PHASE-BEHAVIOR OF RANDOM AND ABC TRIBLOCK METHACRYLIC POLYAMPHOLYTES WITH POLY(VINYL ALCOHOL) IN WATER - EFFECT OF PH AND SALT

ABC triblock and random methacrylic polyampholytes of molecular weight 4,000 g mol(-1) with various base-neutral-acid compositions were exam ined for their phase separation behavior, each in an aqueous mixture w ith poly(vinyl alcohol) of molecular weight 10,000 g mol(-1). Potassiu m chloride concentration and solution pH were varied and the phase beh avior was mapped on the pH-(KCl) space. The block copolymers presented a much broader phase separation region than the random copolymers. Th is difference may reflect the effect of the structure of the block cop olymers which leads to the formation of micelles in solution. The two- phase region of the block copolymers extended over the whole range of potassium chloride concentrations employed in this study, from 0.0 to 0.75 M, and covered the pH range from two pH units below the polyampho lyte isoelectric point up to two units above, with the exception of th e points at alkaline pH without added salt. The two-phase region of th e random copolymers extended from 0.0 to 0.1 M KCl and covered at most one unit in pH, centered near the isoelectric point. The two-phase re gion of the block copolymers comprised two regimes: the low salt conce ntration regime characterized by a compact polyampholyte precipitate i n equilibrium with a low-viscosity poly(vinyl alcohol) phase; the high salt concentration and alkaline pH regime characterized by two coexis ting low-viscosity phases. The one-phase region of the block copolymer s extended in the acidic pH range and covered the whole salt concentra tion range. The ion type effect on the phase behavior of block polyamp holytes was related to the position of the ion in the Hofmeister serie s: high concentrations of salt of low salting out ability resulted in a transition from a two- to a one-phase system.