Water-solution properties of a hydrophobically modified Poly(N-isopropylacrylamide)

To study the water-solution properties of a hydrophobically modified poly(N -isopropylacrylamide) (PNIPAM) which is temperature-sensitive, the copolyme r of N-isopropylacrylamide (NIPAM) and octadecyl acrylate (ODA) was synthes ized. The aggregation behavior of the copolymer was studied by surface tens ion and fluorescence probe methods. Simultaneously, the phenomenon of the l ower critical solution temperature (LCST) of the copolymer in an aqueous so lution with increase of the temperature was also studied using the fluoresc ence probe method. The results showed that phase separation occurred in an aqueous solution of the copolymer when the temperature was increased to its LCST. The pi-A isotherms for the copolymer molecules, as an insoluble mono layer on the water-air interface, was determined by the Langmuir-Blodgett ( GB) method. The abnormal phenomenon, by which the monolayer of the copolyme r molecules became more and more condensed with increase of the temperature , was observed. It further indicated that phase separation of the copolymer occurred by another method. In addition, to prove the thermosensitive effe ct of the copolymer on the release behavior of liposomes, small unilamellar vesicles entrapped with 5(6)-carboxyfluorescein [5(6)-CF] were coated with the copolymer. We found that the coating of the copolymer resulted in the reduction of the release below 30 degrees C and enhancement of the release above 30 degrees C, indicating that there are obvious interactions between the copolymer and the liposomes. (C) 2000 John Wiley & Sons, Inc.