Water‐solution properties of a hydrophobically modified poly( N ‐isopropylacrylamide)

Abstract

To study the water-solution properties of a hydrophobically modified poly(N-isopropylacrylamide) (PNIPAM) which is temperature-sensitive, the copolymer of N-isopropylacrylamide (NIPAM) and octadecyl acrylate (ODA) was synthesized. The aggregation behavior of the copolymer was studied by surface tension and fluorescence probe methods. Simultaneously, the phenomenon of the lower critical solution temperature (LCST) of the copolymer in an aqueous solution with increase of the temperature was also studied using the fluorescence 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 π-A isotherms for the copolymer molecules, as an insoluble monolayer on the water–air interface, was determined by the Langmuir–Blodgett (L–B) method. The abnormal phenomenon, by which the monolayer of the copolymer 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 effect 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°C and enhancement of the release above 30°C, indicating that there are obvious interactions between the copolymer and the liposomes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 247–255, 2000