Unified model of association-induced lower critical solution temperature phase separation and its application to solutions of telechelic poly(ethylene oxide) and of telechelic poly(N-isopropylacrylamide) in water.
The authors present a model describing the coexistence of hydrophobic association and phase separation with lower critical solution temperature (LCST) in aqueous solutions of polymers carrying short hydrophobic chains at both chain ends (telechelic associating polymers). The LCST of these solutions is found to decrease along the sol/gel transition curve as a result of both end-chain association (association-induced phase separation) and direct hydrophobic interaction of the end chains with water. The authors relate the magnitude of the LCST decrease to a hydration cooperativity parameter sigma. The LCST decreases substantially (approximately 100 K) in the case of random hydration (sigma=1), whereas only a small shift (approximately 5-10 K) occurs in the case of cooperative hydration (sigma=0.3). The molecular weight dependence of the LCST drop is studied in detail in each case. The results are compared with experimental observations of the cloud points of telechelic poly(ethylene oxide) solutions, in which random hydration predominates, and of telechelic poly(N-isopropylacrylamide) solutions, in which cooperative hydration prevails.
Okada
Yukinori
Y
Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Kyoto 615-8510, Japan.
Tanaka
Fumihiko
F
Kujawa
Piotr
P
Winnik
Françoise M
FM