SWELLING BEHAVIOR OF A BLEND HYDROGEL MADE OF POLY(ALLYLGUANIDINO-CO-ALLYLAMINE) AND POLY(VINYL ALCOHOL)

A hydrogel was prepared by mixing poly(allylguanidino-co-allylamine) h ydrochloride (FAG) with poly(vinyl alcohol) (PVA) and repeatedly freez ing and thawing the blend. The swelling behavior of the hydrogel was i nvestigated as a function of the pH and ionic strength of the medium. In a salt-free aqueous medium, a size of the hydrogel was reduced belo w pH 3 and above pH IO, bur tile size! was little affected in the pH r ange 3 similar to 10. In a medium of constant ionic strength (mu = 0.1 ), the hydrogel's pH response was different: it was significantly redu ced in size above pH 9, but the size was affected only moderately belo w pH 9. When the ionic strength of medium? was varied at a fixed pH, t he size change of the hydrogel was gradual. A II these phenomena could be understood by observing that FAG displayed multiple protonation st ates due to pH and that the electrostatic interactions among the charg es on the polymer backbone are shielded by the added electrolyte as th e ionic strength of the medium is raised. (C) 1997 Elsevier Science Lt d.