Phase behavior of (polyacrylamides plus water) solutions: concentration, pressure and isotope effects

Phase diagrams of poly(N-isopropylacrylamide) (PNIPAAM) as well as of hydro philically-modified copolymers in aqueous solution were determined. A high- accuracy He-Ne Laser scattering technique was used for the detection of ope rational spinodal (sp) and cloud-point (cp) curves. Polymer concentration w as varied from 0.5 to 20 wt.%. In the case of copoly(PNIPAAM/vinylsaccharid e) several different chain lengths were considered. Pressure (up to 400 bar ) and solvent isotope effects were studied. We predict a closed-loop type p hase diagram for the copolymers, which presents an estimated hypercritical point in H2O solutions at M-w similar to 0.5 x 10(5), although only lower c ritical solution temperature (LCST) is experimentally accessible. At lower molecular weights, the solutions are always in the one-phase region. (C) 20 01 Elsevier Science B.V. All rights reserved.