Effect of phenolic cosolutes on the main parameters, phase separation and theta temperature of dilute aqueous poly(N-vinyl-2-pyrrolidone) solutions

The effect of phenolic cosolutes (phenol, catechol, resorcinol, hydroquinone and phloroglucinol) on the main physicochemical parameters, cloud points (T-cp), phase diagram and theta temperature (Theta) of dilute aqueous poly(N-vinyl-2-pyrrolidone) (PVP) solutions was studied experimentally using various concentrations of cosolutes and polymers at different temperatures. The resulting dependence of T-cp and Theta temperatures (between 300 and 343 K) on the molar concentrations can be determined as sequences showing the decreasing effect of cosolute species in salting out the polymer. The decreasing order of effectiveness of phenolic cosolutes in reducing both T-cp and Theta temperatures is phloroglucinol > resorcinol > hydroquinone > catechol > phenol. It is shown that thermodynamic incompatibility of aqueous PVP/phenolic cosolute solutions strongly depends on the effect of the character of phenolic cosolute, changes taking place in the interactions among polymer, solvent and additive phenolic cosolutes and on the change of water structure in the mixture. (C) 2000 Elsevier Science Ltd. All rights reserved.