double layers formed around the polymer. It is highly plausible that the ionization effect occurs by the adsorption of ionic species on the polymer. For PVP of molecular weight of 4 · 104 and PVA, viscosities in the deionized solutions are higher, but very slightly, than those in the presence of sodium chloride. The viscosities of other neutral polymers are quite independent of the ionic concentration. The deionized polymers of poly(acrylamide-co-acrylic acid), which have a small amount of ionizable groups, are unexpectedly highly stretched by the electrostatic intersegment repulsive interaction because of the very long Debye-screening length.