Phase behavior of temperature- and pH-sensitive poly(acrylic acid-g-N-isopropylacrylamide) in dilute aqueous solution

摘要

Several different composition temperature- and pH-sensitive poly(acrylic acid-g-N-isopropylacrylamide) (P(AA-g-NIPAM)) graft copolymers were synthesized by free-radical copolymerization utilizing macromonomer technique. The phase behavior and conformation change of P(AA-g-NIPAM) in aqueous solutions were investigated by UV-vis transmittance measurements, fluorescence probe, and fluorescence quenching techniques. The results demonstrate that the P(AA-g-NIPAM) copolymers have temperature- and pH-sensitivities, and these different composition graft copolymers have different lower critical solution temperature (LCST) and critical phase transition pH values. The LCST of graft copolymer decreases with increasing PNIPAM content, and the critical phase transition pH value increases with increasing Poly(N-isopropylacrylamide) (PNIPAM) content. At room temperature (20 degrees C), different composition of P(AA-g-NIPAM) graft copolymers in dilute aqueous solutions (0.001 wt ) have a loose conformation, and there is no hydrophobic microdomain formation within researching pH range (pH 3 similar to 10). In addition, for the P(AA-g-NIPAM) aqueous solutions, transition from coil to globular is an incomplete reversible process in heating and cooling cycles. (C) 2008 Wiley Periodicals, Inc.