Abstract
General theoretical scheme for studying phase diagrams of associating polymer solutions is presented. As the simplest example, phase diagrams with lower critical solution temperature (LCST), as seen in aqueous solutions of neutral polymers such as poly (ethylene oxide) and poly (N-isopropylacrylamide), are theoretically derived and compared with the recent experiments. It turns out that miscibility gaps of loop shape and hourglass shape appear depending upon the polymer molecular weight if hydration (association of water molecules onto the polymer chains by hydrogen bonds) takes place randomly and independently, while miscibility gaps of square shape with very flat LCST line appear independently of the polymer molecular weight if hydration is cooperative.
