EXPERIMENTAL AND THEORETICAL-STUDY OF PHASE-SEPARATION IN AQUEOUS-SOLUTIONS OF CLOUDING POLYMERS AND CARBOXYLIC-ACIDS

The phase behavior of different carboxylic acids/nonionic polymer/wate r systems has been studied. The carboxylic acids investigated are acet ic acid, propionic acid, and butyric acid. The polymers used are a lin ear random copolymer of ethylene oxide and propylene oxide (UCON) and ethyl(hydroxyethyl)-cellulose (EHEC). These polymers display a lower c ritical solution temperature (LCST) in water. The decrease of the pola rity in the carboxylic acids as the carbon chain increases causes a de crease of the LCST of the system carboxylic acid/polymer/water. As a c onsequence of this the two-phase region expands. The experimentally de termined phase diagrams can qualitatively be described and compared wi th a theoretical model, based on Flory-Huggins theory of polymer solub ility. The cloud-point temperature of the systems decreases as the dif ference between the effective interaction of polymer-cosolute and coso lute-water increases.